Self-propagating High-temperature Synthesis, Microstructure and Mechanical Properties of TiC-TiB_2-Cu Composites

TiC-TiB2-Cu composites were produced by self-propagating high-temperature synthesis combined with pseudo hot isostatic pressing using Ti, B4C and Cu powders. The microstructure and mechanical properties of the composites were investigated. The X-ray diffraction （XRD） and scanning electron microscopy （SEM） results showed that the final products were only TiC, TiB2 and Cu phases. The clubbed TiB2 grains and spheroidal or irregular TiC grains were found in the microstructure of synthesized products. The reaction temperature and grain size of TiB2 and TiC particles decreased with increasing Cu content. The introduction of Cu into the composites resulted in a drastic increase in the relative density and flexual strength, and the maximum values were obtained with the addition of 20 wt pct, while the fracture toughness was the best when Cu content was 40 wt pct.

Effect of inner oxidant on self-propagating high-temperature synthesis of MnZn-ferrite powder

Using KClO3 as an inner oxidant, MnZn-ferrite powder was synthesized by a self-propagating high-temperature synthesis (SHS) process in normal air atmosphere. The effects of the inner oxidant on combustion temperature, combustion velocity, microstructure and the phase of the product were investigated by XRD and SEM,respectively. The results show that a highly ferritized powder can be obtained as well as the highest combustion temperature and the highest combustion velocity when the inner oxidant content m equals 54(k-16).

Synthesis of SrTiO_3 for immobilization of simulated HLW by SHS

Strontium titanate synroc samples were synthesized by self-propagating high-temperature synthesis （SHS）. Sr directly took part in the synthesis process. As a result, the loading content issue is basically resolved. The products were characterized by density, microhardness X-ray diffraction, and scanning electron microscopy （SEM/EDS）. The leaching rate was measured by the method of PCT （product consistency test）. The results indicate that the Sr^2＋-SrTiO3 compound is of high density, low leach rate and high stability and the synthesis process is feasible in technology and economy. It can be concluded that the strontium titanate synroc is a perfect material to immobilize HLW.

Microstructure and properties of porous Si_(3)N_(4)ceramics by gelcasting-self-propagating high-temperature synthesis(SHS)

Porous silicon nitride ceramics have attracted a considerable attention due to their excellent overall performance,but poor porosity homogeneity and structural shrinkage induced by prolonged high temperature sintering limit its further application.Herein,as a three-in-one solution for the above issues,for the first time we develop a novel approach that integrates the merits of gelcasting-SHS(self-propagating high-temperature synthesis)to prepare porous Si_(3)N_(4)ceramics to simultaneously achieve high porosity,high strength,high toughness,and low thermal conductivity across a wide temperature range.By regulating the solid content,porous Si_(3)N_(4)ceramics with homogeneous pore structure are obtained,where the pore size falls inbetween 1.61 and 4.41 pm,and the elongated grains are interlaced and interlocked to form micron-sized coherent interconnected pores.At the same time,porous Si_(3)N_(4)ceramics with porosity of 67.83%to 78.03%are obtained,where the compressive strength reaches 11.79 to 47.75 MPa and fracture toughness reaches 1.20 to 6.71 MPa-m1/2.

A New Process for Preparing Fine-ceramic-containing Composite Coatings──Flame Spray Synthesis

Flame spray synthesis (FSS), a combination of the flame spray technology and Self-propagation High-temperature Synthesis (SHS) was developed for preparing fine-ceramic-containing composite coatings. It can simplify the preparations of powder to synthesize and deposit the desired materials in one step. The preliminary results obtained from TiC-Fe cermet coatings by FSS process are reported. The peculiar microstructure of the composite coatings, which contains very fine (<1m) and round TiC and alternate TiC-rich (Hv=11€*13GPa) and TiC-poor layers (Hv=3.0 -6.0GPa), is expected to play an important role in their tribological properties.

