Papers by Keyword: Refractory

Abstract: The aim of this study is to analyze the mechanical and physical properties of refractory bricks produced via geopolymerization using volcanic ash. Volcanic ash was combined with 12 M sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) as activators, with a liquid-to-solid ratio of 0.2. Two brick prototypes were produced: a cylindrical specimen for testing compressive strength and water absorption, and a rectangular prism for analyzing thermal conductivity. The bricks were calcined at 600°C and 800°C, showing favorable performance compared to well-known commercial refractory bricks. Cylindrical specimens calcined at 600°C reached an average compressive strength of 5.51 MPa, while those calcined at 800°C averaged 6.60 MPa—more than double the 2.80 MPa of commercial bricks. The average density of the specimens at both temperatures was similar, around 1.58 g/cm³, significantly higher than the 0.95 g/cm³ of commercial counterparts. Moreover, the average thermal conductivity of the geopolymer bricks was 0.008 W/m·K, indicating superior insulating properties compared to the 0.39 W/m·K of commercial refractory bricks. These results demonstrate optimal properties in refractory bricks made from geopolymer-based volcanic ash.

Abstract: Lightweight refractory materials are most used as a second layer in the lining. Many techniques can be used to their production depending on their final application. This manuscript is focused on utilization of sol-gel method as the replacement of hydraulic or ceramic bond in the manufacturing process of grog and castable preparation. The results show possible ways to produce high quality lightweight refractory grog with very high purity and also lightweight refractory castable, which performs good results in terms of bulk density, apparent porosity, cold crushing strength, cold modulus of rupture and permanent linear changes.

Abstract: Impurities and resulting inclusions are an issue when processing higher amounts of scrap during steel making. To increase the recycling rate, the removal of impurities from the scrap in form of inclusions is of great interest. In previous studies was found that inclusions attach primarily on carbon containing refractories, especially if on their surface an interfacial layer (1–3 µm thickness) was formed in-situ. This study investigates the formation mechanism of this in-situ layer in detail by application of computer tomography (CT) measurements on two scales. The large scale CT scans visualized the general appearance whereas the small scale measurement regarded the in-situ formed layer and the attached inclusions in detail. Based on these measurements, previous results and a literature review it was concluded that the layer formed mainly due to carbothermally reduced impurities which moved to the decarburized surface of the refractory in gaseous form and enhanced sintering of the surface region to develop the layer.

Abstract: This paper reports the synthesis, characterizations, microstructure and properties of forsterite powder produced in Thailand from talc and magnesite as raw materials by using mechanical activation with subsequent calcination. The synthesis forsterite powder were mixed by using talc and magnesite at 1:5 mole ratio. The maximum milling time was 24 h in a planetary zirconia ball mill. Afterward, the mixtures were calcined in an electric furnace for 1 h at 900, 1000, 1100, 1200 and 1300°C respectively. The synthesized powder was characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and physical properties. Results of the physical properties of synthesized forsterite showed an increased in density as the calcining temperature increased. In contrast, porosity was decreased with an increase of the calcining temperature. Therefore, forsterite that was calcined at 1300°C provided the best results which were 2.96 g/cm³ of true density and 15.41% of true porosity. Results of XRD of synthesized powder indicated that the forsterite crystallization was constant for which sharpen appeared after 5 h of mechanical activation. Fraction of forsterite was appeared after being calcined at 1000°C for 1 h with an increasing of calcination temperature, the fraction of forsterite phase increased. Based on the mentioned characteristics, the forsterite produced from Thai talc and magnesite exhibited properties of an insulator and can potentially be used as refractory devices.

