Abstract: Lithium and titanium co-doped NiO ceramics have been found to exhibit a giant
low-frequency dielectric constant (ε～105), however, the same system thin films is not yet study. In the present study, Lithium and titanium co-doped NiO thin films were prepared by a chemical solution deposition method using 2-methoxyethanol as a solvent, nickel actate tetrahydrate, lithium acetate dihydrate and titanium isopropoxide as starting materials. The complex oxides such as NiO, Ni0.2O0.8 and NiTiO3 were formed for the Ni0.98Ti0.02O and Ni0.686Li0.294Ti0.02O thin films, and
the addition of the lithium lead to the formation of Li2NiO2.888. The dielectric constant of Lithium and titanium co-doped Ni0.686Li0.294Ti0.02O thin films is about 426 at 100 Hz and much higher than that of the titanium-doped Ni0.98Ti0.02O.
Abstract: Silicon nitride (Si3N4) is one of the most important advanced ceramics due to its high wear resistance, corrosion resistance, and especially high thermal shock resistance at high temperature. It has been used as cutting-tools, high-temperature bearings and turbochargers for car engines etc. But its applications are still limited by the relatively high cost of Si3N4 powders which are now mostly produced by direct nitridation at high temperature for long time with high energy consumption.
Self-propagating high-temperature synthesis (SHS) shows potential as an advanced technology for synthesizing Si3N4. One of the reasons of why SHS Si3N4 powder has not been widely used commercially is that most SHS Si3N4 powder reported in literatures are of high b-phase content and SHS Si3N4 with high a-phase content is very difficult to be made, especially for large samples. Since
1990’s C.C.GE and his group in Laboratory of Special Ceramics and Powder Metallurgy (LSCPM) has been working on the structure formation mechanism of SHS Si3N4 and the nitridation mechanism of large samples of SHS Si3N4. Recently, great effort has been put on the SHS of homogeneous high a-phase Si3N4. In the present work, the effect of nitrogen pressure and purity, the type and amount of
diluents on the a-phase content and microstructure of the product synthesized in a reactor of 10 liter capacity are investigated. Through optimization of processing parameters, SHS Si3N4 powder with high a-phase content up to 96% was synthesized.
Abstract: TiC particle dispersed FeAl intermetallic alloys have been combustion synthesized from mixtures of titanium, carbon, aluminum and iron powders. When the powder mixture was heated in an argon atmosphere to approximately 900 K, an abrupt increase in temperature was observed, which indicates that the combustion synthesis reaction occurred in the powder mixture. The combustion-synthesized alloys consisted of an FeAl matrix phase with homogeneously dispersed fine TiC particles. As the concentrations of titanium and carbon of the powder mixture increased, the volume fraction and average diameter of the TiC particles increased, and Vickers hardness of the sample also increased.
Abstract: The porous Ti-45at.%Al-1.6at.%Mn intermetallic alloys were fabricated by reactive
sintering process using warm extruded mixtures consisting of elemental titanium and aluminum alloy powders and subsequent heat treatment. At the extrusion stage, three different extrusion ratios were tried in order to provide the various types of porous structure in the microstructure. It was clearly found that the shape of pore and porosity are largely dependent on extrusion ratio. With increasing extrusion ratio the porosity decreased, on the other hand, aspect ratio of porous structure
increased. The porosity measured was in the range from 35% to 45%. The maximum porosity of 45% can be obtained when the specimen was reactively sintered with the extrusion ratio of 1. A directionality of pores oriented parallel to the extrusion direction was found when the extrusion ratio of powder mixtures is 6 and above.
Abstract: TiB2 based cermets with different copper content were produced from titanium powder, boron powder and copper powder by Self-propagating High-temperature Synthesis under conditions of Pseudo Hot Isostatic Pressing (SHS/PHIP). In order to obtain the optimal copper content, the effect of copper content on the microstructures and properties of TiB2 based cermets was investigated. The
size of the TiB2 particles in the products decreased with increasing amounts of copper. The hardness (HRA) and bend strength increased firstly, then decreased with copper increasing. Their maximum values appeared at 20 wt.% and 40 wt.% copper, respectively. The porosity of TiB2 based cermets decreased with the copper content increasing due to good fluidity of copper. With the addition of
copper, the fracture toughness of TiB2 based cermets increased gradually. Crack-tip plastic blunting by a ductile metallic phase and crack deflection are the principal mechanisms of toughness improvement of TiB2 based cermets. The range of optimal copper content in the TiB2 based cermets is between 40 wt.% and 50 wt.%.
Abstract: The phase constituent of MoSi2 with 2.0 wt.% La2O3 synthesized by self-propagating high-temperature synthesis (SHS) was studied. It was observed that the addition of La2O3 as a doping agent significantly influences the thermodynamics and kinetics of combustion process when compared with the combustion synthesis of molybdenum disilicide alone. The morphology of the combustion product was investigated using scanning electron microscopy (SEM). The results showed that the addition of La2O3 could obviously decrease the particle size of the
combustion product. Hardness and fracture toughness of the material were directly obtained from the sintered product by using micro-indentation technique. The fracture toughness was found to be significantly enhanced with the addition of La2O3.
Abstract: This paper researched the fabrication of perovskite synrock by self-propagating high temperature synthesis (SHS) and the characterization of the products. This synthesis process is simpler, the fabricated synrock can immobilize waste loading up to 35wt% SrO with satisfied physical properties (density>4.2g•cm-3, open porosity<0.2%, Leach rate<1.0 g•m-2•d-1). The structure analyses by XRD and SEM/EDS show that the major phase is perovskite which well agrees with the design. It proves that SHS offer a suitable Sr-waste synroc which is favorable for
Abstract: α-Si3N4 powders were fabricated through combustion synthesis (CS) process, and the effects of nitrogen purity and pressure on the combustion synthesis of α-Si3N4 specimen with large dimensions were investigated. It is shown that there exists respective nitrogen pressure limits for the initiation and the propagation of the self-sustained combustion. Moreover, it is found that there is an optimum nitrogen pressure for synthesizing tailored α-Si3N4 powders while other parameters were
Abstract: Al2O3-30vol%ZrO2 nano-submicron structured ceramics has been obtained from
high-temperature melts produced by SHS metallurgical process, SEM images show that the multiphase ceramics is mainly composed of Al2O3 matrix eutecticums in which ZrO2 fibers are up to nano-submicron scale, resulting in formation of intra-granular structures. Vickers hardness test indicates that critical value of indentation load which induces median crack to extend is 30kg, and morphologies of Vickers indentation indicate that the ceramics is performed with high fracture toughness and high plasticity. Meanwhile, SEM images show that crack extension is mainly
controlled by fiber eutecticums of intra-granular structures with nano–submicron ZrO2 phases, XRD demonstrates that toughening mechanism of stress induced ZrO2 phase transformation is considered weak through comparing volume fraction of m-ZrO2 before fracture to the one after fracture, and toughening behavior of multiphase ceramics is mainly controlled by nano-submicron phase toughening mechanism.