Fabrication of Al/AlN composites by in situ reaction

The tensile properties and microstructures of various Al alloys fabricated by the pressureless infiltration method under a nitrogen atmosphere were examined. The spontaneous infiltration of molten metal into the powder bed occurred at 800 °C for 1 h under a nitrogen atmosphere. As a result, it was possible to fabricate Al alloys reinforced with AlN particles formed by in situ reaction. A significant strengthening even in the control alloy occurred due to the formation of in situ AlN particle even without an addition of artificial reinforcement. Strength values of the control alloy were increased with decreasing Al powders in bottom powders bed. In addition, tensile strength in Al–Mg alloys was increased with Mg content.     

In situ synthesis of Al–TiC in aluminum melt

In situ technology for the preparation of Al–TiC composite by self-propagating high-temperature synthesis is considered in this paper. It involves the synthesis of the reinforcement phase TiC from elemental powders directly in aluminum melt. Based on thermodynamic calculations, the composition and molar ratio of powders were chosen for the experiments. The effects of initial melt temperature and fluxes on the character of SHS reaction and TiC recovery were studied. The synthesis was shown to result in the formation of Al and TiC phases. The composites Al–TiC with the uncontaminated macrofracture, with the best TiC recovery and with the smallest TiC particles, can be produced at 1000 °C with fluxes.     

In situ Raman analysis of gas formation in NiMH batteries

In this paper Raman spectrometry is introduced in the field of sealed battery research for in situ gas-phase analysis and for longterm measurements. For this purpose, a new method was successfully applied in order to model battery behavior without interfering with operation. It is shown that oxygen, hydrogen, and nitrogen are responsible for the pressure increase that occurs during overcharging. The relative contribution of the different gases depends on the current imposed on the battery as well as the operating temperature. Reproducible and stable signals could be obtained even under severe conditions such as high pressure and elevated temperature. Oxygen and hydrogen are produced in side reactions taking place during battery operation. However, as nitrogen is unlikely to be a reacting gas inside the battery, the change in its partial pressure can be attributed to electrode expansion and a change in the electrolyte volume.     

铝/氮化铝电子陶瓷基板的制备及性能的研究

在675～750℃、氮气气氛下,使用石墨模具压铸的方法将金属纯Al敷接在AlN电子陶瓷基板上,随后利用力学拉伸试验机测试了Al和AlN的结合强度,其界面抗拉强度>15.94MPa,然后使用金相显微镜、SEM等微观分析仪器研究其界面的微观结构,发现在Al/AlN界面没有任何新物质生成,金属铝晶粒直接在AlN陶瓷表面结晶长大.     

Formation of AlN from Secondary Al Resources

Synthesis of AlN by NH4Cl-assisted direct nitridation of secondary Al resources was studied. Aluminum alloy scrap contained Mg and Zn element was used. Milled Al scrap （-1 mm） was mixed with NH4Cl and heated at 1000℃ for 1 h in presence of 1 L/min N2 flow gas. The nitrided product was evaluated by X-ray diffraction semi-quantitative analysis and scanning electron microscopy （SEM）. Aluminium nitride of 90.5% concentration was obtained with a hexagonal crystalline form. AlN is mostly formed in nano-whisker morphology （50～150 nm） which is homogenously distributed.     

Formation of AlN by nitrogen ion implantation

The phase composition of aluminium after bombardment with doses from 1 × 10¹⁶ to 1 × 10¹⁸ N⁺ ions cm^-2 is investigated by high voltage electron microscopy and selected area diffraction. This implantation always produced polycrystalline aluminium nitride (AlN). A thermal treatment to 600 °C did not yield new crystalline phases. At low temperatures the growth of AlN precipitations takes place mainly coherently as a result of a high vacancy density. Larger AlN precipitations grow similarly to the Ostwald ripening process. In this process incoherent precipitations are associated with a high dislocation density with an anisotropic distribution.     

