Synthesis of sub-micron nickel particles coated onto aluminum powders via a modified polyol process

Aluminum is commonly used as a fuel additive for propellants. The main limitations to its use lie in comparatively slow ignition and oxidation/combustion kinetics. Combustion performance of aluminized propellants can be improved through the use of Ni-coated Al particles. Sub-micron to nano-sized particles, with their increased reactivity, also improve combustion performance. Hence, in these contexts, fine Ni particles coated onto commercially available micron-sized Al powders using a modified polyol process were synthesized and evaluated. Ni-coated Al powders of various compositions produced by this method showed significant improvement in oxidation kinetics compared to untreated Al powders. The onset oxidation temperatures for the Ni-coated Al powders were found to be significantly reduced compared to pure untreated Al.     

Removal of inclusions from molten aluminum with actively coated ceramic filters

1　INTRODUCTIONMoltenaluminumissoactivethatitreactseasilywithO2 andH2 OtoproduceAl2 O3inclusionsandH2duringmeltingpractice .However ,someinclusions ,suchasAl2 O3,Al4 C3,MgAl2 O4 etc ,areproducedduringelectrolyticprocess .Aluminum productscon tainingtheseinclusionswill probablyexhibit poortoughnesspropertiesinservice[1,2 ] .Theinclusionsof 30 μmindiametercannotre movedfrommoltenaluminumusing glassfibrouswebsorfoamceramicfilters .Fromkineticsofchemi calreaction ,itisshownthatliquidalu…     

Synthesis and characterization of cerium-modified cubic mesoporous silica

The cerium-modified cubic mobil composition of matters 48 (MCM-48) molecular sieves were synthesized using cetyltrimethylammonium bromide (CTAB) as templates at low molar ratio of surfactant to inorganic precursor. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that the well-ordered cubic mesostructure was obtained when the Ce/Si molar ratio is less than 0.05. With the increase of Ce/Si molar ratio, the increase of unit cell parameters and the change of Fourier transform infrared spectroscopy (FTIR) provide powerful evidences for the incorporation of cerium in the framework of mesoporous molecular sieves. Nitrogen sorption data indicate that the Brunauer-Emmett-Teller (BET) surface area and the average pore diameter of Ce(Ⅲ)-MCM-48 are 1288 m 2·g -1 and 4.2 nm, and those of Ce(Ⅳ)-MCM-48 are 1228 m 2·g -1 and 3.7 nm, respectively. Diffuse reflectance UV-visible (UV-vis) spectroscopy confirms the presence of Ce(Ⅲ) in the octahedral position and Ce(Ⅳ) in the fluorite structure. X-ray photoelectron spectroscopy (XPS) studies further reveal that Ce(Ⅲ) and Ce(Ⅳ) coexist in the framework of mesoporous molecular sieves.     

纯铝微弧氧化陶瓷膜组织及耐腐蚀性能

利用微弧氧化技术,在碱性硅酸盐电解液中对纯铝进行表面改性处理,制备均匀致密的陶瓷膜。利用扫描电子显微镜(SEM)观察氧化陶瓷膜表面形貌及横截面组织结构,利用纳米压入硬度测试仪测量陶瓷膜的显微硬度和杨氏模量的分布,运用电化学方法测量陶瓷膜的耐腐蚀性能。结果表明,铝合金微弧氧化陶瓷膜的表面硬度高达25.3GPa,纳米硬度和杨氏模量在陶瓷膜的横截面分布相似,从膜基结合处向膜层表面呈下降趋势。从极化曲线中的腐蚀电势和腐蚀电流来看,微弧氧化处理后,纯铝的抗腐蚀能力得到很大的提高。     

Tailoring microstructure and mechanical properties of aluminum matrix composites reinforced with novel Al/CuFe multi-layered core-shell particles

Aluminum matrix composites (AMCs), reinforced with novel pre-synthesized Al/CuFe multi-layered core- shell particles, were fabricated by different consolidation techniques to investigate their effect on microstructure and mechanical properties. To synthesize multi-layered Al/CuFe core-shell particles, Cu and Fe layers were deposited on Al powder particles by galvanic replacement and electroless plating method, respectively. The core-shell powder and sintered compacts were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDX), pycnometer, microhardness and compression tests. The results revealed that a higher extent of interfacial reactions, due to the transformation of the deposited layer into intermetallic phases in spark plasma sintered composite, resulted in high relative density (99.26%), microhardness (165 HV_0.3) and strength (572 MPa). Further, the presence of un-transformed Cu in the shell structure of hot-pressed composite resulted in the highest fracture strain (20.4%). The obtained results provide stronger implications for tailoring the microstructure of AMCs through selecting appropriate sintering paths to control mechanical properties.     

