Dip-coating conditions and modifications of lead titanate and lead zirconate titanate films

The modifications of dip-coated lead titanate (PT) and lead zirconate titanate (PZT) films strongly depend on the film thickness and the substrate in addition to the heat-treatment temperature. At 500 to 600 ° C, metastable paraelectric pyrochlore grew on glass plates (amorphous plates) when the thickness of the coated films produced by one coating cycle was below 100 nm, while ferroelectric perovskite formed on crystalline substrates or when thick films were coated on amorphous plates. This tendency is discussed in terms of an inhomogeneous reaction and the epitaxial effect. The perovskite PT films coated on single-crystal SrTiO₃ plate at 700 ° C were strongly oriented to thec-axis.     

Distribution of lead in lead-containing aluminium alloys obtained by liquid phase co-spray forming technique

Liquid phase co-spray forming (LPCSF) technique was employed to produce Al-Pb and Al-Si-Pb alloys to show that it is possible, using this technique, to distribute lead into very fine-sized particles in Al/Al alloy matrix at low melt temperatures. Microstructural studies were carried out to explore the mechanisms governing lead distribution in the matrix of the alloys during processing. Results showed that, regardless of the alloy compositions and experimental conditions, the microstructures of the preforms exhibited great similarity, i.e. less uniform distribution of Pb particles in the base region, and uniform distribution of fine Pb particles in the equiaxed region. During LPCSF process, the behaviour of Pb droplets was similar to that of ceramic particles, except that the shape and size of liquid Pb phase varied corresponding to local solidification condition.     

浸渍-提拉法制备 PS胶晶模板及有序 ZnO多孔薄膜

采用浸渍-提拉法制备聚苯乙烯微球(PS)模板,以醋酸锌(Zn(CH3COO)2·2H2O)、二乙醇胺(NH(C2H2OH)2)、乙醇和水等配制的前驱体溶胶填充PS模板间隙,经过干燥过程原位形成凝胶,最后通过煅烧除去PS微球模板得到有序规则排列的多孔ZnO薄膜。重点讨论了模板在溶胶中的浸渍时间、溶胶的浓度对有序多孔结构形成的影响．通过TG-DTA分析、 XRD、TEM、SEM、IR反射光谱和UV-VIS光谱对结构和性能进行了表征．结果表明, 用无皂聚合制备的PS直径约为400nm,IR反射光谱布拉格反射测定PS模板为fcc结构,平行于基底的密排面为(111),ZnO由无定形向纤锌矿转变温度是460℃,多孔薄膜的孔径约为 280nm,孔壁由晶粒直径约46nm的ZnO粒子构成,．透光率为60％,禁带宽度Eg约为3．24eV．     

The structural influence of aluminium ions on emission characteristics of Sm3+ ions in lead aluminium silicate glass system

Optical absorption and photoluminescence characteristics of Sm³⁺ ions in lead silicate glasses mixed with different concentrations of Al₂O₃ (5–10 mol%) have been investigated. From these studies, the radiative properties viz., spontaneous emission probability A, the total emission probability, the radiative lifetime τ_R, the fluorescent branching ratio β of emission transition of ⁴G_5/2 → ⁶H_7/2 along with other transitions for Sm³⁺ have been evaluated and found to be the highest for the glass mixed with 8.0 mol% of Al₂O₃.The IR spectral studies have indicated that Al³⁺ ions do participate in the glass network with AlO₄ and AlO₆ structural units and further revealed that the concentration of octahedral aluminium ions induce bonding defects in the glass network. Such bonding defects are assumed to be responsible for low phonon losses in these glasses and lead to higher values of radiative parameters for the glass mixed with 8.0 mol% of Al₂O₃.     

The wetting of carbon by aluminium and aluminium alloys

The contact angle made by molten aluminium with vitreous carbon was measured by the sessile drop method in vacuum at temperatures up to 1100° C. The effect on wetting behaviour of the oxide layer on the molten metal was highlighted by using two samples of aluminium in different states of oxidation. The investigation involved the variation of certain parameters affecting the stability of the oxide film, e.g. the temperature, additions of Ti, Si, Cr, Be, Ca and Li to aluminium and the time held at a certain temperature. The state of the molten aluminium surface under various experimental conditions was determined indirectly by surface tension measurements.     

Wettability of aluminium nitride by tin–aluminium melts

The wettability of aluminium nitride by Sn–Al melts was studied by the sessile drop method in a vaccum of 2 × 10^–3 Pa at 1100 °C over the whole concentration region. The minimum interval on the contact-angle concentration dependence curve was observed at intermediate composition. For comparison, experiments were also performed on porous AlN. Wetting of porous nitride is worse than the dense nitride. The results have been analysed on the basis of the relation between wettability and the chemical interface reactivity in solid–liquid metal systems.     

