Salt‐Induced Modulation of the Krafft Temperature and Critical Micelle Concentration of Benzyldimethylhexadecylammonium Chloride

In this work, the effect of some sodium salts on the Krafft temperature (T_K) and critical micelle concentration (CMC) of benzyldimethylhexadecylammonium chloride (C16Cl) in aqueous solution has been studied. It was observed that the T_K can be modulated to lower and higher values and the CMC can be depressed significantly upon the addition of the electrolytes. More chaotropic Br^? and I^? raise the T_K with an increase of the concentration of the ions. On the other hand, less chaotropic NO₃^? initially lowers and then raises the T_K. Kosmotropic F^?, SO₄^2? and CO₃^2? gradually lower the T_K with increasing concentration of the electrolytes. The more chaotropic ions form contact ion pairs with the surfactant and decrease the solubility with a consequent increase in the T_K. On the other hand, kosmotropic ions, being extensively hydrated in the bulk, remain separated from the surfactant by hydrated layers of water molecules. As a result, a significant electrostatic repulsion exists between the charged headgroups of the surfactant, resulting in a decrease in the T_K. The CMC of the surfactant decreases significantly in the presence of these ions. The surface tension at the CMC (γ_CMC) also decreases in the presence of all the salts except for F^?. The electrostatic repulsion between the charged headgroups is significantly reduced because of screening of the surface charge of both micelles and adsorbed monolayers by the associated counterions, resulting in a decrease in both the CMC and γ_CMC.     

Temperature fluctuations and heat transfer in a fluidized-bed combustor of waste oil

Temperature fluctuations and heat transfer characteristics were investigated in a fluidized-bed combustor of 0.102 m ID and 2.5 m in height, which was designed for waste oil combustion. Effects of excess air (A_E), injection height (H_I) and feeding rate of waste oil (Q_F) on the mean bed temperature (T_B), Kolmogorov entropy (K₂) of phase space portraits and heat transfer coefficient (U₀) in the fluidized-bed combustor were determined. T_B increased, but K₂ and U₀ decreased with increasingA _E . K₂ had a local minimum, but T_B and U₀ had a maximum at H_I of 0.4 m. T_B increased, but K₂ had a minimum and U₀ had a maximum with increasing Q_F in the combustor. T_B, K₂ and U₀ obtained at the optimum operating condition (A_E=40%, H_I=0.4 m, Q_F=30 g/min) were about 855 ‡C, 22 bits/s and 382 W/m²K, respectively.     

Rotating spherical interlayer (RSI) measurement of the dynamic mechanical properties of elastomers

An analysis of simple shear in a rotating spherical interlayer is presented. The theory provides design criteria and operating equations for a new method of measuring the dynamic mechanical properties of soft viscoelastic polymers. The storage component of the dynamic shear modulus G′(ω) = 3F₁hm²/2πr⁴(3 sin ? + sin³?) (ΔX_t ? K₁F₁) and the loss tangent than δ = [F₂(ΔX_t ? K₁F₁) ? K₂F₁F₂]/[F₁(ΔX_t ? K₁F₁)? K₂(F₂)²] are expressed in terms of the inner radius r, thickness, h, and are angle ? of sample extending from the rotational equator; the biaxial dynamometer compliances K₁, K₂; the imposed dynamometer displacement ΔX_t; and the spherical interlayer storage and loss forces F₁, F₂. New instrumentation involving a rotating spherical interlayer (RSI) transducer and a rotational accessory to the Instron provides measurements from 0.001 to 45 cycle/sec at temperatures from ?50° to 200°C. A comparison of RSI data, treated by time–temperature superposition, and literature values of dynamic response in polyisobutylene confirms both theory and method.     

