规则多孔铜热膨胀性能的研究

在氢气或氢气和氩气的混合高压气氛中,采用定向凝固技术制备了规则多孔铜材料。测试了不同气孔率的规则多孔铜在平行和垂直气孔方向上的热膨胀系数;研究了气孔、气孔方向和气孔率对其热膨胀系数的影响规律,并对其规律做了理论预测。结果表明,规则多孔铜的热膨胀系数随着温度升高先急剧增大到一定值后趋于平稳;温度在40~130℃,气孔中存在闭孔时,规则多孔铜的CTE值随气孔率的增大而缓慢增大,且比纯铜时略大;当气孔主要以通孔形式存在时,气孔率与孔径的比值越大,规则多孔铜的CTE值越低。温度>130℃时,规则多孔铜的热膨胀系数与纯铜的几乎相同,气孔的存在对铜的膨胀无明显影响。     

Fabrication of Lotus‐type Porous Metals and their Physical Properties

Lotus‐type porous metals whose long cylindrical pores are aligned in one direction were fabricated by unidirectional solidification in a pressurized gas atmosphere. The pores are formed as a result of precipitation of supersaturated gas when liquid metal is solidified. The lotus‐type porous metals with homogeneous size and porosity of the evolved pores produced by a mould casting technique are limited to the metals with high thermal conductivity. On the other hand, the pores with inhomogeneous pore size and porosity are evolved for metals and alloys with low thermal conductivity such as stainless steel. In order to obtain uniform pore size and porosity, a new “continuous zone melting technique” was developed to fabricate long rod‐ and plate‐shape porous metals and alloys even with low thermal conductivity. Mechanical properties of tensile and compressive strength of lotus‐type porous metals and alloys are described together with internal friction, elasticity, thermal conductivity and sound absorption characteristics. All the physical properties exhibit significant anisotropy. Lotus‐type porous iron fabricated using a pressurized nitrogen gas instead of hydrogen exhibits superior strength.     

Fabrication, properties and application of porous metals with directional pores

This paper reviews the recent development of fabrication methods, various properties of porous metals with directional pores and its applications. This porous metals are fabricated by unidirectional solidification in pressurized gas atmosphere such as hydrogen, nitrogen and oxygen. The pores are evolved from insoluble gas when the melt metal dissolving the gas is solidified. The nucleation and growth mechanism of the directional pores in metals are discussed in comparison with a model experiment of carbon dioxide pores in ice. Three fabrication techniques, mold casting, continuous zone melting and continuous casting techniques, are introduced. The latter two techniques can control the solidification velocity and the last one possesses a merit for mass production. The porosity and pore size are able to be controlled by solidification velocity and ambient gas pressure, while the pore direction can be controlled by solidification direction. Not only metals and alloys but also intermetallic compounds, semiconductors and ceramics can be produced by this method. Anisotropy in the mechanical and physical properties is resulted from anisotropic pore morphology. The experimental results on the anisotropy in the elastic property and electrical conductivity are consistent with those calculated with an effective-mean-field theory. The anisotropic behaviors of tensile, compressive and fatigue strength are explained in terms of the dependence of stress concentration on the pore orientation. This porous metals exhibit good sound absorption and vibration-damping properties. Several possible applications are in progress for heat sink, golf putter, biomaterials and so on.     

Anisotropic compressive properties of porous copper produced by unidirectional solidification

Porous copper whose long cylindrical pores are aligned in one direction has been fabricated by unidirectional solidification of the melt in a mixture gas of hydrogen and argon. The compressive yield strength of the porous copper with the cylindrical pores orientated parallel to the compression direction decreases linearly with increasing porosity. For the porous copper whose pore axes are perpendicular to the compressive direction, the compressive yield strength slightly decreases in the porosity range up to 30% and then decreases significantly with increasing porosity. The compressive stress–strain curves depend on the compressive direction with respect to the pore direction, which are due to the stress concentration around the pores and the buckling of the copper between the pores. From two different types of stress–strain curve, the energy absorption capacity of the porous copper with the pores parallel to the compressive direction is higher than that perpendicular to the compressive direction at a given porosity.     

