Differences between internal and external hydrogen effects on slow strain rate tensile test of iron-based superalloy A286

To investigate the evaluation method of hydrogen compatibility of A286 superalloy in high pressure hydrogen gas, SSRT tests of hydrogen-charged specimens were conducted at ambient temperature at various strain rates. The relative reduction in area (RRA), one of the ductility parameters, was determined. The hydrogen content in the hydrogen-charged specimen was the same as the equilibrium hydrogen content on the specimen surface at 150 °C in 70 MPa hydrogen gas. The strain rate dependence of RRA was smaller than that of RRA obtained in 70 MPa hydrogen gas at 150 °C. All the hydrogen-charged specimens showed slip-plane fractures in the grains in their cores. However, the specimens in 70 MPa hydrogen gas at 150 °C showed fracture surfaces morphology ranging from dimples to quasi-cleavages and intergranular fractures with decreasing strain rate. These dissimilarities are expected to arise from differences in the hydrogen concentration behaviors of the specimens during the deformation process.     

Slow strain rate technique for studying hydrogen induced cracking in 34CrMo4 high strength steel

Alloy hardened steels offer excellent combination of mechanical properties, hardenability and corrosion resistance. 34CrMo4 is a medium carbon, low alloy steel widely used due to a good combination of high-strength, toughness and wear resistance. However, this steel experiences hydrogen embrittlement (HE), a complex phenomenon depending on the composition and microstructure. This work estimates de loss of the mechanical properties caused by hydrogen in electrochemically H-charged specimens in absence of mechanical stress but also, at low strain rate and constant load. H-charging for 2 and 6 h induce YS losses of about 40% and 71% and UTS losses of 39% and 59%, respectively. The synergistic effect of the stress and the H-charging process leads to a higher loss, 91%, and a faster brittle fracture even though hydrogen content is similar to those firstly H-charged and then tested in air.     

缓释镍陶粒对废水厌氧处理的影响

以粉煤灰、水泥、石灰、石膏为主要原料,以CaCl2、Na2SO4、Na3PO4为复合添加剂,在制备陶粒过程中加入吸附Ni2+后的硅藻土,采用蒸气养护法制备出缓慢释放微量Ni2+的生物陶粒,并研究其对废水厌氧处理的影响。实验结果表明,陶粒对Ni2+的释放量与陶粒负载Ni2+质量、陶粒蒸养时间有关,陶粒释放平衡时间为9 d,起到了很好的缓释效果;通过在厌氧生物反应器中空白对照组与添加缓释Ni2+陶粒组的对比实验表明,添加缓释Ni2+反应器的COD去除率最高达到89.8%,比空白对照组高出23.6%,缓释陶粒释放出的Ni2+离子能够被微生物很好的吸收利用,提高废水厌氧处理效果,而不会造成水质的污染。     

Virus attenuation by microbial mechanisms during the idle time of a household slow sand filter

The biosand filter (BSF) is a household slow sand filter that is operated intermittently such that an idle time of typically 18-22 h occurs in between daily charges of water. Virus attenuation during the idle time was investigated over repeated daily filtration cycles to capture the effect of media aging that encompasses processes occurring throughout the filter depth rather than restricted to the schmutzdecke at the media surface. A threshold aging period of about one to two weeks was required before virus attenuation began. The observed rates of MS2 and PRD-1 reduction were first-order and reached maxima of 0.061- and 0.053-log per hr, respectively, over seven-to-ten weeks. Suppression of microbial activity by sodium azide eliminated virus reduction during the idle time thus indicating that the operative media aging process was microbially mediated. The mechanism of virus reduction was not modification of media surfaces by physical/chemical or microbial processes. Instead, it appears that the activity of the microbial community within the filter is responsible. The most likely biological pathways are production of microbial exoproducts such as proteolytic enzymes or grazing of bacteria and higher microorganisms on virus particles. Implications of these findings for BSF design and operation and their relevance to other biological filtration technologies are discussed.     

A 2D image-based multiphysics model for lifetime evaluation and failure scenario analysis of self-healing ceramic-matrix mini-composites under a tensile load

We propose a multi-physics numerical model for a self-healing ceramic matrix mini-composite under tensile load. Crack averaged PDEs are proposed for the transport of oxygen and of all the chemical species involved in the healing process and studied in the dimensionless form to perform the most appropriate discretization choices concerning time integration, and boundary conditions. Concerning the fibres’ degradation, a slow crack growth model explicitly dependent on the environmental parameters is calibrated using a particular exact solution and integrated numerically in the general case. The tow failure results from the statistical distribution of the fibres’ initial strength, the slow crack growth kinetics, and the load transfer following fibres breakage. The lifetime prediction capabilities of the model, as well as the effect of temperature, spatial variation of the statistical distribution of fibres strength, and applied load, are investigated highlighting the influence of the diffusion/reaction processes (healing) on the fibre breakage scenarios.     

