Showing papers by "Applied Science Private University published in 1984"

Thermal Transport Measurements in 1.05 µm Laser Irradiation of Spherical Targets

Abstract: Transport and implosion experiments have been conducted on the OMEGA, 24-beam, uniform-irradiation facility that may result in significant revisions in our current understanding of thermal transport in laser-irradiated targets: (a) Thermal transport in spherical irradiation cannot be described in terms of a simple flux-limited inhibition model. (b) Classical transport is found to be inadequate also: the heat front has a different shape (falling more gradually) than that predicted by either classical or flux-limited transport models for any level of inhibition. (c) A multi-group (non-local) treatment of transport in which faster than the average thermal electrons penetrate deeper, results in a temperature profile which is in qualitative agreement with the present measurements. (d) The enhanced inward penetration studied here appears to supercede preheat by resonance-absorption electrons, but to have a weaker dependence on the irradiance than is the case for the latter mechanism; this would reduce the incentive to go to lower irradiance in order to reduce preheat. (e) Target implosion experiments show higher core temperatures than predicted by an inhibited flux model and lower densities than predicted by an uninhibited flux model. (f) Single-beam plane-target experiments appear to show flux inhibition only because of some 2D effects; these may be subtler than simple lateral heat transport. (g) There are indications that in short wavelength irradiation the higher collisionality suppresses the deeper penetration measured here. This would mean that for the same absorbed irradiance the shorter wavelength laser produces a higher pressure gradient (and efficiency).

Thermal shock of ß-alumina with zirconia additions

Abstract: Sodiumβ-alumina electrolyte tubes were prepared from spray dried precursor powders with additions of 2, 5, 10 and 15 wt % ZrO2 made by the sodium zirconate route. The thermal shock behaviour of ring segments cut from the tubes was examined by quenching into water at 0° C. At the 2% ZrO2 level the dispersed ZrO2 particle size was low, <0.5μm, and the tetragonal phase was retained. For higher weight fractions, particle coarsening during theβ-alumina sintering schedule was extensive and the large particles transformed to monoclinic on cooling. At the 15% ZrO2 level theβ-alumina had a slightly reduced strength and high resistance to thermal shock and to thermal shock damage, quenching into water from 800° C effecting only a 43% reduction in strength. These observations are consistent with the effects of microcracking in the vicinity of second phase ZrO2 particles.

The thermal shock of ß-alumina

Abstract: The thermal shock of sodiumβ-alumina with relative densities from 60 to 98% theoretical has been investigated over the temperature range 150 to 700° C by quenching into water. The samples were ring segments cut from electrolyte tubes and were subsequently tested in both compression and tension. For relative densities of 75% and below the thermal shock damage was typical of stable crack growth and a steady decline in strength with sintering temperature was observed. For relative densities of 95% and above, thermal shock causes unstable crack growth and a critical value of ΔT was observed in the range 170 to 250° C depending on initial strength. From the linear relationship between observed ΔTc and the thermal shock resistance parameter,R, it was concluded that the rapid heat transfer during quenching was nucleate water boiling and that cooling from ∼110° C to 0° C was not responsible for damage. The fracture stress after thermal shock above ΔTc was consistent and showed little dependence on initial strength for relative densities ⩾95%. However, the fractional reduction in strength was related to the damage resistance parameterR‴. An estimate of the energy expended in fracture has been made, based on microscopic observation and compared with estimates of the stored strain energy due to thermal stresses.

Study of rubber oxidation by thermoanalysis

Abstract: A method using the DSC was utilized whereby the oxidation of natural rubber was studied by adapting the procedures developed by Kissinger, Doyle, and Ozawa for thermoanalysis. Thus oxidative induction time of several hours for a particular rubber sample can be estimated in a relatively short time. Some of the results of this method are compared with those from other established methods, the estimated oxidative induction time showing a good correlation with some of the systems tested. The validity and limitations of this method are discussed.