Atthakorn Thongtha

Phase Formation and Microstructure of Barium Zirconate Ceramics Prepared Using the Combustion Technique

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.

Fabrication and Characterization of Perovskite SrZrO3 Ceramics through a Combustion Technique

Perovskite SrZrO3 ceramics were successfully prepared via a combustion technique. The effect of calcination temperatures (900-1400oC) and sintering temperatures (1400-1650oC) on phase and morphology evolution of perovskite SrZrO3 ceramics were studied. The highest purity of perovskite phase powder was obtained at 1250 oC and the purity of the perovskite phase of SrZrO3 ceramics were detected in the samples sintered at 1550 oC for 6 h. The SEM results showed the average particle size (84-214 nm) and the average grain size (0.35-2.09 µm) of samples increased with the increase of firing temperatures. The shrinkage of the ceramics increased as the sintering temperatures increased. The maximum density was ~98.4% of the theoretical density for the sample sintered at 1550 oC for 6 h.

Effect of Firing Temperatures on Phase and Morphology Evolution of CaZrO3 Ceramics Synthesized Using the Combustion Technique

The effects of calcination temperatures (900–1400°C) and sintering temperatures (1400–1650°C) on phase and morphology evolution of perovskite CaZrO3 ceramics were studied. The results obtained from DTA-TGA analysis were used to determine the processed conditions of various calcination temperatures. The highest purity of the orthorhombic perovskite phase was obtained from powder calcined at 1200°C and the pure phase was detected in sintered ceramic samples below 1650°C. The SEM results showed that the average particle size and the average grain size of samples increased with the increase of firing temperatures. The shrinkage of ceramics increased as the sintering temperatures increased. The calcium zirconate, which had around 97.6% of the theoretical density, was obtained from the sample sintered at 1500°C for 2 h. More importantly, the highest density with low sintering temperature were be improved by the combustion technique.

Optimum Sintering Temperature for Fabrication of 0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3 Lead-Free Ceramics by Combustion Technique

The effect of sintering temperatures (1050-1200 °C) on the phase formation, microstructure and dielectric properties of a binary system lead-free ceramic bismuth sodium titanate–bismuth potassium titanate were investigated. 0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3; BNKT ceramics were successfully fabricated using the combustion technique. XRD results showed the rhombohedral-tetragonal morphotropic phase boundary (MPB). The SEM results showed the average grain size (0.51-2.59 µm) of the samples increased with the increase of sintering temperatures. The sample sintered at the optimum temperature of 1150 °C exhibited the maximum density, shrinkage, dielectric constant at Curie temperature and remanent polarization (Pr) which were around 5.65 g/cm3, 17.75%, 5014 and 1.6 mC/cm2, respectively. The dielectric constant was related to the XRD results and density of the sintered ceramic.

Influences of Firing Temperatures on Phase and Morphology Evolution of (Ba0.25Sr0.75)(Zr0.75Ti0.25)O3 Ceramics Synthesized via Solid-State Reaction Method

The effect of calcination (1000-1400 oC) and sintering temperatures (1400-1600 oC) on the phase formation and microstructure of barium strontium zirconate titanate [(Ba0.25Sr0.75)(Zr0.75Ti0.25)O3; BSZT] ceramics were investigated. BSZT powders were prepared by the solid-state reaction method. Higher calcination temperatures increased the percentage of the perovskite phase, but decreased the lattice parameter a of BSZT powders. The pure perovskite phase of BSZT powders was detected above the calcination temperature of 1350 oC. 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 the ceramics were increased with the increase of calcination and sintering temperatures. The highest density of the samples was 5.42 g/cm3 which was obtained from ceramic sintered at 1550 oC for 2 h.

Preparation of (Ba1−xSrx)(ZrxTi1−x)O3 Ceramics via the Solid State Reaction Method

The effect of calcination (1000–1400°C), sintering temperatures (1400–1650 °C) and the changing of ions in A and B sites on the phase formation and microstructure of barium strontium zirconate titanate (Ba1−xSrx)(ZrxTi1−x)O3, BSZT, x = 0.25 and 0.50 ceramics were investigated. BSZT powders were prepared by the solid state reaction method. It was found that BSZT samples indexed in a cubic structure. Higher calcination temperatures increased the percentage of the perovskite phase. The pure perovskite phase of BSZT with x = 0.25 was detected above the calcined temperature at 1400°C. For the x = 0.50, the second phase of BSZT with x = 0.25 was found at all calcination temperatures. The purity phase was detected in all the ceramic samples. At the same sintering temperatures, the lattice parameter a of BSZT ceramics with x = 0.50 has higher than with x = 0.25. The microstructure of the BSZT powders exhibited an almost-spherical morphology and had a porous agglomerated form. The average particle size (160–420 nm) and average grain size (0.68–12.45 μm) increased with the increase in calcination and sintering temperatures. The optimized density, around 5.64 and 5.42 g/cm3 for x = 0.25 and 0.50, were obtained from BSZT samples calcined at 1500 and 1550°C for 2 h.

