Dynamic mechanical properties of crosslinked polyisoprene under deformation

Summary Molecular motions of elastomers under deformations were observed through dynamic mechanical measurements. Composite master curves of dynamic moduli E and E and loss tangent tan over a wide range of frequency and in a state of elongation were obtained by the time-temperature superposition procedure. It is found that both moduli increase with strain, . The slope of the dispersion curve of E become more gradual with the increase in , while that of E is almost unchanged. The increment of E is generally larger than that of E, which does not agree with the N. W. Tschoegl prediction, E ^* ()=f() E _o ^* (), where E ^* () and E _o ^* () are complex moduli at the strain of and O, respectively, and f() is the function of only . The difference in the strain dependence of E from E was found to correspond to the strain dependence of the equilibrium modulus.     

New polyisobutylene based model ionomers

Three-arm star polyisobutylene ionomers (¯M_n=8800) with terminal SO₃ M (M=K or Ca²) groups were synthesized and their mechanical properties investigated. Compression molded films displayed high elongations, i.e., -1000% for Ca² ionomers with lower values for the K counterions. Strain induced crystallinity was observed at higher elongations. Mechanical properties in general compared favorably with conventional covalently linked rubbery networks and were comparable and in some cases superior to EPDM-based ionomers carrying randomly distributed SO₃ M groups.For the first two parts see Proceedings, 28th IUPAC Macromolecular Symposium, Amherst, MA, July 11–16, 1982, p. 905 and 906     

Molybdenum nitride for the direct decomposition of NO

The physico-chemical properties of passivated -Mo₂N have been investigated. The material showed high activities for NO direct decomposition: nearly 100% NO conversion and 95% N₂ selectivity were achieved at 450C. The amount of O₂ taken up by -Mo₂N increased with temperature rise and reached 3133.9 molg^–1 at 450C; we conclude that there formation of Mo₂O_xN_y occurred. This oxygen-saturated -Mo₂N material was catalytically active: NO conversion and N₂ selectivity were 89 and 92% at 450C. We found that by means of H₂ reduction at 450C, Mo₂O_xN_y could be reduced back to -Mo₂N and the oxidation/reduction cycle is repeatable; such a behaviour and the high oxygen capacity (3133.9 molg^–1) of -Mo₂N suggest that -Mo₂N is a promising catalytic material for automobile exhaust purification.     

Synthesis of new metal-containing side-chain monomers and polymers

New metal-containing vinyl monomers, hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hexyl-6-oxy-{4-[4-(4-ferrocenoyl phenyl)phenyl]benzoyloxy}methacrylate, and the corresponding homopolymers and random copolymers with hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate were synthesized. The compounds were characterized by¹H NMR; their thermal behavior was investigated by means of differential scanning calorimetry. Monomers and polymers containing the ferrocene unit melt at lower temperatures than those derived from the cyclopentadienyl managanese tricarbonyl moiety. The melting temperatures of the monomers and polymers ranged from 399 to about 515 K, Both monomers and polymers failed to exhibit mesogenic behavior. Values ofM _n,M _w,M _w/M _n, and degree of polymerization were obtained by gel permeation chromatography. TheM _n ranged from 16,500 for the copolymer containing hexyl-6-oxy-{4-[4-(4-ferrocenoyl phenyl)phenyl] benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio to 26,000 for the copolymer containing hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio.M _w/M _n ranged from 1.6 in the case of the copolymer containing hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio to 2.2 in the case of poly(hexyl-6-oxy{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate).     

Synthesis of HFC-134a over CrF3/AlF3 catalysts

The effect of the structure of AlF₃ supports in CrF₃/AlF₃ catalysts and their activity were studied, and a selection of suitable reaction conditions for fluorination of trichloroethylene and HCFC-133a was made. We found that neither AlF₃ (- and -modifications) nor CrF₃/-AlF₃ exhibits significant activity for the reaction of HF with CCl₂=CHC1 or CF₃CH₂Cl. However, CrF₃/-AlF₃ exhibits high activity, which increases with increasing surface area and decreasing crystallite size of the -AlF₃ support, and that dramatically affects the fiuorination of CF₃CH₂Cl. Investigation of a series of CrF₃/-AlF₃ catalysts shows that the turnover rates per unit of the total surface area and of the free CrF₃ surface area significantly increase with increasing content of Cr³⁺ loading. Optimum temperature for the reaction of HF with CCl₂=CHCl is 260°C, while with CF₃CH₂Cl it is 350°C, with flow ratios HFTCE = 61 andHFHCFC-133a = 101.     

