Measuring the light yield in a CaMoO<Subscript>4</Subscript> scintillating crystal

The light yield in CaMoO₄ scintillating crystals irradiated with α particles and γ rays from ²⁴¹Am and ¹³⁷Cs radioactive isotopes, respectively, have been measured. It is shown that the light yield in this crystal for γ rays, measured in the wavelength range of 400–700 nm at room temperature (22°C), is ～3000 photons/MeV, and the ratio α/β is ～0.25.     

Structural analysis and intergranular corrosion tests of AISI 316L steel

Pure AISI 316L steel is investigated after solution heat treatment (1050 °C/H₂O) and structural sensitization (650 °C). Two quite different intergranular corrosion tests are used to determine the degree of structural sensitization due to the precipitation of secondary phases along the grain boundaries (mainly the M₂₃C₆ and σ‐phase): the oxalic acid etch test and the electrochemical potentio‐kinetic reactivation test. Generally, the dissolution of chromium‐rich carbides (M₂₃C₆) is provoked by oxalic acid etch tests, whereas the chromium‐depleted zones, in the vicinity of chromium‐rich carbides (M₂₃C₆), are attacked by electrochemical potentio‐kinetic reactivation tests. Both intergranular corrosion tests are used to determine the maximum degree of structural sensitization. Thus structural analysis by carbon replicas reveals the Laves phase, and both the M₂₃C₆ and (Cr,Mo)_x(Fe,Ni)_y phases. The results of intergranular corrosion tests are related to the findings of the structural analysis.     

Elevated temperature erosion-corrosion of 9Cr-1Mo steel

The combined erosion-corrosion behavior of 9Cr-1Mo steel (where the composition is in approximate weight per cent) was determined at 850°C using a stream of air and Al₂O₃ particles, 130 μm in diameter, from a nozzle at velocities from 10 to 70 m s⁻¹ at two impact angles, α = 30° and α = 90°. The mechanism of surface degradation and the rates of sound metal loss were determined. Corrosion was the dominant mechanism at all the velocities tested. It was determined that at α = 90° there was a change in the scale loss mechanism at about 30 m s⁻¹ from cracking and chipping to periodic spalling. The spalling increased the sound metal loss rates at the higher velocities. At an impact angle α = 30° the erosion mechanism and rates and the resulting scale morphologies were considerably different from those which occurred at α = 90°.     

Use of EBSD to identify phases in interdendrite region of a cast Zn–Al-based alloy (ZA27)

Electron backscattered Kikuchi diffraction methodology was used to identify phases in the interdendrite region of an alloy ZA27. Two Zn‐rich hexagonal close‐packed structure phases η and ɛ phases were distinguished using predetermined lattice parameters of the phases. In relation to studies of scanning electron microscopy and X‐ray diffraction, electron backscattered diffraction results revealed that the Al‐rich precipitates of the α phase were from decomposition of the η′_T, and the four‐phase transformation: α+ɛ→ T′+η, had occurred in the ɛ phase after ageing at 150°C for 8 h.     

Effect of heat treatment and number of passes on the microstructure and mechanical properties of friction stir processed AZ91C magnesium alloy

In this paper, the effect of heat treatment and number of passes on microstructure and mechanical properties of friction stir processed AZ91C magnesium alloy samples were investigated. From six samples of as-cast AZ91C magnesium alloy, three plates were pre-heated at temperature of 375°C for 3 hours, and then were treated at temperature of 415°C for 18 hours and finally were cooled down in air. Three plates were relinquished without heat treatment. 8 mm thick as-cast AZ91C magnesium alloy plates were friction stir processed at constant traverse speed of 40 mm/min and tool rotation speed of 1250 rpm. After process, microstructural characterization of samples was analyzed using optical microscopy and tensile and Vickers hardness tests were performed. It was found that heat treated samples had finer grains, higher hardness, improved tensile strength and elongation relative to non-heat treated ones. As the number of passes increased, higher UTS and TE were achieved due to finer grains and more dissolution of β phase (Mg₁₇Al₁₂). The micro-hardness characteristics and tensile improvement of the friction stir processed samples depend significantly on grain size, removal of voids and porosities and dissolution of β phase in the stir zone.

