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71.
Syed Sohail Akhtar Abul Fazal M. Arif Bekir Sami Yilbas 《The International Journal of Advanced Manufacturing Technology》2012,58(1-4):57-70
Controlled gas nitriding represents one of the most important factors in enhancing the service life of AISI H13 steel dies used for the hot extrusion of aluminum alloys. Such surface-hardening treatment is used repeatedly to re-harden the die surface, which has been exposed to high temperature and abrasion by extruding the aluminum alloy, resulting in the wearing away of the existing nitride layer. Therefore, after certain extrusion cycles, dies require re-nitriding. In the present work, the influence of repeated nitriding on AISI H13 steel is studied. Single-, double-, and triple-nitrided samples, treated under controlled two-stage gas nitriding process, have been included in the study to evaluate their nitride layer morphology, hardness, case depth, and quality. Both experimental and numerical results are presented and compared. In the experimental part, the nitride layers are characterized using different techniques including optical microscopy, scanning electron microscopy, X-ray diffraction analysis, microhardness analysis, and energy-dispersive spectrometry technique. A sequentially coupled heat diffusion analysis of re-nitriding treatments are also conducted numerically using finite element code, ABAQUS. The numerically predicted results are in close agreement with experimental results in terms of nitride layer growth and nitrogen concentration distribution in the diffusion zone. The experimental results reveal that multiple-nitriding treatment on H13 steel has a significant effect on compound layer thickness and its phases, diffusion zone depth and its microstructure, hardness–depth profile, and nitride case depth. It was found that excessive cumulative nitriding time during multiple-nitriding treatment results in greater nitride depth and a significant increase in hardness with deeper effect due to the dense and deeper precipitation of nitrides in the diffusion zone. Multiple-nitrided samples show oxidation and porosity in the near-surface part of the nitrided layer due to the interaction of iron with oxygen of the air upon decomposition of iron nitrides in the compound layer during re-nitriding. This results in reduced toughness and hardness in the near-surface part of the nitride layers. 相似文献
72.
The relationship between molecular gel-forming compound-based double-alkylated l-glutamide-derived functional group-integrated organic phase (Sil-FIP) structure and chromatographic performance is investigated and compared with widely used alkyl phases (C(30), polymeric and monomeric C(18)) as references. The functional group-integrated molecular gel on silica is chemically designed newly in a way that the weak interaction sites are integrated with high orientation and high selectivity can be realized by multiple interactions with the solutes. Its functions can be emphasized by being immobilizable with a terminal carboxyl group and the fact that five amide bonds including β-alanine subunit are integrated per molecule. Furthermore, its self-assembling function can be detected by monitoring of the chiroptical property. Temperature-dependent circular dichroism (CD) intensity was determined as an indicator of chirality for the gel forming compounds. (13)C cross-polarization magic angle spinning (CP/MAS) NMR spectra of the Sil-FIP phase indicate that predominance of gauche conformations exists at higher temperature (above 30 °C). (29)Si CP/MAS NMR were carried out to investigate the degree of cross-linking of the silane and silane functionality of the modified silica. Temperature-dependent (13)C CP/MAS NMR and suspended-state (1)H NMR measurements of the Sil-FIP phase exhibit the dynamic behavior of the alkyl chains. To correlate the NMR and CD results with temperature-dependent chromatographic studies, standard reference materials (SRM 869b and SRM 1647e), column selectivity test mixture for liquid chromatography was employed. Additional shape selectivity text mixtures were also used to clarify the mechanism of shape selectivity performance of Sil-FIP compared with commercially available columns. The evaluation with the spectroscopic and chromatographic analyses presents very important information on the surface morphology of the new organic phase and the molecular recognition process. Integrated and ordered functional groups were investigated to be the main driving force for very high molecular shape selectivity of the Sil-FIP phase. 相似文献
73.
