Microstructure Of Ag Research Articles

Fabrication, microstructure and critical current density of screen-printed Ag-(Bi, Pb) 2Sr 2Ca 2Cu 3O x superconducting tapes

The influence of the sintering conditions on the microstructure and critical current density J c has been studied on screen-printed Ag-(Bi, Pb) 2Sr 2Ca 2Cu 3O x tapes with a ceramics mono-layer core. Three kinds of fabrication processes, which consist of a combination of cold working (rolling and/or pressing) and sintering, are applied. Four times repetition of pressing and sintering after the pre-sintering produces the highest c-axis alignment and achieves J c = 1.5 × 10 4 A/cm 2 (77 K, 0 T). The J c versus θ data with an angle θ between B and the c-axis elucidate the relation between the anisotropy ratio γ=J c( B⊥ c)/J c( B| c and the half-height angular width Δθ of a peak for B ⊥ c . This is related to both grain alignment and the J c value. An increase in J c, which comes from an improvement for grain alignment, enhances γ and narrows Δθ. The J c versus θ data are fitted to the expression J c ( B, θ)= J c ( B, 90°)/[( γ−1)| cos θ| n +1] by regarding both γ and n as adjustable parameters. Fabrication of screen-printed tapes with multilayers (1≤ N≤5) is presented, where the critical current increases from 8.0 A to 30.2 A at 77 K and 0 T as N increases.

Two-dimensional microstructures of submonolayer Ag on Pt(111) induced by elastic strain.

The growth of Ag on Pt(111) has been investigated at submonolayer coverages betwen 80 and 1000 K. Below about 550 K large-scale metastable uniformly strained 2D Ag islands grow pseudomorphically. Heating of the submonolayer film or direct deposition of Ag above this temperature leads to the formation of small, ``strain free'' 2D equilibrium structures, possibly heptamers.

Film growth studies with intrinsic stress measurement: Polycrystalline and epitaxial Ag, Cu, and Au films on mica(001)

Growth and microstructure of thin Ag, Cu, and Au films ultrahigh vacuum deposited onto single-crystalline mica(001) have been studied in situ by intrinsic stress measurements (ISM) and low-energy electron diffraction. Depending on the respective substrate temperature, three different modes of Vollmer–Weber (VW) growth can be clearly distinguished by ISM: (i) VW-type nucleation and subsequent columnar grain growth at low temperatures (110 K) where grain-boundary relaxation is the prevailing stress contribution, (ii) polycrystalline VW mode in a medium temperature range that is characterized by VW-type nucleation and grain growth in the continuous film and dominated by the capillarity stress, and (iii) epitaxial VW growth mode at temperatures above 470 K for Ag and 600 K for Cu and Au; here a novel stress mechanism due to the formation of ‘‘single-crystalline grain boundaries’’ appears during the network stage.

The microstructure and mechanical properties of Bi(Pb)-Sr-Ca-Cu-Ag metallic precursor ribbons produced by the melt-spinning process

Metallic precursor ribbons of Bi-Pb-Sr-Ca-Cu with nominal compositions of 1.4-0.6-2-3-4, respectively, were made by vacuum induction melting followed by melt-spinning. Silver at the level of 12–81 vol% was added to produce precursor-Ag alloy ribbons. These ribbons were subjected to a controlled atmosphere oxidation and annealing to produce superconducting oxide/Ag microcomposites. All of the alloys with up to 73 vol% Ag can be processed into superconducting ribbons with zero resistance atT=104–110 K and a critical current density of 200–600 A cm−2 at 77 K in zero field. The relationship of the Ag content, melt-spinning processes, microstructure and mechanical properties of the metallic precursor ribbons were studied by microhardness tests, bending tests, scanning electron microscopy and electron probe microanalysis. The maximum bending strain of the metallic precursor ribbons was found to increase from 0.3–1.7% as the silver content increased from 12–81 vol%, while the ribbon hardness was found first to increase with silver content increasing from 12–62 vol%, then to decrease with further increases in silver content. The mechanical properties were also strongly affected by the melt-spinning processes,i.e. by the ejection pressure applied to the melt and wheel surface speed. The best bending strain for the metallic precursors with 52 vol% Ag achieved so far is ∼0.85%, which was obtained by using an ejection pressure of 69 kPa and a wheel speed of 9.5 m s−1. The mechanical properties of the precursor ribbons is critically important for producing superconducting coils and long wires, which were made by first winding the metallic ribbons on MgO spools, followed by suitable oxidation and annealing.