Effects of gas bubbles on the current and potential profiles within porous flow-through electrodes

This paper presents a mathematical model to calculate the distributions of currenti(x), potentialE(x), gas void fraction (x) and pore electrolyte resistivity (x) within porous flow-through electrodes producing hydrogen. It takes into consideration the following effects: (i) the kinetics of the interfacial charge transfer step, (ii) the effect of the non-uniformly generated gas bubbles on the resistivity of the gas-electrolyte dispersion within the pores of the electrode (x) and (iii) the convective transport of the electrolyte through the pores. These effects appear in the form of three dimensional groups i.e.K=i _o L where i_o is the exchange current density, is the specific surface area of the electrode andL its thickness.= ⁰ L where ⁰ is the pore electrolyte resistivity and =/Q where is a constant, =tortuosity/porosity of the porous electrode andQ is the superficial electrolyte volume flow rate within it. Two more dimensionless groups appear: i.e. the parameter of the ohmic effect =K/b and the kinetic-transport parameterI=K. The model equations were solved fori(x),E(x), (x) and (x) for various values of the above groups.Nomenclature specific surface area of the bed, area per unit volume (cm^–1) - b RT/F in volts, whereR is the gas constant,T is the absolute temperature (K) - B =[1–(I ² Z/4)], Equation 9a - C =(1–B ²), Equation 9b - E(L) potential at the exit face (V) - E(0) potential at the entry face (V) - E(x) potential at distancex within the electrode (V) - E _rev reversible potential of the electrochemical reaction (V) - F Faraday's constant, 96500 C eq^–1 - i _o exchange current density of the electrode reaction (A cm^–2 of true surface area) - i(L) current density at the exit face (A cm^–2 of geometrical cross-sectional area of the packed bed) - I K =i _oL(/Q) (dimensionless group), Equation 7d - K =i _oL, effective exchange current density of the packed bed (A cm^–2) Equation 7a - L bed thickness (cm) - q tortuosity factor (dimensionless) - Q superficial electrolyte volume flow rate (cm³ s^–1) - x =position in the electrode (cm) - Z =exp [(0)], Equation 7f - transfer coefficient, =0.5 - =K/b=(i ₀ L ⁰ L)/b (dimensionless group) Equation 7e - (x) gas void fraction atx (dimensionless) - = ⁰ L, effective resistivity of the bubble-free pore electrolyte for the entire thickness of the electrode ( cm²) - (0) polarization at the entry face (V) - (L) polarization at the exit face (V) - =q/, labyrinth factor - constant (cm³ C^–1), Equation 3a - =/Q (A ^–1) conversion factor, Equation 3b - porosity of the bed - (x) effective resistivity of the gas-electrolyte dispersion within the pores ( cm) - ⁰ effective resistivity of the bubble-free pore electrolyte ( cm)     

Diffusion-controlled current distributions near cell entries and corners

This paper reports experimental work undertaken to explore diffusion-controlled current distributions immediately downstream of sudden changes in flow cross-sectional area such as may occur at the entry to electrochemical flow cells. Nozzle flows expanding into an axisymmetric circular duct and into a square duct have been investigated using the reduction of ferricyanide ions on nickel micro-electrodes as the electrode process. The spanwise distribution of current has also been studied for the case of the square cell where secondary corner flows are significant.Nomenclature A electrode area (cm²) - c bulk concentration of transferring ions (mol dm^–3) - D cell diameter (cm) - D Diffusion coefficient (cm₂s^–1) - F Faraday number (96 486 C mol^–1) - I limiting electrolysis current (A) - k mass transfer coefficient (cm s^–1) - N nozzle diameter (cm) - u mean fluid velocity (cm s^–1) - x distance downstream from point of entry to cell (cm) - z number of electrons exchanged - electrolyte viscosity (g s^–1 cm^–1) - electrolyte density (g cm^–3) - (Re)_D duct Reynolds number,Du/ - (Re)_N nozzle Reynolds number,Nu/ - (Sc) Schmidt number,/D) - (Sh) Sherwood number,kD/D)     

Critical solution point and chain dimension of branched-polystyrene solutions

Summary Critical solution point and chain dimension were measured for branched polystyrene(BPS) in solution as a function of molecular weight(M) and compared with those for linear polystyrene(LPS). The critical concentration _c of BPS was quite different from that of LPS at a fixed M, but the same at a fixed overlap-concentration ^*, i.e., plots of _c vs. ^* fall on a single straight line for both BPS and LPS (gf_c ^*). Reduced critical temperature _c defined by gt_c=(–T_c)/ [T_c: critical temperature, : the -temperature] was related to _c as _{c c} ² for BPS, whereas _{c c} for LPS.     