Vapor pressure and thermochemical properties of ZrCl4 for ZrC coating of coated fuel particles

Vapor pressure of zirconium tetrachloride（ZrCl4）under vacuum and an argon pressure of 1 × 105 Pa was measured. The thermochemical changes of ZrCl4 during evaporation were studied by thermogravimetry-differential thermal analysis（TG-DTA）, X-my diffractometry（XRD）, scanning electron microscopy（SEM） and energy-dispersive X-ray（EDX） analysis. At the same temperature, vapor pressures of ZrCl4 under vacuum and an argon pressure of 1× 10^5 Pa are approximately the same. The vapor pressure exceeds 1 × 10^5 Pa at 340 ℃, which is high enough for ZrC coating of coated fuel particles. ZrCl4 sample is hydrolyzed to some extent to give ZrO2 and HCl, which however, has little influence on vapor pressure of ZrCl4 at high temperature. No ZrCl3 and Cl2 are produced by decomposition of ZrCl4 during evaporation, which is confirmed by thermodynamic calculation.     

Study on wear behavior of plasma electrolytic oxidation coatings on aluminum alloy

Thick and hard ceramic coatings were fabricated on A356 aluminum alloy by using plasma electrolytic oxidation(PEO) technique.The microstructure and phase composition of the PEO coatings were examined by using SEM and XRD method.It is found that the PEO coatings are mainly composed of crystalline α-Al2O3 and mullite.The dry sliding wear test of PEO coatings were carried out on a ring-on-ring wear machine.Results shows that there is hardly no wear loss of polished PEO coatings while the wear rate of uncoated aluminum alloy is 4.3×10-5 mm3·(N·m)-1 at a speed of 0.52 m·s-1 and a load of 40 N.     

Preparation technology and anti-corrosion performances of black ceramic coatings formed by micro-arc oxidation on aluminum alloys

In order to prepare ornamental and anti-corrosive coating on aluminum alloys, preparation technology of black micro-arc ceramic coatings on Al alloys in silicate based electrolyte was studied.The influence of content of Na2WO4 and combination additive in solution on the performance of black ceramic coatings was studied; the anticorrosion performances of black ceramic coatings were evaluated through whole-immersion test and electrochemical method in 3.5% NaCl solution at different pH value; SEM and XRD were used to analyze the surface morphology and phase constitutes of the black ceramic coatings.Experimental results indicated that, without combination additives, with the increasing of Na2WO4 content in the electrolyte, ceramic coating became darker and thicker, but the color was not black; after adding combination additive, the coating turned to be black; the black ceramic coating was multi-hole form in surface.There was a small quantity of tungsten existing in the black ceramic coating beside α-Al2O3 phase and β-Al2O3 phase.And aluminum alloy with black ceramic coating exhibited excellent anti-corrosion property in acid, basic and neutral 3.5% NaCl solution.     

Production and mechanical properties of aluminum alloys with dispersed nanoscale quasicrystalline and amorphous particles

By the dispersion of nanoscale quasicrystalline and amorphous particles in Al phase, new Al-based alloys with good mechanical properties were developed in a high Al concentration range of 93–95 at.% for Al−Cr−Ce−Co, Al−V−Fe, Al−Ti−M and Al−Fe−Cr−Ti alloy systems. The Vickers hardness of a melt-quenched (MQ) Al_84.6Cr_15.4 alloy with almost a single icosahedral quasicrystalline phase (QC) was 710. The addition of Ce and Co in the Al−Cr binary alloys was effective for the extension of the concentration range of the QC to a lower solute concentration range. The fracture strength (σ_f) increased to 1340 MPa for the MQ Al_94.5Cr₃Ce₁Co_1.5 alloy in which the particle size and volume fraction were approximately 40 nm and 70%, respectively. The σ_f of the MQ Al₉₄V₄Fe₂ alloy was 1390 MPa and the particle size and volume fraction were about 10 nm and 50%, respectively. Similarly, σ_f of the MQ Al₉₃Ti₄Fe₃ alloy was 1320 MPa and the particle size and volume fraction were about 11 nm and 30%, respectively. Power metallurgy (P/M) Al₉₃Fe₃Cr₂Fe₂ alloy with dispersed nanoscale QC exhibited ultimate tensile strength (σ_UTS) of 660 MPa, 0.2 % proof stress (σ_0.2) of 550 MPa, plastic elongation (ε_P) of 4.5%, Young's modulus (E) of 85 GPa, Vickers hardness (Hv) of 192 and specific strength (σ_UTS/ρ) of 2.20×10⁵ Nm/kg at room temperature and σ_UTS of 350 MPa, σ_0.2 of 330 MPa and ε_P of 1.5% at 573 K. The QC structure in the P/M Al₉₃Fe₃Cr₂Ti₂ alloy remained almost unchanged even after annealing for 720 ks at 573 K and good wear resistance against S50C steel was also maintained for the extruded alloy tested at sliding velocity of 0.5 to 2 m/sec. These mechanical properties are promising for the future extension of the new Al-based alloys to practical materials. This article is based on a presentation made in the symposium “The 3rd KIM-JIM Joint Symposium on Advanced Powder Materials”, held at Korea University, Seoul, Korea, October 26–27, 2001 under auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

