Silver Specimen Research Articles

A Micromechanical Analysis to the Viscoplastic Behavior of Sintered Silver Joints under Shear Loading.

Ag paste has been recognized as a promising substitute for Sn/Pb solder in SiC or GaN power electronic devices, owing to its ability to withstand high temperatures and facilitate low-temperature packing. The reliability of these high-power circuits is greatly influenced by the mechanical properties of sintered Ag paste. However, there exist substantial voids inside the sintered silver layer after sintering, and the conventional macroscopic constitutive models have certain limitation to describe the shear stress-strain relationship of sintered silver materials. To analyze the void evolution and microstructure of sintered silver, Ag composite pastes composed of micron flake silver and nano-silver particles were prepared. The mechanical behaviors were studied at different temperatures (0-125 °C) and strain rates (1 × 10-4-1 × 10-2) for Ag composite pastes. The crystal plastic finite element method (CPFEM) was developed to describe the microstructure evolution and shear behaviors of sintered silver at varied strain rates and ambient temperatures. The model parameters were obtained by fitting experimental shear test data to a representative volume element (RVE) model built on representative volume elements, also known as Voronoi tessellations. The numerical predictions were compared with the experimental data, which showed that the introduced crystal plasticity constitutive model can describe the shear constitutive behavior of a sintered silver specimen with reasonable accuracy.

In situ QCM and TM-AFM investigations of the early stages of degradation of silver and copper surfaces

The early stages of atmospheric corrosion of pure copper and pure silver specimens were investigated performing in situ tapping mode atomic force microscopy (TM-AFM), in situ quartz crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS). The information obtained by TM-AFM is the change of the topography of the sample surfaces with emphasis on the shape and lateral distribution of the corrosion products grown within the first hours of weathering. The simultaneously performed in situ QCM measurements are indicating the mass changes due to possibly occurring corrosive processes on the surface during weathering and are therefore a valuable tool for the determination of corrosion rates. Investigations were carried out in synthetic air at different levels of relative humidity (RH) with and without addition of 250ppb SO2 as acidifying agent. On a polished copper surface the growth of corrosion products could be observed by TM-AFM analysis at 60% RH without any addition of acidifying gases [M. Wadsak, M. Schreiner, T. Aastrup, C. Leygraf, Surf. Sci. 454–456 (2000) 246–250]. On a weathered copper surface the addition of SO2 to the moist air stream leads to the formation of additional features as already described in the literature [M. Wadsak, M. Schreiner, T. Aastrup, C. Leygraf, Surf. Sci. 454–456 (2000) 246–250; Ch. Kleber, J. Weissenrieder, M. Schreiner, C. Leygraf, Appl. Surf. Sci. 193 (2002) 245–253]. Exposing a silver specimen to humidity leads to the degradation of the surface structure as well as to a formation of corrosion products, which could be detected by in situ QCM measurements. After addition of 250ppb SO2 to the moist gas stream an increase of the formed feature's volume on the silver surface could be observed by TM-AFM measurements. The results obtained additionally from the in situ QCM measurements confirm the influence of SO2 due to a further increase of the mass of the formed corrosion layer (and therefore an increase of the calculated corrosion rates) compared to the data obtained from the experiment carried out in humidity only.

The formation of self-assembling membrane of hexadecane-thiol on silver to prevent the tarnishing

Artefacts in silver suffer from tarnishing when exposed to atmospheres polluted by sulphide. We have found the optimum conditions to form an efficient, invisible and protective film against the tarnishing appearance on silver in 0.5 M NaCl solution containing 10 mM Na 2S. This solution corresponds to a highly aggressive medium not only by the coupling of two aggressive agents, but also by a high concentration of S 2− (320 ppm). The silver surface was first degreased carefully by successive dippings in three organic solvents, ethanol, acetone and hexane, followed by a slight surface activation in sulphuric acid solution. Then, a silver specimen was immersed in an isopropanol solution with 0.15 M C 16H 33SH during 1 h at 30 °C. The kinetics of tarnishing was tracked by reflectance, quartz-micro balance measurements, and electrochemical impedance spectroscopy. The protection of hexadecane-thiol reaches 90% in terms of reflectance, after 1 h of corrosion test, that is, no alteration by visual inspection. It was deduced that the thiol film has a double structure, an inner self-assembling membrane of one or two monolayers and an outer-layer with some tenths micrometers. This surface film limits markedly the diffusion of dissolved oxygen to the electrode surface, thus slows down the rate of silver sulphide (Ag 2S) formation.

