Papers by Keyword: Mullite

Abstract: This study focuses on the physical and microstructural properties of mullite-based ceramic synthesized by solid-state reaction of rice husk ash (RHA) and alumina (Al₂O₃). Laser Flash analysis (LFA), Field Emission Scanning Electron Microscopy (FESEM) and Energy-dispersive X-ray spectroscopy (EDX) characterized the effects of the mixtures of RHA and Al₂O₃ matrix. The results show that the Al₂O₃rich samples sintered at 1500 °C exhibit the highest thermal diffusivity radiated at 500 °Cwith values varied from 0.258-0.369 mm²/s. The addition of Al₂O₃ (30-60 wt.%) into RHA enhance the crystallization of mullite on the surface of vitreous particles. The presence of diphasic mullite densified the green bodies,and its crystallites size keep increases (400.78-650.52 nm) by theincrement of the sintering temperature (1200-1500 °C). These results suggested that addition of Al₂O₃into RHA enhance the thermal diffusivity as the values closer to the thermal diffusivity of pure mullite and have high potential application as thermal insulation material. The properties of mullite-based ceramics listed above such samples M1, where the composition closes to mullite (3:2) have comparable properties to commercialize mullite ceramics.

Abstract: This paper reports the results of using natural andalusite (Al₂SiO₅) in combination with CaCO₃ and ZrO₂ in order to obtain aluminosilicate product. This work was devoted to the study of the mechanism of new phases creation in the Al₂SiO₅-CaO-ZrO₂ phase system during heating at different temperatures (1000, 1100, 1200, 1300 and 1400°C). Al₂SiO₅, CaCO_3, and ZrO₂ were used in a weight ratio of 45:50:5, respectively. According to the phase composition and chemical analysis in microareas, it was found, that andalusite reacted with CaO giving two calcium aluminosilicates: gehlenite and anorthite at 1400°C. ZrO₂ was presented as the separated phase at this temperature. Other occurring transition phases were: CaZrO₃ at 1000 and 1200°C, Ca₂SiO₄ at 1000, 1100 and 1200°C, Ca₃ZrSi₂O₉ at 1300°C. The synthesis mostly depended on the diffusion of Ca²⁺ ions.

Abstract: Mullite-anorthite as a kind of lightweight refractory combines the low thermal conductivity of anorthite and the excellent thermal properties of mullite. In this work, mullite beads and calcium aluminate cement was used as the main component and bonding agent. The lightweight mullite-anorthite refractory was prepared by difference routes including foaming method, addition of pore-forming agent and sacrificial template method. The phase composition, bulk density, apparent porosity and thermal conductivity of samples were compared. The results showed that anorthite formed as the consequence of the reaction of cement and mullite. Extra addition of foam, cornstarch and polyurethane sponge could decrease the bulk density of samples. The pore size of samples prepared by foaming method was the smallest. The apparent porosity of samples obtained by sacrificial template method was largest, but the thermal conductivity was the highest due to the open pores.

Abstract: This paper reports the effects of γ-Al₂O₃ and α-Al₂O₃ on the properties of lightweight insulation materials. The phase compositions, microstructure and mechanical properties of lightweight insulation materials are separately investigated by XRD, SEM and tabulate thermal conductivity apparatus methods. The results indicate that the increasing of the amount of γ-Al₂O₃ is beneficial to improving the bulk density, compressive strength and acid resistance of the fired specimens. The fact negatively impacts on the increasing of the apparent porosity; however, it has no significant effect on the thermal conductivity of specimens. Meanwhile, the studies highlight that when the content of γ-Al₂O₃ increases, the nucleation and growth of mullite is accelerated at high calcination temperature, which has positive effect on improving the physicochemical properties of lightweight insulation materials. And the γ-Al₂O₃-free SiO₂ glass phase system is guided by theoretical analysis of reaction conditions for non-catalytic system with Factsage modelling.