     

Performance of ionic polymer-metal composite (IPMC) with different surface roughening methods

Based on permeation and double chemical reduction technology, this paper researches the manufacture of Pt-ionic polymer metal composites (IPMCs) and the effect of three types of surface roughening methods on the manufacture and performance of IPMC. The roughening methods include manual polishing, sanding machine polishing, and plasma surface treatment. The appearance and scanning electron microscopy (SEM) features, electro-active deformation and surface resistance characteristics of these IPMC specimens were obtained and compared through specimen tests. The results of the tests indicate that surface roughening technology obviously influences the performance of IPMC. The uniformity and compactness of the metal deposited on the surface and inside the Nafion film are improved by improving surface roughening uniformity. However, the electro-active deformation capability and surface resistance of the specimens decrease at the same time. There is an approximate linear increase relationship between the driving voltage and the bending deformation of the IPMC specimen within a certain voltage range. Under the same specimen dimension, constraints, and driving voltage (3 V), the maximum electro-active bending deformation angles of the specimens are about 60°, 45°, and 15° for manual polishing, sanding machine roughening, and plasma treatment, respectively.     

1‐Pyrenemethanol,a Useful Fluorometric Reagent for the Detection and Determination of Carboxylic Acids in Atmospheric Samples

Abstract

A rapid fluorometric procedure for the selective and sensitive determination of carboxylic acids, based on pre‐column derivatization using 1‐pyrenemethanol, was optimized and applied to atmospheric sampling. The optimum conditions for derivatization were determined to be: reaction solvent–dichloromethane, temperature ?44°C, reaction time ?30 min, and reagent/total acid ratio ?15. Separation of the derivatives of acids up to twenty carbons by reversed‐phase (C₈) chromatography was achieved in 25 min using a water/acetonitrile gradient with a limit of detection for the derivatives of 20 pg for a 20 µL injection. A scanning detector with good spectral resolution allows qualitative identification of the components in complex samples. When used in atmospheric analysis, the recoveries of carboxylic acids from spiked samples were >80% with repeatabilities below 10% RSD. Low molecular weight acids were encountered predominantly in the vapor phase (0.20 to 92 ng/m³), whereas higher molecular weight acids were found mostly in particulate form (0.15–129 ng/m³).     

Facility for rapid preparation of silicon and silicide TEM specimens

A simple chemical jet polishing arrangement, for the thinning of semiconductors or metals for transmission electron microscopy (TEM), is described for the specific case of silicon and silicides. The effect of variation in three mechanical parameters on the profile and quality of the specimen is described, and the optimum conditions are determined. A proposed polishing solution is one part 48% HF mixed with one part fuming HNO₃. Reproducibility is only achieved in the presence of a relatively large concentration of nitrous acid in the polishing solution. The solution must also be relatively concentrated, as the reaction rate falls off rapidly with decreasing concentration.     

A comparison of specimen stage surface temperature and the GA-1 control unit reading in Balzer's Freeze fracture microtome cold stage

The cold stage specimen surface in our Balzer's 300 Freeze-etch instrument, averages 29–43°C warmer than the reading on the GA-1 stage temperature control unit. By introduction of Indium foil seals above and below the stainless steel plug in the stage tower, the specimen cold stage surface temperatures were still 9–10°C warmer than the GA-1 reading. After replacing the stainless steel plug with a copper plug and using Indium seals, the cold stage specimen surface was brought within 2.6°C of the GA-1 temperature reading. In addition, the copper plug, Indium seal modified stage cools about two times faster in going from –100°C to –150°C than the normal stainless steel stage modified with Indium seals.     

Effect of processing parameters of laser on microstructure and properties of cladding 42CrMo steel

Hard-inert materials such as diamond, silicon carbide, gallium nitride, and sapphire are difficult to obtain from the smooth and damage-free surfaces efficiently required by semiconductor field. Therefore, this study proposed a chemical kinetics model to evaluate the material removal rate of diamond in chemical mechanical polishing process and to investigate the material removal mechanism by examining the surface information with optical microscopy, surface profilometry, and atomic force microscopy as well as X-ray photoelectron spectroscopy. The theoretical and experimental results show that chemical and mechanical synergic effect may promote the diamond oxidation reaction in chemical kinetics. The material removal rate is acceptable when the mechanical activation coefficient is smaller than 0.48. The 2.5 μm B₄C abrasives, the polishing temperature of 50 °C, and the polishing pressure of 266.7 MPa are optimal parameters for diamond polishing with potassium ferrate slurry. It provides the highest material removal rate of 0.055 mg/h, the best surface finish (about Ra 0.5 nm) and surface quality (no surface scratches or pits). It then discusses how mechanical stress may promote the chemical oxidation of oxidant and diamond by forming “C-O,” “C=O,” and “O=C-OH” on diamond surface. The study concludes that chemical kinetics mechanism is effective for the investigation of the synergic effect in chemical mechanical polishing hard-inert materials.     

