Reactivity of Solids最新文献

The thermal decomposition course of cadmium acetate dihydrate (CdAc) was examined, on heating to 773 K at various rates (5–30 K min⁻¹) by thermogravimetric and differential thermal analyses, and temperature shifts experienced by the events encountered as a function of the heating rate were employed in determining corresponding non-isothermal kinetic parameters (k, A and ΔE). Gas- and solid-phase products were identified by infrared spectroscopy and X-ray diffractometry. The results obtained showed CdAc to dehydrate at 360–423 K, and then decompose at 508–560 K giving CdO, and (CH₃)CO and CO₂ into the gas phase, encompassing two melting processes at 345 and 500 K. Other gas-phase products of CH₃COOH, CO, CH₄ and (CH₃)₂CHCH₂ were also detected, however in minor proportions, and ascribed to reactions occurring at the gas-solid interface at the expense of some of the initial products. These results were found in good agreement with the results of previous investigations of metal acetates.

The milling of Na-FAU with AlPO₄ · 3H₂O introduces P atoms into the Si-Al network of the zeolite, producing a SAPO molecular sieve with the same adsorption properties, a slightly higher thermal stability and a larger cell parameter. The tribochemical reaction was followed by IR, XRD, DTA, Mossbauer and NH₃ adsorption experiments.

Thermomagnetometric studies of pyrrhotites, Fe(_1−x)S, formed during the decomposition of pyrite, were made in dry, oxygen-free nitrogen, 3% hydrogen in nitrogen, and 1.2% oxygen in nitrogen. Decomposition was demonstrated to be more complex than could be determined by thermogravimetric measurements. X-ray powder diffraction techniques, or chemical analysis of quenched pyrite samples. Thermomagnetometry was shown to be a sensitive and useful technique, enabling the detection of a number of magnetic phases within the decomposition products.

The reduction with pig iron of synthetic liquid slag containing tin oxide was investigated. Pig iron significantly reduces the tin content of slag (0.1%) and improves the rate of tin recovery. The influence of reaction time and temperature, and of amount of pig iron on the extent of reduction was studied.

PbO (litharge) was doped with Ba²⁺ and Sr²⁺ up to 10 mol%. The doped samples were heterogeneous, containing Pb⁴⁺ and/or C0₃²⁻. The tempearture of transformation, T_tr, into massicot increased on doping, whereas it decreased after mechanical treatment. Changes in T_tr are discussed in terms of the mobility of oxygen atoms. The apparent enthalpy of the phase transformation, ΔH_tr was negatively correlated with the lattice distortion consequent on doping and grinding. The feasibility of controlling transformation kinetics by the concurrent effects of doping and lattice distortion is also discussed.

Reactions of the p-substituted anilines p-anisidine (I), p-bromoaniline (II) and p-chloroaniline (III) with p-benzoquinone have been studied in the solid state. The reaction products are 1:1 molecular complexes which may be polymeric or agglomeric in nature. DSC studies revealed that the products obtained from solution and by solid-state reactions are not identical in the systems of I and III, whereas in system II they are identical. However, when the reaction products of system I and III obtained from solution are heated at 150°C, the entrapped solvent molecules become liberated and the products obtained from solution and solid-state reactions become identical. Spectroscopic studies show that the reaction products are charge-transfer complexes stabilized by hydrogen bonding. ESR spectroscopic studies confirm the presence of unpaired electrons in the complexes. Electrical conductivity measurements of solid pellets proved that the reaction products have semiconducting properties.

In the course of the reactions it was found that the p-benzoquinone molecules diffuse towards the p-substituted anilines, forming brown-coloured reaction products. Diffusion occurs through surface migration, which is related to the geometry of the molecules. The higher the dipole moment of the p-substituted anilines, the lower the rate of the reaction. Also, the higher the dissociation constants of the p-substituted anilines, the higher the rate of the reaction. The rate of the reactions have confirmed the validity of the Hammett equation. This equation has been verified for the first time for organic solid-state reactions.

The reduction of magnetite to wustite Fe_0.936O was studied by means of thermogravimetry at 1293 K. Sphere-like samples of constant radius, within the radius range 0.3–5.0 mm, were reduced by flowing a CO₂ + CO gas mixture at nearly atmospheric pressure. Sigmoidal-type kinetic curves were obtained.

The crackling core model proposed in 1975 by Park and Levenspiel fits the data. The model takes into account crackling of solid grains and a chemical reaction. The limits of applicability of the model are discussed in more detail and the original procedure for calculating its parameters was modified to some extent.

The chemical interaction at 250 to 1000°C of aluminium nitrate with chromium carbonate was investigated. The decomposition products of these compounds, and their mixtures with molar ratios of $\text{3}\text{1}$, $\text{2}\text{1}$, $\text{1}\text{1}$,$\text{1}\text{2}$and $\text{1}\text{3}$, were characterized by means of chemical analysis, diffuse reflectance and X-ray diffraction.

At temperatures higher than 215°C mixtures with a chromium carbonate/aluminium nitrate ratio greater than one yielded an amorphous aluminium chromate dichromate with an empirical formula Al_2−x-Cr_xO₃Al₂(CrO₄)₂Cr₂O₇together with crystalline Cr₂O₃. Mixtures with a ratio equal to or less than one yielded an amorphous aluminium hydroxy chromate (empirically, AlCrO₃Al(OH)CrO₄) with Cr₂O₃ and γ-alumina.

Both types of chromates were converted into solid solutions of (Al_0.17Cr_0.83)₂O₃, (Al_0.25Cr_0.75)₂O₃, (Al_0.33Cr_0.67)₂O₃ and (Al_0.5Cr_0.5)₂O₃ at temperatures higher than 480°C. Characteristic phenomena of (Al_1−xCr_x)₂O₃ solid solutions were observed, such as their d spacings and shifts of ⁴A_2g → ⁴T_2g and ⁴T_2g → ⁴T_1g absorption bands towards shorter wavelengths.

The kinetics of carbiding of polycrystalline iron films by carbon monoxide in the millibar range is studied at 573 K. The experimental data are analyzed by the full Avrami theory of nucleation and growth of nuclei, as well as by the simplified one. Crystallographic relations between Hägg-carbide and α-iron are discussed. A model for the carbiding reaction is proposed.

The striking role played by water vapour during the low temperature reduction of hematite into magnetite by carbon monoxide has been reported but the possibility that this effect was not due to hydrogen produced from the H₂O+CO shift reaction had to be eliminated.

A very similar effect by water vapour during the reaction of hematite with hydrogen is reported, the nucleation of magnetite is more regularly distributed and the magnetite layer is much more regular, but the rate of reaction is lower.

As the reduction proceeds to give more iron, another striking effect is observed: in the presence of water, there is no overlap of the steps hematite → magnetite and magnetite → iron; the reduction of magnetite starts once the hematite has disappeared. It is shown that rather than being a problem of transfer through a stagnant film, the clearly different steps may be attributed to the fact that when adsorption-desorption is not fast enough, the surface oxygen chemical potential differs from that of the gas.