Microwave absorption measurements of the electrical conductivity of small particles

A microwave absorption technique based on cavity perturbation theory is shown to be applicable for electrical conductivity measurements of both a small, single-crystal particle and finely divided powder samples when values fall in either the low (<0.1 ^–1 cm^–1) or the intermediate (0.1 100 ^–1 cm^–1) conductivity region. The results here pertain to semiconductors in the latter region. If the skin depth of the material becomes significantly smaller than the sample dimension parallel to theE-field, an appreciable error can be introduced into the calculated conductivity values; however, this discrepancy is eliminated by correcting for the field attenuation associated with the penetration depth of the microwaves. A modification of this approach utilizing the skin depth allows a first-order correction to be applied to powder samples which results in the accurate measurement of absolute values, and results with doped Si powders are compared to values obtained from one small single particle using this microwave technique as well as reported DC values determined with single crystals. The use of this microwave absorption technique with small particles having high surface/volume ratios, such as catalyst supports and oxide catalysts, under controlled environments can provide fundamental information about adsorption and catalytic processes on such semiconductor surfaces. An application to a ZnO powder demonstrates this capability.     

Role of structure and capacity for energy absorption in increasing the strength and crack resistance of refractory ceramics

Conclusions We identified the influence of the parameters of a heterogeneous structure and also of particles possessing the capacity to absorb energy of deformation on the strength _rup and the crack resistance K_lc of refractory ceramics. The proposed relationships facilitate quantitative evaluation of the influence of these factors and indicate ways of increasing the levels of _rup and K_lc. Comparison of the calculated and experimental values of _rup and K_lc obtained from tests of various types of ceramics indicate the suitability of the equations for assessing the characteristics of strength and crack resistance.Translated from Ogneupory, No. 7, pp. 8–13, July, 1987.     

Anisotropy in the strength of cellulosic fibres

Conclusions It is proposed to use the equation of a lemniscate, or the Cassini curve, to determine the destructive stress at break for cellulose films in any direction. Thereupon, to determine , it is necessary to know the destructive stress along two basic directions (₀ and ₉₀).To obtain cellulosic films which are isotropic in plane, a necessary and sufficient condition is ₀=₉₀.Translated from Khimicheskie Volokna, No. 6, pp. 34–35, November–December, 1987.     

Phenomenological model of the scale effect of the strength of polymer fibers

A new derivation of the scale effect equation for polymer fibers is proposed. The equation is: AL ^–, where is the average strength of the fiber; L is the length of the fiber; A and are coefficients. The equation was obtained from the general premises of scale effect theory without indication of the concrete form of the probability function F(S).Ukrainian Scientific-Research Institute of Polymer Fibers, Kiev. Translated from Khimicheskie Volokna, No. 4, pp. 34–36, July–August, 1992.     

A vibrational study of the activation sequence of C–H and C–C bonds of isobutene and 1-butene on Mo(110) and (4 × 4)-C/Mo(110) surfaces

The thermal decomposition pathways of isobutene and 1-butene on both Mo(110) and 4 × 4-C/Mo(110) surfaces have been studied using high-resolution electron energy loss spectroscopy (HREELS) in order to highlight the substantially different activities of these two surfaces towards the cleavage of C–H and C–C bonds. On clean Mo(110), the CH₂ group of isobutene decomposes upon heating to 150 K, producing either a /-bonded isobutenylidene [(CH₃)₂CCH] species or a 1,1-di-/-bonded isobutenyl [(CH₃)₂CC] species. Upon further heating, extensive C–H bond scission occurs to form hydrocarbon fragments which do not contain CH₃ or CH₂ groups, but appear to have largely intact carbon skeletons. By contrast, isobutene is molecularly adsorbed on the carbide-modified surface at 150 K. Further heating produces isobutylidyne [(CH₃)₂HCC] by 300 K, which subsequently decomposes via C–C bond scission to generate surface methyl groups. The different activation sequence of the C–H and C–C bonds of isobutene on clean and carbide-modified Mo(110) surfaces is also qualitatively confirmed by comparative studies of 1-butene on the two surfaces.     

Solutions of the general equations for the radiation dose dependence of the molecular weights of irradiated polymers with an initial Schulz-Zimm distribution

Summary The general equations for the radiation dose dependence of irradiated polymer molecular weights have been solved exactly. For an initial most probable molecular weight distribution (=1), the solutions are analytical and exact. For the general case (1) the solutions are numerical and exact. The present approach has resulted in the solutions for both =1 and 1 being incorporated into a group of FORTRAN computer programs which will solve experimental data for scission and crosslinking yields by both minimization and exact treatments. Simulated data treated using these FORTRAN programs are give. The FORTRAN programs are available from the authors.     

