Artykuły w czasopismach: „Total Synthesis, silicon”

1

Denmark, Scott E., i Shyh-Ming Yang. "Intramolecular Silicon-Assisted Cross-Coupling: Total Synthesis of (+)-Brasilenyne". Journal of the American Chemical Society 124, nr 51 (grudzień 2002): 15196–97. http://dx.doi.org/10.1021/ja028936q.

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Li, Hongze, Hengmu Xie, Zhigao Zhang, Yongjin Xu, Ji Lu, Lu Gao i Zhenlei Song. "Total synthesis of (−)-exiguolide via an organosilane-based strategy". Chemical Communications 51, nr 40 (2015): 8484–87. http://dx.doi.org/10.1039/c5cc02448j.

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An organosilane-based strategy has been used to accomplish the total synthesis of (–)-exiguolide. The key steps involve: (1) geminal bis(silyl) Prins cyclization to construct the A ring; (2) silicon-protected RCM reaction to construct the macrocycle; and (3) Hiyama–Denmark cross-coupling to install the side chain.

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Verma, Rekha, i Sunil K. Ghosh. "A silicon controlled total synthesis of the antifungal agent (+)-preussin". Chemical Communications, nr 17 (1997): 1601–2. http://dx.doi.org/10.1039/a703387g.

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Rodríguez-Escrich, Carles, Fèlix Urpí i Jaume Vilarrasa. "Stereocontrolled Total Synthesis of Amphidinolide X via a Silicon-Tethered Metathesis Reaction". Organic Letters 10, nr 22 (20.11.2008): 5191–94. http://dx.doi.org/10.1021/ol8021676.

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Denmark, Scott E, i Jack H C. Liu. "Silicon-Based Cross-Coupling Reactions in the Total Synthesis of Natural Products". Angewandte Chemie International Edition 49, nr 17 (23.03.2010): 2978–86. http://dx.doi.org/10.1002/anie.200905657.

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Chowdhury, Partha Sarathi, i Pradeep Kumar. "Total Synthesis of Umuravumbolide and Hyptolide Through Silicon-Tethered Ring-Closing Metathesis". European Journal of Organic Chemistry 2013, nr 21 (12.06.2013): 4586–93. http://dx.doi.org/10.1002/ejoc.201300302.

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VERMA, R., i S. K. GHOSH. "ChemInform Abstract: A Silicon Controlled Total Synthesis of the Antifungal Agent (+)-Preussin." ChemInform 29, nr 1 (24.06.2010): no. http://dx.doi.org/10.1002/chin.199801235.

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Magnus, Philip, i Dominick Quagliato. "Silicon in synthesis. 21. Reagents for thiophenyl-functionalized cyclopentenone annulations and the total synthesis of (.+-.)-hirsutene". Journal of Organic Chemistry 50, nr 10 (maj 1985): 1621–26. http://dx.doi.org/10.1021/jo00210a013.

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Denmark, Scott E., i Shyh-Ming Yang. "Total Synthesis of (+)-Brasilenyne. Application of an Intramolecular Silicon-Assisted Cross-Coupling Reaction". Journal of the American Chemical Society 126, nr 39 (październik 2004): 12432–40. http://dx.doi.org/10.1021/ja0466863.

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Li, Fangzheng, i Marvin J. Miller. "Stereoselective Total Synthesis of (+)-Streptazolin by Using a Temporary Silicon-Tethered RCM Strategy". Journal of Organic Chemistry 71, nr 14 (lipiec 2006): 5221–27. http://dx.doi.org/10.1021/jo060555y.

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Singh, Rekha, i Sunil K. Ghosh. "Synthesis of enantiomerically pure all cis-2,3,6-trisubstituted piperidine: a silicon mediated total synthesis of (+)-carpamic acid". Tetrahedron Letters 43, nr 43 (październik 2002): 7711–15. http://dx.doi.org/10.1016/s0040-4039(02)01853-1.

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Denmark, Scott E., i Jack H. C. Liu. "ChemInform Abstract: Silicon-Based Cross-Coupling Reactions in the Total Synthesis of Natural Products". ChemInform 41, nr 29 (24.06.2010): no. http://dx.doi.org/10.1002/chin.201029242.

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de Paula, Gustavo Medeiros, L. A. Lima i Meiry Glaúcia Freire Rodrigues. "SBA-15 Molecular Sieve Using Clay as Silicon Sources". Materials Science Forum 798-799 (czerwiec 2014): 116–20. http://dx.doi.org/10.4028/www.scientific.net/msf.798-799.116.

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New sources of silica as a replacement for TEOS in the synthesis of SBA-15 are been performed by various research teams worldwide. The aim of this work is to describe the synthesis and characterization of SBA-15 made with chocolate B clay as an alternative source of silica by the hydrothermal method. Samples of classic SBA-15 were made with the traditional TEOS method. The samples of the two silica sources were characterized by DRX, EDX, and BET to evaluate the effects of the silica source on the synthesis of the molecular sieve. The chocolate B clay was efficient in the formation of the molecular sieve structure, but there was a great reduction in the surface area and total pore volume in comparison to the surface area of classic SBA-15.

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Kukushkin S. A., Osipov A. V., Osipova E. V. i Stozharov V. M. "Study of silicon-to-silicon carbide transformation stages in the process of atomic substitution by the methods of total external X-ray reflection and X-ray diffractometry". Physics of the Solid State 64, nr 3 (2022): 315. http://dx.doi.org/10.21883/pss.2022.03.53187.232.

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X-ray diffraction and total external reflection of X-rays (X-ray reflectometry) methods were used to study the successive stages of synthesis of epitaxial SiC films on Si (100) X-ray diffraction and total external X-ray reflection (XRD) methods were used to study successive stages of synthesis of epitaxial SiC films on Si (100) surfaces, (110) and (111) surfaces by the atom substitution method. The data on the transformation evolution of (100) surfaces were studied, (110) and (111) Si, into SiC surfaces. A comparative analysis of the X-ray structural quality of the SiC layers grown on Si by the atom substitution method with the quality of SiC layers grown by Advanced Epi by the standard CVD method. A modified technique for the total outer X-ray reflection method, based on measurements of the intensity of the reflected X-rays using a special parabolic mirror. It is shown that the method of total external reflection method makes it possible to obtain important information about the degree of surface roughness of SiC layers, the evolution of their crystal structure and plasmon energy in the process of Si to SiC conversion. Keywords: total external reflection, X-ray reflectometry, silicon carbide, plasmons.

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Kukushkin S. A., Osipov A. V., Osipova E. V. i Stozharov V. M. "Study of silicon-to-silicon carbide transformation stages in the process of atomic substitution by the methods of total external X-ray reflection and X-ray diffractometry". Physics of the Solid State 64, nr 3 (2022): 327. http://dx.doi.org/10.21883/pss.2022.03.54010.232.

