One-pot synthesis of Sb-Fe-carbon-fiber composites with in situ catalytic growth of carbon fibers

A Sb-Fe-carbon-fiber (CF) composite was prepared by a chemical vapor deposition (CVD) method with in situ growth of CFs using Sb₂O₃/Fe₂O₃ as the precursor and acetylene (C₂H₂) as the carbon source. The Sb-Fe-CF composite was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), and its electrochemical performance was investigated by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The Sb-Fe-CF composite shows a better cycling stability than the Sb-amorphous-carbon composite prepared by the same CVD method but using Sb₂O₃ as the precursor. Improvements in cycling stability of the Sb-Fe-CF composite can be attributed to the formation of three-dimensional network structure by CFs, which can connect Sb particles firmly. In addition, the CF layer can buffer the volume change effectively.     

Microstructure characterization of a pressureless infiltrating oxidized SiCp preform by Al-8Mg

The microstructure of a pressureless infiltrating 55vol% oxidized SiC preform by Al-8Mg alloy was characterized by transmission electron microscopy (TEM), high resolution TEM (HRTEM), field emission scanning electron microscopy (FE-SEM), and X-ray diffraction. The TEM image of the interface between Al and SiC shows that the surface of SiC is covered by a rough nanocrystal layer of MgAl₂O₄, Al₂O₃, and Si, produced by the interfacial reaction of Al, Mg, and SiO₂ on the surface of SiC. The Al-SiC interface is also examined by HRTEM to be better understood how MgAl₂O₄ and Al₂O₃ are produced. Dendritic Al₂O₃ crystals are embedded in the pores of the composite generated from the mutual bonding of SiO₂ on the surface of SiC. Columnar AlN crystals of about 250 nm in length are bunched vertically on the SiC particle surface.     

Electroless copper-phosphorus coatings with the addition of silicon carbide (SiC) particles

Cu-P-silicon carbide (SiC) composite coatings were deposited by means of electroless plating. The effects of pH values, temperature, and different concentrations of sodium hypophosphite (NaH₂PO₂·H₂O), nickel sulfate (NiSO₄·6H₂O), sodium citrate (C₆H₅Na₃O₇·2H₂O) and SiC on the deposition rate and coating compositions were evaluated, and the bath formulation for Cu-P-SiC composite coatings was optimised. The coating compositions were determined using energy-dispersive X-ray analysis (EDX). The corresponding optimal operating parameters for depositing Cu-P-SiC are as follows: pH 9; temperature, 90℃; NaH₂PO₂·H₂O concentration, 125 g/L; NiSO₄·6H₂O concentration, 3.125 g/L; SiC concentration, 5 g/L; and C₆H₅Na₃O₇·2H₂O concentration, 50 g/L. The surface morphology of the coatings analysed by scanning electron microscopy (SEM) shows that Cu particles are uniformly distributed. The hardness and wear resistance of Cu-P composite coatings are improved with the addition of SiC particles and increase with the increase of SiC content.     

碳还原粉煤灰制备SiC/Al2 O3系复合材料

在氩气气氛下,以粉煤灰为原料,石墨为还原剂,研究碳还原粉煤灰制备SiC/Al2 O3系复合材料的反应过程,并探索其制备的工艺条件.利用X射线衍射分析还原产物的物相变化规律,使用扫描电镜和能谱仪观察复合材料的微观结构.结果表明：在1673 K粉煤灰中石英相与碳反应生碳化硅,1773 K莫来石相基本分解完全.随着反应温度的升高,生成碳化硅和氧化铝含量增加,较合适的温度条件为1773~1873 K;保温时间的延长,有利于碳化硅和氧化铝的生成,较好的保温时间为3~4 h;增加配碳量对碳化硅和氧化铝的生成有促进作用,较合适的C/Si摩尔比为4~5.在制备出的SiC/Al2 O3复合材料中碳化硅在产物中分散较为均匀,并且粒度小于20μm.     

