Solid-phase Sintering Process Research Articles

Thermal properties of NBT-BT systems

ABSTRACTA conventional solid-phase sintering process was used to fabricate the (1 − x)Na0.5Bi0.5TiO3-xBaTiO3 ceramics (x = 0, 0.04, 0.06, 0.08 and 0.1). X-ray measurements showed that all samples have a perovskite structure. The bulk density of the obtained samples exceeds 95% of the theoretical density. The thermal (DSC, dilatometry) and dielectric properties of these ceramics were investigated in a wide temperature range. Anomalies of the thermal expansion strain were observed at the temperatures which are not related to any phase transitions. The transition temperatures observed by means of thermal measurements are in good agreement with those obtained from dielectric studies.

Effects of PbTiO3 doping on electric properties of Na0.5Bi0.5TiO3 ceramics

ABSTRACTGood quality ceramics of (1−x)Na0.5Bi0.5TiO3(NBT)−xPbTiO3 (PT) (x = 0, 0.03 and 0.05) were prepared by a conventional solid-phase sintering process. The temperature dependence of the dc, ac conductivity ( respectively), the Seebeck coefficient (α), the concentration of charge carriers n and their mobility μ were investigated. The dc conductivity for pure NBT possesses three linear parts with three different activation energies Ea. For 0.97NBT–0.03PT and 0.95NBT--0.05PT ceramics, the dc conductivity also has three linear parts (three different Ea). On the other hand, the ac conductivity possesses three linear parts for pure NBT and four for other compositions. The possible origin of the observed effects is discussed. We suggest that the presented materials can be a good starting point for the development of low-lead electronic ceramics.

Properties of Na0.5Bi0.5TiO3 ceramics after Ba2+ doping

ABSTRACTThe (Na0.5Bi0.5)1-xBaxTiO3 ceramics (x = 0.12, 0.125, 0,13) were fabricated by conventional solid phase sintering process. The samples were characterized by the bulk density which exceeds 95% of the theoretical density. The X-ray diffraction analysis shows an increase of lattice parameters with the rise in Ba2+ content. The electric permittivity broad anomaly is shifted to a lower temperature range after Ba doping of NBT. The hysteresis loops measurements also show changes in comparison to pure NBT. Relaxor behavior of investigated materials was revealed.

Raman and dielectric studies of 0.95Na0.5Bi0.5TiO3-0.05PbTiO3 ceramic

ABSTRACT0.95Na0.5Bi0.5TiO3-0.05PbTiO3 ceramic was prepared by a conventional solid phase sintering process. X-ray diffraction analysis shows that the obtained specimens possess perovskite structure with rhombohedral symmetry. The microstructure study showed a dense structure, in good agreement with the relative density of above 95% as determined by the Archimedes method. The crystal structure, phase transitions behavior and dielectric properties of these ceramics were investigated. Relaxor-like behavior was revealed.

Dielectric and ferroelectric properties of NBT-BT systems

ABSTRACTThe (1-x)Na0.5Bi0.5TiO3- xBaTiO3 ceramics (x = 0.1, 0.135 and 0.17) were fabricated by a conventional solid phase sintering process. The bulk density of the obtained samples exceeded 95% of the theoretical relative density as determined by Archimedes method. Dielectric and ferroelectric measurements of these ceramics were performed. Measurements of the ferroelectric properties show that, above the depolarization temperature Td, the shape of the hysteresis loops approaches that of linear dielectrics. The dielectric study results correlate with the hysteresis loops measurements. The relaxor-like behavior of the investigated materials was revealed.

Effect of Ba doping on the structural, dielectric and ferroelectric properties of Na0.5Bi0.5TiO3 ceramics

ABSTRACTThe (Na0.5Bi0.5)1-xBaxTiO3 (x = 0, 0.08 and 0.09) ceramics are fabricated by a conventional solid phase sintering process. X-ray diffraction analysis and Raman spectra show that the specimens possess perovskite structure with rhombohedral (for x = 0) and tetragonal (for x = 0.08 and 0.09) symmetry at room temperature. The microstructure study shows a dense structure in good agreement with above 95% relative density as determined by Archimedes' method (immersion liquid: distilled water). The main broad anomaly in dielectric permittivity is shifted to lower temperatures and local anomaly shows relaxor behaviour after Ba doping of NBT. The pyroelectric and hysteresis loops measurements show that polarization increases and coercive field decreases, for increasing Ba doping of NBT. The results are discussed in terms of ions/lattice imperfections, which create local electromechanical fields. The investigated ceramics are considered to be promising candidates for lead-free electronic materials.