原位自生TiB_2颗粒增强2024-T4铝基复合材料的损伤断裂行为

利用扫描电子显微镜结合原位拉伸试验研究了颗粒体积分数为4.167%的原位自生TiB_2颗粒增强2024-T4铝基复合材料(TiB_2/2024-T4)的损伤断裂机理。TiB_2/2024-T4在拉伸下的损伤断裂行为依次有微裂纹萌生、微裂纹累积和微裂纹贯通3个典型过程。结果表明,TiB_2/2024-T4中初始微裂纹率先在副产物颗粒、微米级的TiB_2颗粒以及TiB_2颗粒团聚体中萌生。随着加载的进行,更多的微裂纹出现在TiB_2颗粒偏聚带中,最终微裂纹通过颗粒稀疏区域铝合金基体的韧性断裂而贯通,形成宏观裂纹。通过分析单胞有限元模型,研究了颗粒偏聚对偏聚带中的基体微裂纹萌生的影响机理。数值结果表明:相比于颗粒稀疏区域的基体,颗粒偏聚带中的基体最大等效塑性应变和应力三轴度均有提高,诱使微裂纹会因为偏聚带中基体微孔洞长大和聚合进程的加剧而提前萌生,这与原位拉伸试验中的现象是一致的。     

电压对铝合金微弧氧化陶瓷层形成的影响

研究了正向和负向电压对6063铝合金微弧氧化陶瓷层形成的影响,并结合微弧氧化过程中正向电流密度的变化,对影响机理进行了探讨.结果表明,提高正负向电压均有利于提高陶瓷层的厚度与均匀性当正负向电压从420V/120V提高到480V/200V时,陶瓷层厚增加了一倍;负向电压对陶瓷层形成的影响更加显著,当保持正向电压440V不变,负向电压从120V提高到200V时,层厚增加了约60%,均匀性明显提高.正负向电压提高时,通过试样的正向电量随之增大,而且与陶瓷层厚度之间有着较好的线性关系.正向和负向电压分别通过加快物质的迁移和强化膜层的击穿从而促进陶瓷层的形成.     

高强度铝合金微等离子体电解氧化陶瓷质膜层影响因素

微等离子体电解氧化是在阳极氧化基础上发展起来的直接在轻合金表面原位生成γ-Al2 O3和α-Al2 O3陶瓷质膜的一项表面工程新技术.α-Al2 O3对陶瓷质膜层的性能起决定性作用,最大限度地促进α-Al2 O3的形成,是改善铝合金表面综合性能的关键.经过对国内近20个单位的调研,发现该技术在军工、航空、航天、机械等领域有着迫切的需求和广泛的应用前景,有望部分替代硬质氧化膜实现大规模生产.本文从基体材料、溶液特性及电参数三方面分析铝合金微等离子体氧化膜层的影响因素,重点分析基体合金元素对陶瓷质膜层的影响.指出该技术在高强度铝合金应用领域的发展方向并对其前景进行了展望.     

金属铝粉表面纳米膜包覆

采用扫描电镜、透射电镜和X射线光电子能谱仪对包覆有纳米膜的复合金属铝粉进行分析,发现纳米包覆膜的厚度为10 nm左右;金属粉的比表面积(BET)由包覆前的1.46 m2/g,包覆后增加到13.74 m2/g,提高了粉体的分散性;包覆后的铝粉孔径-孔容图呈很好的光滑曲线,表现出良好分散颗粒的孔径-孔容分布特征.热分析研究表明,包覆后的铝粉热量释放更大、更快速、更集中,适合于固体推进剂所要求的能量释放特点.     

镀料粒子脱靶方式对纯铝镀层微观组织的影响

传统磁控溅射的镀料粒子碰撞溅射脱靶后具有较低的离化率和沉积动能,致使制备的纯金属镀层极易形成带有微空隙的柱状结构,降低了镀层的致密性和膜基结合力.针对此问题,在磁控溅射环境下将阴阳极间的电流提升至气体放电伏安特性曲线中的弧光放电过渡区时,受靶面晶界和缺陷处电子逸出功低于晶粒内的影响,靶面微区会形成电子逸出的自增强效应,...     

