Tensile deformation of polychlorotrifluoroethylene in He,N2, Ar,O2, and CO2 environments

The tensile stress—strain behaviour of quenched polychlorotrifluoroethylene (PCTFE) was measured from 77K to T_g in gaseous environments of He, N₂, Ar, O₂, and CO₂ and in water. The partial pressure of the gas was varied from 0 to 1 atm. N₂, Ar, O₂ and CO₂ produced crazing and a lowering of the tensile strength relative to the intrinsic tensile strength at that temperature. The effect of pressure and temperature on the tensile strength was quantitatively similar to the effect of these gases on PC and PMMA, and could be described by an equation of the form: $\text{σ}{}_{\mathrm{c}}\text{σ}{}_{\mathrm{i}}\text{= [P}\text{exp}\text{(}\text{Q}\text{RT}\text{/P1]}{}^{\mathrm{?0.10}}$. The constants Q and $\text{P1}$ depended on the gas, and σ_i is the intrinsic strength. The Q values were approximately the same as the heat of vaporization for each gas. CO₂ produces crazing below as well as above its sublimation temperature. The intrinsic yield point varied from 0.033 to 0.054 of E, Young's modulus, as the temperature varied from 300 to 77K. The experimental value of the yield point extrapolated to 0.055E at OK and compares favourably with existing theories for the yield point of glassy polymers.     

Conversion of bituminous coal in COH2O systems: 2. pH Dependence

Under $\text{CO}\text{H}{}_2\text{O}$ systems at initial pH values s> 12.6, an Illinois No. 6 coal, PSOC-26, was converted to a fully pyridine-soluble product, with benzene and hexane solubilities of 50% and 18%, respectively. The product gases were H₂ and CO₂. However, the expected $\text{H}{}_2\text{CO}{}_2$ ratio of 1.0 based on the water gas shift reaction was not observed, but the deficit in hydrogen was found in the increased hydrogen content of the coal product. 95% coal carbon recovery and good hydrogen balances were obtained, and the coal products were found to be very similar to those from conventional tetralin systems. The results suggest an efficient base-catalysed process, and that $\text{CO}\text{H}{}_2\text{O}$ systems are useful for coal studies.     

Studies of a CuY zeolite as a redox catalyst

The stability and behavior of CuY in the redox cycles with $\text{CO}\text{O}{}_2$, $\text{H}{}_2\text{O}{}_2$, and $\text{CO}\text{NO}$ have been studied using a microbalance operating in the flow mode and with a standard (BET) volumetric system. When CO was used as a reducing agent CO₂ was produced, thus removing oxygen from the zeolite lattice, but when H₂ was used only some of the H₂ consumed was evolved as H₂O. The rest was retained as lattice OH groups, but this was minimal when H₂ was used after treating the sample with CO. Oxidation with NO produced only N₂. At 500 °C the sample was stable and could be reversibly oxidized and reduced through many cycles using either $\text{CO}\text{O}{}_2$ or $\text{NO}\text{CO}$. In all cases the ratio $\text{O}\text{Cu}$ was close to 0.5, i.e., $\text{1e}\text{Cu}$. Treatment in CO at higher temperatures did not affect the reversible nature of the oxidation, but now the valence change was substantially larger; it approached $\text{2e}\text{Cu}$. The crystallinity of the exchanged zeolite was studied using X-ray diffraction and by measurement of the pore filling with liquid N₂. No significant changes could be detected after the different treatments, even those performed at 750 °C. Temperature-programmed reduction, temperature-programmed oxidation, and X-ray diffraction studies were made and the different maxima are reported. CuO and Cu ^o appeared in the oxidized and reduced samples, respectively, after treatment at 750 °C in CO but not at lower temperatures. Subsequent redox cycles at 500 °C did not appear to affect the size or amount of Cu ^o crystallites. CuY was active in the oxidation of CO with O₂ or NO. Its activity was lower than that of FeY zeolite when it exhibited an oxygen-carrying capacity of 0.5 $\text{O}\text{Cu}$. Treatment with CO at 750 °C, however, reversed the situation. Kinetic results showed that the fresh CuY catalyst was close to zero order in CO and fractional order in O₂ with an activation energy of 15 kcal/mole. After treatment at 750 °C in CO, the rate law became dependent upon the $\text{CO}\text{O}{}_2$ ratio. It was close to first order in CO and zero order in O₂ under oxidizing conditions ($\text{CO}\text{O}{}_2\text{≤ 2}$), but the orders were reversed under reducing conditions ($\text{CO}\text{O}{}_2\text{> 2}$). The activation energies were 12 and 15 kcal/mole, respectively. The data suggested that the Cu²⁺ with bound oxygen are the species active in the oxidation reaction.     

