超声波辐射对低品位氧化锌矿氨浸行为的影响

研究超声波辐射对兰坪低品位氧化锌矿氨浸过程的影响规律.研究表明:无超声波辐射时,兰坪低品位氧化锌矿在NH3-NH4Cl-H2O体系中浸出3 h后的最高浸出率为69.4%;引入超声波辐射后,显著缩短了浸出时间,无超声波辐射时Zn浸出率达到61.8%需要80 min,而采用超声波辐射浸出时仅需20 min;反应温度、浸出剂浓度和NH4Cl与NH4OH的摩尔浓度比等参数对超声波辐射的强化作用效果显著.当反应温度和浸出剂浓度较低,NH4Cl与NH4OH的摩尔浓度比较大时,超声波辐射的强化作用显著;超声波辐射可望降低氨浸低品位氧化锌矿的反应温度和浸出所需NH4OH浓度,大幅缩短浸出时间;同时,超声强化氨浸对锌的浸出具有较高选择性.     

炭/炭复合材料航空刹车副的湿态摩擦性能

对两种不同的炭/炭复合材料湿态下的摩擦磨损性能进行对比分析。结果表明:具有粗糙层热解炭的炭/炭刹车副由于其晶格结构较为完善,生长组织择优取向度和各向异性度均高于含有光滑层结构热解炭的炭/炭刹车副。前者的石墨化度及可石墨化能力均大于后者,由于前者的表面缺陷较少,所吸附的水分子较少,因而在湿态下刹车时,其刹车力矩将很快恢复到正常干态刹车时的力矩水平,对环境的适应能力大于光滑层结构的炭/炭刹车副。     

Ablation resistance and thermal conductivity of carbon/carbon composites containing hafnium carbide

Ablation properties and thermal conductivity of carbon/carbon (C/C) composites containing hafnium carbide (HfC) were investigated. The C/C composites containing 6.5 wt.% HfC exhibit the best thermal conductivity and ablation resistance. The improvement of the thermal conductivity is attributed to the increased phonon–defect interaction produced by the thermal motion of CO released from the reaction of carbon and ZrO₂. High thermal conductivity of the composites can slow down the ablation of carbon. When the HfC mass fraction is greater than 6.5 wt.%, cracks generated act as diffusion channels for an oxidizing atmosphere and thus accelerate the ablation of the composites.     

Isothermal reduction kinetics of zinc calcine under carbon monoxide

The reduction kinetics of zinc calcine under a CO atmosphere was evaluated by isothermal reductive roasting in a temperature range of 600−800 °C. The extent of reaction of zinc calcine was measured using thermogravimetry (TG), and the decomposition mechanism of zinc ferrite in zinc calcine was analyzed based on variations in the soluble zinc and ferrous contents. The results indicate that the reaction was controlled by the nucleation of the products, with an apparent activation energy of 65.28 kJ/mol. The partial pressure of CO affected the reaction rate more strongly than the CO intensity (defined as P_CO/(P_CO+P_CO2)). The generation rate of zinc oxide was higher than that of ferrous oxide; therefore, the nucleation of ferrous oxide is the rate-determining step of the reaction.     

Reduction of electrical arc furnace oxidizing slag by coke under microwave irradiation

The reduction of iron from electrical arc furnace oxidizing slag by coke was investigated under microwave irradiation (1.7 kW, 2.45 GHz). The heating behavior of cokes of different sizes were examined and a maximum heating rate of 550 K/min and a maximum temperature of 1783 K were obtained with coke particles smaller than 75 m. In the reduction of the oxidizing slag (15 g) by coke (1.45～1.65 g) under microwave irradiation for 25 min, the maximum recovery ratio of iron was 0.87, obtained when the amount of coke addition was 1.55 g. In addition, the reduced slag composition was modified by adding 5.9 g of CaO. With the addition of 1.55 g coke or more, free CaO in the slag was effectively reduced.     