Effect of PMN addition on the structural, dielectric and ferroelectric properties of BT ceramics

ABSTRACTThe (1-x)BaTiO3-xPb(Mg1/3Nb2/3)O3 ((1-x)BT-xPMN) system with low content of PMN (x = 0, 0.025, 0.05 and 0.075, 0.10 and 0.15) was fabricated by a two-step conventional solid phase sintering process. X-ray diffraction analysis show that the obtained specimens possess the perovskite structure with tetragonal symmetry and undergo a sequence of phase transformations characteristic pure of BT. The microstructure study showed a dense structure, in good agreement with that of above 95% relative density determined by the Archimedes method. Electric permittivity anomaly is shifted to low temperature after PMN doping of BT. The pyroelectric and hysteresis loop measurements show that polarization and coercive field decreases after PMN doping of BT. The results obtained are discussed in terms of ions/lattice imperfections, which create local electrical and mechanical fields. The investigated ceramics are considered to be a good starting point for low-lead electronic materials.

Rapid Fabrication of Eutectic Ceramic Structures by Laser Engineered Net Shaping

Rapid fabrication of dense ceramic structures with high-purity and complex geometry is of high demand, however, it is difficult to attain by traditional solid-phase sintering. In this paper, laser engineered net shaping system and Al2O3, Y2O3 powders were utilized to fabricate ceramic structures directly without doping any binders. Influences of laser power on shaping feature were investigated by experiments and optimal process parameters were successfully achieved. Net-shaped structures of thin-wall and hollow cylinder were attained with about 15mm section sizes. Microstructure features and properties of fabricated specimens were studied by XRD, SEM and Vickers, respectively. The deposited ceramic shows almost 100% density and stable phases mainly consisting of α-Al2O3 and YAG. Microhardness is comparable to that of the product fabricated by laser zone surface melting method. The results of this research indicates that this new fabrication technique for ceramic has more flexibility compared to traditional solid-phase sintering process, and can be used for rapid fabricating of pure and complex ceramic structures.

Effect of Ba addition on the structural, dielectric and ferroelectric properties of Na0.5Bi0.5TiO3 ceramics

Abstract Lead-free (Na0.5Bi0.5)1-xBaxTiO3 (x = 0, 0.04 and 0.06) ceramics were fabricated by conventional solid phase sintering process. X-ray diffraction analysis shows that obtained specimens possess the perovskite structure. The microstructure study shows a dense structure, in good agreement with the relative density determined by the Archimedes method (above 95 %). Electric permittivity anomaly is shifted to low temperature after Ba doping of NBT. The pyroelectric and hysteresis loops measurements show that polarization and coercive field increases and decreases, respectively, after Ba doping of NBT. The obtained results are discussed in terms of ions/lattice imperfections, which create local electromechanical fields. The investigated ceramics are considered to be promising candidates for lead-free electronic materials.

Uniaxial tensile behavior of porous metal fiber sintered sheet

A novel porous metal fiber sintered sheet (PMFSS) with a three-dimensional reticulated structure was fabricated by multi-tooth cutting and high-temperature solid-phase sintering process with copper fibers. A uniaxial tensile test was conducted to investigate the effect of fiber length and natural aging factor on the tensile properties of the PMFSS. Results indicated that, under given stress, the increase of fiber length helped reinforce the tensile strength. The elongation of the PMFSS with medium length fiber of 15 mm exhibited the optimal performance, reaching about 13.5%. After natural aging treatment for a month, the tensile strength of PMFSS significantly decreased, but the change of elongation was negligible except for the one with the shortest fiber length of 5 mm, whose elongation was effectively improved. The morphological fracture features of PMFSSs were also characterized.

Solid-phase sintering process and forced convective heat transfer performance of porous-structured micro-channels

A solid-phase sintering process for the low-cost fabrication of composite micro-channels was developed. Three kinds of composite micro-channels with metallic porous structures were designed. The sintering process was studied and optimized to obtain porous-structured micro-channels with high porosity. The flow resistance and heat transfer performance in the composite micro-channels were investigated. The composite micro-channels show acceptable flow resistance, significant enhancement of heat transfer and dramatic improvement of flow boiling stability, which indicates a promising prospect for the application in forced convective heat transfer.

