Methodology for the determination of the interfacial properties of brittle matrix composites

The interfacial properties of a glass-ceramic matrix composite (SiC/CAS) were determined from single-fibre push-out tests using the interfacial test system. The coefficient of friction, , the residual clamping stress, _c, and fibre axial residual stress, _z , were extracted by fitting the experimental stress versus fibre-end displacement curves using the models of Hsueh, and Kerans and Parthasarathy. Using Hsueh's model, the intrinsic interfacial frictional stress (=_c) was found to be 11.1±3.2 MPa, whereas by using Kerans-Parthasarathy's model it was found to be 8.2±1.5 MPa. Comparisons between these models are included, together with a discussion of data analysis techniques.Nomenclature _z Axial fibre residual stress (Pa) - ^* Effective clamping stress (Pa) - _c Residual clamping stress (Pa) - _p Poisson's effect-induced clamping stress (Pa) - _d ⁰ Debond stress in the absence of residual stresses (Pa) - _d Experimental debond stress (Pa) - Compressive applied stress (Pa) - Interfacial shear stress (Pa) - u Fibre-end displacement (m) - h Debond length (m) - r Fibre radius (m) - E _f Fibre Young's modulus (Pa) - E _m Matrix Young's modulus (Pa) - v _f Fibre Poisson's ratio (dimensionless) - v _m Matrix Poisson's ratio (dimensionless) - f Fibre volume fraction (dimensionless) - k Parameter (dimensionless) - D Parameter (dimensionless) - Interfacial coefficient of friction (dimensionless) - G _i Interface toughness (J m^–2) - C _m Load-train compliance (m N^–1)     

Modelling of dimensional changes during polymer-ceramic conversion for bulk component fabrication

Shrinkage and porosity generation during conversion of polymer-filler systems into ceramic bodies during pyrolysis is examined. In the presence of an inert filler phase such as Si₃N₄ or SiC powder dispersed in an organosilicon polymeric matrix only porous microstructures may be obtained without any shrinkage. By using an active filler phase such as carbide- or nitride-forming transition metals, however, shrinkage of the polymer matrix may be compensated by appropriate expansion of the filler phase. A model is derived to predict the critical volume fractions of various potential active filler systems in inert and reactive gas atmospheres, which can be effective in controlling shrinkage and porosity during the fabrication of ceramic components from polymer-derived precursor materials.Nomenclature P Polymer phase - C Condensed polymer pyrolysis product (ceramic) - G Gaseous polymer decomposition product - F Inert filler phase - T Active filler phase (e.g. transition metal) - M Reaction product of active filler phase (e.g. carbide, nitride) - m Mass - V Volume fraction - V _F,T ^max Maximum packing density of an inert (F) or active (T) filler powder - V _F,t ^* Critical volume fraction of an inert (F) or active (T) filler powder in the starting polymer-filler mixture - V _v Residual porosity in the polymer pyrolysis product - V _v ^pf Residual porosity in the polymer-inert filler system after pyrolysis - Ceramic yield of polymer after pyrolysis - Weight change of active filler phase during reaction pyrolysis - Density ratio of polymer to polymer pyrolysis (ceramic) product - Density ratio of active filler to filler reaction product - ^P Linear shrinkage of the polymer phase during pyrolysis - ^pf Linear shrinkage of a polymer-inert filler system during pyrolysis - ^paf Linear shrinkage of a polymer-active filler system during reaction pyrolysis - Linear shrinkage/expansion of the filler phase during reaction - Density     