Influence of Some Hofmeister Anions on the Krafft Temperature and Micelle Formation of Cetylpyridinium Bromide in Aqueous Solution

In this work, the effect of some Hofmeister anions on the Krafft temperature (T_K) and micelle formation of cetylpyridinium bromide (CPB) have been studied. The results show that more chaotropic anions increase, while the less chaotropic ones lower the T_K of the surfactant. More chaotropic I^? and SCN^? form contact ion pairs with the cetylpyridinium ion and reduce the electrostatic repulsion between the CPB molecules. As a result, these ions show salting‐out behavior, with a consequent increase in the T_K. In contrast, less chaotropic Cl^? and NO₃^? increase the activity of free water molecules and enhance hydration of CPB molecules, showing a decrease in the T_K. A rather unusual behavior was observed in the case of SO₄^2? and F^?. These strong kosmotropes shift from their usual position in the Hofmeister series and behave like moderate chaotropes, lowering the T_K of the surfactant. Because of the high charge density and the strong tendency for hydration these ions preferentially remain in the bulk. Rather than forming contact ion pairs, these ions stay away from the CPB molecules, decreasing the T_K of the surfactant. In term of decreasing the T_K, the ions follow the order NO₃^? > SO₄^2? > Cl^? > F^? > Br^? > SCN^? > I^?. The critical micelle concentration (CMC) of the surfactant decreases significantly in the presence of these ions due to the screening of the micelle surface charge by the excess counterions. The decreasing trend of the CMC in the presence of the salts follows the order SCN^? > I^? > SO₄^2? > NO₃^? > Br^? > Cl^? > F^?.     

K2CaSi4O10: A novel phase in the ternary system K2O–CaO–SiO2 and member of the litidionite group of crystal structures

The main goal of this work was to verify whether a phase with composition K₂CaSi₄O₁₀ exists in the ternary system K₂O‐CaO‐SiO₂. Therefore, a series of solid‐state reactions of stoichiometric mixtures of K₂CO₃, CaCO₃ and SiO₂ was performed at 800 and 900?C which, indeed, resulted in the formation of this previously unknown potassium calcium silicate. More detailed characterizations of this compound were based on single‐crystal X‐ray diffraction experiments. Basic crystallographic data are as follows: triclinic symmetry, space group P‐1, a = 7.0915(7) Å, b = 8.4211(9) Å, c = 10.2779(12) Å, α = 104.491(10)°, β = 100.570(9)°, γ = 113.738(9)°, V = 515.26(10) ų, Z = 2. Structure solution was performed by direct methods. Subsequent refinement calculations using anisotropic displacement parameters for all atoms converged to a residual of R(|F|) = 0.0355 for 1889 independent reflections with I > 2σ(I). From a structural point of view K₂CaSi₄O₁₀ belongs to the so‐called litidionite family of A′AMSi₄O₁₀ compounds for which several natural and synthetic representatives have been described in the literature. Actually, it is the first member where the A′‐ and A‐positions are exclusively occupied by K‐ions. Following the nomenclature for oxosilicates K₂CaSi₄O₁₀ can be allocated to the group of the tubular chain silicates. Fundamental building units are loop‐branched dreier double chains (running parallel to [100]) which can be described using the following structural formula: {lB,}[³Si₈O₂₀]. Ca‐ions are coordinated by 5 nearest oxygen neighbors in form of distorted trigonal bipyramids. By sharing a common edge two adjacent bipyramids are linked into [Ca₂O₈]‐dimers providing linkage between consecutive tubes in the direction of the c‐axis. Charge compensation is achieved by the incorporation of the larger potassium ions into cavities of the heteropolyhedral network. Powder X‐ray diffraction patterns of the bulk material of the synthesis products revealed that, additionally to K₂CaSi₄O₁₀, the 800°C ‐sample contained K₈CaSi₁₀O₂₅ and at least one further, yet unknown crystalline phase. This unidentified so‐called 22‐Å compound was also present in the 900 °C‐specimen together with K₂CaSi₄O₁₀ and K₂Ca₄Si₈O₂₁. Our proof of existence of K₂CaSi₄O₁₀ is a further step towards a better understanding of the ternary system K₂O‐CaO‐SiO₂ and provides a basis for identification and quantification of this compound in phase analysis. It corrects earlier phase‐analytical studies on this system which is of relevance for applied and technical mineralogy including different types of residual materials such as slags or ashes from biomass combustion. The results of our investigation show that even comparatively simple ternary oxide systems are not as well understood as expected.     

