Issue No. 3, December

Abstract

The effect of progressive replacement of limestone by marble waste on the thermo-mechanical properties of a traditional earthenware wall tile composition has been studied. It was observed that the body mixes containing more than 7.5 wt % of marble waste showed a marginal decrease in dry strength and bulk density while particle size distribution were almost identical.The body mixes containing up to 7.5 wt % of marble waste showed improvement in fired properties in the biscuit firing temperature range of 1000 o to 1100 oC.A reverse trend was observed beyond this temperature range due to an increased proportion of high expansion residual quartz.The body mixes containing up to 7.5 wt % of marble waste showed significant reduction in percent thermal expansion at 600 oC in the sample fired at 1100 oC. As a result, the body mixes become more thermal shock resistant compared to the reference body.The study concluded that marble waste can be added in small amounts (7.5 % or less) in earthenware wall tile improving their thermo-mechanical properties.

Abstract

A wet grinding study of ceramic glazes by varying material to pebble ratio established that the increased material to pebble ratio of 1:4 has not only improved the efficiency of grinding leading to increased reduction in particle size but also resulted in reduction of maturing temperature of commercial opaque and transparent raw glazes and bone china fritted glaze by ~ 150 °C due to prolonged grinding to the fineness of ~ 90.0 to 97.0% particles finer than 2 μm and d₁₀₀ value of 3 to 4 μm. However, the glazed surfaces were found not free from defects like crawling, craters etc. A systematic grinding study of the said opaque glaze followed by evaluation of glaze properties such as gloss, smoothness, opacity, maturity etc. has led to the conclusion that the opaque glaze mix containing particles in the range of 72.7 to 85.5% below 10 μm and d₁₀₀ of 25 to 20 μm not only matured at 1160 °C, which is ~ 40 °C lower in comparison to the standard glaze maturing at 1200 °C but also the fired glazed specimens showed improved gloss (90-91 GU), smoothness, opacity etc. without any surface faults. Further, the glaze maturing range has also been enhanced by ~ 40 °C from 1160° to 1200 °C.

Abstract

A clay mixture, a residue in the gypsum extraction process in the Araripina region – PE / Brazil, was characterised by X-ray diffraction (XRD), X-ray fluorescence (XRF), thermo gravimetric analysis (TGA), infrared spectrometry (IR),Atterberg indices and particle size distribution for use in red ceramic products. Extruded clay specimens were tested for mechanical properties, drying shrinkage, water absorption, specific apparent mass and their changes on drying and firing.The results suggest that the studied clay mixture possess properties, which may encourage deeper technological experiments aimed at assessing their suitability to red wall brick and tile production.

Abstract

Two Egyptian carbonaceous fireclay samples from west central Sinai (Roof and Floor samples) were investigated for their chemical and mineralogical composition as well as microstructure and ceramic properties.These investigation were carried out to assess their suitability for production of insulating shaped products.Wet chemical analysis, XRD, DTA,TG and transmission light microscope methods were applied for revealing composition and microstructure of the raw clays. On the other side, microstructure and densification parameters of four shaped clay batches fired up to 1100-1300 oC were investigated by using reflected light microscope as well as Archimedes water-saturation methods and by determining linear changes and crushing strength of the fired bodies. It is concluded that both of the roof (RCC) and floor (FCC) clay samples can be considered as carbonaceous siliceous kaolinitic clays.The FCC sample contains relatively higher carbonaceous material and Al₂O₃/SiO₂ ratio than the former one. The batch containing 70% (RCC):30 (FCC) can be utilized in processing insulating shaped siliceous fireclay products after firing up to 1300 oC.The fired briquettes are mainly composed of quartz, cristobalite,mullite and glassy phase.They have > 45.0% apparent porosity, 1.50g/cm3 bulk density and 160 kg/cm2 crushing strength. Such lightweight siliceous fireclay bricks can be used as face and / or back refractory lining for insulating industrial furnaces up to 1300 oC.

Abstract

Five batches of low cement zircon- magnesia concretes were prepared using dead burned magnesite aggregate, fine zircon sand and high alumina refractory cement.The concretes were shaped and fired at 1500°C. Densification parameters were determined through bulk density (BD) and apparent porosity (AP). High temperature phases were examined by XRD. A correlation between the densification properties and the phases formed was made through SEM examination of the microstructure.The cold crushing strength, thermal shock resistance (TSR) and refractoriness under load (RUL) of the fired concretes were evaluated.The results showed that increasing zircon is beneficial to densification up to 20% after which a decrease in sintering occurred. Zirconia evolved mainly in tetragonal form beside spinel, periclase and CaO, MgO- silicate glassy phases. The concretes showed high cold crushing strength and good resistance to both thermal shock (Dt=1000°C) and refractoriness under load (0.2Mpa).

Abstract

A carbon free precast block was prepared by using high-alumina fused corundum as aggregate, and fused magnesia and ultra-fine Al₂O₃ and SiO₂ powders as matrix materials. A small linear expansion for the precast block was achieved through spinel formation from the reaction of MgO with Al₂O₃.The precast block showed a lower apparent porosity, higher hot modulus of rupture and better slag corrosion resistance compared to the traditional Al₂O₃-MgO-C brick. Moreover, the practical application of the precast block to the ladle lining proved it to possess a better thermal insulation which could effectively prevent the temperature drop of molten steel during the refining process. It can be assumed that the carbon free precast block could possibly be accepted as a new type of ladle lining material for the production of low-carbon and ultra-low-carbon steel.

Abstract

The sintering behavior of nano sized and submicron sized alumina was investigated.Two methods i.e. uniaxial pressing and slip casting were used to shape the samples.The effect of Nd₂O₃ and MgO addition on sintering was also investigated. Samples were sintered at 1250, 1350 and 1450oC for 2 h.Taguchi statistical method was used to design the experiments.The results revealed that the nano sized powder did not show a proper sintering behavior and therefore the density of these samples was less than the samples made of the submicron powder. It is believed that most probably the presence of agglomerates in the nano sized powder is the main reason for this behavior. Due to this effect, the density of the samples made of nano sized powder increased slightly when they were formed through pressing, since the agglomerates crashed slightly during pressing. Also it was demonstrated that Nd₂O₃ had a negative effect and MgO had a positive effect on densification.Temperature, of course, improved densification.

Abstract

The effect of water treatment of Egyptian fumed silica powder at room temperature and 100 oC on its chemical and phase composition as well as morphology and surface area has been investigated. Selected samples that showed maxima of silica content and surface area were dry-pressed and fired up to 800, 1200 and 1400 oC along with the original untreated sample.The fired samples were investigated for their densification parameters, phase composition, microstructure and pore-size distribution in order to assess their suitability for processing ceramic filters. Results show that the original fumed silica powder may be recommended for processing ceramic filters,The amount and distribution of porosity of the original fumed silica powder fired up to 800 oC may suggest a possible use as a ceramic filter, whereas the ultra fine and pure fumed silica treated by boiling in water for 4 h may be recommended for processing dense, pure and refractory cristobalite and/or mullite bodies.