Solid state reactions oxidation

Ba, La-M-substituted hexaaluminate M = Mn Solid state reaction Oxides and/or carbonates and chlorides 1400-1600 Ba-P-Al203 or MP, no surface area data Ceramic materials, Crystallography 6,10... 

Chromates III). Mixed oxides, e.g. FeCr204, having spinel structures and prepared by solid state reactions. 

Copper(II) oxide, CuO. Black solid formed by heating Cu(OH)2, Cu(N03)2, etc. Dissolves in acid to Cu(II) salts, decomposes to CU2O at 800 C. Forms cuprates in solid state reactions. A cuprate(III), KCUO2, is also known. 

Manganaies IV), manganites. Mixed-metal oxides containing Mn(IV). Prepared by solid state reactions. 

The Pb02/PbOx border slowly penetrates into the metal, but only at a very slow rate as a solid-state reaction. Cracks are formed when the oxide layer exceeds a given thickness, on account of the growth in volume when lead becomes converted into lead dioxide (Table 7). Underneath the cracks the corrosion process starts again and again. As a whole, the corrosion proceeds at a fairly constant rate. It never comes to a standstill, and a continually flowing anodic current, the corrosion current is required to re-establish the corrosion layer. 

Some of the reactions which yield MM0O4 or MW04, referred to in Sect. 4.1.4, are closely related to those discussed here in which a carbonate or higher oxide is used as reactant. For example, the solid state reaction... 

These studies show that the thiospinel structure is quite flexible with opportunity for cation vacancies at the 8 a site. Our investigation on such cation-deficient thiospinels is significant in that it shows that additional vacancies are possible in the 8 a site. Most of the cation-deficient compounds known earlier (predominantly copper compounds) were obtained by extraction of Cu by using various oxidizing reagents. These studies show that such cation-deficient quaternary thiospinels can also be obtained by direct solid-state reactions. 

If iron metal would oxidize to form a homogenous oxide layer without flaking off, draw a diagram showing the reaction conditions, the phase boundary formed and the diffusion conditions likely to prevail in the solid state reaction. 

When it is heated to about 840 °C., it forms calcium oxide, CaO, by solid state reaction, vis ... 

In addition to metals, other substances that are solids and have at least some electronic conductivity can be used as reacting electrodes. During reaction, such a solid is converted to the solid phase of another substance (this is called a solid-state reaction), or soluble reaction products are formed. Reactions involving nomnetaUic solids occur primarily in batteries, where various oxides (MnOj, PbOj, NiOOH, Ag20, and others) and insoluble salts (PbS04, AgCl, and others) are widely used as electrode materials. These compounds are converted in an electrochemical reaction to the metal or to compounds of the metal in a different oxidation state. 

In heterogeneous solid-state reactions where the composition of both solid reactants does not change, the electrode s eqnilibrinm potential depends only on the nature of the two phases, not on their relative amonnts. Hence, dnring the reaction the potential does not change. It also remains constant when the cnrrent is interrupted after partial reduction or oxidation. 

Mixed-phase oxide pigments are manufactured by high temperature (800-1000 °C) solid state reactions of the individual oxide components in the appropriate quantities. The preparation of nickel antimony titanium yellow, for example, involves reaction of Ti02, NiO and Sb203 carried out in the presence of oxygen or other suitable oxidising agent to effect the necessary oxidation of Sb(m) to Sb(v) in the lattice. 

Solid state reactions are also very common in producing oxide materials and are based on thermal treatment of solid oxides, hydroxides and metal salts (carbonates, oxalates, nitrates, sulphates, acetates, etc.) which decompose and react forming target products and evolving gaseous products. Solid-state chemistry states that, like in the case of precipitation, powder characteristics depend on the speed of the nucleation of particles and their growth however, these processes in solids are much slower than in liquids. 

Cr-ZSM-5 catalysts prepared by solid-state reaction from different chromium precursors (acetate, chloride, nitrate, sulphate and ammonium dichromate) were studied in the selective ammoxidation of ethylene to acetonitrile. Cr-ZSM-5 catalysts were characterized by chemical analysis, X-ray powder diffraction, FTIR (1500-400 cm 1), N2 physisorption (BET), 27A1 MAS NMR, UV-Visible spectroscopy, NH3-TPD and H2-TPR. For all samples, UV-Visible spectroscopy and H2-TPR results confirmed that both Cr(VI) ions and Cr(III) oxide coexist. TPD of ammonia showed that from the chromium incorporation, it results strong Lewis acid sites formation at the detriment of the initial Bronsted acid sites. The catalyst issued from chromium chloride showed higher activity and selectivity toward acetonitrile. This activity can be assigned to the nature of chromium species formed using this precursor. In general, C r6+ species seem to play a key role in the ammoxidation reaction but Cr203 oxide enhances the deep oxidation. 

Common routes for the synthesis of selenates and tellurates(IV and VI) are the reactions of metal oxides or carbonates with the repsective acids (see Section 4). The disadvantage of this procedure is, that one usually obtains hydrates or, at higher acid concentrations, acidic compounds. Because the oxides E03 and E02 (E=Se, Te) are solids under ambient conditions, solid-state reactions with the respective metal oxides are an alternative route to prepare the anhydrous compounds. 

Monitoring solid state reactions that play a role in catalyst activation forms a useful application of XRD. The example discussed above concerns a catalyst with large iron oxide particles as is used in the water gas shift reaction, and represents a particularly favorable system for XRD analysis. Similar studies with small particles are certainly also feasible, although it may be advisable to use laboratory X-ray sources of higher energy, such as Mo Ka, or a synchrotron [13]. 

The examples illustrate the strong points of XRD for catalyst studies XRD identifies crystallographic phases, if desired under in situ conditions, and can be used to monitor the kinetics of solid state reactions such as reduction, oxidation, sulfidation, carburization or nitridation that are used in the activation of catalysts. In addition, careful analysis of diffraction line shapes or - more common but less accurate-simple determination of the line broadening gives information on particle size. 

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