Purity and Microstructure

Ceramic powder characteristics are important because the purity of the powder sets the maximum purity level of the final processed ceramic part, and the particle size and size distribution play major roles in defining the microstructure and properties of the final parts. Both the purity and the microstructure of sintered ceramics influence the properties of ceramic materials, including mechanical, thermal, electrical, and magnetic properties and chemical corrosion resistance. 

The properties of thin films are primarily determined by the type of chemical element or compound they comprise and by the film thickness. Their optical, electro-optical, electrical and mechanical behaviour is also determined by structure, microstructure, surface and interface morphology, chemical composition, purity and homogeneity. These are strongly influenced by the film preparation method, the chosen parameters, and by post-deposition treatments. 

In contrast to aqueous corrosion typically involving loss of electrons from the dissolving metal, liquid metal corrosion is generally considered to proceed by simple solution mechanisms. The principal variables affecting corrosion in a liquid metal system are temperature or temperature range or cycling, elements present, area-to-volume ratio, purity, flow velocity, surface condition, and microstructure. In reactor applications, the neutron flux may be an additional factor. In combination, these variables produce enough complexity so that in the present state of the art, it is rarely possible to make confident predictions about the performance of a previously untried systan. Empirical tests are usually required. 

CaP synthesis methods and their technological parameters can significantly impact stoichiometry of the synthesis product, its grade of crystallization, particle size, bioceramic phase composition, thermal stability, microstructure and mechanical properties. The important technologic parameters that impact properties of calcium phosphate synthesis product and then also of bioceramic, are temperature of synthesis, pH of synthesis environment, reagent type and concentration, as well as selection of raw materials, their purity and quality. All of the above mentioned also brings a significant impact on the tissue response of these bioceramic implants. 

Despite their heterogeneous microstructure and their complex processing, hybrid processes show a promising route to combine the high material purity and process controllability of the chemical vapour infiltration technique with the less time consuming and in most cases cheaper liquid phase infiltration techniques of LSI and LPI, However, additional research and development have to be done in order to take benefit of the whole potential of combined processes. 

Advanced Ceramics. A general term for ceramics, usually of high purity or carefully controlled composition and microstructure, used in technical applications where their mechanical, thermal, electrical and/or optical properties are important, cf. special CERAMICS, FINE CERAMICS, TECHNICAL CERAMICS, ENGINEERING CERAMICS, ELECTROCERAMICS, OPTICAL APPLICATIONS. 

Silicon Carbide. SiC. A non-oxide ceramic with a wide range of types and uses which depiend on the method of production, the resulting microstructure and purity, and the grain size. 

The uses of SiC are very varied, and depend on the method of production, the resulting microstructure and purity, and the grain size. SiC resists oxidation better than most carbides, due to the formation of a protective surface film of silica. ASTM C863 evaluates the oxidation resistance of SiC. P-SiC is a cubic crystal, stable above 2000C, produced by vapour phase reactions. a-SiC is rhombohedral or (usually) hexagonal, and is the low temperature form. There are many polytypes (q.v.)... 

The isothermal section of the Tb-Co-Ge system at 870 K over the whole concentration region was derived by Starodub (1988) (fig. 89) employing X-ray and microstructural analyses of alloys which were prepared by arc melting the proper amounts of the high-purity constituent elements. The melted buttons were then annealed in evacuated silica tubes at 870 K for 300 hours. Ten ternary compounds were foxmd to exist. 

The Role of Micorchemical and Microstructural Effects in the lASCC of High Purity Austenitic Stainless Steels Conference Sixth International Symposium on Environmental Degradation of Materials in Nuclear Power Systems-Water reactors, San Diego, Califomia,USA, 1-5 Aug. 1993... 

By far the largest, most successful applications of PGC have been to the characterization of synthetic polymer microstructure. PGCs of these compounds yield information such as monomer identity and content, purity, and presence of additives. PGC is even more powerful for solving these types of problems when coupled with spectroscopic detectors. For example, Sahota et al. (48) showed that single-step PGC coupled with mass spectrometry could be used to measure the DNA content of cultnred mammalian cells. 

TLC has been used in the study of many homopolymers polystyrene, poly(methyl methacrylate), poly(ethylene oxide), polyisoprene, poly(vinyl acetate), poly(vinyl chloride) and polybutadiene. Their molecular weight, molecular-weight distributions, microstructure (stereo-regularity, isomerism and the content of polar end groups), isotope composition and branching have been studied. For copolymer characterisation (e.g. purity and compositional inhomogeneity), random copolymers such as styrene-methacrylate, and block copolymers such as styrene-butadiene, styrene-methyl methacrylate and styrene-ethylene oxide have been separated. A good review article on polymers... 

---