Добірка наукової літератури з теми "K2Ti4O9"

The majority of the potassium titanates described in the literature were synthesized, and their Raman spectra recorded. The identity of the compounds K2TiO3, K2Ti2O5, K2Ti4O9, K2Ti6O13, and K2Ti8O17 was confirmed by x-ray diffraction. Raman spectroscopy was then used to study the hydrolysis, under different conditions, of K2Ti2O5 and of K2Ti4O9. On drying of the hydrolysis products, the following species were found to form: K2(H2O)0.66 Ti8O16(OH)2, K1.33(H2O)0.33Ti4O8.33(OH)0.67, and H2Ti8O17. On ignition at temperatures of 500–600°C these species converted, respectively, to K2Ti8O17, K2Ti6O13, and TiO2(B). Raman spectroscopy was used to establish that (1) K6Ti4O11 consists of a mixture of K2TiO3 and a new compound K4Ti3O8; (2) K2Ti3O7 consists of a mixture of K2Ti2O5 and K2Ti4O9, and (3) K2Ti5O11 consists of a mixture of K2Ti4O9 and K2Ti6O13. The temperature of decomposition and the identity of the products of the thermal decomposition of K2Ti8Ol7, K2Ti4O9, K2Ti2O5, and K4Ti3O8 were determined by Raman spectroscopy. The XRD data of the newly identified compounds are reported.

In this work, flux method is used to control the surface morphologies and crystal structures of the fine K2Ti6O13 fibers. When K2CO3 as a flux is added into fine K2Ti6O13 fibers and heated at 1100oC for 2h, the crystal of fibers are transformed to K2Ti4O9 and K2Ti2O5, however, the resulting fibers have no significant change in morphologies. On the other hand, when KCl is used as flux (15wt%) and heated at 1200oC for 2h, the diameters of the resulting fibers become about 2 micron without any change of the crystal structure.

Starting from H2TiO3, potassium teteratitanate (K2Ti4O9) nanofibres with the length of several micrometers and the diameter of 100nm were directly synthesized by solid state reaction. The novel phase transformation and structure change behavior was investigated by the X-ray diffraction technique (XRD), scanning electron microscopy (SEM) in details. In series of hydrothermal reaction, the K2Ti4O9 could transfer to anatase TiO2 and rutile TiO2. Aggregated anatase TiO2 particles and rod-like rutile TiO2 were produced respectively in 1M HCl solutions at 1600C and 2200C. When the 0.01M HCl solution was considered as solvent, the mixture of floral anatase TiO2 and K2Ti4O9 were present together.

AbstractPotassium hexatitanate (K2Ti4O9) whiskers were prepared by the kneading–drying–calcination method. After the preparation of products under different calcination temperatures and holding times, their morphology and structure were characterized by thermogravimetric and differential thermal, X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy. The XRD analysis showed that the reaction mixture was completely converted to K2Ti4O9 crystals at 800 °C when the T/K ratio was 3. Based on the analysis of LS (liquid–solid) growth mechanism, the corresponding transformation reaction mechanism during the roasting was elucidated. K2Ti4O9 whiskers grow mainly through the parallel action at a low temperature. With the increase in temperature, the series effect is obvious.

Potassium hexa and octatitanate fibers have been proposed as reinforcement for friction materials. The aim of this work was to establish a calcination route to produce these fibers, using commercial anatase and potassium carbonate powders. These powders were dry mixed with TiO2/K2O molar ratio, n, of 3.0, 3.5, and 4.0, and then calcined at 950, 1050, and 1150°C for 3 h. Calcined powders were milled, washed in warm water with different pHs, and heat treated to crystallize the fibers. The best conditions to growth long fibers were n=3.0 and 1050°C, in the twofase field (liquid + K2Ti4O9). Controlled ion-exchange with water removed K+ ions from K2Ti4O9 fibers resulting in potassium hexa or octatitanate fibers after the second heat-treatment. Fibers with sub-micrometer thickness (~0.6 μm) and average length of ~20 μm could be prepared.

The composite Ag2S/K2Ti4O9 photocatalyst was synthesized via a precipitation method. The structure of the photocatalyst was determined by powder X-ray diffraction, scanning electron microscope. The photocatalytic properties for organic matter degradation of the photocatalyst were examined under visible light irradiation. The results showed that, the sample which synthesized at 25°C via a precipitation route，using nitric acid silver and thiourea as the raw materials in the absence of any surfactants or templates has the highest crystallinity and investigated its catalytic behavior. RhB as degradation object, different dosing quantity of the degradation rate were examined, The best dosing quantity (1000 MgL-1) degradation rate was 18.93%. And with K2Ti4O9 for ontology, the degradation of different load rate were examined, The best load (25%) of the degradation rate is 20.57%. The results revealed the Ag2S potential applications in photocatalytic degradation for organic pollutants.

