Review on the physicochemical treatments of rice husk for production of advanced materials

The preparation of non-toxic and biocompatible fibres or whiskers is one of the most urgent tasks today, because most of the fibrous materials which have been used (including asbestos which has been used for many years) are thought to be biohazardous. Whiskers of hydroxyapatite (Ca10(PO4)6(OH)2∶HAp), which is expected to be one of the best biocompatible materials, have been successfully synthesized by hydrothermal treatments of beta-tricalcium phosphate (beta-Ca3(PO4)2: beta-TCP) with citric acid. These whiskers were single crystals, elongated along the c-axis, with a length of 20–30 μm and a width of 0.1–1 μm. They were slightly calcium deficient (Ca/P molar ratio = 1.63) and they contained a trace of CO
 3
 2−
 in their structure.

Hydrothermal synthesis of biocompatible whiskers

A review of inorganic fibers other than asbestos, glass, and carbon fibers and optical and hollow fibers. Special emphasis is placed on high-performance fibers. The manufacture, structure, properties, and uses of the selected fibers are discussed.

Inorganic Fibers—A Literature Review

Silicon carbide (SiC) nanowires were synthesized at 900°C by the laser ablation technique. The growth morphology, microstructure, and defects in SiC nanowires were characterized by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The Raman scattering study indicated that the Raman peaks corresponding to the TO and LO phonon modes of the SiC nanowires had larger red shifts compared to those of bulk SiC material. The red shift, broadening peak, and the asymmetry of the Raman peak could be explained by the size confinement effect in the radial and growth directions. The growth mechanism of SiC nano-wires was discussed based on the vapor–liquid–solid reaction.

Laser Ablation Synthesis and Optical Characterization of Silicon Carbide Nanowires

Biologically mineralized tissues are well recognized for their unusual crystal morphologies and hierarchically organized composite structures. The soluble acidic macromolecules associated with biominerals are thought to play an important role in modulating the mineral morphology. Our in vitro studies, which use acidic polypeptide additives to modify crystal growth of calcium-based minerals, have demonstrated a crystallization mechanism that proceeds via a liquid-phase mineral precursor. Various features of the crystals produced via this mechanism, such as "extruded" mineral fibers and mineralized collagen composites, have led us to propose the hypothesis that an amorphous, liquid-phase precursor could play a fundamental role in the morphogenesis of calcium-based biominerals. Although in vivo evidence of this process remains to be determined, we demonstrate crystallization features that mimic bone and dental enamel and suggest that this process could be relevant to biomineralization in both vertebrates and invertebrates.

A New Paradigm for Biomineral Formation: Mineralization via an Amorphous Liquid-Phase Precursor

Beta-silicon carbide whiskers are being grown by a vapour-liquid-solid (VLS) process which produces a very high purity, high strength single crystal fibre about 6μm in diameter and 5–100 mm long. Details of the growth process are given along with a general explanantion of the effects of the major growth parameters on whisker growth morphology.

S. R. Skaggs

Papers

Growth of beta-silicon carbide whiskers by the VLS process