Dry Hydrogen Atmosphere Research Articles

Magnetic properties of grain oriented ultra-thin silicon steel sheets processed by conventional rolling and cross shear rolling

A new procedure consisting of the cross shear rolling (CSR) and the subsequent tertiary recrystallization annealing under dry hydrogen atmosphere was developed to produce the grain oriented ultra-thin silicon sheets less than 0.1 mm with high magnetic property performance. For comparison, the conventional rolling (CR) was also used to process the grain oriented ultra-thin silicon steel sheets. The effect of processing parameters on magnetic properties of the grain oriented ultra-thin silicon steel sheets was investigated. With the increase of annealing temperature and holding time, magnetic properties of the sheets processed by both rolling methods reach saturation as the result of the proceeding of the tertiary recrystallization. The thin sheets rolled by CSR did achieve better magnetic properties than those rolled by CR.

Sintering behavior of Ni/Y 2 O 3 -ZrO 2 cermet electrodes of solid oxide fuel cells

The sintering behavior of Ni/Y2O3-ZrO2(YSZ) cermet electrode coating on 3 mol% Y2O3-ZrO2electrolyte was studied under moist and dry hydrogen atmosphere at 1000°C for up to 2000 h. The sintering behavior of Ni/YSZ cermet electrodes was dominated by the agglomeration and grain growth of Ni particles in the cermets, which was critically related to the content of Ni and YSZ phases in the cermet. For pure Ni electrode coating, the sintering was substantial and cross plane cracks and isolated Ni island were formed after sintering at 1000°C for only 250 h. However with the addition of YSZ phase, the sintering of Ni/YSZ cermet anode coatings was significantly reduced. For the cermet composition of Ni (50 vol%)/YSZ (50 vol%), the change in the surface porosity and pore size distribution after sintering at 1000°C for 2000 h was very small. The microstructural stability of the Ni (50 vol%)/YSZ (50 vol%) cermet electrodes was also demonstrated by the performance stability tested under current load of 250 mAcm−2at 1000°C for over 2500 h.

Acetone transformation over Pt/H[Al]ZSM5 and Pt/H[Ga]ZSM5 catalysts: Evidences of a Pt–Ga interaction

Acetone transformation into methyl–isobutyl ketone (MIBK) under hydrogen atmosphere, using bifunctional catalysts of the platinum supported over medium-pore zeolites (MFI)-type, was studied. This methodology offers a number of advantages; however, since it implies working at low hydrogen pressure ( P H 2 ) with respect to the acetone pressure ( P Ac), a rapid catalyst deactivation is observed. Therefore, to minimize deactivation of bifunctional catalysts, a solid with less strong acidic sites has been considered as a platinum support. In this sense, the use of an MFI-type gallosilicate has been deemed convenient to compare the results with those obtained over a catalyst of the platinum/aluminosilicate MFI-type. The H[Al]ZSM5 and H[Ga]ZSM5 solids were synthesized and evaluated by means of DRX, nitrogen adsorption at −196 °C, TPD–NH 3 and chemical analysis, and later used as a support for the metallic phase. Platinum of 0.50 wt.% was introduced by means of the exchange–impregnation method and the Pt(NH 3) 4Cl 2 salt was used as a platinum precursor. The solids were calcinated under dry air flow at 300 °C for 6 h and then reduced under dry hydrogen atmosphere at 500 °C also for 6 h. The bifunctional catalysts obtained, 0.50Pt/H[Ga]ZSM5 (Si/Ga=42) and 0.50Pt/H[Al]ZSM5 (Si/Al=40), were evaluated by means of chemical analysis, nitrogen adsorption, transmission electronic microscopy (TEM), electronic paramagnetic resonance (EPR), and the model reactions of toluene-hydrogenation and n-heptane hydrocracking under the conditions established in previous works. Acetone transformation was run in a dynamic reactor at 160 °C, atmospheric pressure, P Ac/ P H 2 =3 and variable WHSV. The results obtained with the model reactions and the acetone transformation shows that metallic centers in the Pt-gallosilicate catalysts exhibit a much lower hydro-dehydrogenating activity than that of the metallic centers in the Pt-aluminosilicate catalyst; this, together with the EPR results, seems to indicate that a strong interaction between platinum and a species of structural or extra-structural gallium (EFGS) of the support used has occurred over the Pt/H[Ga]ZSM5 catalyst.

