Search

Lignite combustion class-C (highly-calcareous) fly ash and bottom ash were sintered employing two-step sintering (TSS) and compared to conventionally sintered ones. TSS sintering is a new promising approach mainly used to obtain effectively densified ceramics. This alternative process is generally characterized by the absence of the final stage of grain growth occurring upon conventional sintering and by the development of nanograin microstructure. The ceramic microstructures successfully obtained in the present research were characterized by means of X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-ray analysis as well as by density measurements. The effectiveness of the solidification process was thoroughly studied, and the specific microstructural features attained are compared between each other and evaluated in relation to the sintering method applied. The results show that the valorization of lignite calcareous ashes into ceramic materials is feasible through different sintering techniques.

The aim of the current research is the beneficial utilization of steel mill scale (MS) as admixture in clayey raw materials at high percentages up to 100% for manufacturing innovative engineering ceramics by powder metallurgy processes. Various MS/clay mixtures were cold compacted at 20 tn load using an automated hydraulic press to form series of 5 cm diam. disc-shaped specimens. The specimens so-produced were sintered in a programmable electric furnace for final consolidation by controlled heating up to 950 °C for 2h. Weight and dimensions changes upon sintering, as well as physico-mechanical properties of sintered specimens were determined in relation to the % MS content. Microstructural examination was conducted by SEM-EDAX. From the experimental results, the substitution of MS for clays is feasible and a tendency for mechanical properties enhancement is recorded with increasing the industrial residue percentage, thus rendering MS a suitable and interesting starting material for the elaboration of engineering ceramics. This endeavor can also contribute to the sustainable management of this industrial residue towards circular economy and environmental protection. [ABSTRACT FROM AUTHOR]

Nowadays, several thermal treatment procedures and technologies are being used for in ceramic processing. The application of microwave irradiation in ceramic manufacturing, for the consolidation of the final ceramic structure, has many energy and economical avails, while at the same time it is environmentally benign. In this work, the microwave irradiation potential usage in energyefficient ceramic manufacturing is explored via a comprehensive literature review. Specifically, the advantages/disadvantages of the microwave irradiation compared to conventional heating technologies is discussed. Three different classes of ceramic materials, with industrial significance, are considered: a) bulk ceramics, b) electroceramics and c) bioceramics. Furthermore, future applications which may attract commercial concernment are also pointed out. [ABSTRACT FROM AUTHOR]

The amounts of ashes from circulating fluidized bed (CFB)-combustion steadily increase with the increasing rate of implementation of this environmentally-friendlier technology for firing solid fuels in power generation units. Therefore, beneficial uses of these powdery by-products, which possess particular characteristics, should be identified instead of landfill them at significant environmental and economic impact. Their valorization in the manufacturing of value-added ceramics is a challenging research area. In the present study, CFB-coal combustion fly ashes, mainly bearing Si-Al phases, were utilized as 100% raw materials for the synthesis of ceramics by powder metallurgy (PM) techniques. Test specimens were fabricated by powder cold pressing followed by sintering at 900, 1000 or 1100 °C. The produced materials were characterized by means of XRD and SEM-EDAX. Shrinkage upon sintering, apparent density, water absorption capability and Vickers microhardness were determined. The experimental results show that the recycling of CFB-fly ashes towards PM ceramics development is feasible. In fact, integral light-weight materials are obtained, exhibiting successfully-densified ceramic microstructures where quartz phases prevail. The physico-mechanical properties are proved to be influenced by the starting ash composition and the sintering temperature. The so-produced ceramics possess the potential to be tailored appropriately to meet requirements for specific applications of possible commercial interest. [ABSTRACT FROM AUTHOR]