Thermal Stresses in Porous Materials under Thermal Shock by Cooling Medium-Infiltration Effect on Thermal Stress Distributions-

During thermal shock tests of porous materials by cooling media, the cooling media will infiltrate into the materials. Such as infiltration produces large effects on heat-transfer coefficients on the specimen surface and temperature/stress distributions developed with in the specimen. In this paper, we performed thermal shock tests for porous ceramics using compressed air cooling and water flow cooling to estimate the infiltration effect on temperature/stress distributions. The heat-transfer coefficients were estimated with a thermo-couple implanted in a silver specimen. The temperature distributions in the porous specimens under thermal shock were measured using several thermo-couples implanted in the specimens, and the temperature distributions were simulated using a transient heat-transfer equation, taking into account of the infiltration of the cooling media into the specimen. Thermal stress distributions in the specimens were calculated from the estimated temperature distributions. The results revealed that the temperature distribution in a porous specimen changes drastically compared with a dense specimen, and the maximum thermal stress on the cooled surface of the porous specimen was smaller than that of a dense specimen. These phenomena express the reason why porous materials have high thermal shock resistance despite having small fracture strength.

Immersion test of the Ag−Pd−Cu alloy system

Silver-palladium alloys are widely used as substitutes for gold alloys. Pure silver, three Ag−Cu eutectics, three Ag−Pd solid solutions and nine Ag−Pd−Cu ternary alloys were prepared. The specimens were immersed in three kinds of solutions, Ringer’s, 0.1% sodium sulfide, and 1% lactic acid solutions. The change of the reflectance and the color was examined using CIE, Yxy notation. The reflectance of polished specimens was maximum in the pure silver specimen. It decreased with the decrease of silver content, or with the increase of palladium content. In Ringer’s solution, only Ag−Pd eutectic alloys decreased the reflectance. In sodium sulfide sulution, all of the specimens decreased the reflectance, but pure Ag and Ag−Pd entectics showed the largest decrease. In the lactic acid solution, no reflectance and color change was observed. However, a weight loss was observed in pure silver, Ag−Cu eutectics and one high-copper ternary alloy. Even if the specimen changed color visually to dark yellowish, the measured chroma is still small and remained achromatic.

Comparative study of cooling curves with JIS silver specimens and alloy 600 specimens in relation to additive effectiveness

Quenching- oil cooling curves obtained using a silver specimen (Japanese Industrial Standard K 2242) in-dicate three stages of cooling: vapor blanket, boiling, and convection. The temperatures at which the va-por blanket stage transfers to the boiling stage and the boiling stage transfers to the convection stage are referred to as the characteristic temperature (CT) and the convection- stage starting temperature (CSST), respectively. As the amounts of CT- improving additives are increased in increments of 1,2,3,6, 8, 10, and 12%, the CTs become higher, as clearly shown in the cooling curves obtained using a silver specimen. Likewise, as the amounts of CSST- improving additives are increased from 1 to 2 to 3%, the CSSTs become lower. These tendencies are similarly observed when using an Alloy 600 specimen, and both additives effectively improve cooling performance. However, in the case of 6,8,10, and 12% CT- im-proving additions, the differences among the additive concentrations are more pronounced in cooling curves obtained using the silver specimen than in those obtained using the Alloy 600 specimen. This can be attributed to the greater temperature sensitivity of the silver specimen thermocouple. In field quench-ing operations, such phenomena as insufficient hardness, inverse quench hardening, and unstable distor-tion can be remedied by additive treating. However, one must know what type of additive and how much to use. To this end, cooling curve measurement using silver specimens is useful.