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X-ray diffraction and total external reflection of X-rays (X-ray reflectometry) methods were used to study the successive stages of synthesis of epitaxial SiC films on Si (100) X-ray diffraction and total external X-ray reflection (XRD) methods were used to study successive stages of synthesis of epitaxial SiC films on Si (100) surfaces, (110) and (111) surfaces by the atom substitution method. The data on the transformation evolution of (100) surfaces were studied, (110) and (111) Si, into SiC surfaces. A comparative analysis of the X-ray structural quality of the SiC layers grown on Si by the atom substitution method with the quality of SiC layers grown by Advanced Epi by the standard CVD method. A modified technique for the total outer X-ray reflection method, based on measurements of the intensity of the reflected X-rays using a special parabolic mirror. It is shown that the method of total external reflection method makes it possible to obtain important information about the degree of surface roughness of SiC layers, the evolution of their crystal structure and plasmon energy in the process of Si to SiC conversion. Keywords: total external reflection, X-ray reflectometry, silicon carbide, plasmons.

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16

Lee, Jihoon, i James S. Panek. "Total Synthesis of (+)-Isatisine A: Application of a Silicon-Directed Mukaiyama-Type [3 + 2]-Annulation". Journal of Organic Chemistry 80, nr 6 (10.03.2015): 2959–71. http://dx.doi.org/10.1021/acs.joc.5b00051.

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Hwu, Jih Ru, i John M. Wetzel. "Silicon-promoted ring contractions in the formation of carbocyclic spiro compounds. Total synthesis of (-)-solavetivone". Journal of Organic Chemistry 57, nr 3 (styczeń 1992): 922–28. http://dx.doi.org/10.1021/jo00029a025.

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Hossain, Sakib Tanvir, Fatima Tuz Johra i Woo-Gwang Jung. "Fabrication of Silicon Carbide from Recycled Silicon Wafer Cutting Sludge and Its Purification". Applied Sciences 8, nr 10 (7.10.2018): 1841. http://dx.doi.org/10.3390/app8101841.

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Around the world, silicon carbide (SiC) is used as a raw material in several engineering applications because of its various beneficial properties. Currently, though the Acheson method is one of the most emblematic to manufacture SiC, the direct carbonization of metallic silicon is simple and beneficial. In this reaction, silicon wafer cutting sludge can be used as an alternative silicon source material. The silicon wafer sludge contains silicon, ethylene glycol, cooling water, and a small amount of impurities. In this study, SiC was synthesized using silicon wafer sludge by a carbothermal process. In a typical experiment, the silicon sludge was mixed with carbon at different molar ratios. Then, the mixture was turned into pellets, which were placed in alumina crucibles and heat-treated at a temperature from 1400 °C to 1600 °C to fabricate SiC. To deduce the optimum condition for the synthesis of SiC, an investigation was carried out on the effects of different mixing ratios, temperatures, and heating times. To ensure sufficient carbonization, excess carbon was mixed, and the synthesized SiC was characterized by X-ray diffraction (XRD). Subsequently, purification of the synthesized SiC products by oxidation of excess carbon was performed. The removal of extra carbon could be confirmed by XRD and attenuated total reflectance (ATR) spectroscopy. This process can give basic information for the development of a technology to produce SiC using recycling Si wafer cutting sludge waste.

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Kotani, Shunsuke, Kosuke Kai, Yasushi Shimoda, Hao Hu, Shen Gao, Masaharu Sugiura, Masamichi Ogasawara i Makoto Nakajima. "Concise Asymmetric Construction ofC2-symmetric 1,9-Diarylnonanoids Using a Hypervalent Silicon Complex: Total Synthesis of (−)-Ericanone". Chemistry - An Asian Journal 11, nr 3 (10.12.2015): 376–79. http://dx.doi.org/10.1002/asia.201501080.

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Chiolino, N., A. M. Francis, J. Holmes i M. Barlow. "Digital Logic Synthesis for 470 Celsius Silicon Carbide Electronics". Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2018, HiTEC (1.05.2018): 000064–70. http://dx.doi.org/10.4071/2380-4491-2018-hiten-000064.

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Abstract Advancements in Silicon Carbide (SiC) digital integrated circuit (IC) design have enabled the ability to design complex, dense, digital blocks. Because of the large number of transistors, these complex digital designs make the time and risk of hand-crafted digital design, which has been the norm for SiC, too costly and risky. For large scale integrated digital circuits, computer aided design (CAD) tools are necessary, specifically the use of automatic synthesis, rule-based placement and signal routing software. The tools are used in progression as a design flow and are necessary for the timely and accurate creation of high-density digital designs. Application of an automated digital design flow to high-temperature SiC processes presents new challenges, such as extraction of timing characteristics at high temperatures, specifically above 400°C, as well as managing the complexity of synthesis, optimization of cell placement, verification of timing enclosure, and identifying routing constraints. These activities all require a willingness to extend and enhance the CAD software. Presented is a high temperature SiC digital synthesis flow. This flow is fully integrated with the characterization of a standard cell library that considers the variation of voltage, temperature, and process characteristics. A digital controller for a 10,000-pixel UV focal plan array (FPA) in a SiC CMOS process was designed using this high temperature digital flow. The controller is comprised of a finite state machine (FSM), that monitors several counters, shift registers and combinational logic feedback signals. The FSM is configured to optimize the FPA for different applications and exposures. The Register-Transfer Level (RTL) design of the FSM produces between 900 and 1,000 gates, depending on the temperature-dependent time closure with a total footprint of 14mm2. Typical SiC processes present a non-monotonic clock speed over temperature. The advantage of this digital design flow is that it allows the designer to target a temperature corner for the netlist design but verify its operation over a > 400°C operating range. This flow is currently being enhanced for use with NASA's SiC JFET-R process to create a high temperature communication protocol interface.

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Mohamed, Safaa H., Ayad S. Hameed, Emad Yousif, Mohammad Hayal Alotaibi, Dina S. Ahmed i Gamal A. El-Hiti. "New Porous Silicon-Containing Organic Polymers: Synthesis and Carbon Dioxide Uptake". Processes 8, nr 11 (18.11.2020): 1488. http://dx.doi.org/10.3390/pr8111488.

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The design and synthesis of new multifunctional organic porous polymers has attracted significant attention over the years due to their favorable properties, which make them suitable for carbon dioxide storage. In this study, 2-, 3-, and 4-hydroxybenzaldehyde reacted with phenyltrichlorosilane in the presence of a base, affording the corresponding organosilicons 1–3, which further reacted with benzidine in the presence of glacial acetic acid, yielding the organic polymers 4–6. The synthesized polymers exhibited microporous structures with a surface area of 8.174–18.012 m2 g−1, while their pore volume and total average pore diameter ranged from 0.015–0.035 cm3 g−1 and 1.947–1.952 nm, respectively. In addition, among the synthesized organic polymers, the one with the meta-arrangement structure 5 showed the highest carbon dioxide adsorption capacity at 323 K and 40 bar due to its relatively high surface area and pore volume.

