Conventional Sintered Samples Research Articles

Microwave sintering of β-SiAlON–ZrO 2 composites

Densification, phase transformation, microstructure evolution and hardness of microwave sintered β-SiAlON–ZrO 2 composites were investigated and compared with conventionally sintered samples. Sintering trials were performed by a high vacuum capable 2.45 GHz microwave furnace without decomposition. Microwave sintered samples showed better densification behavior than conventional sintered samples. The higher density observed in the case of microwave sintered samples was attributed to volumetric fast heating. X-ray diffraction results of conventionally sintered samples showed β-SiAlON, tetragonal ZrO 2 and ZrN phases, while, ZrO 2 reacted with nitrogen and completely transformed to ZrN in the case of microwave sintered samples. The aspect ratios of microwave sintered β-SiAlON grains were higher than conventional sintered samples whereas, hardness remained lower.

Comparative Study between Conventional and Microwave Sintered Lead-Free BNKT Ceramics

Lead free [(1-x)Bi 0.5 Na 0.5 TiO 3 -(x)Bi 0.5 K 0.5 TiO 3 ] ceramics with x = 0.18 were prepared by using microwave sintering technique. XRD of these ceramics show co-existence of tetragonal and rhombohedral phases. Smaller grain size and more uniform microstructure were observed in microwave sintered sample. It might result from different diffusion mechanism. The activation energy of grain growth was calculated. The results display in microwave sintered sample is lower (167kJ/mol) than that for conventional one (260kJ/mol). It implies microwave sintered sample just need lower energy for densification. The remanent polarization and piezoelectric constants of microwave sintered samples are higher than that of conventional sintered samples. Relation among processing kinetics, microstructural characteristics and electrical properties was discussed.

A comparative study of Ba0.95Ca0.05Zr0.25Ti0.75O3 relaxor ceramics prepared by conventional and microwave sintering techniques

Abstract A comparative study on the dielectric properties of (Ba0.95Ca0.05Zr0.25Ti0.75O3 (BCZT) ) bulk ceramics prepared by conventional and microwave sintering (MWS) has been done. High-density ceramic materials were obtained in 4 h of cycle time for microwave sintered sample whereas it took 22 h for conventional method. Samples prepared by both sintering techniques showed single-phase formation in XRD with cubic structure. The dielectric properties of the samples were measured as a function of temperature in the frequency range of 100 Hz–100 kHz. Relaxor behaviour was observed in both types of samples. It was observed that the peak value of dielectric constant was higher for microwave sintered sample compared to conventional one and also the dielectric loss was lower. The value of activation energy was found to be ∼0.53 eV and 0.29 eV for microwave sintered and conventional sintered samples, respectively.

Thermal plasma-sintered Ti-doped Al—Zr oxide composites: X-ray photoelectron spectroscopy studies

Ti-doped Al—Zr oxide composites (Zr1− x–Al1+ x–Ti x–O y with x = 0.05, 0.1, 0.15) were sintered to high density end products by an extended arc DC thermal plasma heating technique within a short sintering time as compared with a conventional long range resistive heating schedule. Thermal plasma-sintered samples showed conducting behaviour at room temperature whereas conventional-sintered samples became highly resistive. Specimens were analysed by X-ray photoelectron spectroscopy, X-ray diffraction, and Electron Probe Micro Analyzer studies. Higher binding energy of Zr 3d lines in a plasma-sintered sample showed that ZrO2 has strongly reacted with TiO2, thereby enhancing the possibility of ZrTiO4 phase formation. The increase in Al 2p binding energy for a conventional-sintered sample indicated the reaction of Al2O3 with TiO2, which was likely to enhance Al2TiO5 phase formation. XRD and scanning electron microscope analysis along with density studies corroborated this finding. The existence of elemental Ti at 453.3 eV and the presence of TiC at 455.2 eV were found to be responsible for conducting behaviour of plasma-sintered composites.

Thermal plasma assisted rapid sintering of MgO-doped Al–Zr oxide composites

MgO-doped Al–Zr oxide composites of Zr 0.95Al 1.05Mg x O with x = 0, 0.01, …, 0.05, 0.75, 1 were sintered to high density by both dc thermal plasma assisted rapid sintering as well as conventional sintering. It was observed that the above mentioned MgO-doped Al–Zr oxide composites were sintered to high density end products by the thermal plasma heating technique within a short sintering time (a few minutes) as compared to a conventional long range resistive heating schedule (a few tens of hours). Moreover, the densities of plasma sintered samples were found to be more than that of conventional sintered samples. It was also noticed that there exists a critical limiting point of MgO doping concentration ( x = 0.05 in Zr 0.95Al 1.05Mg x O) for maximum physical densification in both conventional as well as plasma sintered samples. Sintered specimens were analyzed by XPS, XRD and EPMA studies. XRD, XPS and EPMA studies revealed the presence of a high density phase, Mg 2Zr 5O 12 prominently in x = 0.05 sintered sample which resulted in maximum densification of the sample. Thus, MgO doping in small amounts promotes physical densification.