Sarmishtha Ghoshal Abul AM Ansar Sufi O Raja Arpita Jana Nil R Bandyopadhyay Anjan K Dasgupta Mallar Ray 《Nanoscale research letters》2011,6(1):540
A uniformly distributed array of micro test tubes and microbeakers is formed on a p-type silicon substrate with tunable cross-section and distance of separation by anodic etching of the silicon wafer in N, N-dimethylformamide and hydrofluoric acid, which essentially leads to the formation of macroporous silicon templates. A reasonable control over the dimensions of the structures could be achieved by tailoring the formation parameters, primarily the wafer resistivity. For a micro test tube, the cross-section (i.e., the pore size) as well as the distance of separation between two adjacent test tubes (i.e., inter-pore distance) is typically approximately 1 μm, whereas, for a microbeaker the pore size exceeds 1.5 μm and the inter-pore distance could be less than 100 nm. We successfully synthesized superparamagnetic iron oxide nanoparticles (SPIONs), with average particle size approximately 20 nm and attached them on the porous silicon chip surface as well as on the pore walls. Such SPION-coated arrays of micro test tubes and microbeakers are potential candidates for biosensors because of the biocompatibility of both silicon and SPIONs. As acquisition of data via microarray is an essential attribute of high throughput bio-sensing, the proposed nanostructured array may be a promising step in this direction. 相似文献
74.
Guo Zhong Abul Kalam Ayed Sad Al-Shihri Qingmei Su Jie Li Gaohui Du 《Materials Research Bulletin》2012,47(6):1467-1470
We have grown large-scale well-aligned ZnO nanorods/nanowires on commercial flexible graphite sheet (FGS) at low temperature via chemical vapor deposition method. The products were characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The effects of the growth temperature and oxygen flow rate on the morphology of ZnO nanostructures have been investigated. The growth mechanism of ZnO is found to be a self-catalytic vapor–solid process assisted by the immiscibility of ZnO with graphite. The as-grown ZnO/FGS products show strong green emission and their photoluminescence properties can be tuned by changing growth condition or annealing treatment. 相似文献
75.
Solute-solute interactions in pure organic liquids are much easier to determine than solute-solute interactions in a complex organic mixture such as a middle distillate fuel. This paper presents a method for the determination of solute-solute interaction and infinite dilution diffusion coefficient of hydrogen bond donor-acceptor species using ultralow conductance measurement. A theoretical framework was developed to obtain both complexation equilibrium constant (K) and infinite dilution diffusion coefficient, D° from a single set of measurements. These equations were applied for the study in hexadecane, a model hydrocarbon, and in jet fuel. The D° for methanol in jet fuel, 1.38 × 10-4 cm2 s-1, is indicative of hydrophobic environments for the polar solutes in hydrocarbons media. The conditional equilibrium constant, K', was found to be maximum for methanol in jet fuel, which indicates the presence of strong hydrogen bond acceptors in jet fuel. The present method is fairly general and applicable to polar and polarizable species in hydrocarbon media. 相似文献
76.
Abstract The groundwater arsenic contamination problem in Bangladesh is the worst in the world. Two hypotheses are prevailing as the cause (mobilization) of groundwater arsenic contamination in Bangladesh. One is called “pyrite oxidation” and the other is “oxy-hydroxide reduction.” According to the first hypothesis, groundwater arsenic contamination is human-made, which has a relationship with excessive groundwater withdrawal. On the other hand, according to the second one, the contamination is natural. The British Geological Survey (BGS) conducted an investigation to identify the cause of groundwater arsenic contamination in Bangladesh. Based on their findings, they rejected the pyrite oxidation hypothesis and accepted the oxy-hydroxide reduction hypothesis. However, several experts are opposing their research findings. Therefore, a case study is undertaken to examine the validity of the BGS findings. Although we obtained results which are similar to the BGS, the errors in the estimates of percent of wells contaminated, the key parameter of these analyse show that the present as well as BGS results are not dependable to make any conclusion about the cause of contamination. Moreover, the validity test shows that space-dependent relationships among different hydro-geological parameters for the heterogeneous aquifer system are not valid to represent time-dependent phenomena. Therefore, the conclusion made by the BGS is not valid. Still, there is a possibility that the pyrite oxidation hypothesis could be accepted. For a final conclusion we must observe these relationships in a time domain by generating reliable time-dependent field data. 相似文献
77.