Oxidation of hydrogen sulfide over microporous carbons

Microporous carbon of high purity was produced by the carbonization of Saran at 900° followed by activation in either CO₂ at 900°, O₂ at 300°, or air at 425°. The activated carbons were characterized using N₂ adsorption at ?195° CO₂ adsorption at 25°, and mercury and helium displacements. Hydrogen sulfide oxidation (at H₂S pressures between 0.4–3.8 Torr) by O₂ (in excess of stoichiometric amount) was studied between 100–160° using a microbalance, that is by weighing the build-up of sulfur on the carbon. The predominant reaction, $\text{H}{}_2\text{S +}\text{1}\text{2}\text{O}{}_2\text{→}\text{1}\text{2}\text{S}{}_2\text{+ H}{}_2\text{O}$ was first order in H₂S concentration and independent of O₂ concentration. The rate was only slightly reduced by sulfur build-up to at least 36%, by weight, on the carbon. The oxidation rate was significantly higher over the O₂-activated carbon than over the CO₂-activated carbon. Throughout the studies, oxidation rates could be correlated with area active to O₂ chemisorption. It is concluded that H₂S oxidation proceeds via rapid dissociative chemisorption of oxygen on carbon sites followed by reaction with H₂S. Rates of H₂S oxidation were also studies over commercial, granular activated carbons of significant ash contents.     

Selective steam reforming of aromatic hydrocarbons: IV. Steam conversion and hydroconversion of selected monoalkyl- and dialkyl-benzenes on Rh catalysts

Steam conversion and hydroconversion of a series of monoalkylbenzenes (C₆H₅R, R = C₂H₅, n-C₃H₇, i-C₃H₇, tert-C₄H₉) and of dialkylbenzenes (o- and p-xylenes) are studied at 713 K and atmospheric pressure on supported rhodium catalysts ($\text{Rh}\text{Al}{}_2\text{O}{}_3$, $\text{Rh}\text{SiO}{}_2$ and $\text{Rh}\text{TiO}{}_2$), and compared to the toluene steam dealkylation previously studied on the same catalysts. Three types of reaction, namely dealkylation (CC rupture on the side chain), dehydrogenation (on the side chain), and degradation (i.e., ring opening) account for virtually the whole product spectrum. Isomerization, transalkylation, and dehydrocyclization reactions may, in general, be discounted. In the presence of steam, the main initial product of monoalkylbenzene dealkylation is invariably benzene, but the splitting of the CC bonds in the middle or end of the side chain always increases with conversion. As a rule, the specific activities (per metal site) in dealkylation decrease with the degree of substitution in the alkyl group (primary > secondary > tertiary > quaternary carbon). On the other hand, the specific activities in ring opening remain constant for all the hydrocarbons and even for the benzene. In the presence of hydrogen, multiple CC bond splittings are invariably observed and benzene is no longer, in general, the principal initial product. The activities in ring opening are equally constant, but at a lower level than in steam conversion. These results are in overall agreement with the model of the dual active sites: sites I appear operative for dealkylation and dehydrogenation, whereas ring opening takes place at sites II with a high probability, independent of the alkyl group size. Possible adsorbed species on each type of site are described. An attempt is made to rationalize the effects of assorted selectivity-determining factors (metal particle size, support effects, selective poisons such as S and CO) in terms of electronic or geometric effects.     

Reinvestigation of the system C4A.nH2O  C4A.Co2.nH2O

The system C₄A.nH₂O  C₄A.CO₂.nH₂O has been reinvestigated at 22°, 100 % and 65 % relative humidity. Formation conditions, composition and crystallographic properties of the phases C₄A.nH₂O, C₄A.1/2CO₂.nH₂O, C₄A.CO₂nH₂O and their dehydration products have been studied by X-ray and elektron diffraction, infrared and Raman spectroscopy, dynamic weight-loss curves and differential thermal analysis. Only very limited solid solution occurs in the system. X-ray single crystal studies showed the quaternary compound C₄A.1/2CO₂.12H₂O to be trigonal with space group R3c or R$\text{3}$c, lattice parameters $\text{a}{}_{\mathrm{o}}\text{=5.77}\text{a}\text{?}\text{,}\text{C}{}_{\mathrm{<mtext>o</mtext>}}\text{=49.16}\text{a}\text{?}$. C₄A.CO₂11H₂O is triclinic with $\text{a}{}_{\mathrm{o}}\text{=5,}{}_{\mathrm{o}}\text{=5.74}\text{A}\text{?}\text{,}\text{C}{}_{\mathrm{o}}\text{=7.86}\text{A}\text{?}\text{α=92.61°, β=101.96°, δ=120.09°}$. Indexed powder diffraction data of both compounds are given.     