Obtaining corundum-zircon suspensions,their rheological and bonding properties

Conclusions It is shown that the combined grinding of corundum (80%) and zircon (20%) will produce suspensions with high concentrations and binding properties. A study was made of the effect of pH and slip concentration on their rheological properties, density, and the strength of the castings. With a pH of 2.5–3.5 and of 0.50–0.54 we obtained castings with an open porosity of up to 28–30% and _bend of up to 8–9 MPa.Substantial sintering of the material is accomplished even at reduced (1450°C) temperatures. The factors for _bend (on specimens measuring 7×7×70 mm) and _comp (on specimens measuring 10×10×10 mm) with an open porosity of 16–18% are up to 180 and 740 MPa respectively. At 1100 and 1200°C the value of _comp equals 300–340 and 250–300 MPa, respectively.Translated from Ogneupory, No. 6, pp. 22–25, June, 1984.     

Effect of production factors on the properties of siliceous ceramic concrete

Conclusions Using dinas waste as the filler (D_grav=1–40 mm) and a quartz-sand suspension as the binder, we have studied the effect of the production factors on the macrostructure and strength of a siliceous ceramic concrete in the initial (after drying at 105–110°C) state and after heat treatment. The strengthening of the ceramic concrete is not an obligatory technological operation in the case where _cc>12.5 MPa. The value of _cc of the siliceous ceramic concrete is 14.4–105.0 MPa after heat treatment at 100, 1350, or 1450°C.The regression equations which adequately describe the dependence of _cc on the technological factors investigated have been derived.Translated from Ogneupory, No. 6, pp. 36–39, June, 1981.     

Electrical Properties and the Structure of Halogen-Containing Lead Borate Glasses: I. The PbF2–2PbO · B2O3 System

The concentration and temperature dependences of the dc electrical conductivity of glasses in the PbF₂–2PbO · B₂O₃ system is investigated. It is found that, at 20–25 mol % PbF₂, the dependences log = f([F]) and E = f([F]) exhibit kinks. The concentration dependence of the true transport number of fluorine ions _F – is studied using the Tubandt method. It is shown that the introduction of 20–25 mol % PbF₂ leads to a crossover from the protonic conductivity to the unipolar fluorine ionic conductivity ( ). The results obtained are discussed in terms of the Myuller theory of the microinhomogeneous glass structure associated with the selective interaction of the components during the synthesis.     

Electrical conductivity of praseodymia doped ceria

The electrical conductivity () and oxide ion transference number (t ₀) of praseodymia doped ceria systems were measured. The former increased rapidly with the praseodymia content, while the latter decreased. At 600° C, for instance, CeO₂ and Ce_0.6Pr_0.4O₂ under 0.21 atm of oxygen were 2.0×10^–5 and 3.6×10^–2 S cm^–1; andt ₀ in them were 0.59 and 0.11, respectively. This mixed conductor having high electrical conductivity might be useful as a fuel cell electrode if it could be combined with a suitable solid electrolyte.     

The impedance of the alkaline zinc-manganese dioxide cell. II. An interpretation of the data

The impedance of small alkaline zinc-manganese dioxide cells has been interpreted in terms of a controlling charge-transfer and diffusion process at the zinc electrode throughout the early stages of discharge. After about 20% of the available charge has been removed, it becomes necessary to include the manganese dioxide electrode circuit components. This network has the circuit elements for charge transfer and a proceeding chemical reaction. The Warburg component for the manganese dioxide electrode need not be considered since the effective area considerably exceeds that of the zinc. The relative areas are confirmed by the magnitudes of the circuit element components. The decomposition of the impedance data has been successfully accomplished as far as 80% discharge; after this point cells show considerable differences from cell to cell, especially in the low-frequency range, which makes a confident interpretation difficult. It is considered that this is due to the loss of the physical definition of the system.Nomenclature C _m,C _z double-layer capacitances of MnO₂ and Zn electrodes, respectively - C _X,R _X parallel branch accounting for current density varying with fractional electrode coverage - R resistance of electrolyte - V open-circuit voltage of cell - Z, Z, Z impedance of cell,resistive component ofZ and reactive component ofZ, respectively - _m, _z transfer resistance of MnO₂ and Zn electrodes, respectively - , _R, _C in Warburg equation:Z _W = ^–1/2(1–i) orZ _W = _R^–1/2– i_Cco^–1/2     

Determination of assigned configurational parameters for cross propagation in radical copolymerization of methyl methacrylate and trityl methacrylate

Summary Copolymer of methyl methacrylate-d₈(M₁) with a small amount of trityl methacrylate(M₂) was radically prepared in tetrahydrofuran and converted into the copolymer of methyl methacrylate-d₈ with a small amount of undeuterated methyl methacrylate by the selective hydrolysis of the trityl group and subsequent methylation with diazomethane. From the ¹H NMR spectrum of the derived copolymer the assigned coisotactic parameters ₁₂ and ₂₁ were determined to be 0.14 and 0.61, respectively. This may be the first example of the unequivocal determination of assigned configurational parameters in cross propagation for copolymerization.     