浸出高硅锌焙砂中硅胶聚沉的规律

考察了pH值,静置时间,CaO快速中和以及添加Fe^3 离子对浸出高硅锌焙砂时硅胶聚沉的影响,发现pH=2.0-4.8是硅胶的稳定区,此时浸出液过滤十分困难,加速硅胶聚沉以提高过滤速率的有效方法是：用CaO或锌焙砂快速中和越过pH=2.0-4.8范围,以达到pH=5.0-5.5;延长静置时间,在浸出锌焙砂时加入带有相反电荷的胶体,均有利于硅胶的聚沉,实验条件下可使Zn浸出液和硅胶聚沉物分离的过滤速率提高36－60倍,同时使锌的回收率达到88％－90％。     

Drilling delamination and thermal damage of carbon nanotube/carbon fiber reinforced epoxy composites processed by microwave curing

The drilling-induced delamination and thermal damage of carbon fiber reinforced epoxy composite materials are serious problems especially for high value components of the aviation industry. To suppress the delamination and drilling ablation, an innovative approach was employed in this study. The multiwalled carbon nanotubes (MWCNTs) were introduced to the matrix resin to improve the interlaminar strength and thermal conductivity. The as-prepared composite was processed by microwave curing to enhance the interface strength between carbon fiber and the carbon nanotubes modified matrix. During the drilling processes, optical fiber Bragg grating sensors were utilized to precisely measure the drilling temperature. Experimental results indicated that the interlaminar fracture toughness was increased by more than 66% compared to that of the traditional thermal cured samples without MWCNTs. And the delamination factor was decreased by 16% according to the computerized tomography scanning results. The maximum drilling temperature of the MWCNTs reinforced composite was below the glass transition temperature of the matrix resin and declined by 23 °C compared to traditional composites. With this novel method of carbon nanotube modification and microwave curing, we provide the capability of reducing the drilling delamination and thermal damage of carbon fiber composites simultaneously, and explored the possibility of manufacturing and machining integration.     

Self-Diagnosis of GFRP composites containing carbon powder and fiber as electrically conductive phases

The electrical characteristics of glass fiber reinforced plastic (GFRP) composites have been investigated in order to incorporate a self-diagnosis function suitable for monitoring the health of structural materials. The electrical conductivity was introduced by adding carbon powder (CP) or carbon fibers (CF) into GFRP rods and sheets. The self-diagnosis ability of the composites was evaluated by measuring the change in electrical resistance as a function of stress (or strain) in tensile tests. The resistance of CFGFRP changed only slightly at small strain levels and increased nonlinearly with the applied stress due to cutting of the fibers at higher levels. CPGFRP showed high sensitivity to stress and the resistance changed linearly over a wide strain range. During cyclic loading tests, a residual resistance was also observed in CPGFRP composites after unloading. The residual resistance increased with maximum applied strain, showing that it can be used as an indicator of previously applied strain or stress. It is concluded that the CPGFRP composite is a promising material for simple diagnosis of dynamic damage and cumulative strain.     

The effect of zirconium carbide on ablation of carbon/carbon composites under an oxyacetylene flame

Ablation of zirconium carbide (ZrC) modified carbon/carbon (C/C) composites was tested by an oxyacetylene torch. The formation of zirconia from the oxidation of ZrC improves the ablation resistance of the C/C composites because of the evaporation at elevated temperature, which absorbs heat from the flame and reduces the erosive attack to carbon. Zirconia also acts as an accelerator for carbon oxidation as it reacts with carbon during the ablation, increasing the mechanical breakage rate of the fibres. However, the effect of mechanical breakage is inferior in the ablation of the composites. The heterogeneous reactions control the ablation of the composites.     

微波辐射时间对木质陶瓷导电性能影响的研究

以烟杆和酚醛树脂为原料,采用微波辐射制备了高导电性能的烟杆基木质陶瓷。同时,研究了微波辐射时间对木质陶瓷体积电阻率的影响,并采用X射线衍射技术、激光喇曼光谱和扫描电镜对其微观结构进行了研究。实验结果表明:与常规加热制备木质陶瓷相比,采用微波辐射的方法可将制备时间缩短99.4%。当微波辐射时间为80s时,木质陶瓷的体积电阻率仅为0.97Ω·cm。通过样品XRD谱图和激光喇曼谱图的分析,随着微波辐射时间的延长,样品有序化程度的提高,根据Tuinstra-Koening经验公式计算所得的石墨微晶面网直径La与通过XRD图谱计算得到的值相近。通过SEM观察可知,当微波辐射时间达到80s时,样品中由酚醛树脂形成的玻璃炭与由烟杆炭形成的无定形炭已融合为一个整体,呈多孔状。     

Conducting and magnetic behaviors of polyaniline coated multi-walled carbon nanotube composites containing monodispersed magnetite nanoparticles