EXPERIMENTAL SULFUR ISOTOPE STUDIES OF THE PYRITE TO PYRRHOTITE CONVERSION IN A HYDROGEN ATMOSPHERE

Sulfur isotope effects associated with the conversion of pyrite to pyrrhotite in a dry hydrogen atmosphere were measured at temperatures from 500° to 600°C. H 2 S was the primary fluid species produced, although at temperatures of 500° and 525°C native sulfur in amounts up to 30 percent of the total liberated sulfur condensed in the collection system. At temperatures of 550°, 575°, and 600°C, more than 90 percent of the liberated sulfur was in the form of H 2 S. At all temperatures pyrrhotite was the only residual iron sulfide. Native sulfur was characterized by a δ 34 S value of –0.1 per mil relative to the starting pyrite, whereas H 2 S varied from –0.2 to +0.1 per mil (most values were within analytical error of 0‰). The produced pyrrhotite ranged from 0.3 per mil at 500° and 525°C, to 0.2 per mil at all higher temperatures. Pyrrhotite-H 2 S fractionation factors are near equilibrium values for these temperatures and suggest that potential kinetic isotope effects are suppressed at low f O2 conditions where H 2 S is the principal fluid species. Both experimental and empirical studies suggest that very little sulfur isotope fractionation accompanies the conversion of pyrite to pyrrhotite in carbon-rich metapelites. For this reason the isotopic composition of pyrrhotite in graphitic metapelites may serve as a reliable indicator of the isotopic composition of sulfur that was available for assimilation by magmas or hydrothermal fluids, and that may have been involved in later ore genesis.

The effect of managanese addition on the microstructure of W-Ni-Fe heavy alloy

The influence of Mn addition on the growth kinetics and morphology of W grains in W-Ni-Fe heavy alloy has been studied. The addition of Mn was performed by placing a compact of Mn powder on the sintered specimens containing constant Ni/Fe ratio of 8/2 but different W contents of 93 and 97 wt pct followed by resintering. The sintering and resintering treatments were carried out at a temperature of 1485 °C under a dry hydrogen atmosphere. The addition of Mn leads to the deviation of growth rate of W grains from the diffusion-controlled Ostwald ripening: the growth rate is initially enhanced and then decayed. The difference in the average grain radius between the alloys containing high and low W contents is decreased by the addition of Mn. The cause of the change in the growth rate of W particles with the addition of Mn is discussed in terms of the competitive soluble reactions of Mn and W atoms. The addition of Mn also results in the morphological change of W grains from roudish to angular shape. The addition of Mn into the matrix phase, which is artificially made, forms the dendritic W grains. From these results, it is found that the morphological change of W grains is closely related to the precipitation reaction of W atoms on the preferred orientation.

Properties of P/M 316L Stainless Steel Sintered in Dry Hydrogen Atmosphere

The sintering process represents always a critical step in the production of stainless steel sintered parts, limits to increasing the properties of sintered parts are related to some processing parameters and plants. With the aim to deepen the knowledge about the influence of the sintering parameters and to verify the possibility to further improve the characteristics of 316L sintered stainless steel parts, the influence of sintering atmosphere constituted by dry hydrogen has been studied, taking into account for the effects of compacting pressure and of sintering time and temperature. Tests have shown the effect of the compacting pressure and of the increase of sintering time and temperature in producing smaller pores and less interconnection. Two diffusion mechanisms for removing carbon during sintering were highlighted and the influence of processing parameters and of carbon contents on the corrosion resistance of the samples was tested in 0.5 M sulfuric acid.

Defluorination behavior and mechanism of uranium dioxide

The residual fluorine in ammonium uranyl tricarbonate (AUC) cannot be removed, while a large part of residual fluorine in ammonium diuranate (ADU) can be removed, when AUC and ADU are decomposed and reduced under dry hydrogen atmosphere. UO2 was prepared by decomposing and reducing AUC and ADU in dry hydrogen atmosphere. The defluorination kinetics of UO2 at 500–700°C in atmosphere of 50% H2-50% H2O was investigated. The results show that the defluorination kinetics supports the Lindman's assertion that the residual fluorine forms a solid-solution in UO2.