Surface Degradation of Bulk AlN+Al Nano-composites

Bulk AlN + Al nanocomposite materials were Synthesized by sintering the compacts of AlN and Al nanoparticles, which were produced by an active plasma-metal reaction method. The sudeces of as-prepared nanocomposite was investigated by X-ray photoelectron spectroscopy (XPS).Results show the surfaces are much degraded and the degradation products are alumina(Al2O3),boehmite(AIOOH), bayerite(AI(OH)3) layer. The mechanism of degradation behaviour in moist environment was also discussed     

Al2O3/Al composites produced by directed melt oxidation using Zn containing external dopants

Al₂O₃/Al composites have been produced by the directed melt oxidation of Al with externally applied Zn containing dopants. Zn, ZnO and ZnAl₂O₄ are all shown to be capable of initiating the directed melt oxidation of Al without any Mg being present. The external surfaces of the reaction products were covered with a layer of ZnO overlaying a layer of ZnAl₂O₄, however, no Zn was observed within the composite bodies. Doping with ZnO or ZnAl₂O₄ resulted in a fine, dense ceramic microstructure and the amount of growth increased with increasing firing time and increasing ZnO or ZnAl₂O₄ content. Doping with Zn resulted in significantly less dense composites to those produced using ZnO or ZnAl₂O₄ and thus in the Zn system oxide and spinel dopants offer a significant advantage over using metallic Zn.     

In situ X-ray study of order–disorder phase transitions in Cu–Al–Be melt spun ribbons

The disorder–order phase transitions in Cu–Al–Be shape memory alloys were studied by in-situ X-ray diffraction. Isothermal measurements in an inert gas chamber were made on ribbons of Cu–Al–Be alloys, obtained by melt spinning. A position sensitive detector was used for a fast record of the X-ray signal on a θ–θ geometry diffractometer. Each ribbon was used as the heating element, avoiding the need of a heating sample holder and obtaining a better measurement of the temperature with a thermocouple attached directly to the ribbon. The order transition was followed at different temperatures after a high temperature annealing (700 °C) in the disordered β-phase region. A first order transition was observed from disordered β (A2) to ordered β ₁ (DO₃), without prior β (B2) ordering. No precipitation was detected during this fast measuring procedure.     

Synthesis and Characterization of Mixed Al+AlN Nanoparticles

Mixed Al+AlN nanoparticles were synthesized by an active plasma-metal reaction method. Mean particle size of the mixed Al+AlN nanoparticles is about 30-50 nm. Defects were found in some AlN particles. Moreover, the AlN ratio and its particle size in mixed Al+AIN nanoparticles obtained in different atmospheres (N2+Ar) increase with increasing N2 particle pressure, and the specific sudece areas of the mixed Al+AlN nanoparticles increase with the AlN ratio. The surface degradation of the Al+AlN exposed to air is estimated by the infrared absorption spectra     

自蔓延高温合成(SHS)氮化铝反应机制的研究

本文采用自行设计的铝箔包覆淬火新方法,获得了自蔓延高温合成AlN过程中不同阶段的燃烧产物,通过SEM观察和热力学分析,研究了自蔓延高温合成氨化铝的反应机制．研究结果表明,自蔓延高温合成氮化铝的形成过程是铝蒸发后,铝蒸气与氮气反应,最终形成氨化铝．其形成过程以VC机制为主．     

AlN纳米线CVD生长机理分析

采用化学气相沉积（CVD）法,在常压无催化剂的条件下生长出了一维AlN纳米结构,通过调节生长温度控制生长形貌,利用气固原理和Ehrlich—Schwoebel势垒模型着重分析其生长机理,当温度较高时,原子扩散长度变大,并得到较高能量,使其能从上一层跃迁到下一层,且纳米棒底部直径变大,直径变粗。     