Hydrodynamic lubrication of squeeze-film porous bearings

Summary Closed-form analytical solutions for three different types of squeeze-film porous bearing are introduced in this paper. The effects of the permeability parameter on the pressure profile, load-carrying capacity, and time required to squeeze the fluid out of the lubricated conjunction are presented. The results show that as the permeability parameter increases, both the pressure profiles and the load-carrying capacity of the bearing decrease in the case of pure squeeze motion. Furthermore, the results show that for dimensionless permeability parameters less than 0.001, the effect of the porous layer on the hydrodynamic lubrication of squeeze-film porous bearings can be neglected.Notation c Clearance, m - e Eccentricity, m - h Film thickness, m - h _p Porous layer thickness, m - k _x Permeability of the porous layer inx-direction, m² - k _y Permeability of the porous layer iny-direction, m² - k _z Permeability of the porous layer inz-direction, m² - k ₁ Permeability ratio - p Pressure within film region, Pa - p ^* Pressure within porous layer, Pa - P Dimensionless pressure within film region - P ^* Dimensionless pressure within porous layer - r Radial coordinate - Dimensionless radial coordinate - u _a Velocity of surfacea inx-direction, m/s - u _b Velocity of surfaceb inx-direction, m/s - v _a Velocity of surfacea iny-direction, m/s - v _b Velocity of surfaceb iny-direction, m/s - w Squeeze velocity, –h/t, m/s (w _a =–w,w _b =0) - w ₀ Flow velocity into porous layer inz-direction, m/s - w _z Load-carrying capacity per unit width, N/m - W _z Dimensionless load-carrying capacity - x Coordinate, m - X Dimensionlessx-coordinate - y Coordinate, m - z Coordinate, m - Z Dimensionlessz-coordinate - Dimensionless parameter,l/h _p - Lubricant viscosity within film region, Pa s - ^* Lubricant viscosity within porous layer, Pa s - ₀ Lubricant viscosity at atmospheric pressure, Pa s - Lubricant density within film region, Kg/m³ - ^* Lubricant density within porous layer, Kg/m³ - Circumferential coordinate, rad - Dimensionless permeability parameter, - Eccentricity ratio     

A short swirl chamber

The flow in a short air-operated swirl chamber is studied by contactless methods. An engineering technique is suggested to calculate the parameters of a swirled gas flow in this chamber.Notation D ₀,R ₀ peripheral diaraeter and the swirl chamber diameter, m - d ₀,r ₀ diameter and radius of discharge opening of the swirl chamber, m - F total area of intake channels, m² - n power index in the equation for circumferential velocity - V, U, W circumferential, radial, and axial velocities, m/sec - V ₀,U ₀ circumferential and radial velocities at the boundary of the flow core, m/sec - V _in mean-mass velocity in intake channels, m/sec - V _p circumferential velocity at the boundary of the zone of quasipotential flow, m/sec - coefficient of velocity conservation at the boundary of the flow core - G mass flow rate of gas, kg/sec - P static pressure, Pa - T static temperature, K - n ₁ polytrope index - dynamic viscosity, N·sec/m² - P ₀ static pressure at the boundary of the flow core, Pa - T ₀ static temperature at the boundary of the flow core, K - c _p gas heat capacity, J/(kg·K) - R universal gas constant, J/(kg·K) Academic Scientific Complex Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 5, pp. 827–833, September–October, 1995.     