Activated diffusion of methane from coals at elevated pressures

Diffusion of methane from three coals ranging in rank from anthracite to HVA bituminous has been studied at initial methane pressures up to about 2.76 MPa (400 psi). Unsteady-state diffusion conditions existed, the methane pressure within the coal particle decreasing with time while the methane pressure outside the particles remained at atmospheric. The diffusion parameter $\text{D}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{r}{}_0$ increased with increasing methane concentration at high values of methane sorption. Diffusion was activated but the exact magnitude of the activation energy is uncertain owing to the suspected contribution of the heat of sorption to the temperature coefficient. $\text{D}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{r}{}_0$ increased with decreasing particle size of coal studied, but r₀ is clearly less than the particle radius.     

Self-diffusion of poly(ethylene oxide) in aqueous dextran solutions measured using FT-pulsed field gradient n.m.r.

Transport in ternary polymer₁, polymer₂, solvent systems has been investigated using an n.m.r. spin-echo technique. The dependence of the self-diffusion coefficient of poly(ethylene oxide) polymers on the concentration and molecular size of dextran in aqueous solution has been measured. Monodisperse poly(ethylene oxide) fractions ($\text{M}\text{?}{}_{\mathrm{w}}\text{=7.3×10}{}^4$, 2.8·10⁵ and 1.2·10⁶) and dextrans ($\text{M}\text{?}{}_{\mathrm{w}}\text{=2·10}{}^4$, 1·10⁵ and 5·10⁵) have been employed over a range of concentration up to the miscibility limit in each system. It is found that when the molecular size of the diffusant is commensurate with or exceeds that of the matrix polymer, a relationship of the form: $\text{(}\text{D}\text{D}{}_0\text{)}{}_{\mathrm{<mtext>PEO</mtext>}}\text{=}\text{exp}\text{?k(C[η])}$ is applicable, where C[η] refers to the dextran component and is considered to describe the extent of coil overlap in concentrated solution. ($\text{D}\text{D}{}_0$) is independent of the molecular size of the poly(ethylene oxide), at least in the range studied (M_w<300 000).     

Polymorph control of calcium carbonate by reactive crystallization using microbubble technique

In this study, we used the minute gas–liquid interfaces around CO₂/NH₃ microbubbles as new reaction fields where the crystal nucleation progresses and developed a crystallization technique to control the polymorphism of calcium carbonate (CaCO₃). In the regions around the gas–liquid interfaces of CO₂/NH₃ microbubbles, Ca²⁺ and CO₃²⁻ ion concentrations can be adjusted because of the characteristic of the electric charge on the bubble surface and the decrease in CO₂ concentration based on unit bubble caused by minimization of bubble size, and because of the pH difference between local pH at the gas–liquid interface and overall pH in the bulk liquid caused by mixing of NH₃ with CO₂; hence, the polymorph change of CaCO₃ is expected to occur. CaCO₃ was crystallized at 298 K by a semi-batch type reaction in which CO₂/NH₃/N₂ bubbles were continuously supplied to an aqueous Ca(NO₃)₂ solution using a self-supporting bubble generator. The solution pH during crystallization was maintained at a constant level of 6.9–12.0 by adding HNO₃ and NH₄OH solution. The average bubble size (d_bbl) was varied in the range of 40–1000 μm by controlling the N₂ flow rate, and the molar ratio of CO₂/NH₃ (αCO₂/NH₃${\alpha }_{\text{C}{\text{O}}_2\text{/N}{\text{H}}_3}$) was set at a specified value of 0.20–1.00 at a constant CO₂ flow rate. The following results were obtained by varying solution pH, d_bbl, and αCO₂/NH₃${\alpha }_{\text{C}{\text{O}}_2\text{/N}{\text{H}}_3}$: at a constant d_bbl of 40 μm and αCO₂/NH₃${\alpha }_{\text{C}{\text{O}}_2\text{/N}{\text{H}}_3}$ of 0.20, vaterite and calcite were major products at a solution pH lower than 9.0 and at a solution pH greater than 11.0, respectively, while aragonite was crystallized predominantly in the solution pH range of 9.7–10.5; at a constant solution pH of 9.7 the crystallization of aragonite was accelerated remarkably with a decrease in αCO₂/NH₃${\alpha }_{\text{C}{\text{O}}_2\text{/N}{\text{H}}_3}$ and d_bbl.     

The kinetics of the catalytic hydrogenolysis of ethane over Ni/SiO2

The rate of hydrogenolysis of ethane over a Ni/SiO₂ catalyst, studied over a large range of pressure and of temperature, is shown to be related to the degree of hydrogen coverage θ_H, by the equation: with K₀ nearly equal to the number of ethane molecules colliding with the Ni surface, E₀ = 14 ? 1 kcal/mole, Y = ?1 ? 2 and X = 15 ? 2. The rate-limiting step is believed to be the irreversible, dissociative adsorption of ethane on an ensemble of at least 12 adjacent Ni atoms, free from adsorbed hydrogen, resulting in the complete cracking of C₂H₆: C₂H₆ + 12Ni → 2

Irreversible adsorption of ethane is assumed to compete with the reversible adsorption of hydrogen. This mechanism, which is compared with those proposed earlier, is in good agreement with data on ethane adsorption studied by magnetic methods, and with a study of ethane hydrogenolysis over NiCu/SiO₂ catalysts.     