Wetting of aluminium oxide by molten aluminium and other metals

The sessile drop technique has been used to measure the contact angle of molten aluminium, aluminium-nickel and aluminium-copper alloys, copper and gold, with sapphire, ruby and recrystallised alumina. Measurements were madein vacuo, and as a function of time and temperature over the range 800 to 1500° C. Cinematography and time-lapse photography were used. At temperatures below 950° C, sessile drops of aluminium reached equilibrium only after a period of time which increased with decrease in temperature and could be in excess of one hour. A rapid increase in contact area occurred around 900° C. Above 1150° C drops of aluminium and of the aluminium alloys were observed to spread and contract repeatedly. Contractions were observed with both polycrystalline and single-crystal alumina, although they were much more pronounced with the latter, and were associated with the formation of a series of reaction rings on the plaque. Ruby and sapphire behaved similarly. The shape of the rings depended on the crystallographic orientation of the plaque: the reaction profile tended to terminate in certain low index directions. Neither contractions nor reaction was observed with copper or gold. The observations are discussed in terms of the combined effects of evaporation, chemical reactivity and interfacial tensions in the system.     

In-situ observations of the annealing of liquid lead inclusions entrained in an aluminium matrix

The changes in configuration of cylindrical inclusions of molten lead entrained in an aluminium matrix have been observedin-situ using hot-stage high voltage electron microscopy. Three distinct types of events were observed and analysed. The cylindrical inclusions spheroidized over a wide temperature range due to capillary forces; the resultant spherical inclusions migrated in the temperature gradient caused by electron beam heating; and impinging inclusions coalesced due to capillary forces. The kinetics of the spheroidization and sintering events are controlled by the rate of diffusion of Al in liquid Pb and the data yield estimates for this diffusivity at various temperatures. The mechanism operating during thermal migration depends on the radius of the inclusion; volume diffusion kinetics control for the larger inclusions (r>0.8 μm) and interface kinetics dominate the smaller inclusions (r<0.8 μm).     

Influence of tin and bismuth on machinability of lead free 6000 series aluminium alloys

Abstract

The present paper presents the microstructural characteristics of an extruded AA6012A-T6 (AlMgSiBiSn) alloy and the microstructural changes occurring during turning operations, analysing the mechanism involved in chip breaking. An experimental investigation has been conducted to determine the effects of different cutting speed and feedrate on the machinability of the alloy. The machinability of the AA6012A-T6 alloy, where Pb is substituted by Bi and Sn, has then been compared to the standard AA6012-T6 (AlMgSiPb) and AA6082-T6 (AlSiMg) alloys. The results indicate that the extensive plastic deformation induces a preferred orientation of the grain structure and secondary phases along the shear plane, and a local increase in the alloy temperature. Low melting point compounds, such as the Sn and Bi bearing particles, transform into a soft or liquid state, changing their initial compact shape to assume a needle-like morphology. The β-Mg₂Si and α-Al(FeMn)Si particles are not influenced by the working temperature and keep their initial shape. The AA6082-T6 alloy shows a very poor machinability, with long and continuous strips, while the AA6012A-T6 alloy reveals a good chip formation with small and discontinuous C shaped chips, similar to the AA6012-T6 (AlMgSiPb) alloy. In particular, a feedrate higher than 0·2 mm rev^?1 provides short and suitable chips, independently of cutting speed.     

Structural engineering of nanoporous anodic aluminium oxide by pulse anodization of aluminium

Nanoporous anodic aluminium oxide has traditionally been made in one of two ways: mild anodization or hard anodization. The first method produces self-ordered pore structures, but it is slow and only works for a narrow range of processing conditions; the second method, which is widely used in the aluminium industry, is faster, but it produces films with disordered pore structures. Here we report a novel approach termed "pulse anodization" that combines the advantages of the mild and hard anodization processes. By designing the pulse sequences it is possible to control both the composition and pore structure of the anodic aluminium oxide films while maintaining high throughput. We use pulse anodization to delaminate a single as-prepared anodic film into a stack of well-defined nanoporous alumina membrane sheets, and also to fabricate novel three-dimensional nanostructures.     

Synthesis of aluminium nanoparticles by arc evaporation of an aluminium cathode surface

Aluminium nanoparticles (Al Nps) are synthesized using arc discharge method by applying direct current between aluminium electrodes in liquid environment without any use of vacuum equipment, heat exchangers, high temperatures furnaces and inert gases. After synthesis of Al Nps, in situ coating process on the nanoparticles was performed immediately. The effects of media on the yield and morphology of aluminium nanoparticles were investigated. Analysis result of the samples indicated that particle size was less than 30 nm, when 120 A/cm² arc current was used. In addition, coating agent can affect arc velocity, arc stability, morphology and composition of the nanoparticles. Resultant nanoparticles were identified using X-ray powder diffraction (XRD), also their surface morphology was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and finally the accuracy of coating was assessed with infrared (IR) spectroscopy.     

