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1.
Hydrogen is the lightest element in nature, and so, its detection and quantitative analysis is difficult by the conventional
methods utilized for other elements. In the recent years the technique of elastic recoil detection analysis (ERD) using 1–2
MeV He+ beam has been developed to quantitatively and simultaneously analyze hydrogen and its isotopes in solids. Such a facility
has been set up using the 2 MeV Van-de-Graaff accelerator at IIT Kanpur. It facilitates H and D analysis in a material up
to a depth of ∼ 1μm with a detection sensitivity of 0·1 at.% and depth resolution of about 300 ?. The application potential of this setup is
illustrated by presenting the results of measurements performed on Al:H:D systems prepared by plasma source ion implantation
and highT
c YBCO pellets exposed to humid atmosphere. 相似文献
2.
3.
Quantitative fractography: A modern perspective 总被引:1,自引:0,他引:1
K. Banerji 《Metallurgical and Materials Transactions A》1988,19(4):961-971
The important aspects of quantitative fractography as a new analytical tool for understanding material fracture are discussed.
The special considerations that rise in the quantification problems are examined from the purview of stereology. Two major
experimental techniques for obtaining geometrical information about the fracture surface topography are critically evaluated.
These methods are based on stereophotogrammetry or vertical sectioning procedures-both of which yield estimates of the true
fracture surface area. The profile and surface roughness parameters which are required to transform measurements made on flat
SEM fractographs to the true quantities in the fracture surface are introduced. The two roughness parameters are related by
a simple parametric equation, permitting the fracture surface area to be calculated from the experimental measurement of the
profile roughness parameter. Alternatively, it is shown how the fracture surface area can be obtained from the angular distribution
of the profile elements by employing a transform procedure. The concept of “fractals” as it applies to quantitative fractography
is introduced. Recently developed relationships which describe the true variation of the profile and surface roughness parameters
with the size of the measuring unit are presented. Calculations are made of the mean area and perimeter length of dimples
in the fracture surface of a 4340 steel. Three fracture surface configurations are examined: (1) an assumed flat- , (2) an
assumed randomly-oriented- , and (3) the actual partially-oriented fracture surface. Significant differences are demonstrated
between the true and the assumed situations, illustrating the importance of quantitative methods in fractography. By means
of examples, it is shown how the quantitative methods permit detection of subtle changes in the fracture surface topography
as influenced by the materials’ microstructure.
This paper is based on a presentation made at the symposium “Stochastic Aspects of Fracture” held at the 1986 annual AIME
meeting in New Orleans, LA, on March 2-6, 1986, under the auspices of the ASM/MSD Flow and Fracture Committee. 相似文献
4.
The effect of electron beam irradiation on ethylene‐propylene terpolymer (EPDM) was investigated. A 50‐part oil‐extended EPDM with high termonomer (ENB) content (iodine number of base polymer) 19, was selected for this study. An increase in irradiation dose from 0 to 200 kGy resulted in increased crosslinking, measured by an increase in gel contents and better swelling resistance. The effect of the multifunctional monomer trimethylol propane trimethacrylate (TMPTMA) as a crosslink promoter was studied using IR spectroscopy. The IR studies revealed enhanced peak absorbances at 1725, 1257, and 1023 cm?1 as a result of the increased concentration of C = O and C‐O‐C groups and reduced absorbance at 1630 cm?1 due decreased concentration of C = C groups with TMPTMA level in the irradiated samples. The presence of TMPTMA increased the level of crosslinking at a given irradiation dose, which was manifested by improvement in tensile properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 968–975, 2005 相似文献
5.
6.
