Refractory materials must be disposed of or recycled when removed from service. Off-specification or reject material has been reused by the refractory industry for a number of years, with small percentages of these materials added as a part of refractory formulations. Historically, limited reuse of spent refractory materials in other applications has occurred. Environmental legislation, stewardship programs, and other forces have encouraged some businesses to recycle spent refractories. Reuse of spent refractory material varies considerably among different industries and with the location of the industrial user. Efforts to recycle, the driving forces for recycling, and issues and steps to be taken into account when initiating a recycling program will be discussed.
Municipal seawage sludge (MSS) from municipal wastewater treatments plants (WWTP) of different size were thermally transformed into powders which were pressed into specimens submitted to thermodilatometric tests in order to evaluate their shrinkage and then their softening temperatures on heating up to 1100°C. In addition the shrinkage behaviour of a traditional clay normally used for the production of bricks was studied. Powders from calcined MSS were also attrition milled for 1 or 3 h and the behaviour of the relative samples was compared to that of the as calcined products. Specimens obtained by the various treatments were also sintered in an oven at different temperatures for 1h, their density and their composition were determined and finally they were aged in an acidic (HCl) water solution to evaluate the eventual elution of some components.
The fine ground waste from the manufacture of clay bricks fired at 800 - 1000 °C, was used as an additive (from 10 % to 70 wt%) to the basic body of ceramic wall tiles from Egyptian raw materials. The waste which is produced in small factories in most Egyptian governorates as defective bricks, constitutes a major environmental problem. The Samples were fired at 1100 °C, 1125 °C, and 1150 °C for 5, 10, and 15 min soaking time. Firing shrinkage and vitrification parameters were determined and compared to both Egyptian and ISO standards. Analysis of variance (ANOVA) carried on crushing strength data, showed that the percent replacement was the most influential factor rather than temperature or soaking time. The recommended sample consisting of 20 % ground waste was shaped in tile form. The tiles were tested in accordance to both ISO and Egyptian standards. Results of water absorption, crushing strength, MOR, thermal chock resistance, chemicals and staining resistance, and hardness conformed to standards. The 20 % fired clay waste addition is recommended for both its economical and environmental benefits.
The present study deals with energy savings in brick manufacture. Laboratory driven experiments with additions of Greek lignite (low rank coal) and Spanish claystone have been performed. In particular, co-firing of clay raw material with organic additives is performed in order to minimise the fuel consumption while maintaining the good quality of the brick. Using XRD, ESEM and DTA techniques, mineralogical compositions and mineral transformations were observed both in raw material and in clay-lignite mixtures. For the analyses of hydrated phases, a low-cost and useful modification of a traditional diffractometer has been demonstrated. Fuel saving in brick firing was also revealed with the addition of lignite to claystone samples. Due to the natural variability of both clays and lignites, the results of this study do not necessarily imply that coal-clay mixtures may always have similar performance.
Different methods are described for preparing borides and boron carbide by powder technology. The boron carbide was prepared from amorphous boron, graphite, and petroleum coke, and the borides from amorphous boron and atomized aluminium. The compounds are characterized and compared with their commercial counterparts. In the second part of the work, cheaper materials are used: boric acid and boric oxide instead of boron, petroleum coke and mesophse instead of graphite. Another alternative studied in this work is the use of thermal shock in the sintering, a method that is not usually adopted in powder technology.
Porous tubular ceramic membranes from tunisian clay have been prepared. After a pre-calcination in air at 750°C for two hours, a grinding, and a sieving to 300 µm, natural clays noted SI1 and SI2 were mixed with organic additives in view to elaborate a ceramic paste which can be extruded to form porous tubular configuration with uniform porous structures. The mean pore diameter and the porous volume, measured by mercury porosimetry, are equal to 9.2 µm and 39 % for SI1 and 5.9 µm and 48 % for SI2 when they were repectively fired at 1040 °C and 1090°C. These supports could be used for the coatings of microfiltration and ultrafiltration membranes.
The effect of different carbon sources and aluminum powder on porosity, size change and flexural strength of light weight alumina was examined. The results show that carbon sources not only increase the porosity content of sintered samples but also raise the shrinkage. By adding Al powder, the sintering shrinkage reduces and in the presence of carbon sources samples expand. With the same porosity content, samples containing Al powder present lower strength due to pore enlargement as the result of expansion.