Solid-state reactions sintering

Yuan XY, Zhang F, Liu XJ, Zhang Z, Wang SW (2011) Fabrication of transparent AlON ceramics by solid-state reaction sintering. J Inorgan Mater 26 499-502... 

Diffusion rates may, in principle, also be determined from any property or reaction which depends on atomic mobility. By way of illustration, ionic conductivity of the anion is directly proportional to the anion diffusion coefficient (see Electrical conductivity). From high temperature solid state reactions, sintering, oxidation of metals etc. diffusion coefficients may be evaluated provided the detailed mechanism of the processes are known. Examples of this will be given in Chapter 7. 

The defects of the matrix play an important role on luminescent performances in these materials. Taking into consideration the preparation process of these compounds with the solid-state reaction of mixtures of BaC03, H3BO3, and NH4H2PO4 at different molar ratio, non-equal evaporation during the sintering process of these powders is inevitable and thus results in the formation of intrinsic defects, such as cation and oxygen vacancies. Positional disorder of B and Vacant B (Vb)" have been reported in SrBPOs crystals on the basis of... 

Sintering of particles occurs when one heats a system of particles to an elevated temperature. It Is caused by an interaction of particle surfaces whereby the surfaces fuse together and form a solid mass. It Is related to a solid state reaction In that sintering is governed by diffusion processes, but no solid state reaction, or change of composition or state, takes place. The best way to illustrate this phenomenon is to use pore growth as an example. 

If a precipitate is allowed to undergo Ostwald ripening, or is sintered, or is caused to enter into a solid state reaction of some kind, it will often develop into a distribution which has a size limit to its growth. That is, there is a maximum, or minimum limit (and sometimes both) which the particle distribution approaches. The distribution remains continuous as it approaches that limit. The log-probability plot then has the form shown in 5.8.2. on the next page. 

Kondou et al. [5.10] compared the production of PbCZ Tij Oj (PZT) by solid-state reaction between Ti02, Zr02PbO and the freeze drying of the nitrate salt solution. The solid state reaction requires 1100 °C, but the transformation of the freeze dried nitrates only 580 °C. Furthermore, the freeze dried product could be sintered better and showed at the Curie-temperature a two-fold larger dielectric constant than the PZT produced by solid-state reaction. 

YDC has been prepared by various methods, including solid-state reaction, coprecipitation, glycine-nitrate process and metal organic chemical vapor deposition (MOCVD). Table 1.4 shows that the properties depend on the preparation method [118,119,127,129,130], Zha et al. [129] have studied the influence of sintering... 

Deactivation is a common and important phenomenon in FTS. Deactivation effects of water are recorded on all commonly used supports. The suggested mechanisms include oxidation, sintering and solid state reactions rendering cobalt inactive. 

For unsupported catalysts, where particle sizes are typically an order of magnitude larger than those for supported catalysts, the mobility of various species in the bulk structure may be of interest when considering how the bulk structure and composition are reflected in the surface properties of the particle. In addition, bulk mobility is an important consideration in the understanding of solid state reactions and phenomena such as sintering. 

Many important phenomena in solid state ionics, such as ionic conduction, gas permeation through dense solids, solid state reactions, high temperature corrosion, or sintering of polycrystals, involve mobile ionic charge carriers. In most crystalline... 

Thermally induced deactivation of catalysts is a particularly difficult problem in high-temperature catalytic reactions. Thermal deactivation may result from one or a combination of the following (i) loss of catalytic surface area due to crystallite growth of the catalytic phase, (ii) loss of support area due to support collapse, (iii) reactions/transformations of catalytic phases to noncatalytic phases, and/or (iv) loss of active material by vaporization or volatilization. The first two processes are typically referred to as "sintering." Sintering, solid-state reactions, and vaporization processes generally take place at high reaction temperatures (e.g. > 500°C), and their rates depend upon temperature, reaction atmosphere, and catalyst formulation. While one of these processes may dominate under specific conditions in specified catalyst systems, more often than not, they occur simultaneously and are coupled processes. 

Samples were prepared by conventional solid-state reaction. Stoichiometric amount of Li2C03 (Aldrich Co.), V2O3 (High Purity Chemicals) were mixed and sintered at 1100°C for 10 h in a N2 gas flow. 

Catalytic molecular surface species may undergo drastic changes in their structure in the presence of reactants. For example, polymeric clusters may transform into highly distorted monomeric species. A crystalline phase may become mobile at its Tammann temperature, as shown by Raman spectroscopy, and it may spread over oxide supports driven by the reduction of the overall surface free energy. Reactive environments trigger many structural transformations, exemplified by particle sintering, dispersion of bulk phases, segregation of surface species into bulk phases, and solid-state reactions between supported oxides and supports. 

---