Preparation and mechanical properties of carbon/carbon composites with high textured pyrolytic carbon matrix

Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon （C/C） composites was 1.89 g/cm3 after depositing for 150 h. The microstructure and mechanical properties of the C/C composites were studied by polarized light microscopy, X-ray diffraction, scanning electron microscopy and three-point bending test. The results reveal that high textured pyrolytic carbon is deposited as the matrix of the composites, whose crystalline thickness and graphitization degree highly increase after heat treatment. A distinct decrease of the flexural strength and modulus accompanied by the increase of the toughness of the C/C composites is found to be correlated with the structural changes in the composites during the heat treatment process.

Effect of La_2O_3/Ce O_2 particle size on high-temperature oxidation resistance of electrodeposited Ni-La_2O_3/Ce O_2 composites

Ni-La2O3/CeO2 composite films were prepared by electrodeposition from a nickel sulfate bath containing certain content of micrometer and nanometer La2O3/CeO2 particles. The effect of La2O3 or CeO2 particle size on the oxidation resistance of the electrodeposited Ni-La2O3/CeO2 composites in air at 1000 °C was studied. The results indicate that, compared with the electrodeposited Ni-film, Ni-La2O3/CeO2 composites exhibit a superior oxidation resistance due to the codeposited La2O3 or CeO2 particles blocking the outward diffusion of nickel. Moreover, compared with nanoparticles, La2O3 or CeO2 microparticles have stronger effect because La2O3 or CeO2 microparticles also act as a diffusion barrier layer at the onset of oxidation.

TW250型车削中心的主要技术性能分析

对高速、高效和高复合化数控机床TW250型车削中心进行了技术性能分析,简介其特性和关键技术。

Uses of Blast Furnace Slag as Complex Fertilizer

Significant quantities of slag are generated as waste material or by-product every day from steel industries. They usually contain considerable quantities of valuable metals and materials. Transforming these solid wastes from one form to another to be reused either by the same production unit or by different industrial installation is very much essential not only for conserving metals and mineral resources but also for protecting the environment. The sustainable development concept requires a more efficient management of waste materials and preservation of environment. The paper presents the basic characteristics of slag, analyses and it＇s modification by incorporating some essential plant nutrients and the possibility of its application as fertilizer was studied.

Deformation behavior of high performance fiber reinforced cementitious composite prepared with asphalt emulsion

A novel engineered cementitious composite(ECC) was prepared with the complex binder of Portland cement and asphalt emulsion.By adjusting the amount of asphalt emulsion,different mixture proportions were adopted in experiments,including four-point bending test,compressive test,and scanning electric microscopy(SEM).The SEM observation was conducted to evaluate the contribution of polyvinyl alcohol(PVA) fiber and asphalt emulsion to the composite toughening mechanism.The tests results show that the most remarkable deflection-hardening behavior and saturated multiple cracking are achieved when the content of asphalt emulsion is 10%.However,excessive content of asphalt emulsion causes severe damages on the deformation behavior as well as loss in compressive strength of the mixture.SEM observation indicates that the influence of asphalt emulsion on the fiber/matrix interfacial property changes the dominant fiber failure type from rupture into pull-out mode,and thus causes beneficial effects for strain-hardening behavior.

Role of matrix structure and flaw size distribution modification on deflection hardening behavior of polyvinyl alcohol fiber reinforced engineered cementitious composites(PVA-ECC)

The multiple cracking and deflection hardening performance of polyvinyl alcohol fiber reinforced engineered cementitious composites(PVA-ECC)under four-point flexural loading have been investigated.Matrices with different binder combinations and W/B ratios(from 0.44 to 0.78)providing satisfactory PVA fiber dispersion were specially designed.Effect of pre-existing flaw size distribution modification on deflection hardening behavior was comparatively studied by adding 3 mm diameter polyethylene beads into the mixtures(6%by total volume).Natural flaw size distributions of composites without beads were determined by cross sectional analysis.The crack number and crack width distributions of specimens after flexural loading were characterized and the possible causes of changes in multiple cracking and deflection hardening behavior by flaw size distribution modification were discussed.Promising results from the view point of deflection hardening behavior were obtained from metakaolin incorporated and flaw size distribution modified PVA-ECCs prepared with W/B=0.53.The dual roles of W/B ratio and superplasticizer content on flaw size distribution,cracking potential and fiber-matrix bond behavior were evaluated.Flaw size distribution modification is found beneficial in terms of ductility improvement at an optimized W/B ratio.

