Zeitschriftenartikel: „Particle formation and transformation“

1

Hansson, Hans-Christen. „Particle formation and transformation in continental air masses“. Journal of Aerosol Science 26 (September 1995): S549—S550. http://dx.doi.org/10.1016/0021-8502(95)97182-e.

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2

Moon, Jooho, Melanie L. Carasso, Henrik G. Krarup, Jeffrey A. Kerchner und James H. Adair. „Particle-shape control and formation mechanisms of hydrothermally derived lead titanate“. Journal of Materials Research 14, Nr. 3 (März 1999): 866–75. http://dx.doi.org/10.1557/jmr.1999.0116.

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Phase-pure perovskite lead titanate with various morphologies has been synthesized by a hydrothermal method at 150 °C. Particle shapes include cubic, tabular, and aggregated platelike shapes. The feedstock concentration greatly influences particle morphology of the hydrothermally derived PbTiO3. At a concentration of 0.05 M, the tabular particles form while cubic particles are produced at 0.1 M. Aggregated plateletlike particles are synthesized at 0.125 M. It was observed that both tabular and cubic particles directly precipitate from the coprecipitated precursor gel. In contrast, the plateletlike shaped intermediate phase appears during the initial stage of reaction at 0.125 M and in situ transforms into perovskite PbTiO3 during further hydrothermal treatment. The intermediate phase preserves its particle shape during transformation and, acting as a template, gives rise to the final tabular PbTiO3 particles. It is demonstrated that only base reagents such KOH and NaOH, which provide a highly basic condition (i.e., pH > 14), promote transformation of the coprecipitated gel into the perovskite PbTiO3. A Hancock and Sharp kinetic analysis in conjunction with microstructural evidence suggests that the formation mechanism is dissolution and recrystallization in which the degree of supersaturation plays an important role in dictating the crystallographic particle phase and morphology of the particles. An experimentally constructed solubility diagram indicates that an excess lead condition is necessary to compensate for loss of lead species and to increase supersaturation to expedite precipitation of PbTiO3 at highly alkaline conditions.

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Namiki, Norikazu, Yoshio Otani, Hitoshi Emi und Shuji Fujii. „Particle Formation of Materials Outgassed from Silicone Sealants by Corona-Discharge Ionizers“. Journal of the IEST 39, Nr. 1 (31.01.1996): 26–32. http://dx.doi.org/10.17764/jiet.2.39.1.3l026553j1366046.

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Particle formation of LMCS (low-molecular-weight poly-cyclo-dimethyl-siloxane) outgassed from silicone sealants by a corona-discharge ionizer was studied by measuring the number concentration and size distribution of formed particles as well as by qualitative analyses of formed particles with FT-IR (Fourier transformation infrared spectroscopy). Further, the influence of humidity and oxygen on the particle formation was investigated to find the reaction mechanisms. As a result, it was found that the LMCS is polymerized to form particles with two different reaction paths and that the LMCS is one of the major species that contribute to the formation of silicon-containing particles in cleanroom environments.

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BHATTACHARYA, P., und K. CHATTOPADHYAY. „PHASE FORMATION AND TRANSFORMATION OF EMBEDDED ALLOY NANOPARTICLES: CASE OF LEAD INDIUM ALLOY PARTICLES IN ALUMINUM“. International Journal of Nanoscience 04, Nr. 05n06 (Oktober 2005): 909–20. http://dx.doi.org/10.1142/s0219581x05003875.

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The effect of size on the alloying and transformation behavior of multicomponent metallic systems has received very little attention. The present study reports a preliminary result in this direction involving Pb–In nanosized alloy particles embedded in an aluminum matrix. With the help of various techniques including in situ electron microscopy, we show that at small sizes, the Pb–In alloys particles are single-phase solid solution having fcc structure at the composition range covering both Pb and In rich regions. The results of in situ microscopy also indicate that the melting point and roughening behavior of these particles differ from particle to particle. The results are compared with that available for pure Pb particles.

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Cholakova, Diana, Zhulieta Valkova, Slavka Tcholakova, Nikolai Denkov und Bernard P. Binks. „Spontaneous particle desorption and “Gorgon” drop formation from particle-armored oil drops upon cooling“. Soft Matter 16, Nr. 10 (2020): 2480–96. http://dx.doi.org/10.1039/c9sm02354b.

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We study how the phenomenon of drop “self-shaping“, in which oily drops undergo a spontaneous series of shape transformation on colling, is affected by the presence of adsorbed solid particles, like those in Pickering emulsions.

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Wu, Z. J., J. Zheng, D. J. Shang, Z. F. Du, Y. S. Wu, L. M. Zeng, A. Wiedensohler und M. Hu. „Particle hygroscopicity and its link to chemical composition in the urban atmosphere of Beijing, China, during summertime“. Atmospheric Chemistry and Physics 16, Nr. 2 (01.02.2016): 1123–38. http://dx.doi.org/10.5194/acp-16-1123-2016.

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Abstract. Simultaneous measurements of particle number size distribution, particle hygroscopic properties, and size-resolved chemical composition were made during the summer of 2014 in Beijing, China. During the measurement period, the mean hygroscopicity parameters (κs) of 50, 100, 150, 200, and 250 nm particles were respectively 0.16 &pm; 0.07, 0.19 &pm; 0.06, 0.22 &pm; 0.06, 0.26 &pm; 0.07, and 0.28 &pm; 0.10, showing an increasing trend with increasing particle size. Such size dependency of particle hygroscopicity was similar to that of the inorganic mass fraction in PM1. The hydrophilic mode (hygroscopic growth factor, HGF > 1.2) was more prominent in growth factor probability density distributions and its dominance of hydrophilic mode became more pronounced with increasing particle size. When PM2.5 mass concentration was greater than 50 μg m−3, the fractions of the hydrophilic mode for 150, 250, and 350 nm particles increased towards 1 as PM2.5 mass concentration increased. This indicates that aged particles dominated during severe pollution periods in the atmosphere of Beijing. Particle hygroscopic growth can be well predicted using high-time-resolution size-resolved chemical composition derived from aerosol mass spectrometer (AMS) measurements using the Zdanovskii–Stokes–Robinson (ZSR) mixing rule. The organic hygroscopicity parameter (κorg) showed a positive correlation with the oxygen to carbon ratio. During the new particle formation event associated with strongly active photochemistry, the hygroscopic growth factor or κ of newly formed particles is greater than for particles with the same sizes not during new particle formation (NPF) periods. A quick transformation from external mixture to internal mixture for pre-existing particles (for example, 250 nm particles) was observed. Such transformations may modify the state of the mixture of pre-existing particles and thus modify properties such as the light absorption coefficient and cloud condensation nuclei activation.

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Peled, Aaron. „Transformation steps of microstructures in photodeposited films of a-Se“. Journal of Materials Research 4, Nr. 1 (Februar 1989): 177–79. http://dx.doi.org/10.1557/jmr.1989.0177.

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Amorphous selenium (a-Se) colloid particles have been directly photodeposited onto insulating substrates. Scanning Electron Microscopy (SEM) supported by kinetic adsorption measurements reveals the origin of the photodeposition process. The studies show that film formation occurs through a sequence of particle precipitation, growth, and photoadsorption. A plastic flow and coalescence process creates a continuous monolayer before a fast deposition rate of Se on the deposited materials commences. Surface forces seem to have an important role in the creation of the morphological structures of the adsorbed particles.

