Manufacture Process of 8Y2O3 Stabilized ZrO2 from Nano Powders

The manufacture process of 8 mol% Y2O3 stabilized ZrO2 ( YSZ ) from nano powders, including the forming and sintering stages, was studied. During the forming process of YSZ powders, the relative density of YSZ increases lineally with the forming press, and the sintering linear shrinkage of YSZ to the forming press compiles to the parabola trend. When the forming press exceeding 500MPa, the samples with lower shrinkage and high density were obtained. The sintering temperature of YSZ decreases greatly because of the small size and high active surface of YSZ powders. As a result, the beginning sintering temperature of YSZ made in the experiment is as low as 825℃, and the end sintering temperature is 1300-1350℃ . The relative density of YSZ ceramic by solid sintering at 1300-1350℃ is more than 97% , with little and small pores in the uniform microstructure.     

Spark plasma sintering of undoped SnO<Subscript>2</Subscript> ceramics

Various parameters in spark plasma sintering(SPS),such as sintering temperature,holding time,heating rate,and pressure,were adopted to investigate their effects on the densification of pure SnO2 power.The obtained experimental data show that the SPS process enhances densification.The high-density undoped SnO2 ceramics (96.6% of theoretical) was obtained at much lower temperature (1000℃),within a much shorter time,compared to the conventional sintering process.The high-density undoped SnO2 ceramics (96.6% of theoretical) were obtained by SPS,under the condition of temperature:1000℃,pressure:40MPa,heating-rate:200℃/min,and holding time:3min     

Microstructure and corrosive property of Ni-P/nano-CeO<Subscript>2</Subscript> coating electrolessly prepared in acidic condition

Electroless Ni-P/nano-CeO₂ composite coating was prepared in acidic condition, and its microstructure and corrosive property were compared with its CeO₂-free counterpart. Scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and differential scanning calorimeter (DSC) were used to examine surface morphology and microstructure of the coating. Aqueous corrosion was done in 3%NaCl+5%H₂SO₄ solution and high temperature oxidation was done at 750 °C in air. The results showed that Ni-P coating had partial amorphous structure mixed with nano-crystals, while the Ni-P/CeO₂ coating had perfect amorphous structure. At high temperature, Ni3P precipitation and Ni crystallization took place in both coatings at different temperatures. Aqueous corrosion property and high temperature oxidation property of the composite coating were remarkably improved due to the coating’s microstructure change and the rare earth doping effect. During the co-deposition process, some Ce ⁿ⁺(n=3, 4) ions may be adsorbed to metal/solution interface and hinder nickel deposition. Ni-P/CeO₂ coating’s perfect amorphous structure results from the hindered crystal- typed deposition of nickel and the promoted deposition of phosphorous.     

Effect of Mg/Al ratios on hydration mechanism of tabular alumina carbon composites reinforced by Al<Subscript>4</Subscript>C<Subscript>3</Subscript> in situ reaction

Hydration mechanism of tabular alumina carbon composites reinforced by Al₄C₃ in situ reaction with Mg and Al was researched in water steam using super automatic thermostatic water bath from 25 °C to 85 °C. It is shown that hydration mechanism of the composites is chemical reaction control at 44.3 °C-84 °C in H₂O(g). The hydration was controlled by diffusion from 24.7 °C to 33 °C. The ratio of added Mg/Al influences the HMOR of the composites.The mechanism of HMOR of the composites with different ratios of Mg/Al can be discovered by means of SEM analysis. The active Mg/Al powder and flake graphite inside give the composites outstanding hot strength resulting from the interlocking structure of Al₄C₃ crystals at high temperature. Besides, the matrix changes into the Al₄C₃ with high refractoriness. The method of preventing the hydration of tabular alumina carbon composites reinforced by Al₄C₃ in situ reaction was immersed in the wax at suitable temperature or storing them below 33 °C in a dry place or storing them with paraffin-coating.     

Development of Zr/ZrO<Subscript>2</Subscript> high temperature and high pressure sensors for <Emphasis Type="Italic">in-situ</Emphasis> measuring chemical parameters of deep-sea water

In order to in situ measure chemical parameters of deep-sea water and hydrothermal fluids at midocean ridge(MOR), it is necessary to use high temperature and high pressure chemical sensors.Developing new sensors is essential to measure in-situ pH and other chemical parameters(dissolved H2, dissolved H2S) of deep-sea water and hydrothermal fluids in a wide temperature range(2℃―400℃) at MOR vents.The YSZ(Yttria Stabilized Zirconia, 9%Y2O3) ceramic-based(HgO/Hg) chemical sensors possess excellent electrochemic...     