Synthesis,electroconductivity and third-order nonlinear optical property of poly(2-isopropoxy-5-methoxy-1,4-phenylenevinylene)

Summary Asymmetrically disubstituted poly(2-isopropoxy-5-methoxy-1,4-phenylene-vinylene), PIMPV, was prepared in thin films via organic-soluble precursor polymer method. These polymer films could be easily stretched up to 7 times, and the drawn films of the PIMPV could be doped with FeCl₃ and I₂ to give conductivities of 26.9 and 11.3 Scm^-1, respectively. The third-order nonlinear optical susceptibility of the polymer was determined using third harmonic generation(THG) method at 1907 nm, fundamental wavelength. Measured ⁽³⁰⁾ (-3: , , ) value was 3.7x10^-12 esu.     

Electrochemistry of anodic fluorine gas evolution at carbon electrodes: Part II studies on the ‘CF’ film by the current-interruption,AC impedance,ESCA and auger techniques

The CF films that are formed on the surface of carbon anodes used for the fluorine evolution reaction (FER) in KF·2HF melts at 358 K have been studied by bothin situ electrochemical current-interruption and a.c. impedance methods, and byex situ surface spectroscopy [ESCA (XPS) and Auger] techniques. The surface analysis measurements indicate that a thin CF (CF₂) film, 1.7 nm in thickness is formed on the carbon anodesurface. Results from depth profiling analyses of the film indicate that it is not uniform, higher levels of CF and F components being found towards the carbon anode surface. Thein situ electrochemical measurements demonstrate that an abnormally small interfacial capacitance, (1.6–2.7)×10^–7 F cm^–2, arises in the course of the FER at carbon anodes; this was attributed to the presence of a passive dielectric CF film on the carbon electrodes. The determined interfacial capacitance does not change significantly with potential in the potential range studied, which implies that the thickness of the CF film on the fluorine-evolving carbon anodes may be independent of potential.     

The application of Taft-Hancock steric constants to the free-radical initiated copolymerization of N-alkylmaleimides with α-methylstyrene

Summary The rates of free-radical initiated alternating copolymerization of -methylstyrene with N-alkylmaleimides (RMI) decrease in the following order: Me>Et>n-Prn-Bun-Hex>iso-Pr>tert-Bu. A linear relationship was established in the plots of log(k_R/k_Me) against polar substituent constants ^*, true steric factors E_S and corrected steric factors E_S ^C. The best fit was obtained in plots of log (k_R/k_Me) against ^* and E_S ^C while a large scattering of results was observed in the plot of log(k_R/k_Me) against E_S.     

Stress and recovery maxima in LDPE melt elongation

Summary By means of a new tensile rheometer for polymer melts, stress-strain curves () and the elastic recovery _R() of a low density polyethylene melt were measured up to total strains =7, i.e. stretch =1097, at 150°C and two strain rates, =0.03 and 0.1 s^–1. Tensile tests up to very high strains e give relevant results only if the test performance is characterized by quality parameters which are defined and given in this paper. The test results show a maximum in a as well as in _R at about =5.5. Hence, in the range of investigated, a rheologically steady-state of flow does not exist.     

Liquid-phase mass transfer enhancement by gas evolution at inclined plates

The limiting current technique has been employed to determine mass transfer coefficients at vertical and inclined plates with stirring by coplanar electrochemical oxygen evolution. Orientation of the plate has been varied from –45 (down-facing inclined position) to +45 (up-facing inclined position) at ten intervals. At a constant oxygen evolution rate, maximum mass transfer enhancement was achieved at down-facing inclined orientations where (the angle from vertical) is small. The inclination angle at which mass transfer attained its highest value depended on the oxygen evolution rate and is given by _max =a + 10.96 logI _g whereI _g (mA) is the electrochemical current for the oxygen evolution.For the range of the inclination angle, 0 _max, the relationship between the mass transfer coefficient and can be represented byK =K _o +aK _o(sin )^0.3 whereK _o is the mass transfer coefficient at the vertical plate.     