Solid particle erosion of mullite

The solid particle erosion of mullite (3Al₂O₃·2SiO₂ plus approximately 12% glass phase) was investigated using angular A1₂O₃ particles whose mean diameters D were varied between 23 and 270 μm. A range of impact angles α between 15° and 90° was used and the impact velocity V was varied from 60 to 100 m s^?1. The results of these experiments are in agreement with the general predictions of the two models developed to describe erosion in brittle materials on the basis of the formation of lateral cracks. The velocity exponent of the steady state erosion rate ΔW is between 2.2 and 2.8, being larger for smaller particles. For normal incidence, $\text{ΔW ∝ D}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ in accord with both theories. For α > 15° only the normal component of velocity need be considered, but for smaller α there is evidence of plasticity both in the α dependence of ΔW and as observed using scanning electron microscopy.     

Evolution of rapidly solidified NiAlCu(B) alloy microstructure

This study concerned phase transformations observed after rapid solidification and annealing at 500, 700 and 800 °C in 56.3 Ni‐39.9 Al‐3.8 Cu‐0.06 B (E1) and 59.8 Ni‐36.0 Al‐4.3 Cu‐0.06 B (E2) alloys (composition in at.%). Injection casting led to a homogeneous structure of very small, one‐phase grains (2–4 µm in size). In both alloys, the phase observed at room temperature was martensite of L1₀ structure. The process of the formation of the Ni₅Al₃ phase by atomic reordering proceeded at 285–394 °C in the case of E1 alloy and 450–550 °C in the case of E2 alloy. Further decomposition into NiAl (β) and Ni₃Al (γ′) phases, the microstructure and crystallography of the phases depended on the path of transformations, proceeding in the investigated case through the transformation of martensite crystallographic variants. This preserved precise crystallographic orientation between the subsequent phases, very stable plate‐like morphology and very small β + γ′ grains after annealing at 800 °C.     

硼对高铌TiAl基合金γ→α相变的影响

TiAl广泛应用在在航空航天和汽车等领域,研究了硼对高铌TiAl基合金γ→α相变的影响。研究发现:在相同的保温时间下,Ti-46Al-8Nb-0.8B合金α2相的体积分数比Ti-46Al-8Nb合金小,这主要是因为Ti-46Al-8Nb-0.8B合金中的α相从γ晶界析出的形核率低,生长更困难而导致的;微量元素硼的添加能显著促进片状α相从γ晶粒内析出的形核率,抑制块状α相从γ晶界析出的形核率,并能阻碍α相的生长。     

Deformations of a simplified flip chip structure under thermal testing inspected using a real-time Moiré technique

Deformations of a Si-epoxy-FR4 (simplified flip chip) structure under thermal testing were inspected with a real-time Moiré technique. Specimens without cracks and specimens with a crack at the silicon-epoxy interface were prepared. The measurement results showed that the maximum deformation appeared at the edge. When the specimen was cooled to 20 °C, there was residual plastic deformation in the specimen. The creep effect was more dominant in the FR4-epoxy interface. Upon cooling to 20 °C, the specimen experienced partial strain recovery. To characterize the behavior of the interfacial crack, stress intensity factors K_I and K_II, and the strain energy release rate G in the vicinity of the crack tip were calculated using the measured deformations to conduct a quantitative study. It was observed that a sharp strain gradient occurred at the crack tip. K_I and K_II were dependent on temperature, and G was dominated by K_I for the interfacial crack in the specimen.     

Wear and Friction Characteristics of a Selected Stainless Steel

Dry sliding wear tests were performed for 3Cr13 steel with various tempered states at 25–400°C; wear and friction characteristics as well as the wear mechanism were explored. With an increase in test temperature, the wear rate decreased accompanied by an increase in tribo-oxides. The fluctuation of friction coefficient was slight at 25–200°C but became violent at 400°C. At 25–200°C, adhesive wear prevailed due to trace or less tribo-oxides; at 400°C, oxidative wear prevailed with the predominant tribo-oxides of Fe₃O₄ and Fe₂O₃. It can be suggested that the antioxidation of the stainless steel postponed the occurrence of oxidative wear to a higher test temperature. For adhesive wear, the wear resistance, roughly following Archard's rule, was directly proportional to hardness besides the specimen tempered at 500°C with grain boundary brittleness. But for elevated-temperature wear, a better wear resistance required thermal stability and an appropriate combination of hardness and toughness.     

