Preparation of M_2O_3-CeO_2(M=La,Fe,and Al) Compoundoxide Catalyst and Its Degradation Performance

As one of the most active rare earths,CeO_2 has caused extensive concern due to its multifunctional properties.CeO_2-based compound oxide of M_2O_3-CeO_2 (M=La,Fe,and Al) were prepared by coprecipitation and impregnation methods.The photocatalytic performance of the samples for the degradation methylene blue was studied under UV and visible light irradiation.The effects of constituents on the properties of the CeO_2-based catalysts were investigated by XRD,TEM,BET,and UV-Vis spectrophotometer.The highest degradation of methylene blue under 230W UV light was almost 100% at 50 min by La_2O_3/Fe_2O_3-CeO_2/γ-Al_2O_3 catalyst and 99.42% at 50 min by Fe_2O_3-CeO_2/γ-Al_2O_3 catalyst.The methylene blue removal efficiency under indoor natural light reaches 93.81% by La_2O_3/Fe_2O_3-CeO_2/γ-Al_2O_3 catalyst and 92.34% by Fe_2O_3-CeO_2/γ-Al_2O_3 catalyst at 50 min.The order of catalytic degradation activity is La_2O_3/Fe_2O_3-CeO_2/γ-Al_2O_3Fe_2O_3-CeO_2/γ-Al_2O_3La_2O_3-CeO_2/γ-Al_2O_3Al_2O_3,owing to their structural features.The doping of La~(3+) or Fe~(3+) onto CeO_2/γ-Al_2O produced much more oxygen vacancies under light irradiation and reduced the energy laps of CeO_2 with value of 2.86 ev,which improved the photocatalytic redox performance of the composite oxide.     

STUDY ON PREPARATION OF YBa_2Cu_3O_(7-x) ULTRAFINE POWDERS BY SOL-GEL PROCESS

The ultrafine powders of YBa_2Cu_3O_(7-x) withthe size of 100nm were synthesized by Sol-Gel process using cit-rate as complex and ammonium hydroxide to adjust pH of solu-tion. The process of Sol formation and Gel polymerization ofYBa_2Cu_3O_(7-x) in the Sol-Gel synthetic reaction has bee studied.The particle size,pruity,sintering activity and superconductingproperties of YBa_2Cu_3O_(7-x)prepared by Sol-Gel method are betterthan by solid state reaction.     

Microstructure and Wear Behaviour of Laser-Induced Thermite Reaction Al2O3 Ceramic Coatings on Pure Aluminum and AA7075 Aluminum Alloy

Wear-resistant laser-induced thermite reaction Al_2O_3 ceramic coatings can be fabricated on pure Al and AA7075 aluminum alloy by laser cladding(one-step method)and laser cladding followed by laser re-melting(two-step method)using mixed powders CuO-Al-SiO_2 in order to improve the wear properties of aluminum and aluminum alloy,respectively.The microstructure of the coatings was characterized by scanning electron microscopy(SEM)and X-ray diffraction(XRD).The wear resistance of the coatings was evaluated under dry sliding wear test condition at room temperature.Owing to the presence of hardα-Al_2O_3 andγ-Al_2O_3 phases,the coatings exhibited excellent wear resistance.In addition,the wear resistance of the coatings fabricated by two-step method is superior to that of the coatings fabricated by one-step method.     

Preparation of High Performance Grccn Alumina Ceramic Balls by Roller Production Waste

To reuse roller waste as a raw material of high performance green ceramic balls,three kinds of white alumina ceramic balls whose wear resistance were 2-3 times of the best high alumina ceramic ball with 90% Al_2O_3 were prepared,and the Al_2O_3 content of the prepared balls was 75%.It is found that the effect of calcia and magnesia on the wear resistance of ceramic balls is contrast to the accepted one:the wear rate of the ceramic balls prepared in CaO-Al_2O_3-SiO_2 system is the lowest and the wear rate of the ceramic balls prepared in MgO-Al_2O_3-SiO_2 is the highest.The main crystal phase of the ceramic ball is mullite and corundum.The ceramic ball granular is uniform and fine with 4-5μm average size.The pore diameter is about 2μm.The wear way of the ceramic balls is mainly transcrystalline fracture.     