Effect of matrix composition on physical properties of Al<Subscript>3</Subscript>CON in-situ reaction reinforced corundum composite

60% white corundum used for aggregate, 5% aluminium powder for fixed additions and 35% various additives for matrix were prepared for specimens 1#,2#,3#. They were mixed uniformly with the suitable resin as a binder and pressed under pressure of 315 ton forging press, then dried at 200℃ for 24 h. Effects of various additives on 1500 ℃×2 h creep properties of Al3CON reinforced corundum composite were researched. The experimenal results show that creep coefficients of specimens 1#,2#,3# at 1500 ℃×2 h are 1.4×10^- 4, -9.4×10^-4, -22.6×10^-4, respectively. Crushing strength of the slide plate added with suitable additive A after fired at 1500 ℃ ×3 h reaches to 225 MPa, the creep rate is positive all the time from 0% to 0.014% at 1500 ℃ for 2 h. The microstructure result analysis shows that reinforced phases of Al3CON fiber composite have been formed after fired with Al powder in coke at high temperatures for specimen 1#, and the strength of the composite is increased. The hot modulus of rupture is up to 59 MPa at 1400 ℃ and the RUL is obviously higher than that at 1700 ℃. Its service life is two times as that of Al2O3-C slide plate when used in the process of pouring steel. The mechanism of creep rate resistance of the composites can be discovered by means of SEM and EDAX analysis. It is concluded that the active Al3CON and Al2O3 multiphases that were formed by N2 in gas, C, Al and Al2O3 inside the matrix of the composites during in-situ reaction,which gives the composites outstanding creep rate resistance for the dense zone resuiting from Al3CON oxidation that inhibits contraction at the high temperature. Besides, the matrix will turn into the multiphase with high refractoriness, N content and its Al3CON reinforced fiber will further increase accordingly. In addition, Al3CON formed by Al2O3 and C, Al in the matrix with N2 in gas will inhibit the creep rate and also greatly improve the creep rate resistance of the composites.     

Synthesis and Dielectric Properties of Ba3NaBiNb10O30 Ceramics

A new niobate Ba3 NaBiNb10O30 was synthesized by the solid state reaction. The reaction mixture was characterized by thermogravimetric and differential thermal analysis ( TG-DTA ), X-ray diffraction and dielectric constant measurements. The results show that Ba3NaBiNb10O30 has an orthorhombic tungsten bronze structure with space group Cmm2 and the unit cell parameters are a = 1. 7660( 1 ) mm, a = 1. 7626( 1 ) mm, c = 0.78621(6) mm, Z = 4. Ba3 NaBiNb10O30 undergoes two phase transitions at 200℃ and 400℃, respeaively.     

Preparation and microstructure of spinel zinc ferrite ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> by Co-precipitation method

Spinel zinc ferrites ZnFe₂O₄, prepared by co-precipitation method using the zinc nitrate Zn(NO₃)₂·6H₂O and ferric nitrate Fe(NO₃)₃·2H₂O as the raw materials, were characterized by the thermo gravimetric analysis (TG) and differential scanning calorimeter (DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM). The influence of synthesis conditions, such as Zn/Fe molar ratio, pH value, the sintering temperature and time, on the microstructures was detailedly investigated. The relationships between the microstructures and the synthesis conditions were discussed. The results show that the pure spinel zinc ferrites ZnFe₂O₄ are formed when the Zn/Fe molar ratio is 1.05:2 at pH=8.5 or Zn/Fe molar ratio is 1:2 at Ph=9-10, and the precursors are sintered at 1100 °C for 4 h. Especially no other phases are observed when the Zn/Fe molar ratio is 1:2 at pH=10 and the precursor is sintered above 700 for 4 °C h. The higher sintering temperature and longer sintering time contribute to grain growth.     

Preparation and Performance of Si<Superscript>4+</Superscript>-doping Rod-shaped TiO<Subscript>2</Subscript> Powder by Nonhydrolytic Sol-gel Method

Titania (TiO₂) nanorod powder was prepared by nonhydrolytic sol-gel method using titanic chloride (TiCl₄) as titanium source, methylene dichloride (CH₂Cl₂) as solvent, absolute ethyl alcohol (CH₃CH₂OH) as oxygen donor. The effects of Si⁴⁺ doping on the TiO₂ nanocrystalline phase transformation temperature were systematically researched. The results showed that when the molar ratio of Ti⁴⁺ to Si⁴⁺ is 1 to1.3, TiO₂ prepared by calcination at 1100 °C for 1 hour exhibits rod shape and has good photocatalytic activity. Doping of Si⁴⁺ makes glass phase core-shell structure forming on the surface of anatase crystal particles, which can inhibit crystal phase transformation and raise the transformation temperature, making TiO₂ stable in anatase phase at 1200 °C.     

