Issue No. 2, August

Abstract

The nature as well as composition of the Egyptian clay deposits exposed all over the country are summarized. The influence of composition on their ceramic properties in terms of plasticity as well as drying and firing behaviour is discussed. According to their clay mineral composition, they are classified into kaolinite-, smectite- and illite- rich clays. The kaolinite rich clays are mainly exposed in Aswan as well as Gulf of Suez provinces and generally characterized by a slow rate of slaking in water, low plasticity, high Al₂O₃ as well as a high and long vitrification range (1100-1500 °C). Hence, they are used in the production of shaped and unshaped refractories as well as vitreous china and white Portland cement. However, they are not suitable for the production of white wares due to their high colouring iron and titanium oxides content. On the other hand, smectiterich clays cover most of the Eastern as well as Western Deserts and have low Al₂O₃ content with variable amounts of quartz, calcite, gypsum and iron minerals as well as alkali water-soluble salts. They show high plasticity, drying and firing shrinkage as well as a low and short vitrification range (850-1000 °C). Therefore, they are applied for the production of ordinary Portland cement and building bricks. Also, they are recommended for the manufacture of light-weight clay aggregate due to their bloating on firing up to 1250 °C. Meanwhile, illite-rich clays are encountered in El-Bahariya Oasis, Western Desert and contain predominant iron-rich illite clay minerals, i.e. glauconite in addition to variable amounts of kaolinite, smectite, quartz and goethite minerals. They have moderate plasticity, vitrification range (950-1150 °C) as well as drying and firing shrinkage. Hence, they are recommended for manufacturing building bricks and other heavy-clay products, after blending their varieties.

Abstract

Slag was progressively substituted upto 15 (w/w) % to feldspar in a normal porcelain composition and compacts prepared by the usual ceramic processing were sintered at 1100-1300 °C. The effect of thermal cycling on flexural strength of the vitrified samples was studied and the behaviour was correlated with phase and microstructural features. It was found that slag incorporation increased residual strength in thermally cycled samples compared to normal porcelain. The microstructural features of thermally cycled slag-containing porcelain showed limited quartz grain cracking compared to normal porcelain composition, which results in better strength. Formation of anorthite, which has low thermal expansion, in slag-bodies, is also significant in the development of better thermal stability.

Abstract

Slag penetration into a magnesia refractory castable was investigated by the crucible test method. A synthetic calcium aluminate slag system has been used to corrode a commercial magnesia mix refractory for 1, 2, 3, 4, 5 and 6 h at 1450 °C and 1600 °C. It has been shown that the penetration rate was controlled by a diffusion mechanism at 1450 °C, capillaries being the main channels of initial slag penetration into the refractory. In the penetration process, calcium silicate was formed on the surfaces of MgO grains, and around them by reaction between the grain boundary and mayenite, as a main phase of slag with a low melting point. Dissolution of the refractory components in the slag supported the penetration process at 1600 °C. In this case, dissolution of the refractory components in the slag not only makes new open channels, but also changes the local slag composition, resulting in a decrease of viscosity and an increase of surface tension of the slag.

Abstract

One of the major problems facing Blast Furnaces is the occurrence of cracks in taphole mud, as the underlying causes are not easily identifiable. The absence of this knowledge makes it difficult the use of conventional techniques for predictability and mitigation. This paper will address the application of Probabilistic Neural Network using the Matlab software as a means to detect and control such cracks. The most relevant BF operational variables were picked through the statistic tool “Principal Component Analysis - PCA.” Based upon the selection of these variables a probabilistic neural network was built. A set of BF operational data, consisting of 30 controlling variables, was divided into 2 groups, one of which for network training, and the other one to validate the neural network. The neural network got 98% of the cases right. The results show the effectiveness of this tool for crack prediction in relation to clay intrinsic properties and as a result of the fluctuation in operational variables.

Abstract

Rice husk is an agricultural waste, generated by the rice producing countries, mainly being utilized as cattle feed and cheap source of fuel for the boilers of rice mills. Ash generated after burning is regarded as a waste which contains >80% silica and some free carbon. Acid resistance characteristics of silica enable the possibility of the use of rice husk ash for the development of acid resistant ceramic products. Acid resistant porous ceramic pots are useful for electroplating industries. The present study was planned to develop slip cast acid resistant porous ceramic pots using a mix of rice husk ash as the main raw material and clay. Three different compositions were tried with rice husk ash content in the range of 50-70 wt%. Sintering was carried out in the temperature range of 1150-1200 °C. Final products were characterized by various physical, mechanical, phase content and acid resistant properties.

Abstract

The ceramic cutting tool requirements for metal machining are reviewed, taking into account the trends in industry towards dry high-speed cutting and the need for tools with complex geometry. The emphasis will be on bulk materials rather than on coatings and most attention will be devoted to machining of iron-based alloys (steels). In the development of new tool materials, special attention should be given to the chemical matching of tool and workpiece material at elevated temperatures. The chemical compatibility of the tool-workpiece combination can be investigated by means of static interaction couples at elevated temperatures, which have been exposed for times long enough to be able to characterise the interaction layer. Complementary to the experimental investigation, the chemical compatibility of tool and workpiece materials can be predicted from thermodynamic equilibrium solubility calculations of tool materials in a selected workpiece material. Taking into account the mechanical properties needed, new ZrO₂-based composites were defined based on the thermodynamically estimated chemical stability. The selection, development and proof testing of the new ZrO₂-based composites is highlighted and their wear behaviour and performance in high speed dry turning of construction steel is compared with that of state-of-the-art cutting tool materials.