Single-phase calcium titanate (CaTiO3) was successfully synthesized by mechanical milling and the solid-state reaction of CaCO3 and TiO2. The speed of high energy ball milling was 700 rpm with the ball and jar were made from stainless steel. The milling time and ball to powder ratio was 10 h and 50 h, respectively. After milling for 10 h, the mixed powder of CaCO3 and TiO2 experienced heavy milling, which indicated by the average particle size before and after milling was > 1 µm and 85.56 ± 35.62 nm, respectively. Furthermore, the XRD pattern of milled powder revealed the disappearance of CaCO3 peaks and a considerable reduction of TiO2 peaks after milling for 10 h. Moreover, the presence of CaTiO3 peaks in the milled powder was noticeably detected in the XRD pattern, showing the mechanical alloying of CaCO3 and TiO2 was occurred. The milled powder was calcined at 800, 900 and 1000°C for 2 h. The results showed the formation of a single phase of CaTiO3 after calcination at any temperatures. However, the samples indicated the presence of Fe2O3, which from the milling media. The presence of impurities after milling is inevitable due to friction between ball and jar. Further study is needed to obtain the optimum condition of mechanical milling to minimize the contamination.
Nano-sized manganese oxide was synthesized by the solvothermal method. Manganese sulfate was used as a precursor, which is obtained from the Sumbawa manganese ore. Two kinds of the precipitating agent, ammonium persulfate and sodium hydroxide, were used in this study and the effect on the solvothermal product were examined thoroughly. The solvothermal temperature and time were 120°C for 18 hours, respectively, for both precipitating agents. The results showed that the phase of manganese oxide was influenced by the precipitating agent, as indicated by X-ray diffraction analysis. Phase <x-MnO2 was obtained from the reaction between MnSO4 and ammonium persulfate, while Mn3O4 for the sodium hydroxide. The formation of a-MnO2 was influenced by the excess of NH4
+ which came from the manganese ore leaching into MnSO4. One notable finding in this study is that the morphology of manganese oxide was also affected by the precipitating agent. For instance, the shape of MnO2 and Mn3O4 was needle and sphere, respectively. Moreover, the strict long thinner needle of <x-MnO2 was formed and the aspect ratio increased at a higher temperature. While the particle size of Mn3O4 decreased with the increased temperature. These results imply that variation of a precipitating agent is imperative to obtain the specific manganese oxide product, including the shape.
Dense silicon carbide (SiC) was successfully sintered from amorphous polysilazane (PSZ) using hot pressing at 1750oC for 1 hour under an applied pressure of 20 MPa in Ar atmosphere. The effect of β-SiC powder as a filler on the density, phase, micro structure and hardness were examined. Al2O3 and Y2O3 were used as sintering additives through the liquid phase sintering mechanism. The phase analysis showed the formation of SiC after sintering of amorphous PSZ. However, α-SiC was a dominant phase and the amount of α-SiC decreased with the addition of β-SiC powder. The relative density of sintered SiC was obtained in range 99.6 -99.7% regardless of the addition of β-SiC powder. Sintered SiC from amorphous PSZ revealed significant shrinkage compared to sintered SiC from β-SiC powder, while the minimum shrinkage was achieved by the addition of 70% β-SiC into amorphous PSZ. However, the hardness of sintered SiC did not correlate with the addition of β-SiC powder, with highest hardness of 26.4 GPa, which is SiC from solely β-SiC powder. This result indicates that amorphous PSZ is an alternative precursor to fabricate dense SiC.
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