In-situ Synthesis of Ti_3AlC2/TiC-Al_2O_3 Composite from TiO_2-Al-C System

Ti3AlC2/TiC-Al2O3 composite was synthesized by a combustion reaction in TiO2-Al-C system. The effect of the compositions in raw materials on the products was investigated. Ti3AlC2/TiC-Al2O3 composite was obtained at the molar ratio of TiO2：Al：C=3.0：5.0～5.1：1.8～2.0. The reaction path for the 3TiO2-5Al- 2C system was proposed. Al3Ti, Ti203, TiO, and 6-Al2O3 are found to be transitional phases. Finally, Ti3AlC2/TiC-Al2O3 composite forms at～900℃ of furnace temperature. The measured Vickers hardness, fracture toughness, and flexural strength of the nearly dense sample from 3TiO2-5Al-2C are 13.3±1.1 GPa, 5.8±0.3 MPa.m^1/2, and 466±39 MPa, respectively.

Microstructure and evolution of(TiB_2+Al_2O_3)/NiAl composites prepared by self-propagation high-temperature synthesis

（TiB2＋Al2O3）/NiAl composites were synthesized by self-propagation high-temperature synthesis, and their phase compositions, microstructures and evolution modes were studied. The microstructures and shapes vary with the TiB2＋Al2O3 content in the NiAl matrix. TiB2 particles take a great variety of elementary shapes such as white bars, plates, herringbones, regular cubes and cuboids. These results outline a strategy of self-assembly processes in real time to build diversified microstructures. Some TiB2 grains in sizes of 2-5μm are embeded in Al2O3 clusters, while a small number of TiB2 particles disperse in the NiAl matrix. It is believed that the higher the TiB2＋Al2O3 content is, the more the regular shapes and homogeneous distributions of TiB2 and Al2O3 will be present in the NiAl matrix.

Effect of CuO particle size on synthesis temperature and microstructure of Al_2O_(3p)-Al composites from Al-CuO system

Al2O3p-Al composites were synthesized using an in-situ reaction in the 80%Al-20%CuO （mass fraction） system. The effects of the CuO particle size on the synthesis temperature and microstructure of the composites were investigated by various methods. The results indicate that the CuO particle size has a significant effect on the temperature at which the complete reaction in the Al-CuO system occurs：the temperature is 200 ℃ lower in the Al-CuO system containing CuO particles with sizes less than 6μm than that containing CuO particles with sizes less than 100μm. The interfacial bonding between Al2O3 particles and Al is not complete when the temperature is below a critical value. The morphology of the Al2O3 particles varies from ribbon-like shape to near spherical shape when the temperature is above a critical value. These two critical temperatures are affected by the particle size of CuO, and the critical temperature of the sample containing CuO particles with sizes less than 6μm is 100 ℃ lower than that of the sample containing CuO particles with sizes less than 100μm.

Effect of Al_2O_3 Binder on the Precipitated Iron-Based Catalysts for Fischer-Tropsch Synthesis

A series of iron-based Fischer-Tropsch synthesis （FTS） catalysts incorporated with Al2O3 binder were prepared by the combination of co-precipitation and spray drying technology. The catalyst samples were characterized by using N2 physical adsorption, temperature-programmed reduction/desorption （TPR/TPD） and MSssbauer effect spectroscopy （MES） methods. The characterization results indicated that the BET surface area increases with increasing Al2O3 content and passes through a maximum at the Al2O3/Fe ratio of 10/100 （weight basis）. After the point, it decreases with further increase in Al2O3 content. The incorporation of Al2O3 binder was found to weaken the surface basicity and suppress the reduction and carburization of iron-based catalysts probably due to the strong K-Al2O3 and Fe-Al2O3 interactions. Furthermore, the H2 adsorption ability of the catalysts is enhanced with increasing Al2O3 content. The FTS performances of the catalysts were tested in a slurry-phase continuously stirred tank reactor （CSTR） under the reaction conditions of 260 ℃, 1.5 MPa, 1000 h^-1 and molar ratio of H2/CO 0.67 for 200 h. The results showed that the addition of small amounts of Al2O3 affects the activity of iron-based catalysts to a little extent. However, with further increase of Al2O3 content, the FTS activity and water gas shift reaction （WGS） activity are decreased severely. The addition of appropriate Al2O3 do not affect the product selectivity, but the catalysts incorporated with large amounts of Al2O3 have higher selectivity for light hydrocarbons and lower selectivity for heavy hydrocarbons.