High-temperature frictional wear behavior of MCrAlY-based coatings deposited by atmosphere plasma spraying

Al₂O₃-Cr₂O₃/NiCoCrAlYTa coatings were prepared via atmosphere plasma spraying (APS). The microstructure and phase composition of the coatings were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser confocal scanning microscopy (LSCM), and transmission electron microscopy (TEM). The dry frictional wear behavior of the coatings at 500℃ in static air was investigated and compared with that of 0Cr25Ni20 steel. The results show that the coatings comprise the slatted layers of oxide phases, unmelted particles, and pores. The hot abrasive resistance of the coatings is enhanced compared to that of 0Cr25Ni20, and their mass loss is approximately one-fifteenth that of 0Cr25Ni20 steel. The main wear failure mechanisms of the coatings are abrasive wear, fatigue wear, and adhesive wear.     

Microstructure and oxidation behavior of carbon fiber reinforced SiC composite (Cf/SiC) with Mo–57Si–10B oxidation protection coating

Mo–57Si–10B (at.%) coating was prepared by the spark plasma sintering (SPS) technique on a 2D woven C_f/SiC composite, and the oxidation behavior of the bare and the coated C_f/SiC samples at 1300 ?°C were investigated. The coating was composed of a fine MoSi₂/MoB/SiO₂/Mo₂B₅ out layer and the inner SiO₂ interface layer. The mass gain percentage was approximately 0.25% after oxidation at 1300 ?°C for 100 ?h. The coated C_f/SiC substrate was effectively protected, owing to the rapid formation of the dense and protective borosilicate layer on the coating, the excellent microstructure stability of the coating and the inner SiO₂ interface layer.     

Densification behavior of mechanically milled Cu–8 at% Cr alloy and its mechanical and electrical properties

Synthesis and consolidation behavior of Cu–8 at%Cr alloy powders made by mechanical alloying with elemental Cu and Cr powders,and subsequently,compressive and electrical properties of the consolidated alloys were studied.Solid solubility of Cr in Cu during milling,and subsequent phase transformations during sintering and heat treatment of sintered components were analyzed using X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The milled powders were compacted applying three different pressures(200 MPa,400 MPa and 600 MPa)and sintered in H2atmosphere at 900 1C for 30 min and at 1000 1C for 1 h and 2 h.The maximum densification(92.8%)was achieved for the sample compacted at 600 MPa and sintered for 1000 1C for 2 h.Hardness and densification behavior further increased for the compacts sintered at 900 1C for 30 min after rolling and annealing process.TEM investigation of the sintered compacts revealed the bimodal distribution of Cu grains with nano-sized Cr and Cr2O3precipitation along the grain boundary as well as in grain interior.Pinning of grain boundaries by the precipitates stabilized the fine grain structure in bimodal distribution.     

Structure evolution of Y2O3 nanoparticle/Fe composite during mechanical milling and annealing

Fe-25 wt% Y2O3composite powders have been fabricated by mechanical milling(MM) Fe powders of 100 μm in diameter and Y2O3nanoparticles in an argon atmosphere for the milling periods of4,8,12,24,36,and 48 h,respectively.The features of these powders were characterized by using X-ray diffraction(XRD),scanning electron microscopy(SEM),electron probe micro analyzer(EPMA) and transmission electron microscopy(TEM).The experimental results showed that the mean particle size and crystalline size of MM powders decreased with the milling time increasing.All the elements distributed homogenously inside the powders after 48 h of MM.The lattice constant of the matrix α-Fe kept constant with the milling time,and no solid solution took place during MM process.After 8 h of MM,the α-Fe in each powder became nanocrystalline.After 48 h of MM,Y2O3changes from nanostructure into amorphous structure,and the crystalline size of α-Fe further decreased to 10 nm.The Y2O3in the powders mechanically milled for 48 h kept the amorphous structure after being annealed at 400 1C,and starts to crystallize when the powders are annealed at 600 1C.The amorphous Y2O3contains a small amount of Fe,and crystalline FeYO3appears at 800 1C.     