Analysis of the inductance influence on the measured electrochemical impedance

The high-frequency region of the impedance diagram of an electrochemical cell can be deformed by the inductance of the wiring and/or by the intrinsic inductance of the measuring cell. This effect can be noticeable even in the middle frequency range in the case of low impedance systems such as electrochemical power sources. A theoretical analysis of the errors due to inductance effects is presented here, on the basis of which the admissible limiting measuring frequency can be evaluated. Topology deformations due to the effect of inductance in the case of a single-step electrochemical reaction are studied by the simulation approach. It is shown that an inductance can not only change the actual values of the parameters (electrolytic resistance, double layer capacitance, reaction resistance), but can also substantially alter the shape of the impedance diagram, this leading to erroneous structure interpretations. The effect of the size and surface area of the electrode on its intrinsic inductance is also evaluated.Nomenclature A linear dimension of the surface area confined by the circuit (cm) - C _D double layer capacitance (F) - C _M measured capacitance - d diameter of the mean effective current line (mm) - f _max limiting (maximum) frequency of measurement (Hz) - K ₁,K ₂ shape coefficients with values of 2×10^–9 and 0.7 for a circle, and 8×10^–9 and 2 for a square (dimensionless) - L intrinsic inductance of the electrochemical cell assumed as an additive element (H) - R _E electrolyte resistance () - R _M measured resistance () - R _P reaction resistance () - r ₀ specific resistance ( cm) - S electrode surface area (cm²) - T _c time constant (s) - Z impedance () - Z _lm imaginary component of the impedance without accounting for the influence of inductance () - Z _lm imaginary component of the impedance accounting for the influence of the additive inductance () - shape coefficient; =1 for a square and =^1/2/2 for circle (dimensionless) - _L relative complex error due to the influence of inductance (dimensionless) - _L ^A relative amplitude error due to inductance (%) - ^L relative phase error due to inductance (%) - ratio between the effective inductance time constant and the capacitive time constant (dimensionless) - angular frequency (s^–1) - _R characteristic frequency at which the inductive and capactive parts of the imaginary component of impedance are equal (s^–1)     

Behaviour of a tall vertical gas-evolving cell. Part I: Distribution of void fraction and of ohmic resistance

Electrolysis of a 22 wt % NaOH solution has been carried out in a vertical tall rectangular cell with two segmented electrodes. The ohmic resistance of the solution between a segment pair has been determined as a function of a number of parameters, such as, current density and volumetric rate of liquid flow. It has been found that the ohmic resistance of the solution during the electrolysis increases almost linearly with increasing height in the cell. Moreover, a relation has been presented describing the voidage in the solution as a function of the distance from the electrodes and the height in the cell.Notation A _e electrode surface area (m²) - a _s parameter in Equation 12 (A^–1) - b _s parameter in Equation 12 - d distance (m) - d _ac distance between the anode and the cathode (m) - d _wm distance between the working electrode and an imaginary separator (m) - F Faraday constant (C mol^–1) - h height from the leading edge of the working electrode corresponding to height in the cell (m) - h _e distance from the bottom to the top of the working electrode (m) - h _s height of a segment of working electrode (m) - I current (A) - I ₂₀ current for segment pair 20 (A) - I _1–19 total current for the segment pairs from 1 to 19 inclusive (A) - I _x-19 total current for the segment pairs fromx to 19 inclusive (A) - i current density A m^–2 - N _s total number of gas-evolving pairs - n ₁ constant parameter in Equation 8 - n _a number of electrons involved in the anodic reaction - n _c number of electrons involved in the cathodic reaction - n _s number of a pair of segments of the segmented electrodes from their leading edges - Q _g volumetric rate of gas saturated with water vapour (m³ s^–1) - Q ₁ volumetric rate of liquid (m³ s^–1) - R resistance of solution () - R ₂₀ resistance of solution between the top segments of the working and the counter electrode () - R _p resistance of bubble-free solution () - R _p,20 R _p for segment pair 20 () - r _s reduced specific surface resistivity - r _s,0 r _s ath=0 - r _s,20 r _s for segment pair 20 - r _s, r _s for uniform distribution of bubbles between both the segments of a pair - r _s,,20 r _s, for segment pair 20 - S _b bubble-slip ratio - S _b,20 S _b at segment pair 20 - S _b,h S _b at heighh in the cell - T temperature (K) - V _m volume of 1 mol gas saturated with water vapor (m³ mol^–1) - v ₁ linear velocity of liquid (m s^–1) - v _1,0 v ₁ through interelectrode gap at the leading edges of both electrodes (m s^–1) - W _e width of electrode (m) - X distance from the electrode surface (m) - Z impedance () - Z real part of impedance () - Z imaginary part of impedance () - resistivity of solution ( m) - _p resistivity of bubble-free solution ( m) - gas volumetric flow ratio - ₂₀ at segment pair 20 - _s specific surface resistivity ( m²) - _{s, p s} for bubble-free solution ( m²) - thickness of Nernst bubble layer (m) - ₀ ath=0 (m) - voidage - _x,0 atx andh=0 - _0,0 voidage at the leading edge of electrode wherex=0 andh=0 - _,h voidage in bulk of solution at heighth - ₂₀ voidage in bubble of solution at the leading edge of segment pair 20     