Oxidation behaviors of Ni-Cr-Al superalloy foams at 1 000 °C in air

The oxidation behaviors of Ni-16Cr-xAl （x=4.5%, 9.0%, mass fraction） superalloy foams in air at 1000℃ were investigated. The effects of AI content on the resistance to high temperature oxidation were examined. The oxidation mechanisms of the foams were discussed. The results show that the resistance to the oxidation of the Ni-16Cr-xA1 based alloy at 1 000 ℃ increases with the content of A1 increasing from 4.5% to 9.0%. Complex oxide products are formed on the surface of the superalloy foams after the oxidation. Cr203 and A1203 are the predominant oxides for the scales of the foams with 4.5% A1 and 9% A1, respectively. Excellent high temperature oxidation resistance and superior pore conformation stability for the Ni-16Cr-xA1 based superalloy foam with 9% A1 can be mainly attributed to the formation of relatively continuous and protective A1203 oxides on the surface of the foam.

Phase transformation of nano-grained W(Co, C) composite powder and its phase constitute

A new process of WC-Co cemented carbide was developed by using nano-grained W（Co, C） composite powders as raw materials processed by high-energy ball milling. X-ray diffraetion（XRD）, differential thermal analysis （DTA）, thermo-gravimetrie （TG） analysis and coercive forces of the sintered samples were adopted to analyze the phase transformation and constitution, and the microstructures of sintered samples were characterized by scanning electron microscopy（SEM）. The results show that the as-milled powders are transformed into transitional phases W2C and η （Co3W3C or Co6W6C） during sintering, and finally transformed into WC and Co phases completely at 1 250℃ for 30 min, and a large number of fibrous WC grains with about 1.2μm in length and 100 nm in radial dimension are formed in the sintered body at 1 300 ℃.

Comparative study on combined preoxidation by potassium permanganate composites with chlorine and preozonation for enhancing coagulation

Comparative pilot tests were conducted to investigate the coagulation-aid effects of the combined preoxidation by potassium permanganate composites （PPC） with chlorine and preozonation. And the synergistie mechanism of combined preoxidation was discussed. Results showed that 1.0 mg/L PPC with 2. 0 mg/L chlorine could further improve the quality of treated water, as indicated by residual turbidity, TOC and algae. The enhanced efficiency could be explained by the synergistic effect of the preoxidants themselves, or the effect of chlorine and the intermediate such as hydrous manganese dioxide, which was generated by potassium permanga- nate, the main ingredient of PPC.

Composite Cathode Based on Redox-Reversible Nb2TiO7 for Direct High-Temperature Steam Electrolysis

Ni/YSZ fuel electrodes can only operate under strongly reducing conditions for steam elec- trolysis in an oxide-ion-conducting solid oxide electrolyzer （SOE）. In atmosphere with a low content of H2 or without H2, cathodes based on redox-reversible Nb2TiO7 provide a promising alternative. The reversible changes between oxidized Nb2TiO7 and reduced Nbl.33Tio.6704 samples are systematically investigated after redox-cycling tests. The conductivities of Nb2TiO7 and reduced Nb1.33Tio.6704 are studied as a function of temperature and oxygen partial pressure and correlated with the electrochemical properties of the composite electrodes in a symmetric cell and SOE at 830 ℃. Steam electrolysis is then performed using an oxide-ion-conducting SOE based on a Nb1.33Ti0.6704 composite fuel electrode at 830 ℃. The current-voltage and impedance spectroscopy tests demonstrate that the reduction and activation of the fuel electrode is the main process at low voltage; however, the steam electrolysis dominates the entire process at high voltages. The Faradic efficiencies of steam electrolysis reach 98.9% when 3%H2O/Ar/4%H2 is introduced to the fuel electrode and 89% for that with introduction of 3%H2O/Ar.

