Embrittlement of 4130 steel by low-pressure gaseous hydrogen

A study has been made of the embrittlement of fully hardened 4130 steel in low-pressure, <760 torr, gaseous hydrogen. It was found that the embrittlement was caused by hydrogen-induced, slow crack growth. In the range of temperature from 80° to 25°C, the crack growth rate increased with decrease in temperature; in the range from 0° to ?80°C, the rate decreased with decrease in temperature. It was also found that the crack growth rate had a different pressure dependence at high temperatures than at low temperatures. From a consideration of these experimental data as well as data from earlier investigations, it was determined that gaseous-hydrogen embrittlement and the embrittlement of hydrogen-charged steels are basically the same phenomenon. The data are discussed in terms of a surface-reaction model that adequately explains both gaseous-hydrogen embrittlement and the embrittlement of hydrogencharged steels.     

Effects of gaseous hydrogen on fatigue crack growth in pipeline steel

The effects of hydrogen on crack growth rates in a moderate-strength pipeline steel subjected to cyclic loads were studied. Fatigue crack growth experiments were conducted in high-pressure hydrogen and nitrogen environments, and the influences of stress ratio, stress intensity, and cyclic loading frequency on hydrogen-accelerated fatigue crack growth were investigated. Hydrogen acceleration of intermediate-rate (Stage II) crack growth was greatest at low stress ratios and decreased to approximately zero at a stress ratio of about 0.5. However, hydrogen promoted the premature onset of accelerated (Stage III) crack growth. This appeared to be related to a hydrogen-induced reduction of fracture toughnessJ _IC.     

Proteins and glycoproteins of membranes from developing chick red cells

Membrane vesicles produced when chick erythroid cells are disrupted by nitrogen cavitation were isolated by centrifugation in a sucrose step gradient and purified on a linear sucrose gradient. Sodium dodecyl sulfate-polyacrylamide gel analysis of isolated membranes shows eight to ten proteins and four to five glycoproteins. Membranes must be prepared with protease inhibitors, otherwise an endogenous activity degrades high molecular weight polypeptide components. Red cells from several stages of development (5- and 17-day embryos and adult chickens) all appear to have the same major embrane proteins. However, primitive erythroid cells from 5-day embryos lack a Mr = 40,000 glycoprotein that is present in definitive erythrocytes from 17-day embryos and from adult chickens; erythrocytes from young chicks show a decrease in the amount of a glycoprotein of Mr = 50,000. Lactoperoxidase-catalyzed iodination of intact 5-day embryonic red cells detects three surface components which comigrate with the membrane glycoproteins on sodium dodecyl sulfate polyacrylamide gels.     

粉末粒度对储氢合金电化学性能与气态储氢性能的影响

采用真空中频感应熔炼炉熔炼La_(0.67)Mg_(0.33)Ni_(2.5)Co_(0.5)合金,机械研磨成粉,分级过筛得到一系列不同粒度的合金粉末(平均粒度为10μm、53μm、77μm、119μm、196μm),通过XRD、SEM、激光衍射法等方法系统地研究分析了粉末粒度对储氢合金La_(0.67)Mg_(0.33)Ni_(2.5)Co_(0.5)气态储氢性能和电化学性能的影响。不同粒度合金气态吸放氢循环后都发生了不同程度的粉化,大颗粒以表面剥落的方式产生细粉,小颗粒以体断裂的方式粉化,小颗粒的抗粉化能力更强,电化学循环后,合金粉末粉化造成粉末掉渣形成孔洞。粒度越小,气态储氢孕育期越短,活化时间越短,电化学活化性能越好。随着合金粒度的减小,理论最大放电容量和实际测试的最大放电容量也随之减小,而理论容量发挥值却在增加。随循环次数增加,气态饱和储氢量和电化学放电容量急剧下降,小粒度合金循环寿命略好于大粒度合金粉。     

A model for the initiation of hydrogen embrittlement cracking at notches in gaseous hydrogen environments

A model for the initiation of hydrogen embrittlement cracking in gaseous hydrogen environments is presented. The model is based on the stress-induced diffusion of hydrogen atoms to the regions of high triaxial stress ahead of a plastically strained notch. The influence of yield stress and notch geometry on the apparent threshold stress intensity for embrittlement are considered and derived analytically. The time dependence for crack initiation for apparent stress intensities above the threshold is derived from a simple diffusion model. The results of the model are in agreement with reported hydrogen embrittlement phenomena.     

氟化氢脱气系统改造的探析

脱气塔是确保氟化氢生产连续、优质、高产的金属化工设备.文章从生产实际出发,对脱气塔的主要故障"调节余量"进行了分析和研究,并实施了改造.经改造后,大大降低了系统压力,减少了跑、冒现象,提高了氟收率,降低了生产成本.     

