No abstract

The effect of calcination temperatures (900-1400 • C) and sintering temperatures (1400-1650 • C) on phase formation and microstructure of perovskite barium zirconate (BaZrO 3 ) powders and ceramics was investigated. The BaZrO 3 powders were prepared using the combustion technique. The phase purity, crystal structure and microstructure of samples were examined using differential thermal analysis (DTA), thermo gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that BaZrO 3 samples indexed in a cubic structure. The percentage phase purity of perovskite increased with an increase in the calcination temperatures as expected. The purity of perovskite powders was obtained above 1350 • C and the purity phase of ceramics was detected in all samples. The SEM results indicated that the particle size and grain size of samples increased with the increase of calcination and sintering temperatures. The shrinkage of ceramics increased as the sintering temperatures increased. The optimized heat treatment permits sintering a ∼97% highly dense barium zirconate sample at 1600 • C for only 2 h.

This work investigates and improves the thermal dynamics of autoclaved aerated concrete (AAC) wall containing phase change material (PCM). The PCM is paraffin wax loaded into conical holes drilled into the AAC. Filled AAC with three different numbers of PCM-filled holes (2, 3, and 4 conical holes, which are designated as AAC-2H, AAC-3H, and AAC-4H, respectively) as well as the unfilled original AAC were both tested under two different conditions: indoors (with controlled temperature) and outdoors (with actual weather). For the indoor experiment, a heater was used as a thermal source and set up to maintain the testing temperature at one of three levels: 40 °C, 50 °C, or 60 °C. The wall temperature was then measured on the surface with each horizontally-positioned wall as well as four different positions at various depths below the surface of the wall. It was found that AAC-4H was the optimum condition, which can produce outstandingly a time lag of approximately 27%, reduce a decrement factor of approximately 31%, and also decrease the room temperature. This reached approximately 9% when compared with that of ordinary AAC at the controlled testing temperature of 60 °C. All samples were further tested in actual weather to confirm the thermal performances of AAC-4H. Thermal effectiveness of AAC-4H was improved by extending approximately a 14.3% time lag, which reduces approximately a 4.3% decrement factor and achieving approximately 5% lower room temperature when compared with ordinary AAC.

Barium strontium zirconate titanate ((Ba 1−x Sr x )(Zr x Ti 1−x )O 3 ; BSZT, x = 0.25 and 0.75) ceramics with a highly crystalline structure were successfully synthesized using the combustion technique, in which urea performed an important role. The effect of calcination (1000-1300 • C) and sintering temperatures (1300-1550 • C) on the phase formation and microstructure of BSZT ceramics were investigated. The pure perovskite phase of BSZT (x = 0.25 and 0.75) powders with a uniform cubic morphology were detected at the calcination temperature of 1300 • C. At the same calcination and sintering temperature, the lattice parameter a of BSZT powder and ceramics with x = 0.75 is higher than x = 0.25. The microstructure of BSZT powders exhibited an almost-spherical morphology and had a porous agglomerated form. The average particle size and the average grain size of all ceramics increased with the increase of calcination and sintering temperatures, but decreased when the content of x increased. The maximum densities of x = 0.25 and 0.75 ceramics were around 5.85 and 5.62 g cm −3 obtained from the samples sintered at 1500 and 1450 • C, respectively.

The application of AAC has increased considerably in Malaysia since the 1990s. The usage of AAC has some advantages, but it also has negative environmental impacts since rejected concrete will become landfill. This study aimed to use AAC waste powder as a material that would partially replace the sand content to produce a new form of Autoclaved Aerated Concrete (AAC). The physical and mechanical properties of the newly developed AAC were investigated. This paper presents improved mechanical and physical properties of the new form of recycled AAC concrete. Besides these improvements, using recycled AAC could lower production costs. Furthermore, the usage of this recycled waste powder is both economically and environmentally advantageous. This study found that when recycled AAC was substituted for sand, AAC with a fine recycled powder content of 30% had a compressive strength that was around 16% higher than conventional AAC and between 29% and 156% higher than any value attained utilizing an industrial waste product. This study also confirmed that the greater strength could be identical to a higher tobermorite phase and that the recycled AAC surface showed a finer crystalline morphology.