Permeation of Ethylbenzene and Hydrogen Through Untreated and Catalytically-Treated Alumina Membranes

Abstract

Experiments were conducted to measure the transport rates of ethylbenzene and hydrogen through an alumina inorganic membrane in a tubular geometry. The effective diffusivity was estimated from a membrane tube model and interpreted via a four-region picture of the membrane structure. Knudsen diffusion through the 40 Å narrow membrane pores appeared to control the overall separation. The membrane with catalytic treatment yielded effective diffusivities two orders of magnitude lower than the untreated membrane. Ethylbenzene and hydrogen diffuse independently of one another in both treated and untreated membranes.     

表面处理渗氢浅谈

在表面处理过程中,氢以原子状态渗入工件基体或镀层中造成渗氢;钢件渗氢后如不进行驱氢处理,会大大降低钢的疲劳强度和使用寿命,文中阐述了渗氢的危害及影响,对电镀、酸洗、阴极电化学除油或阴极电角腐蚀等表面处理过程中渗氢的原因进行了分析,提出了消除或减少渗氢的措施。     

A Study on the Preparation and Gas Permeation of Porous Alumina Supports

Abstract

The preparation and gas permeation of porous alumina supports were studied. The influences of the amount of PVA on the properties of the alumina slips, microstructure of the supports, and gas permeation were investigated. The experimental results show that the addition of PVA in the preparation process is useful for controlling the porosity of the supports without significantly changing other microstructural properties. Permeation measurements of H₂, He, CH₄, N₂, O₂, and CO₂ showed that gas transport through various supports under low transmembrane pressures (100–220 kPa) at room temperature (26.5°C) was in the transition region, which combined the Knudsen diffusion and Poiseuille flow. The average radii of active pores for the supports, calculated from the gas permeability method, were compared with those measured by mercury porosimetry. The porosity—tortuosity factors and the tortuosity factors of the supports were also estimated and are discussed.     

Zn-Ni合金电沉积过程中的渗氢行为

用电化学渗氢测试方法探讨了氯化物体系、硫酸盐-氯化物混合体系电沉积Zn-N i合金镀层过程中的渗氢行为。结果表明,氯化物体系比硫酸盐-氯化物混合体系渗氢电流小,用电镀过程中的氢覆盖率和镀层孔隙率对渗氢特点进行了解释。     

Residual Stress Measurements in Alumina and Silicon Carbide

Residual stresses were measured in three types of ceramic components. Stresses were measured using X-ray diffraction and an advanced X-ray instrument. Measured stresses in alumina rods were shown to correlate well with breaking strength, and stress variations in an alumina tile were hypothesized to result from inhomogeneous cooling. The compressive stresses induced in a silicon carbide tube, by an outer steel sleeve, were seen to be balanced by tensile stresses in the sleeve.     

Pd-SiO2复合膜的氢气选择渗透特性

Palladium membranes were prepared on an a-alumina support by metal-organic compound chemical vapor deposition (MOCVD) method from palladium(Ⅲ) acetate precursor. Permeation properties of hydrogen and helium gas were studied as a function of the number of times of deposition of palladium on the peeling off phenomenon of palladium, which is common in electroless plated membrane, was observed. Silica was introduced into the pores to prevent the palladium grain from peeling off. The palladium-silica conjugated membrane does not show the peeling off phenomenon and can withstand the high temperature up to 800℃ which is the upper limit of our apparatus.The separation factor for hydrogen gas over carbon dioxide gas was improved with the increase of number of times of silica coating by sacrificing the H2 permeation and finally increased to four times. The improvement on the separation of hydrogen gas over carbon dioxide for pulladium-silica conjugated membrane was evaluated and a model of permeation pattern (palladium and silica) was proposed. This model suggests that the separation factor for hydrogen over carbon dioxide could be improved by introducing silica layer because the silica layer fills the pores and reduces the gas permeation without sacrificing the hydrogen permeation through the palladium region. These results indicate that the introduction of silica into the palladium grain is a promising means to improve the hydrogen separation performance of palladium based composite membranes.     