Metallographic investigation of TiC nucleants in the newly developed Al-Ti-C grain refiner 总被引:8,自引:0,他引:8
For grain refinement of aluminium and its alloys, a new aluminium-based master alloy containing TiC nucleants was developed a few years ago, by reacting carbon with Al-Ti binary alloy melt. However, as the melt was held at the usual melting temperatures of below 1273 K, the resultant master alloy lost its grain-refining efficiency, and so this phenomenon was called the poisoning effect. Nevertheless, a superheating treatment of the melt at higher temperatures (> 1523 K) rejuvenated the nucleant particles. The present investigation, dealing with electron diffraction of carbide particles extracted from the poisoned master alloy, revealed massive formation of Al4C3 and Ti3AlC, of which Al4C3 appears to account for the poisoning of TiC nucleants. On the other hand, subsequent electron diffraction studies on the rejuvenated nucleants confirmed that they were essentially composed of uncontaminated TiC. 相似文献
7.
Phase-precipitation studies have been performed on samples of the metallic glasses Fe79B16Si5 and Fe78B13Si9, heated in the range 300–475 °C for various times (1–16 h) using 57Fe Mössbauer transmission spectroscopy and X-ray diffraction methods. These measurements have helped in identifying the temperature ranges and annealing durations in which the amorphous structure of these metallic glasses is retained. The results revealed that the thermal stability increases as boron is replaced by silicon in the Fe-B-Si metallic glasses and that these alloys remain amorphous below 450 °C. The various phases precipitated above this temperature were identified as -Fe, -(Fe, Si), Fe3B, and Fe2B. The direction of magnetization in the two metallic glasses appears to change upon annealing. 相似文献
8.
The fracture behavior of glass-cloth-reinforced composites has been studied. Fracture of these composites proceeds by tensile failure of fibers rather than by the shear failure of the matrix or the interface. Although the spread of damage in these composites is restricted to small distances away from the crack path due to the interweaving of the fibers, this distance is found to be appreciably larger for the samples with smaller initial crack lengths. Characteristic distances associated with the Whitney-Nuismer criteria are, in turn, found to be smaller for these composites than for the angle ply laminates or randomly oriented short-fiber composites reported in literature in which the spread of the damage is much greater. Analysis through the crack growth resistance also supports this correlation with the extent of damage spread and indicates that the critical crack length for these composites may be equal to the best fit value of the characteristic distance of the average stress criterion. 相似文献
9.
Waisner S Hansen L Fredrickson H Nestler C Zappi M Banerji S Bajpai R 《Journal of hazardous materials》2002,95(1-2):91-106
Biodegradation of 14C-tagged hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was studied in aerobic, anaerobic, and anaerobic/aerobic slurries to identify the conditions maximizing RDX-mineralization in Cornhusker Army Ammunition Plant (CAAP, NE) groundwater. Supplementation with phosphate and adequate quantities of acetate caused 25% mineralization of RDX in 3 weeks by microorganisms native to CAAP. Under anaerobic conditions, the same supplementation resulted in 20% mineralization in 3 weeks and 30% mineralization in 6 weeks. The highest degree of mineralization (50%) was obtained under aerobic conditions when the contaminated groundwater was augmented with a consortium of three microbes isolated from another RDX contaminated soil (Hastings, NE) in addition to supplemented with phosphate and acetic acid. Use of complex organic sources (potato or corn starch) slowed down the rates of mineralization under anaerobic conditions, but rapid mineralization ensued as soon as the aerobic conditions were created. Final RDX concentrations in aqueous phase were below detection limit under most conditions. Assimilation of RDX by the cells was negligible. 相似文献
10.
The stepwise protonation constants of the ligand and the stability constants of Alizarin Red S with some bivalent metal ions, Pb2+, Cu2+, Zn2+, and Hg2+ have been determined at 30° and at various ionic strengths viz. 0.02, 0.05, 0.15 and 0.20, maintained by sodium perchlorate solution. The formation of the chelate is evident from the shift between the (i) ligand and (ii) ligand and metal titration curves. From the values of the stepwise protonation constants and metal ligand stability constants at various ionic strengths, thermodynamic formation constants were evaluated by extrapolation to zero ionic strength. The order of stability constants was found to be: Cu > Pb > Zn > Hg 相似文献