Phase Formation, Microstructure and Dielectric Properties of Bismuth Potassium Titanate Ceramic Fabricated Using the Combustion Technique

The effect of sintering temperature (975–1025°C) on crystal structure, microstructure and dielectric properties of perovskite bismuth potassium titanate (BKT) ceramics was investigated. The pure BKT ceramics were firstly prepared using the combustion technique. The phase purity, crystal structure and microstructure of samples were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The purity phase of BKT samples, which has a tetragonal structure, was observed in all samples. The lattice parameters a, c and the tetragonality tended to decrease with increased sintering temperature. The SEM result showed the average grain size increased (0.37–0.58 μm) with the increase of sintering temperature (975–1025°C). The shrinkage of the ceramics increased when the sintering temperature increased. The maximum density and dielectric constant at Curie temperature were around 5.71 g/cm3 and 3850, and were obtained from the sample sintered at 1020°C for 2 h. Importantly, the preparation using the combustion technique can improve the density and dielectric properties of BKT ceramics.

Improving Mechanical Properties of Autoclaved Aerated Concrete by Sugar Sediment

The comparison of microstructure and mechanical properties between the autoclaved aerated concrete (AAC) and the autoclaved aerated concrete consist of sugar sediment (AAC-SS) was investigated in this work. The microstructure of AAC and AAC-SS was analyzed by the scanning electron microscopy (SEM). The mechanical properties of AAC and AAC-SS were focused on the compressive strength, the density, the water absorption and the flexural strength. To comfirm the tobermorite phase, the phase formation of the samples was tested using X-ray diffraction (XRD). It was found that the microstructure of AAC and AAC-SS surface was the finer needle-like crystalline morphology. The compressive strength (5.9 N/mm2) and flexural strength (1.82 N/mm2) of AAC-SS were higher than that of the AAC (5.0 N/mm2 and 1.64 N/mm2). While, the value of density (0.60 g/cm3) and humidity (23.59%) of AAC-SS had little less than that of the AAC (0.61 g/cm3 and 24.11%). The increasing of the tobermorite phase, which was added by the sugar sediment, had affected to the improvement of the mechanical properties. The specimens of both AAC and AAC-SS were claimed in quality class of 4, which based on the Thai Industrial Standard 1505-1998.

Phase formation and dielectric properties of (Pb0.925Ba0.075)(Zr1− x Ti x )O3 ceramics prepared by the solid-state reaction method

Lead barium zirconate titanate [(Pb0.925Ba0.075)(Zr1− x Ti x )O3] ceramics with 0 ≤ x ≤ 1 were prepared by the solid-state reaction method. The calcination temperatures were between 800°C and 1000°C for 1 h and the sintering temperature was 1200°C for 3 h. It was found that the structure of the calcined powders and sintered pellets was in an orthorhombic phase for x = 0; a rhombohedral phase for x = 0.25 and a tetragonal phase for 0.5 ≤ x ≤ 1. The c/a ratio increased with an increase in the x content. The average particle size and density slightly decreased with an increase in the x content, while the average grain size, linear shrinkage, and Curie temperature increased when the x content increased.

Effects of Calcination Temperatures on Phase and Morphology Evolution of (Ba0.25Sr0.75)(Zr0.75Ti0.25)O3 Powders Synthesized via Solid-State Reaction and Combustion Technique

The effect of calcination temperatures (1000-1400 oC) on the phase formation and microstructure of barium strontium zirconate titanate [(Ba0.25Sr0.75)(Zr0.75Ti0.25)O3 ; BSZT] powders were investigated. BSZT powders were prepared and compared by the solid state reaction method and the combustion technique. The higher calcination temperatures increased the percentage of the perovskite phase, but decreased the lattice parameter a. The same crystallographic pure perovskite phase of BSZT powders, which were prepared via the combustion technique were detected above 1300 oC ; which was lower than the calcinations temperature of mixed oxide method by 50 oC. The TGA-DTA results corresponded to XRD investigation. The microstructure of BSZT powders, which were prepared using both techniques, exhibited an almost-spherical morphology and had a porous agglomerated form. The average particle sizes of BSZT powders prepared via the combustion technique (0.13-0.30 µm) and the solid state reaction method (0.18-0.38 µm) were increased with the increase of calcinations temperatures