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81.
Evaluation of Slow Crack Growth Resistance in Ceramics for High-Temperature Applications 总被引:1,自引:0,他引:1
The slow (subcritical) crack growth (SCG) resistance of Si3 N4 and SiC ceramics has been evaluated by a stepwise loading test on bending bars precracked by Vickers indentation. Three highly refractory materials were selected for the evaluation: i.e., (1) high-purity Si3 N4 sintered by hot isostatic pressing (HIP) without additives and (2,3) α - and β - SiC pressureless sintered with B and C addition. Under the hypothesis of linear elastic behavior at high temperature, which was found satisfied in the present materials, the SCG resistance was expressed in terms of initial stress intensity factor critical for SCG failure within a predetermined lifetime. The present method was found useful in shortening the testing time and consistent with other traditional fatigue tests (e.g., static-fatigue test): It is recommended as a screening test for materials under research and development. Among the materials tested in the present study, the highest SCG resistance up to 1440°C was found in the high-purity Si3 N4 without additives. 相似文献
82.
The interaction between thin films of hydrogenated amorphous silicon and sputter-deposited chromium has been studied. Following
deposition of the chromium films at room temperature, the films were annealed over a range of times and temperatures below
350°C. It was found that an amorphous silicide was formed only a few nanometers thick with the square of thickness proportional
to the annealing time. The activation energy for the process was 0.55±0.05 eV. The formation process of the silicide was very
reproducible with the value of density derived from the thickness and Cr surface density being close to the value for crystalline
CrSi2 for all films formed at temperatures ≤300°C. The specific resistivity of the amorphous CrSi2 was ≈600 μΩ·cm and independent of annealing temperature. 相似文献
84.
85.
86.
E. S. C. O'Connor-Cox E. J. Lodolo B. C. Axcell 《Journal of the Institute of Brewing》1996,102(1):19-25
It is well known that dissolved oxygen fulfils critical roles in brewing yeast physiology and overall fermentative performance. The major and minor roles that have been identified are briefly discussed and another role, that of providing for minimal mitochondrial development and functionality, is suggested. The long accepted theory that mitochondria are irrelevant to fermentative performance is reviewed as to its basis and the evidence in support of it. However, minimal mitochondrial development is required to provide the cell with critical metabolic intermediates and components. These are identified and reviewed and finally, evidence is presented that mitochondria are critical to brewing yeast fermentative performance. The review concludes that when assessing the role of mitochondria, concern should be broader than simply for the energetic function of these organelles. 相似文献
87.
88.
大尺寸氟化铅晶体的生长 总被引:4,自引:1,他引:3
描述了不用高真空条件,在通常的Bridgman-Stockbarger炉中,用高温下的反应方法,消除了原料及生长炉内残存的O^2-及OH^-,生长出优质,大尺寸的β-PbF2晶体。在晶体生长时,出现的主要问题是在晶体中的针状结构及开裂,但可通过控制条件来解决。 相似文献
89.
The photoconductive properties of a carotenoid polyene,β-Apo-8′ carotenal in polycrystalline form has been studied. The growth of the photocurrent shows an overshoot in the growth-time
curve before steady state value is attained. This behaviour of photocurrent is proposed to be due to higher value of recombination
coefficient than trapping coefficient. From the temperature dependence study it is observed that the steady state photocurrent,
at first increases with increase of temperature, attains a maximum at a particular temperatureT
max and then decreases with temperature. TheT
max value agrees with the temperature above and below which steady state photocurrent is attained differently. Monomolecular
and bimolecular recombination processes at two temperature regimes are proposed to account for the observed behaviour. The
dependence of photocurrent with excitation light intensity and wavelength study provide information on the carrier generation
processes. The fast decay of photocurrent have been observed at different temperatures and from this study the decay constant
is calculated and it is found to be temperature independent. 相似文献
90.
In this paper, a unified method is presented: (i) to model delaminated stiffened laminated composite shells; (ii) for synthesising
accurate multiple post-buckling solution paths under compressive loading; and (iii) for predicting delamination growth. A
multi-domain modelling technique is used for modelling the delaminated stiffened shell structures. Error-free geometrically
nonlinear element formulations — a 2-noded curved stiffener element (BEAM2) and a 3-noded shell element (SHELL3) — are used
for the finite element analysis. An accurate and simple automated solution strategy based on Newton type iterations is used
for predicting the general geometrically nonlinear and postbuckling behaviour of structures. A simple method derived from
the 3-dimensionalJ-integral is used for computing the pointwise energy release rate at the delamination front in the plate/shell models. Finally,
the influence of post-buckling structural behaviour and the delamination growth on each other has been demonstrated. 相似文献