Characteristics of poly(AAc5‐co‐HPMA3‐cl‐EGDMA15) hydrogel‐immobilized lipase of Pseudomonas aeruginosa MTCC‐4713

Four series of noble networks were synthesized with acrylic acid (AAc) copolymerized with varying amount of 2‐hydroxy propyl methacrylate or dodecyl methacrylate (AAc/HPMA or AAc/DMA; 5:1 to 5:5, w/w) in the presence of ethylene glycol dimethacrylate (EGDMA; 1, 5, 10, 15, and 20%, w/w) as a crosslinker and ammonium per sulfate (APS) as an initiator. Each of the networks was used to immobilize a purified lipase from Pseudomonas aeruginosa MTCC‐4713. The lipase was purified by successive salting out with (NH₄)₂SO₄, dialysis, and DEAE anion exchange chromatography. Two of the matrices, E_15a, i.e. [poly (AAc₅‐co‐DMA₁‐cl‐EGDMA₁₅)] and I_15c, i.e. [poly (AAc₅‐co‐HPMA₃‐cl‐EGDMA₁₅)], that showed relatively higher binding efficiency for lipase were selected for further studies. I_15c‐hydrogel retained 58.3% of its initial activity after 10th cycle of repetitive hydrolysis of p‐NPP, and I_15c was thus catalytically more stable and efficient than the other matrix. The I_15c‐hydrogel‐immobilized enzyme showed maximum activity at 65°C and pH 9.5. The hydrolytic activity of free and I_15c‐hydrogel‐immobilized enzyme increased profoundly in the presence of 5 mM chloride salts of Hg²⁺, NH₄⁺, Al³⁺, K⁺, and Fe³⁺. The immobilized lipase was preferentially active on medium chain length p‐nitrophenyl acyl ester (C:8, p‐nitrophenyl caprylate). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4636–4644, 2006     

Effect of surfactants on the rate of mass transfer at gas-evolving electrodes

The effect of sodium lauryl sulphate surfactant on the mass transfer coefficient of the cathodic reduction of ferricyanide ion and the anode oxidation of ferrocyanide ion at hydrogen- and oxygen-evolving electrodes, respectively, was studied. Also, the effect of sodium lauryl sulphate on the gas hold-up and cell voltage was studied. The presence of surfactant in the electrolyte was found to decrease the mass transfer coefficient by an amount ranging from 7.6 to 81% depending on the operating conditions. Gas hold-up and cell voltage were found to increase in the presence of surfactant.Nomenclature C concentration - F Faraday constant (96 487 C mol^–1) - I _I limiting current under natural convection - I current consumed in ferricyanide reduction or ferrocyanide oxidation during electrolysis with gas evolution - K mass transfer coefficient - V gas discharge rate - Z number of electrons involved in the reaction - gas hold-up     

MOCVD-derived GdYBCO tapes with smooth surface and low Rs based on a new self-heating technology