Ternary alkali carbonate composition-oxygen solubility relationship under atmospheric and pressurized conditions – a utility model for MCFC

The effect of O₂/CO₂ = 90/10 gas mixtures under pressurized conditions on the diffusion resistance during oxygen reduction was investigated in carbonate melts of variable composition ranging from the eutectics Li–K, Li–Na to ternary Li–Na–K carbonate melts. It was found that pressurization reduced the diffusion resistance of the reactant species in all compositions investigated. This was ascribed to the increase in concentration of the reactive species in the electrolyte. Reaction order plots of Warburg coefficient versus the total pressure in binary melts showed that: (i) mixed diffusion of superoxide ions and CO₂ prevails in lithium rich carbonates, and (ii) mixed diffusion of peroxide ions and CO₂ predominates in potassium rich carbonates. By means of a computerized statistical analysis of the results, a partial cubic model was found to describe the relationship between alkali carbonate compositions, pressure, and Warburg coefficient. The optimum alkali carbonate compositions are: (i) 0.283Li–0.373Na–0.344 K with _app equal to 137.68 cm²s^–0.5 at atmospheric conditions, and (ii) 0.390Li–0.355 Na–0.255 K with _app 87.53 cm² s^–0.5 and 4.2 atm under pressurized conditions.     

On the Charge Carrier Concentration in Sodium–Calcium Aluminophosphate Glasses

The dc and ac conductivities of the xNa₂O–(35 – x)CaO–7.5Al₂O₃–57.5P₂O₅glasses (mol %) with x= 0–35 are studied in the frequency range from 20 Hz to 1 MHz at different temperatures. It is found that the dc conductivity strongly depends on xonly for glasses with x 10. For glasses with x 5, the dc conductivity is virtually composition independent. The dependence of the ac conductivity plotted on the log(()/_dc) vs. log(/_dc) coordinates is analyzed. The ac conductivity represented in these coordinates depends on xonly for glasses with x 5, in which the dc conductivity does not depend on x. For glasses with xin the range from 10 to 35, all the isotherms of the ac conductivity closely coincide with each other. This result is discussed in the framework of two hypotheses: (1) the conductivity () is determined by the dynamic polarization (of the Maxwell–Wagner type at low frequencies) of the material due to spatial fluctuations of the density of paths providing the migration of sodium ions and (2) the concentration of charge carriers is independent of x.     

Fibrous aluminum silicate material

Conclusions The authors have investigated aluminosilicate fiber with organosilicon binder. They show that a rise in pressing pressure from 5 to 50 kPa, a rise in temperature from 300 to 500°C, and a rise in treatment time from 15 to 60 min enables us to obtain products with apparent densities from 0.4 to 0.65 g/cm³.As the apparent density of the products increases, so does _c, reaching 1 MPa at the maximum density; the gas permeability decreases.Articles impregnated with bakelite, chromium acetate solution, aluminum chloride solution, and aluminophosphate binder have enhanced strength and corrosion resistance to fused metals (aluminum, copper, and steel).Translated from Ogneupory, No. 4, pp. 52–55, April, 1980.     

Detonation Properties and Electrical Conductivity of Explosive–Metal Additive Mixtures

Detonation properties of mixtures of condensed high explosives with metal additives are studied. A scheme of measurement of high electrical conductivity of detonation products ( > 10 ^–1 · cm^–1) with a time resolution of 10 nsec is developed. It is shown that the properties of detonation products depend significantly on the content of the additive in the HE and on dispersion and density of the mixture. The electrical conductivity of detonation products of the compositions examined reaches 5 · 10^{3 –1} · cm^–1, which is more than three orders higher than the electrical conductivity of the HE without the additive. Significant variation of electrical conductivity of detonation products over the conducting region thickness has been found. The main conductivity corresponds to a sector 1 mm long near the detonation front. The overdriven state of the detonation wave has a strong effect on electrical conductivity and conducting region thickness. It is assumed that the behavior of electrical conductivity with time is caused by successive processes of shock compression of the HE, excitation of the chemical reaction (including the reaction of the additive with detonation products), and expansion of detonation products. The measurement technique used is highly informative due to the possibility of studying detonation in various regimes.     