The commercialization of Li-ion battery (LIB) in 1990s by Sony Corporation has led to its applications in portable electronic devices such as mobile phones, cameras, laptop computers, etc. Initially, the energy density of commercial LIB was only about 120 Wh Kg-1. However, with sustained improvements in properties of various cell components, the present-day LIB provides energy density of about 250 Wh Kg-1. With future use envisaged for mobility applications such as electric vehicles, research activities have gained momentum for development of high energy density Li-S and Li-O2 batteries. However, due to limited sources of lithium (0.007 % in earth’s crust and 0.2 ppm in sea water) and uneven distribution, concerns arise about its cost and availability which would inhibit bulk production and utilization of lithium-based batteries. Hence, there is an urgent need to switch over to battery systems employing earth abundant and environmentally benign materials. Sodium and potassium-based batteries have received attention in research laboratories as alternatives to lithium-based batteries due to their natural abundance and low cost. Na and K are the metals below Li in the periodic table and their physical and chemical properties are similar to those of Li. Na and K are the sixth and seventh most abundant elements, constituting 2.6 % and 2.4 %, respectively of the earth’s crust. Sea water contains about 10800 ppm Na and 400 ppm K. Although, the standard potentials of Na/Na+ (-2.71 V vs. standard hydrogen electrode (SHE)) and K/K+ (-2.93 V vs. SHE) are less than Li/Li+ (-3.04 V vs. SHE) by about 300 and 100 mV, respectively, the cost and availability factors overweigh the marginal reduction in energy density. The quest for new electrode materials for Na- and K-based batteries, their physicochemical characterizations and electrochemical investigations are described in the thesis. It consists of a comprehensive review of the literature on the evolution of battery systems with a focus on the next generation Na- and K-based batteries. The cathode and anode materials for Na- and K-ion batteries are reviewed along with the current research activities in Na- and K-sulphur, and Na- and K-O2 batteries. It furnishes a brief description of various experimental techniques and procedures adopted at different stages of the present thesis. The amorphous MnO2 has been prepared by two different methods: (i) reduction of KMnO4 using ethylene glycol (EG) and (ii) the redox reaction between KMnO4 and MnSO4.H2O at ambient conditions. The as prepared MnO2 samples in both cases are amorphous in nature and on heating in the temperature range of 300 – 800 °C, they convert to α-MnO2. The MnO2 prepared by reduction by EG has been studied for Na/MnO2 and Li/MnO2 laboratory scale primary cells in non-aqueous electrolytes. The specific capacity of amorphous MnO2 is 300 mAh g-1 in both Na/MnO2 and Li/MnO2 cells. Na/MnO2 cell shows a nominal voltage less than Li/MnO2 cell by 0.35 V, as expected. MnO2 prepared by the redox reaction between KMnO4 and MnSO4.H2O has a specific surface area of 184 m2 g-1 with narrowly distributed mesopores of 3.5 nm pore diameter. The crystallinity increases and specific surface area decreases upon heating. The as prepared sample provides the first discharge capacity of about 300, 200 and 80 mAh g-1 for Li-, Na- and K-MnO2 cells, respectively, at a specific current of 50 mA g-1. The attractively high discharge capacity of the as prepared amorphous MnO2 is attributed to the large specific surface area and mesoporosity. However, the crystalline samples exhibit low specific discharge capacity in comparison with amorphous samples. It deals with electrochemical impedance spectroscopy (EIS) study of Na/MnO2 primary cell fabricated in a non-aqueous electrolyte of Na salt. The EIS data provides a high resistance of Na metal due to the surface passive film. On subjecting the cell for discharge, the surface film causes a delay response of the cell voltage and the closed-circuit voltage reaches the normal discharge level following dielectric break-down of the film. The EIS data measured at different stages of cell discharge are subjected to non-linear least squares fitting with the aid of an appropriate equivalent circuit. The impedance parameters are examined to throw light on state-of-charge of Na/MnO2 primary cells. The study has been further extended to analyze the delay-time behaviour of the non-aqueous Na/MnO2 cells and quantifying the film resistance and break-down field for the film formed on the Na surface. P2-type Na0.67Mn0.65Fe0.20Ni0.15O2 is studied as a cathode material for Na-ion battery and presented. It is synthesized in microspherical and disc-like morphologies using two different synthetic procedures. Microspheres of FeCO3 are first prepared and used as a template to synthesize Mn0.65Fe0.20Ni0.15CO3, followed by its thermal decomposition to the corresponding oxide and finally, thermal fusion of the oxide with Na2CO3 to produce P2-type Na0.67Mn0.65Fe0.20Ni0.15O2. However, disc-like Na0.67Mn0.65Fe0.20Ni0.15O2 is synthesized by sintering the product obtained using a low temperature solution combustion method using aqueous solution of stoichiometric quantities of corresponding metal nitrates and sucrose as the fuel at 800 °C. Cyclic voltammograms in both the samples are characterized by well-defined two pairs of current peaks corresponding to the oxidation and reduction processes in two different stages. The sodiated microspherical oxide provides an initial discharge capacity of about 216 mAh g-1 at C/15 rate cycling with an excellent cycling stability (Fig. 3a). The rate capability is also high, and the discharge capacity is about 100 mAh g-1 at 2C rate. The high discharge capacity and high rate capability are attributed to porous microspherical morphology. When the cells with disc-like morphology cathode sample are cycled at a current density of 35 mA g-1, a specific discharge capacity of 178 mAh g-1 is obtained with close to 100 % coulombic efficiency. Capacity retention of more than 70 % is observed after 50 charge-discharge cycles Potassium tetratitanate (K2Ti4O9) is synthesized by solid-state method using K2CO3 and TiO2 and studied as an anode material for potassium ion batteries (KIB) for the first time. A discharge capacity of 97 mAh g-1 has been obtained at a current density of 30 mA g-1 (0.2 C rate) and 80 mAh g-1 at 100 mA g-1 (0.8 C rate), initially (Fig. 4a). The proposed mechanism of charging involves reduction of two Ti ions from 4+ oxidation state to 3+ oxidation state, which facilitates insertion of two K+ ions per formula unit in the zig-zag layer of TiO6 octahedra separated with K+ ions with interlayer spacing of 0.85 nm. For KIB cathode, K0.27Mn0.65Fe0.35-xNixO2 (0.00 ≤ x ≤ 0.35) is synthesized in microspherical morphology. The potassiated mixed metal oxide formed in microspherical morphology is in pure crystalline phase. The oxide with the composition x = 0.35 i.e., K0.27Mn0.65Ni0.35O2 provides the highest first specific discharge capacity of 97 mAh g-1 at C/10 rate (Fig. 4b). A good cycling stability is observed. It deals with carbonization of milk-free coconut kernel pulp carried out at low temperatures. The carbon samples are activated using KOH and electrical doublelayer capacitor (EDLC) properties are studied (Fig. 5a). Among the several samples prepared, activated carbon prepared at 600 °C has a large specific surface area (1200 m2 g-1). Cyclic voltammetry and galvanostatic charge-discharge studies suggest that activated carbons derived from coconut kernel pulp are appropriate materials for EDLC studies in acidic, alkaline and non-aqueous electrolytes. Specific capacitance (SC) of 173 F g-1 is obtained in 1 M H2SO4 electrolyte for the activated carbon prepared at 600 °C. The supercapacitor properties of activated carbon sample prepared at 600 °C are superior to the samples prepared at higher temperatures. Electrochemical studies are also undertaken for the prepared and activated samples for sodium ion intercalation/deintercalation. It is found that various factors such as surface area, mesoporosity, inter-layer spacing, electrolyte diffusion, solid electrolyte interface formation for high surface area carbon, etc. contribute to the capacity and cycle life of the material. Carbon sample synthesized at 600 °C and having a specific surface area of about 280 m2 g-1 provides the highest discharge capacity of about 200 mAh g-1 with good cycling stability. The thesis ends with a short summary and prospects of the investigations described here in. The work presented in it is carried out by the candidate as a part of Int. Ph.D. program. Some of the results are published in the literature and some more manuscripts are in preparation. A list of publications is enclosed. It is hoped that the studies reported in the thesis are worthy contributions.