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Wu, Z. J., J. Zheng, D. J. Shang, Z. F. Du, Y. S. Wu, L. M. Zeng, A. Wiedensohler und M. Hu. „Particle hygroscopicity and its link to chemical composition in the urban atmosphere of Beijing, China during summertime“. Atmospheric Chemistry and Physics Discussions 15, Nr. 8 (20.04.2015): 11495–524. http://dx.doi.org/10.5194/acpd-15-11495-2015.

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Abstract. Simultaneous measurements of particle number size distribution, particle hygroscopic properties, and size-resolved chemical composition were made during the summer of 2014 in Beijing, China. During the measurement period, the median hygroscopicity parameters (κ) of 50, 100, 150, 200, and 250 nm particles are respectively 0.15, 0.19, 0.22, 0.27, and 0.29, showing an increasing trend with increasing particle size. When PM2.5 mass concentration is greater than 50 μg m−3, the fractions of the hydrophilic mode for 150, 250, 350 nm particles increased towards 1 as PM2.5 mass concentration increased. This indicates that aged particles dominated during severe pollution periods in the atmosphere of Beijing. Particle hygroscopic growth can be well predicted using high time-resolution size-resolved chemical composition derived from AMS measurement on a basis of ZSR mixing rule. An empirical relationship between κ of organic fraction (κorg) and oxygen to carbon ratio (O : C) (κorg= 0.08·O : C+0.02) is obtained. During new particle formation event associating with strongly active photochemistry, the hygroscopic growth factor or κ of newly formed particles is greater than for particle with the same sizes during non-NPF periods. A quick transformation from external mixture to internal mixture for pre-existing particles (for example 250 nm particle) was observed. Such transformations can modify the state of mixture of pre-exiting particles and thus modify properties such as the light absorption coefficient and cloud condensation nuclei activation.

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Berezhnoi, Yu M., D. I. Monastyrsky und O. N. Romanova. „Influence of Polyelectrolytes on the Processes of Structure Formation of Copper Powders“. Solid State Phenomena 299 (Januar 2020): 1069–74. http://dx.doi.org/10.4028/www.scientific.net/ssp.299.1069.

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The results of the studies on the synthesis of ultrafine copper powders are described in the article. The mechanisms of formation of ultrafine powders, using water-soluble polyacrylamide and polyvinyl-pyrrolidone polymers, as particle growth inhibitors, are presented. The processes occurring in the presence of water-soluble polymers and their influence on the structure of the obtained ultrafine copper powders are described. The interaction of the matrix of polymer composite materials with filler particles is analyzed. The kinetics of crystallization and transformation of crystalline phases of the powder, due to the process in the presence of water-soluble polymers, as stabilizers of particle growth, are investigated.

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Zhao, Jun-Ren, Fei-Yi Hung und Truan-Sheng Lui. „Particle Erosion Induced Phase Transformation of Different Matrix Microstructures of Powder Bed Fusion Ti-6Al-4V Alloy Flakes“. Metals 9, Nr. 7 (28.06.2019): 730. http://dx.doi.org/10.3390/met9070730.

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In this study, powder bed fusion Ti-6Al-4V alloy flake was subjected to heat treatment at 800 °C for 4 h for inducing the complete transformation of the α’ phase into the α+β phases. An erosion experiment with 450 µm mean particle diameter of Al2O3 particles at a 90° impact on both the as- powder bed fusion (PBF) Ti-6Al-4V and the 4-h 800 °C heat-treated specimens to clarify the particle erosion-induced phase transformation behavior and its effect on mechanical properties. Particle erosion-induced phase transformation to the α phase was observed on both the as-PBF Ti-6Al-4V and the heat-treated specimens. It brought about a sequential formation from the surface to the bottom: (1) a surface softened zone, (2) a hardened zone, and (3) a hardness stabilization zone. The as-PBF Ti-6Al-4V was positively eroded by erosion particles, decreasing strength and ductility. In the case of the heat-treated specimens, we found decreased strength yet an increased ductility.

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SUGAYA, R. „Cross-field plasma acceleration and potential formation induced by electrostatic waves in a relativistic magnetized plasma“. Journal of Plasma Physics 64, Nr. 2 (August 2000): 109–24. http://dx.doi.org/10.1017/s0022377800008485.

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Relativistic and non-relativistic particle acceleration along and across a magnetic field, and the generation of an electric field transverse to the magnetic field, both induced by almost perpendicularly propagating electrostatic waves in a relativistic magnetized plasma, are investigated theoretically on the basis of relativistic quasilinear transport equations. The electrostatic waves accelerate particles via Landau or cyclotron damping, and the ratio of parallel and perpendicular drift velocities vs||/vd can be proved to be proportional to k||/k⊥. Simultaneously, an intense cross-field electric field E0 = B0 × vd/c is generated via the dynamo effect owing to perpendicular particle drift to satisfy the generalized Ohm's law, which means that this cross-field particle drift is identical to E × B drift. The relativistic quasilinear transport equations for relativistic cross-field particle acceleration are derived by Lorentz transformation of the relativistic quasilinear momentum-space diffusion equation in the moving frame of reference without the electric field and the cross-field particle drift. They can be applied to the investigation of the relativistic perpendicular particle acceleration that may possibly occur in space plasmas.

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12

Wang, Z. B., M. Hu, D. L. Yue, J. Zheng, R. Y. Zhang, A. Wiedensohler, Z. J. Wu, T. Nieminen und M. Boy. „Evaluation on the role of sulfuric acid in the mechanisms of new particle formation for Beijing case“. Atmospheric Chemistry and Physics Discussions 11, Nr. 8 (29.08.2011): 24165–89. http://dx.doi.org/10.5194/acpd-11-24165-2011.

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Abstract. New particle formation (NPF) is considered as an important mechanism for gas-to-particle transformation, and gaseous sulfuric acid is believed as a curcial precursor. Up to now few field-based studies on nucleation mechanisms and the role of sulfuric acid were conducted in China. In this study, simultaneously measurements of particle number size distributions and gaseous sulfuric acid concentrations were performed from July to September in 2008. Totally, 22 new particle formation events were observed during the entire 85 campaign days. The results show that the condensation sink of pre-existing particles is one of the limiting factors to determine the occurrence of nucleation events in Beijing. The concentrations of gaseous sulfuric acid show good correlations with freshly nucleated particles (N3–6) and formation rates (J3 and J1.5). The power-law relationship between H2SO4 concentration and N3–6 or J was adopted to explore the nucleation mechanism. The exponents range from 1 to 5. More than half of the NPF events exhibit an exponent larger than 2.5. For these cases, the thermodynamic process works better than the activation or kinetic nucleation theories to explain the nucleation events in urban atmosphere of Beijing.

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Ulevičius, V., D. Butkus, K. Plauškaitė, A. Girgždys, S. Byčenkienė und N. Špirkauskaitė. „Impact of krypton-85 beta radiation on aerosol particle formation and transformation“. Lithuanian Journal of Physics 49, Nr. 4 (2009): 471–78. http://dx.doi.org/10.3952/lithjphys.49411.

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14

Chen, Nan Chun, Quan Tang, Xiao Hu Zhang, Wei Wang und Meng Ying Li. „Structure Analysis of Type-A Zeolites Molecular Sieve Prepared from Stellerite“. Advanced Materials Research 412 (November 2011): 378–83. http://dx.doi.org/10.4028/www.scientific.net/amr.412.378.

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Type-A zeolites molecular sieve is prepared after crystallization of the type-A zeolites molecular sieve precursor, which is prepared from Stellerite, at temperature of 90 ~ 100°C for 6 hours. It has a complete structure, with crystallinity of 98%, volume average particle size of 3.72µm and particle size distribution which is less than 10µm over 90%. Multi-member rings structure in the type-A zeolites molecular sieve cover each other, forming the cage (β-cage, α-cage, octahedral cage) structure. Nuclei and nanometer particles are formed after the further congregation reaction, and then gather and grow, result in the formation of nanometer crystal particles and transformation to micrometer particles.