Interfacial reaction between the oxidized SiC particles and Al-Mg alloys

The interfacial reactions of oxidized SiC particles reinforced Al-Mg matrix composites were investigated by the field emission-scanning electron microscopy (FE-SEM), TEM and X-ray diffraction. It was found that the nanoscale MgO forms initially due to the interfacial reaction, then whether it reacts with molten Al continuously or not depends on the content of Mg in the matrix and its covering densification at the surface of particles. When there is not enough Mg in the matrix for the formation of dense MgO layer, MgO will transform into MgAl₂O₄ crystal owing to the continuous reaction with SiO₂ and molten Al. When dense MgO layer forms at the surface of the particles due to the affluence of Mg for the initial reaction, it will protect the inner SiC from the attack of molten Al. However, the reaction products of both MgO and MgAl₂O₄ are thermo-stable phases at the surface of the particles under high temperature. The results clarify the interfacial reaction route and they are of great value to the control of the interfacial reactions and their interfacial design of the composites.     

Synthesis of urchin-like Sn–ZnO–C composite and its enhanced electrochemical performance for lithium-ion batteries

Urchin-like Sn–ZnO–C composite have been successfully prepared by thermal annealing of ZnSn(OH)6precursor in acetylene/argon gas(1/9;v/v).The phase of the urchin-like Sn–ZnO–C has been characterized by X-ray diffraction(XRD)and Raman spectrum.The images of scanning electron microscopy(SEM)and transmission electron microscope(TEM)demonstrate that the Sn–ZnO–C composite with an average of 3 lm in diameter is composed of many core–shell nanowires and carbon nanotubes emanated from the center.The thermal annealing temperature and time have crucial effects on the formation of urchin-like structure and carbon content of the Sn–ZnO–C composites.As an anode for lithium-ion batteries,the urchin-like Sn–ZnO–C composite delivers a discharge capacity of 1,034.5 mAh/g in initial cycle and 571.9 mAh/g reversible discharge capacity after 25 cycles at a current density of 50 mA/g.The superior energy storage properties highlight the urchin-like Sn–ZnO–C composite as a potential alternative anode material in lithium-ion batteries.     

Catalytic effect of a novel MgC_(0.5)Co_3 compound on the dehydrogenation of MgH_2

The application of magnesium hydride(MgH_2) is limited due to the high reaction temperature and slow kinetics during dehydrogenation. In order to ameliorate the dehydrogenation property of MgH_2, MgC_(0.5)Co_3 compound with induction and catalytic effects was introduced into the Mg/MgH_2 system via ball-milling and hydriding combustion methods in present study. Compared to the pure MgH_2,the initial hydrogen desorption temperature of MgH_2–MgC_(0.5)Co_3 composite lowered to 237°C, decreasing by 141°C. At 325°C the MgH_2–MgC_(0.5)Co_3 composite could release 4.38 wt% H_2 within 60 min, which is 4.5 times the capacity of hydrogen released by as milled-MgH_2. Besides, the hydrogen desorption activation energy of the MgH_2–MgC_(0.5)Co_3 composite was dramatically reduced to 126.7 ± 1.4 k J/mol. It was observed that MgC_(0.5)Co_3 was chemically stable and no chemical transformation occurred after cycling, which not only inhibited the nucleation and growth of composite particles, but also had a positive effect on the hydrogen desorption reaction of MgH_2 due to its catalytic effect.This study may provide references for designing and synthesizing Mg–C–Co alloy compound for the Mg-based hydrogen storage area.     

Synthesis of dental resins using diatomite and nano-sized SiO2 and TiO2

The mechanical properties of dental composites were improved by porous diatomite and nano-sized silica (OX-50) used as co-fillers.The resin composites,filled with silanized OX-50 and silanized diatomit...     

Formation mechanism of interfacial microstructures and mechanical properties of Ti2AlNb/Ni-based superalloy joints brazed with NiCrFeSiB filler metal

Dissimilar brazing of Ti₂AlNb-based alloy and Ni-based wrought superalloy (GH536) was studied using NiCrFeSiB filler metal. The Ti₂AlNb/GH536 joints were analyzed by scanning electron microscope (SEM) equipped with an electron probe micro-analyzer (EPMA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The formation mechanism of interfacial microstructure and mechanical properties of Ti₂AlNb/GH536 joints were studied. The results indicated that Ti₂Ni(Al,Nb), AlNi₂Ti and TiB₂ reaction layers were formed in the joint adjacent to Ti₂AlNb base metal. These layers resulted in high micro-hardness and the weak link of the joint. γ solid solution was formed through isothermal solidification and β₁-Ni₃Si phase precipitated in the γ solid solution during cooling process. Ni₃B, β₁-Ni₃Si and CrB phases appeared in the centre of the joint. Blocky and needle-like borides formed within the diffusion affected zone of GH536 base alloy. The maximum tensile strength of Ti₂AlNb/GH536 joints reached 425 ?MPa ?at room temperature and the strength value of 373 ?MPa was maintained at 923 ?K.     