Crack propagation of high strength steels in a gaseous hydrogen atmosphere

The crack propagation behavior in delayed fracture was investigated at room temperature under pressure up to 784 kPa of hydrogen gas for high strength steels with the tensile strength of 1500 or 2000 MPa. For specimens with the tensile strength of 1500 MPa, the crack propagation rateda/dt increased with C content from 0.21 to 0.42 wt pct, and then it decreased with increasing C content up to 0.53 wt pct.da/dt increased rapidly with Mn content from 0.009 to 0.84 wt pct, and it increased gradually with Mn content from 0.84 to 2.13 wt pct. The permeation flow of hydrogen from the crack tip surface could be qualitatively estimated from the dependence ofda /dt upon the hydrogen pressure based on the simple assumption. In addition to the grain boundary embrittlement caused by tempering and/or hydrogen, the permeation flow of hydrogen was used to explain qualitatively the dependence ofda/dt upon C or Mn content.     

Effect of scandium and zirconium alloying on microstructure and gaseous hydrogen storage properties of YFe3

RM₃ compounds (R = rare earth metals, M = transition metals) have rarely been studied for gaseous hydrogen storage applications because of unfavorable thermodynamics. In this work, the hydrogen storage properties of a single-phase YFe₃ alloy were improved by non-stoichiometric composition and alloying with Sc and Zr. Only the Y_1.1–ySc_yFe₃ (y = 0.22, 0.33) alloys consist of a single rhombohedral phase. The Sc substitution for Y leads to the reduction in the unit cell volume of the YFe₃ phase, and thus significantly increases the dehydriding equilibrium pressure and decreases the dehydrogenation temperature. The alloy Y_0.77Sc_0.33Fe₃ delivers a decomposition enthalpy change of 33.54 kJ/mol and a lowest dehydrogenation temperature of 135 °C, in comparison with 38.99 kJ/mol and 165 °C for the alloy Y_1.1Fe₃. The Zr substitution causes a similar thermodynamic destabilization effect, but the composition and microstructure of Y–Zr–Fe alloys need to be further optimized.     

A fractographic study of gaseous hydrogen embrittlement and liquid-metal embrittlement in a tempered-martensitic steel

Crack growth in D6ac steel in liquid mercury, gaseous hydrogen, and air environments was studied. Specimens were tested in the as-quenched condition and after tempering at various temperatures up to 700°C. In air, a dimpled transcrystalline fracture mode was observed for all heat-treatments. In mercury and hydrogen environments, the fracture mode and appearance depended on the heat-treatment but was remarkably similar in mercury and hydrogen environments for each condition. Quasi-cleavage, “brittle” intercrystalline fracture, dimpled intercrystalline fracture, and dimpled transcrystalline fracture modes were observed; the dimples observed after fracture in embrittling environments were generally shallower than those observed after fracture in air. The mechanisms of liquid-metal embrittlement and gaseous hydrogen embrittlement are discussed in the light of these observations and other work relevant to understanding the mechanisms of embrittlement. It is concluded that adsorbed atoms at crack tips facilitate dislocation nucleation or possibly decohesion, depending on the fracture mode.     

GalNAc-alpha-O-benzyl inhibits NeuAcalpha2-3 glycosylation and blocks the intracellular transport of apical glycoproteins and mucus in differentiated HT-29 cells

Exposure for 24 h of mucus-secreting HT-29 cells to the sugar analogue GalNAc-alpha-O-benzyl results in inhibition of Galbeta1-3GalNAc:alpha2,3-sialyltransferase, reduced mucin sialylation, and inhibition of their secretion (Huet, G., I. Kim, C. de Bolos, J.M. Loguidice, O. Moreau, B. Hémon, C. Richet, P. Delannoy, F.X. Real., and P. Degand. 1995. J. Cell Sci. 108:1275-1285). To determine the effects of prolonged inhibition of sialylation, differentiated HT-29 populations were grown under permanent exposure to GalNAc-alpha-O-benzyl. This results in not only inhibition of mucus secretion, but also in a dramatic swelling of the cells and the accumulation in intracytoplasmic vesicles of brush border-associated glycoproteins like dipeptidylpeptidase-IV, the mucin-like glycoprotein MUC1, and carcinoembryonic antigen which are no longer expressed at the apical membrane. The block occurs beyond the cis-Golgi as substantiated by endoglycosidase treatment and biosynthesis analysis. In contrast, the polarized expression of the basolateral glycoprotein GP 120 is not modified. Underlying these effects we found that (a) like in mucins, NeuAcalpha2-3Gal-R is expressed in the terminal position of the oligosaccharide species associated with the apical, but not the basolateral glycoproteins of the cells, and (b) treatment with GalNAc-alpha-O-benzyl results in an impairment of their sialylation. These effects are reversible upon removal of the drug. It is suggested that alpha2-3 sialylation is involved in apical targeting of brush border membrane glycoproteins and mucus secretion in HT-29 cells.     