On the thermohydrodynamic analysis of a Bingham fluid in slider bearings

Summary A theoretical analysis of finite slider bearings with the Bingham rheological model is presented which includes a full consideration for thermal effects. Full thermohydrodynamic (THD) as well as simplified ISOADI solutions are presented for a wide range of operating conditions. Results are authenticated with a number of published one-dimensional isoviscous solutions. An extensive set of parametric studies of the Bingham model together with an illustrative example is presented.Notation a Clearance ratio - B Pad length in the direction of motion (m) - c _o Lubricant specific heat (J/Kg K) - f Friction coefficient - F Frictional force (Pa) - H _b Thickness of the stationary component (m) - h Film thickness (m) - h ₁,h ₂ Maximum and minimum film thickness (m) - h _a,h _b Height of the lower and upper boundary of core (m) - h _L,h _H Height of the lower and upper boundary of fluid film (m) - h _conv Convective heat transfer coefficient (W/m² K) - K _f Bearing characteristic number - k _o Thermal conductivity of the lubricant (W/m K) - L Bearing length in the axial direction (m) - m Slope of the slider bearing - P Pressure (Pa) - P _a Ambient pressure (Pa) - P _L Average unit load (Pa) - P _max Maximum pressure (Pa) - P _s Supply pressure (Pa) - Q _in Inlet flow rate (m³/sec) - Q _leakage Leakage flow rate (m³/sec) - S _h Difference between the maximum and minimum film thickness (m) - T Temperature (^oC) - T _a Ambient temperature (^oC) - T _b Stationary component temperature (^oC) - T _max Maximum temperature (^oC) - T _mean Mean temperature (^oC) - T _s Lubricant temperature supplied (^oC) - T _exit Exit temperature (^oC) - U ₁,U ₂ Velocity of the lower and upper surface along the film (m/sec) - U _L,U _H Velocity of the lower and upper boundary of fluid film along the film (m/sec) - U _c,W _c Velocity of core along the film and in the axial direction (m/sec) - u, v, w Velocity component along, across the film and in the axial direction (m/sec) - W Bearing load-carrying capacity (N) - W _L,W _H Velocity of the lower and upper boundary of fluid film in the axial direction (m/sec) - x, y, z Coordinate system (m) - x _b,y _b Coordinate system used in the stationary component (m) - Temperature-viscosity coefficient (1/K) - Yield stress-temperature coefficient (1/K) - Shear rate (1/sec) - Non-Newtonian viscosity (Pa·sec) - ₁, ₂ Temperature-rise parameters - _s Aspect ratio of the slider bearing - Viscosity (Pa·sec) - _i Inlet viscosity (Pa·sec) - _eff Effective viscosity (Pa·sec) - _o Density of the lubricant (Kg/m³) - Shear stress (Pa) - ₀ Critical shear stress (Pa)     

Effect of CO2 partial pressure on oxidation of low-oxygen SiC fibers (Hi-Nicalon) in Ar-CO2 gas mixtures

The oxidation behavior and thermal stability of Si—C fibers (Hi-Nicalon) in Ar-CO₂ gas mixtures were investigated at 1773 K, through mass change determination, XRD analysis, resistivity measurement, SEM observation and tensile tests. Mass gain and cristobalite formation were observed at p _{CO 2} 10³ Pa, showing the occurrence of passive-oxidation of the fibers. On the other hand, the active-oxidation was characterized by the mass loss, no formation of SiO₂ film and a marked increase in resistivity at p _{CO 2} 5 × 10² Pa. The oxygen potential for the active-to-passive oxidation transition in Ar-CO₂ gas mixtures was nearly identical to that in Ar-O₂ gas mixtures. About 50% of the strength in the as-received state was retained after the active-oxidation in Ar-CO₂ gas mixtures.     

Diffusivity and solubility of oxygen in solid palladium

The solid solubility c _O of oxygen in palladium in equilibrium with gaseous oxygen has been determined from absorption-desorption experiments for temperatures T of 1123 and 1173 K and oxygen partial pressures between 2.7 × 10³ and 4.0 × 10⁴ Pa. The relationship between c _O, and T is given by , where R = 8.314 JK⁻¹ mol⁻¹ is the universal gas constant, ΔH _s = −13.55 kJ/mol denotes the heat of solution of oxygen in palladium and the constant a amounts to or . The diffusion coefficient D _O of oxygen in solid palladium has been determined by incomplete isothermal internal oxidation of Pd–Fe alloys using the data on the oxygen solubility in palladium. The temperature dependence of D _O obeys the Arrhenius equation D _O = D ⁰ exp(−E _d/RT) with pre-exponential factor D ⁰ = 2.33 × 10⁻⁷ m²/s and activation energy of diffusion of oxygen in palladium, E _d = 102.76 kJ/mol     

Determination of structural parameters of metallic foams from permeametry measurements