Microstructure and oxidation resistance of SiC–MoSi2 multi-phase coating for SiC coated C/C composites

In order to improve the anti-oxidation of C/C composites, a SiC–MoSi2multi-phase coating for SiC coated carbon/carbon composites(C/C)was prepared by low pressure chemical vapor deposition(LPCVD) using methyltrichlorosilane(MTS) as precursor, combined with slurry painting from MoSi2 powder. The phase composition and morphology were analyzed by scanning electron microscope(SEM) and X-ray diffraction(XRD) methods, and the deposition mechanism was discussed. The isothermal oxidation and thermal shock resistance were investigated in a furnace containing air environment at 1500 1C. The results show that the as-prepared SiC–MoSi2coating consists of MoSi2 particles as a dispersing phase and CVD–SiC as a continuous phase. The weight loss of the coated samples is 1.51% after oxidation at 1500 1C for 90 h, and 4.79% after 30 thermal cycles between 1500 1C and room temperature. The penetrable cracks and cavities in the coating served as the diffusion channel of oxygen, resulted in the oxidation of C/C composites, and led to the weight loss in oxidation.     

Synthesis of Mg2B2O5 whiskers via coprecipitation and sintering process

Mg₂B₂O₅ whiskers with high aspect ratio were synthesized by coprecipitation and sintering process using MgCl₂·6H₂O, H₃BO₃, and NaOH as raw materials and KCl as a flux. Their formation process was investigated by thermogravimetry and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microcopy (SEM). It is found that the products synthesized at 832°C are monoclinic Mg₂B₂O₅ whiskers with a diameter of 200?C400 nm and a length of 50?C80 ??m. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) analyses show that the whiskers obtained at 832°C are single crystalline and grow along with the [010] direction. The growth mechanism of Mg₂B₂O₅ whiskers was also presented.     

Thermodynamic study and methanothermal temperature-programmed reaction synthesis of molybdenum carbide

Nanostructured molybdenum carbide (Mo₂C) was successfully prepared from molybdenum trioxide (MoO₃) using methanothermal temperature-programmed reaction. Thermodynamic analysis indicated that in presence of methane, the formation of Mo₂C from MoO₃ occurs through the path of MoO₃ → MoO₂ → Mo₂C. The carburized MoO₃ was characterized using X-ray diffraction (XRD), CHNS/O analysis, Brunauer–Emmett–Teller (BET) analysis, and field-emission scanning electron microscopy (FESEM). At final carburization temperatures of 700 and 800℃ and at methane contents ranging from 5vol% to 20vol%, Mo₂C was the only solid product observed in the XRD patterns. The results indicated that the effect of methane content on the formation of the carbide phase is substantial compared with the effect of carburization time. Elemental analysis showed that at a final temperature of 700℃, the carbon content of carburized MoO₃ is very close to the theoretical carbon mass percentage in Mo₂C. At higher carburization temperatures, excess carbon was deposited onto the surface of Mo₂C. High-surface-area Mo₂C was obtained at extremely low heating rates; this high-surface-area material is a potential electrocatalyst.     

Bi/BiOCOOH复合光催化剂的制备及其可见光催化性能

采用溶剂热法制备出BiOCOOH,利用NaBH4水溶液为还原剂,原位还原制备了Bi/BiOCOOH复合光催化剂。通过XRD、FESEM、TEM、DRS和PL等测试手段对光催化剂的物相、形貌和光学性质等进行表征。以罗丹明B为模型污染物,考察了NaBH4用量对Bi/BiOCOOH复合光催化剂性能的影响。结果表明:当NaBH4的用量为25mg时,由于单质Bi的SPR效应使得光生电子和空穴的复合率降低,增强了光催化剂对可见光的吸收,从而显著提高其可见光催化性能,可在50min内,完全降解罗丹明B。     

