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Abstract
A new form of semicrystalline sodium titanate was synthesized at high temperature (1100-1150 °C) by a reaction of TiO2 with Na2CO3 in an equimolar ratio. The obtained product was characterized using IR, DTA-TG, X-ray diffraction and elemental analyses. According to X-ray patterns, H2Ti5O11 . nH2O with monoclinic structure has been formed on dehydration of semicrystalline sodium titanate. Kinetic studies of the order and activation energy of a new phase transformation have been determined from DTA-thermograms. The ion exchange behavior of semicrystalline sodium titanate was studied at different g-doses as well as at different drying temperatures. The laboratory-scale ion exchange capacity, distribution studies and exchange performance for some radionuclides of a thermally prepared material were investigated. It was found that the exchange capacity was not changed after 100 kGy irradiation.
Abstract
The microporous titanosilicate ETS-10 synthesized from gel with following molar composition: 1.0 Na2O: 1.49 SiO2 : 0.2 TiO2 : 0.6 KF : 1.28 HCl : 39.5 H2O was subjected to sorption of radioactive cations 115Cd2+, 204Hg2+, 60Co2+ and 137Cs+ (M) from aqueous solution, in the absence of ionic competition. The uptake of these cations on the ETS-10 was compared by means of the distribution coefficient (Kd) versus contact time and sorption capacity (R) at equilibrium. The FT-IR spectra of M-ETS-10 sorption products exhibit a modification of the absorption band, principally at 381 cm-1.
Abstract
A Ti–45.9Al–8Nb (at%) alloy with a lamellar structure (γ+α2) was oxidised in air at 700, 800, 850 and 900°C in isothermal and thermal cycling conditions. The reaction progress was followed by thermogravimetric measurements. In isothermal conditions the oxidation kinetics followed approximately a parabolic rate law and the rate constants ranged from about 10–12 kg2 m–4 s–1 at 700°C to 10–10 kg2 m–4 s–1 at 900°C. The oxide scales were built of Al2O3 and TiO2, the former being the main component of the outermost layer. The oxidation behaviour of Ti–45.9Al–8Nb was referred to a commercial titanium alloy, WT4 (Ti–6Al–1Mn), and selected oxidation-resistant alloys.
Abstract
The aim of this paper is to define the characteristics of crystalline phase ETS-10 obtained from gel with dodecyltrimethylammonium bromide, as an organic template. ETS-10 zeolites has been synthesised under hydrothermal conditions from gels of composition 5Na2O–3KF–TiO2–6.4HCl– xC12TMAB –7.45SiO2–197.5H2O (where x=0.0, 0.25, 0.55, 1.0 and 1.5) with dodecyltrimethylammonium bromide. The crystalline phases synthesised with organic salt have an exothermal peak at ca. 360°C, due to the degradation of organic entrapped in the porous structure. Physical-chemical properties of C12TMAB -ETS-10 are studied by XRD, SEM and thermal analyses.
Abstract
Thermal decomposition of precursor xerogels for TiO2, obtained by gelling of acetylacetonate-modified titanium(IV) tetraisopropoxide (prepared at Ti-alkoxide:acetylacetone molar ratios of 1:1 (Ti-1) and 1:2 (Ti-2)) in boiling 2-methoxyethanol, was monitored by simultaneous TG/DTA/EGA-MS and EGA-FTIR measurements. Thermal degradation processes of Ti-1 and Ti-2 in the temperature range of 30–700C consist of six mass loss steps, the total mass loss being 46.3% and 54.4%, respectively. EGA by FTIR and MS revealed release of H2O below 120C; followed by evolution of acetone and acetic acid between approximately 100 and 320C, and that of CO2 up to 560C. Acetylacetone is evolved to a significant extent from sample Ti-2 at 120–200C.