Defect fine Structures as observed by in situ experiments

An in-situ experiment in an electron microscope is now a well established and useful technique in materials science. In this review recent contributions of in-situ experiments, especially of straining and heating experiments, to materials science will be high-lighted.The earlier works have been reviewed by Saka and Imura.It is believed that an external stress gives rise to an anistropy in the rate at which point defects are absorbed by edge dislocations; this mechanism is considered to explain the irradiation creep. A combined in situ tensile/irradiation experiment in a HVEM has been carried out to study effects of applied stress on the growth of dislocation loops. Fig. 1 shows typical microstructures of Ag irradiated at 403K for 10 min with 1MV electrons in the absence (a), and in the presence of an external stress of 5.5 kg/mm2 (b). Frank loops of interstial type, formed by electron irradiation, grew more rapidly in the direction of the external tensile stress than in the others. These results show that an external tensile stress has a profound effect on climb rates of Frank loops of interstitial type. However, detailed analysis of the results indicates that there is a considerable discrepancy between experiment and theory.

Corrosion of chemically and vacuum deposited Ag films on glass by wet HCl vapor

The corrosion of chemically and vacuum deposited Ag films on an aluminoborosilicate and a commercial soda lime glass by wet HCl vapor was studied. A strong correlation was found between the chemical durability of Ag films and microstructure. A higher concentration of defects in Ag films accelerated corrosion. Chemically deposited Ag films were more corrosion resistant than vacuum deposited films due to their lower microvoid density. Ag films on the aluminoborosilicate glass were corroded less rapidly than those on the soda lime glass.

Ordering and phase separation in the ternary Ag-Cu-Zn β-phase alloys

The microstructure of the ternary Ag x Cu 55− x Zn 45 and Ag x Cu 53− x Zn 47 β-phase alloys was studied by means of electron microscopy. The range of temperature and composition where the mottled and modulated structures appeared was investigated, and the composition dependence of the spinodal decomposition temperature T s was also estimated. The composition dependence of T s had a maximum at about Ag 22 at.%. The critical temperature of the CsCl(B2)-type superstructure T c decreased with increase in Ag content, but was constant in a range of composition where the phase separation was observed. The precipitation of α-phase (f.c.c.) was observed even in the quenched specimens, that suggests the phase separation of β-phase at a high temperature. The composition dependence of T c and T s , was calculated theoretically. The occurrence of the ordering and the spinodal decomposition in the ternary Ag-Cu-Zn β-phase alloys is discussed briefly in terms of the difference of ordering energy that is negative in Ag-Zn and Cu-Zn pairs and positive in Ag-Cu pair.

An x-ray diffraction study on the microstructure of Ag–Cd–In (α-phase) alloys

X-ray diffractometric profiles of α-phase Ag–5Cd–5In, Ag–10Cd–5In, Ag–20Cd–5In, Ag–25Cd–5In alloys were recorded using a proportional counter for annealed and cold-worked states of the samples. Stacking fault parameters were obtained from the peak shift and peak asymmetry of these profiles. Fourier methods were also applied to the line profiles to evaluate compound fault probability, effective particle size, and rms microstrains for these ternary alloys. It was found that there exists a linear relationship between α(=α′−α″) versus combined solute concentration (Cd+In). The effective particle size De and the rms microstrain 〈ε2〉1/2 along [111] and [100] directions were found to be anisotropic and the anisotropy in the particle size was found to increase with solute concentration. The dislocation density ( ρ) and the ratio of stacking fault energy (γ) to shear modulus ( μ) of these alloys were evaluated.