Temperature-dependent formation of Ru-based nanocomposites: structures and properties

A new route to produce Ru-based nanocomposites with mixed valence states of ruthenium is reported in this paper via a solid-phase sintering process. Precursor particles were prepared by an intimate mixing of RuCl3 and native β-cyclodextrin (β-CD) with a molar ratio of 1 : 1, followed by a sintering process at various temperatures ranging from 573 to 1173 K in ambient atmosphere. The so-obtained composite nanomaterials have been characterized by X-ray diffraction and notably the results show that an adjustment of the temperature enabled us to obtain Ru-based nanoparticles with controllable compositions. The surface-enhanced Raman scattering performances of the obtained nanomaterials have been analyzed using Rhodamine 6G (R6G) as the Raman probe. Their magnetic behaviors have been investigated as a function of the field strengths. The present work provides a significant advance in the development of both transformation in valence states of transition metals and in situ nanocomposites of metal/metal oxide combinations.

Influence of Compressive Stress on Dielectric and Ferroelectric Properties of the(Na0.5Bi0.5)0.7Sr0.3TiO3 Ceramics

Good quality lead-free ceramics of (Na0.5Bi0.5)0.7Sr0.3TiO3(NBTS30) have been produced by a solid phase sintering process. The dependence of dielectric and ferroelectric properties on the unaxial pressure (0–1200 bar) were investigated. A shift and decrease of maximum value of ε, decrease of the thermal hysteresis and coercive field and increase of polarization with increasing pressure were observed. The results were discussed in terms of an elastic changes in inter-ionic distances in a crystal structure and switching nanoregions under the action of pressure. The NBTS30 ceramic is expected to be a new promising candidate for lead-free electronic material.

Research of Nano-TiO<sub>2</sub> Composites on Malachite Green Decolorizing Effect

A supporting body of diatomite-based porous ceramics was prepared by a solid-phase sintering process and low-temperature calcination process. nanoTiO2 membrane was loaded on the carrier by the hydrolysis precipitation method and using TiCl4 as the precursor. The influences of various parameters such as the initial concentration of malachite green, the amount of composites, and the initial pH had been investigated. Under the same test conditions, the decolorizing rate of malachite green was higher when the initial concentration was 6 mg/L, the composites dosage was 5 g/L, and the initial pH was 8 respectively. The influence mechanism of the initial concentration of malachite green, the amount of composites, and the initial pH for malachite green was discussed.

Thermal Stability of Gold Catalyst Supported on Mesoporous Titania Nanofibers

By deposition-precipitation with urea method, gold was loaded on mesoporous TiO 2 whisker, which was prepared from a potassium titanate whisker precursor through solid phase sintering process. The morphology and structure of these as-prepared catalysts were characterized by N 2 adsorption-desorption, X-ray diffraction, and transmission electron microscopy. The reduction of 4-nitrophenol to 4-aminophenol by NaBH 4 was evaluated as a probe reaction. After calcination at high temperature, the activity of the catalysts supported on mesoporous TiO 2 nanofiber was well maintained, and the particle size of gold nanoparticles was hardly changed. This might be attributed to the peculiar crystallographic structure and mesoporous nanoarchitecture of the mesoporous TiO 2 whisker. 以二钛酸钾晶须为前驱体, 通过固相烧结工艺制备了介孔 TiO 2 晶须, 然后使用沉积沉淀法将 Au 纳米颗粒担载于其上, 并采用低温 N 2 吸附-脱附 X 射线衍射及透射电镜等技术对催化剂的形貌和结构进行了表征, 以 NaBH 4 还原对硝基苯酚 (PNP) 为探针反应, 评价了催化剂的活性及稳定性. 结果表明, 500 丰C 热处理前后, 介孔 TiO 2 负载的 Au 纳米颗粒的平均粒径变化不大, 且催化 PNP 还原活性得到了很好的保持. 这主要与介孔 TiO 2 晶须独特的双晶构型及介孔结构有关. The unique crystallographic structure and mesoporous architecture of the TiO 2 whisker ensure the excellent sinter-resistant properties of gold nanoparticles. Consequently, the activity of the catalyst supported on the mb-TiO 2 is well maintained after high temperature calcination.

