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Results about the vitrification of several hazardous iron-rich industrial wastes (from productions of Zn and Cu metals, as well as EAFD and MSWA) and the usage of obtained glasses for synthesise of sintered glass-ceramics are summarises. It is shown that the appropriated method of sinter-crystallization mainly depends on the crystallization trend of used glasses. When the parent composition is characterised by formation of a moderate amount of crystal phase low temperature sintering with short crystallization step in the interval 800-900 oC can be used. In addition, attractive granite-like building glass-ceramic can be obtained by mixing fine and coarse glass frits and “free” sintering in refractory moulds at 1000-1050 oC. Contrary, when intensive phase formation carries out the crystallization inhibits the sintering resulting in specimens with scarce degree of densification. However, in some cases a secondary densification process occurs at temperatures near to the eutectic ones, leading to well sintered samples with higher crystallinity and improved mechanical properties. It is also highlighted that the preventing of Fe2+oxidation by using inert atmosphere during the heat-treatments leads to a decreasing of sintering temperature, finer crystalline structure and additional enhancement of the mechanical properties.
Zirconium silicate is generally used as a whitening agent in super white and ultra white porcelain tile compositions. Depend on the market speculation, this material's price fluctuated. To reduce this negative effect of the material on the our profitability, an alternative whitening compositions is developed. The aim of the study is prepare the alternative whitening composition with an innovative approach such as controlling the amount of the amorphous and crystalline phases in the porcelain tile body and produce the new composition with the same property compared standard body such as water absorption, size, strength, color. And also ensure the sustainable production with the same quality.
Spodumene, which is a lithium alumina silicate, has been used as a raw material in the production of thermal shock resistant whitewares and sanitarywares. The presence of spodumene results in enhancement of mullitization and imparts better physical and mechanical properties to ceramics. In this study, the influence of Lithium alumina silicate phases on the mechanical properties of standard porcelain stoneware body was investigated. Especially solid-solid reactions were observed between spodumene and quartz or spodumene and clay. These solid-solid reactions bring about a newly formed lithium alumina silicate (LAS) phases. Spodumene allows the development of a low viscosity liquid phase and results in a decrease in closed porosity, also with increase in bulk density, bending strength and elastic modulus.
Non-destructive testing techniques are widely used for testing ceramic materials. In our studies, two different types of ultrasonic test methods (A-scan and C-Scan) were investigated as non-destructive testing methods for characterization of porcelain tiles. Tiles were sintered in different temperatures to change their porosity and density properties. By changing of ultrasonic time and velocity related with samples’ some physical properties (such as bulk density, apparent density, apparent porosity (%), water absorption (%)) inspected via contact A-scan ultrasonic test method. The results show that without necessity of traditional test methods, some physical properties of ceramics can be determined by using obtained ultrasonic velocity-bulk density, apparent density, apparent porosity (%) and water absorption (%) calibration plots. Additionally, various defects were inspected in samples by using water immersion ultrasonic C-scan method. These results supported this study to obtain the information about defects’ size and place in the ceramic tiles. To support this non-destructive method results scanning electron microscope (SEM) characterization was done and images give the information about the place of the defect.
Durability of building ceramics is determined by phase composition, the presence of various admixtures and porosity structure. Insertion of salts into the ceramic materials of bricks causes a gradual loss of the original properties of the material. The studies presented in this paper relate to the impact of magnesium sulfate salts to the microstructure change of the ordinary ceramic brick treated. Two types of ceramic bricks were selected for the studies with significantly different properties of shard, which through capillary action were brought to full saturation by solutions. Determination of changes in microstructure of the test materials by the process of crystallization of salts derived from solutions and the crystallization of the corrosion products, was carried out by observation of the microstructure in SEM. In selected places, chemical analysis was performed to determine the changes in the phase composition of the test materials. As a very important factor that affects the stability of ceramic brick is its porosity, pore structure determination was performed by mercury intrusion porosimetry. Based on the received results, the categorization of pores was presented with the indication of priority place of accumulation of crystallizing salts.
Investigations were undertaken to assess the chemical and technological characteristics in clay products from the Cretaceous deposit (Moroccan Meseta), in order to use them in refractory products. We have focused mainly on this clay because of its high content of alumina, silica and magnesium oxide, which are very favorable for the synthesis of refractory and ceramic materials. That is why the study has used several techniques of analysis (FX, XRD, SEM and technological tests. The samples were dry pressed on clay bodies and sintered at temperatures ranging from 900 to 1200°C. The relationship between water absorption, shrinkage and flexural strength as a function of the firing temperature was examined in order to enhance the quality of the final products and to optimize the production process. The results revealed that these clays have qualities necessary for the manufacture of ceramic and refractory products.