An experimental technique, permeametry, is carried out in order to determine the dynamic specific surface area and the tortuosity of three nickel foams. A capillary-type model allows calculation of these structural parameters from pressure-drop measurements. Studying pressure drops of two different flow configurations also allows quantification of a third parameter due to the anisotropy of the material structure. The values of the parameters determined throughout this work are compared with those obtained in previous works using different experimental methods.Nomenclature A experimental coefficient defined by Equation 3 (Pa sm^–2) - A _vd dynamic specific surface area, related to volume of solid (m^–1) - A _ve specific surface area, related to volume of porous medium (m^–1) - B experimental coefficient defined by Equation 4 (Pas²m^–3) - Cr precision criterion - D hydraulic diameter of the cell (m) - d equivalent pore diameter (m) - f friction factor - H bed height or thickness of porous material (m) - J coefficient defined by Equation 8 (m^–1) - K coefficient defined by Equation 9 (m^–2) - l pore length (m) - mre mean relative error - n+1 number of pressure taps - P pressure drop (Pa) - R anisotropy factor or shape anisotropy ratio - Re superficial Reynolds number, Re = U _o d/u - Re_i interstitial Reynolds number, Re _i = U _o d/() - T tortuosity - U _o superficial velocity (m s^–1) - porosity - dynamic viscosity (Pa s) - fluid density (kg m^–3)     

The influence of residual gas pressure on the thermal conductivity of microsphere insulations

Experimental results of investigations of the heat exchange by residual gas in microsphere insulations are presented. The results of measurements of microsphere effective thermal conductivity versus residual gas (N₂) pressure in the pressure range of 10^–3–10⁵ Pa are also given. A sample of self-pumping microsphere insulation was prepared and its thermal parameters were tested. In comparison to the standard microsphere insulation, the self-pumping insulation yielded lower thermal conductivity results over the entire pressure range. The stability of its thermal parameters as a result of considerable gas input into the insulation volume is discussed. Measurements of temperature and pressure distributions inside the microsphere layer were performed. Plots of temperature and pressure gradients inside the layer of the microsphere insulation are presented.Nomenclature d _m Mean value of the microsphere diameter - k Apparent thermal conductivity coefficient - ¯k Average thermal conductivity coefficient - k _c Component of the heat transfer by conduction - k _g Modified gas thermal conductivity under atmospheric pressure - k _r Component of the heat transfer by radiation - k _s Thermal conductivity of the sphere material - k _gc Component of the heat conduction by gas - k _go Gas thermal conductivity under atmospheric pressure - k _gr Sphere effective conductivity - k _ss Component of the heat conduction by the solid state - K 1–(k _g/k _gr) - Kn Knudsen number - ¯L Mean free path of gas molecules - m 1–_s; porosity - m Empty volume of a single sphere - p Residual gas pressure - ¯p Average pressure - p _g Pressure measured by gauge - p ₀ Residual gas pressure above the insulation bed - r Radial coordinate - T Temperature - T _c Temperature of the cold calorimeter wall - T _g Temperature of the pressure gauge - T _H Temperature of the hot calorimeter wall - T _i Gas temperature inside the bed - T _y Constant dependent on the sort of gas - v Volume - Accommodation coefficient - Density - _a Local distance between surfaces - _s Solid fraction - Constant dependent on the sort of gas - Time measured from the initiation of insulation cooling     