Abstract
The high-resolution transmission electron microscopy HRTEM study of the atomic scale mechanism of crystal structure organization within the amorphous polymeric structure of the model multicomponent glass TiO2–MgO–Al2O3–SiO2– in the glass transformation temperature range has been undertaken. In the glass transition (T g) temperature range, glass transforms from the solid of rigid amorphous structure into viscoelastic state of weakened chemical bonds. This is an example of nuclei formation and crystal growth in the polymeric amorphous structure of low atomic scale homogeneity due to middle range ordering. It has been demonstrated that in this case crystal structure formation proceeds by successive displacement and local ordering of atoms in the amorphous structure, like disorder-order transformation in crystalline solid bodies. As the consequence in the crystallization by parent structure reorganization mechanism, traditional model of glass crystallization as well as kinetic models of reactions in solid bodies according Avrami or others, are worthy to be revised.
Abstract
A kinetic study of the crystallization processes was performed for some decorative ceramic glazes in the PbO-SiO2-Na2O-K2O-CaO(BaO)-Al2O3-B2O3 system with addition of 10% TiO2 and ZnO. The crystallization kinetics has been studied in non-isothermal conditions using DTA technique. The apparent activation energies of the crystallization processes were calculated using the Kissinger method. The main crystalline phase, which provides the decorative effect, is rutile. This has been identified by X-ray diffraction and it is clearly visible in the optical microscopy images taken in transmitted light, as needle-like or even prismatic crystals arranged in radial-fibrous aggregates.
Abstract
The crystallization kinetics of some glass-ceramics obtained from Romanian (Şanoviţa) basalt has been studied in non-isothermal conditions using DTA technique. The activation energies of the crystallization processes were calculated using the isoconversional methods Kissinger-Akahira-Sunose and Ozawa-Flynn-Wall. The results obtained show a dependence of the activation energy (E α) on the crystallized fraction (α) that proves the complex mechanism of the glass-ceramics crystallization process. It has been proved that the Johnson-Mehl-Avrami model cannot be applied for the studied glass-ceramics crystallization process. The effect of 2% TiO2 as nucleating agent upon the crystallization kinetics and upon the microstructure of the studied glass-ceramics was analyzed.
Abstract
The aqueous-phase partitioning of 59Fe, 147Pm, 234Th and 241Am by complexing compounds from subsurface bacteria has previously been studied in the presence of quartz sand. In this study the aqueous-phase partitioning of pico-to submicromolar amounts of 59Fe, 147Pm, 234Th and 241Am was analyzed in the presence of TiO2 and exudates from three species of subsurface bacteria: Pseudomonas fluorescens, Pseudomonas stutzeri, and Shewanella putrefaciens. All were grown under aerobic conditions and P. stutzeri and S. putrefaciens were grown under anaerobic conditions as well. The supernatants of the aerobic and anaerobic cultures were collected and radionuclide was added. TiO2, with BET surface area of 49.9 m2·g−1, was added to the supernatant radionuclide mix, and the pH was adjusted to approximately 8. After incubation, the amount of radionuclide in the liquid phase of the samples and controls was analyzed using scintillation method. Two types of values were calculated: solution% = the activity maintained in solution relative to the total activity, and Q-values = the quotient between the activity in samples and the activity in controls. Aerobic supernatants had solution% values between 89% and 100% for 59Fe and between 18 and 43% for 234Th. The solution% values for 241Am and 147Pm were less than 2% overall, but the Q-values were between 34 and 115 times more 241Am in bacterial supernatants than in controls. The corresponding values for 147Pm ranged from 6 to 20 times more than in the control. The solution% values for all elements in the presence of anaerobic supernatants were below 2%, but the Q-values clustered around 7 for 59Fe and ranging from 2 to 29 for 234Th, indicated that anaerobic supernatants partitioned these elements to the aqueous phase. Both aerobic and anaerobic supernatants tested positive for complexing compounds when analyzed, using the Chrome Azurol S assay. Complexation with excreted organic ligands is most likely the reason for the higher amounts of metals in samples than in the controls. Hence, aerobically and anaerobically excreted organic ligands seem able to influence the mobility of radionuclides in aerobic and anaerobic environments contaminated with these compounds.
modified Y-zeolite [ 30 ], modified mordenite [ 31 ], montmorillonite ion-exchanged with a multivalent metal ion (e.g., Al 3+ montmorillonite) [ 32 ], mixed metal oxides (e.g., TiO 2 –MoO 3 ) [ 33 ], oxides treated with sulfuric acid at 500 °C (e.g., SO 4
