Preparation of amorphous Ni-Pd-P particles by melt ejection

Amorphous spherical particles with diameters of 0.5 to 1.4 mm have been prepared by melt ejecting Ni-rich Ni-Pd-P alloys into stirred cold water with 1 vol pct surfactive agent. The sphericity of the amorphous particles defined by the difference in diameter was better than 98 pct. Particle diameters (d) are 2 to 3 times larger than the orifice diameter (2r) of the quartz nozzle. The size ratio has been interpreted by the Raplace’s relation (d = 4r) derived from the assumption that an internal pressure of molten alloy is equal between cylindrical stream and spherical droplet. From the result that no spherical amorphous particles are formed in the cold water without surfactive agent, a significant decrease in the surface tension of coolant by the addition of surfactive agent is essential in the formation of spherical liquid particles from the ejected melt stream. The amorphous particles with diameters below about 1.0 mm exhibit hardness, crystallization temperature, and heat of crys-tallization similar to those from the amorphous ribbon with about 40 μm thickness. However, the onset temperature and heat of relaxation are lower by 16 K (4.2 pct) and larger by 130 J/mol (13 pct), respectively, for the particles. It is thus concluded that the amorphous spherical particles have the same thermal stability as that of the amorphous ribbon and its structure is in a more disordered state as compared with the ribbon sample.     

Preparation and thermal stability of Zr-Ti-Al-Ni-Cu amorphous powders by mechanical alloying technique

This study examined the amorphization feasibility of Zr_70−x−y Ti _x Al _y Ni₁₀Cu₂₀ alloy powders by the mechanical alloying (MA) technique. According to the results, after 5 to 7 hours of milling, the mechanically alloyed powders were amorphous basically in the ranges of 0 to 12.5 at. pct Ti and 2.5 to 17.5 at. pct Al. These ranges are larger than those of bulk amorphous alloys prepared by a squeeze mold casting technique. Most of the amorphous mechanically alloyed powders exhibited a wide supercooled liquid region of more than 60 K before crystallization. The glass-transition and crystallization temperatures of mechanically alloyed samples were different from those prepared by squeeze casting. It is suspected that different thermal properties arise from the introduction of impurities during the MA process. The amorphization behavior of Zr₅₀Ti_7.5Al_12.5Ni₁₀Cu₂₀ was examined in detail. The X-ray diffraction and extended X-ray absorption fine structure (EXAFS) results show the fully amorphous powders formed after 5 hours of milling. A kinetically modified thermodynamic phase transformation process was observed for the glass-transition behavior in the Zr₅₀Ti_7.5Al_12.5Ni₁₀Cu₂₀ amorphous powder.     

Ultrasonic effect on the penetration of the metallic melt into submicron particles and their agglomerates

Deagglomeration and wetting of submicron particles in a metal melt under ultrasonic exposure are considered based on the theory of acoustic cavitation and capillary phenomena. Basic dependences linking the exposure time with physicochemical properties of the particles and the melt, as well as with acoustic radiation characteristics, are found. The experimental and calculated times of ultrasonic treatment of the aluminum melt containing submicron aluminum oxide particles are compared, and a satisfactory agreement of results is found.     

非晶态Ni-P合金粉体的脉冲放电制备及其催化性能

采用脉冲放电技术合成Ni-P合金粉体,研究了合金粉体的结构及其对高氯酸铵热分解的影响.结果表明,非晶态Ni-P合金粉体是由微粒组成的团聚结构.脉冲放电电压700、900和1100V对应的弦粒子数依次增大,粉体粒径依次减小,分别为350～500、250～400和150～300nm.Ni-P合金粉体促进高氯酸铵的低温和高温热分解,与纯高氯酸铵相比,高氯酸铵和Ni-P粉体混合物的第1放热峰(低温分解峰)温度降低幅度小于12℃,第2放热峰(高温分解峰)温度降低约53℃;合金粉体粒径减小,第1放热峰强度增强,第2放热峰强度减弱,低温分解失重从高氯酸铵的15.97%增加到42.78%,高温分解失重从81.62%降低到47.58%,高温分解结束时温度的降低幅度为26～43℃.     