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Xie, Yuanyuan, Xingnan Ye, Zhen Ma, Ye Tao, Ruyu Wang, Ci Zhang, Xin Yang, Jianmin Chen und Hong Chen. „Insight into winter haze formation mechanisms based on aerosol hygroscopicity and effective density measurements“. Atmospheric Chemistry and Physics 17, Nr. 11 (16.06.2017): 7277–90. http://dx.doi.org/10.5194/acp-17-7277-2017.

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Abstract. We characterize a representative particulate matter (PM) episode that occurred in Shanghai during winter 2014. Particle size distribution, hygroscopicity, effective density, and single particle mass spectrometry were determined online, along with offline analysis of water-soluble inorganic ions. The mass ratio of SNA ∕ PM1. 0 (sulfate, nitrate, and ammonium) fluctuated slightly around 0.28, suggesting that both secondary inorganic compounds and carbonaceous aerosols contributed substantially to the haze formation, regardless of pollution level. Nitrate was the most abundant ionic species during hazy periods, indicating that NOx contributed more to haze formation in Shanghai than did SO2. During the representative PM episode, the calculated PM was always consistent with the measured PM1. 0, indicating that the enhanced pollution level was attributable to the elevated number of larger particles. The number fraction of the near-hydrophobic group increased as the PM episode developed, indicating the accumulation of local emissions. Three banana-shaped particle evolutions were consistent with the rapid increase of PM1. 0 mass loading, indicating that the rapid size growth by the condensation of condensable materials was responsible for the severe haze formation. Both hygroscopicity and effective density of the particles increased considerably with growing particle size during the banana-shaped evolutions, indicating that the secondary transformation of NOx and SO2 was one of the most important contributors to the particle growth. Our results suggest that the accumulation of gas-phase and particulate pollutants under stagnant meteorological conditions and subsequent rapid particle growth by secondary processes were primarily responsible for the haze pollution in Shanghai during wintertime.

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Hu, Da Wei, und Yan Ming Wang. „Preparation of Hexagonal Fe₃O₄ Nanometer Particles via Weakly Magnetic Field Assisted Oxidation Co-Precipitation“. Advanced Materials Research 418-420 (Dezember 2011): 286–92. http://dx.doi.org/10.4028/www.scientific.net/amr.418-420.286.

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This paper utilized a novel oxidative co-precipitation method to synthesis hexagonal Fe3O4 nanometer particles, which assisted by a weakly magnetic field. The crystallinity, morphology, particle size distribution, compositions and magnetic properties of the as-prepared particles were investigated using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), ultrasonic particle sizer (UPS), X-ray photoelectron spectra (XPS) and vibrating sample magnetometer (VSM). The formation mechanism of the hexagonal Fe3O4 nanometer particles, which assisted by a weakly magnetic field was also discussed. The results shown that the as-prepared hexagonal particles were purity magnetite (Fe3O4), and the weakly magnetic field could accelerate the phase transformation from goethite (α-FeOOH) to magnetite (Fe3O4), increase the particle size and uniform the morphology. The values of saturation magnetization (Ms) and coercivity (H) of the hexagonal magnetic particles are 71.05 emu•g-1 and 474.3 Oe, respectively, which contributed to the morphology anisotropy of the particles.

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Gao, Xin-Yi, Yong-Jiang Guo und Wen-Rui Shan. „Scaling and hetero-/auto-Bäcklund transformations with solitons of an extended coupled (2+1)-dimensional Burgers system for the wave processes in hydrodynamics and acoustics“. Modern Physics Letters B 34, Nr. 34 (16.11.2020): 2050389. http://dx.doi.org/10.1142/s0217984920503893.

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The Burgers-type equations are applied to oceanography, hydrodynamic turbulence, gas dynamics, shock-wave formation, acoustic transmission structure, boundary-layer behavior, continuum-traffic simulation, convection-dominated diffusion, wave formation in the thermo-elastic media, vorticity transport, dispersion in the porous media, particle sedimentation in fluid suspension, colloid evolution, and so forth. Hereby, taking into account the wave processes in hydrodynamics and acoustics, we investigate an extended coupled (2+1)-dimensional Burgers system, and with symbolic computation, work out a scaling transformation, two hetero-Bäcklund transformations and two auto-Bäcklund transformations, with the soliton solutions. Our results are dependent on the coefficients in the system.

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Xu, G. R., C. S. B. Fitzpatrick und J. Gregory. „Floc Formation, Size Distribution, and its Transformation Detected by Online Laser Particle Counter“. Separation Science and Technology 43, Nr. 7 (Mai 2008): 1725–36. http://dx.doi.org/10.1080/01496390801973706.

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Cassidy-Hanley, Donna, Josephine Bowen, John H. Lee, Eric Cole, Lynn A. VerPlank, Jacek Gaertig, Martin A. Gorovsky und Peter J. Bruns. „Germline and Somatic Transformation of Mating Tetrahymena thermophila by Particle Bombardment“. Genetics 146, Nr. 1 (01.05.1997): 135–47. http://dx.doi.org/10.1093/genetics/146.1.135.

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Mating Tetrahymena thermophila were bombarded with ribosomal DNA-coated particles at various times in development. Both macronuclear and micronuclear transformants were recovered. Optimal developmental stages for transformation occurred during meiosis for the micronucleus and during anlagen formation for the macronucleus. Evidence is given for transient retention of the introduced plasmid. Genetic and molecular tests confirmed that sexually heritable transformation was associated with integration at the homologous site in the recipient micronuclear chromosome.

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Jensen, Kirsten, Henrik Andersen, Christoffer Tyrsted, Espen Bøjesen, Nina Lock, Simon Billinge, Bo Iversen und Mogens Christensen. „Formation of γ-Fe2O3 in hydrothermal synthesis: In situ total scattering studies“. Acta Crystallographica Section A Foundations and Advances 70, a1 (05.08.2014): C1180. http://dx.doi.org/10.1107/s2053273314088196.

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The properties of metal oxide nanoparticles are highly dependent on particle characteristics such as size, crystallinity, and structural defects. To obtain particles with tailormade properties, it is crucial to understand the mechanisms that govern these characteristics during material synthesis. For this purpose, in situ studies of particle synthesis have proven powerful.[1] Here, in situ Total Scattering (TS) combined with in situ PXRD studies of the hydrothermal synthesis of γ-Fe2O3 (maghemite) from ammonium iron citrate will be presented. In situ TS with Pair Distribution Function (PDF) analysis has recently shown to be an efficient tool for understanding the fundamental chemical processes in particle crystallization.[2,3] The full γ-Fe2O3 crystallization process from ionic complexes over nanoclusters to crystalline particles is followed and material formation mechanisms are suggested. The study shows that the local atomic structure of the precursor solution is similar to that of the crystalline coordination polymer [Fe(H2citrate)(H2O)]n where corner sharing [FeO6] octahedra are linked by citrate. As hydrothermal treatment of the solution is initiated, clusters of edge sharing [FeO6] units form. Tetrahedrally coordinated iron subsequently appears in the structure and as the synthesis continues, the clusters slowly assemble into nanocrystalline maghemite. The primary transformation from amorphous clusters to nanocrystallites takes place by condensation of the large clusters along corner sharing tetrahedral iron units. The crystallization process is related to large changes in the local structure as the interatomic distances in the clusters change dramatically with cluster growth. The local atomic structure is size dependent, and particles below 6 nm are highly disordered. Whole Powder Pattern Modelling of the PXRD data shows that the final crystallite size (<10 nm) is dependent on synthesis temperature and that the size distribution of the particles broadens with synthesis time.

