Papers by Keyword: Refractory

Abstract: Mullite-cordierite ceramics was prepared by the three composition of talc, kaolin (kaolin from Naratiwas in Thailand) (NT) and alumina. The different amounts of alumina (5, 10, 15 and 20 wt%) were added to produce various mullite-cordierite alumina mixtures which are denoted as NA, NB, NC and ND, respectively. The mixtures were pressed into rectangular shapes by hydraulic press with the pressure of 150 kg/cm² then sintered at temperature of 1300 °C and 1350 °C for 2 hours. The morphology of the synthesized mullite-cordierite samples were characterized by x-ray diffraction spectroscopy (XRD), and physical-mechanical properties were investigated. Mullite-cordierite was successfully synthesized. The XRD result was represented phases of mullite and cordierite. The NA samples sintered at temperature of 1300 °C indicated the best physical-mechanical properties including bulk density (2.23 g/cm³), flexural strength (44.4 MPa) and thermal expansion coefficients (5.00x10^-6). The other NA samples sintered at temperature of 1350 °C exhibited the bulk density, flexural strength and thermal expansion coefficients are 2.21 g/cm³, 47.8 MPa and 4.99 x10^-6, respectively. The thermal expansion coefficient of the NT sintered samples have been plotted the length change relative to measuring temperature ranging of 30-1200 °C. The suitable condition of the synthesized mullite-cordierite ceramics is finally obtained the NA samples with 5 percent weight of alumina composition sintered at the temperature of 1350 °C.

Abstract: The objective of this research is to investigate the potential of geopolymers produced from fly ash, metakaolin and clay as high quality refractory. Geopolymers were synthesized through alkaline activation method and cured at 70°C for 1 hour. The samples were subjected to various characterizations such as compressive and flexural strength, fire resistance and shock thermal measurements. Geopolymers made from fly ash showed higher compressive strength compared to those made from metakaolin and local clay. Fire resistance and thermal shock measurements indicated that the refractory quality of geopolymers made from fly ash, metakaolin, and local clay was very much the same.

Abstract: According to ULCS production practice in domestic steel,in combination with laboratorial data, this paper analyzes the influence factors of ULCS carbonization. The statistical results shows that carburization of ultra-low carbon steel is affected by mold flux、continuous casting process and refractory,and some corresponding control measures are put forward.

Abstract: So far, thermal shock theories have not been well verified in refractories. This paper compared hypothesis and failure mechanism of two typical thermal shock theories, analyzed the applications of two typical theories in refractories from working environment, failure process and microstructure differences. And thinks that the critical stress fracture theory is suitable for nearly ideal brittle refractory with ceramic bond and used in thermal shock extremely harsh environment; thermal shock damage theory suites to evaluate multiple loops thermal shock. Analyzed the factors influencing the thermal shock parameters, and discussed Ways to improve the thermal shock resistance of refractories from destructive force and resistive force of refractories. Conclusions are that choosing small swelling expansion rate and high thermal conductivity material, reducing the micro stress concentration and adding flexible phase, these three methods can be used to make refractories with good resistance to thermal shock.

Abstract: Corrosion of refractories results from reactive transport namely, transport of agents and chemical reactions of these agents with impregnated medium. On one hand, the transport involves either diffusion or impregnation depending on the state of the corrosive agents and the microstructure of the host media. On the other hand, chemical reactions may be very numerous and complex. This study focused on the reactive impregnation of Al₂O₃-CaO slag into porous high alumina refractory.Transport properties of the porous media have been assessed by performing wicking test. Chemical reactions between the solid high alumina skeleton and Al₂O₃-CaO slag involve successive dissolution/precipitation mechanisms forming aluminates of lime. Contrary to the thermodynamic properties of the binary system, the kinetics of these solid/liquid reactions is not well known. Corrosion tests associated with quenching method, XRD and high temperature XRD were performed for a better understanding of the kinetics.

Abstract: 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.

Abstract: It is a common practice to design refractory linings with the help of thermal computations, thermochemistry analyses and strong workman know-how. Their mechanical design is often limited to simple thermo-elastic computations. Sometimes computations are refined considering non-linear mechanical behaviour, even if corrosion often induces additional chemical strain and strong change in service of the mechanical behaviour of the refractory. The aim of this presentation is to briefly recast the irreversible thermodynamic framework in order to underline the implications of some basic thermodynamic concepts in term of refractory behaviour modelling. Then, the use of these concepts to develop fully 3D finite element simulations accounting simultaneously for thermal, mechanical and chemistry phenomena will be illustrated on the particular case of SiC-based refractory. Comparison between long duration oxidation test at high temperature and model prediction allows the validation of the proposed approach. Then, an extension to the industrial case of refractory lining in Waste to Energy plant will be illustrated. The interest of taking into account the thermo-chemo-mechanical coupling effects is shown.

Abstract: 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.

Abstract: This study contains results of carbonaceous SHS-refractory materials application for binding of the graphite products and melting of metals in the induction furnaces. The opportunity of producing strong graphite-graphite bond up to 5 MPa by means of the carbonaceous refractory material that demonstrated high chemical stability in the aggressive liquid metals and alloys environment has been shown. The results of the industrial tests of melting crucibles made of carbonaceous SHS-refractory materials have been presented in the case of aluminium melting. It has been shown that such crucibles stability is 5-6 times higher than that of standard graphite crucibles in aluminium melting conditions. The obtained research results testify that developed carbonaceous material is applied for lining of the induction furnace of melting unit is allow to increase the number of nonferrous metals (bronze) melting cycles from 5 to 6 times in comparison with the traditional graphite crucible melting. High chemical stability of the material to oxidizing environment as well as to metal melts is provided by formation of high-melting compounds in the carbonaceous exothermic systems during SHS-process.

Abstract: The experiment proved the effect of burning urban domestic wastes on alkali-resistant bricks and spalling-resistant high alumina bricks by the Static crucible method. The result indicates that the main erosion mechanism is slag permeable and slag erosion. Burning the waste will emit high temperature gases containing alkali, sulfur and chlorine, and the gases react with refractory materials contribute to the formation of sulfate, chloride and compound salt, which deteriorate and invalid refractory gradually. Through SEM, it is observed that the loose structure of metamorphic layers and easily spalled during thermal stress.