Mechanisms of Iron Activation on Fe-Containing Zeolites and the Charge of α-Oxygen

According to previous Mössbauer data [1] -sites formation at the activation of Fe-containing zeolites is accompanied by irreversible self-reduction of the iron, proceeding without participation of an external reducing agent. Reduced Fe²⁺ ions are inert to O₂ but are reversibly oxidized to Fe³⁺ by N₂O, generating the -oxygen species, O, which provide selective oxidation of hydrocarbons.In this work, the mechanism of -sites formation was studied via quantitative measurement of the dioxygen amount desorbed into the gas phase at the step of self-reduction. A prominent role of the zeolite matrix chemical composition has been revealed. For example, with zeolites of Al–Si composition (FeZSM-5 and Fe-), heating to 900 °C in a closed vacuum space leads to irreversible evolution of O₂, which is accompanied by the immediate formation of -sites. Similar heating of B–Si and Ti–Si zeolites also leads to dioxygen evolution; however, this evolution is reversible and is not accompanied by formation of -sites. Activation of these zeolites occurs only in the presence of water vapor. Stoichiometric measurements showed that in terms of charge one regular O^2- ion, removed at the activation, is equivalent to two -oxygen atoms. So, -oxygen is identified as an ion-radical species O ^-., whose unique oxidation properties still distinguish it from the generally observed O^-. radicals.The mechanism of -sites formation is proposed, in which the process of strong chemical stabilization of reduced Fe²⁺ atoms in the zeolite structure is a key step, making impossible the reoxidation of the iron with O₂.     

Behaviour of a tall vertical gas-evolving cell Part II: Distribution of current

Vertical electrolysers with a narrow electrode gap are used to produce gases, for example, chlorine, hydrogen and oxygen. The gas voidage in the solution increases with increasing height in the electrolyser and consequently the current density is expected to decrease with increasing height. Current distribution experiments were carried out in an undivided cell with two electrodes each consisting of 20 equal segments or with a segmented electrode and a one-plate electrode. It was found that for a bubbly flow the current density decreases linearly with increasing height in the cell. The current distribution factor increases with increasing average current density, decreasing volumetric flow rate of liquid and decreasing distance between the anode and the cathode. Moreover, it is concluded that the change in the electrode surface area remaining free of bubbles with increasing height has practically no effect on the current distribution factor.Notation A _e electrode surface area (m²) - A _e,s surface area of an electrode segment (m²) - A _{e, 1–19} total electrode surface area for the segments from 1 to 19 inclusive (m²) - A _e,a anode surface area (m²) - A _e,a,h A _e,a remaining free of bubbles (m²) - A _e,e cathode surface area (m²) - A _e,c,h A _e,c remaining free of bubbles (m²) - a ₁ parameter in Equation 7 (A^–1) - B current distribution factor - B _r B in reverse position of the cell - B _s B in standard position of cell - b _a Tafel slope for the anodic reaction (V) - b _c Tafel slope for the cathodic reaction (V) - d distance (m) - d _ac distance between the anode and the cathode (m) - d _wm distance between the working electrode and an imaginary membrane (m) (d _wm=0.5d _wt=0.5d _ac) - d _wt distance between the working and the counter electrode (m) - F Faraday constant (C mol^–1) - h height from the leading edge of the working electrode corresponding to height in the cell (m) - h _e distance from the bottom to the top of the working electrode (m) - I current (A) - I _s current for a segment (A) - I ₂₀ current for segment pair 20 (A) - I _1–19 total current for the segment pairs from 1 to 19 inclusive (A) - i current density (A m^–2) - i _av average current density of working electrode (A m^–2) - i _b current density at the bottom edge of the working electrode (A m^–2) - i ₀ exchange current density (A m^–2) - i _0,a i ₀ for anode reaction (A m^–2) - i _l current density at the top edge of the working electrode (A m^–2) - n ₁ parameter in Equation 15 - n _s number of a pair of segments of the segmented electrodes from their leading edges - Q _g volumetric rate of gas saturated with water vapour (m³ s^–1) - Q ₁ volumetric rate of liquid (m³ s^–1) - R resistance of solution () - R ₂₀ resistance of solution between the top segments of the working and the counter electrode () - R _p resistance of bubble-free solution () - R _p,20 R _p for segment pair 20 () - r _s reduced specific surface resistivity - r _s,0 r _s ath=0 - r _s,20 r _s for segment pair 20 - r _s, r _s for uniform distribution of bubbles between both the segments of a pair - r _s,,20 r _s, for segment pair 20 - T temperature (K) - U cell voltage (V) - U _r reversible cell voltage (V) - v ₁ linear velocity of liquid (m s^–1) - v _1,0 v ₁ through interelectrode gap at the leading edges of both electrodes (m s^–1) - x distance from the electrode surface (m) - gas volumetric flow ratio - ₂₀ at segment pair 20 - specific surface resistivity ( m²) - _t at top of electrode ( m²) - _p for bubble-free solution ( m²) - _b at bottom of electrode ( m²) - thickness of Nernst bubble layer (m) - ₀ ath=0 (m) - _{0,i 0} ati - voidage - _x,0 atx andh=0 - _0,0 voidage at the leading edge of electrode wherex=0 andh=0 - _0,0 ati _b - _0,0 ati=i _t - _,h voidage in bulk of solution at heighth - _,20 voidage in bubble of solution at the leading edge of segment pair 20 - _lim maximum value of _0,0 - overpotential (V) - _a anodic overpotential (V) - _c cathodic overpotential (V) - _h hyper overpotential (V) - _h,a anodic hyper overpotential (V) - _h,c cathodic hyper overpotential (V) - fraction of electrode surface area covered by of bubbles - _a for anode - _c for cathode - resistivity of solution ( m) - _p resistivity of bubble-free solution ( m)     