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: Mullite-based ceramics were prepared by utilizing agriculture by-product called as rice husk ash (RHA) from untreated rice husk (RH) and commercial alumina powdermixtures. Various samples were prepared accordingly with the mullite stoichiometric composition and subjected to the uniaxial hydraulic press. The green bodies, then were sintered to various temperatures at 1200 °C, 1300 °C, 1350 °C, 1400 °C, 1450 °C and 1500 °C in an electric furnace. Physical and microstructural characterization were done such as bulk density (BD), linear shrinkage (LS), X-ray fluorescence (XRF), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The sample M1, which composed the slightest RHA (40 %) was considered the optimum composition which produced the highest densification, 3.101 g/cm3 and the lowest linear shrinkage, 8.62 % which compareswith the theoretical mullite density. Besides, it is supported by the evidence of the presenceof mullite in the samples sintered 1300 °C (shown as elongated shape) as primary mullite and continued to grow at higher temperatures at 1400 °C (shown as equiaxed shape) as secondary mullite. The sintered samples showno evidence of mullite inearly at 1200 °C due to insufficient energy to diffuse for mullitization. As the sintering temperature increased, mullitization increased while decreasing the distribution of glassy phase and voids. The results revealed the high dependency of bulk density and linear shrinkage on the Al2O3 content and the values were gradually increased with the increase of sintering temperature. These findingsmay lead to the extended study ofthermal insulationmaterials as mullite ceramic is an excellent candidate for this application due to its properties.

Abstract: Aluminum dross residue is a by-product produced at secondary re-melt plants where aluminum scraps are recycled. In this study, aluminum dross residue was utilized as a major component in the fabrication of unglazed ceramics for wall tile applications. The use of this by-product can reduce the landfill and environmental problems. The amount of aluminum dross residue used in the ceramic compositions varied in the range 50-90 wt.%. Other components utilized in the ceramic compositions included recycled glass alumino-silicate based clays. Firing was carried out between 1140 and 1200°C with 4h holding time which resulted in strong ceramic samples. Alpha-alumina, α-Al₂O₃ was the main crystalline phase found in all sintered ceramic samples. The appearance of mullite phase, Al₆Si₂O₁₃ was evident in all fired samples. Overall, the synthesized ceramics had excellent densification characteristics when the amount of aluminum dross residue was less than 70 wt% in the ceramic composition.

Abstract: Small pellets with differing mullite contents were prepared by a conventional ball-milling and dry-powder pressing technique, followed by firing at temperature of 1300°C and 1600°C for four hours. Kaolin processing waste and high purity aluminum hydroxide were used as starting materials. The sintered samples were examined using X-ray diffraction to determine the weight percent of each identified phase. The results showed that the percentage of mullite in kaolin processing waste can be increased by introducing additional aluminum hydroxide. It was found that sintered samples yielded best results when derived from both types of kaolin processing waste with 40wt% of aluminum hydroxide and a firing temperature of 1600°C.

Abstract: In work investigated effects of zirconium oxide (ZrO₂), spinel (MgAl₂O₄) and mullite (Al₆Si₂O₁₃) nanosized powders on the base oil tribological properties. The nanosized (30-40nm) powders manufactured by plasma chemical synthesis method. Tribological experiments used on ball-on-disc type tribometer, measured coefficient of friction and determined metalic disc wear. Base oil used selectively purified mineral oil (conform SAE-20 viscosity) without any functional additives. Nanosized powders dispersed in base oil at 0.5; 1.0; 2.0; wt.%. At work cocluded, that the adition nanoparticles in base oil, possible reduced friction pair wear and friction coefficient. As the main results include spinel (MgAl₂O₄) nanoparticles 0.5 and 1.0 wt. % concentration ability reduced friction coeffiecient value.

Abstract: Already, we developed a high porosity alumina foam. However, alumina has high thermal conductivity about 36W/mK at room temperature, and it need to achieve to high porosity to decrease thermal conductivity to for application of refractory bricks. Therefore, high porosity mullite refractory brick is developed using GS (Gelation of Slurry) method that is already developed for production of high porosity metal foam. Appling this method to production of mullite foams, the ceramics foams from 93 to 97% porosity can be produced. Also, their thermal conductivities are proportional to densities and obey to Ashby-Glicksman model. Its thermal conductivity is about 0.07W/mK when density is 0.1 g/cm3. The high porosity mullite foams achieved enough thermal insulating properties for refractory brick.