Effect of substrate temperature on the properties of ZrO2 films prepared by d.c. reactive magnetron sputtering

Studies of ZrO2 films prepared by d.c. reactive magnetron sputtering are described. The effects of substrate temperature on the packing density, refractive index, extinction coefficient and crystallinity phase have been investigated in the temperature range 25–450 °C. The refractive index varied from 1.84 to 1.95 and extinction coefficient from 2 × 10−3 to 9.6 × 10−3. This was explained on the basis of an increase in packing density from 0.686 to 0.813. The change in packing density has been attributed to a decrease in the oxygen condensation at higher temperatures. Annealing results in a decrease in refractive index and increase in extinction coefficient. The films deposited at 150 °C showed a monoclinic phase which transforms to a tetragonal phase at higher substrate temperatures.

Grain size effect on the phase transformation temperature of nanostructured CuFe2O4

We report a large decrease in tetragonal to cubic phase transformation temperature when grain size of bulk CuFe2O4 is reduced by mechanical ball milling. The change in phase transformation temperature was inferred from in situ high temperature conductivity and x-ray diffraction measurements. The decrease in conductivity with grain size suggests that ball milling has not induced any oxygen vacancy while the role of cation distribution in the observed decrease in phase transformation temperature is ruled out from in-field Fe-57 Mossbauer and extended x-ray absorption fine structure measurements. The reduction in the phase transformation temperature is attributed to the stability of structures with higher crystal symmetry at lower grain sizes due to negative pressure effect. (C) 2011 American Institute of Physics. doi: 10.1063/1.3493244]

Effect of strain rate on the high-temperature low-cycle fatigue properties of a nimonic PE-16 superalloy

Strain-rate effects on the low-cycle fatigue (LCF) behavior of a NIMONIC PE-16 superalloy have been evaluated in the temperature range of 523 to 923 K. Total-strain-controlled fatigue tests were per-formed at a strain amplitude of +/-0.6 pct on samples possessing two different prior microstructures: microstructure A, in the solution-annealed condition (free of gamma' and carbides); and microstructure B, in a double-aged condition with gamma' of 18-nm diameter and M23C6 carbides. The cyclic stress response behavior of the alloy was found to depend on the prior microstructure, testing temperature, and strain rate. A softening regime was found to be associated with shearing of ordered gamma' that were either formed during testing or present in the prior microstructure. Various manifestations of dynamic strain aging (DSA) included negative strain rate-stress response, serrations on the stress-strain hysteresis loops, and increased work-hardening rate. The calculated activation energy matched well with that for self-diffusion of Al and Ti in the matrix. Fatigue life increased with an increase in strain rate from 3 x 10(-5) to 3 x 10(-3) s-1, but decreased with further increases in strain rate. At 723 and 823 K and low strain rates, DSA influenced the deformation and fracture behavior of the alloy. Dynamic strain aging increased the strain localization in planar slip bands, and impingement of these bands caused internal grain-boundary cracks and reduced fatigue life. However, at 923 K and low strain rates, fatigue crack initiation and propagation were accelerated by high-temperature oxidation, and the reduced fatigue life was attributed to oxidation-fatigue interaction. Fatigue life was maximum at the intermediate strain rates, where strain localization was lower. Strain localization as a function of strain rate and temperature was quantified by optical and scanning electron microscopy and correlated with fatigue life.

Correlation of Kauzman temperature with odd-even effect in n-alkanes

A unique correlation has been established between Kauzmann temperature (Tk1) and the odd–even effect in n‐alkanes. The derived new parameter, i.e., Tm/Tk1 obtained from entropy conservation at Tk1, when plotted against chain length, provides a much sharper odd–even contrast than entropy of fusion plot reported earlier. © 1996 American Institute of Physics.

Linear electro-optic effect and temperature coefficient of birefringence in 4-nitro-4script-methylbenzylidene aniline single crystals

A study of the linear electro?optic effect in single crystals of the organic compound, 4?nitro�4??methylbenzylidene aniline is reported. The reduced half?wave voltages have been found to have values 2.8, 1.3, and 1.1 kV at 632.8, 514.5, and 488.0 nm, respectively and the corresponding values of the largest linear electro?optic coefficient have been calculated. The thermal variation of the birefringence has also been investigated and the temperature variation of the refractive index difference is found to have the value, d?n/dT = 15.8 × 10?5 K?1.

Effect of Strain Rate on Ductile-to-Brittle Transition Temperature of a Free-Standing Pt-Aluminide Bond Coat

The ductile-to-brittle transition temperature (DBTT) of a free-standing Pt-aluminide (PtAl) bondcoat was determined using the microtensile testing method and the effect of strain rate variation, in the range 10(-5) to 10(-1) s(-1), on the DBTT studied. The DBTT increased appreciably with the increase in strain rate. The activation energy determined for brittle-to-ductile transition, suggested that such transition is most likely associated with vacancy diffusion. Climb of aOE (c) 100 > dislocations observed in analysis of dislocation structure using a transmission electron microscope (TEM) supported the preceding mechanism.

Temperature dependence of the levitation effect - Implications for separation of multicomponent mixtures

Sufficiently long molecular dynamics simulations have been carried out on spherical monatomic sorbates in NaY zeolite, interacting via simple Lennard-Jones potentials, to investigate the dependence of the levitation effect on the temperature. Simulations carried out in the range 100-300 K suggest that the anomalous peak in the diffusion coefficient (observed when the levitation parameter, gamma, is near unity) decreases in intensity with increase in temperature. The rate of cage-to-cage migrations also exhibits a similar trend. The activation energy obtained from Arrhenius plots is found to exhibit a minimum when the diffusion coefficient is a maximum, corresponding to the gamma approximate to 1 sorbate diameter. In the linear or normal regime, the activation energy increases with increase in sorbate diameter until it shows a sharp decrease in the anomalous regime. Locations and energies of the adsorption sites and their dependence on the sorbate size gives interesting insight into the nature of the underlying potential-energy surface and further explain the observed trend in the activation energy with sorbate size. Cage residence times, tau(c), show little or no change with temperature for the sorbate with diameter corresponding to gamma approximate to 1, whereas there is a significant decrease in tau(c) with increase in temperature for sorbates in the linear regime. The implications of the present study for the separation of mixtures of sorbates are discussed.