High conductivity and supermagnetism of polyaniline (PANI)-coated multi-walled carbon nanotube (MWCNT) composites containing monodispersed 6 nm iron oxide (Fe₃O₄) nanoparticles has been successfully synthesized by in situ chemical oxidative polymerization using anionic surfactant dodecylbenzenesulfonic acid sodium salt. Hydrophilic 6 nm spherical Fe₃O₄ nanoparticles fabricated by the thermal decomposition process were chemically modified using 11-aminoundecanoic acid tetramethylammonium salt. The modified nanoparticles were further mixed with carboxylic acid containing multi-walled carbon nanotubes (c-MWCNTs) in an aqueous solution to form one-dimensional Fe₃O₄ coated c-MWCNT template and PANI/c-MWCNT nanocomposite were then synthesized via in situ chemical oxidative polymerization in HCl solution. Structural and morphological analysis using FESEM, HRTEM and XRD showed that the fabricated Fe₃O₄ coated c-MWCNT/PANI nanocomposites are one-dimensional core (Fe₃O₄ coated c-MWCNT)–shell (PANI) structures. The electrical conductivity of 1 wt% Fe₃O₄ coated c-MWCNT/PANI nanocomposites at room temperature is 37.7 S/cm, which is decreased to 28.6 S/cm with the loading of 5 wt% Fe₃O₄ nanoparticles. The magnetic properties of Fe₃O₄ coated c-MWCNT/PANI nanocomposites exhibit supermagnetism with saturation magnetization in the range of 0.04–0.15 emu/g, which increases as the amount of Fe₃O₄ nanoparticles increases.     

Wear and transfer characteristics of carbon fiber reinforced polymer composites under water lubrication

The tribological characteristics of carbon fiber reinforced polymer composites under distilled-water-lubricated-sliding and dry-sliding against stainless steel were comparatively investigated. Scanning electron microscopy (SEM) was utilized to examine composite microstructures and modes of failure. The typical chemical states of elements of the transfer film on the stainless steel were examined with X-ray photoelectron spectroscopy (XPS). Wear testing and SEM analysis show that all the composites hold the lowered friction coefficient and show much better wear resistance under water lubricated sliding against stainless steel than those under dry sliding. The wear of composites is characterized by plastic deformation, scuffing, micro cracking, and spalling under both dry-sliding and water lubricated conditions. Plastic deformation, scuffing, micro cracking, and spalling, however, are significantly abated under water-lubricated condition. XPS analysis conforms that none of the materials produces transfer films on the stainless steel counterface with the type familiar from dry sliding, and the transfer of composites onto the counterpart ring surface is significantly hindered while the oxidation of the stainless steel is speeded under water lubrication. The composites hinder transfer onto the steel surface and the boundary lubricating action of water accounts for the much smaller wear rate under water lubrication compared with that under dry sliding. The easier transfer of the composite onto the counterpart steel surface accounts for the larger wear rate of the polymer composite under dry sliding.     

Reinforcing capability of multiwall carbon nanotubes in alumina ceramic hybrid nanocomposites containing zirconium oxide nanoparticles

In this study, we investigate the reinforcing capability of multiwall carbon nanotubes (mwCNT) in alumina (Al₂O₃) ceramic hybrid nanocomposites containing zirconium oxide nanoparticles (ZrO₂np). For this purpose, highly dense hybrid nanocomposites containing well-dispersed ZrO₂np (8 vol%) and mwCNT (4 vol%) were fabricated by the hot-pressing method. The resulting hybrid nanocomposite exhibited a ten-fold finer microstructure and 116% enhanced fracture toughness as well as 12% greater hardness over the benchmarked monolithic Al₂O₃. The superior mechanical performance of the hybrid nanocomposite was attributed to the synergistic role of ZrO₂np and mwCNT in refining the matrix microstructure and inducing unique toughening mechanisms of micro-cracking by ZrO₂np and pull-out as well as crack-bridging by mwCNT. Qualitative and quantitative approaches were utilized to assess the individual and collective role of the reinforcing constituents in enhancing the performance of hybrid nanocomposite. The qualitative analysis by electron microscopes demonstrated strong interfacial adhesion of both reinforcing constituents with the based Al₂O₃ matrix. Furthermore, the quantitative analysis verified that the enhanced mwCNT/Al₂O₃ interfacial shear strength is caused by the intricate physical arrangement of the mwCNT within the matrix grains besides their chemical bonding at the interface. The role of fine-grained microstructure in establishing idiosyncratic mwCNT interlocking with the Al₂O₃ matrix grains was meticulously investigated. Moreover, the influence of mwCNT/matrix interlocking on the mwCNT reinforcing ability and toughening mechanisms efficiency in the hybrid nanocomposite is discussed.     

