Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
SELECTED APPLICATION AREAS. 95 material with the intergranular phase, Re2Fe14B material with a slightly smaller grain size and no intergranular phase has magnetic performance that significantly exceeds the Stoner-Wolfarth limits, with remanences up to 10 kG and energy products in excess of 19 MGOe. The enhancement behavior has been attributed to the intergrain ferromagnetic exchange interaction (Keem et al., 1988). Remanence enhancement is limited to less than full polarization of the adjacent grains because of an accommodation between the intergrain exchange and intergrain anisotropy of the single-domain grains. It has been shown (Keem et al., 1988) that the presence of any intergranular phase damps this intergrain interaction and essentially eliminates the remanence enhancement. POLYMER-SILICA MICROCOMPOSITES Liquid crystalline solutions of rigid-rod macromolecules such as poly-p-phenylenebenzobisthiazole (PBZT) can be solution-processed into high-performance fibers and films. After coagulation into water, the microstructure consists of a highly oriented three-dimensional interconnected network of 20-nm-diameter microfibrils (Cohen and Thomas, 1988) (Figure 30). Figure 30 PBZT-sol-gel glass interpenetrating networks (Cohen and Thomas, 1988). This high-strength and high-stiffness polymer framework has recently been exploited for novel polymer-glass composites. The process involves exchange of the water phase in the wet coagulated PBZT film for an alkoxide solution, which is then hydrolyzed to form a PBZT-sol-gel composite that can then be further densified to yield a PBZT-silica composite in which both phases are continuous. The liquid-crystal solution can be processed to yield a spectrum of variously oriented PBZT networks that can then be infiltrated with a variety of materials for specific applications. A particular target is the improvement of compressive strength of neat PBZT fibers. The low overall