Structure, Energy Band Gap and Electrical Conductivity of Tapioca/Metal Oxide Composite

A natural polymer composite is the main choice to replace composites from petroleum derivatives. A composite is formed in two or more phases （i.e., organic and inorganic phases）. A composite that has specified energy band gap, electrical conductivity, and tensile strength can be used as semiconductor material. The objective of this research was to study the effect of production methods, concentration and type of metal oxide filler （TiO2, A1203, Fe203, and ZnO） on structure, energy band gap, and electrical conductivity of composites. Composites were prepared using a melt intercalation process with tapioca as a matrix and addition of 1%, 3%, 5o and 7% filler concentrations, and sonication processing time in interval of 40, 50, and 60 min. Structure and morphology of the composite were analyzed using FT-IR, XRD, SEM, and TEM. UV-vis was used to measure the energy band gap while electrical conductivity was measured using a potentiostat through determination of resistivity. In addition, tensile strength and elongation were measured by ASTM 822-02. The energy band gap of the tapioca/metal oxide composite was between 4.9-1.62 eV. Electrical conductivity showed a percolation thresholds for concentrations of 3%-5% TiO2, A1203, and Fe203 and 7% ZnO. The tapioca/ZnO composite with 5% ZnO and 50 min of processing time showed a maximum tensile strength of 74.84 kgf/cm2, 6% elongation, 1.27 - 10^-7ohm^-1cm^-1 electrical conductivity and energy band gap of 3.27 eV. The characteristics described show that the tapioca/metal oxide composite can be used as a semiconductor material.

Rare-earth metal amido complexes supported by bridged bis（β-diketiminato） ligand as efficient catalysts for hydrophosphonylation of aldehydes and ketones

A series of rare-earth metal amides supported by a cyclohexyl-linked bis（β-diketiminato） ligand were synthesized, and theft catalytic activities for hydrophosphonylation of aldehydes and ketones were developed. Reaction of [（Me3Si）2N]3RE（ct- C1）Li（THF）3 with the cyclohexyl-linked bis（13-diketimine） H2L （1） （L = Cy[NC（Me）CHC（Me）NAr]2, Cy = cyclohexyl, Ar = 2, 6-i-Pr2C6H3） gave the rare-earth metal amides LREN（SiMe3）2 （RE = Nd（2）, Sin（3）, Dy（4）, Er（5）, Y（6））. All complexes were fully characterized by elemental, spectroscopic and single-crystal X-ray analyses. Investigation of the catalytic properties of the complexes reveals that these complexes exhibited a high catalytic activity towards the hydrophosphonylation of aldehydes and ketones in the presence of a very low loading of rare-earth metal amides （0.1-1 tool%） at room temperature in a short time.

Potential chronic liver toxicity in rats orally administered an ethanol extract of Huangqin(Radix Scutellariae Baicalensis)

OBJECTIVE: To investigate the potential chronic liver toxicity of oral administration of ethanol extract of Huangqin(Radix Scutellariae Baicalensis)(SBE) in Wistar rats.METHODS: SBE was administered to rats by gavage for 26 weeks, at doses of 300, 1250, or 2500 mg·kg-1·d-1 respectively. The rats were euthanized at the end of 13 and 26 weeks daily oral dosing and following 4 weeks of recovery time. The changes of hematology, urinary, blood biochemistry and histomorphology were examined at each time point and focus on liver function and histological changes.RESULTS: When SBE at a dose of up to 2500 mgkg-1 d-1 was fed to male and female rats for 2··6 weeks, the liver tissue showed some inflammatory change that predominated by leukocyte infiltrationbut returned to normal after withdrawal. In addition, high-dose SBE treatment of 26 weeks in rats,glucose, electrolyte and lipid levels also have some changes. In addition, there are no other functional or organic lesions related to SBE treatment.CONCLUSIONS: Long-term and high-dose SBE may cause liver damage, however, the structural damage of the liver can be restored after the ethanol extract stopping. SBE will be well-tolerated for long-term use as a drug or health food, but in order to ensure drug safety, liver function, and serum glucose, electrolyte and lipid levels should be monitored when using SBE long term.

Highly oxidized graphene with enhanced fluorescence and its direct fluorescence visualization

We prepared hyper-oxidized graphene(HOG) as a form of graphene derivative by additional oxidation of graphene oxide(GO) sheets. HOG, which formed more functional groups and isolated conjugated clusters on the sheets, accordingly showed high solubility in water and alcohols, high transmittance and film transparence, longer fluorescence decay constant time, and enhanced fluorescence in states of solution and solid. By contrast, GO has much weaker fluorescence in solution and its fluorescence is totally quenched in solid. The influences of concentration, metallic ions, and pH on HOG fluorescence in aqueous solution were also investigated in detail. Due to HOG's strong fluorescence, direct visualization was realized on substrates and in solution. In addition, direct 3D fluorescence visualizations of HOG phase in polymer composites were achieved. These results show the great potential of HOG in a broad range of applications, from biological labeling, probes, and drug carriers to highperformance composites and nanomanipulation.