Preparation of Al-based amorphous coatings and their properties

Al₈₆Ni₈Co₁La₁Y₂Gd₂ amorphous coatings were prepared using cold gas kinetic spray technology.The results show that Al₈₆Ni₈Co₁La₁Y₂Gd₂ amorphous coatings are achieved with the porosity about 3.2%,thickness about 893 μm,the amount of amorphous phase about 82.5%,the hardness about 300 HV0.2.The corrosion potential and anti-corrosion life of 7075 T6 alloy aluminum are about-0.78 V and 72 h,respectively.The electrochemical analysis and neutral salt spray are about-0.69 V corrosion potential and 274 h anti-corrosion life for amorphous Al-based coatings,respectively.Therefore,the life of the Albased amorphous coatings is about 3.8 times that of 7075 T6 aluminum alloy.Besides,the failure mechanism was analyzed using TEM in this investigation.In a word,Al₈₆Ni₈Co₁La₁Y₂Gd₂ coatings keep dense structure,high amorphous content,favorable amorphous phase stabilizing ability and longer anticorrosion life.That is,Al₈₆Ni₈Co₁La₁Y₂Gd₂ coatings have better comprehensive properties.Therefore,these findings indicate that the present Al₈₆Ni₈Co₁La₁Y₂Gd₂ amorphous coatings prepared using cold gas kinetic spray technique can protect aluminum alloy very well and they can be considered to be used in aviation field.     

Macrosegregation during growth of a dendrite array into a stirred melt at near steady-state conditions

Solidification experiments on tin alloys have been carried out where the interface morphology consisted of an array of dendrites advancing at near steady-state conditions. It was found that a fairly severe degree of mixing changed the dendrite morphology at low temperature gradients but not at higher gradients. In both cases the mixing was relatively ineffective at producing a macrosegregation in the presence of the dendrite array. The results may be interpreted as evidence that in some cases one would expect very little macrosegregation in columnar growth under near steady-state conditions even in the presence of severe liquid convection.     

Shaping of powder particles during the atomization of a melt with water

Conclusions The particle shape of a powder produced by the atomization of a molten metal with water under high pressure, unlike that of a powder atomized with a compressed gas, is determined by the actual density of the energy carrier (the steam:water ratio) in the contact zone, and can vary within wide limits, from spherical to jagged. The actual density of an energy carrier consisting of water and steam is a function of the temperature of the melt and also of the pressure of the water and the geometry of the atomizing device.Translated from Poroshkovaya Metallurgiya, No. 9(165), pp. 5–10, September, 1976.     

CuO纳米线的简单热氧化制备及其气敏特性

传统金属氧化物气敏材料因其灵敏度低、选择性差、工作温度高等缺点已很难满足高性能气敏元件的要求,而纳米气敏材料具有高的比表面积,可显著改善材料的气敏特性.文中采用简单的电热板在330~430 ℃、空气气氛下、一步法成功制备出了具有良好单斜晶体结构的CuO纳米线,平均直径为20~30 nm,长度可达1~5 μm;CuO纳米线气敏元件在100×10-6乙醇气氛中的最佳工作温度约为260 ℃,其灵敏度分别为1.36和1.64,恢复和响应时间均小于5 s.      

利用超重力分离铝熔体中的夹杂颗粒

利用Al-17% Si-4.5% Cu熔体中密度较小的初生硅颗粒模拟金属熔体内部的夹杂物,并采用超重力场分离熔体中的夹杂颗粒,研究了不同重力系数条件下,金属熔体中夹杂物的分离规律.实验结果表明：经过超重力处理后,初生硅颗粒在试样上部区域发生明显的偏聚现象,试样内部出现无初生硅颗粒区域,且随着重力系数的增加,无初生硅颗粒的区域面积逐渐增大,说明重力系数越大,硅颗粒在试样上部区域的聚集程度越好.随着重力系数的增大,试样的净化效率逐渐升高,当重力系数（G）为500时,试样的净化率达到了84.98%.利用DPM离散相模型对超重力场下熔体内部硅颗粒的具体受力情况进行分析,并模拟研究铝熔体内部硅颗粒在不同重力场中的分离行为.数值模拟结果证明了夹杂颗粒在沿着超重力方向上的运动行为近似符合Stokes运动定律.这表明超重力场可以有效分离金属熔体中的夹杂物.     

