bluuebunny/crossref_metadata_2025 huggingface dataset:
Retention of Silica Nanoparticles in a Lab-Scale Membrane Bioreactor: Implications for Process Performance and Membrane Fouling
Authors: Sibag Mark , Lee Soo , Kim Hee , Cho Jinwoo
Published: July 2016

In conventional activated sludge (CAS) involving aerobic biological processes, the retention of silica nanoparticles (SiO2 NPs) has no detrimental effect on chemical oxygen demand (COD) and ammonia nitrogen (NH3–N) removal. However, for the membrane bioreactor (MBR) system, which is also based on the activated sludge process in addition to the membrane separation process, it has implications not only on the process performance but also on membrane fouling. To investigate these two implications in lab-scale experiments, we continuously operated a control MBR and two experimental MBRs, in which the 28 nm SiO2 NPs and 144 nm SiO2 NPs were added separately to the influent at a final concentration of 100 mg/L. Although the retention of SiO2 NPs in the MBR, as confirmed by dynamic light scattering (DLS) analysis, did not compromise the COD and NH3–N removal, it resulted in substantial increases in the transmembrane pressure (TMP) suggesting the onset of membrane fouling. Analyses by batch-dead end filtration revealed the same fouling trend as observed during the continuous MBR experiments; membrane fouling is aggravated in the presence of SiO2 NPs. This was evident from permeate flux decline of between 30% and 74% at very low TMP (5 kPa) and the further increases in the total resistance.
Molecular weight control in organochromium olefin polymerization catalysis by hemilabile ligand–metal interactions
Authors: Mark Stefan , Wadepohl Hubert , Enders Markus
Published: July 2016

A series of Cr(III) complexes based on quinoline-cyclopentadienyl ligands with additional hemilabile side arms were prepared and used as single-site catalyst precursors for ethylene polymerization. The additional donor functions interact with the metal centers only after activation with the co-catalyst. Evidence for this comes from DFT-calculations and from the differing behavior of the complexes in ethylene polymerization. All complexes investigated show very high catalytic activity and the additional side arm minimizes chain-transfer reactions, leading to increase of molecular weights of the resulting polymers.
ERRATUM: “MILKY WAY RED DWARFS IN THE BORG SURVEY; GALACTIC SCALE-HEIGHT AND THE DISTRIBUTION OF DWARFS STARS IN WFC3 IMAGING” (2014, ApJ, 788, 77)
Authors: Holwerda B. W. , Trenti M. , Clarkson W. , Sahu K. , Bradley L. , Stiavelli M. , Pirzkal N. , Marchi G. De , Andersen M. , Bouwens R. , Ryan R. , Vledder I. van , Vlugt D. van der
Published: July 2016

In the catalog of M-dwarfs presented in Holwerda et al. (2014, H14 hereafter), there is an issue with the conversion from celestial coordinates to Galactic ones, done with pyephem a wrapper around a trusted and vetted library ephermis. Here we present the corrected coordinates (using AstroPy) and distances based on AB magnitudes. We have amended the tables and figures accordingly. The relation between vertical scale-height (z
0) and M- dwarf subtype found in H14 is no longer present. We find a scale-height of 600 pc for all types, in part due to the presence of a second Galactic structural component.
Le « plaidoyer fondé sur des preuves » dans l’action sanitaire internationale
Authors: Hunsmann Moritz
Published: July 2016

L’essor récent de l’aide sanitaire à destination de l’Afrique s’est accompagné de l’injonction de plus en plus forte à formuler des politiques « fondées sur des preuves ». Face à ce qu’ils considèrent une insuffisante prise en compte des savoirs sanitaires dans la formulation et la mise en œuvre des politiques de santé en Afrique, certains bailleurs internationaux expérimentent un mode d’action nouveau : le « plaidoyer fondé sur des preuves » (evidence-based advocacy). Cette contribution étudie une telle intervention dans le champ de la santé maternelle et néonatale en Tanzanie et explore les effets politiques contradictoires de ce mode d’action, analysé ici comme un nouveau type d’ingénierie sociale. Porteur de formes de collaboration ouvertes et peu hiérarchisées entre bailleurs et acteurs nationaux, ce mode d’intervention s’avère néanmoins particulièrement intrusif dans la mesure où il traduit une tentative d’avoir prise sur l’intégralité du processus politique des pays recevant l’aide sanitaire. L’analyse du rôle ambivalent mais central du recours aux savoirs dans la légitimation du programme montre comment, tout en renouvelant l’action sanitaire, cette forme d’intervention reproduit des modes de domination propres à l’aide internationale.
Development of a mixed drink made from hydrosoluble soybean extract, coconut water and umbu pulp (Spondias tuberosa)
Authors: Moura Neto Luís Gomes De , Lira Jaqueline De Sousa , Torres Maria Michele Ferreira da Silva , Barbosa Ilsa Cunha , Melo Geiseanny Fernandes do Amarante , Soares Denise Josino
Published: July 2016

The food sector depends on consumers and their social behavior. Since currently more and more consumers seek healthy products, exotic fruits have been increasingly on demand, with great opportunities for innovation. Current study developed a ready-to-drink mixed beverage made from hydrosoluble soybean extract, coconut water and umbu pulp. Four formulations were prepared with two proportions of umbu pulp (25 and 30%) and soluble solids (17 and 25º Brix). Formulations were submitted to chemical, physicochemical, microbiological and sensory analyses. The beverage was prepared with 25% of umbu pulp and the soluble solids were standardized to 25º Brix with commercial sugar for the highest scores in sensory attributes, overall impression and purchase intent. The four formulations presented pH, acidity, moisture, total sugar, vitamin C and microbiological results in accordance with current legislation.
Effects of Seeding with Nanocrystallites and Addition of Inorganic Alumina Sol on Crystallization of Alkoxide Alumina Gel
Authors: Kobayashi Yoshio , Mabuchi Yusuke , Hama Masachika , Yamamura Katsumi , Yasuda Yusuke , Morita Toshiaki
Published: July 2016

