Electron Beam Microprobe Analysis Research Articles

THE MATERIALS OF HOYSALA TEMPLES AND SCULPTURES: A PETROGRAPHIC CHARACTERIZATION

Talcxhlorite schist is the material commonly used by the sculptors and builders of the Hoysala dynasty, which ruled i n the western part of India south of the Deccan from the eleventh to the mid‐fourteenth century. Forty‐one samples from seven Hoysala sites were examined by petrographic microscopy and electron beam microprobe analysis. Although it is difficult to distinguish between some of the rocks from the different sites. many contain minerals that can be valuable in distinguishing between different possible quarry sources.

Equilibrium solidification of Sn-Ag-Sb thermal fatigue-resistant solder alloys

A survey of the liquidus surface and invariant reactions involving liquid has been made for solidification in the ternary Sn-Ag-Sb system. Differential thermal analysis and electron-beam microprobe analysis were used to measure liquidus temperatures and determine the composition of solid phases resulting from solidification. A liquidus projection and the composition of the phases coexisting at the two observed invariant reactions were determined. Ternary alloys based on the Sn-Ag-Sb system have been used as thermal fatigue-resistant solders where high heat loads must be dissipated. An analysis of the properties encountered from such solders is presented, based on the phase constitution resulting from the solidification behavior reported here.

Vapour phase growth and properties of Pb1-xSnxTe single crystals

High quality Pb1-xSnxTe crystals of desired orientation having a diameter of 20 mm and weights up to 100 g were obtained using the vapour phase method. The crystals were grown in sealed quartz ampoules, on cylindrical BaF2 pedestals, without contact with the tube walls. Such contactless conditions cause low dislocation density and are favourable for obtaining less contaminated crystals. In this method, contrary to other vapour phase growth methods, even a relatively large excess of tellurium does not affect noticeably the quality of the crystals. The composition along and across the crystals was examined using electron beam microprobe analysis. The results of measurements of conductivity and Hall effect in as-grown and annealed samples are presented. Some data concerning preparation of the source material are also included.

Studies of the Ga1-xInxAs1-ySby quaternary alloy system I. liquid-phase epitaxial growth and assessment

The liquid phase epitaxial (LPE) growth of Ga1-xInxAs1-ySby alloys lattice-matched to InAs and GaSb substrates has been investigated in the temperature range 520 to 600° C. Theoretical phase diagram calculations have been used to obtain good predictions of the liquid phase compositions required to obtain lattice-matched growth as a function of growth temperature. The relative merits of InAs and GaSb as substrates are discussed. The layers were assessed by single and double-crystal X-ray diffraction, electron beam microprobe analysis and photoresponse of electrolyte Schottky barriers. Good agreement between alloy composition(x, y) measured by microprobe analysis and that deduced from combined lattice parameter and band-gap measurements. The problem of compositional grading in thicker layers due to depletion of arsenic in the growth solution is discussed. To overcome this problem it is necessary to reduce the growth rate of the layer by reducing the cooling rate to ∼1° C hr-1.

The influence of impurities on the quality of bismuth germanate (BGO) scintillator crystals

Abstract The distribution behaviour of prevalent impurities, including Pt, Fe, Si and Ca, in BGO scintillator crystals is described. The possibility of locally high impurity concentrations in the region of major growth defects has been examined by electron beam microprobe analysis, and has been found not to be significant. Conclusions are drawn about the purity requirements for pre-reacted BGO capable of efficient conversion from melt to single crystal and providing the required scintillation performance.

The low temperature impact properties of the meteorite hoba

Charpy V‐notch impact specimens prepared from the high nickel ataxite Hoba have been tested at 77° and 195°K. The specimen tested at 77°K was fully brittle, and the one tested at 195°K was fully ductile. It is concluded that the transition to complete brittleness occurs below about 140°K or 150°K. Thus, high nickel material such as this is ductile at the ambient temperature of an asteroid, which is about 150°K, and does not fragment in a brittle manner when meteoritic material is formed by the collision of asteroids. This confirms a hypothesis put forward by Remo and Johnson [1974] according to which this failure of high nickel material to fragment explains the large average size of high nickel meteorites. The microstructure of Hoba was studied using optical microscopy, scanning electron microscopy, and electron beam microprobe analysis. It was found, in agreement with the results of earlier workers, that Hoba has a fine plessitic structure with prolific small mineral inclusions. Some troilite inclusions were shown to have transverse bands of daubreelite within them.