Self-propagating high-temperature synthesis of ZrO_2 incorporated Gd_2Ti_2O_7 pyrochlore

In this research, Zr-doped Gd_2Ti_2O_7 pyrochlores, with the composition of Gd_2(Ti_(1-x)Zr_x)_2O_7, were firstly synthesized by self-propagating high-temperature synthesis plus quick pressing(SHS/QP) using CuO as the oxidant and Ti as the reductant. To improve the radiation resistance of titanate–pyrochlore, up to 35 at% Zr was incorporated to substitute the Ti site of Gd_2Ti_2O_7 pyrochlore(Gd_2(Ti_(0.75)Zr_(0.35))_2O_7). XRD and SEM microstructural characterizations showed the formation of a composite ceramic with the major pyrochlore phase and the minor Cu phase. The generated temperature of samples decreased from 1702to 1011 ℃ with increasing Zr content. The effects of sintering temperature and pressure time on phase composition and microstructure were systematically studied. Besides, the influence of thermal transmission on the whole combustion process was also explored. The pyrochlore-based waste form possessed high bulk density of 6.25 g/cm^3 and Vickers hardness of 10.81 GPa. The MCC-1 leaching test showed the normalized elemental leaching rates(42d) of Cu, Gd, and Zr are 1.27×10^(-2), 1.33×10^(-3), and 8.44×10^(-7)g·m^(-2)·d^(-1), respectively.

Structural,magnetic and dielectric properties of nano-crystalline Ni-doped BiFeO_(3) ceramics formulated by self-propagating high-temperature synthesis

Ni-doped BiFeO_(3) powders with the composition BiFe_(1-x)Ni_(x)O_(3)(x=0.05,0.1 and 0.15)were prepared by a self-propagating high-temperature synthesis(SHS),using metal nitrates as oxidizers and glycine as fuel.The X-ray diffraction(XRD)patterns depict that Ni-doped BiFeO_(3) ceramics crystallize in a rhombhohedral phase.The scanning electron micrographs of Ni-doped BiFeO_(3) ceramics show a dense morphology with interconnected structure.It is found that,the room-temperature magnetization measurements in Ni-incorporated BiFeO_(3) ceramics give rise to nonzero magnetization.The magnetization of Ni-doped BiFeO_(3) ceramics is significantly enhanced when Ni doping concentration reaches to x=0.1 at 5 K.The variations of dielectric constant with temperature in BiFe_(0.95)Ni_(0.05)O_(3),BiFe_(0.9)Ni_(0.1)O_(3) and BiFe_(0.85)Ni_(0.15)O_(3) samples exhibit clear dielectric anomalies approximately around 450℃,425℃and 410℃respectively,which correspond to antiferromagnetic to paramagnetic phase transition of the parent compound BiFeO_(3).

IR-transparent MgO-Gd_(2)O_(3) composite ceramics produced by self-propagating high-temperature synthesis and spark plasma sintering

A glycine–nitrate self-propagating high-temperature synthesis(SHS)was developed to produce composite MgO-Gd_(2)O_(3) nanopowders.The X-ray powder diffraction(XRD)analysis confirmed the SHS-product consists of cubic MgO and Gd_(2)O_(3) phases with nanometer crystallite size and retains this structure after annealing at temperatures up to 1200℃.Near full dense high IR-transparent composite ceramics were fabricated by spark plasma sintering(SPS)at 1140℃and 60 MPa.The in-line transmittance of 1 mm thick MgO-Gd_(2)O_(3) ceramics exceeded 70%in the range of 4–5 mm and reached a maximum of 77%at a wavelength of 5.3 mm.The measured microhardness HV0.5 of the MgO-Gd2O3 ceramics is 9.5±0.4 GPa,while the fracture toughness(KIC)amounted to 2.0±0.5МPa·m1/2.These characteristics demonstrate that obtained composite MgO-Gd_(2)O_(3) ceramic is a promising material for protective infra-red(IR)windows.