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Brosius, Arthur D., Larry E. Overman i Lothar Schwink. "Total Synthesis of (+)-Aloperine. Use of a Nitrogen-Bound Silicon Tether in an Intramolecular Diels−Alder Reaction". Journal of the American Chemical Society 121, nr 4 (luty 1999): 700–709. http://dx.doi.org/10.1021/ja983013+.

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HWU, J. R., i J. M. WETZEL. "ChemInform Abstract: Silicon-Promoted Ring Contractions in the Formation of Carbocyclic Spiro Compounds. Total Synthesis of (-)-Solavetivone." ChemInform 23, nr 26 (21.08.2010): no. http://dx.doi.org/10.1002/chin.199226254.

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Jänchen, Jochen, Vladimir Penchev, Elke Löffler, Barbara Parlitz i Helmut Stach. "Influence of Silicon Content and Nature of the Template Molecule on Physico-Chemical and Catalytic Properties of SAPO-5". Collection of Czechoslovak Chemical Communications 57, nr 4 (1992): 826–35. http://dx.doi.org/10.1135/cccc19920826.

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Two series of SAPO-5 molecular sieves were synthesized: (i) Using tripropylamine as a template and varying the Si content in the gel, and (ii) varying the template molecule at constant silicon content in the gel. The products were characterized physico-chemically and tested in toluene disproportionation. It was found that the rising silica content in the synthesis gel has only little influence on the SiO2 incorporation into the SAPO. Investigation of the acid character revealed that the concentrations of the adsorbed ammonia molecules are nearly constant and independent of the total silicon content of the crystals. The catalytic activity showed no correlation either with the silicon content of the catalysts or with the acidity measured by temperature-programmed desorption of ammonia. It is concluded that the incorporated silicon exists not only in a monomeric form and that the TPD of ammonia reflects not only the strong Bronsted acidity. The SAPO-5 sample synthesized with triethylamine possessed the strongest acidity corresponding to the highest catalytic activity. It is supposed that in the presence of TEA molecules silicon replaces mainly P atoms in the AlPO4-5 framework.

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Shofiyani, Anis, Fara Chitra, Winda Rahmalia, R. Rudiyansyah i Andi Hairil Alimuddin. "Synthesis of Nanosilica from Padas Stone to Reduce The Total Organic Carbon of Palm Oil Waste". Jurnal ILMU DASAR 20, nr 1 (22.01.2019): 39. http://dx.doi.org/10.19184/jid.v20i1.8679.

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Padas stone is one of the natural mineral containing 67.5% of SiO2 compounds. In this research, synthesis of nanosilica was carried out by sol-gel method asistanced by 2.45 GHz microwave radiations with low (10%), medium (50%) and high (100%) power at 30 and 60 minutes of contact times. It was analyzed by XRD, BET, FTIR spectrophotometry and SEM. The synthesized silica was then used as absorbent for total organic carbon (TOC) of palm oil waste. The results show that the synthesized silica was a mixture of cristobalite and quartz type minerals according to ICDD No. 00-003-0271 and 01-083-287. The surface area and silicon dioxide contains are 12.174 m2/g and 76.325% for silica without microwave assistance (SiO2-TPMW); 12.796 m2/gand 86.385% for silica with 30 minutes on 10% microwave assistance(SiO2 -MW 10A); 12.735 m2/gand 86.254% for silica with 60 minutes on 10% microwave assistance (MW 10B); 13,659 m2/gand 87.211% for MW 50A; 13,583 m2/g and 86.684% for MW 50B;7.883 m2/gand 57.527% for MW 100A; also 8.752 m2/g and 37.725% for MW 100B, respectively. The use of silica as an absorbent of TOC shows the effectiveness of 62.89% (TPMW); 63.68% (MW 10A); 62.96% (MW 10B); 65.25% (MW 50A); 64.61% (MW 50B); 62.37% (MW 100A) and 61.18% (MW 100B) from the initial TOC of 1520 mg/L. Keywords: synthesis, nanosilica, padas stone, total organic carbon, oil waste.

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Brosius, Arthur D., Larry E. Overman i Lothar Schwink. "ChemInform Abstract: Total Synthesis of (+)-Aloperine. Use of a Nitrogen-Bound Silicon Tether in an Intramolecular Diels-Alder Reaction." ChemInform 30, nr 26 (15.06.2010): no. http://dx.doi.org/10.1002/chin.199926233.

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Fukaya, Yuki, Izumi Mochizuki, Masaki Maekawa, Ken Wada, Toshio Hyodo, Iwao Matsuda i Atsuo Kawasuso. "Structure determination of two-dimensional atomic sheet of silicene using TRHEPD". Acta Crystallographica Section A Foundations and Advances 70, a1 (5.08.2014): C1605. http://dx.doi.org/10.1107/s2053273314083946.

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This study reports determination of the atomic coordinates of a two-dimensional atomic sheet, silicene, by using total reflection high-energy positron diffraction (TRHEPD) [1]. TRHEPD method, formerly called as RHEPD, is a surface-sensitive tool owing to the total reflection of positrons. Since the sign of the potential energy for positrons in crystals is positive, opposite to that for the electrons, the positron beam at a grazing incidence are totally reflected at a crystal surface. The penetration depth of the positron beam in the total reflection region is estimated to be approximately a few Å, which corresponds to the thickness of 1-2 atomic layers. Thus, the positron beam selectively sees the topmost surface layer and hence the TRHEPD method is very useful for structure determinations of crystal surface and two-dimensional atomic sheet on the substrate. Silicene is a two-dimensional atomic sheet of silicon. Since the silicene has an intriguing property such as a Dirac cone like a graphene, it attracts increasing attention as a candidate for future devices. Recently, the synthesis of silicene on a Ag(111) surface was successfully performed [2]. Although the atomic coordinates of the silicene in this system was theoretically calculated, they were not confirmed experimentally. It is very important to experimentally determine the magnitude of the buckling in silicene and the spacing between the bottom of the silicene and the substrate because the dispersion of the Dirac cone is closely related to these structure parameters. We thus investigated the atomic positions of the silicene on the Ag(111) surface using the TRHEPD [3]. From the rocking curve analysis based on the dynamical diffraction theory of positrons (see figure), the existence of the buckling (0.83 Å) in silicene was verified experimentally. Moreover, the spacing between the silicene and the substrate was determined as 2.17 Å. The structural difference with the graphene will be also discussed.

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Nussupov, K. Kh, N. B. Beisenkhanov, S. A. Kukushkin, A. T. Sultanov, S. Keiinbay, D. S. Shynybayev i A. Zh Kusainova. "FORMATION OF CRYSTALLINE SiC IN NEAR-SURFACE SILICON LAYERS BY METHOD OF COORDINATED SUBSTITUTION OF ATOMS". Herald of the Kazakh-British technical university 20, nr 2 (1.07.2023): 27–35. http://dx.doi.org/10.55452/1998-6688-2023-20-2-27-35.

