Effect of nano-ZrO2 on microstructure and thermal shock behaviour of Al2O3/SiC composite ceramics used in solar thermal power

The Al2O3-ZrO2(3Y)-SiC composite ceramics used in solar thermal power were prepared by micrometric Al2O3,nano-ZrO2 and SiC powders under the condition of pressureless sintering.The bulk density and bending strength of samples with 10vol% nano-ZrO2 sintered at 1480℃ were 3.222 g/cm3 and 160.4MPa,respectively.The bending strength of samples after 7 times thermal shock tests (quenching from 1000℃ to 25℃ in air medium) is 132.0MPa,loss rate of bending strength is only 17%.The effect of nano-ZrO2 content on the microstructure and performance of Al2O3-ZrO2(3Y)-SiC composite ceramic was investigated.The experimental results show that the bending strength of samples with above 10vol% nano-ZrO2 content has decreased,because the volume expansion resulting from t-ZrO2 to m-ZrO2 phase transformation is excessive;Adding proper nano-ZrO2 would be contributed to improve the thermal shock resistance of the composite ceramics.The Al2O3-ZrO2(3Y)-SiC composite ceramic has promising potential application in solar thermal power.     

Preparation of Bauxite Ceramic Microsphere

Ceramic microspheres were prepared by using Chinese bauxite as raw materials through the centrifugal spray drying method. The control technology of microsphere size, degree of sphericity was researched. The ceramic microspheres were sintered by a double sintering process. The microstructure and composition of ceramic microsphere were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and X-ray energy spectroscopy. The results show that the degree of sphericity of the ceramic microsphere was good and the particle size was 10-100 μm. The XRD analysis reveals that the main crystalline phase of the ceramic microsphere was a-Al2O3 and mullite （3Al2O3·2SiO2）. The product can be used as reinforced material for composite material, especially for antiskid and hard wearing aluminum alloy coating.     

Self-Propagating High-Temperature Reductive Synthesis of TiB_2-Al_2O_3 Composite Powders

TiB2-Al2O3 composite powders were produced by self-propagating high-temperature synthesis(SHS) method with reductive process from B2O3-TiO2-Al system. X-ray diffraction(XRD) and scanning electron microscopy(SEM) analyses show the presence of TiB2 and Al2O3 only in the composite powders produced by SHS. The powders are uniform and free-agglomerate. Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) observation of microstructure of the composite powders indicate that the interfaces of the TiB2-Al2O3 bond well, without any interfacial reaction products. It is proposed that the good interfacial bonding of the composite powders can be resulted from the TiB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.     

Self-Propagating High-Temperature Reduetive Synthesis of TiB2-Al2O3 Composite Powders

TiB2-Al2O3 composite powders were produced by self-propagating high-temperature synthesis（SHS） method with reductive process from B2O3-TiO2-AI system. X-ray diffraction（XRD） and scanning electron microscopy（SEM） analyses show the presence of TiB2 and Al2O3 only in the composite powders produced by SHS. The powders are uniform and free-agglomerate. Transmission electron microscopy （TEM） and high resolution electron microscopy （HREM） observation of microstructure of the composite powders indicate that the interfaces of the TiB2-Al2O3 bond well, without any interfacial reaction products. It is proposed that the good interfacial bonding of the composite powders can be resulted from the TiB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.     

The Characteristics of the Surface Topography of Excimer Laser Processed Al2O3 Ceramic

Surface of Al2O3 ceramic was processed by an excimer laser and the characteristics of topography were examined based on the application of thesystem(MEMS). It is indicated that the statistic pararueters of surface topography processed by the excimer laser have an obvioas regularity. The arithmeticmean value Ro and the root-mean square value Rq change with the changing of processing parameters in the same step and trend, and there is a quantitative relation between them. A simplified nuuIel is proposed for the excimer laser processing surface profile, whose results of the analysis and calculation agree basically with the experimental data. Furthermore, the surfaces processed by excimer laser are greatly fiat. Skewness root-mean-square value Zq changed little with the change of the technological parameters. The above characteristics depend on the processing principle of excimer laser, quite different from the cutting processing.     