High- K dielectric PZN-based materials prepared by microwave sintering for reduction of defects

The high- K dielectric ceramics of x(0.94Pb(Zn 1/3Nb 2/3)O 3+0.06BaTiO 3)+(1− x)PbZr y Ti 1− y O 3 (PBZNZT) have been prepared by conventional sintering (CS) and microwave sintering (MS). The dielectric properties were improved by MS process when the sintering temperature was increased. The dielectric constants of MS samples increase with the sintering temperature due to the larger grain size. The MS process not only can enhance the homogeneity but also suppress the segregation of PbO and ZnO to grain boundaries. This leads to the substantial improvement on the dielectric properties of PBZNZT samples. The maximum dielectric constant of MS samples sintered at 1100 °C for 2 h is about 25,200, which is markedly greater than that of CS samples.

POLARIZATION REVERSAL AND ELECTROMECHANICAL STUDIES ON Ba(NdxTi1-2xNbx)O3 DIELECTRIC RELAXOR CERAMICS PREPARED THROUGH CONVENTIONAL AND MICROWAVE SINTERING ROUTE

Polarization and capacitance studies as a function of applied electric field were done on the Nd and Nb -doped polycrystalline ceramic samples. The result indicates that the ceramic samples show low values of remnant polarization. The capacitance value indicates that microwave sintered samples shows higher capacitance tunability when compared to conventional sintered samples. The results obtained from electromechanical studies are also discussed.

Microwave Plasma Sintering and In Vitro Study of Porous HA/β-TCP Biphasic Bioceramics

Porous HA/β-TCP biphasic calcium phosphate (BCP) bioceramics were prepared by microwave plasma in order to solve the problems on sintering of Ca-P bioceramics by a conventional furnace. The plasma-sintered samples exhibit a higher densification rate, smaller grain size and higher compressive strength compared to those of conventional sintered samples. The [Ca2+] concentration and the dissolution rate are also higher than those of conventional sintered samples in physiological saline. After immersed in simulated body fluid (SBF) and simulated inflammation body fluid, the amount of bone-like apatite formed on plasma-sintered samples is more than that formed on conventional sintered samples. The results indicate that plasma sintered porous BCP bioceramics have better mechanical properties and may also have better biological properties. On the other hand, the surface of samples that underwent a simulated inflammation procedure is smoother and the amount of bone-like apatite formed on them is less than that formed on the samples immersed in normal SBF all the time, which may indicate that the light acid in an inflammation response would affect the bone reconstruction when Ca-P bioceramics implanted in living body.

The low field microwave effective linewidth in polycrystalline ferrites

High precision measurements on the low and high field effective linewidth ΔHeff at 10GHz have been made on ultradense (UD) and conventionally sintered (CS) polycrystalline yttrium iron garnet (YIG) materials. The high field data confirm previous results on the role of two magnon scattering to low wave number (k) electromagnetic Larmor branch spin waves that lie below the light line. The low field data reveal two important contributions to the effective linewidth. For a field regime from the low k edge of the usual dipole exchange spin wave band down to the point in field (H=HX) where above-the-light-line electromagnetic branch Larmor (EML-HI) spin waves appear, ΔHeff is connected with scattering to relatively high k dipole exchange Larmor (DEL) spin waves. The coupling to these modes comes from grain boundaries in the YIG materials. A grain boundary scattering theory gives reasonable agreement with the data. While the high field effective linewidth due to pseudo in-manifold scattering is larger for the CS samples compared to that for the UD samples, the high k DEL scattering is larger for the UD samples compared to that for the CS samples. This is due to the dominant role of the grain boundaries in the low field ΔHeff. For fields below HX, additional scattering appears for the EML-HI modes. The abrupt appearance of an additional ΔHeff component for H<HX provides direct experimental evidence for the presence of such modes in the spin wave dispersion. Part of the loss contribution for H<HX may be due to subthreshold nonlinear effects.

Electric Fatigue in Ferroelectric Lead Zirconate Stannate Titanate Ceramics Prepared by Spark Plasma Sintering

Ferroelectric lead zirconate stannate titanate ceramics were prepared by spark plasma sintering (SPS). Compared with its counterpart densified by conventional sintering (CS), the SPS material shows a smaller remanent polarization and maximum strain as well as a higher coercive field. Electric fatigue in both materials was investigated. In contrast to CS samples, the SPS specimens show a lower resistance to bipolar electric cycling, characterized by a faster decrease in remanent polarization and maximum strain at cycle number below 106.5 and a subsequent slower reduction of the properties at high cycle numbers up to 108.