The flow of a fluid film entrained by a supersonic flow of gas

We have conducted an experimental study into the flow of a high-viscosity fluid directed through an orifice of small diameter onto the surface of a body contained within a supersonic flow of air.Notation M Mach number for the outlet cross section of the nozzle - Re_D Reynolds number calculated from the parameters of the unperturbed flow at the outlet section of the nozzle and from the diameter of model rounding - P₀ total pressure in the pressure chamber of the wind tunnel, Pa - T₀ deceleration temperature - sweepback angle of leading edge of plate (between the normal to the direction of the unperturbed flow and the generatrix of the leading edge), deg - d orifice diameter, mm - angle between direction of unperturbed flow and radius vector of orifice, deg - frictional stress at boundary separating fluid and gas, Pa - Q volumetric fluid flow rate, cm³/sec - kinematic viscosity of fluid, cSt - q /q_g ratio of the velocity head of the fluid at the outlet from the orifice to the local velocity head of the gas - thickness of fluid film, mm - b width of fluid film, mm - angle between tangents to the side boundaries of the fluid film, deg - s coordinate calculated from the center of the orifice along the midline of the film or along the axis of wedge symmetry, mm - z coordinate calculated along the normal to the axis, mm Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 2, pp. 181–186, August, 1990.     

Evaporation of liquids from cylindrical vessels under conditions of free concentrational convection in a gas phase

An analytical solution is obtained for the axisymmetric problem of free concentrational convection in a vapor-gas mixture with isothermal evaporation of liquids from open cylindrical vessels. Formulas are derived to calculate concentration fields, local and integral mass fluxes of vapor. A comparative analysis of the results of analytical and numerical simulation is carried out for the processes of the evaporation of liquids under the conditions of convective mass transfer.Notation p pressure, Pa - density, kg/m³ - v velocity, m/sec - , dynamic and kinematic viscosity, Pa·sec, m²/sec - D diffusion coefficient, m²/sec - ₁, ₂ mass fractions of vapor and gas in a mixture - g free fall acceleration, m/sec² - M ₁,M ₂ molar masses of vapor and gas, kg/kmole - _r , _z radial and axial components of the velocity of a gas-vapor mixture, m/sec - r, z cylindrical coordinates, m - R, H radius and height of vessel, m - j local mass flux of vapor, kg/(m²·sec) - j vessel cross-sectional area-averaged mass flux of vapor, kg/(m²·sec) - j vessel cross-sectional area-averaged mass flux Chelyabinsk State Technical University, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, pp. 403–407, May–June, 1995.     

Influence of radiation on the limits of heterogeneous combustion of a particle in two parallel reactions on its surface

The influence of radiation on critical parameters of heterogeneous ignition and extinction of a carbon particle in air is analyzed with allowance for two heterogeneous reactions.Notation Q _chem surface power of heat release through chemical reactions, W/m² - Q _h overall density of heat flux by molecular convectionQ _m.c. and radiationQ _i, W/m² - d particle diameter, m - t time, sec - T ₁,T ₂,T ₂,T _w particle gas, and reaction chamber wall temperature respectively, K - ₁, ₂ particle and gas density, kg/m³ - c ₁,c ₂ specific heat of particle and gas, J/(kg·K) - n _ox relative mass concentration of oxidant in the gaseous medium - q _i thermal effect of the first (i=1, C+O₂=CO₂) and the second (i=2, 2C+O₂=2CO) chemical reactions, J/kg - _i stoichiometric coefficient - E activation energy, J/mole - k _0i preexponential factor, m/sec - R universal gas constant, J/(mole·K) - Nu Nusselt number - ₂ thermal conductivity coefficient of gas, W/(m·K) - D ₂ diffusion coefficient of gas, m²/sec - ₂₀, ₂₀,D ₀ density, thermal conductivity, and diffusion coefficients of gas atT ₀ - emissivity coefficient - Stefan-Boltzmann constant, W/(m²·K⁴) - , heat- and mass-transfer coefficients, W/(m²·K), m/sec. Indexes: 1, particle - 2 gas - ign ignition - ext extinction - w wall - st steady - cr critical - in initial - c combustion - m maximum - lim limiting I. I. Mechnikov Odessa State University. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, pp. 466–473, 1995.     