Adsorption behavior of heavy metal ions by carbon nanotubes grown on microsized Al2O3 particles

Carbon nanotubes （CNTs） were grown on the surface of microsized Al2O3 particles in CH4 atmosphere at 700℃ under the catalysis of Fe-Ni nanoparticles. The CNTs on Al2O3 were used for adsorbing Pb^2＋, Cu^2＋, and Cd^2＋ from the solution and the results were compared with active carbon powders, commercial carbon nanotubes, and Al2O3 particles. The as-grown CNTs/Al2O3 have demonstrated extraordinary absorption capacity with further treatment or oxidation, as well as hydrophilic ability that other CNTs lacked. The adsorption capacity of CNTs on Al2O3 is superior to other adsorbents and the preference order of adsorption on composite Al2O3 is pb^2＋〉Cu^2＋〉Cd^2＋. It seemed that the adsorption of those Pb^2＋, Cu^2＋, and Cd^2＋ did not change the surface properties of composite particles. The adsorption behaviors of Pb^2＋, Cu^2＋, and Cd^2＋ by CNTs on Al2O3 match well with the Langmuir isothermal adsorption model and the second order kinetic model. The calculated saturation amount adsorbed by 1 g of CNTs on Al2O3 are 67.11, 26.59, and 8.89 mg/g for Pb^2＋, Cu^2＋, and Cd^2＋ in single adsorption test, respectively.     

3D evaluation method of cutting surface topography of carbon / phenolic (C/Ph) composite

3D evaluation method of cutting surface topography for C/Ph composites was established.The cutting surface was measured by Talyscan 150,using 3D non-contact measurement.Through the results of 2D and 3D roughness evaluating for C/Ph composite and Duralumin,the 2D evaluation method of the cutting surface topography of C/Ph composite loses a lot of information,the characteristics of the surface topography of C/Ph composite can be comprehensively and authentically evaluated only by 3D evaluation method.Furthermore,3D amplitude and spatial parameters were adopted to evaluate the surface.The results show that: the topography of the C/Ph composite is anisotropic,there are more valleys in the machined surface of C/Ph than that of duralumin,and there are not obvious feeding textures for C/Ph,which indicates the machining mechanism is different from the metal.In conclusion,the topography of the C/Ph composite cutting surface is anisotropic;the cutting surface of C/Ph composite needs 3D evaluation method.     

Comparison of PVDF porous membranes modified by two different methods using composite nano-particles

To improve the hydrophilicity and anti-fouling performance in water treatment,both entrapped method and deposited method were used to modify polyvinylidene fluoride(PVDF)porous membrane with composite Al2O3/TiO2 nano-particles.Neat PVDF membrane was prepared and its property was also compared with that of the modified membranes.Membrane permeation flux and anti-fouling performance were measured using a membrane cell.The contact angle between water and membrane surface was detected in order to denote the membrane hydrophilicity.Membrane morphology and surface structure were examined by atomic-force microscopy(AFM)and scanning electron microscopy(SEM).Experimental results showed that modified membranes had higher permeation fluxes than that of the neat PVDF membrane.The addition of nano-particles altered membrane surface morphology and increased surface roughness.Due to the hydrophilicity of nano-particles,however,the membrane anti-fouling performance was improved instead of worsened.The entrapped membrane exhibited better anti-fouling performance than the deposited membrane and the neat membrane.     

Fabrication of homogenous dispersion TiB<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites

In order to get a homogenous mixture and compact of TiB2-Al2O3, hybridization as a surface modification method was used to prepare nano-scale Al2O3 coated TiB2 particles. PE-wax particles were first coated onto TiB2 particles by hybridization, and then the nano-scale Al2O3 particles were coated onto the surface of TiB2 coated by PE-wax particles again. SEM, TEM and EDS were used to characterize the microstructure of as-received core/shell particles and its compacts. The experimental results show that a particle-scale homogenous dispersion of TiB2 and Al2O3 can be formed not only in mixed powder but also in dewaxed compacts. The compacts then were sintered by gas-pressing sintering (GPS). Finial products show improved mechanic properties comparing with reference samples fabricated by normal ways.     

Bonding mechanism of X10CrNi18-8 with Ni/Al_2O_3 composite ceramic by pressureless infiltration

An alloy steel/alumina composite was successfully fabricated by pressureless infiltration of X10CrNi18-8 steel melt on 30%(mass fraction) Ni-containing alumina based composite ceramic(Ni/Al2O3) at 1 600 ℃.The infiltration quality and interfacial bonding behavior were investigated by SEM,EDS,XRD and tensile tests.The results show that there is an obvious interfacial reaction layer between the alloying steel and the Ni/Al2O3 composite ceramic.The interfacial reactive products are(FexAly)3O4 intermetallic phas...     