Comparative study of β-Si_3N_4 powders prepared by SHS sintered by spark plasma sintering and hot pressing

β-Si3N4 powders prepared by self-propagating high-temperature synthesis （SHS） with additions of Y2O3 and Al2O3 were sintered by spark plasma sintering （SPS）. The densification, microstructure, and mechanical properties of Si3N4 ceramics prepared using this method were compared with those obtained by hot pressing process. Well densified Si3N4 ceramics with finer and homogeneous microstructure and better mechanical properties were obtained in the case of the SPS technique at 200°C lower than that of hot pressing. The microhardness is 15.72 GPa, the bending strength is 716.46 MPa, and the fracture toughness is 7.03 MPa·m1/2.

STUDY OF PREPARATION PROCESS OF TUNGSTEN POWDER BY SHS WITH A MAGNESIUM THERMIT STAGE

Tungsten powder was fabricated from the system CaWO4-Mg by self-propagating high-temperature synthesis (SHS) with a magnesium thermit stage. The physic-chemical change during heating and the effects of pressure of sample and diluents (W powder) on product have been studied. The experimental results show that the porosity of combustion product and the particle size of final tungsten powder decrease with increasing pressure of sample. Addition of diluents could increase the particle size of final tungsten powder. The purity of tungsten is improved by leaching in NaOH solution. The results of spectral analysis and particle size distribution of final tungsten powder show that the final Tungsten powder has a median diameter of 0.87μm,specific surface area of 1.09m2/g and purity of above 99.0%.

Effects of Forming Conditions and TiC–TiB_2 Contents on the Microstructures of Self-Propagating High-Temperature Synthesized NiAl–TiC–TiB_2 Composites

The NiAl–TiC–TiB2 composites were processed by self-propagating high-temperature synthesis（SHS） method using raw powders of Ni, Al, Ti, B4 C, TiC, and TiB2, and their microstructure and micro-hardness were investigated. The TiC–TiB2 in NiAl matrix, with contents from 10 to 30 wt%, emerged with the use of two methods： in situ formed and externally added. The results show that all final products are composed of three phases of NiAl, TiC, and TiB2. The microstructures of NiAl–TiC–TiB2 composites with in situ-formed TiC and TiB2 are fine, and all the three phases are distributed uniformly. The grains of NiAl matrix in the composites have been greatly refined, and the micro-hardness of NiAl increases from 381 HV100 to 779 HV100. However, the microstructures of NiAl–TiC–TiB2 composites with externally added TiC and TiB2 are coarse and inhomogeneous, with severe agglomeration of TiC and TiB2 particles. The samples containing externally added 30 wt% TiC–TiB2attain the micro-hardness of 485 HV100. The microstructure evolution and fracture mode of the two kinds of NiAl–TiC–TiB2 composites are different.

Dispersion of ultrafine SiC particles in molten Al-12Si alloy

The bulk A1-12 Si eutectic composites were fabricated through a conventional liquid metal casting route, especially with the help of ultrafine ceramic powders made by self-propagating high-temperature synthesis （SHS） process. The SHS powders were fabricated by the chemical reaction between micro-sized SiC and A1 particles at very high combustion temperatures, producing the coarse A1 particles （several tens of microns） containing ultrafine SiC ceramic particles. Microstructural observation revealed that the addition of ultrafine SiC particles has a crumbling tendency of Si eutectic phase. It is suggested that the casting method combined with SHS process is promising for fabricating the Al-based MMC with ultrafine ceramic particles.

RELATION BETWEEN THE ORDERING PARAMETERS AND FORMING PRESSURE IN AINi_3

The degree of ordering and ordered domain size in solid solution AlNi3 prepared by SHS have been deter-mined -with XRD. The reszilts indicate that the greater the form-ing pressure on the raw materials , the higher the degree of or-dering,the larger the ordered domain size.