The effect of temperature on the surface tension and adsorption functions of the Fe-S-O melts - an analysis based on interaction parameters

The present investigation analyses the thermodynamic behaviour of the surfaces and adsorption as a function of temperature and composition in the Fe-S-O melts based on the Butler's equations. The calculated-values of the surface tensions exhibit an elevation or depression depending on the type of the added solute at a concentration which coincides with that already present in the system. Generally, the desorption of the solutes as a function of temperature results in an initial increase followed by a decrease in the values of the surface tension. The observations are analyzed based on the surface interaction parameters which are derived in the present research.

Effect of Reagent Addition Rate and Temperature on Synthesis of Gold Nanoparticles in Microemulsion Route

Nanoparticle synthesis in a microemulsion route is typically controlled by changing the water to surfactant ratio, concentration of precursors, and/or concentration of micelles. The experiments carried out in this work with chloroauric acid and hydrazine hydrate as precursors in water/AOT-Brij30/isooctane microemulsions show that the reagent addition rate can also be used to tune the size of stable spherical gold nanoparticles to some extent. The particle size goes through a minimum with variation in feed addition rate. The increase in particle size with an increase in reaction temperature is in agreement with an earlier report. A population balance model is used to interpret the experimental findings. The reduced extent of nucleation at low feed addition rates and suppression of nucleation due to the finite rate of mixing at higher addition rates produce a minimum in particle size. The increase in particle size at higher reaction temperatures is explained through an increase in fusion efficiency of micelles which dissipates supersaturation; increase in solubility is shown to play an insignificant role. The moderate polydispersity of the synthesized particles is due to the continued nucleation and growth of particles. The polydispersity of micelle sizes by itself plays a minor role.

Effect of spinel second phase on high temperature deformation in alumina

Constant stress compression creep experiments were carried out on high purity alumina composites with spinel contents of 8 and 30%, corresponding to a situation with isolated and interconnected second phases. The creep experiments were conducted over a stress and temperature range of 10 to 150 MPa and 1623 to 1723 K, respectively. Analysis of the experimental data indicated that the variation in spinel content did not have any influence on high temperature deformation in the composite. The spinel phase retards grain growth, and this may enhance superplasticity in alumina-spinel composites.

Temperature effect on hydrocarbon-enhanced nitric oxide conversion using a dielectric barrier discharge reactor

Experimental investigations into the effect of temperature on conversion of NO in the presence of hydrocarbons (ethylene, acetylene and n-hexane) are presented. An AC energized dielectric barrier discharge reactor was used as the plasma reactor. The experiments were carried out at different temperatures up to 200 degreesC. The discharge powers were measured at all the temperatures. The discharge power was found to increase with temperature. NO conversion in the presence of ethylene and n-hexane was better than that of acetylene at all temperatures. The addition of acetylene at room temperature showed no better conversion of NO compared to no additive case. While at higher temperatures, it could enhance the conversion of NO. A slight enhancement in NO and NOx removal was observed in the presence of water vapor. (C) 2003 Elsevier Science B.V. All rights reserved.

Effect of annealing temperature on electrical and nano-structural properties of sol-gel derived ZnO thin films

Zinc oxide (ZnO) thin films have been prepared on silicon substrates by sol-gel spin coating technique with spinning speed of 3,000 rpm. The films were annealed at different temperatures from 200 to 500 A degrees C and found that ZnO films exhibit different nanostructures at different annealing temperatures. The X-ray diffraction (XRD) results showed that the ZnO films convert from amorphous to polycrystalline phase after annealing at 400 A degrees C. The metal oxide semiconductor (MOS) capacitors were fabricated using ZnO films deposited on pre-cleaned silicon (100) substrates and electrical properties such as current versus voltage (I-V) and capacitance versus voltage (C-V) characteristics were studied. The electrical resistivity decreased with increasing annealing temperature. The oxide capacitance was measured at different annealing temperatures and different signal frequencies. The dielectric constant and the loss factor (tan delta) were increased with increase of annealing temperature.

Effect of rolling temperature and reduction in thickness on microstructure and mechanical properties of ZM21 magnesium alloy and its subsequent annealing treatment

In this present paper, the effects of non-isothermal rolling temperature and reduction in thickness followed by annealing on microstructure and mechanical properties of ZM21 magnesium alloy were investigated. The alloy rolled at four different temperatures 250 degrees C, 300 degrees C, 350 degrees C and 400 degrees C with reductions of 25%, 50% and 75%. Non-isothermal rolling resulted in grain refinement, introduction of shear bands and twins in the matrix alloy. Partial to full recrystallization was observed when the rolling temperature was above recrystallization temperature. Rolling and subsequent annealing resulted in strain-free equiaxed grains and complete disappearance of shear bands and twins. Maximum ultimate strength (345 MPa) with good ductility (14%) observed in the sample rolled at 250 degrees C with 75% reduction in thickness followed by short annealing. Recrystallization during warm/hot rolling was sluggish, but post-roll treatment gives distinct views about dynamic and static recrystallization. (C) 2011 Elsevier B.V. All rights reserved.