Thin films of Al-1.27 wt %Y were deposited by dc magnetron sputtering. Adding yttrium to the aluminum drastically reduced the metal’s grain size and also improve the uniformity of grain size distribution. Upon anneal...
Thin films of Al-1.27 wt %Y were deposited by dc magnetron sputtering. Adding yttrium to the aluminum drastically reduced the metal’s grain size and also improve the uniformity of grain size distribution. Upon annealing at a temperature of 450 °C for 30 min, grain growth was insignificant, while the electrical resistance dropped from 6.05 to 2.95 μΩ cm. The as deposited films consisted of Al4Y and α-Al supersaturated with yttrium. After annealing, β-Al3Y precipitated instead of α-Al3Y. The Al–Y films had much higher resistance to hillock formation than did Al-1 wt %Si films.
Interaction between 96% alumina and three binary glasses used as frits in thick-film technology is studied, A possible interfacial reaction mechanism where a melt glass penetrates into the alumina through the grain bo...
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Interaction between 96% alumina and three binary glasses used as frits in thick-film technology is studied, A possible interfacial reaction mechanism where a melt glass penetrates into the alumina through the grain boundaries dissolving SiO2, one of the grain boundary components, is suggested, The formulation expressing the glass penetration rate into the alumina based on Poiseuille's law, assuming the driving force for the glass penetration is the capillary force, is consistent with the experimental growth rate of the reaction layer in the alumina, The formulation also clearly explains the relationship of the degree of glass penetration to the viscosity and the surface tension of the melt glass, The extraordinary difference in K, designated as the coefficient of penetration, between the calculated result and the experimental result suggests that the process of dissolving SiO2 into a melt glass at the alumina grain boundaries retards the glass penetration.
Using the "Statistical Theory of Fracture for Brittle materials" and performing tests for long lengths of fibers at distinct proof stresses and different velocities, the performance of a high velocity test m...
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Using the "Statistical Theory of Fracture for Brittle materials" and performing tests for long lengths of fibers at distinct proof stresses and different velocities, the performance of a high velocity test machine and detected level of damage in the fiber samples, are assessed. To confirm the damage and to know the strength of the fiber samples after proof tests, tensile tests were performed.
Combustion synthesis was explored as an alternate synthetic route to producing oxide phosphors with improved luminescent properties. The technique involves the highly exothermic reaction of metal nitrates (oxidizers) ...
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Combustion synthesis was explored as an alternate synthetic route to producing oxide phosphors with improved luminescent properties. The technique involves the highly exothermic reaction of metal nitrates (oxidizers) with an organic fuel (e.g., urea, carbohydrazide, glycine) at 500 °C. We have synthesized Tb3+, Eu3+, Tm3+ and Cr3+-activated Y3Al5O12 (YAG), Y2O3:Eu3+, and Y2SiO5:Ce3+ phosphors. As-reacted powders are well-crystallized, luminescent, and have a small particle size. The effects of processing parameters such as type of fuel and fuel/oxidizer ratio on the spectral energy distribution were determined using photoluminescence measurements. Low-voltage (100-1000 V) efficiency of combustion-synthesized phosphors was compared with efficiencies obtained for phosphors prepared via hydrothermal synthesis and high-temperature solid-state reaction.
One of the ultimate objectives for sintering studies is to be able to predict densification results under different thermal histories for a given processing method, It has been reported that the geometric parameters r...
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One of the ultimate objectives for sintering studies is to be able to predict densification results under different thermal histories for a given processing method, It has been reported that the geometric parameters related to sintering often are functions only of density for a given powder and green-body process, provided that one diffusion mechanism dominates in the sintering process, Based on this report, the concept of a master sintering curve has been developed that characterizes the sintering behavior for a given powder and green-body process regardless of the heating profiles, The formulation and construction of the master sintering curve are given in this paper, A model experiment on sintering of alumina is used and analyzed to demonstrate this new concept, Examples of the master sintering curves obtained from other powder systems (ZnO, nickel, Al2O3(5 vol% TiO2), and Al2O3(5 vol% ZrO2)) are presented, When this new method is used, densification behavior can be predicted under arbitrary temperature-time excursions following a minimal set of preliminary experiments, and these predictions can be used in planning sintering strategies, Moreover, deviations from the assumption of a single mechanism can be observed readily.
The integrated absorption cross section, the spontaneous emission probability, and the stimulated emission cross section of Yb3+ were determined in silicate, phosphate, borate, germanate, aluminate, gallate, and ZBLAN...