Reactive sputtering characteristics of silicon in an ArN2 mixture

A silicon target was sputtered in a planar r.f. magnetron system into which nitrogen was admitted during glow discharge in argon. The reactive sputtering characteristics, such as the deposition rate and the nitrogen concentration in the film, are measured as a function of the flow rates of argon and nitrogen. At lower argon flow rates the reactive sputtering characteristics show an abrupt change at critical nitrogen flow rates as well as hysteresis with regard to the nitrogen flow rate. In contrast, at higher argon flow rates they show a smooth change and no hysteresis. A model was proposed which considers the relation between the nitrogen consumption rate in the film and the nitrogen exhaust rate from the chamber. The model successfully explains the change in reactive sputtering characteristics. Moreover, it is found that the nitrogen consumption rate dependence on the nitrogen partial pressure, which has a peak at a particular nitrogen partial pressure, plays an important role in the determination of the reactive sputtering characteristics.     

Evolution of Pore Size Distribution and Mean Pore Sizein Lotus-type Porous Magnesium Fabricated with Gasar Process

The effect of gas pressures on the mean pore size, the porosity and the pore size distribution of lotus-type porous magnesium fabricated with Gasar process were investigated. The theoretical analysis and the experimental results all indicate that there exists an optimal ratio of the partial pressures of hydrogen pH2 to argon pAr for producing lotus-type structures with narrower pore size distribution and smaller pore size. The effect of solidification mode on the pore size distribution and pore size was also discussed.     

工艺参数对磁控溅射TiN膜成分影响的研究

在不同的工艺参数条件下 ,采用磁控溅射技术制备了大量的TiN膜样品。通过对实验结果的仔细分析 ,得出了膜层颜色与氩气分压无关 ,而与溅射功率和氮气分压的比值有关的结论 ,并得到了微观结构分析的证实。对磁控溅射法制备TiN膜技术具有一定的参考价值     

Mass flow limitations in reactive sputtering

Reactive sputtering may be accomplished by mixing the inert gas argon with some reactive gas during sputtering. To form ZrN, sputtered zirconium atoms must react with nitrogen. At a specific deposition rate, a certain number F_N0 of nitrogen atoms must arrive at the substrate. This requirement is fulfilled at the partial pressure P_N = P_N0. The minimum partial pressure P_N0 to obtain a nitride is often detected by a sharp decrease in sputtering rate at a specific N₂ partial pressure. However, during reactive sputtering of for example ZrN we found that the value of P_N0 was strongly dependent on the total gas throughout in the vacuum system. An increase in total gas throughput causes a decrease in the value of P_N0.

The decrease in sputtering rate has indirectly been measured by optical emission spectroscopy from the sputtering plasma.     

Partition of nitrogen in solidifying iron-carbon-silicon alloys

The partition of nitrogen between austenite and liquid iron was examined from the measurement of solubilities of nitrogen in these phases. On primary austenite crystallization, nitrogen was rejected into liquid iron at high temperatures and the partition behaviour was reversed at low temperatures. Silicon lowered the critical temperature where the partition behaviour of nitrogen changed. The partition of nitrogen between cementite and austenite was investigated by analysis of nitrogen in iron-carbon-silicon alloys, which were quenched in ice-water from an equilibrium state at subeutectic temperatures, and in the cementite extracted from them. Nitrogen was enriched in cementite for Fe-C-0.5 wt% Si alloy, similar to the case of pure Fe-C alloy. However, silicon reduced the degree of enrichment of nitrogen in cementite. By the use of the partition coefficients, the variations of nitrogen concentrations in the coexisting phases were evaluated during the solidification of cast irons. In the irons with lower carbon concentrations, the supersaturation of nitrogen in liquid iron attained during solidification increased with increasing silicon content, and silicon had a detrimental effect to promote the formation of nitrogen gas blowholes in low-carbon cast irons.     

