Solid state reactive sintering

During sintering of multicomponent green bodies, solid state reactions can take place. Examples of solid state reactive sintering are 

The solid state reaction was discussed in detail in Chapter 5. The volume fraction reacted is given by 

Solid state sintering was discussed previously in this chapter. The sintering kinetics depend upon the rate determining step, which can be either viscous flow, grain boundary diffusion, or lattice diffusion. These sintering kinetics are summarized in Tables 16.4 and 16.6 for the initial and intermediate stage and Section 16.3.2.3 for the final stage. 

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Liu WB, Li J, Jiang BX, Zhang D, Pan YB (2012) 2.44 KW laser output of Nd YAG ceramic slab fabricated by a solid-state reactive sintering. J Alloy Compd 538 258-261... 

Liu Q, Liu J, Li J, Ivanov M, Medvedev A, Zeng Y et al (2014) Solid-state reactive sintering of YAG transparent ceramics for optical applications. J Alloy Compd 616 81-88... 

Lee SH, Kochawattana S, Messing GL, Dumm JQ, Quarles G, Castillo V (2006) Solid-state reactive sintering of transparent polycrystalline Nd YAG ceramics. J Am Ceram Soc 89 1945-1950... 

In this chapter shock modification of powders (their specific area, x-ray diffraction lines, and point defects) measurements via analytical electron microscopy, magnetization and Mossbauer spectroscopy shock activation of catalysis, solution, solid-state chemical reactions, sintering, and structural transformations enhanced solid-state reactivity. 

The measures of solid state reactivity to be described include experiments on solid-gas, solid-liquid, and solid-solid chemical reaction, solid-solid structural transitions, and hot pressing-sintering in the solid state. These conditions are achieved in catalytic activity measurements of rutile and zinc oxide, in studies of the dissolution of silicon nitride and rutile, the reaction of lead oxide and zirconia to form lead zirconate, the monoclinic to tetragonal transformation in zirconia, the theta-to-alpha transformation in alumina, and the hot pressing of aluminum nitride and aluminum oxide. 

Burke J E and Rosoiowski J H 1976 Sintering Reactivity of Solids (Treatise on Solid State Chemistry vol ed N B Hannay (New York Pienum) pp 621-59... 

A pellet is pressed of an intimate mixture of finely divided reactants and reaction induced either by arc melting and high-T annealing or by solid-state sintering in an electrical or high-frequency furnace. Isolating the borides from reactive container components can be a problem. The use of boron nitride liners has proved effective. In some cases the protective liner is made of sintered boride containing the same elements as the boride in preparation. 

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. 

Gas-solid reactive sintering can also be used in the oxidation of most metals or, more important, mixtures of metals. After oxidation, solid state sintering takes place. With mixtures of metals, a mixed oxide is produced which can be sintered by either solid state or liquid phase sintering. One example of alloy oxidation to produce a ceramic is in the synthesis of the superconductor YBa2Cu3Q. ... 

Many different mechanisms have been proposed in the literature for the agglomeration of bed particles. Viscous flow sintering of liquid silicates, reactive liquid sintering of molten salt systems, chemical reaction sintering by formation of new compounds, solid state sintering and vaporisation followed by re-condensation have been reported by several investigators Chemical equilibrium models have... 

Historically, stabilized (and partially stabilized) zirconia ceramics were prepared from powders in which the component oxides are mechanically blended prior to forming and sintering. Because solid state diffusion is sluggish, firing temperatures in excess of 1800°C are normally required. Furthermore, the dopant was nonuniformly distributed, leading to inferior electrical properties. Trace impurities in the raw materials can also lead to enhancement of electronic conductivity in certain temperature ranges, which is also undesirable. To overcome these problems, several procedures have been developed to prepare reactive (small particle size) and chemically pure and homogeneous precursor powders for both fully stabilized and partially stabilized material. Two of these are alkoxide synthesis and hydroxide coprecipitation. 

One possible way to maintain the large surface of active perovskite phase is to load the active perovskite on a thermally stable support, but high activity for solid-state reaction to the support oxide becomes the damaging factor at high temperatures. The ease of redox reaction corresponds to mobile and active nature of bulk oxide ion, and hence high reactivity of oxide ion and high sinter-ability cannot be fully avoided. 

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