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The integrated absorption cross section, the spontaneous emission probability, and the stimulated emission cross section of Yb3+ were determined in silicate, phosphate, borate, germanate, aluminate, gallate, and ZBLAN host glasses, The compositional dependence of the stimulated emission cross section of the F-2(5/2) --> F-2(7/2) transition is determined mainly by the integrated absorption cross section in the glasses. A peak stimulated emission cross section above 1 pm(2), which is the highest value in glasses, was obtained in a gallate glass with a composition of 40K(2)O . 20Ta(2)O(5) . 40Ga(2)O(3). The factors affecting the integrated absorption cross section are discussed using the Judd-Ofelt parameters of Er3+ calculated in previous studies.
Tin dioxide thin films of various thicknesses up to 150 nm were prepared on quartz glass substrates from a sol solution of SnO2 (particle size 3 nm) by a spin-coating method and subjected to calcination at different t...
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Tin dioxide thin films of various thicknesses up to 150 nm were prepared on quartz glass substrates from a sol solution of SnO2 (particle size 3 nm) by a spin-coating method and subjected to calcination at different temperatures up to 800 degrees C for 30 min, The grain size of SnO2 was found to be far smaller than those obtained from the SnO2 sol-derived powder under the same calcination conditions, The suppression of grain growth of SnO2 was more conspicuous as the film thickness decreased so that in the thinnest film (20 nm thick) the SnO2 grain size remained as small as 6 nm after calcination at 800 degrees C, It is suggested that the SnO2 grains in the ultrathin film deposited on the substrate are restrained from moving and coalescing with each other, resulting in the suppression of grain growth.
Accurate refractive indexes of oxide glasses--silica, silicate, berate, aluminate, tellurite, antimonate, and heavy metal gallate glasses-are presented in the wavelength range 0.265 to 1.710 mu m. Factors affecting th...
Accurate refractive indexes of oxide glasses--silica, silicate, berate, aluminate, tellurite, antimonate, and heavy metal gallate glasses-are presented in the wavelength range 0.265 to 1.710 mu m. Factors affecting the refractive index dispersion are discussed by using the single-oscillator Drude-Voigt equation. The values of n(d) at 0.5876 mu m are affected mainly by the average resonance wavelength at the ultraviolet region through all of the glass systems, The distinguishing features of berate glasses-relatively high refractive index and low dispersion-are related to the large number of molecules, N, in a unit volume, compared with those of the other glasses, The number N determined by density measurements is related to the fraction of the four-coordinated borons estimated by Greenblatt and Bray.
Indentation cracking under blunt indenters is analyzed using nonlinear fracture mechanics. The usual assumptions of linear elastic fracture mechanics have been replaced with a nonlinear load vs load-point displacement...
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Indentation cracking under blunt indenters is analyzed using nonlinear fracture mechanics. The usual assumptions of linear elastic fracture mechanics have been replaced with a nonlinear load vs load-point displacement curve while assuming the material is linear elastic, The load, the load-point displacement, and a function of the crack area have been related to the crack driving force, J, while assuming a cone fracture under the Hertzian sphere, Experimentally, it was found that the load-displacement curve during loading, cracking, and unloading is nonlinear. The crack length is empirically shown to be proportional to the load-point displacement for several indenters, The experimentally measured relations between indenter load, load-point displacement, and crack geometries are then analyzed with mechanical energy balances based on the similitude of crack lengths with load-point displacements. The Hertz hardness that describes the nonlinear load vs load-point displacement relation during cracking is derived on the constant J line in load-displacement space. Finally, well-known experimental expressions that relate load to crack length are shown to be indistinguishable from the load-point displacement analysis reported.
Indentation cracking under sharp-pointed indenters is analyzed using compliance-based, nonlinear, fracture mechanics, The stress intensity factor, K, in linear elastic fracture mechanics is well known to be proportion...
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Indentation cracking under sharp-pointed indenters is analyzed using compliance-based, nonlinear, fracture mechanics, The stress intensity factor, K, in linear elastic fracture mechanics is well known to be proportional to the load, P;in this nonlinear analysis K is proportional to P-3/4. The observed relation between indenter load-point displacement and crack length is based on similitude of crack lengths with load-point displacements as a strain-controlled fracture. The equations that relate load and a function of the crack length to the crack driving force, J, have been found for Vickers indentations. Analysis of the nonlinear load vs displacement assumes an equilibrium crack in the elastic material surrounding the indent, The hardness that describes the load vs load-point displacement during cracking is derived on a constant J line in load-displacement space. The crack length is shown experimentally to be proportional to the load-point displacement after crack initiation for several different indenters in ZnS. The measured loading curves are nonlinear and display crack initiation during loading, The K-Ic expressions found here are very similar to correlations that have been applied to indentation cracks.
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