The surface structure and composition of the low index single crystal faces of the ordered alloy Pt3Sn

The surface composition and structure of 111, 100, and 110 oriented single crystals of the ordered alloy Pt₃Sn (Ll₂ or Cu₃Au-type) were determined using the combination of low energy electron diffraction (LEED) and low energy ion scattering spectroscopy (LEISS). The clean annealed surfaces displayed LEED patterns and Sn/Pt LEISS intensity ratios consistent with the surface structures expected for bulk termination. In the case of the 100 and 110 crystals, preferential termination in the mixed (50% Sn) layer was indicated, suggesting this termination to be the consequence of a thermodynamic preference for tin to be at the surface.     

Beta-silicon carbide whisker-polymer composites

Summary The beta silicon carbide whiskers, as prepared by the Los Alamos Process, have been found to have conductivities as high as 300 (cm)^–1. Random, uniform incorporation of these whiskers in two high temperature polymers (polybenzimidazole and polypyrrone) in 10 and 20 wt% concentrations generated films with conductivities as high as 1 × 10^–9 (cm) and 1 × 10^–5 (cm)^–1 respectively. The polymers without the whiskers had conductivities in the 10^–10 to 10^–17 (cm)^–1 range.     

Kinetics and Mechanism of Copolymerization of α-terpineol with Methylmethacrylate in Presence of Azobisisobutyronitrile as an Initiator

The radical copolymerization of -terpineol with methyl-methacrylate in xylene at 80±0.1C for 50 minutes in the presence of azobisisobutyronitrile (AIBN) follows ideal kinetics and results in the formation of a functional and random copolymer. The activation energy is 33 KJ/mole. The IR spectrum and NMR spectra of the copolymer(s) shows the bands at 1750 and 3400 cm^–1 for ester group of methylmethacrylate and alcoholic group of -terpineol and peaks at 3 to 4 for methoxy group and at 6.5 to 7.5 due to alcoholic group of methylmethacrylate and -terpineol repectively. The values of reactivity ratios, calculated by Kelen–Tüdos method, are r ₁ (MMA) = 0.18 and r ₂ (-terpineol) = 0.046. The Alfrey-Price; Q–e parameters for -terpineol has been calculated as 0.149 and 2.486. The mechanism of copolymerization has been elucidated and it is concluded that the double bond present in the monocyclic ring of -terpineol is an active site for copolymerization and the alcoholic group of -terpineol remain to give functional copolymer.