This paper reports a method for producing α-Al2O3 at low temperature from aluminum alkoxide using a combination of seeding of α-Al2O3 nanocryatallites and adding of inorganic alumina sol. An alkoxide alumina sol was obtained by hydrolyzing aluminum isopropoxide in water at 80°C and then peptizing the hydrolyzed aluminum isopropoxide using acetic acid at 80°C. An inorganic alumina sol was obtained by producing aluminum compound with a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution and then peptizing the aluminum compound using acetic acid at room temperature. α-Al2O3 nanocrystallites were added to the alkoxide alumina sol containing the inorganic alumina sol. The addition of inorganic alumina sol provided successful fabrication of a crack-free α-Al2O3-seded alumina film by a spin-coating technique. The sol containing α-Al2O3 nanocrystallites was transformed to an α-Al2O3-seeded alumina gel by drying the sol at room temperature. The non-seeded alumina gel was crystallized into γ-Al2O3 at a temperature below 900°C. In contrast, the alumina seeded at 1% α-Al2O3 nanocrystallites content began to be transformed to α-Al2O3 by annealing at the temperature. The seeding and the adding promoted crystallization of the alumina gel into α-Al2O3. The promotion of crystallization was significant with an increase in α-Al2O3 nanocrystallites content by weight in the final seeded alumina gel.
Cellulose-Silica Composite Aerogels Prepared with Sodium Silicate by Freeze Drying Method
Authors: Sai Hua Zheng , Fu Rui , Xing Li , Xiang Jun Hui , Li Zhen You , Zhang Ting , Zhang Fu Shi
Published: July 2016

The cellulose-silica composite aerogels (CAs) were fabricated through a permeation sol-gel process in the regenerated cellulose hydrogels followed by freeze drying. The precursor Na2SiO3 instead of traditional organic precursor was diffused in the cellulose matrix followed by permeating the catalyst into the cellulose nanofibers network gradually to promote the in situ condensation of Na2SiO3 to form a SiO2 gel skeleton from outside to inside. The obtained CAs displayed the interpenetrating network (IPN) structure of the regenerated cellulose nanofibers network and the SiO2 gel skeleton in nanoscale. In the IPN structure, the flexible cellulose nanofibers network was supported by the hard inorganic network effectively to sustain the compression and the silica gel skeleton protect the cellulose nanofibers to avoid the remodeling of their shape in the process of solvent replacement before freeze drying. Due to the synergic effects of the different network, the IPN structure endows the CAs with high compression modulus (as high as 15.48 MPa), high specific surface area (as high as 621 m2 g-1) and low density (less than 0.182 g cm-3).
Pore Forming Mechanism of Forsterite Insulation Materials Synthesized by Molten Salt Method
Authors: Song Yun Fei , Deng Cheng Ji , Zhu Hong Xi , Ding Jun
Published: July 2016

Abstract. The forsterite thermal insulation materials were synthesized by molten salt method with forsterite and NaCl-Na2CO3 salt, sintered at 1000°C, 1050 °C, 1100°C and 1150°C respectively. Studying complex pore structures is the key to understand the mechanism of pore-forming. The mechanism of the variation in the heterogeneous pore structure was analyzed based on differential thermal analysis, thermogravimetry, high-pressure mercury intrusion porosimetry and scanning electron microscope. The results show that the NaCl-Na2CO3 salt play the role of promoting sintering in liquid environment at high temperature as well as forming pore as placeholder. The mechanism of pore-forming contains three parts: the pores < 6.6 μm are mainly formed by sodium carbonate decomposition under high temperature and vapor pressure; the forming way of 6.6~66μm derives from carbonate decomposition and salt evaporate jointly; The salt stay in the slender and curved space shaped by the rearrangement of forsterite particles, forms the pore diameter of > 66 μm after salt dissolves in water.
Study on the Gel Casting Process of Silicon Carbide
Authors: Li Han , Xu Hong Zhao , Zhou Chang Ling , Wang Yan Yan
Published: July 2016

Silicon carbide possess high performances such as high hardness and strength, oxidation and high temperature resistance, high thermal conductivity and low thermal expansion coefficient. Widely used methods of molding green body for sintered pressureless bonded silicon carbide comprise dry pressing molding and casting molding. The former fails in preparation of complex shapes, while those prepared by casting molding are prone to have defects such as nonuniformity of density and easy cracking. Gel-casting is a net-shape modeling technology caused by the polymerization of organic monomer (acrylamide). The green bodies molded by gel-casting have uniform structure, high density, high strength and machinability. In this study, gel casting molding and pressureless sintering were used to prepare silicon carbide. The effect of the parameters of gel casting and sintering on the microstructure of the obtained silicon carbide was examined
Zirconyldichloride Modified Polycarbosilazane as Precursors for SiZrCNO Ceramics
Authors: Han Jia Jie , Su Dong , Yu Yang , Zhao Xue Ting , Wang Xiao Jing , Zhao Zhi Peng , Yan Xiao , Jin Zheng Guo
Published: July 2016

