Zr-Hf interdiffusion in polycrystalline Y2O3-(Zr+Hf)O2

Lattice and grain-boundary interdiffusion coefficients were calculated from the concentration distributions determined for Zr-Hf interdiffusion in polycrystalline 16Y₂O₃·84(Zr_1–x Hf _x )O₂ withx=0.020 and 0.100. The lattice interdiffusion coefficients were described byD=0.031 exp [–391 (kJ mol^–1)/RT] cm² sec^–1 and the grain-boundary diffusion parameters byD=1.5×10^–6exp [–309(kJ mol^–1)/RT] cm³ sec^–1 in the temperature range 1584–2116° C. Comparison of the results with those for the systems CaO-(Zr+Hf)O₂ and MgO-(Zr+Hf)O₂ indicated that the Zr self-diffusion coefficient was insensitive to the dopants in the fluorite-cubic ZrO₂ solid solutions.     

Oxygen self-diffusion in single and polycrystalline magnesio-ferrites

Self-diffusion coefficients of oxygen ion in polycrystalline and single-crystal magnesioferrites have been measured by a gas-solid isotopic exchange technique using¹⁸O as a tracer at temperature in the range 975 to 1465° C. A new method was considered for the oxygen volume diffusion in polycrystalline magnesio-ferrite, and its reliability is discussed. The volume diffusion coefficients of polycrystalline magnesio-ferrite (MgO/Fe₂O₃=0.95 in mole ratio) can be expressed asD=1.51×10^–1exp (–78 600/RT) cm² sec^–1 (1135 to 1465° C) andD=1.2×10^–7exp (–38 000/RT) cm²sec^–1 (975 to 1135° C). The volume diffusion coefficients of the polycrystal in the high temperature range were very close to those of single crystal ferrite of the same composition as the polycrystal. The activation energy of grain-boundary diffusion in this polycrystal was expected to be greater than that of the volume diffusion. A possible interpretation of this unusual behaviour is given in terms of an increased enrichment of Fe²⁺ ion along the grain boundary with temperature elevation, by which oxygen vacancies increase.     

Effect of BaO and SiO2 addition on PTCR BaTiO3 ceramics

The influence of Ba-excess and liquid phase sintering with SiO₂ on the electrical conduction and microstructure in PTCR BaTiO₃ has been investigated. Dense (95–96%), small grain (5–10 m) PTCR materials were obtained in Ba-excess (Ba/Ti=1.006) BaTiO₃. The materials exhibit low room temperature resistivity _RT (10⁰–10² ·cm) and high PTCR respond (more than 5 orders). Solid state sintering was found to inhabit the semiconducting and PTCR behavior in Ba-excess materials. Liquid phase sintering, using SiO₂ in the Ba-excess BaTiO₃, resulted in low _RT and significant PTCR response. Through domain observation, interior Polaron deficient zones were found in samples which exhibit limited liquid phase sintering, leading to non-uniform directional domains and low charge carrier mobility. Proper control of the SiO₂ concentration was found critical for obtaining uniform directional domain microstructures and low _RT.     

The surface diffusion coefficients of MgO and Al2O3

From the measurement of neck size and neck curvature during the sintering of two spheres the surface diffusion coefficients of MgO and Al₂O₃ were determined. The spheres of both materials were machined from single crystals. The following values of surface diffusion coefficients were found: for MgO,D _{s s} = 3.7 × 10^–4 exp (407.8 kJ mol^–1/RT m³ sec^–1; for Al₂O₃,D _{s s} = 1.5 × 10^–2 exp (518.7 kJ mol^–1/RT) m³ sec^–1.     