Low-temperature Rapid Synthesis of Ultrafine Hafnium Carbide Ceramic Powders

Nano hafnium carbide(HfC) powders were synthesized by sol-gel combining hightemperature rapid heat treatment process using citric acid and hafnium tetrachloride as the raw materials. The effects of ball milling treatment on the phase and morphology of pyrolysis products(HfO_2-C) and final HfC product were investigated and the influences of heat treatment temperature and holding time on the structure and properties of the synthesized hafnium carbide powders were also studied. The experimental results showed that the HfO_2-C powders with good uniformity and small particle size were prepared by controlling the milling time. Pure HfC powders with an average particle size of 500 nm were obtained at 1 700 ℃ with a holding time of 3 min, and the oxygen content was about 0.69 wt%, lower than that of the hafnium carbide powders prepared by SPS(0.97%).     

Structure and Electric Conductivity of Ce-doped Bi_2O_3 Electrolyte Synthesized by Reverse Titration Chemical Coprecipitation

Ce-doped Bi_2O_3 nanopowders were prepared by reverse titration chemical coprecipitation from Bi~(3+)and Ce~(4+)containing aqueous solution.Techniques of X-ray diffraction(XRD),transmission electron microscopic(TEM)and Fourier transform infrared spectroscopy(FTIR)were employed to characterize the as-synthesized materials.The XRD patterns indicated that the peaks can be easily indexed toβ-Bi_2O_3 and no diffraction peaks of Ce or other impurity phases were detected in the prepared samples.The calculated average crystalline size decreased from 31.72 to 11.96 nm when the Ce content increased from 1 wt%to 10 wt%.The morphology changed from flake-like into the spherical-like with increase in Ce content.The electric conductivity of Ce-doped Bi_2O_3 electrolyte was also investigated by two probe DC method.Conductivity analysis exhibited that the rate of conductivity increased with increasing Ce~(2+)ratio,when the Ce concentration was up to 5 wt%,the as-synthesized Ce-doped Bi_2O_3 electrolyte showed the maximum value of conductivity(0.295 S?cm~(–1)).     

Preparation and structure characteristics of nano-Bi2O3 powders with mixed crystal structure

The nano-Bi2O3 powders were prepared by a chemical precipitation method with Bi(NO3)3, HNO3 and NaOH as reactants. The structural characteristics and morphology of nano-Bi2O3 powders were investigated by X-ray diffraction and transmission electron microscopy, respectively. The results show that under the optimum condition that 300g/L Bi(NO3)3 reacts at 90℃ for 2 h, the Bi203 powders with 60 nm on the average and 99.5% in purity are obtained. The prepared nano-Bi2O3 powders contain a mixed crystal structure of monoclinic and triclinic instead of traditional structure of monoclinic α-Bi2O3. And the mixed crystal structure is stable in air. The reason for the appearance of the mixed crystal structure may be that the ionic radius ratio of Bi^3 to O^2- changes easily during the formation of nano-Bi2O3 particles by a chemical precipitation method.     

Hydrothermally Synthesizing Nanospheres of Pd Loaded TiO_2 for Photocatalytically Reducing CO_2 in Isopropanol to Isopropyl Formate

Photocatalytic reduction of CO_2 was carried out on villiform spherical catalysts of Pd-TiO_2 in isopropanol solution.The catalysts were synthesized by hydrothermal method,their structures,morphologies and optical absorption properties were characterized by X-ray diffraction(XRD),energy dispersive X-ray spectroscopy(EDS),scanning electron microscopy(SEM),transmission electron microscopy(TEM),highresolution transmission electron microscopy(HRTEM)and UV-vis absorption spectroscopy(UV-vis).The photocatalytic activities with different loading amounts and morphologies were evaluated for determining the dominant effect and optimizing the catalyst preparation.Based on a villiform spherical TiO_2 with the largest specific surface area in our experiments,we prepared a set of catalysts with various loading amounts of palladium and tested them by bubbling CO_2 through the slurry of catalyst and isopropanol.The highest formation rate of isopropyl formate was 276.6μmol/g?cat/h.Eventually we proposed the reaction mechanism.     