The regeneration of activated carbon was studied using the wet air oxidation process in the temperature range of 150–240°C and oxygen partial pressure range of 0.2 to 1.0 MPa. Phenol was used as substrate. The overall mechanism of regeneration has been analysed and the different steps taking place during the regeneration process were individually investigated. Kinetics of oxidation of phenol and oxygen mass transfer coefficients have been estimated in the ranges of temperature and pressure studied. Oxidative degeneration characteristics of activated carbon were also studied. The conditions of temperature and pressure have been found at which the extent of regeneration is favourable. 相似文献
78.
Abdalla M. ABDALLA Shahzad HOSSAIN Pg MohdIskandr PETRA Mostafa GHASEMI Abul K. AZAD 《Frontiers in Energy》2020,14(2):359
The main concerns in the world today, especially in the energy field, are subjected to clean, efficient, and durable sources of energy. These three aspects are the main goals that scientist are paying attention to. However, the various types of energy resources include fossil and sustainable ones, but still some challenges are chasing these kinds from energy conversion, storage, and efficiency. Hence, the most reliable and considered energy resource nowadays is the utilized one which is as highly efficient, clean, and everlasting as possible. So, in this review, an attempt is made to highlight one of the promising types as a clean and efficient energy resource. Solid oxide fuel cell (SOFC) is the most efficient type of the fuel cell types involved with hydrogen and hydrocarbon-based fuels, especially when it works with combined heat and power (CHP). The importance of this type is due to its nature of work as conversion tool from chemical to electrical for generation of power without noise, pollution, and can be safely handled. 相似文献
79.
Mohammad Abul Kashem Hongzhao Li Lewis Ruxi Liu Binhua Liang Robert Were Omange Francis A. Plummer Ma Luo 《International journal of molecular sciences》2021,22(15)
FREM1 (Fras-related extracellular matrix 1) and its splice variant TILRR (Toll-like interleukin-1 receptor regulator) have been identified as integral components of innate immune systems. The potential involvement of FREM1 in HIV-1 (human immunodeficiency virus 1) acquisition was suggested by a genome-wide SNP (single nucleotide polymorphism) analysis of HIV-1 resistant and susceptible sex workers enrolled in the Pumwani sex worker cohort (PSWC) in Nairobi, Kenya. The studies showed that the minor allele of a FREM1 SNP rs1552896 is highly enriched in the HIV-1 resistant female sex workers. Subsequent studies showed that FREM1 mRNA is highly expressed in tissues relevant to mucosal HIV-1 infection, including cervical epithelial tissues, and TILRR is a major modulator of many genes in the NF-κB signal transduction pathway. In this article, we review the role of FREM1 and TILRR in modulating inflammatory responses and inflammation, and how their influence on inflammatory responses of cervicovaginal tissue could enhance the risk of vaginal HIV-1 acquisition. 相似文献
80.
Shahzad Hossain Abdalla M. Abdalla Nikdalila Radenahmad A.K.M. Zakaria Juliana H. Zaini S.M. Habibur Rahman Sten G. Eriksson John T.S. Irvine Abul K. Azad 《International Journal of Hydrogen Energy》2018,43(2):894-907
The BaCe0.7Zr0.1Y0.2?xZnxO3?δ (x = 0.05, 0.10, 0.15, 0.20) has been synthesized by the conventional solid state reaction method for application in protonic solid oxide fuel cell. The phase purity and lattice parameters of the materials have been studied by the room temperature X-ray diffraction (XRD). Scanning electron microscopy (SEM) has been done for check the morphology and grain growth of the samples. The chemical and mechanical stabilities have been done using thermogravimetric analysis (TGA) in pure CO2 environment and thermomechanical analysis (TMA) in Argon atmosphere. The XRD of the materials show the orthorhombic crystal symmetry with Pbnm space group. The SEM images of the pellets show that the samples sintered at 1200 °C are highly dense. The XRD after TGA in CO2 and thermal expansion measurements confirm the stability. The particles of the samples are in micrometer ranges and increasing Zn content decreases the size. The conductivity measurements have been done in 5% H2 with Ar in dry and wet atmospheres. All the materials show high proton conductivity in the intermediate temperature range (400–700 °C). The maximum proton conductivity was found to be 1.0 × 10?2 S cm?1 at 700 °C in wet atmosphere for x = 0.10. From our study, 10 wt % of Zn seems to be optimum at the B-site of the perovskite structure. All the properties studied here suggest it can be a promising candidate of electrolyte for IT-SOFCs. 相似文献