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Makonese, T., P. Forbes, L. Mudau und H. J. Annegarn. „Aerosol particle morphology of residential coal combustion smoke“. Clean Air Journal 24, Nr. 2 (03.12.2014): 24–28. http://dx.doi.org/10.17159/caj/2014/24/2.7064.

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A study carried out at the University of Pretoria characterised aerosol particle morphology of residential coal combustion smoke. The general approach in this study was on individual particle conglomerations because the radiative, environmental, and health effects of particles may depend on specific properties of individual particles rather than on the averaged bulk composition properties. A novel, miniature denuder system, developed and tested at the University of Pretoria, was used to capture particle emissions from the coal fires. The denuder consists of two silicone rubber traps (for gas phase semi-volatile organic compound monitoring) in series separated by a quartz fibre filter (for particle collection). The denuders were positioned 1 m away from the fire and were connected to pumps that sampled ~5 litres of air over a 10 min sampling interval. A JSM 5800LV Scanning Electron Microscope with a Thermo Scientific EDS was used to analyse the structure and morphology of different aerosol samples from the quartz fibre filters. Eight samples from the different fire lighting methods were selected for SEM analysis. The punched samples were sputter coated with gold for ~15 minutes using a K550 Emitech Sputter Coater. Results show that apart from the fine and ultra-fine particles, coal smoke from domestic burning also contains aerosols greater than 5 μm in diameter. Consequently, we describe the potential for generation of ‘giant’ carbonaceous soot conglomerates with outer diameters of 5 to 100 μm. However, the exact mechanism for formation of such large soot conglomerates remains to be determined. We also describe the presence of spherules and solid ‘melted toffee’ irregular surfaces. Circumstantial evidence is used to postulate and discuss the possible modes of formation in terms of condensation, and partial melting. This work provides a description of the modes of formation and transformation of conglomerates originating from low temperature (<8000C) coal combustion.

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Wang, Z. B., M. Hu, D. L. Yue, J. Zheng, R. Y. Zhang, A. Wiedensohler, Z. J. Wu, T. Nieminen und M. Boy. „Evaluation on the role of sulfuric acid in the mechanisms of new particle formation for Beijing case“. Atmospheric Chemistry and Physics 11, Nr. 24 (15.12.2011): 12663–71. http://dx.doi.org/10.5194/acp-11-12663-2011.

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Abstract. New particle formation (NPF) is considered as an important mechanism for gas-to-particle transformation, and gaseous sulfuric acid is believed as a crucial precursor. Up to now few field-based studies on nucleation mechanisms and the role of sulfuric acid were conducted in China. In this study, simultaneously measurements of particle number size distributions and gaseous sulfuric acid concentrations were performed from July to September in 2008. Totally, 22 new particle formation events were observed during the entire 85 campaign days. The results show that in the case of both higher source and sink values, the result of the competition between source and sink is more likely the key limiting factor to determine the observation of NPF events in Beijing. The concentrations of gaseous sulfuric acid show good correlations with freshly nucleated particles (N3-6 and formation rates (J3 and J1.5. The power-law relationship between H2SO4 concentration and N3-6 or J is adopted to explore the nucleation mechanism. The exponents are showed a great range (from 1 to 7). More than half of the NPF events exhibit an exponent larger than 2.5. For these cases, the thermodynamic process works better than the activation or kinetic nucleation theories to explain the nucleation events in urban atmosphere of Beijing.

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Shimizu, T., Y. Yamamoto und N. Tenma. „Methane-Hydrate-Formation Processes in Methane/Water Bubbly Flows“. SPE Journal 22, Nr. 03 (05.10.2016): 746–55. http://dx.doi.org/10.2118/176156-pa.

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Summary Offshore natural-gas production from methane-hydrate (MH) reservoirs has received considerable attention. In this study, the offshore production method is briefly described, followed by the flow loop experiments performed to investigate the formation processes of MH in methane-in-water bubbly flows. Transient processes of phase transformation are characterized by phase paths, flow morphologies, pump heads, and in-situ particle-size measurements. It is realized that an MH slurry is generated by MH shells covering unconverted bubbles, whereas it can be transformed into a colloidal flow with fine crystalline particles under an intense turbulent shear. This study suggests that, in practice, the flow pattern under MH formation would be determined by the phase path and the flow velocity in the pipeline, which is one of the important factors considered in the evaluation of flow-assurance risks.

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Hofmeister, H., G. L. Tan und M. Dubiel. „Shape and Internal Structure of Silver Nanoparticles Embedded in Glass“. Journal of Materials Research 20, Nr. 6 (01.06.2005): 1551–62. http://dx.doi.org/10.1557/jmr.2005.0197.

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The structural characteristics of silver nanoparticles embedded in glass by various routes of fabrication were studied in detail using high-resolution electron microscopy to find out if they are influenced by interaction with the surrounding glass matrix. Besides the formation conditions, the strength of the interaction between metal and glass governs the size-dependent changes of lattice spacings in such nanoparticles. However, determination of these changes is not straightforward because of complicated particle configurations and the interference nature of the lattice imaging technique. Imaging of lattice plane fringes and careful diffractogram analysis allowed the exclusion of any kind of tetragonal lattice distortion or transformation to hexagonal lattice type that may be deduced at first sight. Instead, the formation of twin faults in these nanoparticles turned out to be the essential structural feature and the main source of confusion about the lattice structure observed. The variety of particle forms is comparable to particles supported on oxide carriers. It is composed of single-crystalline particles of nearly cuboctahedron shape, particles containing single twin faults, multiple twinned particles containing parallel twin lamellae, and multiple twinned particles composed of cyclic twinned segments arranged around axes of 5-fold symmetry. The more twin planes involved in the particle composition, the more complicated is the interpretation of lattice spacings and lattice fringe patterns due to superposition of several twin segments.

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Bid, S., und S. K. Pradhan. „Preparation and microstructure characterization of ball-milled ZrO2powder by the Rietveld method: monoclinic to cubic phase transformation without any additive“. Journal of Applied Crystallography 35, Nr. 5 (18.09.2002): 517–25. http://dx.doi.org/10.1107/s0021889802008725.

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The phase transformation kinetics of high-energy ball-milled monoclinic ZrO2have been studied in detail by Rietveld powder structure refinement analysis. In the present study, no stabilizing compound was required to obtain the cubic phase. The fine-grain powder was milled in a planetary ball mill for up to several hours at different BPMRs (ball to powder mass ratios): 10:1, 20:1, 35:1 and 40:1. During the process of ball milling, the monoclinic phase is gradually transformed to the cubic phase. The relative phase abundances of the respective phases, the particle sizes, the r.m.s. strains, the lattice parameter changes,etc., have been estimated from Rietveld analysis of X-ray powder diffraction data. It has been found that a higher BPMR exerts more influence on rapid phase transformation. In them- toc-ZrO2phase transformation, no formation of an intermediate tetragonal ZrO2phase has been found. The small change in the lattice volume ofm-ZrO2, which is very close to the lattice volume ofc-ZrO2, caused by ball milling may be attributed to this phase change. The formation of thecphase is noticed, in general, after just 1 h of ball milling, and the particle size of themphase is reduced to a large extent at the first stage of milling and remains almost unchanged with increasing milling time. However, the particle size of thecphase increases with increasing milling time for the samples milled with higher BPMRs (35:1 and 40:1), suggesting that quenching caused by a high impact energy followed by an annealing effect may play a vital role, which is further manifested in the agglomeration of small particles.