Controlled growth and magnetic properties of α-Fe2O3 nanocrystals: Octahedra, cuboctahedra and truncated cubes

A series of α-Fe2O3 crystalline materials with fascinating polyhedral morphologies, such as octahedral, cuboctahedral and truncated cubic structures, were prepared through a novel solid-phase sintering process. Our results demonstrated that the structural transformations among the polyhedra were easily controlled by the sintering times. This suggested that the Wulff polyhedra transformation could occur in a hexagonal crystal system. Furthermore, we found that the magnetic properties of the α-Fe2O3 crystals were associated with their size and shape.

Monte Carlo simulation of microstructure evolution in nano-composite ceramic tool materials

Abstract The formation of microstructure of nano-composite ceramic materials is a complicated process, which is controlled by many factors such as components, the size and content of nano-particles as well as sintering process. Monte Carlo Potts′ model is widely applied to simulate the microstructure evolution during the solid-phase sintering process of ceramics due to its simplicity and flexibility. In this paper, a new Monte Carlo Potts′ model for the sintering process of two-phase nano-composite ceramic materials is proposed. In this model, the driving forces for grain-boundary migration are the interfacial energy between two phases and the boundary energy inside each phase, and the grain growth process for different sizes and area fractions of nano-particles is successfully investigated in the absence of pores. The simulation results show that the nano-phase can pin the matrix phase and reduce the growth rate of matrix phase during the microstructure evolution, this effect becomes stronger with the addition of smaller size or higher area fraction nano-particles. It is also observed that the nano-phase can influence the microstructure type of nano-composite ceramic, smaller nano-particles are predominantly in intragranular positions, whereas larger nano-particles retain in intergranular positions. The simulation results are in accordance with the experiment results.

Numerical simulation of microstructural evolution of ceramic tool materials

The preparation of ceramic tool materials includes powdering, forming, hot-press fabrication and machining process, and the sintering is a key process, which governs the mechanical properties of the ceramic tool materials as well as the components and content. However, the sintering is a very complicated process. With the rapid development of the computer simulation technology and the computational material science, modeling and numerical simulation of ceramic sintering process become a novel way to investigate the sintering process on the micro- or macro-scale. Monte Carlo Potts’ model is widely applied to simulate the solid-phase sintering process of ceramics. Because of no assumption of the particle shape, the model can be properly used to simulate the mass-transport mechanisms. In this paper, a new Monte Carlo Potts’ model is proposed to investigate the single- and two-phase material systems, which is based on the Potts’ model of the description of the single-phase sintering without the presence of pores. The new simulation algorithm has been utilized to simulate the microstructural evolution in the single- and two-phase ceramic tool material sintering process with considering the presence of pores. Different types of interface, different types of grain boundary energy, initial grain size, the composition content, the initial pore size and the content of pore are considered in the new simulation algorithm. It is found from simulation results that the pore and the phase-two can pin the matrix phase and decrease the growth rate of matrix phase during the microstructural evolution, which has been invalidated by the experiment. The second-phase particle is useful for the refinement of matrix grain. The high rate of grain growth is disadvantage of the pore exhalation. The simulation results are consistent with the experiment results.

Formation and Photoluminescence Characterization of Transparent Silica Glass Prepared by Solid-Phase Reaction of Nanometer-Sized Silica Particles

We investigate the structural transformations of nanometer-sized silica particles during the solid-phase sintering process using infrared and Raman spectroscopy and field emission scanning electron...

Zinc oxide thin films by spray pyrolysis method

ZnO thin films were deposited by spraying of zinc acetate solution onto heated glass substrates at 670 K. Highly textured in the (002) direction undoped ZnO films, exhibiting exciton emission bands in photoluminescence spectra at 8 K, were grown. The initial stages of the thin film growth and effect of doping with In, Ce and Eu were studied. A spraying time of 30 s leads to continuous crystalline films with well-shaped grains with narrow granulometric distribution and mean grain size close to 35 nm. Depositing times longer than 2 min lead to the solid phase sintering process. Wide granulometric distribution of the grains in the range of 50–400 nm was found for undoped films. It is shown that the size and orientation of crystallites in the film, the optical and electrical properties of the films are determined by the dopant concentration. As a result dense ZnO films with high optical transmittance were produced.