Evaluation of amorphous ursodeoxycholic acid by thermal methods

PURPOSE: The purpose of this study was to characterize the amorphous state of ursodeoxycholic acid (UDCA) samples by using isothermal microcalorimetry, X-ray diffraction, infrared (IR) spectroscopy and solid state carbon 13 nuclear magnetic resonance (13C-NMR) spectroscopy, and to demonstrate the application of the thermal methods (microcalorimetry and differential scanning calorimetry (DSC) for studying the amorphous state and clarifying the dissolution mechanism of UDCA. METHODS: Amorphous UDCA was prepared by grinding and rapid cooling of the melts. The heat of solution of UDCA was measured by an isothermal heat-conduction twin microcalorimeter at 25.0 degrees C. Some physicochemical properties of amorphous UDCA were also studied. RESULTS: The intensities of X-ray diffraction peaks of crystalline UDCA decreased with an increase in grinding time. The heat levels of solution of crystalline UDCA and UDCA ground for 1 min were endothermic, and became exothermic with an increase in grinding time. A good correlation was obtained between the heat of solution and the heat of crystallization determined from the peak area in DSC. Although no significant difference was observed in X-ray diffraction patterns of amorphous UDCA prepared by the two methods, significant differences were recognized in DSC, IR and 13C-NMR, and the heat of solution indicated different values among the two samples. The stability of amorphous UDCA samples stored under 74.5% relative humidity at 40 degrees C was found to depend upon the preparation methods. CONCLUSIONS: Different states of amorphous UDCA were obtained depending on the preparation method. The application of thermal methods to evaluate the amorphous state was demonstrated. The mechanism of dissolution of UDCA was discussed from the results of the heat of solution examination.     

Strength and plastic properties of amorphous cobalt alloy wires produced by various melt quenching methods

The strength and plastic properties of amorphous wires produced by melt spinning, in-rotatingwater spinning (INROWASP), and the Taylor-Ulitovskii method are studied. The wire produced by the Taylor-Ulitovskii method is found to have the highest level of strength and plasticity. The fracture and lateral surfaces of the amorphous wires are subjected to fractographic analysis. The high plasticity of this wire is shown to be caused by sequential formation of various families of shear bands and their interaction. The structure of the surface layer in an amorphous wire is assumed to be controlled by thermomechanical treatment to form a one-dimensional nanoamorphous composite material.     

Investigation into the influence of microstructural parameters of fuel pellets on their stability under the effect of thermal shocks

The parameters of tests and the main results of investigations into the behavior of VVER- and RBMK-type domestic fuel pellets under the effect of thermal shocks are investigated. Fine-grain pellets with a high level of closed porosity are shown to be more resistant to failure, which can appear in the pellets during startup and while maneuvering over the reactor power, as well as if there is cladding failure of the fuel cell. The pellet strength decreases as the grain size increases to ≥25 μm. The residual failure resistance of pellets simultaneously decreases, which leads to a loss in their integrity.     

Trapping of gas mixtures by amorphous water ice

Our studies on gas trapping in amorphous water ice at 24-100 K were extended, by using mixtures of CH4, CO, N2, and Ar, rather than single gases. In 1:1 gas:(water vapor) mixtures, the competition among these gases on the available sites in the ice showed that the trapping capacity for the various gases is determined not only by the structure and dynamics of the ice, but is also influenced by the gas itself. Whereas at 24-35 K all four gases are trapped in the ice indiscriminantly, at 50-75 K there is a clear enhancement, in the order of CH4 > CO > N2 > or approximately Ar. This order is influenced by the gas-water interaction energy, the size of the trapped gas atom or molecule, the type of clathrate-hydrate formed (I or II) and, possibly, other factors. It seems that the gas can be trapped in the amorphous ice in several different locations, each being affected in a different way by the deposition temperature and gas composition. Once a gas atom or molecule is trapped in a specific location, it is predestined to emerge in one of eight different temperature ranges, which are associated with changes in the ice. The experimentally observed enhancements, together with the findings on the gas composition of comet Halley, might enable an estimation of the gas composition in the region of comet formation.     

机械合金化制备Fe-Co系非晶合金

在高纯氩气保护下采用高能球磨法对原子组成为Fe44Co44Zr3.5Nb3.5B4Cu1的混合粉末进行机械合金化(MA)实验,成功地制取了非晶合金粉末.利用X射线衍射(XRD)、扫描电镜(SEM)、差热分析(DTA)对其进行测试,结果表明:Fe-Co系的混合粉末在MA过程中,通过原子之间的相互固溶、扩散可形成非晶态.此非晶合金的形成是晶粒细化、球磨过程中的缺陷、应力和致密堆垛结构等多种因素综合作用的结果,这与机械合金化的合成机理之一的扩散型机制相吻合.用非晶化的热力学条件判据和动力学条件判据对此合金进行计算,其结果也表明此合金已非晶化.