Zirconyldichloride modified polycarbosilazane (PZrSZO) has been synthesized from two-component dichlorosilanes (methyldichlorosilane and methylvinyldichlorosilane), zirconyldichloride, and ethylenediamine using triethylamine as acid-absorbing agent and tetrahydrofuran as solvent. 1H nuclear magnetic resonance analysis of the as-synthesized PZrSZO suggest a structure of ethylene-bridged polycarbosilazane having –Si–N–C–C–N– as backbone chain with –CH=CH2, –H and –CH3 attached to Si as side groups, which is similar to that of non-modified PSZO precursor. Fourier transform infrared spectroscopy shows Zr–N stretching vibration peak appears at 532 cm-1 suggesting the incorporation of Zr into PSZO through aminolysis reaction between zirconyldichloride and ethylendiamine. SiZrCNO ceramic with the ceramic yield of 63 wt% is obtained through subsequent pyrolysis treatment at 1000 °C for 1 h under argon flow. EDS analysis shows its composition of SiZr0.01C1.03N0.25O0.84 with the Zr percentage of 1.45 wt%. X-ray diffraction analysis shows SiZrCNO ceramics are of mixed amorphous silicon carbonitride oxygen phase embraced with SiO2 nanocrystalline.
Preparation of Camphene Carbon/Silicon Carbide Slurry for 3D Printing
Authors: Huang Xiao Ting , Hu Chuan Qi , Sun Hao Ran , Liu Hai Lin , Huo Yan Li , Liang Hai Long , Chen Yu Feng
Published: July 2016

The 3D printing ceramic body was prepared by camphene carbon/silicon carbide slurry, which were prepared with camphene, carbon and silicon carbide, dispersant, binder as rawmaterial, according to certain stoichiometric ratio. The effects of the choice of dispersants on the dispersion of the slurry performance were investigated. The amount of dispersant were determined.
Fabrication and Properties of Porous Carbon Preforms for Making Reaction Formed SiC
Authors: Hu Chuan Qi , Huang Xiao Ting , Liang Hai Long , Chen Shu Guang , Huo Yan Li , Liu Hai Lin , Tang Jie , Chen Yu Feng
Published: July 2016

This paper describes a proper low cost way to fabricate defects free porous carbon preforms with interconnect pore structure for making reaction formed SiC (RFSC). Taking charcoal , poplar powder, camphene and polymer dispersant together, making slurries by milling under 55 °C for several hours, controlling the content of charcoal and poplar powder, after casting, sublimating and carbonizing, the porous carbon performs with a series density (0.66 g/cm3-0.78 g/cm3) and porosity (62.9 vol.%-68.6 vol.%) were prepared; through the Si infiltrating process under a vacuum condition (~5.0 Pa) at 1500°C for about 0.5 hour, the RFSCs with fine mechanic performance were fabricated, one RFSC sample has the density, Weibull modulus, and the max three points flexural strength is 2.91 g/cm3, 9.5 and 505.0 MPa respectively.
Effect of Sintering Aids on the Properties of Porous YAG Ceramics
Authors: Xu Ming Han , Song Jie Guang , Wang Rui Hua , Li Shi Bin , Wang Ning , Yu Si Yuan , Yan Han Xing , Xiao Ting Ting , Chen Fei
Published: July 2016

Yttrium aluminum garnet (YAG) with a chemical composition of Y3Al5O12 is an important advanced structural and functional material due to some excellent properties. The porous YAG ceramics were prepared via vacuum sintering technology, the effect of sintering aids on the properties of porous YAG ceramics were investigated in this paper. Through an analysis and discussion, the conclusions are that the porosity increases with the increasing sintering temperature from 1300°C to 1500°C, the pore is moved to the surface of sample, which forms the open pore to make the porosity increase, the more and bigger sintering neck is increased. Porous YAG ceramics are sintered at 1500°C, the regular outside shapes of porous YAG ceramic are kept using CaO and MgO as sintering aids, the outside shape of porous YAG ceramic is wrecked using Al2O3 as sintering aids, which shows the over fired phenomenon.
Preparation and Characteristics of Nanocrystalline Yttria by Microwave-Induced Solution Combustion Method
Authors: Zhang Yan Shuang , Zhang Yu Jun , Li Teng , Li Qi Song
Published: July 2016

Nanocrystalline yttria powders were successfully synthesized by microwave-induced solution combustion method using a binary yttrium salt system with yttrium nitrate as oxidant and yttrium acetate as reductant. The process involved the redox reaction between the two yttrium salt under the heat generated by absorbing microwaves. The prepared powders were characterized by X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) to study the structure and powder morphology. The prepared powders were indicated to exhibit single-phase cubic crystalline yttria structure. The oxidant/reductant ratios and the calcination temperatures had an effect upon the particle size and powder morphology. The size of the crystallites varied in the range of 16 nm~27 nm with different reductant proportion. The powders were observed to show loosely agglomerated fractals.
Effects of Particle Size on Densification Behavior of Si3N4 Ceramics
Authors: Wang Lu Jie , Yang Xiao , Liu Xue Jian , Jiao Zheng , Huang Zheng Ren
Published: July 2016

Silicon nitride (Si3N4) ceramics with Y2O3-Al2O3 as sintering additives were prepared by pressureless sintering technology using two kinds of Si3N4 powders as raw materials. The particle size of Si3N4 powders ball-milled with various times were characterized and the effects of particle size on the densification behavior of Si3N4 ceramics were investigated. The relative density and microstructure of the sintered bodies at different sintering temperatures were determined. The experimental results show that the powders with longer milling time have finer particle size and the samples with fine particle display higher shrinkage-rate at lower sintering temperature than the one with coarse particle. By extending milling time, the density gap between the sintered ceramics using different Si3N4 powder become narrower. The main factor resulting in the difference of sintering densification behavior is the particle size of Si3N4 powders rather than metallic oxide impurity of raw powders.
Dielectric Breakdown and Failure of Ferroelectric Films as the Dielectric for Electrowetting Systems
Authors: Wang Wei Qiang , Niu Jia Qi , Xie Zhen Kun , Yue Zhen Xing
Published: July 2016

