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Spinel pigments of sea-green, light blue and moderate blue color were prepared from exhausted catalysts containing γ - Al2O3 as main phase, MoO3 as secondary phase and CoO, NiO or both as accessory phases, after slight correction of their composition. The color indices of the pigments were determined using a computer program, as well as their color according to the CIE standard.
The aim of this work is to evaluate the effects of incorporating river silt originated from washing silica sands extracted in “Ria de Aveiro” as a raw material in the manufacturing process of traditional ceramic building products such as bricks and tiles and on their final properties. The solid river silt waste was physicochemically characterized for particle size distribution, morphology and XRF. The thermal behaviour was investigated by DTA and TGA analysis, and the mineralogical phases were identified by XRD. Testing bars made of several compositions incorporating amounts in the range of 0 to 10-wt% of river silt and of an industrial standard paste were produced in a pilot-plant extruder, and fired at different temperatures in the range of 950-1100 °C. The characterisation results of sintered specimens (water absorption, linear shrinkage and mechanical bending strength) have shown that products with final properties similar to those obtained from the standard industrial body could be achieved from a composition incorporating up to 5 wt.% of river silt waste.
The possible use of silica sludge for the production of lightweight aggregates is reported. The results show that the investigated silica sludge can serve as a raw material for the production of lightweight aggregates. The following parameters have been found to significantly influence the process: (i) the mineral composition of the basic materials, (ii) foaming agents, and (iii) the temperature range of firing/foaming. The silica sludge contains about 70 wt.% of quartz, about 5-7 wt.% of feldspar, and the rest is clay. The grain size of silica sludge is below 100 mm, and 58 wt.% is below 20 mm. In order to improve the properties of the obtained aggregate some additional waste materials (paper mud, waste glass) were added to the silica sludge. Depending on the pore forming/foaming agents and firing regime lightweight aggregate with densities between 0.6 and 1.8 g/cm3 were obtained and tested for their suitability as a construction aggregate.
The changes in magnesia-spinel bricks from preheater cement kilns using alternative fuels were studied. An analysis of the wear mechanism of bricks was made based on the evolution of apparent porosity, the variation of their chemical compositions and investigation of their microstructure in relation to the internal temperature gradient. The investigation shows that persistence of a coating on the basic refractory lining of the sintering zone does not only effectively protect it against the direct influence of the temperature and corrosive reactions with components of the sintered Portland clinker, but also alleviates the influence of volatile components of the kiln atmosphere on the refractories. Dramatic variations of the volatile components in the kiln atmosphere with simultaneous change of manufactured cement clinker type may lead to coating disappearance and direct exposure of the lining to the influence of the high temperature and aggressive corrosion by components of the sintered Portland clinker and the kiln atmosphere. Excess of chloride and SO3 leads to MgO corrosion. Substantial excess of R2O (R = K, Na) leads to intensive corrosion of main components in the colder part of bricks and weakening of the bricks texture.
The effects of nano calcium carbonate on the properties of corundum-based castables were investigated. White fused alumina, ultra-fine alumina, nano calcium carbonate, calcium aluminate cement and hydratable alumina were used as raw materials. The results show that the phase compositions and phase changes of the mixture with nano calcium carbonate addition treated above 900 °C are the same as those of the mixture with calcium aluminate cement. The hot and cold modulus of rupture of the castables with nano calcium carbonate above 800 °C is improved by the bonding of in-situ reaction products and is higher than that of the castables with calcium aluminate cement, especially at 800 °C. The thermal shock resistance of the castable is enhanced by adding nano calcium carbonate or calcium aluminate cement. There is no evident difference between the effects of the two additives. The slag corrosion resistance of the castable is deteriorated by adding a small amount of nano calcium carbonate or calcium aluminate cement compared to the castable without CaO, but it is improved with higher CaO content. The castable with nano calcium carbonate is better in slag resistance than the one with calcium aluminate cement, in spite of their similar CaO content.
Cylindrical laboratory samples (∅11 mm) were prepared from a mixture of kaolin and clay (35 wt.%), corundum and chamotte (35 wt.%), and feldspar (30 wt.%) from a wet mass by a vacuum extruder. Other samples (cross-section 11x11 mm) were cut from the interior of the large blank. The mechanical strength, the Young’s modulus and the thermal expansion were measured on both types of the samples before and after firing. It was noted that: a) the glaze significantly influences the values of mechanical strength and Young’s modulus of the samples; b) the mechanical strength and the Young’s modulus of the green cylindrical laboratory samples may be 3 times higher than the mechanical strength and the Young’s modulus of the green samples cut from the blank; c) the mechanical strength and the Young’s modulus of the laboratory samples after high-temperature firing are 1.2-1.4 times higher than those of the samples cut from the blank interior; d) the thermodilatometric curves of both types of green samples are slightly different in the temperature intervals 20-150 °C and 450-850 °C; e) the thermodilatometric curves after high-temperature firing of both types of samples are identical.
