硬脂酸复合铝粉的制备表征及声光性能研究

雾化铝粉是一种高能金属燃料,广泛应用于推进剂、可燃剂、发光剂等领域。为防止雾化铝粉氧化及吸水团聚,本研究以硬脂酸(Stearic Acid,SA)为包覆剂,通过溶液共混法对雾化铝粉进行表面包覆处理,制备了复合铝粉(SA/Al),并对复合铝粉的耐腐蚀及抗吸湿性能进行了测试。在此基础上,采用复合铝粉制备了声光剂,并测试了其安定性及声光性能。结果表明,硬脂酸可对铝粉实现有效包覆,所得复合铝粉的耐腐蚀性、抗吸湿性均有显著提高;以复合铝粉制备的声光剂声光性能有所提高,安定性良好,其中8%SA/Al的综合性能最优,其吸湿性的数值为0.0219%,仅为原料铝粉的1/60;1.5 m处声压级为179.27 dB,较原料铝粉提高了1.7 dB;发光强度为0.95×10^(7)Cd,与原料铝粉持平。

高氯酸铵/铝粉—复合改性双基推进剂燃速与热分解的相关性研究

利用高压差示扫描量热（PDSC）法研究了高氯酸铵/铝粉—复合改性双基（AP/Al-CM-DB）推进剂在1.0~13.0 MPa压强范围内的燃速与高压热分解特性的相关性。研究结果表明,AP/Al-CMDB推进剂在1.0~13.0 MPa压强范围内的燃速与高压热分解的相关性模型中需将压强p和放热速度ΔHd/Δθ两个影响因子对推进剂燃速的影响程度分开独立考虑,该相关性符合模型关系式u=kupa[ΔHd/Δθ]b,利用该相关性模型所得的燃速计算值与实测值之间的误差低于2.50%.

爆炸载荷下铝粉与橡胶复合材料中的冲击波传播特性

为研究爆炸载荷下冲击波在铝粉与橡胶复合材料中的传播规律,利用药柱加载的试验方法,采用锰铜压阻传感器测得铝粉体积含量为30%~60%的试样中6.50~14.25 GPa范围内的冲击波压力数据,结合材料的细观结构分析其对冲击波的衰减机理。通过试验与数值模拟相结合的方法获得冲击波在50%铝粉含量试样中的衰减规律。结果表明:在相同装药特性产生的爆炸载荷作用下,15 mm传播距离处的冲击波压力随铝粉含量的增加而先减小、后增大;铝粉含量为50%的含铝橡胶对冲击波的衰减能力最强,这与其表现出较强的黏性本构行为相关,数据拟合得到其冲击波压力衰减系数为0.0668.

Process−microstructure−properties relationship in Al−CNTs−Al2O3 nanocomposites manufactured by hybrid powder metallurgy and microwave sintering process

Al−2CNTs−xAl2O3 nanocomposites were manufactured by a hybrid powder metallurgy and microwave sintering process.The correlation between process-induced microstructural features and the material properties including physical and mechanical properties as well as ultrasonic parameters was measured.It was found that physical properties including densification and physical dimensional changes were closely associated with the morphology and particle size of nanocomposite powders.The maximum density was obtained by extensive particle refinement at milling time longer than 8 h and Al2O3 content of 10 wt.%.Mechanical properties were controlled by Al2O3 content,dispersion of nano reinforcements and grain size.The optimum hardness and strength properties were achieved through incorporation of 10 wt.%Al2O3 and homogenous dispersion of CNTs and Al2O3 nanoparticles(NPs)at 12 h of milling which resulted in the formation of high density of dislocations and extensive grain size refinement.Also both longitudinal and shear velocities and attenuation increase linearly by increasing Al2O3 content and milling time.The variation of ultrasonic velocity and attenuation was attributed to the degree of dispersion of CNTs and Al2O3 and also less inter-particle spacing in the matrix.The larger Al2O3 content and more homogenous dispersion of CNTs and Al2O3 NPs at longer milling time exerted higher velocity and attenuation of ultrasonic wave.

Microstructure,mechanical and wear properties of aluminum borate whisker reinforced aluminum matrix composites

The microstructural features and the consequent mechanical properties were characterized in aluminium borate whisker(ABOw)(5, 10 and 15 wt.%) reinforced commercially-pure aluminium composites fabricated by conventional powder metallurgy technique. The aluminium powder and the whisker were effectively blended by a semi-powder metallurgy method. The blended powder mixtures were cold compacted and sintered at 600 ℃. The sintered composites were characterized for microstructural features by optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), transmission electron microscopy(TEM) and X-ray diffraction(XRD) analysis. Porosity in the composites with variation in ABOw contents was determined. The effect of variation in content of ABOw on mechanical properties, viz. hardness, bending strength and compressive strength of the composites was evaluated. The dry sliding wear behaviour was evaluated at varying sliding distance at constant loads. Maximum flexural strength of 172 MPa and compressive strength of 324 MPa with improved hardness around HV 40.2 are obtained in composite with 10 wt.% ABOw. Further increase in ABOw content deteriorates the properties. A substantial increase in wear resistance is also observed with 10 wt.% ABOw. The excellent combination of mechanical properties of Al-10 wt.%ABOw composites is attributed to good interfacial bonds, less porosity and uniformity in the microstructure.