Microstructural and mechanical properties of biodegradable iron foam prepared by powder metallurgy

Research into biodegradable porous materials has been increasingly focused on iron-based materials because such materials possess suitable properties for orthopedic applications. In this study, we prepared porous iron with porosities of 32–82 vol.% by powder metallurgy using ammonium bicarbonate as a space-holder material. We studied the influence of initial powder size and compacting pressure on sample microstructure, contamination and mechanical characteristics. The experimental results were analyzed as well, using Gibson–Ashby model and this analysis showed a good agreement in theoretical and experimental data. Whereas increasing compression pressure decreased porosity, the use of finer iron powder led to an increase in porosity. Increasing the amount of space-holder material in the initial mixture increased the total porosity, improved compressibility and consequently decreased the number of pores originating from imperfect compaction. A higher compacting pressure and the use of finer powder enhanced both the flexural and compressive properties. Even the most porous samples prepared from the fine iron powder possessed mechanical properties comparable to human cancellous bone. Based on these results, we can claim that the use of fine initial iron powder is necessary to obtain highly porous iron, which appears to be suitable for orthopedic applications.     

直流溅射中氮气分量对氮化锆薄膜性质的影响

用直流溅射方法制备氮化锆薄膜,其晶体结构,氮原子组分以及电阻率都与溅射气氛中氮气分量有直接关系。用X射线衍射分析薄膜结构,随氮气分量由5％至30％增加,玻璃衬底上的氮化锗薄膜首先呈(111)和(200)两主要生长取向;然后(200)取向逐渐消失,只有(111)单个优化生长取向;最后,没有衍射峰出现,薄膜趋于无定型结构。     

Formation of Porous Structures in Metal–Hydrogen Systems

Crystallization of hydrogen-saturated melts under controlled conditions enables one to obtain a new class of porous materials (gasars). The technological parameters of the process such as the partial hydrogen pressure, the total gas pressure, the temperature of the melt, and the crystallization rate affect the porosity, size and form of pores, which enables one to control the structure of gasars. Using methods of quantitative metallography, we determine conditions of its formation. The most homogeneous nickel ingots of gasars are obtained with increase in the total gas pressure in the system during crystallization of the melt and the decrease in the partial hydrogen pressure. The gas gap between the chill and the ingot appearing in the process of directional crystallization of hydrogen-saturated melts limits heat exchange and leads to a disturbance of the cooperative growth of gas bubbles and crystals. However, the negative influence of this process considerably decreases with increase in the partial hydrogen pressure, which also favors the production of homogeneous ingots of gasars.     

装饰薄膜ZrN的中频反应磁控溅射沉积工艺研究

利用中频反应磁控溅射技术在1Cr18Ni9Ti不锈钢基底上沉积ZrN薄膜。通过控制N/Ar、溅射功率和基体偏压等参数,得到不同实验条件的ZrN膜层。通过对膜层颜色测量和AES分析,研究N分压强对ZrN膜层质量的影响。实验结果表明：工作气压0.3Pa,溅射功率5kW,基体偏压-150V、占空比50%等工艺参数一定的前提下,N分压强在不同的范围内,可以分别制备出视觉效果类似于18K、23K和纯金的氮化锆膜层。     

Investigation of two-photon-induced polarization spectroscopy of the a-X (1,0) transition in molecular nitrogen at elevated pressures

Two-photon-induced polarization spectroscopy of molecular nitrogen in the alpha 1IIg(nu' =) <-- X 1Sigma(g)+ (nu" =) system near 283 nm was performed, and its signal dependence investigated over the pressure range from 1.2 to 5 bars at 300 K. A significant increase of the signal intensity with pressure beyond the expected square law for a two-photon process was observed for pure nitrogen. Similar behavior was also found for a constant nitrogen partial pressure with increasing partial pressures of argon buffer gas. In both cases the spectral linewidth of the excited transitions increased dramatically with overall pressure. A possible explanation is given for the observed behavior in terms of contributions to the nonlinear susceptibility of the medium from the population of one-photon resonantly absorbing excited-state nitrogen and ground state N(2)(+) ions created in the multiphoton absorption process at the high laser intensities required.     