Ferromagnetism of nanostructured zinc oxide films

The paper presents a review of the causes of the occurrence of ferromagnetic properties in zinc oxide. It is shown that ferromagnetism only occurs in polycrystals at a fairly high density of grain boundaries. The critical grain size is about 20 nm for pure ZnO and over 1000 nm for zinc oxide doped with manganese. The solubility of manganese and cobalt in zinc oxide increases considerably with diminishing grain size. Even at the critical grain size, the ferromagnetic properties depend significantly on the film texture and the structure of intercrystalline amorphous layers.     

Synthesis of titanate/anatase composites with highly photocatalytic decolorization of dye under visible light irradiation

Titanate/anatase nanocomposites consisting of titanate nanotubes and leaf-like anatase TiO₂ nanoparticles were successfully prepared via a novel combinational hydrothermal method. The samples were characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The activity of the nanocomposites was examined by photocatalytic decolorization of rhodamine B under visible light irradiation. It is found that the nanocomposites exhibited a much improved photocatalytic activity in comparison with titanate nanotube, anatase TiO₂ nanoparticle, and even the commercial Degussa P-25. The photocatalytic mechanism of the as-prepared nanocomposites was discussed.     

锌蒸气高温气相氧化动力学

用热重法测定了锌蒸气在不同温度和气氛下的氧化动力学曲线,用扫描电镜观察分析产物的结晶形貌.结果表明:氧化动力学遵守直线规律时,产物的结晶形貌是无定形、颗粒状和单针状;氧化动力学曲线为抛物线规律时,产物的结晶形貌是四针状和多针状.氧化动力学转变规律的原因是锌蒸气中存在超细锌微粒与气态锌原子的动态平衡.应用动力学理论和上述结果推断了相关条件下的动力学机理函数和动力学常数,研究了锌微粒的氧化过程并求出了锌原子通过氧化膜层的扩散系数.     

Study of fluorhydroxyapatite coatings on carbon/carbon composites

Fluorhydroxyapatite coatings were prepared on the surface of carbon/carbon composites using the combined action of ultrasonic-electrodeposition and ion exchange. The morphology, structure and composition of the prepared coatings after ion exchange were investigated by scanning electron microscopy, X-ray energy spectrum analysis, infrared spectroscopy and X-ray diffraction. Results show that the crystallinity of the coating as well as the intensity of the diffraction peaks (112) and (300) of hydroxyapatite increased, whereas the intensity of the diffraction peaks of tricalcium phosphate decreased. The small lamellar crystals were converted into large ones. The fluorine content in the coating was 4.59%. The bonding strength between the coating and the carbon/carbon matrix increased slightly after immersion, reaching 4.12 MPa. The mechanism of the ion exchange during which hydroxyapatite turned into fluorhydroxyapatite is discussed.     

微波预处理对载醋酸锌废触媒锌浸出的影响

提出微波预处理废触媒-酸浸提锌新工艺,测定废触媒在微波场中的温升曲线,探索微波预处理温度和保温时间对浸出率的影响,并对微波预处理废触媒机理进行分析.结果表明:微波预处理可显著提高锌的浸出率,当微波预处理温度和时间分别为950 ℃和12 min时,锌的浸出率达到96.58%.微波预处理打开了堵塞的废触媒孔道,增大了浸出剂与锌的接触面积.     

Kinetics of the reactions in the smelting furnace of the Mitsubishi process

In this paper, the authors present the results of theoretical calculations on the rates at which copper concentrate particles and silica particles dissolve in the matte in the smelting furnace of Mitsubishiprocess. Those calculations indicate that the concentrate particles dissolve rapidly in matte, in less than 1 ms, whereas silica particles dissolve at a much slower rate, and they dissolve mainly in the bulk matte in the smelting furnace. Some advantages of bath smelting over flash smelting are given. For more information, contact Zenjiro Asaki, Mitsubishi Materials Corporation, Central Research Institute, 1-297 Kitabukuro-cho, Omiya, Saimtama, 330-8508, Japan.