The room-temperature dissociation of the compound Au 3Si

Three gold-18.6 at.% silicon specimens which were solidified by quenching from above the liquidus temperature have been re-examined after being stored at room temperature for about 8 years. It was found that the “metastable” compound Au 3Si formed on quenching had begun to dissociate by a surface nucleated, solid-state reaction. The reaction front had advanced about 0.2 mm from the surface, leaving a rim of dissociation products. These dissociation products were studied using optical and scanning electron microscopy, electron beam microprobe analysis and an X-ray micro-diffraction technique. It was concluded that the reaction produces elemental gold and silicon, as at higher reaction temperatures, but that the scale of dispersion is so extremely fine that the resulting microstructure cannot be resolved by scanning electron microscopy. Examination of a number of similarly quenched specimens containing 25 at.% silicon prepared about 2 years earlier revealed that the reaction had occurred to a limited extent in these also. Nucleation of the reaction was found to have occurred at primary silicon particles, cracks, cavities, and internal interfaces of Au 3Si with the eutectic mixture, as well as at free surfaces.

Croissance par épitaxie en phase liquide et diagramme de phase du système Ga 1−xAl xSb

The liquids and solidus lines in the Ga-rich region of the Ga-Al-Sb system have been established. The weight loss technique was used to determine the liquidus data at 500, 518 and 536°C. Solidus data were measured by means of electron beam microprobe analysis on epitaxial layers. A phase diagram which is in excellent agreement with these experimental data has been obtained. The calculations are based on a quasi-regular solution model for the three binary liquids and on an ideal solution for the ternary solid.

Investigations on laser welding

A welding method has been developed that makes use of fundamental mode laser pulses. These pulses show single-mode relaxation oscillations with a high peak power first spike causing breakdown of the material surface. The laser emission following the first spike can be adapted to the welding requirements and the material properties. Metallurgical problems of intermixing of dissimilar materials in the weld puddle have been investigated with an electron beam microprobe analysis. In the case of materials which normally show bad weldability uniform welds with maximum strength could be achieved by local addition of welding agents to the weld puddle. The lap weld of a stainless-steel spring with a nickel-iron baseplate has been performed with Nb as welding agent.

Reflectivity spectra of some first row transition metal intercalates of NbS2

Abstract The room temperature reflectivities from the basal planes of the first row transition metal intercalation compounds Mn0·26NbS2, Fe0·33NbS2, Co0·32NbS2, and Ni0·34NbS2 have been measured in the energy range 25 meV to 6 eV. The transition metal concentrations have been determined by electron beam microprobe analysis. The changes in the reflectivity spectra of NbS2 after intercalation have been interpreted in terms of a rigid band model and charge transfer from the ionized intercalate to the host NbS2 dz 2 conduction band. The reflectivities in the region of the Drude edge have been fitted by a theoretical model from which the optical parameters appropriate to this edge have been obtained

Information about the Growth Process from Aluminium Concentration Profiles in Ga1−xAlxAs Liquid Phase Epitaxial Layers

AbstractThe variation in the composition of Ga1−xAlxAs LPE layers with x < 0.37 as a function of layer thickness is examined by electron beam microprobe analysis. From the combination of these results with the experimentally established relation between layer thickness and cooling interval information is obtained about the onset of homogeneous nucleation in the LPE growth.

