The surface morphology and crystal structure change of dental zirconia after hydrofluoric acid (HF) etching were evaluated. Four groups of sintered zirconia specimens were 1) control group, 2) immersion in 9.5%HF at 25 o C for 1, 2, 3, or 24 h, 3) immersion in 9.5%HF at 80o C for 1, 3, 5, or 30 min and 4) immersion in 48%HF at 25 o C for 30 or 60 min. The specimens were evaluated under SEM and XRD. The SEM analysis revealed changes in surface topography for all the HF-etched zirconia specimens. The irregularities surface increased with increasingly longer immersion times and higher etching solution temperatures. The XRD analysis of the HFetched zirconia specimens revealed the presence of a crystalline monoclinic phase along with a tetragonal form. It was concluded HF can etch dental zirconia ceramic, creating micro-morphological changes. Tetragonal-to-monoclinic phase transformation was induced on the etched zirconia surface.

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A SiC/SiC composite in a disc preform of 120 mm in diameter and 3.2 mm in thickness was fabricated by the chemical vapor infiltration (CVI) process. The composite was reinforced with plain-woven high-crystalline Tyarnno-SA fiber. Microstructure examinations and density measurements indicated a quite dense and very good space homogeneous matrix deposition in the composite. The fracture behavior and statistic reliability of the flexural strength upon three-point bending loading were investigated. The composite had an average flexural strength 597 MPa with a standard deviation 70 MPa. The statistic analysis of the strength showed good consistency among the bending specimens, with a Weibull modulus of 10.2, which is much higher than that for the Nicalon and Hi-Nicalon fibers reinforced CVI-SiC matrix SiC/SiC composites.

In this research, waste gypsum (CaSO4·2H2O), a by-product material from industrial factory, was upgraded and then used as raw material for building materials. The by-product gypsum possessed a high acidic value of 3-point pH scale and moisture content of 40 %. The two properties had an impact on setting reaction and hardening of gypsum. Therefore, the studies of gypsum phase transformation to calcium sulfate hemihydrate (CaSO4·0.5H2O) were focused on washing process and amount of calcium carbonate (CaCO3) added at 0, 1, 3 and 5 % wt. After washing, waste gypsum and washed water were reduced from high acidic value to neutralization (pH = 7) as a result of CaCO3. Next, the neutralized gypsum was heated to the optimal temperature at 160 °C for 2 hours and transformed to hemihydrate gypsum phase observed by XRD. Finally, the relationship of amount of CaCO3-mechanical property such as bending strength will be investigated.

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Reflective pigment was prepared by using Fe2O3 and Al2O3 as starting materials. Fe2O3 and Al2O3 powders were mixed at 0.8:2, 1:2 and 1.2:2 mole ratio using ball milling. The mixed powders were dried and calcined at temperature of 1500°C, 1600°C and 1700°C for various soaking time at 2, 8 and 20 h. Phase data were analyzed by x-ray diffractometry. It was found that (Al1-x, Fex)2O3 presented as a new phase in calcined powders at temperature of 1500°C to 1700°C for 2 h. The other new phase such as FeAl2O4 was detected in calcined powders at temperature of 1700°C for 8 and 20 h. From the experimental results indicated that complete reaction was occurred when higher calcination temperature and longer soaking time were used, resulting in spinel structure (FeAl2O4) generated. Then, the synthesized powders were mixed with exterior paint by mass ratio of 0:100, 10:90, 20:80, 30:70 and 40:60, respectively. The mixed paints were sprayed on metal sheets. Then the coated metal sheets were exposed under 200 watts lamb and measured the temperature difference between the exposed side and opposite side. The result showed that at the ratio of 30:70 exhibited the highest temperature difference of 14°C approximately. From the result, we concluded that spinel structure (FeAl2O4) is a candidate for near-infrared (NIR) reflective pigment of exterior paint.

Magnesium aluminate spinel (MAS) glass-ceramics composite has excellent mechanical and optical properties. It can be obtained from porous ceramic by infiltrating the proper choice of glass. In this study, porous MAS ceramic was prepared by conventional sintering from MAS powder to reach a bulk density of 2.48 g∙cm-3 (70.1% of relative density). The porous MAS ceramic was then infiltrated with molten lithium tetraborate glass (Li2B4O7; LTB) at 950℃ for 30 (IF30) and 60 (IF60) min. They were left to cool down to 700℃ inside the furnace before being taken out to quench in ambient. The glass-ceramics composite was obtained with 98.7% and 92.1% relative density for IF30 and IF60 cases, respectively. SEM images reveal a lower degree of porosity in the IF30 case, which achieves higher flexural strength of 119.7 MPa. X-ray diffraction and Raman spectroscopy indicate that Mg2B2O5 phase (at 2q =35°) and B2O5 functional group (at 847 cm-1) are formed during infiltration. Consequently, their micro vickers hardness increased (3.41®5.53®6.16 GPa).