Solution of Mixed Contact Problems in the Theory of Nonstationary Heat Conduction by the Method of Summation‐Integral Equations

The laws governing the development of spatial nonstationary temperature fields in a bounded cylinder and a halfspace where one of the end surfaces of the cylinder touches the surface of the halfspace in a circular region are determined. A solution of a mixed axisymmetric nonstationary problem of heat conduction is obtained in the region of Laplace transforms. In solution of this problem, there appear summationintegral equations with the parameter of the integral Laplace transform (Lparameter) and the parameter of the finite integral Hankel transform (Hparameter).     

Influence of Metal Oxides on the Arc Erosion Behaviour of Silver Metal Oxides Electrical Contact Materials

In the present work investigations have been made to see the role of metal oxides on the performance of the silver metal oxides electrical contact materials. Silver metal oxide materials of three different compositions Ag-10CdO, Ag-7.6SnO2-2.3ln2O3 and Ag-10ZnO were prepared by internal oxidation process under identical processing conditions. These materials were tested for electrical conductivity, hardness, and erosion loss. Performing an accelerated test on the actual contactor assessed the electrical performance, involving erosion loss and temperature rise of the processed materials. The arc-eroded surface was characterized under scanning electron microscope. The study of the eroded surfaces of contacts indicates that the thermal stability of metal oxides depends on nature of silver-metal oxide interface and their mode of erosion. An attempt is made to correlate the surface features of the eroded contacts with the thermal stability of metal oxides.     

Investigation of Mass Transfer in the Complex System Te—Tl by the Contact‐Melting Method

An investigation of the kinetics of contact melting of the complex system Te—Tl under unsteady diffusion conditions is made. The growth of the contact interlayer obeys a parabolic law. The interdiffusion coefficient is calculated in the temperature range 260–300°C. It has been found that virtually does not change within the temperature range 260–280°C. The effect of decrease in the temperature of contact melting relative to the equilibrium eutectic is established. A relationship between the superheating of a melt of the stable eutectic and the magnitude of its supercooling is found.     

The effect of Ag additions on the microstructure of aluminium–lithium alloys

Minor quantities of Ag have been added to Al–Li–Cu–Mg–Zr alloys. Their microstructure has been studied by means of optical metallography, transmission electron microscopy and X-ray diffraction. In the high Li, low Cu:Mg ratio alloys the main phases found were , , S and T1, while fewer T2 and Al7Cu2Fe precipitates were also observed. The addition of up to 0.5 wt% Ag diminishes the and T1 precipitates size. This is attributed to a small increase of Li solubility in the matrix. In the low Li, high Cu:Mg ratio alloy the addition of 0.2 wt% Ag resulted in the precipitation of phase simultaneously with , , S and T1 phases. Due to the low Li concentration an unusual growth of the / precipitates at the expense of the precipitates was also observed. © 1998 Kluwer Academic Publishers     

The effect of Ag additions on the microstructure of aluminium–lithium alloys

Minor quantities of Ag have been added to Al–Li–Cu–Mg–Zr alloys. Their microstructure has been studied by means of optical metallography, transmission electron microscopy and X-ray diffraction. In the high Li, low Cu : Mg ratio alloys the main phases found were , , S and T₁, while fewer T₂ and Al₇Cu₂Fe precipitates were also observed. The addition of up to 0.5 wt% Ag diminishes the and T₁ precipitates size. This is attributed to a small increase of Li solubility in the matrix. In the low Li, high Cu : Mg ratio alloy the addition of 0.2 wt % Ag resulted in the precipitation of phase simultaneously with , , S and T₁ phases. Due to the low Li concentration an unusual growth of the / precipitates at the expense of the precipitates was also observed.     

The Morphology of Rolling Contact Fatigue Fracture of Hardened Steels

Rolling Contact Fatigue(RCF) is a cumulativedamage phenomenon when metals are subjectedto repeated contact stresses. The fomationof pitting on the contact surface is the resultof the rolling contact fatigue. The morphologiesof rolling contact fatigue fracture of the har-dened steels (86CrHoV7, 42CrMo) show that strongresemblance in fractuye mechanisms exists betweenrolling contact fatigue and uni-axial fatigue.Since fatigue striations are hardly observedin hardened steels under uni-axial fatigue,it is interesting to note that the state ofstress in rolling contact fatigue is more favor-able to ductile fractures than in uni-axialfatigue.     