Effect of the composition and sintering process on the electrical properties in Pb(Mg 1/3 Nb 2/3)O 3–PbTiO 3 ceramics

The effects of the composition and the sintering process on the ferroelectric, dielectric and electromechanical properties in (1– x)Pb(Mg 1/3Nb 2/3)O 3– xPbTiO 3 ceramics with 0.1⩽ x⩽0.4 were investigated. It was found that the densification process was strongly dependent on the amount of PT. For the lowest concentration of PT the microstructure of the both hot-pressed and conventional sintered samples were very similar, reflecting in almost identical electrical properties. Nevertheless, it was noticed that the higher amount of PT higher was the deviation of the electrical properties between the conventional and the hot-pressed samples. The gradual decreasing of the physical properties of the conventional sintered ceramics was related to the gradual decrease of the density and inhomogeneous microstructure. The results also revealed that for the lower concentration of lead titanate a relaxor behavior is noticed with a high electrostrictive effect, which was almost hysteretic free. However, higher amount of lead titanate led to a “normal” ferroelectric behavior.

Development of low-power loss Mn-Zn ferrites using microwave sintering method

Microwave sintering (MS) method has been successfully used for densifying Mn- Zn ferrites used for high frequency applications. This method needs only a short time to obtain high density when compared to conventionally sintered (CS) Mn- Zn ferrites. The lowest power loss was also achieved at 100 kHz and 200 mT condition for the microwave sintered samples. Conductor- embedded ferrite transformers were constructed using CS and MS samples and output power, efficiency, and surface rise of temperature were measured at sinusoidal voltage of 25 V with frequency, 1 MHz. The efficiency and surface rise of temperature of transformer were found to be high and low, respectively.

ＨＩＰ／ＣＩＰおよび関連技術 焼結方法の異なる多孔質アルミナの内部摩擦現象

Internal friction phenomena of porous alumina were investigated to evaluate the damping capacity. Raw powder was formed into a rectangular parallelepiped by a uniaxial press, then cold isostaticaly pressed. The compacts were sintered by conventional sintering and capsule-free-Hot Isostatic Pressing (HIPing) at various temperatures between 1150 to 1500°C for 1h. Internal friction phenomena were evaluated by Q-1 obtained by resonance method. The value of Q-1 for conventional sintered samples were higher than that for HIPed ones at a given porosity and for a given Young's modulus. For the samples sintered at the same temperature, Q-1 showed a similar tendency. We reported previously that capsule-free-HIPing can enhance surface diffusivity by gas pressure. It is concluded that sintering process affects damping capacity on porous alumina, Young's modulus and damping capacity of porous alumina can be controlled independently by controlling the diffusion process.

Preparation yttria-stabilized zirconia electrolyte by spark-plasma sintering

Miscellaneous sintering conditions of spark-plasma sintering (SPS) were investigated to obtain high-density yttria-stabilized zirconia (YSZ) electrolytes for solid oxide fuel cells (SOFC). Nano-size YSZ raw powder (50 nm) was densified to a relative density of 99.1% at 1400 °C, with an applied uniaxial pressure of 23 MPa, and a total of four consecutive sintering cycles at 3 min per cycle. Impedance spectroscopy was used to elucidate the electrical properties of the YSZ electrolyte. It was found that SPS could significantly improve the ionic conductivity of the YSZ electrolyte over conventional sintered (using an electrical resistance furnace) samples at similar sintering temperatures. These phenomena were due to the diverse microstructures obtained by SPS samples as compared to the conventional sintered samples. For SPS samples, most of the pores were found to exist within the grains. While for the conventional sintered sample, most of the pores were encountered at the grain boundaries, which would significantly increase the grain boundary resistance in the samples.

Microstructure and strength modification of relaxor ferroelectric ceramics through microwave sintering for multilayer capacitors

Relaxor ferroelectric ceramics with the composition ofxPb(Mg1/3Nb2/3)O3-yPb(Zn1/3Nb2/3)O3-zPbTiO3 was fast sintered in a 2.45 GHz microwave system. Microwave-sintered samples illustrate more rapid densification and much smaller grain size microstructure than conventional sintered samples. Also the microwave processing significantly increases the dielectric strength and flexural strength of the relaxor so that its strength becomes comparable with modified BaTiO3, and could obtain comparable dielectric properties in comparison with conventional sintering process. Microwave processing has many advantages for sintering of relaxor ferroelectric ceramics used as multilayer capacitors.

Fluorescence of Nd 3+ in lithium yttrium fluoride

The effects of vacuum sintering and conventional sintering on the structure and high-temperature electrical properties of Ca1-xYxCeNbWO8 ceramics have been comparatively studied. X-ray diffraction (XRD) result shows that the conventional-sintered ceramic is a single CaWO4 phase with a scheelite structure, whereas the vacuum-sintered ceramics are composed of a major CaWO4 phase with scheelite structure and a minor CeNbO4 phase with fergusonite structure. The grain size of the conventional-sintered Y-doped ceramics is smaller than that of the undoped samples. The grain size of the vacuum-sintered samples increases firstly and then decreases with increasing the Y concentration. The activation energy of the conventional-sintered and vacuum-sintered ceramics all decreases with increasing the Y content. The activation energy of the vacuum-sintered samples is smaller than that of conventional-sintered samples at the given compositions. The change of activation energy should be attributed to the variation of Ce3+ ion concentration.