Local structural evolutions of CuO/ZnO/Al2O3 catalyst for methanol synthesis under operando conditions studied by in situ quick X-ray absorption spectroscopy

In situ quick X-ray absorption spectroscopy(QXAFS) at the Cu and Zn K-edge under operando conditions has been used to unravel the Cu/Zn interaction and identify possible active site of CuO/ZnO/Al_2O_3 catalyst for methanol synthesis. In this work, the catalyst, whose activity increases with the reaction temperature and pressure, was studied at calcined, reduced, and reacted conditions. TEM and EDX images for the calcined and reduced catalysts showed that copper was distributed uniformly at both conditions. TPR profile revealed two reduction peaks at 165 and 195 °C for copper species in the calcined catalyst. QXAFS results demonstrated that the calcined form consisted mainly of a mixed Cu O and Zn O, and it was progressively transformed into Cu metal particles and dispersed Zn O species as the reduction treatment. It was demonstrated that activation of the catalyst precursor occurred via a Cu^+intermediate, and the active catalyst predominantly consisted of metallic Cu and Zn O evenunder higher pressures. Structure of the active catalyst did not change with the temperature or pressure, indicating that the role of the Zn was mainly to improve Cu dispersion.This indicates the potential of QXAFS method in studying the structure evolutions of catalysts in methanol synthesis.

Dynamic recrystallization behavior and mechanical properties of bimodal scale Al2O3 reinforced AZ31 composites by soild state synthesis

In this paper,(500 nm 1%+5μm 3%)bimodal scale Al2O3p/AZ31 composites was fabricated by solid state synthesis and the effect of bimodal scale Al2O3 particulates on its dynamic recrystallization behavior and mechanical properties was investigated.The optical microscopy,scanning electron microscopy,transmission electron microscopy and electron universal strength tester composites were used to characterize the composites.The results indicate that the grains size of the composites are significantly refined and the mechanical properties are obviously improved.Due to the presence of the bimodal scale Al2o3 particulates,the high-density dislocation zone is formed around nano-Al2o3p and the particle deformation zone is formed near micron-ABOap.These zones are ideal sites for the formation of recrystallization nucleus.Meanwhile,the addition of the bimodal scale Al2o3 particulates may delay or hinder the growth of matrix grain through the pining effect on the grain boundaries,resulting in significantly improving the yield strength and tensile strength of Al2O3p/AZ31 composites.

Characterization and performance of Cu/ZnO/Al_2O_3 catalysts prepared via decomposition of M(Cu,Zn)-ammonia complexes under sub-atmospheric pressure for methanol synthesis from H_2 and CO_2

Methanol synthesis from hydrogenation of CO2 is investigated over Cu/ZnO/Al2O3 catalysts prepared by decomposition of M（Cu,Zn）-ammonia complexes （DMAC） at various temperatures.The catalysts were characterized in detail,including X-ray diffraction,N2 adsorption-desorption,N2O chemisorption,temperature-programmed reduction and evolved gas analyses.The influences of DMAC temperature,reaction temperature and specific Cu surface area on catalytic performance are investigated.It is considered that the aurichalcite phase in the precursor plays a key role in improving the physiochemical properties and activities of the final catalysts.The catalyst from rich-aurichalcite precursor exhibits large specific Cu surface area and high space time yield of methanol （212 g/（Lcat·h）;T=513 K,p=3MPa,SV=12000 h-1）.

Hydrothermal synthesis of Y(OH)_3,Y(OH)_3:Eu^(3+) nanotubes and the photoluminescence of Y(OH)_3:Eu^(3+),Y_2O_3:Eu^(3+)

The phase and morphology transformation during the hydrothermal treating process of Y2O3 was evaluated with X-ray difference (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size and specific surface area determination. The results showed that the cubic Y2O3 did not transfer into hexagonal Y(OH)3 in pure water. Therefore, pure hexagonal Y(OH)3 with nanotube and microrod morphologies were obtained by hydrothermal treating Y2O3 at 150 oC for 12 h in 15 ml of 2 mol/L NaOH solution with and without PVA or PEG. It was suggested that the characteristic preferential growth of Y(OH)3 was attributed to the structure anisotropy of hexahedron Y(OH)3. The addition of PVA or PEG could promote the forming process of nanotubes by selective adsorption on different crystal planes, which altered the growth rate along different directions and resulted in the diffusion limit of constructing ions in the center top of rods. Finally, Y(OH)3:Eu and Y2O3:Eu nanotubes were also synthesized by using this method, and their photoluminescence properties were evaluated.