Surface characterization of zirconium titanate (ZrTiO4) powder by measurements of electrical photoconductance and photoassisted oxygen isotope exchange

The photosensitivity of a ZrTiO₄ sample (33 m²/g) prepared by a sol-gel method has been assessed in the presence of O₂ by both photoconductance and oxygen isotope exchange (OIE) measurements at room temperature at wavelengths > 290 nm. For oxygen pressures < ca. 13.3 Pa, the steady-state photoconductance of ZrTiO₄ was unaffected by , which indicated that the direct recombination of the photoproduced charges played the dominant role. At higher pressures, varied as the reciprocal of , which was consistent with the fact that the electronic equilibrium was then governed by O₂ + e^– O ₂ ^– . OIE over ZrTiO₄ occurred predominantly via the overall mechanism which involves the exchange of two surface oxygen atoms for each exchange act. It was very slow as compared with OIE over photocatalytically active anatase samples which, in addition, occurs via another mechanism. These results allow one to predict that this ZrTiO₄ sample is a poorly active photocatalyst for oxidations involving gaseous oxygen, and further illustrate the interest of and OIE measurements to evaluate the photosensitivity of semiconductor oxide samples.     

Gas induced bath circulation in aluminium reduction cells

Gas induced bath circulation in the interpolar gap of aluminium cells was studied in a room temperature physical model and by computer simulation. The circulation velocity increased with increasing gas formation rate, increasing angle of inclination and decreasing bath viscosity, while it was less affected by anode immersion depth, interpolar distance (in the normal range), and convection in the metal. A typical bath velocity near the cathode was 0.05 m s^–1. The flow velocity decreased with decreasing bubble size. The results were fitted to a simple semi-empirical expression, and the velocities measured in the model experiments were in good agreement with the findings of the computer simulation.Nomenclature A Surface area (m²) - c _D Drag coefficient (l) - c _pr Concentration of 1-propanol (ml/1000 ml) - d _e Equivalent diameter of gas bubble (m) - F Faraday constant (96 487 C mol^–1) - g Acceleration due to gravity (9.82 m s^–2) - g Gravity component along anode surface (m s^–2) - h Vertical dimension of gas-filled layer (m) - H Anode immersion depth (m) - i Current density (A m^–2) - k Turbulent energy (m² s^–2) - P Pressure (N m^–2) - q Gas formation rate (m³ s^–1 m^–2) - R Universal gas constant (8.314 J mol^–1 K^–1) - t Time (s) - U Liquid velocity parallel to anode surface (m s^–1) - U _b Bubble velocity parallel to anode surface (m s^–1) - U _rel Relative velocity between bubble and liquid (m s^–1) - V Liquid velocity perpendicular to anode surface (m s^–1) - x Distance from centre of anode (m) - y Vertical distance from cathode (m) - Y Interpolar distance (m) - Angle of inclination referred to the horizontal (deg.) - Dissipation rate of turbulent energy (m² s^–3) - Volume fraction of liquid (1) - v Kinematic viscosity / (m² s^–1) - Dynamic viscosity (kg m^–1 s^–1) - _t Turbulent viscosity (kg m^–1 s^–1) - Density of liquid (kg m^–3) - /g9 Kinematic surface tension (m³ s^–2) - Bubble void fraction (1) Paper presented at the 2nd International Symposium on Electrolytic Bubbles organized jointly by the Electrochemical Technology Group of the Society of Chemical Industry and the Electrochemistry Group of the Royal Society of Chemistry and held at Imperial College, London, 31st May and 1st June 1988.     

Studies on electrical conductivity of gamma irradiated polyaniline

Summary de electrical conductivity at surface of -irradiated polyaniline (PAn) has been studied. EPR spectroscopic results indicate that the variation of spin concentration is consistent with the increase of _de. Electrical conductivity (_de) versus temperature (T) characteristics of unirradiated and irradiated PAn were performed, which demonstrate that the unirradiated curve can fit to ln_deT₁, while the irradiated curve fit to ln_deT_1/4.     

Transcrystallization of maleated polypropylene in the presence of various carbon fibers

Summary In this paper, the influence of the fiber surface sizing on development of transcrystallization, TCR, as well as the fiber-matrix interactions were analysed. Sized (CT) and unsized (CU) high-strength carbon fibers and maleated polypropylene, mPP, were used in model systems. Transcrystallization was followed by polarizing optical microscopy, in isothermal regime (Tc=124–130 °C). Besides the radius, distribution of the thickness and growth rate of the transcrystalline layer and the surface energetic parameters have been also determined. Lower value for was obtained for the system with surface treated C fibers ( ^CT =1,145x10 ^-7 J/cm ² ) which also contribute for their higher nucleation activity. Using FTIR microscopy and model reaction, an attempt was made to analyse the chemical interactions at fibedmatrix interface.