The metal organic chemical vapor deposition (MOCVD) method was used to prepare GdYBCO films on LaMnO₃/ homo epitaxial-MgO/ ion-beam-assisted-deposition-MgO/ solution-deposition-planarization-Y₂O₃ buffered Hastelloy tapes. By adopting a simple self-heating technique, the substrates were heated by the joule effect after applying a heating current (I_h) through Hastelloy metal tapes. The effects of substrate temperature and (Gd, Y)/Ba ratio (r_c) in the precursor on the biaxial texture, surface morphology and superconducting performance of GdYBCO films were systematically investigated by varying the values of I_h and r_c. Needle-like outgrowths formed on the substrate surface were characterized using a scanning electron microscope, energy dispersive spectrometer and X-ray diffraction system. The results show that a high I_h or r_c leads to the formation of needle-like outgrowths. Therefore, I_h and r_c are crucial process parameters that control the growth of needle-like outgrowths on the surface of GdYBCO films. Three hundred nanometer thick GdYBCO films were prepared at different I_h and r_c by the MOCVD process. At an I_h of 27.0?A and an r_c of 0.6, the surface of the GdYBCO film was very smooth and dense, which can provide a good template for multiple depositions of GdYBCO films. The critical current density of the deposited 300?nm-thick GdYBCO film was 4.4 MA/cm² (77?K, 0?T), which is attributed to good biaxial texture and appropriate film composition. Furthermore, the microwave surface resistance (77?K, 10?GHz) of the GdYBCO film was merely 0.581?mΩ.     

Temperature Stability of Electrical Properties of (K0.5Na0.5)1−xLixNb0.95Sb0.05O3 Lead-Free Ceramics

(K_0.5Na_0.5)_1−xLi_xNb_0.95Sb_0.05O₃ (KNLNS-x, x=0–10 mol%) lead-free piezoelectric ceramics were prepared by the conventional mixed-oxide method. The temperature stability of the dielectric, piezoelectric, and ferroelectric properties of the two typical compositions (KNLNS-2 with orthorhombic phase, and KNLNS-7 with mixed phases) was investigated systematically. The relationship between the orthorhombic–tetragonal polymorphic phase transition (PPT) of the ceramics and the temperature stability of their electrical properties was also discussed. The electromechanical coupling factors (k_p and k₃₁) of the ceramics show the maximum values near the PPT, where the temperature stability of the resonance frequency is relatively poor. After the occurrence of the PPT, the remnant polarization (P_r) of the ceramics shows a marked decrease, and a maximum peak in the coercive field (E_c) is observed. Related mechanisms for the temperature stability of electrical properties were also discussed.     

Structural and spectroscopic properties of Nd:Y2Si2O7 phosphors

Phosphors of α-Y₂Si₂O₇ doped with Nd³⁺ ions were prepared using the sol–gel technique. Nano-sized crystalline phosphor powders were obtained by annealing the dried gels at 960 °C. The crystallization properties of the phosphor powders were determined from their XRD patterns. The α-Y₂Si₂O₇ phase was the only phase observed in all compositions. As the amount of amorphous SiO₂ in the composition was increased, the crystalline sizes and the widths of the size distribution curves were found to decrease from 17.8 nm to 10.6 nm and from 15.6 nm to 12.2 nm, respectively. The spectroscopic properties of the powders were studied by measuring the luminescence and the decay patterns of the ⁴F_3/2→ ⁴I_9/2 and ⁴F_3/2→ ⁴I_11/2 transitions between 50 K and 310 K. No appreciable effect of the crystallite sizes on the average lifetime of the ⁴F_3/2 level was observed at temperatures below 100 K. The effect of temperature, however, becomes relevant above 100 K as the size of α-Y₂Si₂O₇ nano-crystal becomes smaller.     

Effect of grain size on R-curve behaviour of alumina ceramics

Alumina samples with average grain sizes ranging from 2.6 to 67.4 μm were prepared by sintering at 1500–1900°C for 2–20 h in high vacuum. Crystallographic and thermal expansion mismatch between adjacent grains during cooling involved residual stresses in these ceramics. The effect of these stresses on fracture behaviour of alumina ceramics was investigated by testing controlled crack growth during three point bending of single-edge-notched samples. After initiation, the crack grew slowly by repeated loading and unloading. The crack length c, was measured and registered in situ by means of a CCD camera coupled to an appropriate microscope, which was fitted to the test equipment by a system of elevator stages driven by stepping motors. The force P, necessary to produce an increasing crack length was computer controlled. The stress intensity factor K_I, was calculated from values of the crack length c, and force P. The data of K_I=f(c) obtained in the range of crack lengths studied were fitted by a linear function y=ax+b. As a result, the slope was used as a parameter describing R-curve behaviour of ceramics. The tests showed that R-curve behaviour of alumina ceramics strongly increases with the increase of Al₂O₃ grain size. This phenomenon was explained by analysis of microstructures and residual stresses found in ceramics by piezospectroscopic measurements. In several samples the crack growth tests were performed without unloading. The time dependent displacement d of the sample was measured and recorded together with values of force P. The stress intensity factor K_I, maximal stress intensity factor K_Imax, resistance to crack initiation K_Ii, and work-of-fracture γ_F, were inferred from measured data.     