THE ACCURATE MOLECULAR FORMULA OF "Ti_(11)Ni_(14)" PHASE

From the orientation relationship between 'Ti11Ni14' phase and matrix phase (B2),the accurate molecular formula of 'Ti11N14' phase has been derived in this paper. The results also show that the rhombohedral unit cell of the 'Ti11Ni14' phase includes six Ti atoms, seven Ni atoms and one vacancy, belonging to space group R3.

Microstructure and Mechanical Properties of Cu Matrix Composites Reinforced by TiB_(2)/TiN Ceramic Reinforcements

Cu matrix composites reinforced by TiB_(2)/TiN ceramic reinforcements(Cu/TBN composites)were prepared by hot pressing method.Prior to the hot pressing,Cu/TiB_(2)/TiN composite powders(CTBN powders),which were used as the starting materials of Cu/TBN composites,were fabricated by self-propagating high-temperature synthesis method.The CTBN particles were found to be in a special core–shell structure with a Cu–Ti alloy core and a TiB_(2)/TiN ceramic shell.The test results presented obvious improvements in mechanical properties.The highest ultimate tensile strength reached up to 297 MPa,77 MPa higher than that of Cu.And the highest hardness reached up to 70.7 HRF,15.7 HRF higher than that of Cu.A comparative study indicated that the core–shell structured particles could bring about more obvious strengthening eff ect than the traditional irregularly shaped particles,which was due to the improved Cu/ceramics interfacial bonding,the linkage strengthening effect of both TiB_(2) and TiN,and higher load bearing ability of the core–shell structured reinforcements.

Fabrication,Pore Structures and Mechanical Properties of (TiB_2–Al_2O_3)/NiAl Porous Composites

Open-celled porous （TiB2-Al2O3）/NiAl composites were successfully fabricated by using spherical carbamide as space holders via self-propagating high-temperature synthesis （SHS）. Effects of 10Al-3B2O3-3TiO2 contents （0-20 wt%） on the pore structures and the quasi-static compressive behaviors of the resultant materials were investigated. The porous （TiBE-Al2O3）/NiAl composites exhibit composite pore structure consisting of homogeneously distributed and interconnected millimeter pores and micropores. The millimeter pores virtually inherit the shape and size of carbamide particles, while the pore size of micropores increases with increasing the 10Al-3BEO3-3TiO2 content. Depending on the volume fraction of the carbamide, the porosity of the porous materials can be easily controlled in a range of 55%-85%. When the porosity is about 72%, the compressive strengths of porous NiAl and porous （TiBE-Al203）/NiAl composite with 15% 10Al-3B2O3-3TiO2 in green compact are 19 and 32 MPa, and the corresponding strains are 2.9% and 5.7%, respectively. Furthermore, the quasi-static compressive behavior of porous （TiB2-AlEO3）/NiAl composites can be estimated by Gibson-Ashby model.

Study on Oxidation Activity of CuCeZrO_x Doped with K for Diesel Engine Particles in NO/O_2

CuCeZrO_x and KCuCeZrO_x catalysts were synthesized and coated on the blank diesel particulate filter(DPF)substrate and a particulate matter(PM)loading apparatus was used for soot loading.The catalytic performances of soot oxidation were evaluated by temperature programmed combustion(TPC)test and characterization tests were conducted to investigate the physicochemical properties of the catalysts.The reaction mechanism in the oxidation process was analyzed with diffuse reflectance infrared Fourier transform spectroscopy.The results demonstrated that CuCeZrO_x catalyst exhibited high activities of soot oxidation at low temperature and the best results have been attained with Cu_(0.9)Ce_(0.05)Zr_(0.05)O_x over which the maximum soot oxidation rate decreased to 410~?C.Characterization tests have shown that catalysts containing 90%Cu have uniformly distributed grains and small particle sizes,which provide excellent oxidation activity by providing more active sites and forming a good bond between the catalyst and the soot.The low-temperature oxidation activity of soot could be further optimized due to the excellent elevated NO’s conversion rate by partially substituting Cu with K.The maximum particle oxidation rate can be easily realized at such a low temperature as 347~?C.