In this paper, we study the electrical properties and breakdown phenomena of PZT ferroelectric thin film in electrowetting systems. The experimental results indicate that irreversible charge trapping occurred with repeated voltage actuation, resulting in contact angle relaxation and reduction of the ferroelectric film breakdown strength. The breakdown voltage depends on DC voltage polarity, and this polarity dependence was found to be related to the thickness of the ferroelectric layer. When AC voltage was applied, the breakdown voltage increased directly with voltage frequency. These phenomena are interpreted in terms of electrochemical reactions at the liquid/solid interface, an empirical model was used to estimate the amount of trapped charge in the ferroelectric film.
The Electrical Properties of Epitaxial Grown Sc-Doped (Na0.85K0.15)0.5Bi0.5TiO3 Thin Film Prepared by Sol-Gel Method
Authors: Wu Yun Yi , Wang Xiao Hui , Zhong Cai Fu , Li Long Tu
Published: July 2016

Sc-doped (Na0.85K0.15)0.5Bi0.5TiO3 (NKBT-Sc) thin film was deposited on electrical conductive Nb-doped SrTiO3 [100] (Nb:STO) single crystal substrate via an aqueous sol–gel method. Structure analysis by x-ray diffraction and high resolution transmission electron microscopy proves the epitaxial growth relationship between the NKBT-Sc thin film and Nb:STO substrate. Well saturated ferroelectric hysteresis loops with remnant polarization of 26.14 μC/cm2 and typical butterfly shape displacement–voltage loop with effective piezoelectric coefficient d33* of 92 pm/V were observed, which were much higher than the NKBT-Sc thin film deposited on platinized silicon substrate. The precision LCR Meter exhibits a butterfly shape of dielectric constant and electric field curve, which is typical nature for the ferroelectric characteristics of the [001]-epitaxial NKBT-Sc thin film.
Electrode Interface Polarization in BaTiO3-Based PTC Ceramics
Authors: Yang Ai Mei , Li Gui Zhong , Zhen Shao Ying , Liu Lai Jun
Published: July 2016

Electrodes play a vital role on the electrical properties of positive temperature coefficient (PTC) ceramics. An ohmic contract between ceramics and electrodes is necessary for the PTC effect. In this work, silver mixed aluminium electrode and pure silver electrode were pasted on BaTiO3-based PTC ceramics, which results in an ohmic contact and non-ohmic contact, respectively. Impedance spectroscopy and dielectric and conductivity properties was investigated at different temperature for the two contacts. Small difference of electrical properties was found between the two contacts above the Curie temperature. Below the Curie temperature, however, carriers could pass through the interface of ohmic contract but gather on the interface of non-ohmic contact. The latter resulted in a space charge polarization, which increased low-frequency dielectric permittivity.
Preparation and Resistivity of Zirconia Oxygen Sensor Probe
Authors: Zhang Bo , Zhang Xiang Zhao , Wang Hui , Liu Gui Wu , Shao Hai Cheng , Qiao Guan Jun
Published: July 2016

A ZrO2/Al2O3 (molar ratio of 1: 1, ZA) composite ceramic was formed by slip casting as solid electrolyte in a zirconia oxygen sensor. The bonding of the ZA ceramic green body to 95% Al2O3 ceramic green body support tube was carried out at 900 oC for 60 min by the gradient joining technique using pure Al2O3 slurry as the interlayer. Subsequently, the Pt slurry was coated on the surface of the pre-sintered composite ceramic, and then co-sintered at 1550 oC for 60 min to fabricate a Pt/ceramic composite probe. The interface microstructure and bonding mechanism were briefly investigated, and the electrical conductivity of the probe was tested. The experimental results show that the two high-quality ZA/Al2O3 and ZA/Pt interfaces were obtained. In particular, the relationship between the logarithm of conductivity (lnρ) and the reciprocal of temperature was well in accord with the Arrhenius equation. The Pt/ceramic composite probe presented the typical characteristic of high-temperature ionic conduction.
Photocatalytic Properties of WO3 Particles with Different Grain Sizes
Authors: Shen Zhen Guang , Peng Zhi Jian , Qian Jing Wen , Fu Xiu Li
Published: July 2016

WO3 particles with different grain sizes were prepared by a thermal evaporation method. The composition, morphology, and optical properties of the samples were analyzed by powder X-ray diffraction, scanning electron microscopy, and UV–vis absorption and photoluminescence spectroscopy. Their photocatalytic properties were evaluated by decomposing methylene blue in aqueous phase. It was found that the smaller the grain size of the prepared WO3 particles, the better the degradation effect on methylene blue.
Hardness and Electromagnetic Properties of YSZ/NiZn Ferrite Composites
Authors: Zhang Long Ding , Qu Zhi Xue , Wang Qun , Waheed Khan
Published: July 2016

In this paper, a series of YSZ/NiZn ferrite composites with seven varying volume fractions of NiZn ferrite (0 vol%, 20 vol%, 40 vol%, 50 vol%, 60 vol%, 80 vol% and 100 vol %) were prepared. The complex permeability of the composites was measured in frequency range from 1 MHz to 100MHz and the effect of the composition on the hardness and complex permeability was investigated. The results show that the Vickers hardness of the composites decreases slightly first and the dramatic decrease occurs when the content of NiZn ferrite is above 0.5. Meanwhile, the permeability of the composites increases sharply when the volume fraction of NiZn ferrite is above 0.6, which can be considered to be the magnetic percolation with a percolation threshold of about 0.6.
Effect of Al Powder Content on Performance of MgO-Al2O3 Composite at 1700°C under N2 Atmosphere
Authors: Tong Shang Hao , Li Yong , Hong Yang , Yue Dan Dan , Ma Jia Jia
Published: July 2016