A new analytical modeling for the determination of thermodynamic quantities of refrigerants

A new analytical fundamental equation of state (EOS) is presented for fluids. The equation is explicit in the effective molecular potentials and allows calculation of all thermodynamic properties over the whole fluid surface (gas, liquid, supercritical and gas–liquid phase transition). Outside the critical area (± 0.05T_c), it is valid in a vast range of temperature and pressure (0.8T_c to 7.5T_c and up to 120P_c,). The EOS is applicable for a variety of refrigerants such as C₃H₂F₄ (HFO-1234ze (E)), hydrofluorocarbons (HFCs) including C₃F₈ (R218), C₃H₂F₆ (R236ea), C₃H₂F₆ (R236fa), C₃H₃F₅ (R245ca), C₃HF₇, C₄F₈ (RC318), C₄F₁₀, C₅F₁₂, natural refrigerants including NH₃, CO₂, hydrocarbons, monatomic gases and some other fluids. Calculations of second derivatives properties of fluids are sensitive tests of EOS behavior. Therefore, estimation of the thermodynamic properties including Joule-Thomson coefficient, μ_JT, and speed of sound, w, has been considered.     

Electrochemical promotion of the oxidation of propane on Pt/YSZ and Rh/YSZ catalyst-electrodes

The effect of electrochemical promotion (EP) or non-faradaic electrochemical modification of catalytic activity (NEMCA) was studied in the catalytic reaction of the total oxidation of propane on Pt and Rh films deposited on Y₂O₃-stabilized-ZrO₂ (or YSZ), an O²⁻ conductor, in the temperature range 420–520 °C. In the case of Pt/YSZ and for oxygen to propane ratios lower than the stoichiometric ratio it was found that the rate of propane oxidation could be reversibly enhanced by application of both positive and negative overpotentials (“inverted volcano” behavior), by up to a factor of 1350 and 1130, respectively. The induced rate increase Δr exceeded the corresponding electrochemically controlled rate I/2F of O²⁻ transfer through the solid electrolyte, resulting in absolute values of the apparent faradaic efficiency Λ=Δr/(I/2F) up to 2330. The Rh/YSZ system exhibited similar EP behavior. Abrupt changes in the oxidation state of the rhodium catalyst, accompanied by changes in the catalytic rate, were observed by changing the O₂ to propane ratio and catalyst potential. The highest rate increases, by up to a factor of 6, were observed for positive overpotentials with corresponding absolute values of faradaic efficiency Λ up to 830. Rate increases by up to a factor of 1.7 were observed for negative overpotentials. The observed EP behavior is explained by taking into account the mechanism of the reaction and the effect of catalyst potential on the binding strength of chemisorbed reactants and intermediates and on the oxidative state of the catalyst surface.     

Slow crack propagation in Y-TZP/metal composites

The paper presents results of investigation on slow crack propagation of two composites in TZP/metal system, where 10 vol.% of tungsten and molybdenum were used as dispersed phase. The mean grain size of the inclusions was about 2 μm. Composites were prepared by intensive attrition milling/mixing of the constituent phases in ethyl alcohol and densified by hot-pressing at 1500 °C under 25 MPa in argon atmosphere. Strength, fracture toughness and hardness were investigated. The threshold value (K_I0) of slow crack propagation is higher for both composite materials when compared with TZP. Both investigated composites show similar K_I0 values and maximum values of the critical stress intensity factor (K_Ic) by using different methods.     