Some observations of grain-boundary sliding in aluminium bicrystals tested at constant strain rate and constant rate of stress increase

Bicrystals of pure aluminium, aluminium/0.05 wt% and aluminium/0.30 wt% copper have been deformed in shear within the temperature range 350 to 600°C at a constant rate of grip displacement (300 m/h) and constant rates of increase of grain-boundary shear stress (0.30 to 1.04 g/mm^–2 min^–1). The stress/time, sliding/time and sliding/stress curves for these tests are presented together with metallographic observations. The stress/time curves exhibited changes in the strain-hardening rates which were accompanied by the occurrence of extensive crystal deformation. In many cases, following the change in strain-hardening rate and onset of extensive crystal slip, the extent of grain-boundary sliding was proportional to the shear stress on the boundary. The ratio of the extent of sliding to the grain-boundary shear stress increased with increasing test temperature. The temperature-dependence of the sliding behaviour, as reflected by the sliding/stress results, yielded apparent activation energies of 31 Kcal/mole in the temperature range 600 to 475°C and 8 Kcal/mole in the range 475 to 350°C.     

Enhancement of the diffusional creep of polycrystalline Al2O3 by simultaneous doping with manganese and titanium

The effect of simultaneous doping with manganese and titanium on diffusional creep was studied in dense, polycrystalline alumina over a range of grain sizes (4–80m) and temperatures (1175–1250° C). At a total dopant concentration of 0.32–0.37 cation %, diffusional creep rates were enhanced considerably such that the temperature at which cation mass transport was significant was suppressed by at least 200° C compared to that observed in undoped material. The Mn-Ti (and Cu-Ti) dopant couple was far more effective in enhancing creep rates and suppressing sintering temperatures than the Fe-Ti couple. The enhanced mass transport kinetics are believed to be caused by significant increases in both aluminium lattice and grain-boundary diffusion. When aluminium grain-boundary diffusion is enhanced by increasing the concentration of divalent impurity (Mn²⁺, Fe²⁺) or by creep testing at low temperatures, creep deformation is Newtonian viscous.     

Characterizations of InzGa1?z As1?x?yN xSbyP-i-N structures grown on GaAs by molecular beam epitaxy

The GaAs-based double-heterojunction P-i-N structures using In_zGa_1–zAs_1–x–yN_xSb_y as the i-layer is investigated for the first time using solid source molecular beam epitaxy. High quality coherent bulk InGaAsN_3.45%Sb (0.5 m) with a lattice-mismatch of 2.6 × 10^–3 can be achieved due to the surfactant properties of antimony, while the bulk InGaAsN_2% at 0.5 m with 1.06× 10^–3 mismatch is fully relaxed. Rapid thermal annealing (RTA) resulted in 25 meV low temperature (LT) photoluminescence (PL) full-width half-maximums (FWHM) for the bulk InGaAsNSb layers. InGaAsNSb experiences 30% less blueshifting with subjected under the same annealing conditions as InGaAsN with similar N content. Room temperature (RT) absorption measurements are in the range of 0.9–1.4 eV. The absorption edge of 1.41 m is achieved for sample D4.     

Coherent diffusion of isotopic impurities in solid helium

A theory of coherent diffusion (impuriton propagation) of dilute isotopic impurities in solid He is described. An expression for the mean square distance R ² (t) traveled by the impurity is derived. For short times pure band propagation occurs and so R ² (t) grows as t ². For times longer than a characteristic impurity-phonon scattering time this time dependence becomes linear, and a diffusion constant can be defined. This characteristic scattering time is estimated to be ~7 × 10^–5 T ^–9 sec (T in K) for a ³He impurity in ⁴He at V _m = 21 cm³/mole. The corresponding diffusion constant is consistent with that measured in the NMR experiment of Allen and Richards if the ³He-⁴He tunneling frequency J ₃₄ is taken as 7 × 10⁵ sec^–1.     