Preparation of Palladium-Silica Conjugated Membrane for Selective Hydrogen Permeation

Palladium membranes were prepared on an a-alumina support by metal-organic compound chemical vapor deposition (MOCVD) method from palladium(Ⅱ) acetate precursor. Permeation properties of hydrogen and helium gas were studied as a function of the number of times of deposition of palladium on the peeling off phenomenon of palladium, which is common in electroless plated membrane, was observed. Silica was introduced into the pores to prevent the palladium grain from peeling off. The palladium-silica conjugated membrane does not show the peeling off phenomenon and can withstand the high temperature up to 800CCCC which is the upper limit of our apparatus. The separation factor for hydrogen gas over carbon dioxide gas was improved with the increase of number of times of silica coating by sacrificing the H2 permeation and finally increased to four times. The improvement on the separation of hydrogen gas over carbon dioxide for palladium-silica conjugated membrane was evaluated and a model of permeation pattern     

电沉积Zn-Fe合金的渗氢行为研究

用双电解池测氢法研究氯化物镀液体系中电沉积Zn-Fe合金过程中的渗氢行为.结果表明:在所考察的工艺参数中,镀液pH值对渗氢电流的影响最大.用慢应变速率拉伸试验法(SSRT)考察了电镀Zn-Fe合金试样的氢脆特性,并用扫描电子显微镜(SEM)对断口的微观形貌进行了表征.所有Zn-Fe合金镀层的试样均显示出不同程度的氢脆敏感性.     

Effect of Surface Concentration of Lu on Oxygen Permeation of Polycrystalline Alumina at High Temperatures

The effect of Lu surface concentration on oxygen permeation in polycrystalline α‐alumina wafers was determined at 1773 K under limited oxygen potential gradients (Δ), where the two surfaces of the wafer were deliberately subjected to different oxygen partial pressures [ (I) ?  (II)]. When oxygen permeation occurred mainly by oxygen GB diffusion under a Δ generated by a combination of low values, the Lu‐coating on the (I) [ (II)] surface decreased [increased] the oxygen permeability constants. When Δ was the result of a combination of high values, where oxygen permeation proceeded mainly by aluminum GB diffusion, the oxygen permeability constants were decreased only by the Lu‐coating on the (I) surface. The analysis of mass transfer parameters, such as the chemical potentials, GB diffusion coefficients, and fluxes of aluminum and oxygen in the wafers, suggested that ambient oxygen molecules were effectively attracted toward Lu‐coated surfaces exposed to low‐ environments, leading to a change in oxygen permeability.     

Initial Stages of Sintering of Alumina by Thermo-Optical Measurements

The behavior of nanostructured and submicrometer α-Al₂O₃ powders during the initial stages of field-assisted sintering technique (FAST), conventional, and microwave sintering was investigated using the laser-flash technique for thermo-optical measurements (TOM). An enhanced neck formation due to surface diffusion at very early stages of sintering was found in FAST samples. No significant difference due to heating rate has been found in these various samples.     

活性氧化铝在双氧水生产中的应用

介绍活性氧化铝在蒽醌法双氧水生产中的重要作用 ,总结影响氧化铝活性的因素及使用中应注意的问题     

Grain Boundary Sliding Microdisplacement Measurements During the Creep of Alumina

Grain boundary sliding (GBS) is thought to be the principal driving force for the nucleation, growth, and coalescence of grain boundary cavities during compressive creep of polycrystalline ceramics. It has been shown theoretically that stochastic GBS gives rise to continuous cavity nucleation and transient cavity growth and coalescence, eventually leading to crack formation and failure. This paper will show through experimental measurements, using stereoimaging techniques, that GBS is in fact stochastic. Also, mode II GBS, in-plane grain rotation, and in-grain shear displacements, strains, and strain rate measurements during creep of Lucalox Al₂O₃ will be presented. These displacements, measured on a machine vision system, will be presented in terms of the surrounding microstructural constraint and their lack of angular relation to the compressive load axis.     

J-Integral Measurements of the Fracture of 50% Alumina Refractories

The J -integral experimental technique was used to study fracture initiation in burned refractory bricks and refractory casta-bles of the 50% alumina variety. In a comparison of J _Ic and G_Ic, and 2 y_wof it is consistently observed that G _Ic Ic<2ry _Wof. The quantities ( J _Ic -G _Ic) or ( J _IC/ G _IC), as well as ( 2y _wof/ G _Ic), can be applied to estimate the inelastic energy contribution to the crack-tip process zone of these refractories. The latter two parameters distinctly classify the burned bricks and the casta-bles into different fracture characteristics. As such, these parameters are potentially very useful in the microstruetural design of refractories.     

Differential Permeation of Hydrogen Sulfide through a Microporous Vycor-Type Glass Membrane in the Separation System of Hydrogen and Hydrogen Sulfide

Abstract

The differential permeation of hydrogen sulfide through a microporous Vycor-type glass membrane was found in the hydrogen and hydrogen sulfide separation system. Separation factors of less than 1.0 were obtained at 10°C under higher pressures of a feed gas mixture having a low hydrogen concentration.     