Eleetrodeposition and Characterization of CulnSe2 Thin Films for Solar Cells

CulnSe2 （CIS） thin films were prepared by electrodeposition from the de-ionized water solution consisting of CuCl2, InCl3, H2SeO3 and Na-citrate onto Mo/soda-lime glass （SLG） substrates. A thermal processing in Se atmosphere at 450℃ was carried out for the electrodepositied films to improve the stoichiometry. The composition and morphology of selenized CIS thin films were studied using energy dispersive spectroscopy （EDS） and scanning electron microscopy （SEM）, respectively. X-ray diffraction （XRD） studies show that the annealing in Se atmosphere at 450℃ promotes the structural formation of CIS chalcopyrite structure.     

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)     

Low-temperature sintering and microwave dielectric properties of Ba<Subscript>2</Subscript>Ti<Subscript>3</Subscript>Nb<Subscript>4</Subscript>O<Subscript>18</Subscript> ceramics

The effects of CuO and H3BO3 additions on the low-temperature sintering,microstructure,and microwave dielectric properties of Ba2Ti3Nb4O18 ceramics were investigated.The addition of less amount of CuO (< 1 wt%) considerably facilitated the densification of Ba2Ti3Nb4O18 ceramics.Appropriate addition of H3BO3 (< 3.5 wt%) remarkably improved the microwave dielectric properties of ceramics.The addition of H3BO3 and CuO successfully reduced the sintering temperature of Ba2Ti3Nb4O18 ceramics from 1300 to 1050 ℃.B...     

Effect of ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass addition on the microwave dielectric properties of BaO-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The effect of ZnO-B₂O₃(ZB) glass addition on the sintering behavior, microstructures and microwave dielectric properties of BaO-Nd₂O₃-TiO₂-Bi₂O₃ (BNTB) system was investigated with the aid of X-ray diffraction, scanning electron microscopy and capacitance meter. It is found that the ZB glass addition, acting as a sintering aid, can effectively lower the sintering temperature of BNTB system to 850 °C. The dielectric constant of BNTB-ZB ceramics increases with the increase of soaking time and the value of dielectric loss decreased with increasing soak time. The optical dielectric properties at 1 GHz of ɛ=74, tan δ=4×10⁻⁴, and TCC=25 ppm/°c were obtained for the BNTB system doped with 25 wt% ZB glass sintered at 850 °C for 2 h, representing that the BNTB-ZB ceramics could be promising for multilayer low temperature co-fired ceramics applications.     

A light-weight high-entropy alloy Al<Subscript>20</Subscript>Be<Subscript>20</Subscript>Fe<Subscript>10</Subscript>Si<Subscript>15</Subscript>Ti<Subscript>35</Subscript>

A light-weight high-entropy alloy (LWHEA) Al₂₀Be₂₀Fe₁₀Si₁₅Ti₃₅ has been developed to have unique mechanical properties and oxidation resistance. One major and two minor phases are observed in the as-cast microstructure. The density of the alloy is 3.91 g cm^?3, and its hardness is HV 911, which is higher than quartz. The hardness and hardness to density ratio are the highest of all light-weight alloys reported before. In addition, it has excellent oxidation resistance at 700°C and 900°C, which far exceeds that of Ti-6Al-4V. Thus, the combination of properties is promising for high-temperature applications, which require light weight, wear-resistant and oxidation-resistant components.     

Influences of heat treatments on crystallization in SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO-K<Subscript>2</Subscript>O-F glass-ceramics

Five kinds of heating treatment processing were chosen according to the experiment result of differential scanning calorimeter to prepare SiO2-Al2O3-MgO-K2O-F glass ceramics samples.The effects of heat treatment processing on the crystallization of these samples were explored by X-ray diffraction and scanning electron microscopy techniques.The results indicate that phase separations can occur in the bulk regions of the glass sample when holding at 670 ℃ for 3 h.The phase separation can accelerate the precip...     

Hot-corrosion mechanism of Ni-Cr coatings at 650°C under different simulated corrosion conditions

The oxidation and lower temperature hot corrosion (LTHC) processes occurring on the surface of Ni-Cr coatings produced by high velocity arc spray (HVAS) were studied. Several different conditions were studied under simulated boiler conditions at 650°C. The protection effect of an Al coating deposited by HVAS onto the Ni-Cr coating was also investigated. Microscope, X-ray diffraction and corrosion rate curves have been used to analyze corrosion mechanisms. The experimental results show that: 1) The oxidation rates are almost superposed in both air (no SO₃) and in simulated coal-fired gas (containing SO₃) as long as no salt was present on the surface. These rate curves show a logarithmic relationship. 2) When the surface is coated with salt (75%K₂SO₃ + 25%Na₂SO₃) the rate curve for LTHC of the Ni-Cr coated surface shows a parabolic shape in the simulated coal-fire flue gas. In air only the oxidation reaction takes place, the second type of LTHC was not seen. And 3) the Al over coating on the Ni-Cr enhances resistance to LTHC because an inter-metallic compound, Al₃Ni₂, forms at the Al/Ni-Cr interface and because of the increase in coating thickness.     

