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.
In this study, the perlite-based insulating material is developed to meet ASTM C610 standards in a form of the board. Expanded perlite powders with a tapped density of 53 and 150 kg/m³ were used in this study. Sodium silicate used as a proper binder at various concentrations was mixed with perlite powders. The homogeneous moist mixture was formed by uniaxial pressing at different compaction ratios. Specimens were dried at low temperatures (250-400°C). Measurements of physical properties e.g., fl exural strength, bulk density and thermal conductivity, were conducted. Perlite foam was set after drying, leading to an increase in its moisture resistance and strength. Compression molding also affected the density and strength of the products. Heat treatment after forming was carried out in order to dehydrate water molecules and bond particles together. The specimens were tested in accordance with ASTM C610 as a result of optimum conditions from perlite powder with a tapped density of 53 kg/m3. Perlite foam board had been successfully fabricated with a bulk density of 205 kg/m3, fl exural strength of 434 kPa, compressive strength of 764 kPa and room temperature thermal conductivity of 0.056 W/m.K.
PZTs can be classified into two types, i.e., soft and hard PZTs, which are categorized by the piezoelectric and ferroelectric properties such as coercive field, piezoelectric strain, mechanical quality factor etc. It is known that the combination effect of the soft/hard PZT composites can generate large strain/actuation compared to monolithic PZT ceramics. In this study, soft and hard PZT powders were co-pressed into bi-layer disks with various ratios between soft and hard PZT powders, ranging from 0:100~100:0 vol. % (with 10 % increments) and then they were co-sintered. Due to the difference in the planar shrinkage of the two layers and thermal expansion coefficient mismatch, dome-shaped bi-layer composites with various dome heights were obtained. It was shown that the constrained layer either soft PZT or hard PZT affected various properties including the dome geometry, the strain-E-field response, and the displacement hysteresis loop. The electromechanical properties and actuation performance of such bi-layer composite actuators have been investigated and compared to the soft and hard PZT single layer counterparts.
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