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In this work, monocrystalline films of silicon carbide were synthesized on the surface of a Si(100) silicon wafer using the method of coordinated substitution of atoms. The films were synthesized at temperatures of 1200 °C and 1300 °C for 20 minutes in a CO gas flow at a pressure of 0.8 Pa. The effect of 1200–1300 °C temperatures on the formation of single- and polycrystalline layers, as well as nanostructured SiC phases in the near-surface region of silicon by the method of atom substitution, is analyzed. The formation of a high-quality crystalline silicon carbide film and the influence of synthesis conditions on the total volume of SiC structural phases, microstructure and nanostructure of the surface are shown. It was found that an increase in temperature from 1200 °C to 1300 °C led to a more intensive formation of silicon carbide and an increase in the number of Si–C bonds by 1.9 times due to an increase in the thickness of the synthesized silicon carbide layer. There is an increase in the proportion of the crystalline phase due to a more intense transformation of the nuclei of nanocrystals into micro- and nanocrystals. Intense processes of penetration of carbon atoms deep into silicon at a temperature of 1300 °C with amorphization of its structure and the formation of Si-C, which can transform into crystalline phases at temperatures above 1300 °C, are assumed. The proportion of the SiC crystalline phase increases to 50.2% of the film volume due to the intensive transformation of nanocrystal nuclei into micro- and nanocrystals. It has been experimentally shown that the formation of various SiC structures on Si (100) occurs in full accordance with the main principles of the method of coordinated substitution of atoms.

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Sherwood, Toby, i Richard T. Baker. "Effects of Strontium Content on the Microstructure and Ionic Conductivity of Samarium-Doped Ceria". Solids 2, nr 3 (10.08.2021): 293–313. http://dx.doi.org/10.3390/solids2030019.

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Due to its high oxygen ion conductivity at elevated temperatures, samarium-doped ceria (SDC) is a very promising material for application in solid state electrochemical devices and especially in the electrolytes of solid oxide fuel cells. Several prior studies have reported a further improvement in the ionic conductivity of SDC on doping with small amounts of strontium. It is suggested that strontium acts as a sintering aid—improving the microstructure of SDC—and as a scavenger of silicon impurities, decreasing its tendency to form resistive phases at grain boundaries. However, because of the range of preparation methods and the resulting differences in microstructure and silicon levels, some inconsistencies exist in the literature. Furthermore, the effect of strontium on the intrinsic (bulk) conductivity of SDC is not often discussed. To address these issues, a systematic, combined microstructural and conductivity study has been performed on a compositional series with a range of strontium contents, Ce0.8−xSm0.2SrxO2−δ (x = 0, 0.002, 0.005, 0.01, 0.02, 0.03, 0.04). A low temperature synthesis affording products with low silicon was employed. Total bulk and grain boundary conductivity data were obtained over a wide temperature range. Increasing strontium content caused a general decrease in total and intrinsic conductivity, but there was an improvement in grain boundary conductivity at the lowest strontium levels. These results were interpreted by reference to the microstructures using, among other parameters, the blocking, and normalised blocking, factors.

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Marina Vargas Rodríguez, Y., Hiram I. Beltrán, Eloy Vázquez-Labastida, Carlos Linares-López i Manuel Salmón. "Synthesis and characterization of montmorillonite clays with modulable porosity induced with acids and superacids". Journal of Materials Research 22, nr 3 (marzec 2007): 788–800. http://dx.doi.org/10.1557/jmr.2007.0098.

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The structural transformation of natural montmorillonite clay with different acids and superacids (hydrochloric, HCl; sulfuric, H2SO4; hydrofluoric, HF; perchloric, HClO4; chlorosulfonic, HSO3Cl; and trifluoromethanesulfonic, HSO3CF3 acids) is evaluated by various techniques, allowing its full characterization. The process involves the modulated digestion of the aluminum and silicon atoms from the original clay without the loss of the original mass in the material from a careful drying methodology. The x-ray diffraction technique suggests that the process is disruptive, causing different magnitudes of modification, depending on the acidic source, taking the material with natural lamellar structure as reference. By 27Al and 29Si magnetic resonance, it is also shown that all the silicon and aluminum atoms were removed from the chemical structure to be physisorbed or dispersed in the interstices of the clay lattice when HF, HSO3Cl, and H2SO4 acid treatments were carried out. However, with treatment of HClO4, the results suggest that only was achieved partial digestion and physisorption of the aluminosilicate core. Treatment with HCl led to a mild digestion that increased the laminar distance of the montmorillonite. Finally, HSO3CF3 acid achieved a total disorder of the lamellar structure of the clay. In addition, by infrared spectrometry, the disappearance of the absorption peaks assigned to Al2OH, AlMgOH, and Al-O-Si are other evidence of the complete digestion of silicon and aluminum atoms caused by the acidic medium. On the other hand, the Brunauer–Emmett–Teller (BET) surface areas of the acidified clays showed a great enlargement in comparison with the unmodified clay. The porosimetry measurements demonstrate the presence of mesopores and hysteresis as observed in the physisorption isotherms, which indeed exhibited a capillary condensation into the porous structures. The present results are the first full characterization research and structural comparison between the acidic and the not-extensively-studied superacidic modified clays of this type.

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Adams, D. P., M. A. Rodriguez, C. P. Tigges i P. G. Kotula. "Self-propagating, high-temperature combustion synthesis of rhombohedral AlPt thin films". Journal of Materials Research 21, nr 12 (grudzień 2006): 3168–79. http://dx.doi.org/10.1557/jmr.2006.0387.

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Sputter-deposited, Al/Pt multilayer thin films of various designs exhibited rapid, self-propagating, high-temperature reactions. With reactant layers maintained at ∼21 °C prior to ignition and films adhered to oxide-passivated silicon substrates, the propagation speeds varied from approximately 20 to 90 m/s depending on bilayer dimension and total film thickness. Contrary to current Al–Pt equilibrium phase diagrams, all multilayers reacted in air and in vacuum transformed into rhombohedral AlPt having a space group R-3(148). Rietveld refinement of AlPt powder (generated from thin film samples) yielded trigonal/hexagonal unit cell lattice parameters of a = 15.634(3) Å and c = 5.308(1) Å; the number of formula units = 39. Rhombohedral AlPt was stable to 550 °C with transformation to a cubic FeSi-type structure occurring above this temperature.

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Fan, Qinbai, i Lily M. Ng. "In situ Fourier transform infrared‐attenuated total reflection spectroscopy monitoring of polyaniline synthesis mechanism on the p‐type silicon electrode". Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 14, nr 3 (maj 1996): 1326–29. http://dx.doi.org/10.1116/1.579949.