An assessment of expressions for the apparent thermal conductivity of cellular materials

Diverse expressions for the thermal conductivity of cellular materials are reviewed. Most expressions address only the conductive contribution to heat transfer; some expressions also consider the radiative contribution. Convection is considered to be negligible for cell diameters less than 4 mm. The predicted results are compared with measured conductivities for materials ranging from fine-pore foams to coarse packaging materials. The dependencies of the predicted conductivities on the material parameters which are most open to intervention are presented graphically for the various models.Nomenclature a Absorption coefficient - C _v (Jmol^–1 K^–1) Specific heat - E Emissivity - E _L Emissivity of hypothetical thin parallel layer - E ₀ Boundary surfaces emissivity - f Fraction of solid normal to heat flow - fics Fraction of total solid in struts of cell - K(m^–1) Mean extinction coefficient - k(W m^–1 K^–1) Effective thermal conductivity of foam - k _cd(W m^–1 K^–1) Conductive contribution - k _cr(W m^–1 K^–1) Convective contribution - k _g(W m^–1 K^–1) Thermal conductivity of cell gas - k _r(W m^–1 K^–1) Radiative contribution - k _s(W m^–1 K^–1) Thermal conductivity of solid - L(m) Thickness of sample - L _g(m) Diameter of cell - L _s(m) Cell-wall thickness - n Number of cell layers - r Reflection coefficient - t Transmission coefficient - T(K) Absolute temperature - T _m(K) Mean temperature - T _N Fraction of energy passing through cell wall - T ₁(K) Temperature of hot plate - T ₂(K) Temperature of cold plate - V _g Volume fraction of gas - V _w Volume fraction of total solid in the windows - w Refractive index - (m) Effective molecular diameter - (Pa s) Gas viscosity - Structural angle with respect to rise direction - (W m^–2 K^–4) Stefan constant     

Theory for incongruent crystallization: Application to a ZBLAN glass

Equations which describe incongruent nucleation and subsequent crystal growth have been derived. A ZrF₄-BaF₂-LaF₃-AlF₃-NaF glass was used to test the validity of these equations. Nucleation rate measurements were fitted to theory and some growth rate measurements were found in reasonable agreement with theoretical predictions. Both nucleation theory and crystal growth theory were used for computer simulations of the crystallization behaviour during heat treatments. Some heat treatments were performed in a differential scanning calorimeter to verify the theories. The experimental results were in good agreement with the numerical data. Using these theoretical results it is possible to estimate fibre scattering losses due to crystallization. Depending on drawing temperature, estimated losses can vary from 0.014 (310 °C) to 25 (320 °C) or more dB km^–1.Nomenclature a _s the chemical activity of component A in solution referred to the activity of the component in crystalline form - c _c ^A the concentration of A in the crystalline form (mol m^–3) - c _r ^A the concentration of A in the liquid at the interface (mol m^–3) - c ₁ ^A the concentration of A far from the interface in the bulk (mol m^–3) - c _e ^A the equilibrium concentration of A (mol m^–3) - D the diffusion coefficient (m²s^–1) - G the free energy difference between the liquid and the crystal, equal to the molar Gibbs' free enthalpy of component A in solution minus the molar Gibbs' enthalpy of the crystalline form of A (J mol^–1). - -G free energy difference between crystal A and pure liquid A (J mol^–1) - G _a activation energy for growth (J mol^–1) - G _r free energy difference between the liquid (of composition c _r ^A ) at the interface and the pure liquid A - G ₁ free energy difference between the liquid (of compositionc ₁ ^A ) far from the interface and the pure liquid A - H _f heat of fusion of the pure component A (J mol^–1) - I the nucleation frequency (1 m^–3 s^–1) - k Boltzmann constant (J K^–1) - K a constant of the order 10³²–10³³ Pa m^–3 K^–1 - r the radius of the spherical crystal - R gas constant (J mol^–1 K^–1) - t time (s) - T temperature (K) - T T ₁ - T the undercooling of the melt of compositionx ^A (T ₁ is the liquidus of the melt and depends onx _A). - T ₁ liquidus temperature (K) - T _m melting temperature of pure component A (K) - T _p temperature at the top of the DSC peak (K) - u crystal growth rate (ms^–1) - V _m molar volume of the crystallizing phase (mol m^–3) - x _A molar fraction of the precipitating component A in the melt (for an example: see Appendix) - viscosity (Pa s) - jump distance of the order of molecular dimensions (m) - ₀ frequency of vibration (s^–1) - surface tension of the crystal-liquid interface (J m^–2) - the thickness of the diffusion layer     