The structure and thermal stability of tungsten-based contact metallizations to n-GaN

Thermally stable contacts to n-GaN have been obtained using W and WSi. Low specific contact resistance was achieved for the W metallization with limited reaction between the metal and semiconductor up to 1000°C. The formation of the β-W₂N and W-N interfacial phases were deemed responsible for the electrical integrity observed at these annealing temperatures. The W_x-N_1-x interfacial phases functioned as efficient barriers to the outdiffusion of Ga. For WSi, the β-W₂N interfacial phase formation was observed after annealing at 700° and 800°C. This phase also prevented Ga outdiffusion at these elevated temperatures. Optimization of this phase and moderate suppression of interfacial irregularities occurred after annealing at 800°C. This investigation demonstrates that both W and WSi contacts appear to be reasonable contact choices for high-temperature electronics applications.     

Effect of Mixed Rare Earth Fluorides on the Mechanical and Tribological Characteristics of Ni-Based Alloy

In this paper, Ni-based alloys with different addition amounts of mixed rare earth fluoride were prepared using a P/M method in an intermediate frequency inductive furnace. The effect of mixed rare earth fluoride (30.9 wt.% LaF₃ and 69.1 wt.% DyF₃ in composition) additions on the mechanical strength of the alloy was investigated and compared with that of a CeF₃ addition. The findings indicated that by adding 3 wt.% mixed rare earth fluorides the improved toughness can be obtained. By adding 3 wt.% and 5 wt.% of mixed rare earth fluorides the compressive strength at 700°C were increased. The friction and wear behavior of the composite sliding against a high temperature self-lubricating composite at room temperature and 600°C in air were investigated on a pin-on-disk tribometer. The composites showed better tribological performances at 600°C than at room temperature.     

A controlled atmosphere specimen holder for transmission electron microscopy

A controlled atmosphere specimen holder (CASH) has been developed for transmission electron microscopy (TEM) experiments. It is designed for studying the specimen's microstructure before and after treatments in various gases (H₂, O₂, N₂, Ar, etc.) at temperatures up to 600°C. The experiments are carried out without exposing the specimen to the ambient atmosphere. No modification of the electron microscope itself is needed. The same area of the specimen can be easily located after each gas treatment, thus the changes in the microstructure can be studied directly. Preliminary results on the cyclic oxidation and reduction of a model cobalt catalyst are presented.     

Tribo-oxidation of Self-mated Ti3SiC2 at Elevated Temperatures and Low Speed

The tribological behavior of self-mated Ti₃SiC₂ is investigated from ambient temperature to 800?°C at a sliding speed of 0.01?m/s in air. The results show that at the temperatures lower than 300?°C, friction coefficient and wear rates are as high as 0.95 and 10^?3?mm³/N?m, respectively. With the temperature increasing to 600?°C, both the friction coefficient and wear rates show consecutive decrease. At 700 and 800?°C, friction coefficient and wear rates are 0.5 and 10^?6 mm³/N?m, respectively. According to the wear mechanism, the tribological behavior of Ti₃SiC₂ can be divided into three regimes: mechanical wear-dominated regime from ambient temperature to 300?°C characterized by pullout of grains; mixed wear regime (mechanical wear and oxidation wear) from 400 to 600?°C; and tribo-oxidation-dominated wear regime above 700?°C. The tribo-oxides on the worn surfaces involve oxides of Si and Ti. And, species transformation occurs to these two oxides with the increasing temperature. In the competition oxidation of elements Ti and Si, Si is preferably oxidized because of its high active position in the crystal structure. Additionally, plastic flow is another notable characteristic for the tribological behavior of self-mated Ti₃SiC₂.     

Studying kinetics of scintillation process in a CaMoO<Subscript>4</Subscript> crystal

The kinetics of scintillation process in Czochralski-grown CaMoO₄ crystals excited by α particles and γ rays from ²³⁸Pu and ¹³⁷Cs radioactive isotopes, respectively, is investigated. Kinetics of scintillations is shown to be complex and multicomponent in character. Fast and slow scintillation components are observed, and their relative contributions to the total light yield in the scintillator are determined. The possibility is demonstrated of discriminating between scintillator signals due to α particles and γ rays.