Diffusion Processes at the MnSi1.75 /Cr Contact

Diffusion processes between chromium and the higher manganese silicide MnSi_1.75 in MnSi_1.75/Cr and MnSi_1.75/Cr/Ni contact regions are studied by microstructural analysis and x-ray microanalysis. The results demonstrate that, at elevated temperatures, the composition and sequence of layers in the diffusion zone between MnSi_1.75 and Cr are consistent with the phase equilibria in the Cr–Mn–Si system. In MnSi_1.75/Cr/Ni samples, a larger portion of the diffusion zone between MnSi_1.75 and Cr consists of several Mn–Ni–Si phases and only one Cr–Mn–Si phase. The intermetallic phases forming in the diffusion zones exhibit metallic conduction and high thermal conductivity, which makes it possible to reduce energy losses in the hot junctions of thermoelements at the interface between an MnSi_1.75-based thermoelectric material and metal. It is shown that the use of chromium as a diffusion-impervious layer in MnSi_1.75/Cr/Ni contacts not only slows down Ni diffusion in MnSi_1.75 but also improves the mechanical properties of the contact.     

Role of the reaction product in the solidification of Ag–Cu–Ti filler for brazing diamond

In order to reveal the mechanism for brazing diamond using Ag–Cu–Ti filler metal, thermoanalysis of elemental metals (silver and copper) either with added diamond micropowder or with added titanium carbide micropowder as nucleant were investigated to detect undercoolings. No undercooling for the solidification of silver with added titanium carbide powder was detected by the thermoanalytical curve, and also no undercooling for copper with added diamond powder was detected. These phenomena suggest that titanium carbide powder acts in the solidification of silver effectively as a nucleant and that diamond powder also acts in the solidification of copper as a nucleant. Fine-grained silver was observed in the micrograph of the silver added with titanium carbide powder. The results of the calculations on the planar disregistry, , and the dispersion energy, Edisp revealed that the Ag (100)–TiC(100) interface and Cu(100)–diamond (100) interface are more stable than the other combinations. The results of undercoolings of various specimens correlated with both planar disregistry and dispersion energy. According to these results, the titanium carbide reaction product is considered to play an important role in the solidification of silver. The brazing strength is considered to arise from the solidification of the brazing filler metal from the titanium carbide reaction product. © 1998 Chapman & Hall     

Theoretical study of the optical absorption behavior of Au/Ag core–shell nanoparticles

The dependence of linear optical response properties of bimetallic core–shell spherical nanoparticles is investigated as a function of size and relative composition. Two kinds of schematic models have been tested for describing the dielectric behavior of bimetallic particles and the related linear electromagnetic response: (i) Drude model, in conjunction with bulk dielectric data relative to the pure metals, in the assumption of a simple combination law; (ii) DFT-based approach to the dynamic polarizability of a binary particle, with the nature of the metals involved taken into account through their Wigner–Seitz radius.     

Effects of temperature and dispersants on the phases and morphology of Ag–Cu nanoparticles

Ultrafine Ag–Cu nanoparticles (NPs) have been synthesized by a rapid one-step reduction within only 10 min. Effects of temperature and dispersants on the phases and morphology of Ag–Cu NPs were investigated. Results showed that citric acid exhibited an advantageous nature to avoid the formation of Cu₂O and form uniform morphology over PVP. The average particle size of the Ag–Cu NPs synthesized simply in ice-cubes bath could be controlled in 8.6 nm about a quarter of that synthesized at room temperature. The synthesized Ag–Cu NPs presented alloy states near the eutectic composition of 72:28. Due to the lower Ostwald ripening rate and citric acid protection, smaller Ag–Cu NPs were achieved in ice-cube bath. Results also showed that the ultrafine Ag–Cu NPs could be expected to sinter at about 330 °C which was much lower than the eutectic temperature (779 °C) of bulk Ag–Cu alloy. The ultrafine Ag–Cu NPs could be applied as potential die attach materials for SiC power devices.     