Brazing diamond grits onto a steel substrate using copper alloys as the filler metals

Surface-set diamond tools were fabricated by an active metal brazing process, using bronze (Cu-8.9Sn) powder and 316L stainless steel powder mixed to various ratios as the braze filler metals. The diamond grits were brazed onto a steel substrate at 1050 °C for 30 min in a dry hydrogen atmosphere. After brazing practice, an intermediate layer rich in chromium formed between the braze filler metal and diamond. A braze filler metal composed of 70 wt % bronze powder and 30 wt % stainless steel powder was found to be optimum in that the diamond grits were strongly impregnated in the filler metal by both mechanical and chemical types of holding. The diamond tools thus fabricated performed better than conventional nickel-plated diamond tools. In service, the braze filler metal wore at almost the same rate as the diamond grits, and no pullout of diamond grits or peeling of the filler metal layer took place.

Influence of Atmosphere on the Final‐Stage Sintering Kinetics of Ultra‐High‐Purity Alumina

The influence of sintering atmosphere on the final‐stage sintering of ultra‐high‐purity alumina has been investigated. Model final‐stage microstructures were tailored via a latex sphere impregnation and burnout technique. Critical experiments have been conducted to quantitatively examine the influence of the oxygen partial pressure on the final‐stage sintering kinetics. Samples were sintered at 1850°C in either dry hydrogen (Po2∼ 3 × 10−17 atm) or wet hydrogen Po2∼ 5 × 10−10 to 2 × 10−11 atm), and their microstructures were characterized as a function of sintering time, Sintering in dry hydrogen decreased the susceptibility of the final‐stage microstructure to pore/boundary breakaway. In the kinetic analysis, the variation in the number of pores per grain, Ng, was taken into account. It was found that in both atmospheres, the densification rate was controlled by grain boundary diffusion, and that sintering in dry hydrogen increased the densification rate by a factor of 2.25. In addition, it was determined that the grain growth rate in both atmospheres was controlled by the rate of surface diffusion of matter around the pores and that sintering in dry hydrogen enhanced the grain growth rate by a factor of 5.6. The overall effect of the dry hydrogen atmosphere was that it enhanced the coarsening rate relative to the densification rate by a factor of 2.5, and consequently shifted the grain size‐density trajectory to much lower densities for a given grain size.

Mechanical properties of Fe-36 Ni base alloys with chromium addition up to 5 mass%

Mechanical properties, such as yield strength (σ0.2), tensile strength (σb), elongation (δI), strain-hardening coefficient (n) and modulus of elasticity (E), for chromium added Fe-36 mass% Ni with chromium addition of up to 5 mass% were studied as a function of annealing temperature from 1053 to 1423 K in a dry hydrogen atmosphere. When chromium was added to Fe-36 Ni, σ0.2 decreased, butn andE increased. σB and δI scarcely changed with the chromium addition. σ0.2, σB, δI andE decreased with the increase in annealing temperature. The relation between σ0.2 and grain size was in agreement with Petch's equation.

Matteucci effect of rapidly quenched Co-Fe alloy ribbon and its application

Ribbon-shaped 70% Co-Fe and 12-14% A1-2% Co-Fe alloys were formed by a rapid quenching method with a single roller. The Matteucci effect was measured on the ribbon after annealing in a dry hydrogen atmosphere. The ribbon were very flexible. A sharp voltage pulse was induced between both ends of the ribbon when placed in an ac field due to the Matteucci effect. The voltage was sufficiently high and increased with an increase in frequency and/or field strength. The temperature dependence of the pulse voltage was measured in the temperature range from 50 to 200°C. Furthermore, experimental results are shown for an a.c. current sensor as an application of these ribbons.

Sintering atmosphere effects on tensile properties of heavy alloys

The sintering atmosphere has a direct bearing on the residual porosity which in turn has a strong negative influence on the tensile properties of W-Ni-Fe heavy alloys. The present investigation uses various sintering atmospheres to understand pore formation, densification, microstructure, and tensile properties of heavy alloys with tungsten contents ranging from 88 to 97 wt Pct. Pore formation when sintering in a dry hydrogen atmosphere is linked to water vapor generation and its entrapment in pores. A hydrogen dew point effect is associated with solution-reprecipitation of tungsten during liquid phase sintering. The beneficial effect of vacuum sintering has been analyzed in terms of removal of the gases before pore closure. Property degradation during long time vacuum sintering is attributed to preferential matrix vaporization. The negative effect of long sintering times in dry hydrogen is attributed to pore coarsening, which is removed by a three-stage sintering atmosphere treatment.