IR Spectra Analysis of SiO2-TiO2-GeO2 Gel Glass of CO2 Laser Transmitting Hollow Waveguide

Both titanium and germanium were introduced into silicon dioxide system by sol-gel method to move its region of anomalous dispersion caused by IR resonance absorption towards the wavelength of CO₂ laser. It is indicated by IR absorption spectra that as the content of SiO₂ decreases in this glass system TiO₂ and GeO₂ tends to exist in their own phases. As for the gel glass with a composition of 40 SiO₂·30TiO₂·30GeO₂, when the temperature is below 600°C, germanium atoms exist mainly in Ge−O−Ge bonds. With the temperature increasing from 800°C to 1000°C, titanium atoms in Si−O−Ti bonds abmost transform into Ti−O−Ti bonds. Furthermore, a large number of Si−O−Ti and Si−O−Ge bonds formed when the temperature approaches 800°C, which makes a notable IR absorption band round the wavelength of CO₂ laser. Therefore, sol-gel based SiO₂−TiO₂−GeO₂ gel glass is a candidate material for CO₂ laser hollow waveguide. JING Cheng-bin: Born in 1974. This work was partly financially supported by the Foundation of Key Teachers of Ministry of Education, China.     

Combustion Synthesis of TiB2 Ceramics Powder from B2O3-TiO2-Mg System in Air Atmosphere

TiB2 ceramics powder was syuthesized from B2O3 - TiO2 - Mg system. The effects of TiB2 addition as diluent on the conbustion synthesis process were investigated. The results of thermodynanmic calculation and experiments stow that the increase of TiBz content ranging from 0 to 20wt% can reduce the adiabatic temperature Tad from 3100 Kto 2896 K and combustion temperature T,. from 2139 K to 1621 K respectively. The particle size and half width of the particle distributhm are also increased with the addition of TiB2 increasing from 0 to 20wt% . The combustion product is a mixture of TiB2 , MgO , and other intermediate phases. The leached produet contains mairdy TiBz, TiOz and TiN, and its oxygen content is 7.77wt% .     

Fabrication and microstructure of SiO2−GeO2 sol-gel glass coatings

SiO₂−GeO₂ sols and gel glass coatings with different contents of germanium dioxide were fabricated. Stable and transparent sols could only be obtained when the content of GeO₂ was under 35%. It is shown by SEM that only one continuous phase is observed in the coating of 65SiO₂·35GeO₂ and plenty of Ge, O and Si were all found in it. However, the separated phase is found in the coating of 60SiO₂·40GeO₂ and a large number of Ge and O. It is proved by the Raman scattering investigation that the separated phase in the coating of 60SiO₂ ·40GeO₂ is germanium dioxide. The congeries of hydrolystates of Cl₃ GeCH₂ CH₂ COOH play the main role in the formation of the separated phase when the proportion of GeO₂ is much higher. Si−O−Ge, Si−O−Si, and Ge−O−Ge bonds form in the coating of 65SiO₂·35GeO₂ and this coating is homogenous. Jing Cheng-bin: Born in 1974 This work was partly financially supported by the Foundation of Key Teachers of Ministry of Education, China     

Microstructures and Properties of SiC／Al2O3 ／Al- Si Composites Prepared by Reactive Penetration

The composition, microstructures and properties of SiC/Al2O3/Al-Si composites formed by reactive penetration of the molten aluminum into the preforms of SiO2 and SiC were investigated. The composition of the composites was measured by X-ray diffraction ( XRD ). The microstructures of the composites were also measured by scanning electron microscopy (SEM) and optical microscopy. In addition, the factors affecting the properties of the composites were discussed. The experiments show that the mechanical properties of the composites depend on their relative densities and the sizes of the fillers“ SiC gains“. The denser the SiC/Al2O3/Al-Si composites, the higher their bending strength. As the filler “SiC gains“ become fine, the bending strength of the composites increases.     

Preparation and Properties of Ag—TiO2 Thin Films on Glass SUbstrates

Ag-TiO2 thin films were prepared on glasses.The morphology and structure of Ag-TiO2 films were investigated by XRD.SEM and FT-IR.The photocatalytic and hydrophilic properties of Ag-TiO2 thin films were also evaluated by examining photocatalytic degradation dichlorophos under sunlight illumination and the change of contact angle respectively.The research results show that the Ag-TiO2 thin film is mainly composed of 20-100nm Ag and TiO2 particles,The Ag-TiO2 thin films possess a super-hydrophilic ability and higher photocatalytic activity than that of pure TiO2 thin film.     