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Evans, P. Andrew, Jian Cui, Santosh J. Gharpure, Alexei Polosukhin i Hai-Ren Zhang. "Enantioselective Total Synthesis of the Potent Antitumor Agent (−)-Mucocin Using a Temporary Silicon-Tethered Ring-Closing Metathesis Cross-Coupling Reaction". Journal of the American Chemical Society 125, nr 48 (grudzień 2003): 14702–3. http://dx.doi.org/10.1021/ja0384734.

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Gridley, Daila S., Michael J. Pecaut i Gregory A. Nelson. "Total-body irradiation with high-LET particles: acute and chronic effects on the immune system". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 282, nr 3 (1.03.2002): R677—R688. http://dx.doi.org/10.1152/ajpregu.00435.2001.

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Although the immune system is highly susceptible to radiation-induced damage, consequences of high linear energy transfer (LET) radiation remain unclear. This study evaluated the effects of 0.1 gray (Gy), 0.5 Gy, and 2.0 Gy iron ion (56Fe26) radiation on lymphoid cells and organs of C57BL/6 mice on days 4 and 113 after whole body exposure; a group irradiated with 2.0 Gy silicon ions (28Si) was euthanized on day 113. On day 4 after 56Fe irradiation, dose-dependent decreases were noted in spleen and thymus masses and all major leukocyte populations in blood and spleen. The CD19+ B lymphocytes were most radiosensitive and NK1.1+ natural killer (NK) cells were most resistant. CD3+ T cells were moderately radiosensitive and a greater loss of CD3+/CD8+TC cells than CD3+/CD4+TH cells was noted. Basal DNA synthesis was elevated on day 4, but response to mitogens and secretion of interleukin-2 and tumor necrosis factor-α were unaffected. Signs of anemia were noted. By day 113, high B cell numbers and low TC cell and monocyte percents were found in the 2.0 Gy56Fe group; the 2.0 Gy 28Si mice had low NK cells, decreased basal DNA synthesis, and a somewhat increased response to two mitogens. Collectively, the data show that lymphoid cells and tissues are markedly affected by high linear energy transfer (LET) radiation at relatively low doses, that some aberrations persist long after exposure, and that different consequences may be induced by various densely ionizing particles. Thus simultaneous exposure to multiple radiation sources could lead to a broader spectrum of immune dysfunction than currently anticipated.

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Brovko, R., N. Lakina i V. Doluda. "Synthesis and Acidity Study of Mixed MFI-MORD Type Zeolite". Bulletin of Science and Practice, nr 12 (15.12.2022): 60–66. http://dx.doi.org/10.33619/2414-2948/85/07.

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Zeolites of various nature are widely used in the chemical industry, the fuel and energy sector of the economy as sorbents, catalysts and materials for the creation of inorganic membranes for various purposes. At the same time, it is possible to change the acid properties of the surface of zeolites both by varying the ratio of silicon to aluminum or silicon to phosphorus, and by joint synthesis of zeolites of various types with different acidic properties. The presented article provides a method for the sequential production of a zeolite of a mixed structure type MFI and mordenite. Synthesis of the original MFI type zeolite was carried out using seed grains by the hydrothermal method for 72 hours, followed by washing and drying of the zeolite. To obtain a layer of mordenite on the surface of the MFI type zeolite, the initial zeolite was pretreated with alkali and then treated with n-butylamine. In this way, nine samples of zeolite with different acidic surface properties were obtained. Determination of the acidic properties of the surface was carried out by the method of ammonia chemisorption followed by its desorption from the surface of the zeolite. For this purpose, the test sample was loaded into a quartz cuvette, purged with argon at a temperature of 800°С, after which the temperature dropped to 150°С, and the surface of the zeolite was treated with ammonia. Subsequently, the test sample was heated up to 800°С with registration of desorption curves. The amount of adsorbed ammonia was carried out according to previously prepared calibration curves. The synthesized samples of zeolites had different acidity from 0.48 to 0.72 mmol(NH3)/g(sample). In this case, the total acidity of the samples correlated with the ratio of silicon to aluminum in the zeolite samples. Also, depending on the ratio of the MFI and mordenite structures in the zeolite sample, it is possible to vary not only the number, but also the strength of the formed acid sites. So, an increase in the content of mordenite contributes to an increase in the strength of acid centers. The developed method for the synthesis of mixed structure zeolites of the MFI type mordenite made it possible to control the surface acidity of the synthesized samples.

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Filatova, D. G., A. P. Bogdanova, V. V. Krivetskiy, T. N. Penkina i M. N. Rumyantseva. "Quantification of Si dopant in β-Ga<sub>2</sub>O<sub>3</sub>-based semiconductor gas sensors by total reflection X-ray fluorescence spectroscopy (TXRF)". Industrial laboratory. Diagnostics of materials 88, nr 8 (21.08.2022): 5–9. http://dx.doi.org/10.26896/1028-6861-2022-88-8-5-9.

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Developing of chemical sensors is relevant for solving environmental problems of monitoring the atmosphere of cities and industrial zones. Semiconductor sensors based on metal oxides are a promising type of chemical gas sensors due to their high sensitivity, low cost, small size, and low energy consumption. First attempts of pilot operation of atmospheric air monitoring systems based on such sensors revealed an insufficient stability of their response. Doping silicon in the basic material can solve the problem. At the same time, data on the amount and distribution of the dopant in the material are necessary to determine the relationship «synthesis conditions – composition – properties». We propose an approach to the determination of the composition of novel semiconductor materials based on β-Ga2O3 with a silicon dopant content from 0.5 to 2 %at. The approach included grinding of samples using a planetary mill and preparation of suspensions in ethylene glycol, followed by TXRF determination of the analytes on sapphire substrates using the method of absolute contents (Si) with Sr 0.08 and the method of external standard (Ga) with Sr 0.04. X-ray fluorescence analysis of the samples was performed on a S2 PICOFOX spectrometer (Bruker Nano GmbH, Germany). MoKα radiation was used to excite X-ray fluorescence. The spectrum acquisition time is 250 sec. It is shown that the homogeneity of the dopant distribution in the material can be estimated using the suspension analysis. The studied materials demonstrate an irreproducible sensory response which we associated with the revealed inhomogeneity of the silicon distribution over the surface of β-Ga2O3.

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Pavanello, Elizandra Pivotto, Auri Brackmann, Ivan Francisco Dressler da Costa, Vanderlei Both i Vagner Ludwig. "Use of sodium metasilicate for management of peach brown rot". Pesquisa Agropecuária Tropical 46, nr 3 (wrzesień 2016): 245–53. http://dx.doi.org/10.1590/1983-40632016v4641221.