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Bielefeldt, Brent R., Jacob D. Hochhalter und Darren J. Hartl. „Shape memory alloy sensory particles for damage detection: Experiments, analysis, and design studies“. Structural Health Monitoring 17, Nr. 4 (28.08.2017): 777–814. http://dx.doi.org/10.1177/1475921717721194.

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Developing novel techniques for monitoring structural integrity has become an important area of research in the aerospace community. One new technique exploits the stress-induced phase transformation behavior in shape memory alloy particles embedded in a structure. By monitoring changes in the mechanical and/or electromagnetic behavior of such particles, the formation or propagation of fatigue cracks in the vicinity of these particles can be detected. This work demonstrates sensory particle response to local structural damage using finite element modeling for the first time. Using an optimization method to minimize the difference between experimentally measured strain and simulated results, a good approximation of sensory particle properties can be determined and the strong sensory response of the transforming particle demonstrated. To illustrate an application of this method, a multi-scale finite element model of sensory particles embedded in the root rib of an aircraft wing is then considered. In particular, this unique model utilizes substructure modeling to maintain computational efficiency while relating globally applied loads to local structural response, allowing for the consideration of predicted particle response to crack propagation during wing loading. The effect of particle position relative to the crack tip on particle sensory response is assessed. Finally, this work demonstrates how sensory particles can be used to approximate the location of structural damage by interpolating a stress field based on the responses of multiple sensory particles in the vicinity of a propagating crack.

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Kang, Chin-Shuo, und Edward Evans. „Synthesis and Transformation of Hollow Rutile Titania Wires by Single Spinneret Electrospinning with Sol-Gel Chemistry“. Fibers 9, Nr. 3 (06.03.2021): 18. http://dx.doi.org/10.3390/fib9030018.

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The work described below was carried out to understand how to control the morphology of nanostructured titania calcined from electrospun nanofibers. This is the first report of hollow rutile nanofibers synthesized from electrospun nanofibers with short calcination time. Titanium isopropoxide was incorporated into the nanofibers as the titania precursor. The electrospinning technique was used to fabricate ceramic/polymer hybrid nanofibers. The electrospun nanofibers were then calcined to produce rutile titania nanofibers with different morphologies (hollow or solid nanofibers), which were characterized by SEM and TEM. The initial concentration of ceramic precursor and the calcination time were shown to control the morphology of the nanofiber. The hollow morphology was only obtained with a concentration of the precursor within a certain level and with short calcination times. The heat treatment profile contributed to particle growth. At longer times, the particle growth led to the closure of the hollow core and all the nanofibers resembled strings of solid particles. A formation mechanism for the hollow nanofibers is also proposed.

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Pfrang, C., M. Shiraiwa und U. Pöschl. „Chemical ageing and transformation of diffusivity in semi-solid multi-component organic aerosol particles“. Atmospheric Chemistry and Physics Discussions 11, Nr. 4 (27.04.2011): 13003–33. http://dx.doi.org/10.5194/acpd-11-13003-2011.

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Abstract. Recent experimental evidence underlines the importance of reduced diffusivity in amorphous semi-solid or glassy atmospheric aerosols. This paper investigates the impact of diffusivity on the ageing of multi-component reactive organic particles representative of atmospheric cooking aerosols. We apply and extend the recently developed KM-SUB model in a study of a 12-component mixture containing oleic and palmitoleic acids. We demonstrate that changes in the diffusivity may explain the evolution of chemical loss rates in ageing semi-solid particles, and we resolve surface and bulk processes under transient reaction conditions considering diffusivities altered by oligomerisation. This new model treatment allows prediction of the ageing of mixed organic multi-component aerosols over atmospherically relevant time scales and conditions. We illustrate the impact of changing diffusivity on the chemical half-life of reactive components in semi-solid particles, and we demonstrate how solidification and crust formation at the particle surface can affect the chemical transformation of organic aerosols.

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Pfrang, C., M. Shiraiwa und U. Pöschl. „Chemical ageing and transformation of diffusivity in semi-solid multi-component organic aerosol particles“. Atmospheric Chemistry and Physics 11, Nr. 14 (26.07.2011): 7343–54. http://dx.doi.org/10.5194/acp-11-7343-2011.

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Abstract. Recent experimental evidence underlines the importance of reduced diffusivity in amorphous semi-solid or glassy atmospheric aerosols. This paper investigates the impact of diffusivity on the ageing of multi-component reactive organic particles approximating atmospheric cooking aerosols. We apply and extend the recently developed KM-SUB model in a study of a 12-component mixture containing oleic and palmitoleic acids. We demonstrate that changes in the diffusivity may explain the evolution of chemical loss rates in ageing semi-solid particles, and we resolve surface and bulk processes under transient reaction conditions considering diffusivities altered by oligomerisation. This new model treatment allows prediction of the ageing of mixed organic multi-component aerosols over atmospherically relevant timescales and conditions. We illustrate the impact of changing diffusivity on the chemical half-life of reactive components in semi-solid particles, and we demonstrate how solidification and crust formation at the particle surface can affect the chemical transformation of organic aerosols.

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Liu, Yang, Qinwei Wang, Bingqing Yao, Daibo Zhu, Deshan Chen und Peng Zhang. „Microstructure and Mechanical Evolution of Cu-2.7Be Sheets via Annealing“. Metals 10, Nr. 2 (11.02.2020): 241. http://dx.doi.org/10.3390/met10020241.

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The microstructure and mechanical properties of cold-rolled Cu-2.7Be sheets under various annealing processes and conditions were investigated in this research. The increased beryllium content in the Cu-2.7Be alloy facilitates the formation of brittle secondary phases. Consequently, the study highlights the functionality of annealed Cu-2.7Be alloys as more favorable dynodes than the traditionally used Cu-2.0Be alloys. The mechanism of recrystallization used for the transformation of Cu-2.7Be alloys was that of continuous static recrystallization (cSRX). Moreover, the relationship between the orientation of the β phases and that of the surrounding Cu-matrix was determined to be (111)α∥(110)β and (011)α∥(001)β. The β phase has a body-centered cubic (bcc) structure with a = b = c = 0.281 nm. The β phase undergoes a morphology transformation from primitive lath-shaped β particles to quadrangle-shaped β particles during the annealing process. Such transformations could potentially have an effect on the mechanical properties of Cu-2.7Be sheets. There was a noticeable decline in the yield strength of the Cu-2.7Be after annealing, and the samples annealed at 770 °C for 15 min achieved the elongation with deep and uniform dimples caused by suitable β particle sizes, appropriate grain sizes, and the maximum volume fraction of ∑3 boundaries.

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Sakthinathan, Indherjith, Manivannan Mahendran, Karthik Krishnan und Selvakumar Karuthapandi. „Selenium tethered copper phthalocyanine hierarchical aggregates as electrochemical hydrogen evolution catalysts“. Sustainable Energy & Fuels 5, Nr. 14 (2021): 3617–31. http://dx.doi.org/10.1039/d1se00595b.

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Oxidative transformation of (n-OctSe)₈CuPc in different solvent systems leads to the formation of hierarchically structured fibrous and particle aggregates that allow the HER to occur at a very low overpotential.

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Liang, Changhao, Yoshiki Shimizu, Takeshi Sasaki und Naoto Koshizaki. „Synthesis, characterization, and phase stability of ultrafine TiO2 nanoparticles by pulsed laser ablation in liquid media“. Journal of Materials Research 19, Nr. 5 (Mai 2004): 1551–57. http://dx.doi.org/10.1557/jmr.2004.0208.

