Sintering reactive

In the case of reactive sintering chemical potentials are the driving forces for the sintering processes.The ceramic compound is actually formed during sintering by 

RBSC (reaction-bonded silicon carbide) is another example of a material formed by a chemical reaction between a solid and a liquid. In this case liquid silicon and solid carbon are the reactants. The sintering temperature (1410°C) is slightly above the melting point of silicon and because the reaction with carbon is strongly exothermic, the rates are high and thermal stresses may develop. If carefully controlled, however, the product has an acceptable density and high strength. 

In the Lanxide process for the synthesis of fiber-reinforced ceramic composites a liquid alloy (A1 based), impregnated in a whisker felt or fiber preform, is gradually oxidized in air to form an oxide matrix. 

When solid CoO and Ti02 react to form the two possible mixed oxides, the mechanism of a reaction in an oxygen ambient diflFers from that in an inert gas (N2) or in vacuum. Why Derive the position of the marker threads in the reaction zone of a diffusion couple of these oxides. 

Solid state reactions involving chromia and sintering of Cr203 are helped by an oxygen atmosphere. Why Give the reaction mechanisms. 

FIGURE 16.37 (a) The WC-Co phase diagram, (b) The liquid phase, WC + 6% Co, smterrng shrinkage versus temperature for WC + 6% Co. 

Heterogeneous systems As the ceramic is heated to sintering temperatures, a liquid phase is formed which persists through out sintering. During cooling, the liquid is solidified. 

There are four stages to liquid phase sintering. 

Particle rearrangement stage After melting, the solid particles are drawn together by the capillary action caused by the liquid. This leads to rapid shrinkage and pore elimination. 

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Effects of particle size and pressure on the reactive sintering were studied by Gobran et al. (2004). The synthesis of RuAl was described it was observed that reactive systems containing low-melting constituents such as aluminium are assisted in densification by the formation of a transient liquid phase. Reactive sintering using... 

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

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. ... 

Current methods for depositing ternary crystallite compounds include coevaporation of elements, or alloys, electrodeposition, reactive-sintering, and flash evaporation, which are often followed by sulphuriza-tion/selenization steps, at elevated temperatures. The current world record cell has been reported by NREL with an efficiency of 19.2% based on their patented three-stage process. ... 

Reactivity, sinterability Crystallinity Reproducibility Process controllable... 

Besides clay-bound ware, there are also products composed of pure SiC, which, however, require very high firing temperatures and are utilized in special applications only. Silicon nitride or oxynitride can also serve as the binding phase the materials are highly refractory and can be produced at comparatively low temperatures by reactive sintering (cf. Chapter IV, Section 6.5). 

Dacheux N, Chassignetrx B, Brandel V, Coustumer PL, Genet M, Cizeron G (in press) Reactive sintering of the thorirrm phosphate-diphosphate. Study of physical, thermal and thermomechanical properties. Chem Mater... 

Dacheux, N., Chassigneux, B., Brandel, V., Le Coustumer, P., Genet, M., Cizeron, G., Reactive sintering of the thorium phosphate-diphosphate. Study of physical, thermal, and thermomechanical durability during leaching tests, Chem. Mater., 14, (2002), 2953-2961. Cited on pages 325,669. 

The manufacturing process (especially the cold and hot compaction stages) of pcBN is very similar to that of pcD, summarized in Section 1.3.3. However, the types of binders used and liquid phase sintering mechanisms can be quite different. In pcBN production, reactive sintering plays a major role in terms of driving the densification process, whereas in pcD, dissolution and precipitation and/or adhesion/coalescence are the main driving mechanisms. A typical example for pcBN would be the following reaction [162]. 

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