Generally, the deformations of ceramic materials during and after firing may have a complex origin. If the products are made up of a single material, such deformations are mainly due to pyroplastic phenomena. In the case of glazed materials, two further factors must be considered: the state of tension established between glaze and body, and their differences in behaviour during sintering.
The use of rhyolite from a local source as an alternative fluxing agent in a commercial porcelain stoneware formulation was investigated. The experimental work was achieved in two parts: in the first part, standard tests were applied to the porcelain tiles obtained from the experimental bodies incorporated with varying amounts of rhyolite (up to 12 wt. %) as a substitution of albite in the standard formulation after single fast-firing under industrial conditions. Reactions during firing were studied by thermal analysis (DTA/TGA/DTG). The vitrification behaviour of the standard and rhyolite containing bodies was evaluated using a double-beam optical non-contact dilatometer. In addition, XRD was used to analyse the phases formed after firing. SEM was also employed in order to observe the microstructural characteristics of the selected fired bodies with respect to increasing rhyolite content. In the second part, the most suitable rhyolite containing formulation was further developed by modifying its clay fraction for cost saving purposes. Physical, thermal and optical properties of the all the investigated bodies such as water absorption, linear firing shrinkage, bulk density, linear thermal expansion coefficient and chromatic coordinates were measured. According to the results, it was possible to incorporate rhyolite into a porcelain stoneware formulation as a fluxing agent and to obtain meaningful technological properties.
An alumino-silicate based fireclay used in the production of refractory materials contains iron impurity which is not in the desired limits. The magnetic conversion conditions have been experimented in the reduction of iron content in the fireclay by magnetic separation. Effects of heating temperature, heating time and grain size and coal addition were investigated in the magnetization of fireclay samples. An artificial neural network was developed for modeling the dependency of magnetization on temperature, time and grain size as well as on coal addition during heating and an optimization problem was formulated in order to achieve the optimum conditions of magnetization. The results indicate that heating clay particles of 5/7 mesh (average 3.36 mm) grain size at 458 °C for 15 min without any coal addition will give the optimum magnetization.
Starting from an industrial body mix for porcelain stoneware tiles, part of its fluxing agent, sodium feldspar was replaced by a fine-grained microgranite. Sintering behaviour of the studied porcelain stoneware bodies with and without microgranite was investigated using a double beam optical non-contact dilatometer according to the corresponding industrial firing profiles. The degree of vitrification of the densified samples and the other samples separately heated at different temperatures were determined by measuring the shrinkage, bulk density, water absorption and flexural strength. Furthermore, the colour measurements were carried out on the fired samples. X-ray diffraction (XRD) was used in order to analyze the phases formed after firing. In addition, scanning electron microscopy (SEM) was undertaken to observe the microstructural characteristics of fired bodies with respect to peak firing temperature. The results indicate that possible use of fine-grained microgranite as an effective fluxing agent in porcelain tile bodies.
The mineralogical composition and technological characteristics of an industrial porcelain type body mixed with 3 wt.%, 6 wt.%, 9 wt.%, 12 wt.% and 15 wt.% of carbonates respectively have been studied. The added components were two samples from limestones and dolomites from carbonate formations of Kozani area, northwestern Macedonia, Greece and one magnesite from Gerakini formation of Chalkidiki peninsula, northern Greece. After firing the prepared ceramic specimens at 1200 °C for half an hour, the addition up to 9 wt.% of magnesite, up to 6 wt.% of dolomite and 3 wt.% of limestone gave better values of shrinkage, porosity and water absorption compared to the reference porcelain type body. The addition of carbonates lowers in general the compressive strength of the fired specimens. No correlation of the amorphous phase and the technological properties was found. Limestone addition favoured the formation of feldspars, dolomite the formation of feldspars, cordierite and forsterite and magnesite the formation of cordierite and forsterite.
Thermite welding of rails is now a standard operating practice to successfully join rails conjunctions in the field. Alumina crucible, an essential component of this operation, will be damaged and unusable after not more than 30 operations. This is due to direct contact of crucible with molten iron. Factors influencing this damage, including chemical reactions, penetration and infiltration of molten iron into the body, were studied using a scanning electron microscope equipped with X-ray spectroscopy (SEM/EDS) and X-ray diffraction. The results of this study supported by the kinetics of reaction between iron melt and alumina crucible in thermite welding showed that the thermite process does not significantly affect the crucible body component chemically; i.e. corrosion was not a major factor in crucible deterioration. The penetration and infiltration of melts into the crucible body via the grain boundaries and porosities were the major factor. A higher rate of the melt penetration into the parts containing impurities especially the silica was more harmful.
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