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ABSTRACT Peach brown rot, caused by the Monilinia fructicola fungus, is the main disease affecting peach crops, and it is mainly controlled via frequent fungicide applications. This study aimed at searching for alternatives to the intensive use of chemicals, evaluating silicon doses to control pre and postharvest peach brown rot and their influence on maturation parameters and fruit quality. Treatments consisted of control (water) and sodium metasilicate doses (2 g L-1, 4 g L-1, 6 g L-1, 8 g L-1 and 10 g L-1 of water). The following assessments were made: spore germination and in vitro mycelial growth, brown rot incidence, soluble solids, titratable acidity, flesh firmness, total polyphenol content and fruit ethylene production and respiration rate. The 2 g L-1 dose reduced spore germination by 95 %. Doses of 6 g L-1 and 8 g L-1 satisfactorily reduced the disease incidence in the field, with 77 % and 89.2 % control, respectively. Sodium metasilicate resulted in the maintenance of great fruit firmness, reduced respiration and ethylene production and increased total polyphenol synthesis, but it did not influence the titratable acidity or soluble solids. Applying 6 g L-1 may potentially control pre and postharvest peach brown rot, besides increasing the total polyphenol synthesis and maintaining a higher flesh firmness.

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Grabowski, Jacob P., Gregory M. Ferrence i T. Andrew Mitchell. "Efforts toward the total synthesis of (±)-toxicodenane A utilizing an oxidopyrylium-based [5+2] cycloaddition of a silicon-tethered BOC-pyranone". Tetrahedron Letters 61, nr 38 (wrzesień 2020): 152324. http://dx.doi.org/10.1016/j.tetlet.2020.152324.

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Almeataq, Mohammed S., i Eid M. Alosime. "Synthesis Based on a Preceramic Polymer and Alumina Nanoparticles via UV Lithography for High Temperature Applications". Materials 13, nr 5 (4.03.2020): 1140. http://dx.doi.org/10.3390/ma13051140.

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Because of the increased demand for preceramic polymers in high-tech applications, there has been growing interest in the synthesis of preceramic polymers, including polysiloxanes and alumina. These polymers are preferred because of their low thermal expansion, conformability to surfaces over large areas, and flexibility. The primary objective was to evaluate the aspects of polymer-derived ceramic routs, focusing on the UV lithography process of preceramic polymers and the pyrolyzing properties of the final ceramics. We found that the p(DMS-co-AMS) copolymer was effective in scattering the hydrophilic Al2O3 nanoparticles into the exceedingly hydrophobic solvent. The physico-chemical behavior of characterized copolymers was explored during their pyrolytic transformation into amorphous silicon-based ceramics. The results indicate that an increase of the pyrolysis temperature degraded the Si–O network through the carbothermic reaction of silicon. We also found a rapid elimination of copolymer pores and densification when the temperature increased (1100 to 1200 °C). At different but specific temperature ranges, there are different distinct rearrangement reactions in the conversion of polymer to ceramic; reductions of the melting point (Tm) of the total heat of melting (ΔHm) of the pyrolysis process resulted in the crystallization of ceramic materials; hence, lithography based on pyrolysis properties of preceramic polymers is a critical method in the conversation of polymers.

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de Oliveira, Amanda Sayure Kasuya, Adriana Perpetua Figueiredo Paulista, Ana Ellen Valentim de Alencar i Tiago Pinheiro Braga. "Gelatin Template Synthesis of Aluminum Oxide and/or Silicon Oxide Containing Micro/Mesopores Using the Proteic Sol-Gel Method". Journal of Nanomaterials 2017 (2017): 1–11. http://dx.doi.org/10.1155/2017/2504796.

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Aluminum oxide and/or silicon oxide-based supports were synthesized by proteic sol-gel method. The characterization was performed through the analysis of TG, XRD, FTIR, SEM, and N2 physisorption. The XRD diffractograms showed an amorphous material profile. TG results indicate the total liberation of the organic and inorganic material in the calcination temperature used, occurring in different mass loss range. This piece of information was reaffirmed by the FTIR spectra, which presented characteristic bands of gelatin structure before calcinations which disappear in the spectrum of the solid after calcinations, indicating the loss of organic matter from gelatin after heat treatment. The spectra exhibited M-O stretching vibration at low wavenumbers after calcinations related to metal oxides. The acquired images by SEM suggest the obtaining of a highly porous material with very different characteristics depending on the composition of the support. The N2 isotherms indicate the presence of a micro/mesoporous oxide with interesting textural properties, particularly for the supports containing aluminum and silicon oxide. The ethanol dehydration results showed greater selectivity to diethyl ether compared to ethylene. From the reaction data, the following order of acid strength was obtained: 2Si-Al > Si-2Al > Si-Al > Al, which is related to the Si-Al ratio.

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Քոթանյան, Ա․Հ, Ա. Մ. Մկրտչյան i Մ․Հ․ Քոթանյան. "ՍԻԼԻՑԻՈՒՄԻ ՀՆԱՐԱՎՈՐ ԲԱՐԵՆՊԱՍՏ ԱԶԴԵՑՈՒԹՅՈՒՆՆ ԱՌՈՂՋՈՒԹՅԱՆ ՎՐԱ". MEDICINE, SCIENCE AND EDUCATION, nr 35 (maj 2023): 55–62. http://dx.doi.org/10.56936/18291775-2023.35-55.

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Silicon is one of the most common elements in the earth’s crust. It is always present in water and food in varying amounts. Higher amounts of Si are found in plant-based foods. About 20% of the total amount of silicon ingested with food and water comes with drinking water and drinks (including beer, which contains in average 20–25 mg/l of silicon)․ For higher animals and humans, silicon is generally not considered to be an essential nutrient. However, the importance of this element for human health is now supported by increasing research evidence. The biological role of silicon in human organism is still not clear, but it assumed to be necessary for processes of bone mineralization, collagen synthesis. It has a positive effect on the skin, hair, and nails, contributes to the prevention of atherosclerosis and Alzheimer disease. In the population of most Western countries, dietary Si intakes range from 20 to 50 mg/day. In addition to the beneficial effect of Si on health, questions regarding the adverse effect of this element on the body are also discussed in the literature. First of all, we are talking about the Russian authors’ researches in the field of drinking water hygiene. At present, the adequate and maximum admissible levels of Si consumption have not yet been established. Taking into account the results of research on humans and animals, some scientists have suggested a dietary intake of Si of about 25 mg/day. As for the standards of silicon content in drinking water, it is not regulated in the drinking water quality guidelines of the WHO and the European Union, as well as in the national normative documents of different countries. In the Russian Federation, as well as in the Republic of Armenia, in the hygienic requirements for water quality, Si is normalized according to the sanitary-toxicological index, with the value of the maximum admissible concentrations in drinking water amounting to 10 mg/l.

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Tan, Yan Ni, Yong Liu, Zhang Qing, Gurpreet Birdi i Liam M. Grover. "Synthesis of Pure Dicalcium Silicate Powder by the Pechini Method and Characterization of Hydrated Cement". Materials Science Forum 787 (kwiecień 2014): 387–94. http://dx.doi.org/10.4028/www.scientific.net/msf.787.387.