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We synthesized ultrafine TiO2 nanoparticles by pulsed laser ablation of a titanium target immersed in an aqueous solution of surfactant sodium dodecyl sulfate (SDS) or deionized water. The surfactant concentration dependence of TiO2 nanocrystal formation was systematically investigated by various characterization techniques. The maximum amount of ultrafine anatase nanocrystalline particles (with mean size of 3 nm in diameter) was obtained in an aqueous solution of 0.01 M SDS. A probable formation process was proposed based on the laser-induced reactive quenching and surfactant-mediated growth. The phase transformation and particle growth of as-prepared products were also investigated by heat treatment up to 500 °C. Single-phase anatase nanoparticles with a mean size of 8 nm were obtained by heat treatment of samples prepared in water or in a 0.01 M SDS solution. Particle size did not substantially increase through annealing, probably due to the relatively homogeneous size distribution and crystallinity of as-prepared titania nanoparticles.

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Korolev, Alexei. „Limitations of the Wegener–Bergeron–Findeisen Mechanism in the Evolution of Mixed-Phase Clouds“. Journal of the Atmospheric Sciences 64, Nr. 9 (01.09.2007): 3372–75. http://dx.doi.org/10.1175/jas4035.1.

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Abstract Phase transformation and precipitation formation in mixed-phase clouds are usually associated with the Wegener–Bergeron–Findeisen (WBF) process in which ice crystals grow at the expense of liquid droplets. The evolution of mixed-phase clouds, however, is closely related to local thermodynamical conditions, and the WBF process is just one of three possible scenarios. The other two scenarios involve simultaneous growth or evaporation of liquid droplets and ice particles. Particle evolution in the other two scenarios differs significantly from that associated with the WBF process. Thus, during simultaneous growth, liquid droplets compete for the water vapor with the ice particle, which slows down the depositional growth of ice particles instead of promoting their growth at the expense of the liquid as in the WBF process. It is shown that the WBF process is expected to occur under a limited range of conditions and that ice particles and liquid droplets in mixed-phase clouds are not always processed in accordance with the WBF mechanism.

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Grahn, A. Marika, Rimantas Daugelavičius und Dennis H. Bamford. „The Small Viral Membrane-Associated Protein P32 Is Involved in Bacteriophage PRD1 DNA Entry“. Journal of Virology 76, Nr. 10 (15.05.2002): 4866–72. http://dx.doi.org/10.1128/jvi.76.10.4866-4872.2002.

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ABSTRACT The lipid-containing bacteriophage PRD1 infects a variety of gram-negative cells by injecting its linear double-stranded DNA genome into the host cell cytoplasm, while the protein capsid is left outside. The virus membrane and several structural proteins are involved in phage DNA entry. In this work we identified a new infectivity protein of PRD1. Disruption of gene XXXII resulted in a mutant phenotype defective in phage reproduction. The absence of the protein P32 did not compromise the particle assembly but led to a defect in phage DNA injection. In P32-deficient particles the phage membrane is unable to undergo a structural transformation from a spherical to a tubular form. Since P32− particles are able to increase the permeability of the host cell envelope to a degree comparable to that found with wild-type particles, we suggest that the tail-tube formation is needed to eject the DNA from the phage particle rather than to reach the host cell interior.

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Soltis, Jennifer A., Joshua M. Feinberg, Benjamin Gilbert und R. Lee Penn. „Phase Transformation and Particle-Mediated Growth in the Formation of Hematite from 2-Line Ferrihydrite“. Crystal Growth & Design 16, Nr. 2 (19.01.2016): 922–32. http://dx.doi.org/10.1021/acs.cgd.5b01471.

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Jacot, Alain, und Amin Rostamian. „A Numerical Model for the Description of Massive and Lamellar Microstructure Formation in Gamma-TiAl“. Materials Science Forum 539-543 (März 2007): 1481–86. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.1481.

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A phenomenological modeling approach has been developed to describe the massive transformation and the formation of lamellar microstructures during cooling in gamma titanium aluminides. The modeling approach is based on a combination of nucleation and growth laws which take into account the specific mechanisms of each phase transformation. Nucleation of both massive and lamellar γ is described with classical nucleation theory, accounting for the fact that nuclei are formed predominantly at α/α grain boundaries. Growth of the massive γ grains is calculated with a mathematical expression for interface-controlled reactions. A modified Zener model is used to calculate the thickening rate of the γ lamellar precipitates. The model incorporates the effect of particle impingement and rapid coverage of the nucleation sites due to growth. The driving pressures of the phase transformations are obtained form Thermo-Calc based on actual temperature and matrix composition. The model permitted investigating the influence of alloy chemistry, cooling rate and average α grain size upon the amount of massive γ and the average thickness and spacing of the lamellae. Calculated CCT diagrams were compared with experimental data collected from the literature and showed good agreement.

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Park, Jong-Chul, Jae-Hwan Pee und Hyung-Ho Park. „Effect of presynthesis of Ta precursor on the formation of Ta nitrides“. Journal of Materials Research 25, Nr. 5 (Mai 2010): 835–41. http://dx.doi.org/10.1557/jmr.2010.0114.

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We synthesized Ta3N5 by ammonolysis of Ta(OH)5. Ta(OH)5 was prepared by titration using TaCl5. The stirring speed and the amount of NH4OH to be added were important factors for controlling the particle size and formation of Ta(OH)5 during titration. During transformation of Ta(OH)5 to Ta3N5, the color changed from white to red. A small particle size and high level of formation of Ta(OH)5 improved nitridation, which was related to the color value. An x-ray diffractometer was used for phase identification. A scanning electron microscope was used to determine the microstructure, particle shape, and size. A colorimeter was used to obtain CIELab values. Ultraviolet–visible (UV–VIS) spectroscopy was carried out to determine the absorbance of colored powders. Thermogravimetry and a differential scanning calorimeter were used in air with a heating rate of 5 °C/min for thermal stability and behavior. An ON detector was used for detecting oxygen and nitrogen contents in Ta3N5.

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Dong, Yan, Yang Zhou, Xue Lin Han und Wei Jie Gu. „Aluminate Green Phosphor with Small Particle Size Used for PDP via Co-Precipitation Method“. Advanced Materials Research 295-297 (Juli 2011): 890–95. http://dx.doi.org/10.4028/www.scientific.net/amr.295-297.890.

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Mg doped BaAl12O19:Mn2+ phosphor is one of the most efficient green phosphors for PDP. It is difficult to prepare the phosphor both have small particle size (< 3μm) and high luminescence. In the present work, a BaAl12O19:Mn2+ phosphor with small particle size was synthesized by the chemical co-precipitation method. Phase transformation and particle growth process during calcining process were investigated. The nucleation process was also discussed. The results show that, the phase transformation is complicated, the transition phases include BaCO3, γ-Al2O3, BaF2, BaAl2O4 and two phases contain Mn; The BaAl12O19 phase is formed from the reaction between BaAl2O4 phase and γ-Al2O3 phase, no a-Al2O3 phase appears during the entire process; The formation temperature of pure BaAl12O19 phase is 1200°C, which is lower than that in the high-temperature solid state reaction method. High efficiency BaAl12O19:Mn2+ phosphor with small particle size (< 2μm) and hexagonal flaky shape can be prepared by this method.

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Lin, Hong-Ming, Chi-Ming Hsu, Ching-Shung Huang, Ming-Shyong Lay und Pee-Yew Lee. „HRTEM Image of Twin Structure in Nanocrystalline Platinum“. Proceedings, annual meeting, Electron Microscopy Society of America 51 (01.08.1993): 1160–61. http://dx.doi.org/10.1017/s0424820100151635.

