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Journal of Thermal Analysis and Calorimetry
Authors:
Rodica Mariana Ion
,
Irina Dumitriu
,
Radu Claudiu Fierascu
,
Mihaela-Lucia Ion
,
Simona Florentina Pop
,
Constantin Radovici
,
Raluca Ioana Bunghez
, and
V. I. R. Niculescu

oxides (SiO 2 , Al 2 O 3 , CaO, Fe 2 O 3 , K 2 O, MgO, MnO, Na 2 O, and TiO 2 ). The content of some minor elements (Cu, Cr, Ni, Pb, and Zn) were also detected by ICP-AES and EDXRF. The EDXRF results obtained in the analyzed sample are presented

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The study presents results of examination on Na0.5Bi0.5TiO3 (NBT) ferroelectric synthesis through intermediate binary compound Bi4Ti3O12 (BIT). The first stage of the study related to obtaining BIT from oxide precursors, i.e. Bi2O3 and TiO2. The second stage included obtaining NBT from Bi4Ti3O12, Na2CO3 and TiO2. Two polymorphic modifications of TiO2 (anatase, rutile) and diversified initial homogenization of raw material batches were applied during examination.

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Gamma-ray treatment in the presence of ozone (O3) and titanium dioxide (TiO2) showed an efficient removal of trichloroethylene (TCE) and perchloroethylene (PCE). Without gamma-irradiation, TCE and PCE were not sufficiently decomposed to comply with the water quality limit of groundwater. However, near 100% of TCE and PCE were removed at a dose of 300 Gy in the presence of O3 and TiO2, where TiO2 showed an explicit enhancement of decomposition. Cytotoxicity test using Chinese hamster V79 cells showed no toxicity of the TCE and PCE decomposition products.

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Thermal behaviour of the glass series (100–y)[0.5ZnO0.1B2O30.4P2O5]yTiO2 (with y=0–39 mol% TiO2) was investigated by DSC and TMA. The addition of TiO2 results in a non-linear increase of glass transition temperature. The compositional dependences of thermal stability, evaluated by two criteria exhibit two maxima for the glasses doped with 10.7 and 35.9 mol% TiO2. All the glasses crystallize on heating in the temperature range of 576–670C. The crystallization mechanism was studied at the glasses with 19.4 and 35.9 mol% TiO2 and the results showed that surface nucleation mechanism prevails in these glasses over the internal one.

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Different combination of raw materials and nucleating agents were incorporated in the batch of nepheline-pyroxene glass to demonstrate their effect on the crystallization process. The effect of TiO2, Cr2O3 and LiF with respect to crystallization of base glass was studied by differential thermal analysis (DTA).These materials improved the crystallization of glass between 50 to 150C of heat treatment. When LiF+TiO2 and TiO2+Cr2O3 were put together in the glass batches, the rate of crystallization of glass was increased in the same manner. The presence of TiO2+LiF+Cr2O3 improved the crystallization of the glass by decreasing the heat temperature by about 60C. CaO/MgO and CaO/Na2O ratios played an important role in the rate of crystal growth. The increase in the CaO/MgO ratio lowers the crystallization temperature by values ranging between 37 and 46C.

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A solvothermal continuous-flow method for the scalable and shape tunable synthesis of rod-like/spherical TiO2 nanocrystals (NCs) has been developed. The as-prepared colloidal NCs show photocatalytic activity in an addition–cyclization cascade under continuous-flow conditions.

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The enthalpic relaxation of the title glasses, studied by differential scanning calorimetry, is well described by a mathematical model based on the stretched exponential relaxation function with the relaxation time proportional to the actual viscosity. The dependence of viscosity on temperature and the fictive temperature was expressed by Mazurin's approximation. The relaxation parameters obtained correlated significantly with the glass composition, indicating the changes in the structural of the TiO2 role near a TiO2 content of 3–4 mol%.

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Silica-titania gels containing 25, 50 and 75 mol% TiO2 were prepared and the sorption of alkali and alkaline earth metal ions by these materials has been studied. Distribution coefficient values for Cs+ and Sr2+ ions were found to pass through broad maxima as a function of TiO2 content except in the case of Sr under alkaline conditions where there was a continuous increase. Capacity values also increased with TiO2 content and samples containing 50% (for K+ and Cs+), 75% (for Li+ and Na+) and 25%/50% (for Ca2+, Sr2+ and Ba2+) TiO2 exhibited maximum capacities. However, unlike with alkali metals, capacities of a given sorbent for the three alkaline earth ions were almost the same. Large capacities obtained for the latter ions seem to indicate a mineral-forming reaction with 25% and 50% materials. On the other hand, the 25% TiO2 gel seems to sorb Sr at trace level by an ion exchange mechanism. Coupled with its Cs sorption capability, this material may find potential use in large scale decontamination of low level waste solutions.

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DTA was used to study thermal properties and thermal stability of (50-x)Li2O-xTiO2-50P2O5 (x=0–10 mol%) and 45Li2Ot-yTiO2-(55-y)P2O5 (y=5–20 mol%) glasses. The addition of TiO2 to lithium phosphate glasses results in a non-linear increase of glass transition temperature. All prepared glasses crystallize under heating within the temperature range of 400–540°C. The lowest tendency towards crystallization have the glasses with x=7.5 and y=10 mol% TiO2. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were LiPO3, Li4 P2O7, TiP2O7 and NASICON-type LiTi2(PO4)3. DTA results also indicated that the maximum of nucleation rate for 45Li2O-5TiO2-50P2O5 glass is close to the glass transition temperature.

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The possibility of concentrating Pt, Ir, Au, Ag, Re and some other elements from samples of chromites, sulfide ores, laterites, shales, titanium magnetites, and ultrabasic rocks was studied. A new simple procedure is based on sublimation of elements to be determined in air stream at 1200 °C in the presence of some powdered reagents /e.g., TiO2, Nb2O5, Nb/ to enhance the yield, and on the use of chemical filters /CaO, MgO, TiO2, Al2O3, Nb2O5/ absorbing the interfering volatile elements from the gas phase. Neutron activation and X-ray fluorescence isotopic excitation were used to analyze the obtained concentrates.

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