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

Rice husk (RH) has now become a source for a number of silicon compounds, including silicon carbide, silica, silicon nitride, silicon tetrachloride, zeolite, and pure silicon. The applications of such materials derived from rice husks are very comprehensive. The methods of synthesizing these silicon-based materials from RHs and their applications are reviewed in this paper.

Silicon-Based Materials from Rice Husks and Their Applications

Lignocellulosics represent the organic matter produced by trees. Biopolymers such as cellulose, hemicellulose and lignin are the major macromolecular constituents of ligneous cell walls which are distinguished by a hierarchical fibrilar composite micro structure. Fundamental aspects of anatomy of wood and molecular structure of wood cell wall affecting the bioorganic–inorganic conversion process are reviewed. Basic approaches to convert the native biopolymeric materials into non-oxide as well as oxide ceramic products include: (i) pyrolytic decomposition resulting in a porous carbon replica (template) which may subsequently be reacted to form carbide phases or may be infiltrated with non-reacting sols or salts which can further be processed to yield oxide reaction products; (ii) infiltration of chemically preprocessed native lignocellulosic products with gaseous or liquid organometallic and metalorganic precursors and subsequent oxidation to remove the free carbon phase. Conversion of native (wood tissue) lignocellulosics into ceramics with a microstructure pseudomorphous to the bioorganic template anatomy offers a great potential for designing novel ceramics with anisotropic cellular morphologies. These might be of interest for applications as high temperature resistant exhaust gas filters and catalyst carriers in energy, environmental and automotive industries, bioinert and corrosion resistant immobilization supports for living cells, microbes, or enzymes in biotechnology and medicine.

Biomorphous ceramics from lignocellulosics

Models describing the transient behavior of phase-change energy storage (PCES) units are presented. Simulation techniques are used in conjunction with these models to determine the performance of solar heating systems utilizing PCES. Both air-based and liquid-based systems are investigated. The effects of storage capacity, storage unit heat transfer characteristics, collector area and location on the system performance are investigated for systems utilizing sodium sulfate decahydrate and paraffin wax as storage media. Optimum ranges of storage sizes are recommended on the basis of systems' thermal performance. Comparison is made between systems utilizing PCES and those using sensible heat storage, viz. rock beds in air-based systems and water tanks in liquid-based systems. The variation of the solar supplied fraction of load with storage size and collector area is given for systems utilizing both types of storage. The effects of location and collector energy loss coefficient on the relative performance of PCES and sensible heat storage are also investigated.

Effects of phase-change energy storage on the performance of air-based and liquid-based solar heating systems

Performance enhancement of a Building-Integrated Concentrating Photovoltaic system using phase change material

Recently the synthesis of ultrafine powders has drawn considerable attention because these powders can have physical and chemical properties superior to those of bulk specimens. In particular, emphasis is on the preparation of ultrafine ceramic powders for their applications in the development of sintered products having higher density and lower sintering temperature. One such industrially important ceramic material is SiC. In many cases ultrafine SiC has been prepared by thermal plasma processes [1]. However, these processes require one or more reactive/corrosive gases. This letter describes a new method to overcome such problems. For this purpose thermally pretreated rice hull was used as the solid precursor. Rice hull, an agricultural waste product, was first used by Cutler [2] as a starting material for the production of silicon carbide. Since the rice hull route promises to be most economical, much attention has recently been paid to it [3-6]. Rice hull consists of silica in hydrated amorphous form, and cellulose which yields carbon when thermally decomposed. The relative abundance of silica with very high surface area in close proximity to active carbon in rice hull makes it amenable for SiC formation during the pyrolysis process. The possible reaction was given by Lee and Cutler [7] as

E. Pfender

Papers

Thermal plasma synthesis of SiC from rice hull (husk)

Heat transfer—a review of 1983 literature

Heat transfer — A review of 1973 literature

Heat transfer—a review of 1981 literature

Heat transfer—a review of 1984 literature