Reactivity of Solids最新文献

Numerous polycrystalline ceramic specimens of yttria-doped gallia, have been prepared in the solid state, have been studied by powder X-ray diffraction IR and UV spectroscopy. The electrical conductivities (D.C.) measured for various yttria contents and at various temperatures up to 150°C, and the bulk and true density, and the percentage porosity of the test samples are compared. Correlations of the results obtained have been determined. Some evidence of compound formation could be traced if prior firing had been carried out at 1350 °C, this was not the case when firing was carried out at 800°C. Doping gallia with yttria results in a decreased conductivity and an unaltered mode of conduction.

X-ray diffraction and Auger depth profiling were performed to investigate the reaction of Ti thin films with single crystalline (100) Si by rapid thermal annealing under N₂ and Ar. Within a few seconds titanium silicides are formed at temperatures between 620 and 700°C. The silicides consist of TiSi₂, TiSi and titanium-rich subsilicides like Ti₅Si₄ and Ti₅Si₃. TiSi₂ is the metastable, poorly-conducting C49 modification. Growth of this phase takes place near the substrate interface, and the Ti-rich silicides are situated closer to the surface. The crystallites of the different silicides exhibit a strong texture. Annealing under N₂ leads to the formation of titanium nitrides TiN_x near the surface and subsequent growth towards the suicide during prolonged thermal treatments. When the silicide and nitride reaction fronts coalesce the available Ti is consumed for these reactions. Further silicide growth can occur only via complex phase transformations.

Three hydrated aluminas, gibbsite, bayerite and boehmite, were ground in air for 0.25–20 h by a planetary ball mill. The effect of grinding on their texture, structure and thermal behaviors has been examined by means of XRD, TG, DTA, SEM, IR, particle size distribution and nitrogen gas adsorption. It was found that in the initial stages of grinding (within the first 1 h), the specific surface area, S, had increased in the gibbsite, decreased in the bayerite and had a maximum in boehmite, and then proceeded to achieve their respective equilibrium values. These behaviors were correlated with changes in the median size, d₅₀, as a measure of the aggregate size of the particles. Prolonged grinding times, led to a decrease in the intensity of X-ray diffraction lines and an increase in the half-maximum line breadth. After 4 or 8 h grinding all the hydrated aluminas had been changed to the amorphous phase without mechanochemical dehydration. Moreover, the DTA endotherms attributable to the dehydration of the hydrated aluminas gradually diminished on grinding, and a set of broad endotherms appeared at about 150 or 200 °C for the amorphous phases. Whereas the transformation sequences of the unground hydrated aluminas to α-Al₂O₃ showed gibbsite → χ → κ → α, bayerite → η → θ → α and boehmite → γ → δ → θ → α, all the amorphous phases showed the amorphous hydrated alumina → amorphous alumina → η → α and the temperature of α-transformation had been lowered by more than 200°C.

Recently it has been established that 11 Å tobermorite (a calcium silicate hydrate, closely related to Ca₅Si₆O₁₈H₂·4H₂O) shows remarkable ion exchange capacity for several ions in neutral and alkaline mediums. The Zn²⁺ ⇌ Ca²⁺ exchange data by 11 Å tobermorite in nearly neutral medium is described. A 0.92–12.8 wt.-% of zinc was achieved by placing tobermorite in dilute solutions of Zn²⁺ (100–2000 ppm) the X-ray powder diffraction data reveal that the crystallinity of the exchanger remains intact after cation exchange. The thermodynamics of the exchange reaction has also been developed. This new ion exchanger resembles clays and zeolites in some respects.

The hydrolysis of Co^III and Mn^III coordination compounds with 3 M LiOH yields different phases in the Li-Co-O and Li-Mn-O systems. The hydrolysis of Co(NH₃)₆³⁺ gives mixtures of LiCoO₂ (O3)/HCoO₂ as ultrafine particles. A high [OH⁻]/[Li⁺] ratio results in a higher HCoO₃ content. The hydrolysis of Mn(acac)₃ and Mn(C₂O₄)³⁻₃ in the presence of O₂ gives a mixture of orthorhombic LiMnO₂ and a phase structurally related to LiMn₂O₄. The product after aging is the spinel phase that is characterized by an Mn oxidation state of less than 3.5 and an $\text{Li}\text{Mn}$ ratio higher than 0.5. The thermal behaviour of this product involves the oxidation of Mn to an oxidation state close to 3.5.