Papers by Keyword: Alumina (Al₂O₃)

Abstract: In the modern world with an extensive improvement of science and technologies, alumina (Al₂O₃) ceramics have been identified as one of the usable materials in production of electronic components. This project attempts to investigate the magnesite (MgCO₃) effect to Al₂O₃ sintering for heat sink application. The effect of MgO percentage varying from 0% to 50% has been in investigated, emphasizing on the flexural strength test, thermal conductivity test, elastic modulus test, shrinkage percentage and density measurement. The result revealed that the MgO give an effect to the final thermal conductivity and mechanical properties of Al₂O₃ material at high sintering temperature (i.e. at temperature of 1600°C). Throughout an X-ray diffraction (XRD) analysis of Al₂O₃ and MgO compositions, it was revealed that spinel, periclase and corundum phases exist for all sintered temperature which contributes to strengthen grain boundaries and improved mechanical properties.

Abstract: Alumina ceramic tools have played an important role in metal working industry as mainly applied ceramic tool materials. They have already become modern ceramic materials with better physical properties and cutting performances. The sorts and developing status of alumina ceramic tools are introduced here. The cutting performances and applications are elaborated. Furthermore, the matching issues are analyzed between alumina ceramic tool and its cutting object.

Abstract: In this paper, aluminum nitride powder was prepared by carbothermal reduction. Alumina and carbon black powder were used as the starting material to synthesize aluminum nitride powder in a nitrogen atmosphere at 1500~1900°C. The experimental data, SEM photographs and XRD analysis showed that higher temperature was conducive to the increase in conversion ratio of Al2O3, the growth of particles, and improving the degree of crystallization and purity of AlN. But it made the particles’ size larger with poor dispersion.

Abstract: The aim of this research is to study the mechanical properties such as hardness ,wear resistance etc , of the magnesium oxide (MgO) doped alumina (Al₂O₃) and yttria stabilized zirconia (YSZ) composite, We first prepared MgO-doped Al₂O₃ (denoted as Al₄) by mixing Al₂O₃ powder and 0.4 wt% of MgO powder. After that Al₄ powder was mixed YSZ powder, with the formula [(x)Al₄ - (100-x)YS when x was varied from 0 - 100 by wt%. The samples were sintered at 1450, 1500, 1550, 1600 and 1650 °C. In addition, microstructure of the surface was studied employing both optical and scanning electron microscopes. The hardness of the surface was investigated by Vickers indentation technique and pin on disk apparatus was employed for wear rate measurement. The results showed that the density and volume shrinkage decreased with the increase of Al₄ content. The grain size and porosity of the specimens tend to decrease when the sintering temperature increases. The hardness and wear resistance of the samples increased with the increase of Al₄ up to 90 %. It was also found that the material is not toxic to the body.

Abstract: This study involved a two-step method of adding multi-walled carbon nanotube (MWCNTs) and alumina (Al₂O₃) nanoparticles to paraffin wax, forming nanocomposite-enhanced phase change materials (NEPCMs). The NEPCMs in a phase change experiment were influenced by the concentrations of the nano-materials and the heating temperature of water. The objective of this paper is to investigate the optimal parameters of added nano-materials. The experimental results show that the phase change temperature of the paraffin wax slightly increases after adding the nano-materials to the paraffin wax. In addition, the nano-materials in the paraffin wax will reduce the temperature difference between test samples and heating water, indicating that adding the nano-materials can effectively reduce the thermal resistance of the experimental samples and improve the efficiency of thermal energy storage.

Abstract: Nanostructured ceramic bulk materials were achieved from nano-Al2O3 ceramic powders via direct selective laser sintering (SLS). SLS as a non-traditional machining technology of Rapid Prototyping was introduced and compared with other ceramic forming technologies. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were applied to analyze the microstructure of the ceramic bulk materials. These results demonstrated that the nano-Al2O3 ceramic powders can be sintered into bulk materials maintained nanostructure with some technological parameters. It was found that the nanostructured ceramic bulk exhibited unique microstructure and was free formed rapidly by this sintering technology.

Abstract: Al2O3 compacts with various phases were prepared by hydrolysis and spark plasma sintering (SPS) process of Al powder. The bayerite (
-Al(OH)3) phase was derived by hydrolysis of commercial Al powder with micron size, whereas the bohemite (AlO(OH)) phase was obtained by hydrolysis of nano Al powder synthesized by pulsed wire evaporation (PWE) method. Compaction as well as dehydration of both bayerite and bohemite was carried out simultaneously by SPS method, which is used to fabricate nano powder into dense compacts with a rapid heating rate of about 100 °C per min. under the pressure of 50 MPa. After compaction in the temperature ranges from 350 °C to 1100 °C, the bayerite and bohemite phases change into various alumina phases depending on the compaction temperatures. The bayerite shows the phase transition of Al(OH)3  -Al2O3  -Al2O3  -Al2O3 sequences. On the other hand, the bohemite experiences the phase transition from AlO(OH) to
-Al2O3 at 350 °C showing AlO(OH) 
-Al2O3  -Al2O3  -Al2O3  -Al2O3 sequences.