Nopsiri Chaiyo

Non-isothermal kinetics of the thermal decomposition of sodium oxalate Na2C2O4

The thermal transformation of Na2C2O4 was studied in N2 atmosphere using thermo gravimetric (TG) analysis and differential thermal analysis (DTA). Na2C2O4 and its decomposed product were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique (XRD). The non-isothermal kinetic of the decomposition was studied by the mean of Ozawa and Kissinger–Akahira–Sunose (KAS) methods. The activation energies (Eα) of Na2C2O4 decomposition were found to be consistent. Decreasing Eα at increased decomposition temperature indicated the multi-step nature of the process. The possible conversion function estimated through the Liqing–Donghua method was ‘cylindrical symmetry (R2 or F1/2)’ of the phase boundary mechanism. Thermodynamic functions (ΔH*, ΔG* and ΔS*), calculated by the Activated complex theory and kinetic parameters, indicated that the decomposition step is a high energy pathway and revealed a very hard mechanism.

Preparation and Properties of Lead Free Bismuth Sodium Titanate−Bismuth Zinc Titanate Ceramics

Lead-free piezoelectric ceramics based on (1–x)Bi 1/2 Na 1/2 TiO 3 – x Bi(Zn 1/2 Ti 1/2 )O 3 (x = 0.0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, 0.30, 0.40, and 0.5) were obtained via solid-state processing techniques. The influence of BZT addition on BNT characteristics, sintering, microstructure and properties was investigated. A single perovskite phase with rhombohedral symmetry was obtained for Bi(Zn 1/2 Ti 1/2 )O 3 substitutions of up to 10 mole%. A small amount of BZT was effective for improving both sintering behavior and dielectric properties of BNT ceramics. Optimized dielectric properties were obtained for samples with a maximum density of ρ = 98.3% for the composition, x = 0.1.

Synthesis and Morphology Evolution of Lead-Free Piezoelectric K1/2Na1/2NbO3 Powder at Low Temperature

A synthetic route for modified solid state reaction has been developed for the synthesis of the perovskite phase of potassium sodium niobate, K1/2Na1/2NbO3 (KNN). Potassium oxalate monohydrate (K2C2O4.H2O) and sodium oxalate (Na2C2O4) were employed as a source of potassium and sodium, respectively. The formation of the K1/2Na1/2NbO3 phase was investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology and particle size were determined via an SEM technique. It was found that the minor phases of Na2CO3 and K2CO3 tend to form together with K1/2Na1/2NbO3, depending on calcination conditions. The perovskite phase was successfully synthesized at a low temperature of 400°C. As calcination temperatures increased from 600° to 850°C, the KNN solid solution became more homogeneous, XRD peaks became narrower, and a pattern similar to that expected for orthorhombic K1/2Na1/2NbO3 was achieved after 600°C, as indicated by the separate peaks of 0 2 2 and 2 0 0.

Combustion Synthesis of Lead-free Piezoelectric Alkali Metal Niobate Family

Nano-crystalline alkali metal niobate (ANbO3; A = K and Na) powders were synthesized by the combustion of nitrate compounds and Nb2O5 using glycine as the fuel. The chemical reaction, nucleation mechanisms and influence of the fuel-to-oxidizer ratio to phase formation were studied. The precursor and product powders were characterized, using the thermo gravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) technique, and scanning electron microscopy (SEM). Different fuel-to-oxidizer ratios were found to be a key factor of the process. As-prepared and calcined powders provided the perovskite structure with a nano-scale of mean crystalline size.

Synthesis and Characterization of Thermochromic La0.75Ca0.25MnO3 Perovskite Manganites Nano-powders by Microwave-assisted Solution Combustion Synthesis

The microwave-assisted solution combustion synthesis was developed for application with initially synthesized thermochromic perovskite manganese oxide La0.75Ca0.25MnO3 nano-powders. Dry and very fine powders were obtained after one-step combustion reaction for less than 10 min in a modified domestic microwave oven. The thermal behavior, phase formation and purity of the precursor, and as-synthesized and calcined powders, were investigated by TGA/DTA, X-ray diffraction (XRD) and FT-IR techniques. The morphology of the powder obtained was characterized using a scanning electron microscope (SEM). The XRD pattern and FT-IR results showed that as-synthesized La0.75Ca0.25MnO3 powders were crystalline, and the monophasic perovskite phase occurred with an average crystallite size of 30.46 ± 5.54 nm for 6 h at a relatively low calcination temperature of 900°C. The small particle size obtained by SEM suggested a high specific surface area and high sinterability. This method was found to be simple, rapid and cheap, and an effective way to prepare nano-size perovskite powders.