The development of selective adsorbents for radioactive Sr ions is one of the most important subjects for the safety decontamination in Fukushima NPP-1[1]. In this study, the selective adsorption properties of Sr, characterization and stable solidification were clarified by using the novel adsorbent of potassium titanates (KT-1). The adsorption properties of Sr2+ ions for original and calcined specimens were examined by batch method under the following conditions; V/m = 100 cm3/g, Mixed solution: 10,000 ppm Na+, 10 ppm Cs+, 10 ppm Ca2+, 1 ppm Mg2+ and 1 ppm Sr2+, 85Sr tracer: 5,000 cpm/cm3, centrifugation: 2,500 rpm, 25°C, shaking time: 1∼24 h, calcination temp.: 300∼900°C. Relatively large uptake percentage above 90% was obtained for the original and calcined specimens below 800°C, while the Sr uptake for calcined specimens above 900°C was lowered due to the thermal decomposition of K2Ti2O5·xH2O. The Sr distribution in the column was examined by flowing the mixed solution through the columns packed with KT-1. The Sr distribution profiles were obtained by the measurement of γ-activity in the column at 5 mm intervals. In either case, no breakthrough of Sr was observed. The distribution profile tended to smooth with increasing flow rate; Sr adsorption band and flow rate have a linear relationship. The leachability of Sr for the solid forms was further examined under the following leaching conditions; leachant: pure water and 1 M HCl; leachant temp.: 25°C and 90°C, leaching period: 4 weeks; calcining temp.: 500∼1,100°C. The leached percentage of Sr in pure water was less than the detection limit of ICP-AES, and that in 0.1 M HCl tended to markedly decrease with calcining temperature; the formation of SrTiO3 phase above 800°C was effective for the lowering of leachability. The novel adsorbent of KT-1 is thus effective for the selective decontamination and stable solidification of Sr in Fukushima NPP-1.