Microstructure and Thermal Properties Analysis of （1-x）As2S3-x CdBr2 Glass System

The homogeneous glass sample for the ( 1 - x ) As2S3-xCdBr2, where x=0. 015,0. 035,0.05, was prepared by the conventional melt-quenched method. Amorphoas ( 1 - x ) As2S3-xCdBr2 alloys were determined by X-ray diffraction, thermal compreheasive analysis and Raman scattering. The glass transittion temperature (TR) deereases a bit with the addition of CdBr2 . Based on the experimental data, the microstrtucture is considered to be the discrete molecule species of AsBr3 and Cd - S atomic bonds or clusters are honigeneously dispersed in a disordered polymer network formed by AsS3 pyramids interlinked by sulfur bridges.     

Microstructural Probing of （1-x） GeS2- x Ga2S3 System Glasses By Raman Scattering

Roman scattering measurement of （ 1 - x ） GeS2-x Ga2S3 system glasses was conducted in order to understand the microstructural change caused by the addition of Ga2S3 . According to the change of Raman spectra with the addition of Ga2S3, two main structural transformations were deduced ： the gradual enhancement of ethane- like structural units S3 Ge- GeS3 （ 250 cm ^- 1） and S3 Ga- GaS3 （270 cm ^- 1 ） and the appearance of charge imbalanced units [ Ga2 S2 （ S1/2 ）4 ]^2- and [Ga（ S1/2 ）4 ]^- . And this change of structural aspect seems to give as a clue to understanding the cause of the increased rare-earth solubility.     

Microstructures and mechanism of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al composites fabricated by the reaction between SiO<Subscript>2</Subscript> and molten aluminum

Al₂ O₃/Al composite was fabricated by the reaction between SiO₂ and molten aluminum. The microstructures of the composite obtained under different reaction conditions were analyzed. The formation mechanism of the composite microstructure was discussed. Results show that the reaction kinetics is influenced remarkably by the reaction temperature, reaction time and the quantity of SiO₂. The morphologies of Al₂O₃ have different features, depending on the reaction temperature. The composite has equaxed Al₂O₃ grains when materials reacted below 1200°C, and the composite is composed of a large number of fine Al₂O₃ grains and aluninum. The composite has a frame-shaped Al₂O₃ microstructure at the reaction temperature of above 1250°C. CHENG Xiao-min: Born in 1964 Funded by the National Natural Science Foundation of China (No. 91522)     

Effect of Rare Earth Oxides on the Microstructure and Microwave Dielectric Properties of CaO-MgO-Nb2Os-TiO2 System Ceramics

La2O3 and SrO-doped CaO-MgO-Nb2O3-TiO2 system ceramics were prepared by solid-state ceramic technique.The microstructure and microwave dielectric properties of CaO-MgO-Nb2O5-TiO2-La2O3 cermics can be adjusted by varying the amount of La^3＋ or Sr^2＋ ions respectively.The replacement of Ca^2＋ by La^3＋ at A-site of the ceramics increases the quality factor Q value（ at 7.6GHz）as well as the temperature coefficient of resonant frequency τf and decreases the dielectric constant εr and the substitution of Sr^2＋ at A-site in this ceramics system exhibits opposite characteristics.The microwave properties of La^3＋,Sr^2＋-doped CaO-MgO-Nb2O5-TiO2 system ceramics depend on the degree of octahedral distortion inside materials.     

Preparation and Gas Permeation of Supported γ-Al2O3 Membranes Used as Substrate Layer for Microporous Membranes

γ-Al₂O₃ membranes were successfully deposited on the top of porous α-Al₂O₃ support by sol-gel process and characterized by means of XRD, SEM, N₂ adsorption and gas permeation. The γ-Al₂O₃ membranes, free of pin-holes and cracks, adhere tightly to the supports and have a thickness of about 7 μm. When sintered at 400°C, γ-Al₂O₃ membranes have a narrow pore size distribution, with a pore diameter of 3.6nm, and the transport of both H₂ and CO₂ in supported γ-Al₂O₃ membrane is governed by Knudsen mechanism, with H₂ permeance of 3.3×10⁻⁶ molm⁻² Pa⁻¹ s⁻¹ and H₂/CO₂ permselectivity close to the ideal Knudsen value at 50°C. The γ-Al₂O₃ membranes are suitable for being used as the substrates of microporous membranes. Founded by the Doctor Science Foundation of Chinese Education Ministry (Grant No. 98053301).