The study of desulfurization kinetics in grain oriented 3 percent silicon iron

The desulfurization kinetics in grain oriented 3 Pct Si-Fe have been studied by using the model proposed by Swiftet al.1 The model assumes the desulfurization is diffusion controlled and the sulfur is present as dispersed sulfide particles. Desulfurization experiments were conducted at temperatures ranging from 899 °C to 1171 °C in a dry hydrogen atmosphere with the thickness of sample ranging from 0.138 mm to 0.325 mm. There are wide variations among the published sulfur solubility data in 3 Pct Si-Fe, but theoretical calculations showed good agreement with the experimental results only when the sulfur solubility data published by Brown were used. The effect of MgO coating on desulfurization has also been studied.

Transmission Electron Microscope characterization of a slip propagation event in alpha brass

Slip propagation through grain boundaries is a process which is, in part, responsible for grain size strengthening. TEM characterization of a slip propagation event combined with quantitative stress analysis allows determination of the critical stress and micromechanism for the event. Such an analysis is presented here.Commercially pure alpha brass(30 w/o Zn) was rolled to 125um and was then annealed in a dry hydrogen atmosphere at 800°C for one hour. The material was lightly deformed, and samples prepared using standard electopolishing techniques. This was then examined in a JEOL 200CX operating at 200keV.

Preparation of high purity chromium

The purification of chromium is important in investigations of its true properties. High purity chromium was prepared by overlap floating zone refining in a dry hydrogen atmosphere at about 100 kPa. The purity was estimated from the values of the residual resistivity ratio RRR 4.2K and activation analyses using neutrons, charged particles and γ rays. The concentrations of residual carbon and oxygen were less than 10 ppm for purified chromium, and the highest value of RRR 4.2K was 667 which is higher than previously reported values. The rolling reduction of the purified chromium was over 50% at room temperature, showing a relatively good ductility.

Effect of Sintering Temperatures on Mechanical Properties of Fe—P—Mo Powder Premixes

AbstractIn the present investigation, the effect of varying sintering temperatures (1050–1200°C) on the mechanical properties of Fe–P–Mo powder compacts sintered for 45 min in a dry hydrogen atmosphere was studied. Molybdenum content in iron or phosphorus- containing iron was varied from 1 to 4 wt-% while phosphorus was in the range 0 to 0·6 wt-%. It was observed that with an increase in sintering temperature there was an increase in linear shrinkage and mechanical properties of all the alloy systems. However, the magnitude of increase in properties was greater in the case of P-containing Fe–Mo compacts than in plain Fe-Mo compacts. The results are discussed on the basis of diffusivity data for the various alloying elements and liquid-phase sintering modes. PM/0203

Hydrogen reduction of atomized iron powders

1. Virtually complete removal of oxygen (to a residual level of less than 0.1%) from atomized iron powders of various fractions occurs in a very dry hydrogen atmosphere (with a dew point not exceeding −40°C) at an end reduction temperature of 500°C. 2. The reduction time of iron powders subjected to ultrasonic treatment is one-half that of untreated powders.

Effect of annealing on the magnetic characteristics of iron-27% cobalt alloys

This paper describes the changes in magnetic properties of iron-27% cobalt alloys undergoing various annealing treatments. Two commercial heats (0.2 and 0.1 mm thick respectively) of similar compositions were studied. The anneals were carried out in both dry hydrogen and vacuum for a variety of temperatures up to 1200°C. After annealing, the magnetic properties were measured, the samples were examined metallographically, and the residual carbon and sulfur contents were determined. Results indicated that annealing in a dry hydrogen atmosphere was superior to heat treating under vacuum. The best annealing temperature to obtain good overall magnetic properties was 900°C. A slightly higher annealing temperature, 925°C, caused severe degradation in magnetic properties. It is suggested that the poorer properties are related to the presence of the alpha/gamma phase transformation at 925°C. Annealing at temperatures above 925°C caused improvement in some of the magnetic properties. Coercive force (H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> ) seemed most sensitive to annealing conditions, with a strong positive correlation being found between H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> and the carbon plus sulfur contents after annealing.