Specimen was made with fused magnesia (the mass percent is 65%) as aggregates and Al fine powder, sintered magnesia, tabular alumina and α-Al2O3 fine powder as co-mixture powder (the mass percent is 35%) . Specimen were prepared in nitrogen atmosphere at 1700°C. The results indicate that the MgAlON was formed under the prevailing conditions. Al powder content has an important effect on properties of Al-MgO-Al2O3 composites. With the Al powder content increasing, the amounts of MgAlON increases. When the content of Al powder is 6%, the MgAlON composite has the best comprehensive performance.
Preparation and Characterization of Al-Al2O3 Metal Ceramics via Powder Metallurgy Methods
Authors: Du Da Ming , Wang Rui Hua , Song Jie Guang , Yu Si Yuan , Li Yao Qi , Liu Ning , Cao Gui Lian , Dong Shuang , Ji Gang Chang
Published: July 2016

Metal ceramics are a important new engineering materials with the advantages of ceramics and metal materials. The Al-Al2O3 metal ceramics were prepared via the powder metallurgy methods and characterized in this paper, which lay the base for preparing the high performance cermet materials. Through the results and analysis, the conclusions are shown that the relative density is increased with a increasing forming pressure, the electrical resistivity is decreased with a increasing forming pressure. The relative density is increased with a increasing sintering temperature under 700°C, the relative density decreases with a increasing sintering temperature above 700°C, the electrical resistivity is shown the opposite tendency. Through the optimizing the technological parameter, such as the sintering temperature at 700°C, the forming pressure under 20MPa, the Al content for 75wt%, Al-Al2O3 metal ceramics are successfully prepared with the high relative density and the low electrical resistivity, the relative density is 97.52%, and the electrical resistivity is 101.34Ω·m
Preparation and Characterization of Al2O3/ZrO2 Composite Ceramics
Authors: Ju Yin Yan , Gan Xue Xian , Song Jie Guang , Wang Fang , Zhang Wang Nian , Yang Wen Liang
Published: July 2016

Alumina-zirconia (Al2O3-ZrO2) composite ceramics were prepared by means of cross spraying and hydrothermal method under atmospheric pressure with nanometer powders doped with ZrO2 as the raw material. Then, the prepared powders and ceramics were characterized by SEM, XRD and BET methods. The results showed that combining cross spraying with hydrothermal method under atmospheric pressure could improve the dispersity of the ZrO2 composite ceramics nanopowders, while adding Al2O3 accelerated the low temperature sintering for 3Y-ZrO2 and improved the bending strength, fracture toughness and density of ZrO2 composite ceramics. In addition, through optimization the bending strength and fracture toughnessof the obtained ceramic, were 1,150 MPa and 8.2 MPa∙m1/2 respectively.
Preparation of ZrB2 Powders with Different Morphologies by Pressureless Reactions
Authors: Hai Wan Xiu , Huang Yi Hui , Jiang Yong , Wei Zhen Bang
Published: July 2016

The ZrB2 powders with different morphology were prepared by pressureless reactions, using ZrO2, B2O3, B4C, and graphite as raw materials. Three kinds of chemical reaction system were employed. The ratio of raw materials and reaction temperature were adjusted to prepare ZrB2 powders of different morphology and particle size. The phase composition and purity of the as-prepared powders were analyzed by XRD, while the morphology and particle size were analyzed by SEM. The ZrB2 powders were purified by removing impurities at 600 °C in a muffle furnace in air atmosphere. The results showed that in the reaction systems of ZrO2-B2O3-C and ZrO2-B4C-C, the ZrB2 could be generated at 1500 °C. The morphology of the as-prepared ZrB2 powders were particles, rod-like or near spherical for ZrO2-B2O3-C system and particles for ZrO2-B4C-C system. In the reaction system of ZrO2, B2O3, B4C, and C with a mole ratio of 3:2:1:8, the ZrB2 powders with high purity could be produced at 1700 °C. The ZrB2 powder was near spherical. After heat treatment, the particle size and morphology changed to some extent.
Synthesis and Characterization of LaMgAl11O19 as Thermal Barrier Coatings Material
Authors: Huang Ze Ya , Lu Hao Ran , Wang Chang An
Published: July 2016

LaMgAl11O19 was synthesized at 1550 °C using La2O3, MgO and Al2O3 as raw materials. The samples were characterization by XRD and SEM. The tablet shaped crystals free of impurity phase formed under this condition. The thermal diffusivities were measured by laser flash method and the determined intrinsic thermal conductivities decreased as temperature increases from 25 °C to 1000 °C. As comparison, intrinsic thermal conductivities of LaMgAl11O19 are lower than that of 7YSZ. The synthesized LaMgAl11O19 was heat treated at higher temperature from 1600 °C to 1700 °C and no change in the phase indicates that the LaMgAl11O19 phase is stable under 1700 °C, which is very important for thermal barrier coatings (TBCs) serving at elevated temperature.
Synthesis and Characterization of Magnesium Aluminate Spinel Porous Ceramics by Novel Molten Salt Method
Authors: Deng Xian Gong , Wang Jun Kai , Zhang Hai Jun , Liu Jiang Hao , Zhang Shao Wei
Published: July 2016

Magnesium aluminate spinel (MgAl2O4) porous ceramics were in-situ synthesized by heating the mixture of Al2O3 and MgCO3 with MgCl2 salt at 1400~1600 °C for 3 h, and then characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The morphology of as-prepared MgAl2O4 porous ceramics was dependent on the addition of MgCl2, and it indicated that the MgCl2 molten salt not only acted as a template for pore formation of the porous ceramics, but also provided a liquid environment for the synthesis of MgAl2O4.
Preparation and Performance of Neutron Absorbing Dysprosium Oxide Ceramic
Authors: Zhang Yu Bai , Zhang Yu Jun , Zhao Jia Xing
Published: July 2016