Development of a comprehensive visual dataset based on a CIE blue color center: Assessment of color difference formulae using various statistical methods

The objectives of this work were to develop a comprehensive visual dataset around one CIE blue color center, NCSU‐B1, and to use the new dataset to test the performance of the major color difference formulae in this region of color space based on various statistical methods. The dataset comprised of 66 dyed polyester fabrics with small color differences ($\Delta E_{{\rm ab}}^* < 5$ ) around a CIE blue color center. The visual difference between each sample and the color center was assessed by 26 observers in three separate sittings using a modified AATCC gray scale and a total of 5148 assessments were obtained. The performance of CIELAB, CIE94, CMC(l:c), BFD(l:c), and CIEDE2000 (K_L:K_C:K_H) color difference formulae based on the blue dataset was evaluated at various K_L (or l) values using PF/3, conventional correlation coefficient (r), Spearman rank correlation coefficient (ρ) and the STRESS function. The optimum range for K_L (or l) was found to be 1–1.3 based on PF/3, 1.4–1.7 based on r, and 1–1.4 based on STRESS, and in these ranges the performances of CIEDE2000, CMC, BFD and CIE94 were not statistically different at the 95% confidence level. At K_L (or l) = 1, the performance of CIEDE2000 was statistically improved compared to CMC, CIE94 and CIELAB. Also, for NCSU‐B1, the difference in the performance of CMC (2:1) from the performance of CMC (1:1) was statistically insignificant at 95% confidence. The same result was obtained when the performance of all the weighted color difference formulae were compared for K_L (or l) 1 versus 2. © 2009 Wiley Periodicals, Inc. Col Res Appl, 2011     

A model for the Kolbe reaction of acetate in a parallel-plate reactor

A mathematical model is developed for the study of the Kolbe oxidative dimerization of acetate to ethane and carbon dioxide in a parallel-plate reactor operating at a fixed cell potential, with hydrogen evolution being the cathode reaction. The volume of gas evolved into the interelectrode gap is tracked by constructing a hypothetical gas layer which increases in thickness with the streamwise direction in a manner determined by solution to the model equations; concurrently, the liquid flows in a hypothetical layer which decreases in thickness. The three-component gas phase is assumed to be ideal, and the liquid phase is an aqueous mixture of five species: acetate, proton, sodium and hydroxyl ions and acetic acid. The model predicts the concentration profiles and the streamwise variation of the gas-void fraction, reaction current density and liquid and gas velocities. Gas evolution causes a decreasing current density in the streamwise direction and an increasing gas and liquid velocity. The concentrations of acetic acid and proton decrease in the streamwise direction, while hydroxyl concentration increases; the decrease in acetate concentration, however, is not significant until the local base-to-acid ratio is near unity because of the buffering effect from undissociated acetic acid. The average current density increases with inlet solution velocity and cell potential and asymptotically approaches the secondary current limit. There exists an optimal interelectrode separation where the cell resistance is minimum. The average current density exhibits a shallow maximum with the baseto-acid ratio of the feed, but decreases precipitously when the ratio is near unity due to the rapid decrease in the proton concentration.Nomenclature b _a anodic Tafel constant of the Kolbe reaction of acetate (V) - b _c cathodic Tafel constant of hydrogen evolution reaction (V) - c ₁ acetate concentration, mol cm^–3 - c ₁, ref reference concentration of acetate (mol cm^–3) - c ₂ acetic acid concentration (mol cm^–3) - c ₃ proton concentration (mol cm^–3) - c ₃, ref reference concentration of proton (mol cm^–3) - c ₄ hydroxyl concentration (mol cm^–3) - C _A stoichiometric concentration of acetic acid in the feed stream (mol cm^–3) - C _B stoichiometric concentration of sodium hydroxide in the feed stream (mol cm^–3) - c _B/A C _B/C _A, base-to-acid ratio in the feed stream (sodium hydroxide to acetic acid) - c _i(0) concentration of species i at cell inlet (mol cm^–3) - c _i ^* c _i/c _A - E _d decomposition potential (V) - E _neq,a ^o standard open-circuit potential of the Kolbe reaction of acetate (V) - E _eq,a ^o open-circuit potential of the Kolbe reaction of acetate (V) - E _eq ^c standard open-circuit potential of hydrogen evolution reaction (V) - E _eq,e open-circuit potential of hydrogen evolution reaction (V) - F Faraday constant (96 487 C equiv.^–1) - f gas-void fraction - h cell height (cm) - IR ohmic-voltage drop in the electrolyte (V) - i current density (A cm^–2) - i _a,ref exchange current density of acetate Kolbe reaction at reference concentration (A cm^–2) - i _c,ref exchange current density of hydrogen evolution reaction at a reference concentration (A cm^–2) - i _avg average current density (A cm^–2) - i(0) current density at the inlet of the cell (A cm^–2) - i ^* i/i(00) - Ka ionization constant of acetic acid (mol cm^–3) - K _a ^* K _a/c _A     