Effect of anions on preparation of ultrafine α-Al2O3 powder

Ultrafine alumina power was obtained by calcining the precursor at 1 200 ℃ for 2 h, which was prepared by homogeneous precipitation method using aluminium salts and urea as raw materials. The effects of anions on the morphology, particle size, surface area and configuration of the precursors were studied. The results show that the reactions of urea with aluminium nitrate and aluminium chloride result in agglomerates gels with bad filtering performance, the morphology is fibrillar. Aluminium sulphate-urea reactions result in the direct formation of amorphous powders with good filtering performance, of which morphology are regular spherical particles with larger granularity and smaller surface area. The reaction of mutual compound of aluminium sulphate and aluminium nitrate with molar ratio of 40:60 with urea can produce precursor with good filtering performance, spherical morphology, and uniform granularity distribution in the particle size range of 2-3 μm.     

Temperature-insensitive microwave absorption of TiB_2-Al_2O_3/MgAl_2O_4 ceramics based on controllable electrical conductivity

The design of the high-temperature microwave absorbing materials (MAMs) with temperature-insensitive and considerable microwave absorption (MA) capacity is a tremendous challenge.Ti B_2-Al_2O_3/Mg Al_2O_4 MAMs are prepared by the spark plasma sintering (SPS).Further,the influences of the Al_2O_3 content on the flexural strength,thermal stability,high-temperature electrical conductivity,dielectric and MA properties are discussed.The results show that the Al_2O_3 content is associated with flexural strength,high-temperature thermal stability,electrical conductivity,dielectric and MA properties.Meanwhile,the temperatureinsensitive and considerable MA properties with the minimum reflection loss (RL_(min)) ranging from -19.4 to -14.3 dB and the effective absorption bandwidth (EAB,RL-5 dB) of 3.19–3.55 GHz are attained at 25°C–700°C in 8.2–12.4 GHz as the Al_2O_3 content increases from 70.6 wt%to 80.6 wt%.This is ascribed to the compensating effect of the positive and negative temperature coefficient materials on the high-temperature electrical conductivity as well as the co-play of the dipolar and interfacial polarization at elevated temperatures.Consequently,Ti B_2-Al_2O_3/Mg Al_2O_4 ceramics exhibit the ideal prospect as the high-temperature MAMs.     

Synthesis of sodium beta alumina films by heat treatment of sodium aluminum oxides

Sodium beta alumina(Na-β-alumina) films were synthesized by heat treatment of NaAl_6O_(9.5)and γ-NaA1O_2 films at temperatures of 1 373-1 573 K.Single-phase γ-NaA1O_2 and NaAl_6O_(9.5) films were prepared by laser chemical vapor deposition at the deposition temperatures of 976 and 1 100 K,respectively.Subsequent heat treatment of the films resulted in the formation of Na-β-alumina with α-Al_2O_3 at temperatures above 1 373 K for NaAl_6O_(9.5) and 1 473 K for γ-NaA1O_2.On heat treatment at temperatures of 1 473-1 573 K,the faceted morphology with terraces of the as-deposited(110)-oriented γ-NaAlO_2 films transformed to a porous morphology with platelet grains comprising Na-β-alumina and α-Al_2O_3.On heat treatment at temperatures of1 373-1 473 K,the pyramidal,faceted grains of as-deposited NaAl_6O_(9.5) films transformed to planer,shapeanisotropic morphology in the film of mixed Na-β-alumina and α-Al_2O_3.A dense morphology was observed in both the as-deposited and heat-treated NaAl_6O_(9.5) films.     