Dysprosium is a kind of potential neutron absorption material with the thermal neutron absorption cross area of 950 Barn. In this paper, dysprosium oxide (Dy2O3) ceramic was prepared by pressureless sintering. The density, bending strength, fracture toughness and hardness of Dy2O3 ceramics under different sintering schedule were analyzed. The density of Dy2O3 ceramics was enhanced accompanied with the increase in sintering temperature, and it was close to the theoretical value when heated at 1630 °C. Bending strength reached a maximum of 117 MPa when sintering temperature was 1570 °C. However, fracture toughness was inversely proportional to the hardness approximately. As a consequence, the optimum sintering temperature for mechanical property of Dy2O3 ceramics was 1570 °C. The morphology of fracture surface was examined by SEM. The results showed that the porosity of Dy2O3 ceramics decreased with increasing temperature. Meanwhile, the Monte-Carlo software was used to simulate the neutron absorption property. The absorbtivity was about 99.13% when the neutron source was uniform energy spectrum of 10-11 Mev~10-5 Mev and the thickness of Dy2O3 was of 20 mm.
Characterization of SiO2 Aerogel/SiO2 Fiber Composites Prepared by Sol-Gel Method
Authors: Zhai Ping , Duan Xiao Feng , Zhang Qing Li , Wang Hong Sheng , Cheng Hong Hao , Zhang Xun Hu
Published: July 2016

Quartz fiber composites filled with nanosized SiO2 were prepared by sol-gel method with vacuum impregnation , supercritical drying and surface modification. The silica sol for vacuum impregnated were made from tetraethyl orthosilicate (TEOS), anhydrous ethanol, water and acid catalyst as the starting materials. The water adsorption rate, apparent porosity and electrical properties of composites were investigated by means of archimedes method and waveguide method while the surface area and pore size of the aerogel samples were tested by BET, the mechanism of hydrophobicity was also discussed. The results showed that the moisture absorption rate of products was decreased to 1.21% from 17.36% that without filled with nanosized SiO2, with a decreasing range of 93%. Additional coating could make the rate even as low as 0.052%.The dielectric constant had no significant change while the loss tangent decreased from 3.1╳10-3 to 1.4╳10-3,with a decreasing range of 51.2%.
Effect of Binders on Preparation of High Temperature Rigid Thermal Insulation Materials
Authors: Yang Jie , Liu Rui Xiang , Sui Xue Ye , Zhou Chang Ling , Wang Chong Hai , Zhang Wen Yuan
Published: July 2016

With the development of ultra high temperature rigid heat insulation materials in the space field, it is an important strategic significance to prepare and research insulation materials of 1500°C high temperature. In our paper, the material was achieved through the process of wet suction filter forming and high temperature heat treatment, during which the high temperature alumina fiber was used as main ingredient. The fiber binder directly influences the mechanical and thermal properties of the material, and our samples were prepared using boron carbide and silicon carbide (both), borosilicate glass, alumina sol and aluminum dihydrogen phosphate as binder, respectively. The results show that borosilicate glass was the best one. Coefficient of thermal conductivity at 1000°C, lift strength and plane direction compression strength (10% compression) of the high temperature material were 0.12 W/mK, 0.35 MPa, and 1.1 MPa, respectively.
Study on the Cause and Control of Defects on Process of CVD SiC
Authors: Huo Yan Li , Liu Hai Lin , Hu Chuan Qi , Huang Xiao Ting , Wang Chun Peng , Tang Jie , Chen Yu Feng
Published: July 2016

CVD SiC material with many excellent physical and chemical properties was used widely in the field of aerospace as reflector materials. In addition, CVD SiC thin film materials because of its compact structure, high purity can also be used as precision optical components of semiconductor industry. But the CVD process is a complex chemical process and the reaction process is very time consuming. Research of chemical vapor deposition for preparing silicon carbide process mechanism is important significance for the expansion of the application of silicon carbide. In this paper, CVD SiC coatings were fabricated by the pyrolysis of methyltrichlorosilane (MTS) in hydrogen at a low pressure. XRD and EDS were used to characterize the component of intermediate. SEM was used to observe the surface morphology and microstructure of coatings. The results indicated that key problem to be solved is to control the growth rate of SiC for high quality deposition coating, while the growth rate is also affected by process parameters. To obtain the materials to meet the use requirements, the need for control of each parameter in the reaction process.
Effect of Additives on Bond Property for Phenolic Resin-Based Adhesive
Authors: Zhang Feng , Wang Guang Hai , Chen Yu Feng , Hu Chuan Qi , Sun Hao Ran , Zhang Shi Chao , Sun Xian Kai , Fang Kai
Published: July 2016

Modified phenolic resin-based adhesive is used as the high temperature binder, which is prepared by adding different additives, zirconium diboride, boron carbide as modified fillers, and H3PO4, AlPO4 as curing agents. The influence of additives for phenolic resin-based adhesive on bond property of SiC ceramic was studied after heat treatment at 400 oC , 800 oC , 1200 oC , 1600 oC. The results show that the improvement of adhesion property for curing agents is not obvious. B4C modified phenolic resin-based adhesive exhibits better adhesion performance than ZrB2 modified phenolic resin-based adhesive. Bonding property of B4C modified phenolic resin-based adhesive is best at 1200 oC , and the adhesive strength is reduced above 1200 oC along with rising of the heat treatment temperature. Because of the formation of shrinkage micro-defects of phenolic resin, bond strength exists a sharp decline after 1200 oC heat treatment.
Structural-Functional Integrative Mullitef/SiBN Composites with Excellent Wave-Transparent and Mechanical Properties
Authors: Li Guang Ya , Liang Yan Yuan , Liu Jia Chen
Published: July 2016

