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Two different batches of zero-cement castables composed of 85 wt. % fused MgO-spinel aggregate with 10 wt.% hydratable alumina and 5 wt.% of either kaolin or alumina/silica fine powder mixture were prepared and compared with other two conventional castables of the same composition where hydratable alumina is replaced by high alumina cement. The densification parameters, cold crushing strength as well as refractory properties (thermal shock and creep resistance) were tested. Zero-cement castables, specially those containing kaolin showed a compromise between considerable mechanical properties and good refractory behaviour as compared with the corresponding conventional ones.This behaviour is strongly related to the absence of lime that causes many deleterious effects on the properties of conventional castables.
Elimination of the physically bonded water and dehydroxylation take place simultaneously in the green electroceramic body during its firing for a diameter of the sample d >= 5 cm and heating rate >= 2 °C/min.The larger the sample diameter the wider the overlap of these processes and the higher the temperature of their completion.
Zirconia-mullite composites containing 0-6 mol% yttria were prepared by the reaction sintering process.The main raw materials were Indian coastal sillimanite sand and zirconia and alumina.After milling, samples were isostatically pressed, sintered at 1500-1600°C for 2 h and characterized in terms of phase coexistance, martensitic start (Ms) temperature, thermal expansion coefficient, thermal shock resistance and microstructure.The addition of yttria improves the thermo-mechanical, thermo-physical and physical properties of the resulting composites. The thermal expansion coefficient and martensitic transformation temperature decrease with yttria content. The relative densities of yttria bearing samples are higher.
An experimental and a theoretical study of the heat and mass transfer mechanism, and of the mechanical behaviour which occur during convective drying of clay material are reported.The model is valid only for biphasic media and it describes the critical first stage of the drying process where the material is exposed to shrinkage which may lead to large deformations and cracks. Some essential physico-chemical properties of three variety of clay are determined by experimental investigations.To check the validity of the mathematical model, drying experiments were carried out at different conditions of temperature, air velocity and relative humidity. Representative drying curves as well as moisture and temperature profiles are presented and discussed. Comparison between predicted and experimental results provides satisfactory agreement for this model. Displacement and stress fields using the elastic behaviour of the material are also presented and commented.
The processing of new waste-based lightweight aggregates is described. Main components are sludges generated from potable water filtration/cleaning operations and clay-based by-products from cutting process of igneous rocks. The complete characterization of residues is reported, including physical and chemical parameters, and their thermal behaviour. Several mixtures were designed, prepared, and fired at different temperatures, trying to use the materials such as they are available. First we attempted to reproduce typical properties of common lightweight aggregates based on natural resources, such as clays.Then, a further approach was followed, involving the production of aggregates with improved mechanical strength. In this attempt, the firing cycle seems to play an important role.The bulk density of this new aggregate is somewhat higher but still low due to the formation of an internal cellular structure made of closed pores and an external shell that is partially vitrified. Microstructural evolution was also evaluated (by SEM) while the expansive behaviour of the most promising formulations was studied by hot stage microscopy.
Polishing granite mud, i.e. the residue of the polishing process of granite stone blocks, has been studied for its potential use in heavy clay industry. Due to its properties waste stone mud could be used as a filler (an opening agent) in clay-based industry, e.g. in the production of clay bricks, blocks, panels, roofing tiles, or facing bricks. Different mixtures of clay of normal use in brickworks and up to 30 wt.% of mud were prepared on the laboratory scale.The influence of the stone mud addition on the drying and firing process, as well as on the properties of finished products, such as water absorption and compressive strength, was studied. From the laboratory results it can be concluded that a substantial amount (up to 10 wt.%) of granite stone mud may possibly be added into the regular production of heavy clay products. In this way a significant decrease in costs could be achieved due to the partial replacement of basic raw materials and due to the fact that the land-filling of waste stone mud may be avoided.
Due to the classification of crystalline silica as a human carcinogen, health regulations necessitate the determination of a-quartz in respirable dust and bulk materials in the industrial environment.A variety of analytical methods, including X-ray diffraction and infrared spectroscopy (IR), have been used to determine crystallinity degree of quartz in bulk materials. In addition to determination of crystalline silica in respirable dust, Murata and Norman (1976) proposed a semi-quantitative XRD method for measuring quartz crystallinity in bulk materials as well as minerals.The determination of full-with-at-half-maximum (FWHM) for quartz diffraction line in sample such as clay, coal and cement containing quartz an accessory mineral can be used to evaluate Murata’s crystallinity index for the quartz.The measurement of FWHM for quartz in bulk materials will accelerate practically the determination of crystallinity of quartz.
The modulus of rupture of four different refractory mixtures for coke ovens repair by hot gunning was determined.The materials were characterized by chemical, granulometric and phase analyses, optical microscopy and apparent density measurements. MOR values were determined by three points flexural test using prismatic specimens obtained by ramming of aqueous mixtures of the monolithic materials and firing.These values were related with the aggregate and bonding phase characteristics of the refractory materials and with the fired bar microstructures. MOR values were also considered to analyze the cohesion of each fired material and correlated with hot adhesion of mixtures on silica bricks. Results show that even though the refractory behavior at working temperatures cannot be directly derived from the modulus of rupture at room temperature (MOR), this value may give some useful indication to make a first selection of hot gunning refractory mixtures.
An artificial neural network (ANNs) with modular neural network (MNN) has been created in order to predict the compressive strength of high alumina refractory bricks.The parameters used as inputs for modeling include chemical composition (SiO2 %,Al2O3 %,TiO2 %, Fe2O3 %, CaO %, MgO %, Na2O % and K2O %), sintering temperature, brick volume, bulk density and apparent porosity.The output parameter of the artificial neural network is compressive strength. A sigmoid function was used as the transfer function in the model. The feedback of the errors was performed by using back propagation algorithms (BPA).The utility of the model is in the potential ability to predict the compressive strength of high alumina bricks.The optimal result was obtained after 65500 iterations with an average error of 3.07 %.The model has proven that artificial neural networks may be used to aid manufacturing and designing of the refractory brick with properly selected variables.
Capillary ceramic filters were prepared from a quartz-natural zeolite-lead borosilicate glass mixture by uniaxial pressing and sintering at various temperatures. Sintered specimens were characterized by their bending strength, apparent porosity, pore size distribution, and microstructure.The filter sintered at 960°C shows promising engineering properties for the capillary-system: maximum pore size, bend strength and porosity being 0.6 mm, 30 MPa and 33.45%, respectively.
Weathered granitic rocks from Al-Madina Al-Munawwarah area were experimented for the preparation of cheap technical glass-ceramic materials. The weathered granitic rocks were about 53.17 wt% of the batch constituents, depending on the composition.The batches were melted and then casted into glass, which was subjected to heat-treatment to induce crystallization.The resulting glass-ceramic materials were mainly composed of diopside, anorthite and wollastonite and mullite, exhibiting fine grains and uniform texture. It
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