Equilibrium of partially dried porous media influenced by dissolved species and the development of new interfaces

The equilibrium state of partially dried porous media is modeled using continuum thermodynamics as a framework for identifying the equilibrium state. Entropy of the interfaces within the porous material are taken into account in the thermodynamic analysis of the system. Additionally, the effect on the equilibrium condition of increasing concentration of dissolved species in the fluid within the pores caused by moisture loss to the surroundings is examined. Both the presence of dissolved species in the fluid within the pores and the development of new interfaces during the drying process suppress internal vapor pressure, indicating that the equilibrium internal vapor pressure within the porous media will be lower than that of the boundary at equilibrium.     

Porous materials prepared by heating derivatives from halloysite

Halloysite clay was subjected to serious treatment by trimethylsilylation and hydrochloric acid. The resulting derivatives were heated below 1473 Kin nitrogen or air to prepare thermally stable porous materials including larger pores than those in zeolite. The trimethylsilylated halloysite resulted in a thermally stable porous material, in an amorphous state, including extremely uniform pores of 1.7 nm. Another derivative also resulted in a thermally cable porous material but consisted of very heterogeneous pores. The thermal degradation behaviour of both derivatives is discussed in detail.     

NMR study of the solidification and melting of3He in porous glasses

TheP-T phase diagrams of the liquid-solid phase transition of³He in three porous glasses with different pore sizes have been determined from spin-lattice relaxation measurements in the temperature range 0.5–4.2 K. The onset of solidification of³He in the pores occurs at excess pressure over the bulk phase transition. The excess pressure depends on the pore size. A model of the phase transition in small pores which takes into account the contribution of the surface energy to the free energy is described and compared with experimental results. TheT ₁ relaxation mechanism of³He in the pores is found to be due to the surface relaxation when³He is in the liquid phase and due to the relaxation of bulk solid³He when it is in the solid phase.     

退火气氛对SnO2薄膜结构与成分的影响

研究了低氧分压反应溅射法生长的SnO2薄膜于600℃ O2气氛和Ar气氛退火处理后的表面形貌、晶体结构以及表面成分,发现经氧化性气氛退火处理的SnO2为具有金红石结构的表面多孔薄膜.相比较而言,Ar气氛退火处理后的SnO2薄膜表面较为致密,相结构包含朱氧化完全的β-Sn.XPS分析进一步表明,氧化性气氛退火形成单一组分的SnO2,而惰性气氛退火后薄膜表面含有Sn、SnO和SnO2.另外,研究还发现薄膜表面吸附氧形态与退火气氛有关.     

Structure property relationships in porous sintered steels

The flat bending fatigue strength of a variety of carbon-free iron base sintered materials has been investigated varying density, sintering temperature and particularly the morphology of the base powder. All effects that lead to round pores improve the fatigue performance.The porosity of sintered iron and steel is characterised by a large majority of tiny spherical pores and a few big pores of high irregularity. It is this small fraction of large and irregular pores with their pronounced internal stress concentration which determines the fatigue strength of sintered porous materials, next to overall density and alloying effects.     

Supercooled liquid foaming of a Zr-Al-Cu-Ag bulk metallic glass containing pressurized helium pores

Foaming of a Zr-based metallic glass in the supercooled liquid is successfully performed by introducing pressurized pores and subsequent isochronal annealing. Melting of a Zr₄₈Cu₃₆Al₈Ag₈ powder under 12 MPa pressurized helium atmosphere followed by water quenching introduces spherical helium pores, whose average diameter and volume fraction are estimated respectively to be 30 μm and 7%, into a fully glassy bulk Zr₄₈Cu₃₆Al₈Ag₈ alloy. The isochronal annealing of the porous alloy below the crystallization temperature under atmospheric pressure of argon enables the expansion of pores by viscous flow deformation of the supercooled liquid, resulting in a high porosity structure up to 70% with a uniform cell size and cell distribution.