Corrosion Protection by electro-deposited aluminium

Aluminium can be deposited on various substrates by using a nonaqueous organic electrolytic system. The metallic deposit has a very high purity and good corrosionprotection properties. It can be used as a substitute for the highly toxic cadium, which is dangerous to the environment. Possible fields of application are protection against corrosion of highstrength steels without any danger of hydrogen embrittlement, the coating of lightweight materials like aluminium, magnesium and titanium alloys and the fabrication of fibre-reinforced metal matrix composites. MBB have installed a facility for the electro-deposition of aluminium and have worked in this field for more than three years. This paper discusses the experience and experimental results of the new technology and the possible advantages compared with other techniques.     

Reactive wetting of rutile by liquid aluminium

Sessile drop wetting experiments of liquid Al on polycrystalline rutile (TiO2) were conducted in the 973.1273 K temperature range under a low total pressure (9.3 10.3 Pa, Ar) and a low oxygen partial pressure ( 1.33 10.7 Pa), as a function of temperature and time. A non-wetting (150., 973 K, t >120 min.) to partial wetting (85., 1273 K, 50.60 min.) transition reflects reactive wetting characteristics. Microstructural investigations of the metal-ceramic interface shows that TiO2 is reduced by liquid Al, resulting in the formation of Al2O3. The steady-state contact angle at 1273 K of Al on -Al2O3 and Al on rutile are very similar, and the role of Ti segregation is minimal. It appears that spreading of the Al drop on TiO2 is governed by the reduction reaction at the solid-liquid interface. The measured activation energy corresponds well to the activation energy for volume diffusion of Al, Ti and O in rutile and the volume diffusion of Al in polycrystalline -Al2O3.     

Superplasticity of aluminium alloys grain-refined by zirconium

The superplasticity of aluminium alloys containing magnesium, oint, iron and manganese as well as zirconium as a grain-refining addition element was investigated by high-temperature tensile tests. The tool elongation and the strain rate sensitivity as a function of strain rate and temperature were determined. The activation enthalpy and activation volume were also determined in the superlastic region of the deformation. !n addition to the tensile tests metallo-graphic investigations were also made. The results obtained show that the superplasticity of the alloys investigated is increasing by the addition of iron but it is decreasing by the simultaneous addition of iron and manganese.     

Remediation of phosphate-contaminated water by electrocoagulation with aluminium, aluminium alloy and mild steel anodes

The present study provides an electrocoagulation process for the remediation of phosphate-contaminated water using aluminium, aluminium alloy and mild steel as the anodes and stainless steel as the cathode. The various parameters like effect of anode materials, effect of pH, concentration of phosphate, current density, temperature and co-existing ions, and so forth, and the adsorption capacity was evaluated using both Freundlich and Langmuir isotherm models. The adsorption of phosphate preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. The results showed that the maximum removal efficiency of 99% was achieved with aluminium alloy anode at a current density of 0.2 A dm(-2), at a pH of 7.0. The adsorption process follows second-order kinetics.     

Growth of aluminium nitride whiskers by sublimation-recrystallization method

Aluminium nitride (AlN) with various morphologies was fabricated through a sublimation-recrystallization method. The influences of type of reactor and temperature gradient were explored, as well as the orientations and growth mechanism of the obtained AlN whiskers. In the early stage of preparation, a vapour-liquid-solid (VLS) mechanism dominated, producing AlN pillars, whiskers and noncrystalline fibres. In the later stage, as the catalyst liquid was removed by volatilization, the pillars and noncrystalline fibres stopped growing, but the growth of AlN whiskers continued through a vapour-solid (VS) mechanism. By Laue method and rotating-crystal method of x-ray diffraction, together with electron diffraction, most of the AlN whiskers were discovered to grow on planes , or , where l=0, 1, 2, 3, along crystal axes , or , where w=0, 1, 2, 3. Oblique grown whiskers also appeared, with a growth direction at an angle of about 54° to the growth plane, .     

Synthesis of aluminium borate nanowires by sol-gel method

A sol-gel process followed by annealing was employed to fabricate single crystal aluminium borate (Al₄B₂O₉ and Al₁₈B₄O₃₃) nanowires. The diameter of Al₄B₂O₉ nanowires synthesized at 750 °C annealing is ranging from 7 to 17 nm, and that of Al₁₈B₄O₃₃ nanowires synthesized at 1050 °C annealing is about 38 nm. Instead of the well-known vapor-liquid-solid (VLS) mechanism, self-catalytic mechanism was used to explain the growth of the nanowires.