Sintering of aluminium nitride: Particle size dependence of sintering kinetics

The effect of particle size (0.78 4.4 m) on the sintering kinetics of AIN powder was investigated in the temperature range from 1600 to 2000° C and the results were analysed on the basis of vacancy diffusion models. The mechanisms of sintering are discussed.Fractional shrinkage is proportional to the nth power of soaking time with n = 0.20 for 4.4 m and 1.5 m powders and 0.33 for 0.78 m powder. For the 0.78 m powder at 1900° C, however, n decreases gradually as grain growth proceeds. The experimental activation energy for sintering is between 92 kcal/mole for 4.4 m and 129 kcal/mole for 0.78 m powder. Unlike this activated energy, the rate of sintering and the diffusion constant calculated from it increase drastically with decrease of particle size; the derived diffusion constant for 1.5 m powder is 10¹ to 10² times larger than that of 4.4 m powder, and for 0.78 m powder the diffusion constant is estimated to be still higher.The particle-size dependence of parameter n and the diffusion constant seems to be caused by a variation in predominant diffusion mechanisms; namely, bulk diffusion in coarse powder and surface or grain-boundary diffusion in fine powder.     

Proton conducting polymer electrolyte: II poly ethylene oxide + NH4l system

A new proton conducting polymer electrolyte PEO + NH₄l system has been investigated. The solution-cast films of different stochiometric ratios have been prepared and characterized. Proton transport has been established using various experimental studies, namely optical microscopy, X-ray diffraction, differential thermal analysis, infrared, coulometry transient ionic current and electrical conductivity measurements at different temperatures and humidity. The maximum conductivity of the complexed material has been found to be 10^–5 S cm^–1. Both H⁺ ion and I^– anion movements are involved with respective transference numbers and mobilities ast _H+=0.74, ,t _l–=0.09, _H+=4.97 × 10^–6 cm² V^–1 s^–1 and _l–=7.65.     

Static recrystallization kinetics of 304 stainless steels

Static restoration mechanism during hot interrupted deformation of 304 stainless steel was studied in the temperature range from 900 to 1100°C, various strain rate from 0.05 to 5/sec and pass strain of 0.25–3 times peak strain. It was clarified that the static recrystallization was happened after 3–10 seconds at first deformation. The static restoration was depended on the pass strain, deformation temperature and strain rate and fractional softening (FS) values increased with increasing strain rate, deformation temperature and pass strain. Recystallization kinetics was explained with Avrami equation and Avrami constant was 1.113. This value was independent of deformation variables significantly. The time of 5, 50, 95% recrystallization was evaluated using such equations: t _0.05 = 2.9 × 10^{–12 –1.17 –0.94} D exp(222000 J/mol/RT), t _0.5 = 2.0 × 10^{–10 –1.56 –0.81} D exp(197000 J/mol/RT), t _0.95 = 1.9 × 10^{–8–1.63 –0.76} D exp(173000J/mol/RT). The predicted values by use of upper equations had a good agreement with a measurement.     

Prediction of thermal diffusion in binary mixtures of nonelectrolyte liquids by the use of nonequilibrium thermodynamics

A derivation based on nonequilibrium thermodynamic leads to this expression for the thermal diffusion factor, _T=M ₂(h ₂ ^xs -h ₁ ^xs )/RT ₂, where M ₂ is the molecular weight of the lighter of the two components, h ₁ ^xs is the partial excess enthalpy of component i, J/g, R is 8.314 J · K ^–1 · mol ^–1, T is temperature in K, and ₂ is the thermodynamic correction factor (1 + d ln ₂/d ln X ₂), where ₂ is an activity coefficient and X ₂ is the mole fraction. The correctness of this theoretical prediction is verified for the liquid system ethanol-water at 298 K.Paper submitted to the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Grain-boundary sliding measurements in Al2O3 by machine vision photogrammetry

The nucleation, growth and coalescence of grain-boundary cavities is the primary damage mechanism observed during creep of structural ceramics. Furthermore, grain-boundary sliding (GBS) has been identified as the driving force process. Although the creep characteristics of structural ceramics have been extensively studied, very little is known about the details of GBS during creep and how GBS relates to cavitation kinetics. This paper presents the results of a study using a machine vision system to measure Mode II GBS displacements in a Lucalox Al₂O₃. Specifically, sliding displacements as large as 0.4 m were measured. The measured displacements indicate that some grain boundaries experienced shear strains and strain rates of 4200% and 2.3×10^–2 s^–1, respectively. The techniques utilized for these measurements are described in detail, and data gathered during a 2 1/2 h compressive creep test under a stress of 138 MPa at 1600 °C are presented and discussed.     