Abstract: The exhaust dust is an industrial waste that results from the sand molded casting process in the foundry sector. The metal casting industry plays an important role in the reduction of the environmental impact by recycling industrial waste. The idea of manufacturing thermally resistant refractory bricks made of exhaust dust from the foundry industry has motivated managers and researchers. The purpose of this study is to analyze the manufacturing process of refractory bricks made of 10, 20 and 30% exhaust dust and their properties. The dust was analyzed by using the SEM/EDX and XRD techniques. Results show that the specimens used in this study did not meet the required water absorption specifications. However, the 10% and 20% samples presented a desirable porosity. The manufactured bricks were classified as dense, insulating and semi-insulated, respectively. In relation to compression resistance the rupture stress proved to be lower than the level of stress detected in commercial bricks. The temperature test showed that bricks made of exhaust dust cannot be considered refractory for commercial purposes. Although the exhaust dust does have some refractory properties it still cannot be used as raw material in the manufacturing of refractory bricks since it does not meet all the necessary specifications as proposed by this study.

Abstract: Aqueous solutions of sodium polytungstate were used to fractionate samples of sugarcane bagasse ash by heavy media separation. Practically no cenospheres were recovered from the ash samples. The method was successful in separating fibrous carbonaceous particles with a uniform surface from particles containing more silica and having a less uniform surface. A geopolymer refractory brick having satisfactory durability was produced from sugarcane bagasse ash with metakaolin and ball clay fillers and a sodium metasilicate/hydroxide activator liquor. Drying and firing shrinkage, bulk density and ultimate compressive strength tests were performed to determine the most feasible combination of ingredients. Geopolymer samples produced using aluminium powder instead of ball clay were found to be very brittle and unsuitable for refractory service.

Abstract: In this paper, effects of incorporation of Narathiwat clay (NT), talc and silica on the mechanical properties of cordierite-mullite refractories were investigated. The starting raw materials were mixed in different ratios and fired at 1300 °C for 2 hours. XRD patterns of fired refectories indicated cordierite and mullite phases. The fired samples were studied the firing shrinkage, water absorption, bulk density, apparent porosity and bending strength of the cordierite-mullite refractories. The optimum condition was achieved for the composition of 20% Talc that had shrinkage: 11.78%, water absorption: 4.16%, bulk density: 2.28 g/cm³, apparent porosity: 9.2% and bending strength: 330.82 kg/cm². The results thus showed that Narathiwat clay, talc and silica was a potential materials for use kiln furniture cordierite-mullite refractories.

Abstract: In the paper were reviewed mechanical and chemical properties of the modern refractories applied in the metallurgical industry and was provided their classification for the goal of optimal selection of refractories kind for specific technological conditions, reducing costs and solving the environmental issues. For various applications in the steel industry, in the furnace linings for iron and steel making, metal and slag transport, heat treatment furnaces and the flues for the hot gas conduction, refractories are widely used. The refractories can also be classified according to the raw materials, which are used in the preparation and to the predominant minerals after production. Nowadays, hardly any standard bricks are used and there is a trend towards using monolithic refractories. Due to the improvement in the service life and highly productive modern steel making processes, the consumption of refractories is reduced.

Abstract: The aim of this work is to propose the utilization of aluminium buff from aluminium part manufacturer as a raw material for cordierite batch composition. The powder mixtures were compacted by uniaxial pressing. The green compacts were sintered at temperature in the range 1300-1400°C for 2 hours in air. The physical properties were characterized by Archimedes method, Brazilian test and dilatometry. Phase and microstructural analysis were done by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis showed the major phase was cordierite along with sapphirine as a secondary phase. The fired properties of materials were demonstrated that the optimal properties was achieved from the specimen sintered at 1375 °C.

Abstract: This study utilized aluminum dross residue obtained from secondary process of aluminum production as the main component in the fabrication of ceramic refractories. The amount of residue varied in the range 60-90 wt% and other components in the ceramic formulations were a combination of alumino-silicate based clays. Alpha-alumina, a-Al₂O₃ was the main crystalline phase found in all sintered samples according to x-ray diffraction analysis. Mullite phase, Al₆Si₂O₁₃ was also found in all the sintered refractories. It appeared as the main second phase which gave high strength and refractoriness. All the synthesized refractories had excellent heat-resistant characteristics when tested for thermal shock resistance. Samples were heated at 1200°C and subsequently quenched to cold water and ambient air. Refractories produced from aluminum dross residue in this study are advantageous for various applications such as high alumina bricks, high duty firebricks for steel and glass melting industry.