Fabrication and characterization of Al_2O_3-metal composite coating on steel plate with nonpressure combustion synthesis

Al2O3-metal composite coatings with different reactants and diluents were fabricated on mild steel plate with nonpressure combustion synthesis process. The coat-ings were characterized by means of X-ray diffraction, scanning electron microscopy, and energy-dispersive spec-trometry, respectively. Thermal shock tests were carried out to determine the bond strength of the coating with the steel substrate. The results indicate that the coating is composed of α-A1203, α-（Fe-Cr） and Al2SiO5 as the main phases. It is found that the coating with the diluents of Al2O3-SiO2 and transition layer of Al2O3-Cr presents the hi.ghest hardness of 2270 HV0.2 and the lowest porosity of 3.93 %. Owing to a metallurgical bond of the coating-to-substrate, the coating exhibits a good thermal shock resistance.

Oscillations during partial oxidation of methane to synthesis gas over Ru/Al_2O_3 catalyst

Oscillations in temperatures of catalyst bed as well as concentrations of gas phase species at the exit of reactor were observed during the partial oxidation of methane to synthesis gas over Ru/Al2O3 in the temperature range of 600 to 850℃. XRD, H2-TPR and in situ Raman techniques was used to characterize the catalyst. Two types of ruthenium species, i.e. the ruthenium species weakly interacted with Al2O3 and that strongly interacted with the support, were identified by H2-TPR experiment. These species are responsible for two types of oscillation profiles observed during the reaction. The oscillations were the result of these ruthenium species switching cyclically between the oxidized state and the reduced state under the reaction condition. These cyclic transformations, in turn, were the result of temperature variations caused by the varying levels of the strongly exothermic CH4 combustion and the highly endothermic CH4 reforming （with H2O and CO2） reactions （or the less exothermic direct partial oxidation of methane to CO and H2）, which were favored by the oxidized and the metallic sites, respectively. The major pathway of synthesis gas formation over the catalyst was via the combustion-reforming mechanism.

Preparation of TiAl/Al_2O_3 composites by combustion synthesis

Studies the combustion synthesis of Al Ti TiO 2 system and concludes that, due to its low exothermic nature, a stable combustion wave can be maintained only when the system is ignited at a certain preheating temperature, and coupled with appropriate pseudo HIP process, dense TiAl/Al 2O 3 composites with density as high as 97% of the theoretical value can be produced, and points out. Microstructure observation shows in situ formed Al 2O 3 particles are of an average size smaller than one micron, and the hardness of TiAl matrix is enhanced by introduction of these particles.

Hydrothermal Synthesis of H_3PW_(12)O_(40)/TiO_2 Nanometer Photocatalyst and Its Catalytic Performance for Methyl Orange

H3PW12O40/TiO2 nanometer photocatalyst was prepared by one step hydrothermal synthesis from H3PW12O40·nH20 and Ti（OBu）4, simultaneously realizing the load and modification of H3PW12O40. The catalyst was characterized by Fourier transform infrared spectroscopy（FTIR）, powder X-ray diffraction（XRD）, nitrogen adsorp- tion-desorption analysis and scanning electron microscopy（SEM）. The results show that the catalyst is Keggin struc- ture and crystallized in anatase structure, the diameter and specific area of the prepared catalyst are 3.8 nm and 177.9 m^2/g, respectively, and its dispersity is better. The photocatalytic properties were compared for TiO2H3PW12O40/TiO2 prepared by impregnation and H3PW12O40/TiO2 prepared by hydrothermal method with methyl orange as a probe. The effects of H3PW12O40 loadings, crystallization method, initial pH and concentration of dye solution on the degradation of methyl orange were investigated.