Laves phase precipitation in Fe-Ta alloys

Development of an iron-base alloy hardened by particles of an intermetallic compound rather than a carbide is a desirable goal because of the greater thermal stability of such a dispersion. As a first step in the development of iron-base alloys hardened with the Laves phase, structural studies of binary Fe-Ta alloys have been undertaken. The structures of two phase Fe-Ta alloys have been studied by means of optical and transmission electron microscopy, X-ray diffraction, electron beam microprobe analysis, and scanning electron microscopy. The hardness change as a function of time at 600°, 700°, and 800°C has been determined for binary alloys with 1 at. pct Ta and 2 at. pct Ta in iron. Also, the uniaxial tensile strengths of solution treated, quenched, and aged samples have been determined. These studies suggest that the compound, Fe2Ta, is isomorphous with the structure type, MgZn2, (C14) and has a range of compositional homogeneity. The latter results correspond with the predictions of the Engel-Brewer correlation. Also, it has been found that precipitation occurs at grain boundaries, dislocations, and randomly throughout the matrix. Particles which form at dislocations have a (100)α habit plane; whereas a (110)α habit plane has been reported by others1,3 for the hexagonal Laves phase in α iron. Hypereutectoid composition alloys quenched from the o phase field have a completely retained § structure. Isothermal decomposition at 600°, 700°, and 800°C of alloys with the retained § structure results in a sizable hardness increase in 2 at. pct Ta alloys but only a modest increase in 1 at. pct Ta alloys. Brittle fracture of aged tensile specimens tested at room temperature reveals that the ductile-brittle transition temperature in tension is above room temperature.

Anodic Spark Deposition from Aqueous Solutions of NaAlO2 and Na2SiO3

Coatings were deposited on Cu0, Ni0, and Al0 anodes from aqueous solutions of NaAlO2 and Na2SiO3 by anodic spark deposition. Some coatings formed at constant current density (1.0 A/cm2) were characterized by scanning electron microscopy, electron beam microprobe analysis, X-ray diffraction, and emission spectroscopy. A relation for the current decay during a multiple-spark, constant-voltage process was determined. This relation, which describes the behavior of most of the systems studied, is where φt, φ0, and φ∞ are the current densities at time t, at the start of the decay (t=0), and at the steady state, respectively. K is a constant that is voltage and system dependent.

Reaction Between Nitrogen and Spinel in Chromium

The reaction between nitrogen dissolved in chromium and a dispersion of magnesium aluminate particles in chromium at high temperatures is discussed. The equilibrium state for various nitrogen concentrations in a 94 chromium-6 spinel mixture was investigated between 1200° and 1400°C. Experimental techniques included electron-beam microprobe analysis and mass spectrometry. Partitioning of nitrogen between chromium and spinel was strongly in favor of the spinel. Mass spectrometry indicated coordination of nitrogen with magnesium in the spinel lattice. The spinel-nitrogen reaction is important because it can prevent the embrittling of chromium by nitrogen.

Sampling of noctilucent cloud particles

Sampling of noctilucent cloud particles by means of sounding rockets has been successfully carried out from northern Sweden in the Summer of 1962. Two successful flights were achieved, one in the presence of noctilucent clouds and one when no such clouds could be visually observed from the ground or from aircraft. The collecting surfaces were exposed between the altitudes of approximately 75 and 98 kilometers during ascent only. The particle concentration in a vertical column through the noctilucent cloud display is found to be greater than 8 × 1010 particles per square meter which is at least one thousand times greater than in the case when no clouds were observed. The integral size distribution of the cloud particles is of the form N = Ad-p where 3 < p < 4. A significant fraction of the collected cloud particles had a volatile coating prior to collection. The particles were analyzed by electron diffraction, neutron activation, and electron beam microprobe techniques. Electron-beam microprobe analysis has given evidence for iron particles with high nickel content. Calcium films were used as indicators of moisture associated with the collected particles. Study of the exposed and unexposed films flown in the sampling experiments has revealed evidence for moisture. Laboratory simulation of a ring- or halo-patterns found in the electron microscopic examination of the noctilucent cloud particles has been attempted. This was done by impacting ice-coated nickel particles on collecting surfaces similar to those used in the sampling experiment. Ring patterns similar to those observed on the rocket sampling surfaces have been produced. The primary conclusions are that the cloud particles are probably of extraterrestrial origin and that a significant fraction appears to have been coated with terrestrial ice. Plans for future experiments are briefly outlined.