A structural-functional integrative wave-transparent material, consisted of BN coating and SiBN substrate, is synthesized through precursor infiltration pyrolysis (PIP) process. Then the technical parameters and procedures are obtained according to the key properties of the precursors. Studies on the microstructures and properties of the composite show that compact substrate and weak interface enhance the strength, and porous structure improves the dielectric performance of the composite. The composite exhibites good bending strength (~95.12 MPa), tensile strength (~34.95 MPa) and compressive strength (~80.92 MPa). Moreover the composite displays a low dielectric constant (4.17) and a low loss tangent (9.7×10-3) at room temperature. The composite has a low changing rate of dielectric constant (~2.01% per 100°C). These results imply that the composite with excellent mechanical and dielectric properties can be an excellent wave-transparent material applied in the fields of aerospace.
Preparation and Properties of High-Purity Porous Calcium Hexaluminate Material
Authors: Wu Meng Fei , Li Yuan Bing , Li Shu Jing , Li Ya Wei , Sang Shao Bai
Published: July 2016

In this paper, high-purity porous calcium hexaluminate materials were prepared with α-alumina, nano-meter calcium carbonate and ρ-alumina as raw materials. The properties of the prepared porous materials, such as bulk density, true density, thermal conductivity, and cold crushing strength, were investigated. The increase in sintering temperature led to the increase of true density. Bulk density and cold crushing strength of the specimen fired at 1500°C had the lowest values. As ρ-alumina content increased, bulk density, true density, and cold crushing strength had no obvious changes, but the thermal conductivity decreased at first and then increased. The calcium hexaluminate formation was intense from 1450°C to 1500°C and finished at 1500°C. Above 1500°C, the main phase of specimens was calcium hexaluminate (CA6). And CA6 grains were regular hexagonal plates morphology and widely spread after firing at 1550°C.
Gel Casting and Properties of SiCp/Al Composite
Authors: Liu Hai Lin , Huang Xiao Ting , Huo Yan Li , Hu Chuan Qi , Wang Chun Peng , Liang Hai Long , Wang Guang Hai
Published: July 2016

In this paper, high volume fraction SiCp/Al composite was fabricated by pressureless technique with silicon carbide porous preform which fabricated through gel casting process. The effects of solid loading on the rheological properties of SiC slurry were discussed. High solid loading SiC slurry of 65vol% with low viscosity and high stability was fabricated. Also microstructure, flexural strength of the SiC preform and SiCp/Al composite were studied, the results showed gel casting process and pressureless infiltration technique were suitable for fabricating high volume fraction, homogeneous structure and high performance SiCp/Al composite.
Effect of Zircon Content on the Microstructure and Physical Properties of Chamotte Refractories
Authors: Xiang Ruo Fei , Li Yuan Bing , Li Shu Jing , Ma Xin Yan , Li Ya Wei , Sang Shao Bai
Published: July 2016

In this work, chamotte with dispersions of up to 30wt% zircon is sintered at 1500 °C to investigate the effect of zircon content on the microstructure and physical properties of chamotte refractories. The microstructure and physical properties of samples are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), three-point bending and dilatometer. The result shows that the main phases of chamotte with and without sintering at 1500 °C are mullite and cristobalite, the addition of zircon has no impact on the main phase compositions of chamotte matrix. For the sintered samples, zircon grains are wrapped with glass and no obvious bonding are detected between the interface of zircon and mullite grains. Increasing zircon content leads to the increase in bulk density and has a negative effect on the flexural strength, besides, linear thermal expansion ratio decreases as the zircon content increases.
Synthesis and Characterization of Asparagine-Modified and Terbium-Doped Spherical Hydroxyapatite Nanoparticle
Authors: Xing Xiao Feng , Luo Liang Liang , Guo Yu Ping , Gao Wei Min , Hu Liang
Published: July 2016

The spherical hydroxyapatite nanoparticles (HAP) were synthesized by hydro-thermal method, and calcium nitrate, terbium oxide, diammonium hydrogen phosphate were used as raw materials with the help of surfactant L-Asparagine. Meanwhile, different amount of Tb was added to investigate the effect of different terbium dropping amount on the properties of HAP. The structure, morphology and luminescent of the obtained HAP that was characterized via X-ray powder diffraction (XRD), fluorescence spectrometer (PL) and transmission electron microscope (TEM). Results showed that spherical HAP which in average of 30 nm with good dispersion showed remarkable fluorescent properties and their maximum emission were observed at 543 nm, which could be also excited at uv light region of 377 nm.The optimum mole fraction of Tb was 3%. Therefore terbium-doped spherical HAP of prepared sample would be tracked by flourescence.
Mechanical Properties of Polymer-Infiltrated-Feldspar for Restorative Composite CAD/CAM Blocks
Authors: Cui Ben Cang , Li Jing , Wang Hui Ning , Lin Yuan Hua , Shen Yang , Li Ming , Nan Ce Wen
Published: July 2016

Polymer-infiltrated-feldspar used for restorative composite CAD/CAM blocks were prepared by infiltrating polymerizable monomers into the partially sintered feldspar blocks. The flexural strength was tested according to the standard of ISO-4049. The micro-structure was examined by SEM. The effects of sintering temperature, high pressure and the addition of SiO2 and Al2O3 on the ultimate flexural strength were evaluated. The flexural strength corresponding to infiltration with pressure was much higher than that without pressure at high sintering temperature. The addition of SiO2 and Al2O3 into the natural feldspar mineral increased the flexural strength of the blocks significantly.
Analysis on High Cycle Fatigue Properties and Fatigue Damage Evolution of TC25 Titanium Alloy
Authors: Zhao Rong Guo , Liu Ya Feng , Jiang Yong Zhou , Luo Xi Yan , Li Qi Bang , Yan Yi , Cai Peng , Chen Yue
Published: July 2016