Grain Boundary Sliding Measurements during Tensile Creep of a Single-Phase Alumina

The grain boundary sliding (GBS) behavior of a single-phase (relatively coarse-grained) alumina material was studied after tensile creep experiments were performed at 1500°C at stress levels of 20 and 35 MPa. Specimens tested at 35 MPa exhibited a number of modes of GBS, including Mode II (shear) displacements, Mode I (opening) displacements, out-of-plane sliding displacements, and in-plane grain rotation. Strains in the grain boundaries due to Mode II GBS ranged from 940% to 4400%. Average Mode II GBS displacements ranged from 0.08 to 0.29 µm in samples tested for 120 and 480 min, respectively, at 35 MPa. The GBS displacements were shown to fit a Weibull distribution. Tensile creep under a 35 MPa stress yielded a GBS rate of 9.5 10^-6µm/s, while the 20 MPa stress resulted in a GBS rate of 2.2 10^-6µm/s. The average Mode II GBS displacements increased linearly with specimen strain, suggesting that GBS may play an important role in creep cavitation during tensile creep. The data also revealed that compatibility and constraint rules appear to govern GBS behavior during tensile creep. GBS behavior during compressive creep will be compared to the tensile creep GBS measurements presented.     

Sintering of Translucent Alumina in a Nitrogen–Hydrogen Gas Atmosphere

The sintering of alumina doped with magnesia-based additives to translucency previously has been possible only in atmospheres of hydrogen or oxygen or under vacuum. This paper reports on the sintering of alumina in N₂–H₂ atmospheres that contain as little as 2% H₂, where optical transparency that is equivalent to that of normal H₂ sintering is achieved. In an effort to explain these results, experiments that vary the content of H₂ and H₂O, as well as the changes in the dynamic atmosphere, have been conducted. The evidence indicates that the final-stage sintering involves a point-defect pair mechanism that includes hydrogen interstitials and nitrogen solutes.     

In Situ Measurements of Frictional Bridging Stresses in Alumina Using Fluorescence Spectroscopy

Fracture of a large-grained alumina polycrystal has been examined in situ by optical microscopy. Concurrently, local bridging stresses, as generated by friction or tension of unbroken ligaments in the wake of the crack path, were measured by piezospectroscopy. Stress measurements were performed both at fixed sites as a function of the external load and at a fixed external load along the crack profile. Frictional stresses were similar/congruent50 MPa, while unbroken ligaments between the crack faces were found to support tensile stresses up to similar/congruent100 MPa. The maximum bridging stress was dictated by the weak (intrinsic) interface bonding of the polycrystal. Average bridging stresses, either theoretically calculated from R -curve data or experimentally measured by piezospectroscopy on frictional/bridging sites, were similar. Such a circumstance enables us to explain the fracture behavior of polycrystalline alumina by considering crack-wake shielding as the main micromechanism contributing to toughening.     

硝酸浸渍法再生废活性氧化铝的微观结构研究

采用稀硝酸浸渍后再进行煅烧处理再生废弃活性氧化铝,从稀硝酸浓度、浸渍时间、两个方面探讨稀硝酸浸渍法对废活性氧化铝性能与结构影响.采用XRD,SEM等测试方法表征氧化铝的微观结构,采用N2吸附方法表征氧化铝的比表面与孔结构.结果表明:在煅烧温度为500℃,保温时间为2h的条件下,各试样形成的主晶相是(Al2O3)1.333间隙固溶体;最佳的稀硝酸浓度为8%,最佳的浸渍时间为10min,其对应的比表面积达到最大为:251.97m2/g.     

Measurements of Hydrogen Peroxide and Formaldehyde in Glendora,California

Gas-phase hydrogen peroxide (H₂O₂) and formaldehyde (HCHO) were measured in Glendora, CA from August 14 to 21, 1986. These measurements were part of the Carbonaceous Species Methods Comparison Study sponsored by the California Air Resources Board. Both of these species were measured using enzymatic techniques, H₂O₂ by the peroxidase catalyzed dimerization of p-hydroxyphenylacetic acid and formaldehyde by the formaldehyde dehydrogenase catalyzed reduction of NAD+ to NADH. Both H₂O₂ and HCHO showed a strong diurnal variation with the highest concentrations measured during the period of maximum photochemical activity. H₂O₂ concentrations ranged from < 0.1 ppbv at night to a maximum of 3 ppbv for the hourly average on one day. The HCHO concentrations ranged from a low of 5 ppbv a night to a maximum of 20 ppbv during the day.