Use of slow filtration columns to assess oxygen respiration, consumption of dissolved organic carbon, nitrogen transformations, and microbial parameters in hyporheic sediments

Biogeochemical processes mediated by microorganisms in river sediments (hyporheic sediments) play a key role in river metabolism. Because biogeochemical reactions in the hyporheic zone are often limited to the top few decimetres of sediments below the water-sediment interface, slow filtration columns were used in the present study to quantify biogeochemical processes (uptakes of O2, DOC, and nitrate) and the associated microbial compartment (biomass, respiratory activity, and hydrolytic activity) at a centimetre scale in heterogeneous (gravel and sand) sediments. The results indicated that slow filtration columns recreated properly the aerobic-anaerobic gradient classically observed in the hyporheic zone. O2 and NO3- consumptions (256 +/- 13 microg of O2 per hour and 14.6 +/- 6.1 microg of N-NO3- per hour) measured in columns were in the range of values measured in different river sediments. Slow filtration columns also reproduced the high heterogeneity of the hyporheic zone with the presence of anaerobic pockets in sediments where denitrification and fermentation processes occurred. The respiratory and hydrolytic activities of bacteria were strongly linked with the O2 consumption in the experimental system, highlighting the dominance of aerobic processes in our river sediments. In comparison with these activities, the bacterial biomass (protein content) integrated both aerobic and anaerobic processes and could be used as a global microbial indicator in our system. Finally, slow filtration columns are an appropriate tool to quantify in situ rates of biogeochemical processes and to determine the relationship between the microbial compartment and the physico-chemical environment in coarse river sediments.     

Effect of liquid oilfield-related media on slow crack growth behavior in polyethylene pipe grade materials

Polyethylene, as non-polar material, shows a high affinity especially to liquid non-polar aromatic and aliphatic hydrocarbons, and liquid hydrocarbons (LHC) to a certain extent migrate into the bulk material by sorption, leading to material plasticization (i.e., drop in modulus and yield stress). This paper aims to study the crack growth mechanism and failure behavior of commercial pipe grade materials when exposed to deionized water or LHC (90/10 wt% i-octane/toluene) under the simultaneous application of cyclic loads. The results of the cyclic crack growth experiments with three PE 100 pipe grades, using cracked round bar (CRB) specimens and performed at two different temperatures (35 °C and 60 °C), are compared in terms of the specimen lifetimes, and the micro-modes and kinetics of failure by referring to concepts of fracture mechanics. Most importantly, while crack advance is preceded by crack-tip crazing in water, shear yielding takes place at crack-tips in the LHC environment.     

Hydrogen embrittlement behavior of high strength low carbon medium manganese steel under different heat treatments

Hydrogen embrittlement (HE) behavior was investigated in a low carbon medium Mn steel with three different volume fraction of retained austenite (RA), which was obtained after different heat treatments. The hydrogen permeation test showed a higher permeability for directly water quenched specimen compared to quench-tempered specimens. Melt extraction test showed hydrogen concentration increased with hydrogen charging current density in the order of directly quenched specimen, QLA, quenched with low-temperature annealed specimens and QHA quenched with high-temperature annealed specimens. Slow strain-rate tensile test was employed to examine the HE behavior, the HE indices decreased with the increase of RA irrespective of increased hydrogen concentration. HE susceptibility can be suppressed by raising intercritical annealing temperature because Mn enrichment increases the stability of RA.     

Insight into biochar properties and its cost analysis

Biochars (BCs) are widely produced and used for the remediation of environmental contaminants as bio-sorbents. In this review, statistical analysis of different BC physico–chemical properties was conducted. It was observed that woody materials are the most suitable for preparing BCs, among many other potential raw materials such as food wastes and agricultural materials. Currently BCs are produced through a variety of thermal treatment processes between 300 and 900 °C, among which slow pyrolysis is widely used due to its moderate operating conditions and optimization of BC yields. Hydrothermal carbonisation (HTC) is also an effective approach for BC production under certain conditions. As pyrolysis temperature is increased, the carbon content, ash content, surface area, and pore volume tend to be increased while the yield, hydrogen, oxygen, nitrogen content, and H/C and O/C molar ratios tend to decrease. The economic feasibility of BCs depends on a range of factors from raw material price to efficient production technologies. Thus, the overall cost equation of a pilot BC production plant together with the cost equation for BC regeneration has been proposed. The future research directions of BCs are also elaborated.