Papers by Keyword: Refractory Materials

Abstract: This study investigates the in-situ synthesis of cordierite–mullite ceramic using stevensite-rich-Ghassoul (39.6 wt.%), Bio-kaolin (24.7 wt.%), and andalusite (35.7 wt.%) as starting materials. Uni-axially pressed mixtures at 96 MPa were subjected to sintering at 1250, 1300, 1350, and 1380°C to determine the optimal temperature for cordierite–mullite composite. The phase evolution, microstructure, porosity, and thermal expansion of samples sintered 1250 to 1380° C for 2 h were investigated. The behavior and mechanical properties were evaluated using 3-point bending and indirect tensile tests. Results revealed the crystallization of cordierite and mullitization of andalusite at temperatures of 1190°C and 1300°C, respectively. Cordierite and andalusite were the predominant phases observed at 1250°C, with a gradual mullitization of andalusite as the temperature increased up to 1380°C. Rietveld quantitative phase analysis results indicate that, at a sintering temperature of 1380°C, cordierite and mullite constitute 57.4 wt% and 31.4 wt%, respectively. The sample sintered at 1380°C exhibited the optimal performance with the following properties: maximum bending and indirect tensile strengths of 31.9 ± 1.1 MPa and 26.6 ± 2.8 MPa, respectively, a flexural modulus of 34.9±2.5 GPa, a coefficient of thermal expansion of 3.6±0.4x10-6 𝐂𝐂−𝟏𝟏 and an open porosity.

Abstract: In a laying of a hearth it is usually used to ten different types of the flameproof materials. The characteristics of materials declared by the manufacturer can differ from the actual. For creation of the mathematical model [1, 2] temperatures distributions in a laying of the concrete furnace it is necessary to know thermal conductivity of materials of the specific parties used at construction of the furnace. Definition of the thermal conductivity coefficient allows adapt mathematical model for specific conditions of use. The technique of determination of thermal properties of refractory materials on the temperatures acceleration curve at blowing-in of the blast furnace is described.

Abstract: The heating furnace in CSP plant of WISCO has a lightweight lining which is built by all fiber templates. In light of its good thermal insulation performance and short service life, the lining material for heating furnace was optimized in this article by using heat transfer calculation while the thickness stays light and the insulation performance stays good. The castable was applied to substitute for lightweight fiber materials to prolong the service life of heating furnace lining. Also, this article shows a contrast analysis of heat insulation layer while using different insulation material: the fiber felt, nanoinsulation board and super hydrophobic insulation board. The effect on the temperature of external shell and heat loss was analyzed and discussed. The results generate a new design of material composition, which not only prolongs the service life of heating furnace lining, but also reduces the cost.

Abstract: Silica is used for lining of the upper parts of glass furnaces and their regenerators and for lining of the lids of arc furnaces and for the coke oven batteries construction. Silica bricks represent 60% of refractory material used for a coke battery construction. Coke ovens are generally the largest oven aggregates, where silica material is used. The whole coke oven battery may reach the length up to 80 m due to the chamber sizes. A single coke oven battery contains up to 50.000 tons of refractories [1]. From the material science point of view, the durability of silica bricks depends on numerous parameters including first of all porosity and mineral composition. Microstructure of silica bricks changes during their application due to the heat load, repeated heating and cooling, and direct contact with the oven atmosphere. The paper discusses the possibility of reducing the apparent porosity and increasing of bulk density of coke oven silica bricks. It describes the effects of an iron dust, microsilica and influence of the compaction pressure on the coke oven silica microstructure. Functional characteristics of the material prepared according to the new standard recipes are compared with the properties of standard silica products.

Abstract: Al (OH)₃, Suzhou kaolin, AlF₃ and V₂O₅ were premixed and pelleted to form the precursor for fabricating the mullite whisker, and then the precursor was added into the calcined bauxite and Suzhou kaolin mixture according to a certain mass percent. The mullite-corundum refractory materials with well-dispersed needle-like mullite formed in-situ were prepared. Through studying the effect of different sintering temperatures on the performances of the as-fabricated mullite-corundum refractory materials, it was concluded that the appropriate sintering temperature was 1450 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM), water absorption, bending strength, coefficient of thermal expansion and the first thermal stress fracture factor were used to characterize and evaluate the materials. The results show that the sintering character and thermal expansion coefficient of the refractory materials increase with the rising sintering temperature. The bending strength of the refractory materials sintered at 1500 °C presented the maximum value and the first thermal stress fracture factor appeared the highest value at 1450 °C.

Abstract: Traditionally, calcium aluminate cement is always used as the binding agent for refractory castable applied in steel and iron, but cement contains many impurities, it is easy to generate low-melting additives and excessive liquid phase may be formed in material calcination, so the thermal shock resistance and moderate temperature intensity of corundum castables bonded with cement is worse; in addition, the flowability of cement-bonded castables also is poorer and it is difficult to construction. In the recent years, China and other countries have started to study properties of colloidal sol bonded castables to improve physical/chemical properties and workability of cement castables. This paper summarizes some characteristics of silica sol bonded materials via test and analysis.

Abstract: A part of a soldier block, placed in a float glass furnace near the hot spot area, was investigated to learn about the changes in the microstructure during the production of the block, during the use for glass melting and after the shut down of the furnace and the cooling of the block. Beside the three phases after the production (baddeleyite, corundum, vitreous phase) during use as a soldier block mullite and secondary corundum as well as secondary zirconia may occure. Cooling down the used block after the furnace campaign the beginning of the crystallisation of feldspars may be seen.

Abstract: The disintegration of 6 different Nb-Zr-Fe alloys and their hydrogen storage properties due to hydrogenation have been investigated. The hydrogenation was performed in a 0.1MPa hydrogen pressure held at room temperature in arc melting chamber without exposure to air atmosphere. The thermal stability of hydrogen dissolved in disintegrated powder was measured in the temperature range from room temperature to 600°C by using the thermal analysis equipment. Hydrogen contents in alloys were evaluated from the mass difference of TG curve and chemical determinations for hydrogen gas analysis. The values of hydrogen content are in accordance with both chemical and mass difference methods. The hydrogen contents of disintegrated alloys synthesized were in the range of 1.2-2.0 wt% which depend on the composition of alloys.

Abstract: The paper presents the results of investigations on the influence of the starting mass grain size distribution on microstructure of sintered magnesia-spinel products. The model investigation was conducted using magnesia clinkers and fused spinel. The grain size distribution of starting mixes were selected according to Dinger and Funk's theoretical curves with different values of n coefficient. The results clearly indicate that the best properties were achieved when n value changed in the range of 0.22 - 0.30 and forming pressure was contained in the range of 160 - 200 MPa.

Abstract: The design of composite materials leads to the development of multi-component systems where each constituent has a specific function in the material, from technological and/or application points of view. Examples of such composite systems are the cordierite-mullite refractory materials investigated in this contribution. Two different commercially available compositions were selected for evaluation of the influence of microstructure on fracture behaviour under thermal shock conditions. The materials were exposed to water-quench tests from 1250°C and subsequently the fracture toughness was evaluated using the chevron notched specimen technique. The results were compared to those obtained on as-received materials. Microstructural damage was also studied applying fractographic techniques with the aim to gain knowledge on the thermal shock damage mechanisms acting in the materials.