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Carolina D. Roveri, Letícia H. Godoy, Antenor Zanardo, Luciano L. Silva, Maria Margarita T. Moreno, Fabiano C. Navarro, Sylma C. Maestrelli
Lavrinhas, a city located 234 km northeast of São Paulo, Brazil, presents syenitic rocks with high content of nepheline, whose preliminary field assessment indicated its potential to be used in the production of ceramic products. The paper aimed to study this raw material with fluxing properties and to determine the best processing methods based on mineralogy and texture, in order to achieve better removal efficiency of the nepheline. Petrographic characterization was carried out in two rock samples, as well as the particle size characterization of the untreated material, the split into fractions for magnetic separation tests and optical microscope observation of the products. In addition, chemical and particle size analysis and melting tests were performed. The latter concerned the material melting color evaluation before and after the magnetic separation, as well as its potential use in glazes and engobes, compared to a standard sample of Nepheline, and inferences for the use in porcelain masses. Preliminary tests showed that after the removal of residual iron oxide, the nepheline raw material bearer has potential to be used in the formulation of porcelain masses, replacing other fluxing materials with higher benefit.
During the operation of industrial vessels at high temperatures both elastic and inelastic behaviour of refractories may occur under intense thermomechanical loads. The latter one brings about an irreversible strain, which may cause mechanical failure of refractories and be responsible for the opening of joints. Besides material failure under tensile or shear loads, creep of refractories also may contribute to the occurrence of the irreversible strains. For quantitative assessment of the thermomechanical behaviour of an industrial vessel lining by the simulations, the accurate determination and description of creep behaviour of refractories at service related load levels is of importance. In this paper, a newly developed high temperature compressive creep testing equipment is introduced. Compared with conventional creep testing machines it enables the application of higher load levels as they occur under service conditions. A general testing procedure and displacement/time curves for various temperatures and loads are shown. For simulation purposes a Norton Bailey type creep law representing strain hardening is identified from the test results. An inverse evaluation procedure is performed for this purpose which exhibits high efficiency and robustness.
A deep understanding of the mould flux effect on the wear mechanisms of Al2O3-C nozzles (AG) is relevant to avoid premature damage and to decrease the cost of black refractories in the industry. In this paper, a post mortem study on a nozzle was carried out to identify the causes of the wear mechanisms during the continuous casting of billets. Physical properties such as viscosity and surface tension of the mould fluxes were determined at operation temperature (1550ºC), in order to correlate with microstructural results obtained by light and scanning electron microscopy (SEM). Also dihedral angle f measurements were carried out at high magnification by SEM. Applying EDS analysis the infiltrated mould flux chemical composition was determined. The study was completed by EBSD. The EBSD technique contributed to increase the knowledge on wear mechanisms because of the possibility of identifying and localizing phases together with crystalline condition. The phases, the grain orientations and the properties of grain boundaries, have a large influence on the corrosion behaviour. Therefore, it is essential to have a characterization technique that can provide information such as: grain size, orientation, misorientation angle and the present phases. In this context, EBSD can provide relevant information on crystallographic and structural analysis of AG nozzle including the insert of ZrO2-C.
The work presented here deals with simulation assisted evaluation of fracture testing of ordinary ceramic refractory materials. Two tests are applied. One of them, a wedge splitting test, is already established for this purpose. An inverse evaluation procedure was developed to derive more information from the test results: It enables the simultaneous determination of the specific fracture energy, the tensile strength and the Young’s modulus. Moreover specific fracture energy can also be determined in the case that the test has to be interrupted at some residual load due to relatively low material brittleness. The other test method, a laser irradiation disc test, was developed in order to determine specific fracture energy and tensile strength for fine ceramic refractory materials behaving relatively brittle. From the time elapsed until crack initiation occurs (t1) and a stable/instable transition of crack propagation takes place (t2), respectively, the tensile strength and the specific fracture energy are calculated based on a simulation of the mode I fracture behavior which applies the fictitious crack model according to Hillerborg.
This paper deals with the characterization of crack networks on the surface of refractory castable slabs, which are induced by stresses arising during the curing and drying (CD) stages. Images of the surface of castable samples placed in a house-made climatic chamber were recorded during the CD stages with a digital camera and processed by Digital Image Correlation (DIC) to measure the displacement field. Post-processing of DIC results were performed to estimate the length, orientation and opening of cracks in networks. The methodology is detailed and first analyses of experimental results are shown.
Gasifiers are reaction vessels used to process carbon feedstock such as coal and/or petcoke at elevated temperature, high pressure, and in a reducing atmosphere (low oxygen partial pressure) to form CO and H2, called synthesis gas or syngas. Syngas is used as a fuel in power generation or as a feedstock material in chemical production. By-products of the gasification process include unreacted carbon, gases such as CO2 and H2S, and slag formed from mineral impurities or organic metallic compounds in the carbon feedstock that liquefy during gasification. In the gasifier, slags interact with the high chrome oxide refractory liner, causing wear and eventual failure of the refractory lining by two primary means - spalling (structural and chemical) and chemical dissolution. Failure of the refractory lining causes the gasifier to be shut down for repair, with increased service time identified by users as important for greater usage of gasification as an industrial process. Phosphate additions to high chrome oxide refractories have been found to increase service life during commercial service by reducing spalling and lowering chemical dissolution of the refractory liner. The mechanism of how they improve service life is not well understood. The microstructure and physical properties of high chrome oxide refractories with and without phosphate additions removed from a commercial gasifier after approximately eight months of exposure to a coal slag are evaluated in this report, with the emphasis on evaluating slag/refractory interaction in refractory pores. Details of the investigation are presented and possible mechanisms of how phosphate additives improve wear resistance discussed.
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