An assessment of expressions for the apparent thermal conductivity of cellular materials

Diverse expressions for the thermal conductivity of cellular materials are reviewed. Most expressions address only the conductive contribution to heat transfer; some expressions also consider the radiative contribution. Convection is considered to be negligible for cell diameters less than 4 mm. The predicted results are compared with measured conductivities for materials ranging from fine-pore foams to coarse packaging materials. The dependencies of the predicted conductivities on the material parameters which are most open to intervention are presented graphically for the various models.Nomenclature a Absorption coefficient - C _itv(J mol^–1 K^–1) Specinc heat - E Emissivity - E _L Emissivity of hypothetical thin parallel layer - E _o Boundary surfaces emissivity - f Fraction of solid normal to heat flow - f _s Fraction of total solid in struts of cell - K(m^–1) Mean extinction coefficient - k(Wm^–1 K^–1) Effective thermal conductivity of foam - k _cd(Wm^–1 K^–1) Conductive contribution - k _cr(Wm^–1 K^–1) Convertive contribution - k _g(Wm^–1K^–1) Thermal conductivity of cell gas - k _r(Wm^–1 K^–1) Radiative contribution - k _s(Wm^–1 K^–1) Thermal conductivity of solid - L(m) Thickness of sample - L _g(m) Diameter of cell - L _s(m) Cell-wall thickness - n Number of cell layers - r Reflection coefficient - t Transmission coefficient - T(K) Absolute temperature - T _m(K) Mean temperature - T _N Fraction of energy passing through cell wall - T ₁(K) Temperature of hot plate - T ₂(K) Temperature of cold plate - V _g Volume fraction of gas - V _w Volume fraction of total solid in the windows - w Refractive index - (m) Effective molecular diameter - (Pa s) Gas viscosity - Structural angle with respect to rise direction - (Wm^–2 K^–4) Stefan constant     

Use of metastable, dissociated and charged gas species in synthesis: a low pressure analogue of the high pressure technique

Oxidation of silver using microwave-induced oxygen plasma and oxygen-ozone gas mixture was studied as a function of temperature and partial pressure. The oxide Ag₂O was formed at temperatures well above its normal decomposition temperature in oxygen plasma at a pressure of 5 Pa. The higher oxide AgO_1–x was formed in O₂₊O₃ gas mixtures at lower temperatures. The oxygen chemical potentials for the oxidation of Ag to Ag₂O, Ag₂O to AgO_1–x and AgO to Ag₂O₃ were evaluated from thermodynamic data and compared with the experimental results to obtain information on the chemical potential of oxygen in microwave plasma and gases containing ozone. The oxygen potential of the gas phase in microwave plasma operating at a pressure of 5 Pa was found to be in excess of 36 kJ/mol at 750 K. This is equivalent to a pressure of diatomic oxygen gas greater than 3 × 10⁷ Pa. In the O₂₊O₃ mixture at ambient pressure containing 5 mole percent O₃, the oxygen potential is 112 kJ/mol at 465 K. The equivalent pressure of diatomic oxygen is 4 × 10¹⁷ Pa. Thus, metastable species such as O₃ or charged species such as O^– present in plasma can be used as a powerful reagent for the syntheses of metastable oxides. Similar techniques can be used for other metastable inorganic solids such as nitrides for functional applications.     