化学镀制备SiC/Ni-P功能梯度材料

通过对化学复合镀Ｎｉ－Ｐ－ＳｉＣ复合镀层的研究，找到了制备ＳｉＣ／Ｎｉ－Ｐ功能梯度材料的工艺方法．并采用光学显微镜、电子探针分析仪、透射电镜等方法和手段对ＳｉＣ／Ｎｉ－Ｐ功能梯度材料的组织、形貌和成分进行了研究．结果表明，功能梯度材料的微观结构与材料成分梯度分布之间有很好的对应关系．     

Effect of heat treatment on microstructures and properties of a novel Al-Zn-Mg-Cu alloy for oil drilling

In view of the special requirements for strength, heat resistance and corrosion resistance of Al-Zn-Mg-Cu alloy for oil drilling, the Al-6.2 Zn-2.5 Mg-1.6 Cu alloy was prepared by increasing Cu content on basis of Russian Series 1953 alloy. The effect of heat treatment on the microstructures and properties of the alloy was characterized by optical microscope(OM), scanning electron microscope(SEM) and transmission electron microscope(TEM), and investigated by tensile test at room temperature, thermal exposure test and corrosion test. The results show that the strength after T6 aging treatment exhibit a decrease trend as an increase of the solution temperature from465 °C to 480 °C. After the solution treated by the rate of 470 °C/1 h, second phases dissolve into the matrix very well and the strength property reaches optimum. The alloy has better comprehensive properties treated by a solution treatment of 470 °C/1 h and then followed by an aging treatment of 120 °C/24 h + 170 °C/1 h + 120 °C/24 h. Under the aging state, the precipitated phases inside the grains are suitable in size, while on the grain boundary distribute discontinuously and the precipitate-free zone is obvious. Besides, the alloy still maintain high tensile properties. The yield strength, tensile strength and elongation are 650 MPa, 686 MPa,12.0%, respectively. The yield strength retention after heat exposure is 92%. The alloy has good corrosion resistance and the exfoliation corrosion degree. The average corrosion rate in the H_2S and CO_2 environment is 0.0024 mm/a, which is far less than the required 0.12 mm/a. It is insensitive to H_2S and CO_2 environments.     

不同冷却条件SiCp／ZA—27复合材料界面的TEM观察

主要用透射电子显微技术（TEM）、电子探针显微分析（EPMA）和选区电子衍射技术（SAD）分析了不同冷却条件下SiCp/ZA-27复合材料的界面特征和结构,发现冷却速度明显影响复合材料的界面结构、界面相组成和复杂金属氧化物的分布以及枝晶生长过程的溶质二次分配,且复合材料慢冷时的界面比液淬时的界面复杂得多。复合材料浆液液淬快冷时的界面特征是初生α（Al)相与 SiC颗粒直接机械结合,界面光滑无界面反应产物和中间过渡相及非晶氧化物;电磁搅拌随炉冷却条件下,复合材料界面绝大部分是共晶组织与SiC颗粒直接结合,少部分是由共晶组织／岛状非晶组织／SiC组成;随炉慢冷时的界面主要是由共晶组织／非晶组织／SiC组成,金属基体与SiC直接结合的界面非常少。不同冷却条件制备的复合材料的界面存在不同厚度的非晶组织。根据界面形貌和选区电子衍射花样并结合计算机模拟计算,发现部分界面处存在第三相（如MgAl2O3,Mg6Cu3Al7等相）,合成电子衍射花样表明这些第三相与SiC或基体间无晶体学位相关系。未发现SiC与基体间有晶体学位相关系,说明α（Al)或共晶相在SiC或基体间无晶体学位相关系。未发现SiC与基体间有晶体学位相关系,说明a(Al)或共晶相在SiC表面成核的可能性较小。复合材料浆液水淬后的基体轻微衍射分析得出饱和a(Al)已发生分解反应,由白色稳定的af相和黑色中间过渡相α′及存在于黑色区域中的η相组成,af与a′的晶格常数有微小差异,晶体结构相同,两相具有良好的共格关系。η相与af的位相关系为：[-1-10]α//[-12-10]η,(1-11)a//(0002)η。