Diffusion of hydrogen in hafnium and titanium

We measured the coefficients of diffusion of hydrogen in the hydride phases of hafnium and titanium at 1073–1273°K on the basis of the solutions of Fick's second law for diffusion in a finite cylinder and in a sector of it.Notation C_o initial concentration of gas in the metal, ncm³/cm _Me ³ - C(r,, z, t) instantaneous gas concentration in the finite cylinder - i, k, m, n ordinal numbers (indices) - J_n(_n ⁱr/R) Bessel function of order n - _n ⁱ i-th root of the Bessel function of order n - R,l radius and thickness of the specimen, cm - D diffusion coefficient, cm²/sec - t time, sec - V calibrated volume above specimen, cm³ - F admittance of gas pumping channels, ncm³/sec - dQ_re1/dt rate of gas release, ncm³/sec - p pressure of released gas, torr - dp/dt change in released-gas pressure per unit time, torr/sec - tan tangent of the angle of inclination of the straight line in equation (6), 1/sec - IH₂ ion current of hydrogen - (n) gamma function - W coefficient of variation, % - mean-square deviation - D_o preexponent, cm²/sec - E activation energy, kJ/mole - T absolute temperature of specimens - B universal gas constant, kJ/ deg·mole Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 643–648, October, 1980.     

Coarsening of precipitates and dispersoids in aluminium alloy matrices: a consolidation of the available experimental data

Experimental data on the coarsening of precipitates and dispersoids in aluminium-based matrices are reviewed. Available data are tabulated as K=(r ³–r ₀ ³ )/t where r ₀ is the initial particle radius and r is its value after time t at temperature T, and then plotted as log (KT) against 1/T for consolidation and assessment. The considerable body of data for -A₃Li in Li-containing alloys is well represented by K=(K ₀/T) exp (–Q/RT) with K ₀=(1.3 _–0.5 ^+3.0 ) × 10^–13m³Ks^–1 and Q=115±4kJ mol^–1. The relatively limited data for and in Cucontaining alloys are representable by the same relationship with K ₀4 × 10^–8 and — 4 × 10^–10 m³ Ks^–1, respectively, and Q — 140 kJ mol^–1. Available data for coarsening of L1₂ ^– Al₃(Zr, V) and related phases in Zr-containing alloys and of Al₁₂Fe₃Si and related phases in Al-Fe based alloys indicate (i) rates of coarsening at 375 to 475 °C (0.7 to 0.8T_m) five to eight orders of magnitude less than would be expected for , and in this temperature range, and (ii) high activation energies of 300 and 180 kJ mol^–1, respectively.     

Oxygen self-diffusion in a potassium strontium silicate glass using proton activation analysis

Oxygen self-diffusion coefficients were measured in a 20K₂O-20SrO-60SiO₂ (wt%) glass above and below the glass transition temperature using the single spectrum proton activation analysis of oxygen-18 using the nuclear reaction ¹⁸O(p, )¹⁵N. The -particle spectrum recorded during proton irradiation is used to determine the ¹⁸O concentration profile. The self-diffusion coefficients, D, determined for the three diffusion times of about 22 h, 3 1/2 and 7 1/2 days were in good agreement within experimental error, except for the two lowest temperatures of the short-time run possibly because of the shallow depths of diffusion and surface exchange. In the temperature range 600 to 1000 K, D values with the relations, above the glass transition temperature D=7.6×10¹⁴ exp(–119 kcal/RT) cm²sec^–1, and below the glass transition temperature D=1×10^–12 exp(–10 kcal/RT) cm²sec^–1, were obtained.     