Synthesis of Al_2O_3/WC powder by aluminothermic reduction and carbonization method

Al2O3/WC powder was synthesized by means of aluminothermic reduction-carbonization with metallic Al powder, yellow tungsten oxide and carbon black or graphite as raw materials under the protection of coke granules. The effects of Al2O3 content, temperature, C/WO3 molar ratio, and atmosphere on the synthesis of Al2O3/WC powder were studied. The results show that the relative content of WC and W2C is strongly influenced by the factors mentioned-above. Carbon black has higher reactivity than graphite. Al2O3-WC composite is easier to obtain under the protection of coke granules than under argon atmosphere. The CO in the coke layer can easily react with tungsten to form WC and to transfer from W2C to WC.

In-situ hydrothermal synthesized γ-Al_2O_3/O-g-C_3N_4 heterojunctions with enhanced visible-light photocatalytic activity in water splitting for hydrogen

In this work, γ-Al2O3and hydrogen peroxide treated g-C3N4(O-g-C3N4) were combined through a novel in-situ hydrothermal method to form heterojunction structured photocatalysts. These photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy and photoluminescence spectroscopy (PL). FT-IR results indicate that oxygen functional groups can be grafted on the surface of O-g-C3N4by hydrogen peroxide treatment. The visible light photocatalytic hydrogen evolution rate was investigated in 10 vol% TEOA aqueous solution. The optimal Al2O3mass content is set to be 20 wt% and the corresponding hydrogen evolution rate is 1288 µmol/h/g which is approximately 6, 3 folds that of pristine g-C3N4and O-g-C3N4respectively and 1.6 folds that of mechanical mixed composite with the same Al2O3mass content. The photocurrent density–time curves were carried out under visible light illumination for four on–off cycles. The electrochemical impedance spectroscopy (EIS) measurements verified the enhanced separation efficiency of electron–hole pairs. This work raised a new method to form the heterojunction structured photocatalysts and achieved a remarkable improvement of the photocatalytic activity in water splitting for hydrogen under visible light irradiation. © 2016

Microwave synthesis and characterization of new red long afterglow phosphor Sr_3Al_2O_6:Eu

Nanoparticles of red long afterglow phosphor Sr3Al2O6: Eu2+ were prepared by microwave irradiation method at a power of 680 W and a processing time of 15 min. The phosphors nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fluorescence spectrophotometer techniques. The results reveal that the samples are composed of single Sr3Al2O6 phase. The resultant nanoparticles show small size (80?100 nm) and spherical shape. The excitation and emission spectra indicate that excitation broad band chiefly lies in visible range and the nanoparticles emit much strong light at 612 nm under around 473 nm excitation. And the long afterglow phosphorescence of Sr3Al2O6 doped with Eu2+ was observed in the dark with naked eye after the removal of the excitation light. The effect of Eu2+ doping concentrations of the samples on the emission intensity is studied systematically. Furthermore, the microwave method requires a very short heating-time and the energy consumption.

Effect of reaction conditions and kinetic study on the Fischer-Tropsch synthesis over fused Co-Ni /Al_2O_3 catalyst

Co-Ni/Al2O3catalyst was prepared by the fusion method and used in Fischer-Tropsch synthesis(FTS).The catalysts were characterized by means of nitrogen sorption and scanning electron microscopy.The effect of some reaction conditions such as temperature,pressure and H2/CO feed ratio on the catalytic performance of Co-Ni/Al2O3in CO hydrogenation was investigated in a fixed-bed reactor.The results indicate that the optimum reaction conditions are 250℃,0.3 MPa,H2/CO feed ratio of 2.0,and GHSV of 3 000 h-1.Kinetically,the reaction rate was correlated with the Langmuir-Hinshelwood-Hougen-Watson type models.The activation energy for the best fitted model is 88.41 kJ/mol,suggesting that the intra-particle mass transport is not significant.