Highly ameliorated gaseous and electrochemical hydrogen storage dynamics of nanocrystalline and amorphous LaMg12-type alloys prepared by mechanical milling

Nanocrystalline and amorphous LaMg12-type alloy-Ni composites with a nominal composition of LaMg11 Ni+x wt.% Ni (x=100, 200) were synthesized via ball milling.The influences of ball mill-ing duration and Ni adding amount x on the gaseous and electrochemical hydrogen storage dynamics of the alloys were systematically studied.Gaseous hydrogen storage performances were studied by a differential scanning calorimeter and a Sievert apparatus.The dehydrogenation activation energy of the alloy hydrides was evaluated by Kissinger method.The electrochemical hydrogen storage dynam-ics of the alloys was investigated by an automatic galvanostatic system.The H atom diffusion and ap-parent activation enthalpy of the alloys were calculated.The results demonstrate that a variation in Ni content remarkably enhances the gaseous and electrochemical hydrogen storage dynamics perform-ance of the alloys.The gaseous hydriding rate and high-rate discharge (HRD) ability of the alloys ex-hibit maximum values with varying milling duration.However, the dehydriding kinetics of the alloys is always accelerated by prolonging milling duration.Specifically, rising milling time from 5 to 60 h makes the hydrogen desorption ratio (a ratio of the dehydrogenation amount in 20 min to the saturat-ed hydrogenation amount) increase from 57% to 66% for x=100 alloy and from 57% to 70% for x=200.Moreover, the improvement of gaseous hydrogen storage kinetics is attributed to the descending of dehydrogenation activation energy caused by the prolonging of milling duration and growing of Ni content.     

Effect of electrodeposited metals on the permeation of hydrogen through iron membranes

The permeability of electrolytically charged hydrogen through annealed Ferrovac E iron membranes was found to decrease significantly upon coating the charging surface of iron with thin layers of either Pt, Cu or Ni (Watts or electroless). The absorption of hydrogen was delayed for a period which depends on the nature and the thicRness of the metallic coating. The results show that such coatings do not have to be thicR or even continuous to be effective, in which case a catalytic mechanism is proposed to explain the marRed reduction in hydrogen permeation through the iron. Experimental confirmation is presented of this catalytic mechanism and of the barrier mechanism which is operative in the presence of dense continuous coatings. It is also shown that a decrease in catalytic activity occurs with time (aging) and is pronounced in the presence of As³⁺ ion. Formerly Research Associate, The Pennsylvania State University     

Evaluation of fluoride uptake by enamel in children from fluoride dentifrices

Fluoride dentifrices are well accepted for their caries preventive effects. Although it is generally accepted that the presence of fluoride in the enamel protects teeth against carious attack, at the same time, there is some concern that ingestion of fluoride from toothpastes may substantially contribute to the total intake of this element. The present study was undertaken to clinically evaluate the fluoride uptake by human enamel after the use of lower concentrations of fluoride dentifrices and compare their potency to higher concentration in increasing the uptake of fluoride by enamel. Enamel biopsy was conducted on first permanent molars of 100 school children, aged 6-8 years before brushing and at intervals of one hour, 3 weeks, 6 weeks and 12 weeks following brushing with different concentrations of fluoride dentifrices. The fluoride content of the enamel biopsy samples were estimated using the Orion microprocessor ion analyser and by taking into consideration the enamel biopsy mass and depth of the etch. The results of the present study suggest that low fluoride concentration dentifrices provide similar fluoride uptake by enamel when compared with that of higher concentrations.     

A comparison of gaseous hydrogen embrittlement,slow-strain-rate hydrogen embrittlement,and stress-corrosion cracking InTi-8Ai-1Mo-1V

Metallographic, fractographic, and acoustic-emission studies have been carried out on the near-α commercial alloy, heat treated to produce the Widmanstätten structure and in some cases aged to precipitate α₂. Both aged and unaged material underwent GHE in ～ 10 kPa gaseous hydrogen, failure occurring along the α-β interface. Electron-diffraction studies established the presence of a layer of fee titanium hydride at the fracture surfaces, and acoustic-emission and fractographic observations indicated that propagation was discontinuous. The aged alloy underwent SSRHE in inert environments and SCC in 3 pct aqueous NaCl and, in contrast to GHE, failure occurred across the α-plates in both cases, producing indistinguishable cleavage-like fracture surfaces. Again, titanium hydride was detected at the fracture surfaces and, from acoustic-emission studies, crack propagation appeared to be discontinuous. Based on these observations, it is suggested that the three forms of failure occur by a common mechanism, namely by the repeated formation and rupture of the hydride phase.     

气态进样-电感耦合等离子体原子发射光谱法测定固体混合碱中的碳酸钠和碳酸氢钠

建立了带有气态二氧化碳发生技术的电感耦合等离子体原子发射光谱(ICP-AES)法测定固体碳酸钠和碳酸氢钠的方法。通过在线连续混合稀盐酸和含无机碳的样品溶液,使样品溶液中的无机碳形成气态二样化碳被测定。分别测定混合碱原样中的无机含碳量和原样品经120℃加热1 h后的无机含碳量,通过计算,从而获得样品中的碳酸钠和碳酸氢钠的含量。样品分析结果与常规的化学滴定法的分析结果有很好的吻合。