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Calcium silicate (CS) is a main component of Portland cement and is responsible for the strength development. Recent research has shown that dicalcium silicate cement (CSC) is bioactive and is a potential candidate for bone replacement. Traditionally, dicalcium silicate powder is synthesized by a solid state reaction or a sol-gel method. The solid-state reaction, however, usually needs a higher temperature and a longer calcination time. Furthermore, the dicalcium silicate powder made by the sol-gel method is not pure, and contains a significant quantity of CaO which is harmful to the strength and biological properties of the CSC. The Pechini technique is an alternative, low temperature polymeric precursor route for synthesis of high purity powders. In this study, purer CS powder was synthesized via the Pechini method by calcination at 800°C for 3h. DSC-TGA, XRD, SEM were used for characterization of CS powder and the hydrated cement. The DSC-TGA curves showed that the main exothermic peak was at 479°C and the total mass loss was 79.2%. The XRD patterns of CSC after hydration for 7, 14, and 35 days illustrated that dicalcium silicate hydrate (Ca1.5SiO3.5·xH2O, C-S-H) was formed in the hardened CS paste. The XRD peaks on the diffraction pattern of the C-S-H of the day 35 sample were of greater intensity than those at day 7 and day 14. This demonstrates that the hydration speed was slow and complete hydration could take more than one month. Flake-like crystals were observed on scanning electron micrographs following hardening. The degradation study result showed that there was no mass loss of CSC after the samples were soaked into phosphate buffered saline (PBS) for 40 days. The silicon assay revealed that orthosilicic acid could be released from CSC after the samples were soaked in simulated body fluid (SBF). Silicon is known to be critical to skeletal mineralization. The existence of silicon may stimulate the proliferation of bone and activate cells to produce bone. Investigation of cell attachment confirmed that the MC-3T3 cells attached well to the surfaces of CSC after seeding.

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Dezhatkina, S. V., Sh R. Zyalalov i M. E. Dezhatkin. "PHYSIOLOGICAL AND BIOCHEMICAL STATUS OF COWS IN CASE OF INTRODUCTION OF A SILICON-CONTAINING SUPPLEMENT INTO THEIR RATION". Vestnik of Ulyanovsk state agricultural academy 212 (22.03.2021): 170–74. http://dx.doi.org/10.18286/1816-4501-2021-1-170-174.

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The article raises questions about development of organic food market in Russia. One of the options for obtaining organic livestock products by using silicon-containing natural minerals as feed additives is proposed. The main carrier in the supplement is a highly activated natural zeolite, the filler is an amino acid complex of animal origin, the supplement is a 100 % natural product. The work was carried out in Ulyanovsk region at OOO “Agrofirma Tetyushskoye” on dairy cows of the black-and-white breed. There were two groups, 10 cows in each were selected: according to live weight, age, productivity, physiological state. The first group (control) received only the ration accepted on the farm. As for the second group (experimental), a silicon-containing additive based on modified zeolite enriched with amino acids was included in the ration once a day at a dose of 250 g per cow. All the animals were kept in the same conditions, there was stable housing. In the course of the experiment, improvement of morphological composition of cows’ blood and nitrogen metabolism parametres was revealed when an additive based on highly activated zeolite enriched with amino acids was introduced into the ration. The additive promoted an increase of: erythrocytes by 14.38 %, hemoglobin - by 12.17 % (p <0.05), leukocytes - by 20.44 % (p <0.01); total protein - by 11.84 %, albumin - by 11.11%, globulins - by 12.24 %; decrease of urea by 22.22 and ALT activity by 8.0%. In general, the parametres show protein metabolism intensification and effective usage of feed nitrogen for synthesis processes in the body, including milk synthesis.

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Müllner, Sebastian, Tobias Michlik, Michael Reichel, Tilo Held, Ralf Moos i Christina Roth. "Effect of Water-Soluble CMC/SBR Binder Ratios on Si-rGO Composites Using µm- and nm-Sized Silicon as Anode Materials for Lithium-Ion Batteries". Batteries 9, nr 5 (26.04.2023): 248. http://dx.doi.org/10.3390/batteries9050248.

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Silicon-containing materials are still the most promising alternatives to graphite as the negative electrodes of lithium-ion batteries. However, the different Li+ storage mechanism combined with the high capacity result in new requirements for the passive electrode components, such as the binder. To ensure sufficient cycling stability, silicon must be embedded in a suitable carbonaceous matrix. For this purpose, we used a simple ball milling process with reduced graphene oxide (rGO) to produce Si-rGO composites with µm- and nm-sized silicon particles. The rGO was synthesized previously from a two-step thermal synthesis method developed in-house. Subsequently, electrodes with varying CMC/SBR ratios (3:1, 1:1, and 1:3) were prepared from the composites containing the different Si particle sizes. It was found that the optimal binder ratio depends on the size of the Si particles. For the nm-Si-rGO composite, a CMC/SBR ratio of 3:1 results in a total capacity over 51 cycles of 20.6 Ah g−1, which means an improvement of 20% compared to CMC/SBR = 1:3 (17.1 Ah g−1). In contrast, we demonstrate that for µm-Si-rGO composites with an optimal CMC/SBR ratio of 1:1 (13.0 Ah g−1), compared to nm-Si-rGO, a higher SBR content is beneficial for the cycling behavior. Moreover, a comparison with graphite from the literature indicates that a rGO-matrix reduces the need for SBR.

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Maksimov, S. K., i V. N. Kukin. "Electron Microscopy investigations of buried Si3N4 isolation layers". Proceedings, annual meeting, Electron Microscopy Society of America 48, nr 4 (sierpień 1990): 642–43. http://dx.doi.org/10.1017/s0424820100176344.

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Formation of buried Si3N4 layers obtained by using repeated cycles of implantation and annealing has been investigated. Structure investigations were made with the use of a CM30 Twin electron microscope (whose diaphragm is 0.18 nm-1 ). In HREM studies, axial micrographs in Si reflections of the 000, 111 and 220 types were employed. Two types of samples were used: "plane view" samples and those of a "cross section". Si3N4 precipitates were identified by application of the EELS method on the LN and Lsiedges.N+ - ions were implanted into silicon wafers (of p-type, (001), 10 Ω cm) at a room temperature- The dose pf ions implanted in each cycle was 5.1010 cm-2 . The total dose was 5.1017 cm-2 , The energy of ions - 150 keV, the current density of the ion beam 25 μA/cm-2 . Annealing in the atmosphere of nitrogen was made at 1100° C which lasted 2 hours after the first cycle of implantation; in the other cycles it lasted 0.5 hours at 850° C. After the operation of ion beam synthesis was completed a silicon epitaxial layer 0.8-1 μm thick was grown.

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Ortiz-Gómez, Inmaculada, Víctor Toral-López, Francisco J. Romero, Ignacio de Orbe-Payá, Antonio García, Noel Rodríguez, Luís Fermín Capitán-Vallvey, Diego P. Morales i Alfonso Salinas-Castillo. "In situ synthesis of fluorescent silicon nanodots for determination of total carbohydrates in a paper microfluidic device combined with laser prepared graphene heater". Sensors and Actuators B: Chemical 332 (kwiecień 2021): 129506. http://dx.doi.org/10.1016/j.snb.2021.129506.