原位合成铝基复合材料凝固组织中TiB2粒子的特征

分析了原位合成制备的ＴｉＢ２ 粒子强化铝基复合材料不同凝固组织中ＴｉＢ２ 粒子的分布规律和形貌特征。研究结果表明, ＴｉＢ２ 在该复合材料中细化晶粒的作用较弱, 但有明显的聚集倾向, 其聚集程度与熔炼方式和加热温度有关; 经半固液成型处理的组织中ＴｉＢ２ 的分布特征未改善; 六边形和长条形ＴｉＢ２ 可以是同一形态的粒子在空间不同方位的表现, 六边形ＴｉＢ２ 的侧面为｛１２１０｝ 面; 测定了ＴｉＢ２粒子的尺寸分布。     

3,5-二硝基水杨酸改性硅胶脱除稀土料液中的铝

针对离子吸附型稀土矿浸出液中铝元素含量高、对稀土后续分离影响大的问题,本研究以3,5-二硝基水杨酸(DNS)作为有机配体,以硅胶作为基体材料,通过化学合成3,5-二硝基水杨酸化学键合硅胶进行吸附除铝研究。结果表明:当3,5-二硝基水杨酸与Al³⁺的配位比为1:1、溶液pH=3.5、3,5-二硝基水杨酸改性硅胶用量为2g时,溶液中Al³⁺去除率达90%以上,稀土几乎无损失。采用紫外吸收的方法对机理进行研究,结果显示稀土料液中的Al³⁺通过取代3,5-二硝基水杨酸分子中羟基上的H+与其形成络合物,进而实现稀土与铝的分离。由吸附动力学研究可知,3,5-二硝基水杨酸改性硅胶对Al³⁺的吸附符合二级吸附动力学模型,其R²为0.98813。     

基于扫描Kelvin探针和FT-IR的7B04铝合金/涂层体系丝状腐蚀研究

对7B04铝合金进行硫酸或铬酸阳极氧化后再喷涂底漆或底漆+面漆,从而制备四类试样,而后开展标准丝状腐蚀试验,利用扫描 Kelvin 探针（SKP）和傅里叶变换红外光谱（FT-IR）技术对7B04铝合金/涂层体系的腐蚀行为和机理进行研究。光学显微镜观察发现四类试样上腐蚀丝的数量较少,且长度不超过3 mm,表明四类试样均具有较好的耐蚀性。SKP测试结果表明,四类试样跨划痕区域的伏打电位随试验时间的变化规律相似,划痕处与周围的涂层-金属界面之间的电位差引起丝状腐蚀的发生,腐蚀机理为阳极破坏;单个腐蚀丝的伏打电位值朝着头部降低,朝着尾部升高,头部和尾部之间的电位差促进腐蚀丝的传播。FT-IR分析显示丝状腐蚀产物的成分主要为Al(OH)3 、Al2O3和AlCl3及其部分水解产物,发生的电化学反应类似于7B04铝合金在氯离子作用下的点蚀过程。对比分析结果表明两种阳极氧化方式对丝状腐蚀的影响差异性较小。     

Microstructure and properties of mechanical alloying particles reinforced aluminum matrix composites prepared by semisolid stirring pouring method

Aluminum matrix composites reinforced with mechanical alloying particles(SiC_p) were fabricated by the semisolid stirring pouring method. The inf luence of mechanical alloying particles and Mg on the microstructure and mechanical properties of the composites was investigated by means of optical microscopy(OM), X-ray diffraction scanning(XRD), electron microscopy(SEM) and energy dispersive spectroscopy(EDS). Results show that the addition of Mg converts the agglomerate mechanical al oying particles in ZL101 matrix composites into dispersed distribution in ZL101-Mg matrix composites, large matrix grains into f ine equiaxed matrix grains, and eutectic phase into f ine particles. So the mechanical properties of ZL101-Mg matrix composites are better than those of ZL101 matrix composites. The mechanical properties of ZL101/ZL101-Mg matrix composites are gradually increased with the increase of the volume fraction of mechanical alloying particles. When the volume fraction of mechanical alloying particles is 3%, the Vickers hardness and ultimate tensile strength of the ZL101/ZL101-Mg matrix composites reach their maximum values.     

钢基电镀铝层阳极氧化处理后的组织结构和性能

用扫描电镜（SEM）和X射线衍射分析（XRD）测定了Q235钢上电镀铝层在硫酸溶液中不同时间阳极氧化处理后的组织结构和表面形貌，并对其硬度和耐蚀性能进行了测试。结果表明：电镀铝层经不同时间阳极氧化处理后，表面由非晶态Al2O3相和Al相组成，其上存在有纳米级的孔洞。随着氧化时间的延长，非晶态Al2O3相增多，Al相减少，氧化膜厚度增加，表面孔洞尺寸增大；氧化膜的硬度呈现先增加后降低，最后趋于稳定，且都显著高于电镀铝层的硬度。并且电镀铝层经阳极氧化处理后，在3．5％NaCl溶液中的电化学耐蚀性能大幅度增加，但随着阳极氧化处理时间的延长，电镀铝层的耐蚀性能降低。