Utilization of Rice Husk, an Abundant and Inexpensive Biomass in Porous Ceramic Membrane Preparation: A Crucial Role of Firing Temperature

The influence of firing temperature on characteristics and bacterial filtration of the porous ceramic membrane prepared from rice husk (20 wt%) and kaolin has been investigated. As firing temperatures increased from 900 to 1100°C, the compressive strength of membrane increased from 555.3 N/cm2 to 2992.3 N/cm2, whereas the porosity decreased from 49.4 to 30.2% due to structural condensation and mullite formation. The condensation caused pore contraction that finally improved bacterial removal efficiency from ~90% to 99%. The results suggested that the porous ceramic membrane prepared from rice husk and kaolin should be fired at ~1050°C to attain both strength and filtration efficiency.

Factors Influencing Mullite Formation in Refractory Grog

The mineral mullite has many outstanding refractory properties. The content of aluminum oxide in the raw material is the basic factor influencing the content of mullite in the final product. Depending on Al2O3 content, silica-alumina materials can be divided into fireclay and high-alumina with the Al2O3 content of 45 % and more. The study describes the influence of raw material, the influence of homogenization of raw material and influence of firing temperature on the mullite formation in fireclay refractory material. Three kinds of refractory clay with different chemical composition were used as raw material for fireclay grog production. Three kinds of homogenization and three different temperatures were studied as factors influencing mullite formation. Powder X-ray diffraction was used to determine mullite content in material. Quantitative phase analysis was conducted by the Rietveld method. Mullite crystals morphology was observed by scanning electron microscopy.

Microwave vs conventional porcelain firing: Greenware to biscuit crystallochemical transformations

This work reports and compares the structural crystallochemical transformations occurring during the microwave and conventional porcelain manufacture. Batches of greenware (just dried) porcelain pieces are microwave and electrically fired at increasing temperatures, from 420 °C up to 1100 °C. Crystallochemical transformations are identified by XRD analysis, and compared the results from samples microwave and conventionally fired. Microwave fired samples show the full and rapid collapse of kaolinite structure for firing temperatures just above 500 °C, whereas the collapse of kaolinite structure of the electrically fired samples is progressive, from about 500 °C up to 950 °C. Muscovite structure totally collapses at about 950 °C for microwave fired greenware samples, whereas muscovite structure total collapse only occurs at about 1050 °C for electrically fired greenware samples. Microwave and electric firing lead to appreciable differences in the sanidine – orthoclase – microcline structural transformations. Mullite formation could be identified in the microwave fired samples at temperatures 50 °C lower than in the electrically fired ones, especially for the conventional firing temperatures above 1050 °C, the same temperature reported in the literature.

Effect of TiO2 on mullite formation in mixture of Nigeria sourced kaolinite and calcined alumina

In this study, the effect of TiO2 when added to a mixture of Nigerian sourced of kaolin and calcined alumina powder (50:50) was investigated. The influence of Ti4+ ion on the physico-mechanical property (apparent porosity, bulk density and modulus of rupture), phase and microstructural evolution was studied at sintering temperature of 1600?C when mullitisation has been maximized based on previous reports. The sintered samples showed considerably high porosity of about 16 %, a slight reduction of about 5 % in porosity was observed on TiO2 addition. There was no appreciable change in the bulk density due to TiO2 doping, but the modulus of rupture (MOR) reduced appreciably from 43 MPa to 36 MPa on TiO2 doping. As shown by the XRD, mullite was seen as the major phase with negligible cristobalite phase for the undoped sample. The TiO2 doped sample displayed mullite as major and corundum as minor phases. There appeared more mullite phases in the doped sample than the undoped sample indicating a higher percentage of mullite formation. The microstructural study shows the presence of acicular mullite with round edges and good aspect ratio. The presence of inter-granular and intra-granular pores in TiO2 doped samples might have contributed to the reduction in strength observed at 1600?C.

Cement free castable. Part 5. CFC on alumina hydraulic binder

Cement free castables (CFC) based on alumina hydraulic binders by the hardening mechanism are similar to low-cement castables (LCC) and ultra-low-cement castables (ULCC). They are characterized by significant strengthening in the heat treatment temperature range of 200‒300 °C and sharp softening in the 600‒1000 °C range. By introducing silica sols or microsilica into their composition, it is possible not only to reduce or eliminate the softening effect, but also to increase their strength after firing due to the process of mullite formation. Compared to LCC, CFC based on alumina binders are characterized by improved thermomechanical properties. A comparative assessment of CFC based on hydraulic binders with other types of refractory concretes is given.

Researches in the field of composite HCBS and of the refractory materials on their base in Al2O3‒SiO2‒SiC system. Part 4

The effect of long heat treatment (single and double firing in a tunnel kiln) of samples based on a HBCS in Al2O3‒ SiO2‒SiC-system on their indicators was studied. Samples containing 15 % SiC and 1 and 2 % Si are characterized by a significant increase (up to 9 %) an increase in porosity and a decrease in strength compared to the original samples (without SiC) after long heat treatment (120 hours in the range of 1300‒1400 oC). A significant increase in the volume of the samples is due not only to the oxidation of SiC or Si, but also to additional mullite formation. It is assumed that sequentially following the process of oxidation of SiC at a certain stage of heat treatment, the process of mullitization proceeds due to the interaction of the newly formed SiO2 in the form of cristobalite with Al2O3 bauxite. Ill. 6. Ref. 19.