The hydrodynamics of a magnetoelectrolytic cell

The characteristics of induced flow in a cylindrical magnetoelectrolytic cell under the influence of uniform and non-uniform magnetic fields are analysed. Experimental surface velocity values are predicted with reasonable accuracy by magnetohydrodynamic models incorporating open-channel flow concepts.Nomenclature A, D parameters in Equation 7 [Gak equation] - B magnetic flux density vector;B _r,B _z its radial and axial components;B ₀ its magnitude, ¯B its average magnitude - B ₁ (pr) auxiliary function in the annular Hankel transform technique (Equation 6) - e unit vectors in the cylindrical coordinate system with componentse _r,e _o,e _z - F magnitude of the MHD force density in the-direction - f _c friction coefficient of energy loss due to curvature - g acceleration due to gravity - H height of the electrodes in electrolytic cell - h _f energy head loss due to friction - h _c energy head loss due to curvature - I electric current flow - J electric current density vector - K lumped parameter;K=IB _o/2H - K _f,K _c K factors in terms of friction and curvature losses - k geometric shape factor,R/r _o - P pressure - p annular Hankel transform parameter - R radius of the outer electrode - r _o radius of the inner electrode - r radius measured from the centre of the electrolytic cell - V _gq velocity in the-direction - ¯V its average - _n regression coefficients in Equation 13 - dynamic viscosity of electrolyte - gn kinematic viscosity of electrolyte - density of electrolyte - (p) function defined in Equation 8a - (r) surface profile function (Equation 29)     

Study on poly (ethylene-co-vinyl acetate), acrylonitrile butadiene copolymer,and their blend reinforced with carbon black using position annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy (PALS) have been used to investigate the effect of filling each of poly (ethylene-co-vinyl acetate) (EVA), acrylonitrile butadiene rubber (NBR), and their blend (50/50wt-%) with different concentrations of high-abrasion furnace (HAF) (0–60?phr). PALS is characterised by the free-volume parameters (V_h and F %), which is a measure of the size and fraction of free-volume holes in the composites. The results show that the variation in V_h and F % of free-volume holes depends on the chemical structure and the degree of crystallinity of each polymer. The NBR has a smaller size (127.78?ų) and lower fraction (4.18%) of free-volume holes than the corresponding free-volume holes (177.48?ų and 7.03%) in EVA. The size of the free-volume holes increases in EVA with increasing HAF content up to 20 phr in polymer matrix while it decreases in NBR. The fractions (F %) of free-volume holes decrease due to the reduction in positronium formation in polymer and positron trapping at polymer interface. The results also show an inverse correlation between free-volume parameters (V_h and F %) and tensile strength value, and a direct correlation with elongation at break as a function of HAF content in EVA and NBR. The electrical properties are negatively correlated with lifetime of free positron, τ₂, and positively with its relative intensity (I₂).