The high cycle fatigue tests for smooth specimens of TC25 titanium alloy under different stress ratios are carried out on a MTS 809 Material Test Machine at a given maximum stress level of 917MPa at ambient temperature, the high cycle fatigue lifetimes for such alloy are measured, and the effects of stress amplitude and mean stress on high cycle fatigue life are analyzed. The initial resistance is measured at the two ends of smooth specimen of TC25 titanium alloy, every a certain cycles, the fatigue test is interrupted, and the current resistance values at various fatigue cycles are measured. The ratio of resistance change is adopted to characterize the fatigue damage evolution in TC25 titanium alloy, and a modified Chaboche damage model is applied to derive the fatigue damage evolution equation. The results show that the theoretical calculated values agree well with the test data, which indicates that the modified Chaboche damage model can precisely describe the accumulated damage in TC25 titanium alloy at high cycle fatigue under unaxial loading. Finally, the high cycle fatigue lifetimes for TC25 titanium alloy specimens at different strain hardening rates are tested at a given stress ratio of 0.1, the effect of strain hardening on fatigue life is investigated based on a microstructure analysis on TC25 titanium alloy, and an expression between fatigue life and strain hardening rate is derived
Research on Transition from Short to Long Fatigue Crack Propagation of GH4133B Superalloy Used in Turbine Disk of Aero-Engine
Authors: Zhao Rong Guo , Li Qi Bang , Jiang Yong Zhou , Luo Xi Yan , Liu Ya Feng , Yan Yi , Cai Peng , Chen Yue
Published: July 2016

The fatigue crack propagation tests for circular notched compact tension specimens of GH4133B superalloy used in a turbine disk of aero-engine are carried out at room temperature. The test data shows that in the transition region from short to long crack growth, the crack growth rate appears as a fluctuation form with acceleration following deceleration. A quasi harmonic function is constructed to model the fatigue crack growth in the transition region, and the result indicates that such function is suitable to describe the crack growth behavior. A metallographic analysis with respect to microscopic observation for the specimen’s surface suggests that the wave period, that is, a step length of a cycle fluctuation from acceleration to deceleration on the crack growth rate curve is agree well with the intrinsic scale of grain size, which indicates that in the transition region from short to long crack growth, grain boundary plays a dominant role in crack growth rate. Finally, the fracture surfaces of specimen are observed using a scanning electron microscopy. It can be found from the fracture surface morphologies that in the transition region from short to long crack growth, the stress intensity factor range is still lower than the fatigue crack growth threshold ΔKth, the effect of microstructure, such as grain size, grain boundary, secondary phase particle, and inclusion ahead of the crack tip, and the effect of crack closure on crack growth behavior should be considered, the local further plastic deformation at crack tip will meet larger resistance, so some twin bands are observed on the fracture surface. As crack length increases with increasing fatigue cycle, the crack propagation is noted to change from a transgranular crack propagation mode, a mixed transgranular and intergranular crack propagation nature, to intergranular crack propagation manner.
Thermal Property of Cu/Ti3SiC2 FGM
Authors: Chen Yan Lin , Li Jin , Shan Shang Shang , Gao Wei , Li Zong Yu , Zeng Cheng Wen
Published: July 2016

A four-layer functionally gradient material (FGM) of Cu/Ti3SiC2 was fabricated by hot pressing (HP) in vacuum. Oxidation behavior of Cu/Ti3SiC2 FGM was also investigated. The results show that the oxidation dynamics of Cu/Ti3SiC2 FGM at 600~800 °C for 30 h in air followed parabolic rate law. The hardness was increased with increasing content of Ti3SiC2. Thermal shock resistance was well owing to the effect of thermal stresses mitigated with FGM.
ZrO2 Ceramic Composite Added with MgAl2O4: Thermal Shock Resistance and Corrosion Resistance in Molten Uranium
Authors: Yu Nian , Zhang Tong , Cai Shu , Wang Ding Ding , Luo Li Ping
Published: July 2016

A kind of ceramic composite consisted of Mg-Y co-doped ZrO2 and MgAl2O4 was prepared as candidate material to replace the high destiny graphite crucible which was often used in nuclear industry. When the addition of MgAl2O4 was 7 wt%, samples with good thermal shock resistance were obtained. The obtained samples were tested up to 12 h in molten uranium, and no apparent cracks were found on the corrosion surface. Meanwhile, the corrosion rate decreased significantly from 30 mg·cm-2·h-1 to 3 mg·cm-2·h-1 as the corrosion time prolonged from 2 h to 12 h due to the formation of a protection layer consisted of UO2, Al3Zr2 and ZrC during the uranium corrosion test. These results suggested that the ceramic composite prepared in this study owned both good corrosion resistance to the molten uranium and thermal shock resistance at high temperatures,so it’s a high potential material to replace the high density graphite crucible in nuclear industry.
Effects of Solvent on the Optical Nonlinearities of Multi-Walled Carbon Nanotubes under the Picosecond Laser Pulses
Authors: Chang Qing , Liu Xi Wen
Published: July 2016

Based on Z-scan technique, the nonlinear absorption and refraction characteristics of multi-walled carbon nanotubes (MWNT) in chloroform , deionized water and isopropyl alcohol have been studied under the picosecond (ps) laser pulses, respectively. The experimental results show that the nonlinear absorption characteristics of the MWNT in chloroform, deionized water and isopropyl alcohol are all saturable absorption, and their nonlinear absorption coefficients are 1.83×10-11 m/W, 1.97×10-11 m/W, 2.31×10-11 m/W, respectively. The nonlinear refraction characteristics of the three solutions are all self-focusing, and the nonlinear refractive coefficients are 4.37×10-12 esu, 1.68×10-12 esu, 8.34×10-13 esu, respectively. The third-order nonlinear susceptibilities of the three solutions are 6.32×10-13 esu, 5.62×10-13 esu, 7.11×10-12 esu, respectively. The experimental results indicate that the nonlinear optical property of the MWNT isopropyl alcohol solution is the strongest, and the MWNT deionized water solutions is the weakest. The solvents have a big effects on the nonlinear optical properties of MWNT solutions.