Effect of nitrogen on diamond growth using unconventional gas mixtures

The influence of nitrogen on the growth of diamond using unconventional gas mixtures of CH₄---CO₂ by microwave plasma chemical vapor deposition was investigated. A clear improvement in the surface morphology and quality of the diamond films indicates the beneficial effect of adding nitrogen to CH₄-CO₂ gas mixtures. However, most interestingly, for lower methane concentration, the addition of small amounts of nitrogen resulted in the formation of isolated diamond particles possessing a vacant “cage-like” structure with completed {100} facets This result indicates that the continued addition of nitrogen gives rise to the deterioration of {111} facets and the retention of {100} facets. Analysis using Auger electron spectroscopy and secondary ion mass spectroscopy shows very low and uniform levels of nitrogen in the diamond films. Although the amount of atomic hydrogen in the ground state decreased and CN radicals increased with increasing amounts of added nitrogen, good-quality diamond films were deposited resulting from a larger amount of atomic oxygen and the decrease in the C₂ emissions in the gas phase under optimum conditions.     

AlN涂层在C_(f)/Al复合材料中的行为研究

用AlN聚合物先驱体溶液浸渍、烧结的方法,在C纤维表面制备AlN涂层。用挤压铸造法制备有涂层的C_((t))/Al复合材料。研究了AlN涂层在C_((t))/Al复合材料中所起的作用,结果表明:AlN涂层可有效地改善C纤维与Al基体的相容性,提高C_((t))/Al复合材料界面的高温稳定性。     

Mechanism of surface hardened layer formation on titanium alloys in a rarified nitrogen atmosphere

Translated from Fiziko-Khimicheskaya Mekhanika MaterLalov, Vol. 27, No. 2, pp. 38–42, March–April, 1991.     

Study of granule growth kinetics during in situ fluid bed melt granulation using in-line FBRM and SFT probes

Objective: The aim of this work was to study the granule growth kinetics during in situ fluid bed melt granulation process using real-time particle size measurement techniques. In addition, the usefulness of these techniques during scale-up of melt granulation was evaluated.

Materials and methods: Focused beam reflectance measurement (FBRM) and spatial filtering technique (SFT) probes were used within the process chamber of fluid bed granulator for real-time in-line granule size analysis.

Results: The results demonstrated that the use of in-line particle size probes in fluid bed granulator during the process offers an insightful view of granule growth and allows in-process monitoring of granule chord length changes. The effect of selected critical parameters (binder content, inlet air temperature and product endpoint temperature) on the granule growth was clearly presented by in-line measurements in a laboratory scale. A comparison of granule size measurements from both FBRM and SFT probes showed similar particle growth trends, which were in close correlation to the product temperature. Comparable trends in end granule particle size were observed when comparing different in-line, at-line and off-line particle size measurements.

Conclusion: The in-line FBRM and SFT probes were successfully employed in in situ fluid bed melt granulation process to study the influence of critical formulation/process parameters on the granule growth kinetics. The scale-up experiment confirmed the potential of these in-line granule size measurement techniques as a viable tool for process monitoring during the transfer of granulation to the larger scale or another manufacturing site/equipment.     

Normally off transistors based on in situ passivated AlN/GaN heterostructures

A molecular beam epitaxy technology of in situ passivated SiN/AlN/GaN heterostructures with an ultrathin AlN barrier has been developed. Based on these structures, normally off transistors with maximum current density of about 1 A/mm, saturation voltage of about 1 V, transconductance up to 350 mS/mm, and breakdown voltage above 60 V have been fabricated, in which the drain and gate current collapse phenomena are virtually absent.

     

Preparations of porous AlN particles from an aluminum–magnesium alloy melt solution

Porous AlN particles were prepared from an aluminum–magnesium melt solution. These samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and N₂-adsorption isotherms. The results show that there are many pore formations in every AlN particle, and the wall thickness of the pores is about 10 nm, the diameter of the pores is hundreds of nanometers and the Brunauer–Emmett–Teller (BET) surface area of the samples is 65.183 m²/g.