Stability of operation of an apparatus containing a granular bed fluidized by a gas stream

The results of numerical experiments on the investigation of the stability of the fluidization process relative to finite perturbations and its behavior upon crossing the boundary of stability are presented.Notation H bed height - H₀, H_* bed heights in motionless and steady fluidized states - g free-fall acceleration - k₁, k₂ coefficients of resistance of gas-supply system and gas-distributing device, respectively - M molecular weight of gas - m mass of bed per unit cross-sectional area - p^*, p⁰ pressure at inlet and outlet of apparatus - Q₀, Q_b minimum fluidization velocity and average velocity of gas in the bubble phase - q, q_v total mass-flow rates of gas supplied to the bed and to the free cavity - R gas constant - S cross-sectional area of bed - V volume of cavity below gas-distributing grid accessible to the gas - gas density - T absolute temperature - c,, q₀ parameters introduced into (4) - t time - z dimensionless bed height - x dimensionless time - A, B, C, D, N, n dimensionless complexes introduced into (5) - v dimensionless volume - parameter introduced into (5) - z_* dimensionless bed height in steady fluidized state - circular frequency Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 5, pp. 889–892, November, 1977.     

A study of mechanical configuration optimisation in micro-systems

This paper shows that there are three main categories of factors that make the optimum mechanical design of micro-systems different from macro-systems: scale effects, a limited range of materials, and a limited range of production processes. The combined effect of these factors can make the optimum configuration of a micro-system potentially very different from that of the same system on a macro-scale. In particular, the use of flexible elements for hinges is much more feasible and desirable on a micro-scale.Notation a acceleration (m/s²) - A cross-sectional area (m²) - B magnetic flux [wb/m²] - b width [m] - C constant - d depth [m] - D drag [N] - E Young's modulus [N/m²] - E*= - f resonant frequency [Hz] - F _D drive force [N] - F _E electrostatic pulling force [N] - F emmisivity function - F _G geometric view factor - g gravitational constant [m/s²] - h _c convention heat transfer coefficient [W/m²K] - h height [m] - i current [A] - I _A second moment of area [m⁴] - I _I moment of inertia [kg m²] - J polar second moment of area [m⁴] - k stiffness [N/m] - K thermal conductivity [W/m K] - l length [m] - m mass [kg] - M moment [N m] - P load [N] - P _H Hertz contact pressure [N/m²] - P _C cylinder pressure [N/m²] - q heat transfer rate [W] - R, r radius [m] - Re Reynolds number - T, t temperature [K] - T _A atomic friction torque [N m] - T _D drive torque [N m] - T _F Coulomb friction torque [N m] - T _I inertial resistive torque [N m] - u velocity [m/s] - mean velocity [m/s] - V volume [m³] - V _e voltage [V] - x distance between electrodes [m] - y maximum distance to neutral axis [m] - angular acceleration [rad/s²] - _d thermal diffusivity [1/K] - rolling friction factor - P pressure difference [N/m²] - ₀ dialectric constant [F/m] - strain - dynamic viscosity [Pa s] - scale factor - _S coefficient of sliding friction - _R coefficient of rolling friction - _{1, 2} Poisson's ratio - density (kg/m³) - temperature rise [°C] - _B bending stress [N/m²] - _y yield strength [N/m²] - shear stress [N/m²] - reliability constant     

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.     

Some electrical properties of mixed amorphous thin films of germanium and silicon monoxide before electroforming

The co-evaporated SiO _x -Ge system was studied. Thin-film MIM sandwich structures were deposited by vacuum evaporation at a pressure of 10^–4 Pa and were measured at a pressure of 10^–3 Pa. The conductivity at low temperature and under d.c. fields has been found to be governed by a combination of an electronic hopping process and free-band conduction. At fields greater than 2 × 10⁶ V m^–1, it is concluded that the conduction process is governed by the Poole-Frenkel effect. Comparison with earlier results on SiO _x -GeO₂ films showed small differences in activation energy for conduction for samples of broadly similar overall composition.