Synthesis of free-standing Ga_2O_3 films for flexible devices by water etching of Sr_3Al_2O_6 sacrificial layers

Flexible electronic devices have attracted much attention due to their practical and commercial value. Integration of thin films with soft substrate is an effective way to fabricate flexible electronic devices. Ga_2O_3 thin films deposited directly on soft substrates would be amorphous mostly. However, the thickness of the thin film obtained by mechanical exfoliation method is difficult to control and the edge of the film is fragile and easy to be damaged. In this work, we fabricated free-standing Ga_2O_3 thin films using the water-soluble perovskite Sr_3Al_2O_6 as a sacrificial buffer layer. The obtained Ga_2O_3 thin films were polycrystalline. The thickness and dimension of the films were controllable. A flexible Ga_2O_3solar-blind UV photodetector was fabricated by transferring the free-standing Ga_2O_3 film on a flexible polyethylene terephthalate substrate. The results displayed that the photoelectric performances of the flexible Ga_2O_3 photodetector were not sensitive to bending of the device. The free-standing Ga_2O_3 thin films synthesized through the method described here can be transferred to any substrates or integrated with other thin films to fabricate electronic devices.

Synthesis of Al_2O_3/TiCN-0.2%Y_2O_3 Composite by Hot Pressing

Al2O3/TiCN composites were synthesized by hot pressing.The influences of components and HP temperature on mechanical properties,such as bending strength,breaking tenacity and Vickers hardness were investigated.The results showed that the mechanical properties of Al2O3/TiCN composite increased with temperature when hot pressing temperature is below 1650 ℃.The mechanical properties reached their maximums when the composites were sintered at 1650 ℃ for 30 min under hot pressing pressure of 35 MPa,the value of bending strength,breaking tenacity and Vickers hardness was 1015 MPa,6.89 MPa·m1/2,and 20.82 MPa,respectively.When hot pressing temperature was above 1650 ℃,density decreased because of decomposition with increased temperature,and mechanical properties dropped because of rapid growth of grains in size at high temperature.Microstructure analysis showed that the addition of Y2O3 led to the formation of YAG phase so as to inhibit the growth of crystals.This helped to improve breaking tenacity of the composites.TiCN particles with diameters of 1 μm dispersed at Al2O3 grain boundaries,inhibited grain growth and enhanced mechanical properties of the composites.SEM study of the propagation of indentation cracks showed that the bridge linking behavior between matrix and strengthening phase might lead to the formation of the coexisted field of crack deflection,branching and bridge linking.The mechanism of this phenomenon was that the addition of Y2O3 improved the dispersion of TiCN particles so as to enhance the tenacity of the composites.The breaking tenacity was changed from 5.94 to 6.89 MPa·m1/2.

In situ formation of Zr_2Al_3C_4/Al_2O_3 composites by combustion synthesis with PTFE and thermal activations

Preparation of Zr2Al3C4-Al2O3 in situ composites was investigated by self-propagating high-temperature synthesis(SHS)involving both aluminothermic reduction of ZrO2 and chemical activation of PTFE(Teflon).The starting materials included ZrO2,Al,carbon black and PTFE.In addition to the conventional SHS method,the experiments were conducted by a chemical-oven SHS(COSHS)route to thermally assist the synthesis reaction.The threshold amount of 2%(mass fraction)PTFE was required to induce self-sustaining combustion.When the conventional SHS scheme was utilized,due to low combustion temperatures between 1152 and 1272°C and insufficient reaction time,the dominant carbide forming in the composite was ZrC instead of Zr2Al3C4.On the other hand,the COSHS technique increased the combustion temperature of the reactant compact to about 1576°C,lengthened the high-temperature duration for the reaction,and prevented Al vapor from escaping away.As a consequence,Zr2Al3C4-Al2O3 composites with a small amount of Zr3Al3C5 were obtained.The microstructure of the COSHS-derived product showed that plate-like Zr2Al3C4 grains were about 2μm in thickness and 10-30μm in length,and most of them were closely stacked into a laminated configuration.

ZrB_2/Al_2O_3 composite powders prepared by self-propagating high-temperature synthesis

Self-propagating high-temperature synthesis（SHS） method was used to synthesize ZrB2/Al2O3 composite powders from B2O3-ZrO2-Al system. X-ray diffractometry（XRD） and scanning electron microscopy（SEM） analyses show the presence of ZrB2 and Al2O3 as the primary phases in the composite powders, while the presence of a very small amount of ZrO2 is thought to be unreacted zirconium oxide. Transmission electron microscopy（TEM） and high resolution electron microscopy（HREM） observations of microstructure of the composite powders indicate that the interfaces of ZrB2/Al2O3 bond well without any interfacial reaction products. It is proposed that the good interfacial bonding of composite powders results from the ZrB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.