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Akopdzhanyan, T. G., E. A. Chemagina i I. P. Borovinskaya. "Study into the feasibility of obtaining dense materials based on AlN-SiC solid solution in one stage by SHS gasostatiс processing". Izvestiya vuzov. Poroshkovaya metallurgiya i funktsional’nye pokrytiya, nr 3 (16.11.2020): 34–40. http://dx.doi.org/10.17073/1997-308x-2020-3-34-40.

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The synthesis and sintering of the (AlN)x(SiC)1–x solid solution were studied under the conditions of SHS gasostatiс processing at high nitrogen gas pressures (up to 110 MPa). Phase formation during the combustion of aluminum and silicon carbide mixtures with the different amount of a combustible component (aluminum content is 35 to 60 wt.%) was studied. It was shown that the optimal amount of aluminum mixed with silicon carbide to obtain a single-phase solid solution (with the complete Al conversion to AlN and without SiC dissociation) is 45–50 wt.%. A mixture with 55–60 wt.% Al leads to excessively high temperatures, which in turn leads to the silicon carbide decomposition to Si + C elements. The optimal parameters for obtaining a dense material in one stage were determined. The measured porosity and density of materials obtained demonstrated that preforming is essential for the final density of samples containing 50 wt.% Al: maximum density was achieved at a preforming pressure of 10 MPa. It was found that the 5 wt.% yttrium oxide additive increases the material density by almost 10 %. A similar effect is also obtained by increasing the initial gas pressure from 80 to 110 MPa. The maximum density in this case reached 2.7 g/cm3, i.e. 83 % of the theoretical density. The total volumetric shrinkage of the material was 10 ± 0.5 %, and this indicator can be almost completely smoothed over by the 3 wt.% boron additive. The microhardness of samples was 2000 kg/mm2.

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Кукушкин, С. А., i А. В. Осипов. "Механизм образования углеродно-вакансионных структур в карбиде кремния при его росте методом замещения атомов". Физика твердого тела 60, nr 9 (2018): 1841. http://dx.doi.org/10.21883/ftt.2018.09.46408.083.

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AbstractThe mechanism of formation of carbon-vacancy structures in silicon carbide SiC from silicon vacancies that inevitably form during synthesizing SiC from Si by atomic substitution has been studied. It is shown that it is useful for one of four nearest carbon C atoms to be displaced to the place of a silicon vacancy with the decrease in the total energy by 1.5 eV in the case of polytype 3C and by 0.9–1.4 eV in the case of polytype 4H. In this case, the C atom must overcome the activation barrier of 3.1 eV in the case of polytype 3C and by 2.9–3.2 eV in the case of polytype 4H. This transition is realized during synthesizing SiC due to thermal fluctuations, since the synthesis temperature is T ≈ 1200–1300°C. Thus, the carbon–vacancy structure is a nearly flat cluster of four C atoms and related carbon vacancy with a characteristic diameter of ∼4 Å at a distance of 2.4 Å from it. All the characteristics of this transformation, namely, the energy profile, the transformation pathway, the transient state, its frequency spectrum, the eigenvector corresponding to the only negative eigenfrequency are calculated by the elastic band method. The infrared spectrum (IR) and the permittivity of SiC containing carbon–vacancy structures are considered. The new line at 960 cm^–1 detected recently in the IR spectrum of grown by the atomic substitution is unambiguously identified with vibrations of C atoms in carbon–vacancy structures. It is concluded that carbon–vacancy structures stabilize cubic polytype SiC–3C.

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Pashova, Katya, Elyes Dhaouadi, Ivaylo Hinkov, Ovidiu Brinza, Yves Roussigné, Manef Abderrabba i Samir Farhat. "Graphene Synthesis by Inductively Heated Copper Foils: Reactor Design and Operation". Coatings 10, nr 4 (25.03.2020): 305. http://dx.doi.org/10.3390/coatings10040305.

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We report on the design of a reactor to grow graphene via inductively heating of copper foils by radio frequency (RF) magnetic fields. A nearly uniform magnetic field induced by Helmholtz-like coils penetrates the copper foil generating eddy currents. While the frequency of the current is being rapidly varied, the substrate temperature increases from room temperature to ~1050 °C in 60 s. This temperature is maintained under Ar/H2 flow to reduce the copper, and under Ar/H2/CH4 to nucleate and grow the graphene over the entire copper foil. After the power cut-off, the temperature decreases rapidly to room temperature, stopping graphene secondary nucleation. Good quality graphene was obtained and transferred onto silicon, and coated with a 300 nm layer of SiO2 by chemical etching of the copper foil. After synthesis, samples were characterized by Raman spectroscopy. The design of the coils and the total power requirements for the graphene induction heating system were first estimated. Then, the effect of the process parameters on the temperature distribution in the copper foil was performed by solving the transient and steady-state coupled electromagnetic and thermal problem in the 2D domain. The quantitative effects of these process parameters were investigated, and the optimization analysis results are reported providing a root toward a scalable process for large-sized graphene.

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Venâncio, Jefferson Bittencourt, Nildo da Silva Dias, José Francismar de Medeiros, Patrícia Lígia Dantas de Morais, Clístenes Williams Araújo do Nascimento, Osvaldo Nogueira de Sousa Neto, Luciara Maria de Andrade i in. "Effect of Salinity and Silicon Doses on Onion Post-Harvest Quality and Shelf Life". Plants 11, nr 20 (20.10.2022): 2788. http://dx.doi.org/10.3390/plants11202788.

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Salt stress during pre-harvest limits the shelf life and post-harvest quality of produce; however, silicon nutrition can mitigate salt stress in plants. Thus, we evaluated the effects of salinity and fertilization with Si, in pre-harvest, on the morpho-physiological characteristics of onion bulbs during shelf life. The experiment was set up in randomized complete blocks, with treatments arranged in split-split plots. The plots had four levels of electrical conductivity of irrigation water (0.65, 1.7, 2.8, and 4.1 dS m−1). The subplots had five fertilization levels with Si (0, 41.6, 83.2, 124.8, and 166.4 kg ha−1). The sub-sub plots had four shelf times (0, 20, 40, and 60 days after harvest). Irrigation water salinity and shelf time reduced firmness and increased the mass loss of onion bulbs during shelf life. Salt stress reduced the contents of sugars and total soluble solids of onion bulbs during storage; however, Si supply improved the contents of these variables. Salinity, Si supply, and shelf time increased the concentrations of pyruvic and ascorbic acids in onion bulbs during shelf life. Si doses between 121.8 and 127.0 kg ha−1 attenuated the impacts caused by moderate salinity, increasing the synthesis of metabolites and prolonging the onion bulbs’ shelf life.

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