P.K. Roy

Rice husk/rice husk ash as an alternative source of silica in ceramics: A review

ABSTRACT Use of waste or by-products from different industries and the agricultural sector has received increasing attention in the scientific, technology, ecological, economic and social spheres in recent years. Rice husk (RH) is a by-product of rice milling and rice husk ash (RHA) is generated by combustion in a separate boiler. Both RH and RHA are abundantly accessible in rice growing countries such as China, India, Brazil, the USA, and Southeast Asia. RH has therefore been recycled by burning it for energy production. This generates RHA, which contains a huge quantity (85–95%) of amorphous silica. Over the past two decades, RHA has been used extensively in numerous fields for manufacturing of different silicates, zeolites, catalysts, nanocomposite, cement, lightweight construction materials, insulators, and adsorbents. This paper presents a comprehensive overview on the processing of nano-silica from RH/RHA. It tries at the same time, to present a critical review of the application of RHA as an ingredient for the production of various ceramic materials, e.g. refractory, glass, whiteware, oxide and non-oxide ceramics, silica aerogel and SiO2/C composites. In summary, amorphous silica derived from RHA or RH provides a potential alternative to conventional silica sources (e.g. quartz) for the manufacture of value-added ceramics for practical applications.

Study of physical and dielectric properties of bio-waste derived synthetic wollastonite

ABSTRACT The aim of this study is to fabricate synthetic wollastonite from chicken eggshells (CES) and rice husk ash (RHA) through an economical solid-state route. Wollastonite was formulated with a stoichiometric amount of calcined eggshells (~99% CaO) and heat-treated RHA (~93% SiO2) as ingredients and calcined at 1000, 1100, 1150 and 1200°C for 120 min. The XRD spectrum revealed single-phase para-wollastonite (monoclinic, P21/a) after annealing at 1100°C and 1200°C with calcined powder contents comprising mainly a phase of pseudo-wollastonite (anorthic, C-1). For dielectric measurement, only the para- and pseudo-wollastonite pressed powder was sintered at 1100 and 1200°C for 240 min. The obtained results showed a stable, low dielectric constant (ε׳) of about 4.5 to 6, losses (tanδ) of about 0.0026 to 0.00361 and resistivity of around 6–9 × 108 (Ώ-cm) at 100 kHz. These are highly promising characteristics which suggest that waste-derived synthetic wollastonite may be useable as an ingredient in electrical porcelain applications.

Comparison between conventional, vacuum and microwave sintering of Cu-Cr-4 wt.% SiC nanocomposites

Attempts have been made to synthesize Cu99Cr1, Cu99Cr1-4 wt.% SiC nanocomposites for thermo-electric applications. The blend compositions were ball-milled for 50 h in a stainless steel grinding media. The compact specimens were subjected to vacuum sintering (900°C and 1000°C for 1h), conventional sintering (900°C and 1000°C for 1h) and microwave sintering (800°C, 900°C and 1000°C) duration of 30 min using a furnace of 2.45 GHz frequency and 900 W power. The micro-structural characterization was carried out by X-ray diffraction and scanning electron microscopy. The mechanical properties like Vickers hardness and electrical conductivity of the sintered specimens were also investigated. In the present investigation, the best combination of mechanical properties and electrical conductivity were obtained for the microwave sintered specimens. This is possibly due to the enhanced densification achieved through microwave sintering technique. Possible sintering characteristics and strengthening mechanisms were analyzed.