水素雰囲気による鋼の脱窒に関する研究

A study of the removal of nitrogen from rimmed sheet steel and high carbon piano wire has been performed. The denitrogenizing annealing was carried out at temperatures from 500 to 1000°C in dry or wet hydrogen atmosphere and also in alternating atomspheres of dry hydrogen and vacuum. The following results were obtained.The rate of nitrogen removal from rimmed sheet steel containing 004 to 005% C is increased appreciably with increase in temperature up to about 700 to 720°C, where the gamma phase appears, while it is decreased with further increase in temperature. The rate of nitrogen removal is also increased with an increase in flow rate of hydrogen up to 350cc/min under the present experimental condition, but any more increase in the rate is hardly observed with further increase in the flow rate of hydrogen.When the flow rate of hydrogen is higher than 350cc/min under the present experimental condition, the rate of nitrogen removal is controlled by the diffusion of nitrogen in steel, and when the flow rate of hydrogen is lower than 100cc/min the rate of nitrogen removal follows the first order rate law, i.e., the logarithm of the ratio of nitrogen content to that of initial nitrogen is proportional to the time of treatment.The water vapor up to about 20 vol% in hydrogen of 350ccimin has no effect on the rate of nitrogen removal from sheet steel, and the water vapor up to about 2 to 5 vol% in hydrogen of 100cc/min has a slight effect to increase the rate of nitrogen removal while the rate is decreased with further increase in water vapor.Decarburization is not observed by dry hydrogen atmosphere while by the small addition of water vapor to hydrogen the rate and extent of decarburization are increased appreciably.Judging from the present experimental results and the previous investigations, it is concluded that 1) if the process of nitrogen removal is performed in hydrogen of high flow rate, the rate of nitrogen removal is controlled by the diffusion of nitrogen in steel while 2) if it is performed in hydrogen of low flow rate the rate of nitrogen removal is controlled by the rate of outgoing transfer of the gases produced by denitrogenizing reaction from the reaction chamber.It is suggested that the annealing by alternating treatment by hydrogen and vacuum can save the hydrogen consumption and the rapid and homogeneous nitrogen removal throughout the coil may be possible with a relatively small consumption of hydrogen when this technique is applied to the open coil annealing.

The influence of crystalline anisotropy on neck growth during the sintering of zinc

Polycrystalline zinc wires of two grain sizes and zinc single crystal wires of four orientations all of them 0.010 in. in diameter were grown. Pairs of wires from each of the six groups were sintered together at 365°C for 8 hr in a pressurized dry hydrogen atmosphere and the widths of the necks formed between pairs were measured. In the single crystal pairs, the neck width depended upon the relative orientation of the basal planes in the wire with the largest width up to 2.7 times as large as the smallest. In the polycrystalline samples those with fine grain size, of the order of neck width, had small necks, while those with coarse grain size, of the order of the wire diameter, had large necks. The observed variations in the width of the neck with relative orientation and with grain size must be caused by the anisotropy of those properties of zinc which determine the rate of material transport during sintering. For sintering by diffusional flow these are specific surface free energy and diffusivity, for sintering by evaporation and condensation they are specific surface free energy and vapor pressure. Since for these mechanisms approximate equations for the rate of neck growth exist, the maximum ratios of neck width due to the anisotropies of specific surface free energies, diffusivities and vapor pressures can be estimated. They are considerably smaller than the observed ratio of up to 2.7. The remaining material transport mechanism for the early stages of sintering is plastic flow which, in zinc, is highly anisotropic, since even at temperatures near the melting point the critical resolved shear stress for slip on the basal slip system is five to ten times lower than for slip on any other system. The measured neck width of the single crystal wire pairs can be directly related to the ease of basal slip. Those pairs which are oriented so that no basal slip is possible have small necks, while those which are favorably oriented for basal slip have large necks. The small neck width in the fine-grained wires must be due to constraint which inhibits basal slip. No such constraint exists in the necks of the coarse grained wires. Material transport by plastic flow must play an important role in the sintering of the zinc wires.