Surface tension of liquid3He and4He near the liquid-gas critical point

The surface tension of liquid³He and⁴He was measured near the gas-liquid critical points in the reduced temperature range 3×10^–4–1, where t (T _c –T)/T _c . The critical exponents were found to be ₃=1.289±0.015 for³He and ₄=1.306±0.017 for⁴He. These values are very close to those for classical liquids, and are consistent with the value of 1.28 predicted by Widom, but are apparently different from the exponents previously obtained for liquid helium isotopes, which are near unity. The critical coefficients show good agreement with the quantum-corrected corresponding states theory for the Lennard-Jones 6–12 potential discussed by Young. The interface thickness is deduced from Widom's theory to bed=d ₀t^–v withd ₃₀=0.14±0.03nm and v₃=0.57±0.04 for³He, andd ₄₀=0.37±0.07 nm and v₄=0.58±0.01 for⁴He.     

Ion-implantation technology for improved GaAs MESFETs performance

Electrical properties of Si-implanted and co-implanted with Mg or Be in semi-insulating GaAs was studied. The Si-implanted MESFETs with and without buried p-layer (formed by Mg or Be) have been fabricated and characterized by their d.c. and r.f. performance. The experimental results showed that the device with a buried p-layer can effectively suppress the substrate leakage current (thus good pinch-off characteristic) and obtained higher gain linearity than these without a buried p-layer. For 1 m×100 m MESFETs device with co-implantation of Si (8×10¹² cm^–2) and Be (6×10¹¹ cm^–2) demonstrated uniform transconductance (g_m) of 115 mS mm^–1 with the gate voltage ranging from –1 to 1 V and reduced pinch-off voltage compared to those with co-implantation of Si and Mg (6×10¹¹ cm^–2). The measured f_T and f_max of a 1 m×25 m MESFET with co-implantation of Si and Be are 10 and 39 GHz, respectively. However, FETs with increased Mg dose (from 6×10¹¹ cm^–2 to 2×10¹² cm^–2) in a buried p-layer can obtain higher transconductance and saturation current.     

Thermophysical Property Measurements of Supercooled and Liquid Rhodium

The density, the isobaric heat capacity, the surface tension, and the viscosity of liquid rhodium were measured over wide temperature ranges, including the supercooled phase, using an electrostatic levitation furnace. Over the 1820 to 2250 K temperature span, the density can be expressed as (T)=10.82×10³–0.76(T–T _m ) (kgm^–3) with T _m =2236 K, yielding a volume expansion coefficient (T)=7.0×10^–5 (K^–1). The isobaric heat capacity can be estimated as C _P (T)=32.2+1.4×10^–3(T–T _m ) (Jmol^–1K^–1) if the hemispherical total emissivity of the liquid remains constant at 0.18 over the 1820 to 2250 K interval. The enthalpy and entropy of fusion have also been measured, respectively, as 23.0 kJmol^–1 and 10.3 Jmol^–1K^–1. In addition, the surface tension can be expressed as (T)=1.94×10³–0.30(T–T _m ) (mNm^–1) and the viscosity as (T)=0.09 exp[6.4×10⁴(RT)] (mPas) over the 1860 to 2380 K temperature range.     

Initial density dependence of experimental viscosities and of calculated diffusion coefficients of the binary vapor mixtures methanol-benzene and methanol-cyclohexane

The paper reports experimental results for the viscosity of the vapor mixtures methanol-benzene (five mole fractions with densities up to 1.5kg·m^–3 and 0.022 mol·L ^–1) and methanol-cyclohexane (four mole fractions with densities up to 1.9kg·m^–3 and 0.026 mol·L ^–1). In analogy to the pure components, the measurements on the mixtures were carried out with an oscillating-disk viscometer with small gaps, completely made of quartz, beginning as near as possible to room temperature and continuing to a maximum temperature of 630 K. A first evaluation by means of the Chapman-Enskog theory of dilute gases has shown differences in the resulting values of the interaction viscosity _ij ⁽⁰⁾ in the limit of zero density exceeding the experimental errors. Consistent results were obtained by taking into account the initial density dependence of the viscosity within the framework of the modified Enskog theory for gaseous mixtures. The values of _ij ⁽⁰⁾ were also used to estimate binary diffusion coefficients of the mixtures.