Facile Preparation of Al_2O_3 Hollow Microspheres Via a Urea-mediated Precipitation Process

Al_2 O_3 hollow microspheres without noticeable aggregation have been prepared via a facile templating route with urea-mediated precipitation. The precipitation process is different from the surfaceadsorption method which is confined to the adsorption capacity of the template surface. TEM and SEM images indicate that most of these Al_2 O_3 hollow microspheres with shell thickness of tens of nanometers and diameters in a narrow range of 100-200 nm consist of a shell of closely packed nanoparticles. The optimal amount of H_2 O and EtOH are 40 and 120 m L, respectively. The specific surface area, average pore size and pore volume of the Al_2 O_3 hollow microspheres(calcinated at 600 ℃) are 328.52 m~2/g, 17.496 nm and 1.985 cm~3/g, respectively. As the calcination temperature increases from 600 to 1 100 ℃, the phase composition changes from γ-Al_2 O_3 to θ-Al_2 O_3 and a-Al_2 O_3, and the surface morphology appears to change from a relatively rough surface formed by nanoparticles to a smooth surface formed by lamellar, which lead to the closure of pore channels and the reduction of specific surface.     

Comparative study of β-Si3N4 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 homo- geneous 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.     

Effect of Na_3AlF_6 Addition and Surface Modification of SiCp on the Microstructure and Mechanical Properties of SiCp/Al Composites

Al-matrix composites reinforced with 56.5 vol% SiC were prepared by powder metallurgy with different amounts of additives and surface modifications of SiC_p. The crystalline phase, morphology, elements on the surface of SiC_p and the interface between SiC_p and Al were characterized by XRD, SEM, EDS and EPMA. The results show that it is favorable for the reaction between TiO_2-C on the surface of SiC_p and Al at the SiC_p-Al interface at 1 050 ℃. Besides, the process of Na_3 AlF_6 melting, dissolving and then contacting with Al_2 O_3 formed the NaF-AlF_3-Al_2 O_3 system, which generated OAlF2-, promoting the dessolution of Al_2 O_3 film on the surface of Al powder. Na_3 AlF_6 meets the needs of chemical reaction in TiO_2-C-Al system at the SiC_pAl interface in the way of offering more molten Al. After 0.75 wt% Na_3 AlF_6 was added into raw materials, the whole TiO_2-C film and most SiO_2 film were destroyed and the interfacial bonding between SiC_p and Al was keeping good, in which no obvious void and crack were observed. Meanwhile, no brittle Al_4 C_3 phase formed in the system. At this time, the flexure strength and density of samples presented optimal values, reaching up to 106.5 MPa and 90.77% respectively.     

Preparation of Fe-M Intermetallic/TiC-M_2O_3 Ceramic Composites from Ilmenite by SHS

Fe-Al intermetallic/TiC-Al_2O_3 ceramic composites were successfully prepared by self- propagating high-temperature synthesis(SHS)from natural ilmenite,aluminium and carbon as the raw materials.The effects of carbon sources,preheating time and heat treatment temperature on synthesis process and products were investigated in detail,and the reaction process of the FeTiO_3-Al-C system was also discussed. It is shown that the temperature and velocity of the combustion wave are higher when graphite is used as the carbon source,which can reflect the effect of the carbon source structure on the combustion synthesis; Prolonging the preheating time or heat treatment temperature is beneficial to the formation of the ordered intermetallics;The temperature and velocity of the combustion wave are improved,but the disordered alloys are difficult to eliminate with the preheating time prolonged.The compound powders mainly containing ordered Fe3Al intermetallic can be prepared through heat treatment at 750℃.     