Transient NMRON of brute force oriented110mAgAg

A novel technique involving electrodeposition has been used to prepare an elemental silver specimen wherein radioactive110mAg probe nuclei are confined to a surface layer of approximately 0.1 μm depth. This specimen was then brute force oriented in a field of 8T and the continuous wave (CW) nuclear magnetic resonance on oriented nuclei (NMRON) spectrum showed an integrated destruction of some 58%. Moreover the transient NMRON techniques of single and modulated adiabatic passage were successfully applied, resulting in a determination of the electric quadrupole interaction strength at the110mAg site in polycrystalline silver of P/h=+0.74(5)kHz with a FWHM of ΔP/h=0.75(8)kHz. The resulting mode electric field gradient is Vzz=+1.87(23)×1018Vm−1. Analysis of the single passage data provides an estimate for the nuclear spin lattice relaxation constant in silver at 8T of Ck=1.6(3)s.K.

A surface analysis of ion transport in the surface layer of fast ion conductors

Abstract EPMA, AES and XPS experiments have been performed on silver and copper fast ion conductors. In the EPMA and AES experiments, under the action of the electron beam the mobile cation in the fast ion conductors moved towards the beam bombardment point. On the other hand, the anions moved away. It was found that the apparent silver and copper contents increased with bombardment time, as deduced from the silver and copper X-ray counts on the Auger peak-to-peak intensity. There was an opposite effect for XPS. The patterns of crystallization for the silver specimen in EPMA are discussed. Morphological observation of the silver and copper distribution on ion conducting glasses after electron bombardment reveals the interrelation between silver and copper ion transport characteristics and the microstructures.

New instrument for measuring contact resistance developed for studying electrical contact phenomena

A new experimental apparatus for measuring the electrical contact resistance is described. This apparatus is essentially a conventional balance, modified for the examination of electrical contact resistance changes of silver and some other metal specimens due to increases and decreases in load and current. The results obtained show that plastic deformation takes place at the contact spots in response to an initial increase in load and elastic deformation occurs on a subsequent decrease in load. When a pair of Nichrome rods, which have a much higher resistivity than the silver specimen, are brought into contact with each other, the areas of the contact spots appear to be larger than those calculated. A fritting phenomenon, first studied in detail by Holm, occurred on the contact surfaces of the rods when they were subjected to heat and oxidation in the course of the experiment.

A method to judge the quench-hardening of steel from cooling curves of quenching oils

The features of cooling curves for oils using a silver specimen (JIS K-2242) were shown. The cooling curves of steel specimens for the same oils were also measured and compared with those of silver specimen. The CCT diagrams of steels were classified into four types and the temperature range in which rapid cooling is required for quench-hardening for each type of steel was determined and compared with the temperature range for the boiling stage in the quenching of steel, converted from the results obtained from a silver specimen. The V-value is defined as the ratio of the temperature range of the boiling stage to the temperature range which requires rapid cooling. The V-value is a better criterion for quench hardening in oil quenching for given steel than the H-value as a measure of quench severity.

Cyclotron wave propagation in silver

Azbel'-Kaner cyclotron resonance in metals is accompanied by electromagnetic waves propagating in a direction perpendicular to the magnetic field. Taking into account the anisotropy of the silver Fermi surface, the dispersion relation for these waves is calculated in the limit where the wavelength is much smaller than the orbit diameter of the electrons. Thus it is shown that a number of previously observed oscillations in the surface impedance of a semiinfinite silver specimen arise from points of zero-group velocity on the dispersion relation. Physically, the oscillations reflect a matching of the electron-orbit diameter with an integer number of wavelengths. They may, therefore, be looked upon as geometric resonances in the surface impedance, complementary to the temporal cyclotron resonances. The surface impedance is calculated under the assumption of specular surface scattering. Satisfactory agreement with experiments is obtained by using an independent-particle model for the electron gas and band parameters based on APW calculations. The influence of the Fermi-surface geometry is demonstrated by comparing with calculations for a cylindrical and a spherical Fermi surface. The electric field in the metal is calculated for selected magnetic fields, and the expected result of a transmission experiment is presented. Finally, the absence of Fermi liquid effects in the experiments is briefly discussed.