Rapid Synthesis of Potassium Sodium Niobate (K1/2Na1/2NbO3) Lead-free Piezoelectric Powder Using the Combustion Method

Potassium sodium niobate (K1/2Na1/2NbO3) powder was synthesized successfully by the combustion synthesis. The raw materials of KNO3, NaNO3 and Nb2O5 were used with glycine as fuel. The thermal behaviour of the precursor was determined using thermo gravimetric analysis (TGA) and derivative thermo gravimetric (DTG) analysis. The conditions for preparing perovskite phase formation, influence of the fuel-to-oxidizer molar ratio, and crystal structure were characterized by the X-ray diffraction technique (XRD) and Fourier transform infrared (FTIR) spectroscopy. The morphology and particle size were investigated through a scanning electron microscope (SEM).

Microwave-Assisted Solution Combustion Synthesis and Characterization of Thermoelectric Ca3Co2O6 Powders

The microwave-assisted solution combustion synthesis was applied to the initial synthesizing of Ca3Co2O6 powder using glycine as a fuel and nitrate as an oxidant. The as-synthesized powders were calcined at 700-1,000ºC for 4h. Product characterization was performed using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Scanning electron microscope (SEM). The fuel-to-oxidizer molar ratio was found to affect the combustion reaction and character of the powder obtained. The phase composition of powder after calcination at various temperatures has shown that the formation of Ca3Co2O6 occurs directly. The calcined powder possesses a rhombohedral crystal structure with an X-ray diffraction pattern that could be matched with the Ca3Co2O6JCPDS: 89-0629. This method is a simple way of synthesizing fine Ca3Co2O6 powder with a low calcination temperature.

Facile Synthesis of Lead-Free Piezoelectric Sodium Niobate (NaNbO3) Powders via the Solution Combustion Method

Nanocrystalline perovskite sodium niobate, NaNbO3 (NN), was prepared by means of the glycine-nitrate combustion process (GNP). This was achieved by using sodium nitrate and niobium pentoxide as starting materials. The X-ray diffraction technique (XRD) was used to investigate the phase formation and purity of synthesized powder. The morphology of the powder obtained was characterized using a scanning electron microscope (SEM). The amount of glycine in the starting solution was found to have significant influence on the combustion process and the final phase purity. The fuel-rich ratio (fuel-to-oxidant molar ratio of 1.0) was found to produce NaNbO3 powder of an average crystalline size (defined by XRD) of 31.31 ± 4.37 nm. Calcination at 400°C for 4 h produced single phase NN with an average crystalline size of about 26.60 to 37.14 nm.

Effect of Annealing on the Structure and Dielectric Properties in PZT-PCoN Ceramics

he solid solution between the normal ferroelectric Pb(Zr1/2Ti1/2)O3 (PZT) and relaxor ferroelectric Pb(Co1/3Nb2/3)O3 (PCoN) was synthesized by the solid state reaction method. Sintered PZT-PCoN ceramics were annealed at temperatures ranging from 850 to 1,100°C for 4 h. X-ray diffraction patterns revealed changes of crystalline structure after annealing, which could be correlated to the accompanied changes in dielectric properties. Furthermore, significant improvements in the dielectric responses were observed in this system. After annealing, a huge increase of up to 200% occurred in the dielectric constants, especially near the temperature of maximum dielectric constant.

Synthesis, Phase Formation and Characterization of Co4Nb2O9 Powders Synthesized by Solid-State Reaction

A corundum-type structure of cobalt niobate (Co4Nb2O9) has been synthesized by a solid-state reaction. The formation of the Co4Nb2O9 phase in the calcined powders was investigated as a function of calcination conditions by differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. Morphology and particle size have been determined by scanning electron microscopy (SEM). It was found that the minor phases of unreacted Co3O4 tend to form together with the columbite CoNb2O6 phase at a low calcination temperature and short dwell time. It seems that the single-phase of Co4Nb2O9 in a corundum phase can be obtained successfully at the calcination conditions of 900°C for 60 min, with heating/cooling rates of 20°C /min.