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This paper presents recent result on the observation of microstructure of nanocrystalline platinum. Nanocrystalline powders of Pt are made by gas condensation method, and examined by using TEM and HRTEM. Twin structure is found first within the individual particle of as evaporated nanophase Pt particles which form twin during the nucleation and growth of particle. Twin also appears while neck growth take place during the sintering of as evaporated pt with Al2O3. The formation of these twins during sintering was due to the fact that the neck growth will induce a tensile stress which is high enough to pull the nanocrystalline powders to form twin structure. Twin plane of nanophase sintering Pt powder was identified by using the Fourier transformation as {111} plane. It is the same as usually found in fcc bulk materials.The pure nanocrystalline Pt particles with a diameter less than 100 nm had been produced by the gas evaporation in helium atmosphere.

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Mahato, Anirban, Yang Guo, Narayan K. Sundaram und Srinivasan Chandrasekar. „Surface folding in metals: a mechanism for delamination wear in sliding“. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, Nr. 2169 (08.09.2014): 20140297. http://dx.doi.org/10.1098/rspa.2014.0297.

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Using high-resolution, in situ imaging of a hard, wedge-shaped model asperity sliding against a metal surface, we demonstrate a new mechanism for particle formation and delamination wear. Damage to the residual surface is caused by the occurrence of folds on the free surface of the prow-shaped region ahead of the wedge. This damage manifests itself as shallow crack-like features and surface tears, which are inclined at very acute angles to the surface. The transformation of folds into cracks, tears and particles is directly captured. Notably, a single sliding pass is sufficient to damage the surface, and subsequent passes result in the generation of platelet-like wear particles. Tracking the folding process at every stage from surface bumps to folds to cracks/tears/particles ensures that there is no ambiguity in capturing the mechanism of wear. Because fold formation and consequent delamination are quite general, our findings have broad applicability beyond wear itself, including implications for design of surface generation and conditioning processes.

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Guo, Yi, Shaohong Wei, Sheng Yang, Yubin Ke, Xiaoyong Zhang und Kechao Zhou. „Precipitation Behavior of ω Phase and ω→α Transformation in Near β Ti-5Al-5Mo-5V-1Cr-1Fe Alloy during Aging Process“. Metals 11, Nr. 2 (05.02.2021): 273. http://dx.doi.org/10.3390/met11020273.

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In this work, the precipitation behavior of the ω phase and ω→α transformation in Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy was investigated during isothermal aging at 450 °C. The results show that the α precipitates increase with the increasing of aging time, resulting from the β→α and ω→α transformations. The ω→→α transformation involves the formation and evolution of the isothermal ω phase. The formation of the isothermal ω phase occurs after 30 min and ends at 120 min, which is caused by the embryonic ω phase to isothermal ω phase transformation. Small angle neutron scattering (SANS) results indicates that the evolution of the isothermal ω phase goes through the increasing average size and aspect ratio from 24.7 to 47.0 nm and from 2.1 to 2.7 respectively, and the morphology evolution of the ω particle from ellipsoid to spindle-like. Moreover, the isothermal ω phase assists the α phase to nucleate at the ω/β interface, which involves the changes in elemental composition. The α phase is enriched in Al. Compared to the α phase, the element of Mo, V and Cr in the isothermal ω phase is lower. The Fe element is uniformly distributed in the isothermal ω phase and β matrix but lean in the α phase.

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Li, Ying, Wei Dong, Yi Fan Fu, Yi Tan, Ayako Miura und Akira Kawasaki. „The Critical Cooling Rate of Fe-Based Mono-Sized Spherical Particles with Fully Glassy Phase“. Advanced Materials Research 509 (April 2012): 185–91. http://dx.doi.org/10.4028/www.scientific.net/amr.509.185.

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A new method to evaluate the critical cooling rate, Rc of Fe-based metallic glass alloy was proposed and discussed. [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 alloy particles were prepared with narrow size distribution and high sphericity by Pulsated Orifice Ejection Method in Ar, He and 50%Ar+50%He mixed atmosphere, respectively. Phase transition of a particle from amorphous to amorphous-crystalline and fully crystalline occurred with the increase of particle diameter. Rc of the formation of fully amorphous phase was estimated to be in the range of 700-1100 K/s, lower than that measured by time-temperature transformation diagram of bulk metallic alloy. No change of Rc occurred in Ar, He or 50%Ar+50%He mixed atmosphere, which proved it an effective method to evaluate the critical cooling rate of Fe-based metallic glass alloy.

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Barrientos-Hernández, F. R., M. Pérez-Labra, A. Lobo-Guerrero, M. Reyes-Pérez, J. C. Juárez-Tapia, J. Hernández-Ávila, E. Cardoso-Legorreta und J. P. Hernández-Lara. „Effect of Particle Size and Sintering Temperature on the Formation of Mullite from Kyanite and Aluminum Mixtures“. Advances in Materials Science and Engineering 2021 (26.02.2021): 1–13. http://dx.doi.org/10.1155/2021/6678297.

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The effect of particle size and sintering temperature of the mixtures of kyanite and metallic aluminum related to the thermal transformation of kyanite into primary mullite and free silica was studied. In addition, the reaction between α-Al2O3 (in situ produced by aluminum oxidation) and the silica was obtained in cristobalite structure from kyanite to obtain secondary mullite. The kyanite powders were milled by 0.5, 3, 6, and 12 hours and then were mixed with aluminum powder, which were previously milled by 3 hours. After that, the powders were characterized by X-ray diffraction technique (XRD), scanning electronic microscopy (SEM), differential thermal analysis (DTA), and thermogravimetric analysis (TGA), and the particle size was determined in a centrifugal analyzer particle size Shimadzu model SA-CP4. The mixed powders were pressed uniaxially into cylindrical samples (compacts), and then sintering was conducted at 1100, 1200, 1300, 1400, 1500, and 1600°C; these samples were characterized by XRD, SEM, and thermodilatometry analysis (TD); density and open porosity measurements were performed by the Archimedes method. The samples were thermally etched to observe the microstructure, which consisted of mullite equiaxial grains contained in a glassy phase. It was observed that the nonmilled kyanite mineral becomes into mullite plus silica at temperatures between 1400 and 1500°C. When the particle size was reduced at sizes less than 1 µm, the transformation temperature was low until 200°C; the X-ray patterns of the sintered samples at 1400°C, ground for 6 hours, showed mullite peaks with small reflections of cristobalite and α-Al2O3, and these samples exhibited high density and low open porosity.

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Janaćković, Dj, V. Jokanović, Lj Kostić-Gvozdenović, Lj Živković und D. Uskoković. „Synthesis, morphology, and formation mechanism of mullite particles produced by ultrasonic spray pyrolysis“. Journal of Materials Research 11, Nr. 7 (Juli 1996): 1706–16. http://dx.doi.org/10.1557/jmr.1996.0214.

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Submicrometer spherical particles of mullite powder were synthesized by ultrasonic spray pyrolysis of emulsion and solutions, using tetra-ethyl-orthosilicate (TEOS) or silicic-acid and Al(NO3)3 · 9H2O as initial compounds. Crystallization of mullite phase was determined by differential thermal (DT), thermogravimetric (TG), infrared (IR), and x-ray analyses. The synthesis of mullite from TEOS emulsion occurs by crystallization of γ–Al2O3 (or Al, Si-spinel) from the amorphous phase and its subsequent reaction with amorphous SiO2, as well as by crystallization of pseudotetragonal mullite below 1000 °C and its subsequent phase transformation into orthorhombic mullite. In the powders produced from silicic acid solutions, synthesis of mullite occurs only by crystallization of γ–Al2O3 between 900 and 1000 °C and its further reaction with amorphous SiO2 between 1100 and 1200 °C. Particle formation mechanism depended directly on the initial emulsion or solution preparation, i.e., on the phase separation in the emulsion and on the silicic-acid crosslinking conditions.

