Ceramic powders chemical stability

In some solvents, ceramic powders can react with the solvent or decompose chemically or dissolve. Prediction of the chemical stability of a ceramic powder in a solvent is a complex problem which has facets that include thermodynamics and kinetics. 

Once the thermod3mamics of chemical reaction is determined as spontaneous, the reaction kinetics will establish the importance of this reaction to the degradation of the ceramic powder in the solvent. Reaction kinetics of this t3rpe between a solid and a (liquid) fluid were discussed in Chapter 5. Under some conditions the reaction kinetics are very slow, limited by either a slow surface reaction or a slow product layer diflusion. As a result, this reaction can be n ected in its importance to the ceramic powder s chemical stability. Unfortunately little information is found in the literature on the reaction kinetics for ceramic powders reacting with organic solvents. Therefore, trial and error seems to be the only dependable way to determine the chemical stability of ceramic powders in nonaqueous solvents. This is the way that the chemical decomposition of YBa2Cu3Q,. in alcohols was determined. 

HA is an inorganic material that has been used as the stationary phase for biopolymer chromatography since 1956. The early materials were soft powders (Tiselius apatite), but more recently ceramic HA and also fluoroapatite (FA) beads have also become available, which are much more suitable to the requirements of chromatography in terms of mechanical strength and chemical stability. Both apatites are stable at elevated pH, but will dissolve rapidly below a pH of 5.0. 

The aforementioned embroidered textiles were integrated on a low-loss and highly flexible polymer substrate. We employed PDMS as our substrate due to its mechanical flexibility and stretchability, inherent chemical stability, and water resistance (Koulouridis et al., 2006). As demonstrated in Wang et al. (2012b), the resultant PDMS composite had a dielectric constant of er = 3.0 and a low-loss tangent of tan < 0.02. Another advantage of PDMS is that its permittivity can be increased from 8r = 3.0-13.0 by dispersing ceramic powder into the PDMS matrix (Koulouridis et al., 2006). 

Bulk ceramics are produced conventionally by the sintering of powders. The strength, toughness, thermal stability, and dielectric properties of the fired ceramic depend strongly on the size and uniformity of the precursor powder and on the chemical properties of the powder smface. 

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