Preparation and characterization of nanocomposite MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>

Nanocomposites MgFe₂O₄/SiO₂ were successfully synthesized by the sol-gel method in the presence of N, N-dimethylformamide (DMF). The formation of pure MgFe₂O₄ was confirmed by powder X-ray diffraction (XRD) and electron diffraction. The structural evolution of MgFe₂O₄ nanocrystals was followed by powder X-ray diffraction and IR absorption spectroscopy. The formation of spinel structure of MgFe₂O₄ started at 800 °C, and completed at 900 °C. The transmission electron microscopy (TEM) measurements suggest that the particle sizes increase with the increasing annealing temperature, and the mean particle sizes of the spherical samples annealed at 800 °C, 900 °C and 1 050 °C are ca. 3 nm, 8 nm and 11 nm, respectively. Magnetization measurements at room temperature and 78 K indicate superparamagnetic nature of these MgFe₂O₄ nanocrystals. Funded by the National Natural Science Foundation of China(No. 30771676), the Natural Science Foundation of Jiangsu Province (No. BK20081842), and the Foundation of Nanjing Bureau of Personal for the Returned Overseas Chinese Excellent Scholars     

Synthesis and properties of Li<Subscript>2</Subscript>MnSiO<Subscript>4</Subscript>/C cathode materials for Li-ion batteries

Carbon was coated on the surface of Li₂MnSiO₄ to improve the electrochemical performance as cathode materials, which were synthesized by the solution method followed by heat treatment at 700 °C and the solid-state method followed by heat treatment at 950 °C. It is shown that the cycling performance is greatly enhanced by carbon coating, compared with the pristine Li₂MnSiO₄ cathode obtained by the solution method. The initial discharge capacity of Li₂MnSiO₄/C nanocomposite is 280.9 mAh/g at 0.05 C with the carbon content of 33.3 wt%. The reasons for the improved electrochemical performance are smaller grain size and higher electronic conductivity due to the carbon coating. The Li₂MnSiO₄/C cathode material obtained by the solid-state method exhibits poor cycling performance, the initial discharge capacity is less than 25 mAh/g.     

Preparation and anti-oxidation mechanism of mullite/yttrium silicate coatings on C/SiC composites

In order to enhance the oxidation resistance of C/Si C composites, mullite/yttrium silicate coatings were fabricated on C/Si C composites through dip-coating route. Al_2O_3-SiO_2 sol with high solid content was selected as the raw material for mullite and "silicone resin + Y_2O_3 powder" slurry was used to synthesize yttrium silicate. The microstructure and phase composition of coatings were characterized, and the investigation on oxidation resistance and anti-oxidation mechanism was emphasized. The as-fabricated coatings consisting of SiO_2-rich mullite phase and Y_2Si_2O_7 phase show high density and favorable bonding to C/Si C composites. After oxidized at 1 400 ℃ and 1 500 ℃ for 30 min in static air, the coating-containing C/Si C composites possess 91.9% and 102.4% of the original flexural strength, respectively. The desirable thermal stability of coatings and the further densification of coatings due to viscous flow of rich SiO_2 and Y-Si-Al-O glass are responsible for the excellent oxidation resistance. In addition, the coating-containing composites retain 99.0% of the original flexural strength and the coatings exhibit no cracking and desquamation after 12 times of thermal shock from 1 400 ℃ to room temperature, which are ascribed to the combination of anti-oxidation mechanism and preferable physical and chemical compatibility among C/Si C composites, mullite and Y_2Si_2O_7. The carbothermal reaction at 1 600 ℃ between free carbon in C/Si C substrate and rich SiO_2 in mullite results in severe frothing and desquamation of coatings and obvious degradation in oxidation resistance.     

Effect of annealing temperature on the ferroelectric properties of BiFeO<Subscript>3</Subscript> thin films prepared by sol-gel process

Sol-gel process was adopted to prepare BiFeO₃ films. BiFeO₃ films were deposited on LaNiO₃ coated Si(100) substrates annealed at 500 and 550 °C, respectively. The X-ray diffraction results reveal that BiFeO₃ film has a rhombohedrally distorted perovskite structure with space group R3c. The film annealed at 500 °C has larger remnant polarization (P _r) of 35.3 μC/cm². For the film annealed at 550 °C, smaller remnant polarization of P _r=4.8 μC/cm² is observed for its low breakdown electric field. Lower leakage conduction is observed in the film annealed at 500 °C at low applied field.