Phongthorn Julphunthong

Phase formation, microstructure and dielectric properties of Bi0·5(Na0·74K0·16Li0·10)0·5TiO3–Ba(Zr0·5Ti0·95)O3 ceramics prepared via combustion technique

Abstract Binary lead free electroceramics with the composition of (1–x)Bi0·5(Na0·74K0·16Li0·10)0·5TiO3–x(BaZr0·05Ti0·95)O3 or BNKLT–100xBZT with 0·025≤x≤0·150 were synthesised via the combustion technique. The results showed how BZT content affects typical properties of a BNKLT–100xBZT system such as phase formation and dielectric properties. The XRD investigation revealed that BNKLT–100xBZT exhibits the coexistence of rhombohedral and tetragonal phases. By adding BZT, the rhombohedral phase decreases and tetragonal phase increases. From a dielectric properties investigation, BNKLT–100xBZT shows two dielectric loss peaks at ∼190 and ∼320°C defined as Td and Tm respectively. Increasing the BZT fraction makes Tm shift to a lower temperature but has no effect on the Td shifting. The maximum ϵr and ϵmax with their respective values of 1380 and 4050 are observed from the sample with the composition BNKLT–5BZT, which can be attributed to its location near the MPB region.

Investigation of Gamma Ray Shielding and Compressive Strength of Concrete Containing Barite and Ferrophosphorous

This work emphasizes on the improvement of the gamma shielding ability of concrete using heavyweight materials of barite and ferrophosphorous. The physical properties and chemical composition of the selected aggregate materials were also studied. The specific gravity test results suggested barite and ferrophosphorous show excellent characteristics for improving shielding ability due to their high specific gravity of 4.21 and 5.35, respectively. The samples which applied barite and ferrophosphorous as aggregates, show high densities of 3,233 kg/m3 and 4,288 kg/m3, respectively. The sample applied ferrophosphorus material as an aggregate, had the highest linear attenuation coefficients with the highest density. The computed linear attenuation coefficients indicated higher values when compared with measured values due to low homogeneity of samples.

Investigation of Gamma Radiation Shielding of Concrete Containing Blast Furnace Slag Waste via Experimental and Calculation Methods

This study aims to evaluate gamma-ray shielding characteristics of concrete produced from blast furnace slag. The chemical and physical properties of the aggregates including the chemical composition and specific gravity were investigated to evaluate their radiation shielding properties. The samples were prepared with a cement content of 400 kg/m3, a water to cement ratio of 0.4, and fine aggregate of 43% and coarse aggregate ratio of 57%. Blast furnace slag was replaced with sand at 25%, 50%, 75% and 100% by volume to improve the shielding properties. The compressive strengths at 3, 7 and 28 days and the unit weight of the prepared samples were determined. The linear attenuation coefficient was measured and calculated at photon energies of 0.662 MeV, 1.17 MeV and 1.33 MeV. The WinXCom program was employed to calculate the attenuation coefficient from the chemical composition of samples and the results were compared to the measured results. The study results suggest that the use of blast furnace slag is effectively in improving the compressive strength and shielding properties of concrete. The increase of blast furnace slag caused an increase in the linear attenuation from 0.190 cm-1 to 0.210 cm-1 at 0.662 MeV.

Low Temperature Fabrication of Dense Calcium Titanate Ceramics via Combustion Technique

In this work, dense calcium titanate ferroelectric ceramics were successfully synthesized using the combustion technique. Urea, glycine and the mixture of urea-glycine were selected as fuels and added to the mixed powders to accelerate the chemical reaction of raw materials. The mixtures were calcined and sintered from 600 to1150°C and 1150 to 1450°C, respectively. The effects of firing temperatures on the phase formation, crystal structure, microstructure, density and dielectric properties of the prepared samples were investigated. The X-ray diffraction patterns exhibited a pure perovskite structure which was identified for the glycine and urea-glycine mixed samples calcined at 1000°C for 2 h. The calcined powders exhibited an irregular shape and a wide range of particle size distribution at a low calcination temperature. By increasing the calcination temperature, the average particle size tended to increase and the samples expressed a more spherical shape which decreased the particle size distribution. The microstructure, density and dielectric properties results demonstrated that the optimum sintering temperature was 1400°C. The ceramic sintered at this temperature showed dielectric constant and loss of 194 and 0.004, respectively.

Influence of Firing Temperatures on Phase Formation and Microstructure of La0.92Mg0.18Fe0.90O3 Ceramics Synthesized via the Combustion Route

A novel combustion technique has been developed to synthesize La0.92Mg0.18Fe0.90O3 or LMF ceramics. The NH2CH2COOH was used as the fuel to accelerate the chemical reaction of raw materials. Thermogravimetric TG and differential thermal analysis DTA were used to estimate the calcination temperature in the range from 800 to 1000°C. The pure perovskite phase was obtained for the samples calcined at 900°C for 2 h. This calcination temperature was selected for the pellets sintered between 1000°C and 1200°C for 2 h. The effect of calcination and sintering temperatures on the phase and morphology evolution of perovskite LMF was investigated. The XRD patterns indicated that LMF exhibited orthorhombic perovskite structure. With increasing the firing temperatures, the lattice parameters and the unit cell volume changed only slightly; the average particle size and the average grain size tended to increase from 133 to 227 nm and 0.40 to 0.92 μm, respectively. The density of sintered ceramics changed between 3.19 and 3.37 g/cm3 depending on the sintering temperature.

The Effects of Firing Temperatures and Dwell Time on Phase and Morphology Evolution of LaNi0.6Fe0.4O3 Ceramics Prepared via the Combustion Technique

The optimization of the preparation condition of single phase LaNi0.6Fe0.4O3 or LNF by the combustion technique was examined. The phase formation and the crystal structure were investigated using X-ray diffraction pattern. The highest percent of the perovskite phase at 93.5% was exhibited in the sample calcined at 1000°C for 4 h and repeatedly calcined again at 1200°C for 4 h. A higher than optimum calcination temperature lead to an occurrence of a secondary phase which included a tiny amount of La4Ni3O10. After being sintered between 1250–1450°C for 2 h, the pure perovskite phase was obtained from the samples sintered in the range of 1250 to 1350°C while a higher sintering temperature induced a tiny amount La4Ni3O10. Moreover, increasing the sintering temperature affected the crystal structure which changed from rhombohedral to orthorhombic. The SEM observation revealed that the grain boundaries of sintered ceramics melted when the sintering temperature was higher than 1300°C. From the SEM and density investigation, the results proved that the optimum sintering condition is 1300°C for 2 h. Using the combustion technique, both firing temperature and soaked time is lower than the conventional method preparation.