Untersuchungen zur elektronenangeregten Exoelektronenemission an Metallen

The exoelectron-emission from electron irradiated metal specimens was measured in a heatable Geiger-Muller-counter. For a silver specimen the term data (activation energy, frequency factor) of the traps were determined from the shape of the glow curve, using the methods applied on thermoluminescence glow curves. The comparison of the glow curve with theoretical emission curves of monoenergetic traps showed that the glow curve consisted of several emission curves, which had not been resolved in the measurement. For the activation energies of the traps responsible for the emission in the temperature range from 20 to 180 °C we got values of about 1 eV. The computed frequency factors are rather uncertain; they cover the range between 109 and 1014 sec−1.

Microwave measurement of permittivity and tan δ

A method of measuring the permittivity and loss tangent of dielectric specimens at 9375 Mc/s over a temperature range 20–700°C is described. Circular specimens 0.900in in diameter and λ/4 or 3λ/4 thick are measured in a 0.900in-diameter silver specimen chamber, using a slotted line, and in circular waveguide. The method is based on the short-circuited-line method and allows for the gaps produced by the differential expansion of the chamber and specimen and the variation in wavelength along the waveguide due to expansion.The effect of errors in the measurements is given. Typical measurements of permittivity and loss tangent of alumina and beryllium oxide specimens are given.

Direct Melting-Point Calibration of a High-Temperature X-Ray Camera

Detailed measurements in a high-temperature x-ray camera have shown that optical observations in polarized light of the melting of suitable specimens in silica capillaries provide a satisfactory temperature calibration with an internal consistency of ±1°C. The measurements covered the range from room temperature to 800°C. The thermal gradients within the specimen were also measured. These were reduced from 7 to 2°C (at 600°C) by a simple radiation shield. Calibration against the lattice spacings of a silver specimen (consistency ±2°C) was not suitable in the present case and would only be valid if conductivity and emissivity differences between standard and specimen were absent. The use of a movable thermocouple gave erroneous results.

XXI. The magnetic susceptibilities of copper, silver and gold and errors in the Gouy method

Abstract A direct determination has been made of the absolute magnetic mass susceptibility of copper, silver and gold. The values at 23°c are: Copper, −0·08599±0·00027 × 10−6; silver, −0·18128±0·00054 × 10−6; gold, −0·14216±0·00048 × 10−6 c.g.s. e.m.u. per gram. The probable errors of the relative values are 0·09%, 0·07% and 0·16% respectively. The correction for ferromagnetic impurities is discussed. From an experimentally determined magnetization curve of the ferrromagnetic impurities in a silver specimen, it is shown that, although the error inherent in the long specimen method is greatly reduced by using a short specimen, an error may remain even when the smallest field acting on any part of the specimen is 6000 gauss. The method of calibrating the field by means of a current-carrying loop and of making allowance for the variation of the field strength in the plane normal to the axis of the specimen are described in detail. A pole piece design which is particularly suitable for the short specimen meth...

焼入冷却剤の研究（第11報）銀試片による冷却曲線と鋼の焼入との関係

A correlation chart by which it is capable to derive quenching severity, H, from the cooling curves with silver specimen which are readily measurable, were made out by establishing the relationship between the cooling curves with silver specimen and the results of quenching of steels based upon the data presented in our 9th and 10th reports. Thus, it becomes possible to obtain the H value of any coolants readily and the application of many available charts presented by Grossmann and others may be strongly promoted, and furthermore it can be said that reasonable working procedure of quenching way be readily planned.

焼入冷却剤の研究（第13報）砿油の冷却能の再検討

The cooling curves were measured with silver specimen as to several typical mineral oils having widely different viscosities and flash points with one another in order to correlate the properties of mineral oils with the quenching severity, H, derived from the cooling curves here obtained, and the examinations of the results presented in the 7 th report were also done with the findings in this experiment. The H values of mineral oils increase with oil temperature up to a point at which maximum value of H is reached and subsequently decrease. The maximum values of H, the temperature at which the H value rises to the maximum and the variation of H value with oil temperature are correlated with the flash points of oils. Paraffinic mineral oils have smaller values of H as compared with naphthenic ones and the H value decreases so much so that the degree of refining is elevated. It is also referred to the improving reagent of cooling ability of mineral oils.

焼入冷却剤の研究（第8報）銀試片の寸法による冷却過程の変化

焼入冷却剤の研究（第8報）銀試片の寸法による冷却過程の変化