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Wolff, S., F. Jirasek, S. Beuermann und M. Türk. „Crystal phase transformation of α into β phase poly(vinylidene fluoride) via particle formation caused by rapid expansion of supercritical solutions“. RSC Advances 5, Nr. 82 (2015): 66644–49. http://dx.doi.org/10.1039/c5ra12142f.

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Stiegler, J., Y. von Kaenel, M. Cans und E. Blank. „Space filling by nucleation and growth in chemical vapor deposition of diamond“. Journal of Materials Research 11, Nr. 3 (März 1996): 716–26. http://dx.doi.org/10.1557/jmr.1996.0086.

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Phase transformations, including chemical vapor deposition (CVD) of diamond, taking place by nucleation and growth are commonly described by Avrami or Johnson-Mehl type models. In order to avoid the restrictions of such models with respect to assumptions concerning nucleation rates and growth velocities, the variation with time of nucleation and growth of diamond particles during the deposition of microwave plasma-assisted CVD was studied. The size distributions obtained from image analysis enabled us to trace back details of the nucleation and growth history. Three sources of particle formation were operating during deposition. A general growth law suitable for all particles did not exist. These observations limited the applicability of Avrami-type models to describe space filling. Computer simulation of surface coverage and particle growth was successful because one particular mode of particle formation and growth dominated surface coverage. Based on image analysis and the determination of the film growth rate, the evolution of the diamond volume fraction with time, starting from three-dimensional particle growth followed by a continuous transition to one-dimensional film growth, was described.

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Distaso, Elia, Riccardo Amirante, Giuseppe Calò, Pietro De Palma und Paolo Tamburrano. „Evolution of Soot Particle Number, Mass and Size Distribution along the Exhaust Line of a Heavy-Duty Engine Fueled with Compressed Natural Gas“. Energies 13, Nr. 15 (03.08.2020): 3993. http://dx.doi.org/10.3390/en13153993.

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An experimental study has been conducted to provide a characterization of the transformations that particle size distributions and the number density of soot particles can encounter along the exhaust line of a modern EURO VI compliant heavy-duty engine, fueled with compressed natural gas. Being aware of the particles history in the exhausts can be of utmost importance to understand soot formation and oxidation dynamics, so that, new strategies for further reducing these emissions can be formulated and present and future regulations met. To this purpose, particle samples were collected from several points along the exhaust pipe, namely upstream and downstream of each device the exhaust gases interact with. The engine was turbocharged and equipped with a two-stage after-treatment system. The measurements were carried out in steady conditions while the engine operated in stoichiometric conditions. Particle emissions were measured using a fast-response particle size spectrometer (DMS500) so that size information was analyzed in the range between 5 and 1000 nm. Particle mass information was derived from size distribution data using a correlation available in the literature. The reported results provide more insight on the particle emission process related to natural gas engines and, in particular, point out the effects that the turbine and the after-treatment devices produce on soot particles. Furthermore, the reported observations suggest that soot particles might not derive only from the fuel, namely, external sources, such as lubricant oil, might have a relevant role in soot formation.

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Tomiak, Florian, Bernhard Schartel, Michael Wolf und Dietmar Drummer. „Particle Size Related Effects of Multi-Component Flame-Retardant Systems in poly(butadiene terephthalate)“. Polymers 12, Nr. 6 (09.06.2020): 1315. http://dx.doi.org/10.3390/polym12061315.

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Aluminum tris-(diethylphosphinate) (AlPi) is known to have an efficient flame-retardant effect when used in poly(butadiene terephthalates) (PBT). Additionally, better flame-retardant effects can be achieved through the partial substitution of AlPi by boehmite in multi-component systems, which have been shown to be an effective synergist due to cooling effects and residue formation. Although the potential of beneficial effects is generally well known, the influence of particle sizes and behavior in synergistic compositions are still unknown. Within this paper, it is shown that the synergistic effects in flammability measured by limiting oxygen index (LOI) can vary depending on the particle size distribution used in PBT. In conducting thermogravimetric analysis (TGA) measurements, it was observed that smaller boehmite particles result in slightly increased char yields, most probably due to increased reactivity of the metal oxides formed, and they react slightly earlier than larger boehmite particles. This leads to an earlier release of water into the system enhancing the hydrolysis of PBT. Supported by Fourier transformation infrared spectroscopy (FTIR), we propose that the later reactions of the larger boehmite particles decrease the portion of highly flammable tetrahydrofuran in the gas phase within early burning stages. Therefore, the LOI index increased by 4 vol.% when lager boehmite particles were used for the synergistic mixture.

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Tang, M. J., M. Shiraiwa, U. Pöschl, R. A. Cox und M. Kalberer. „Compilation and evaluation of gas-phase diffusion coefficients of reactive trace gases in the atmosphere: volume 2. Organic compounds and Knudsen numbers for gas uptake calculations“. Atmospheric Chemistry and Physics Discussions 15, Nr. 4 (25.02.2015): 5461–92. http://dx.doi.org/10.5194/acpd-15-5461-2015.

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Abstract. Diffusion of organic vapours to the surface of aerosol or cloud particles is an important step for the formation and transformation of atmospheric particles. So far, however, a database of gas phase diffusion coefficients for organic compounds of atmospheric interest has not been available. In this work we have compiled and evaluated gas phase diffusivities (pressure-independent diffusion coefficients) of organic compounds reported by previous experimental studies, and we compare the measurement data to estimates obtained with Fuller's semi-empirical method. The difference between measured and estimated diffusivities are mostly < 10%. With regard to gas-particle interactions, different gas molecules, including both organic and inorganic compounds, exhibit similar Knudsen numbers (Kn) although their gas phase diffusivities may vary over a wide range. Knudsen numbers of gases with unknown diffusivity can be approximated by a simple function of particle diameter and pressure and can be used to characterize the influence of diffusion on gas uptake by aerosol or cloud particles. We use a kinetic multi-layer model of gas-particle interaction to illustrate the effects of gas phase diffusion on the condensation of organic compounds with different volatilities. The results show that gas-phase diffusion can play a major role in determining the growth of secondary organic aerosol particles by condensation of low-volatility organic vapours.

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Amrute, Amol P., Zbigniew Łodziana, Hannah Schreyer, Claudia Weidenthaler und Ferdi Schüth. „High-surface-area corundum by mechanochemically induced phase transformation of boehmite“. Science 366, Nr. 6464 (24.10.2019): 485–89. http://dx.doi.org/10.1126/science.aaw9377.

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In its nanoparticulate form, corundum (α-Al2O3) could lead to several applications. However, its production into nanoparticles (NPs) is greatly hampered by the high activation energy barrier for its formation from cubic close-packed oxides and the sporadic nature of its nucleation. We report a simple synthesis of nanometer-sized α-Al2O3 (particle diameter ~13 nm, surface areas ~140 m2 g−1) by the mechanochemical dehydration of boehmite (γ-AlOOH) at room temperature. This transformation is accompanied by severe microstructural rearrangements and might involve the formation of rare mineral phases, diaspore and tohdite, as intermediates. Thermodynamic calculations indicate that this transformation is driven by the shift in stability from boehmite to α-Al2O3 caused by milling impacts on the surface energy. Structural water in boehmite plays a crucial role in generating and stabilizing α-Al2O3 NPs.

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