Microstructural characterization and mechanical properties of friction surfaced AA2024-Ag composites

The effects of Ag on the microstructure, mechanical properties, and electrical conductivity of AA2024 aluminum alloy coating were investigated. It was fabricated by friction surfacing as an additive manufacturing process. To carry out this investigation, Ag was added by 5.3, 10.6, and 16.0 wt.% to an AA2024 consumable rod by inserting holes in it. It was found that due to the strengthening by solid solution and the formation of precipitates and intermetallic containing Ag, the driving force for grain growth is reduced and consequently the grain size of the coating is decreased. After artificial aging heat treatment, the electrical conductivities of the coatings containing 0 and 16.0 wt.% Ag are increased by 4.15%(IACS) and decreased by 2.15%(IACS), respectively. While considering a linear relationship, it can be proposed that for a 1 wt.% Ag increase, the strength and hardness of the coating will be increased by 1.8% and 1.0%, respectively. It was established that the effect of Al6(Cu,Ag)Mg4 precipitate formation on strengthening is greater than that of Ag-rich intermetallic.

Dry sliding wear characterization of Al 6061/rock dust composite

The influence of rock dust size（10-30 μm） and mass fraction（5%-15%） on density, hardness and dry sliding wear behavior of Al 6061/rock dust composite processed through stir casting was investigated. Wear behavior of the developed composite was characterized at different loads, sliding velocities and distances using pin-on-disc setup. The experiments were conducted based on Taguchi＇s L27 orthogonal array and the influence of process parameters on wear rate was studied using ANOVA. The experimental results reveal that the applied load and reinforcement size are the major parameters influencing the specific wear rate for all samples, followed by mass fraction of reinforcement, sliding velocity and sliding distance at the level of 47.61%, 28.57%, 19.04%, 9.52% and 4.76%, respectively. The developed regression equation was tested for its accuracy and made evident that it can be used for predicting the wear rate with minimal error. With the help of SEM images, the worn surfaces of the novel composite were studied and the analysis proves that the wear resistance of aluminium alloys can be well improved with the addition of rock dust as reinforcement.

Influence of rutile(TiO_2) content on wear and microhardness characteristics of aluminium-based hybrid composites synthesized by powder metallurgy

The effect of rutile（TiO_2） content on the wear and microhardness properties of aluminium（Al）-based hybrid composites was explored. The proposed content of TiO_2（0, 4%, 8%, 12%, mass fraction） was blended to Al-15% SiC composites through powder metallurgy（P/M） process. Wear test was conducted using pin-on-disc apparatus under dry sliding conditions. Fabricated preforms were characterized using X-ray diffractometer（XRD）, scanning electron microscope（SEM） and energy-dispersive X-ray spectrometer（EDS）. Optical micrographs of the composite preforms display uniform distribution of TiO_2 throughout the matrix. Quantitative results indicate that wear resistance and microhardness increase with the increase of TiO_2 content. SEM images unveil that high wear resistance is attributed to high dislocation density of deformed planes and high hardness of TiO_2. SEM images of wear debris display gradual reduction in mean size of debris when TiO_2 content increases. EDS spectra confirm the presence of oxide layer which obviously reduces the effective area of contact between the sliding surfaces thereby lowers the wear loss of composites. The observation concludes that delamination and adhesive wear are the predominant mechanisms.

Fabrication and Characterization of Alumina/CNTs Nanocomposite Powders, by CCVD Method and Investigation of the Parameter Involved

Ceramics in general and particularly alumina （Al2O3） are important materials in various industries, but the main problem with these materials is related to some of their mechanical properties including low resistance against mechanical shock （hardness-toughness）, which makes them to be so brittle, and possession of high degree of porosity which reduces their strength and gives them fragile characteristics. Researchers report indicates that the presence of the second phase with suitable properties can improve some of the mechanical properties of these materials and optimize their characteristic. Carbon nanotubes with unique physical characteristics such as large aspect ratio, high strength and Young＇s modulus and improved thermal properties could be suitable candidates for this purpose. In this study, the growth of multi wall carbon nanotubes （MWCNTs） on the alumina support as the matrix of the composite has been carried out, using catalytic chemical vapor deposition （CCVD） method in which the iron nanoparticles has been selected as catalyst materials. Ethylene gas is used as feed materials for carbon source and argon as the carrier gas. In order to achieve a more comprehensive results, we have investigated the effects of some fabricating parameters like catalyst particle size, its weight percentage related to support material, alumina and to the some synthesizing temperature gases flow rate. Fabricated ceramics composites samples structures were analyzed using SEM images as well as Raman scattering spectra and X-ray diffraction pattern.

Study on extracting alumina from fly ash by compound additive activation method

According to the chemical and mineral composition characteristics of the fly ash,alumina can be extracted from fly ash through the calcining method by using sodium carbonate and calcium carbonate additives.The effects on leaching rate of alumina have been investigated. The results showed that the fly ash can be activated effectively and the leaching rate of alumina can be improved to more than 92% through this method. The best process parameters were the ratio of raw materials,i. e. the material weight ratio of fly ash,calcium carbonate and sodium carbonate was 1. 0∶1. 2∶0. 9. The activating temperature was 850℃-900℃,activating time was 3 h. This process has a potential application prospect and improves the value of comprehensive utilization of fly ash.