Stabilization, microstructures

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. 

But we are only at the beginning for composites. To fully exploit their potential, we must gain a much deeper understanding of surface chemistry, rheology of polymer systems, thermal and oxidative stabilization, microstructure and failure analysis and so on. The development of this knowledge and its use in all parts of the world are major challenges. And certainly we have only to look at nature to see how far we have yet to go with composites. 

Not prone to coarsening Stabilize microstructure under aging... 

The final microstructure of the three composites is characterized by the formation of Ta-containing solid solutions, which grew epitaxially on the matrix grain. The misfit between the core and the shell was accommodated by corrugated grain boundaries. These features suggest a solubility of Ta in ZrC and HfC and confirm the wide range of fee TaC stability. Microstructural features indicated that ZrC is the most prone to host Ta atoms. 

As is well recognized, various macroscopic properties such as mechanical properties are controlled by microstructure, and the stability of a phase which consists of each microstructure is essentially the subject of electronic structure calculation and statistical mechanics of atomic configuration. The main subject focused in this article is configurational thermodynamics and kinetics in the atomic level, but we start with a brief review of the stability of microstructure, which also poses the configurational problem in the different hierarchy of scale. 

There are methods to manipulate the backbones of polymers in several areas that include control of microstructures such as crystallinity, precise control of molecular weight, copolymerization of additives (flame retardants), antioxidants, stabilizers, etc.), and direct attachment of pigments. A major development with all this type action has been to provide significant reduction in the variability of plastic performances, more processes can run at room temperature and atmospheric pressure, and 80% energy cost reductions. 

Establishment of the detailed microstructure of PVC has attracted considerable interest. This has been spurred by the desire to rationalize the poor thermal stability of the polymer (Chapter 1). Many reviews have appeared on the chemical microstruclure of PVC and the mechanisms of defect group formation.56 60... 

Comprehension of the interactions among microstructures composed of tethered chains is central to the understanding of many of their important properties. Their ability to impart stability against flocculation to suspensions of colloidal particles [52, 124, 125] or to induce repulsions that lead to colloidal crystallization [126] are examples of practical properties arising from interactions among tethered chains many more are conceivable but not yet realized, such as effects on adhesion, entanglement or on the assembly of new block copolymer microstructures. We will be rather brief in our treatment of interactions between tethered chains since a comprehensive review has been published recently of direct force measurements on interacting layers of tethered chains [127]. 

The yield of cross-linking depends on the microstructure of polybutadiene and purity of the polymer as well as on whether it is irradiated in air or in vacuum. The cross-link yield, G(X), has been calculated to be lowest for trans and highest for vinyl isomer [339]. The introduction of styrene into the butadiene chain leads to a greater reduction in the yield of cross-linking, than the physical blends of polybutadiene and polystyrene [340]. This is due to the intra- and probably also intermolecular energy transfer from the butadiene to the styrene constituent and to the radiation stability of the latter unit. 

In order to prevent the irrevisible adhesion of MEMS microstructures, several studies have been performed to alter the surface of MEMS, either chemically or physically. Chemical alterations have focused on the use of organosilane self-assembled monolayers (SAMs), which prevent the adsorption of ambient moisture and also reduce the inherent attractive forces between the microstructures. Although SAMs are very effective at reducing irreversible adhesion in MEMs, drawbacks include irreproducibility, excess solvent use, and thermal stability. More recent efforts have shifted towards physical alterations in order to increase the surface roughness of MEMS devices. 

The past two decades have produced a revival of interest in the synthesis of polyanhydrides for biomedical applications. These materials offer a unique combination of properties that includes hydrolytically labile backbone, hydrophobic bulk, and very flexible chemistry that can be combined with other functional groups to develop polymers with novel physical and chemical properties. This combination of properties leads to erosion kinetics that is primarily surface eroding and offers the potential to stabilize macromolecular drugs and extend release profiles from days to years. The microstructural characteristics and inhomogeneities of multi-component systems offer an additional dimension of drug release kinetics that can be exploited to tailor drug release profiles. 

As can be seen from this figure, the heat-resistance was remarkably improved by the drastic changes in the microstructure from amorphous to polycrystalline structure. Another type of SiC-based fiber, SA fiber (2), has a sintered SiC polycrystalline structure and includes very small amounts of aluminum. This fiber exhibits outstanding high temperature strength, coupled with much improved thermal conductivity and thermal stability compared with the Nicalon and Hi-Nicalon fibers. The fabrication cost of the SA fiber is also reduced to near half of that of the Hi-Nicalon Type S [ 17]. The SA fiber makes SiC/SiC composites even more attractive to the many applications [18]. In the next section, the production process, microstructure and physical properties of the SA fiber are explained in detail. 

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