Preparation of AgSnO2 composite powders by hydrothermal process

Silver-tin oxide powders were synthesized by the hydrothermal method with Ag（NH3）2^＋ solution and Na2SnO3 solution as raw materials and Na2SO3 as reductant. The precipitation conditions of Na2SnO3 solution and the reduction conditions of Ag（NH3）2^＋ were also investigated. The powders prepared were characterized by differential thermal analysis （DTA）, X-ray diffraction analysis （XRD）, scanning electron microscope （SEM） and energy spectrum analysis, The results show that pH value of the solution is a key parameter in the formation of Sn（OH）4 precipitate and the reduction reaction of Ag（NH3）2^＋ can release H^＋ ions, which results in synchronous precipitation of Sn（OH）6^2- as Sn（OH）4. The reduction of Ag（NH3）2^＋ and precipitation of Na2SnO3 occur simultaneously and the coprecipitation of silver and tin oxide is reached by the hydrothermal method. The silver-tin oxide composite powders have mainly flake shape of about 0.3 μm in thickness and there exists homogeneous distribution of tin oxide and silver in the powder synthesized.     

Phase and Rietveld Refinement of Pyroehlore Gd_2Zr_2O_7 Used for Immobilization of Pu （Ⅳ）

The phase of pyrochlore Gd_2Zr_2O_7 used for immobilization of Pu （Ⅳ） was investigated, tetravalent cerium was used as the simulacrum for plutonium with tetravalence, and the compounds in the system Gd_2Zr_2-_xCe_xO_7 （0.0≤x≤2.0） were synthesized via a high temperature solid reaction method with Gd_2O_3 and ZrO_2 powders being used as the starting materials. Based on the collected XRD data of the gained samples, the phase and microstructural change of compounds were calculated by means of rietveld structural refinement method. The experimental results indicated that the phases of compounds were changed from pyrochlore to fluorite-type phase with the increasing x. The linear relation between a and x was discovered in the range of fluorite-type phase, which accorded with a = 0.52748 ＋ 0.00825 x （0.2≤x≤2.0）, while V= 0.14668 ＋ 0.00711 x （0.2≤x≤2.0） was also achieved.     

THE NANOCOMPOSITE FILM OF POLYMER INTERCALATION IN V_2O_5 XEROGEL

The nanocomposite films were prepared by poly(ethylene oxide), PEO, intercalation in V_2O_5 xerogel in sol-gel. The synthesis and state of the films are in vestigated by the XRD, IR, SEM, etc. The results show that V_2O_5 xerogel is a layered structure which arranges in c-direction. The interlayer distance of V_2O_5 xerogel increases remarkably when PEO is intercalated in V_2O_5 xero gel interlayer. PEO has strong interaction with V_2O_5 host. The surface of the films is homogeneous without holes and cracks.     

In Situ Growth of Vanadium Oxide on Reduced Graphene Oxide for the Low-Temperature NO-SCR by NH_3

The vanadium oxide/reduced graphene oxide(V_2 O_5/rGO) composite catalyst which determined the selective catalytic reduction activity(SCR) of NO with NH_3 was prepared by a simple solvothermal method. The physicochemical properties of the catalysts were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), Raman, X-ray energy spectrometer(XPS) and N_2 sorption isotherm measurement(BET). Results of NH_3-SCR showed that the NO conversion of V_2 O_5/rGO catalyst could reach 54.3% at 100 ℃. And the removal of NO increased to 74.6% when the temperature was up to 220 ℃. By characterizing the microstructure and morphology of the V_2 O_5/rGO catalysts prepared by in-situ growth and mechanical mixing methods, it was further shown that V_2 O_5 nanoparticles were highly dispersed and in situ growth on the rGO surface. Based on X-ray energy spectrometer, V_2 O_5/r GO catalyst had good low temperature denitrification performance due to the chemical adsorption oxygen and low-valent vanadium oxide contained in V_2 O_5/rGO catalyst, which was beneficial to the redox reaction between V_2 O_5 and graphene.