Check of the paradoxical results of experiments on resonance self-absorption of γ-quanta of109Ag in silver crystals

The temperature dependence of the intensity of -quanta of¹⁰⁹Ag with an energy of 88 keV, emitted in the horizontal and vertical directions from a single crystal plate of silver containing¹⁰⁹Cd, the radioactive decay of which produces excited nuclei of¹⁰⁹Ag, is investigated. The gamma radiation of this specimen and a control -source of⁵⁷Co were recorded by two Ge(Li)-detectors. When the specimen is cooled from 77 K to 12 K there is a relative drop in the intensity of -quanta of¹⁰⁹Ag emitted in the horizontal direction by 0.00064 ± 0.00044. For the vertical direction the analogous quantity turned out to be of opposite sign and equal to –0.00047 ± 0.00051. These preliminary data would appear to favor existing suggestions of a slight broadening of the -resonance of the¹⁰⁹Ag nuclei in silver single crystals. However, in further experiments, in which the accuracy is increased considerably, it will have to be established whether the difference in these quantities is due to some apparatus effects.Translated from Izmeritel'naya Tekhnika, No. 3, pp. 52–55, March, 1995.We wish to thank G. E. Buna for her considerable contribution in developing the technology for introducing the¹⁰⁹Cd into the single-crystal specimen of silver and for helping to construct the silver -source used in this research, and also S. I. Semenov for constructing the control -source of⁵⁷Co.     

Effect of crystal and domain orientation on the visible-light photochemical reduction of Ag on BiFeO₃

The reduction of silver from an aqueous solution on BiFeO? surfaces, activated by visible light, was investigated as a function of crystal and ferroelectric domain orientation. When excited by light with energy between 2.53 and 2.70 eV, BiFeO? photochemically reduces silver cations from solution in patterns corresponding to the underlying ferroelectric domain structure. Silver is preferentially reduced on domains with a positive polarization directed toward the surface. The amount of reduced silver depends on whether the component of the domain polarization normal to the surface is positive or negative, but is relatively insensitive to the crystal orientation. It is concluded that the ferroelectric polarization decreases electron drift to the surface in domains with a negative polarization, causing spatially selective photochemical behavior, and that the direction of the polarization is more important than the amplitude.     

Formation of Silver-Containing Polymeric Nanocomposites by the Reduction of Ag+ Ions in Polyelectrolyte–Metal Complexes Under the Action of Electric Fields

Materials Science - By the methods of wide-angle X-ray diffraction and small-angle X-ray scattering, we study the specific features of the structural organization of pectin–Ag0–P4VP...     

INRIM–NMC Comparison of Pt/Pd Calibration Above the Ag Point

A comparison of a Pt/Pd calibration above the Ag point between the INRIM and NMC was arranged with the aims of evaluating measurement systems and exploiting the potential of the Pt/Pd thermocouples. Two commercial Pt/Pd thermocouples were used as transfer thermometers. A calibration method using a blackbody cavity as a transfer source and a radiation thermometer as a reference thermometer was adopted in both institutes. The T ₉₀ carried by the radiation thermometers is established by an extrapolation technique for INRIM and by scale realization according to ITS-90 definition for NMC and, therefore, this exercise is also a useful comparison of different approaches to disseminate T ₉₀ above the Ag point. The comparison results are presented and analyzed.     

500°C Section of the Y–Ag–Sb Phase Diagram

The 500°C phase relations in the Y–Ag–Sb system were studied by x-ray diffraction analysis. No dissolution of the third component in binary compounds was detected. The existence of the ternary compound YAgSb₂ was confirmed, and its structure was refined by the Rietveld method (sp. gr. P4/nmm, structure type HfCuSi₂, a= 0.42711(2) nm, c = 1.04968(9) nm, R _i = 0.097, R _p = 0.150).     

A New Model of Interfacial Physical Contact in Diffusion Bonding

Through eliminating voids not affecting the primary bonding process, and incorporating interlayer and flexible base material, the interface geometry character and brief mathematics process were put forth. Through analyzing contact process of diffusion bonding, contact area model was settled. It can interpret the phenomenon of different interface areas taking on different strengths. In the course of physical contact, shear stresses serve an important function for the plastic deformation and the cohesion of interface voids.     

Influence of sulphur on the microstructure and properties of Ag–Cu–Zn brazing filler metal

Abstract

The effect of sulphur on the microstructure and properties of Ag45–Cu30–Zn25 brazing filler metal was investigated. Under the given experimental conditions, the sulphuration products mainly consisted of CuS, ZnS, Ag₂S, Cu₂S and Ag₃CuS₂. These sulphides not only distributed on the surface but also diffused into the interior of the filler metal and cut apart the matrix thereby significantly damaging the tensile strength of the filler metal from 658 to 283 MPa. The corresponding fracture characterisation turned from ductile fracture to brittle fracture. The sulphides existed as solid particles, which hinder the spreading of the liquid filler metal and the spreading area dramatically decreased from 317?09 to 18?55 mm², which indicates that the filler metal rarely wets the base metal.