In situ laser raman spectroscopy of the sulfiding of Moγ-Al2O3 catalysts

Raman spectra of sulfided $\text{Mo}\text{γ-}\text{Al}{}_2\text{O}{}_3$ catalysts were obtained using in situ techniques for two sulfiding methods. For samples sulfided by 10% $\text{H}{}_2\text{S}\text{H}{}_2$ at 400 °C, MoS₂ structures were observed. A stepwise sulfiding using 10% $\text{H}{}_2\text{S}\text{H}{}_2$, with spectra recorded at 150, 250, and 350 °C, resulted in observation of molybdenum oxysulfide, reduced molybdate, and surface “MoS₂” phases. Reexposure of these samples to air led to radical modification of the oxysulfide structures as well as transformation of some sulfide phases. A model incorporating terminal and bridging MoS bonding and anion vacancies is proposed. This model is based on the conversion of isolated and aggregated molybdate and MoO₃ species to oxysulfide and reduced molybdenum phases. Conversion of reduced molybdenum phases to sulfides is observed to be slow.     

Effects of gas environment on mineral reactions in Colorado oil shale

The effects of various sweep gases (N₂, CO₂, and H₂O) on the decomposition and reaction of calcite and dolomite (ankerite) in Colorado oil shale is reported. The disappearance of reactants and formation of products in the temperature range of 500 to 900 °C is monitored by using powder X-ray diffraction. The results show that, over this temperature range, the effect of gas environment on the rate of silicate formation follows the order $\text{H}{}_2\text{O}\text{s}\text{?}\text{>}\text{CO}{}_2\text{s}\text{?}\text{>}\text{N}{}_2$. The ‘final’ silicate-product phases are observed to be a mixture of melilite, diopside, and merwinite. Global reaction kinetics are developed that describe the rate of CO₂ evolution during decomposition of dolomite and calcite in the presence of various partial pressures of steam. Such data are useful in numerical models of oil shale retorting. Finally, the implications of these results on processing and on environmental aspects of oil shale retorting are discussed.     

Kinetics of the graphite-oxygen reaction near 1000°K

The kinetics of oxidation of spectroscopic grade polycrystalline graphite have been studied by a flow method which allowed the partial pressure of oxygen (P_o2) to be changed abruptly during the course of the reaction. The changes were made in two alternative ways: by changing the total pressure of an oxygen/nitrogen mixture of constant composition or by changing the composition at constant total pressure. After the effect of diffusion resistance on the rate had been shown to be negligible and the effects of self-heating, burn-off and traces of gaseous impurities allowed for, the order of reaction (ń in the empirical expression: rate α ) was found to vary from 0.34 (at 993°K and mean ) to 0.19 (at 963°K and mean P_o2 = 245 torr). In certain circumstances, the response of the rate to changes in P_o2 is subject to a “memory” effect. This is attributed to fast, diffusion-controlled chemisorption of a minute amount of hydrogenous impurity on part of the active surface of the graphite.     

Phase structure and adhesion in polymer blends: A criterion for rubber toughening

The effects of rubber particle size and rubber-matrix adhesion on notched impact toughness of nylon-rubber blends are analysed. A sharp tough-brittle transition is found to occur at a critical particle size, when the rubber volume fraction and rubber-matrix adhesion are held constant. The critical particle size increases with increasing rubber volume fraction, given by $\text{d}{}_{\mathrm{<mtext>c</mtext>}}\text{= T}{}_{\mathrm{<mtext>c</mtext>}}\text{{(}\text{π}\text{6Φ}{}_{\mathrm{<mtext>r</mtext>}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{? 1}}{}^{\mathrm{?1}}$, d_c is the critical particle diameter, T_c the critical interparticle distance, and ø_r the rubber volume fraction. The critical interparticle distance is a material property of the matrix, independent of rubber volume fraction and particle size. Thus, the general condition for toughening is that the interparticle distance must be smaller than the critical value. Van der Waals attraction gives sufficient adhesion for toughening. Interfacial chemical bonding is not necessary. Even if there is interfacial chemical bonding, a polymer-rubber blend will still be brittle, if the interparticle distance is greater than the critical value. The minimum adhesion required is about 1000 J m^?2, typical for van der Waals adhesion. In contrast, chemical adhesion is typically 8000 J m^?2. The present criterion for toughening is proposed to be valid for all polymer—rubber blends which dissipate the impact energy mainly by increased matrix yielding.     

Properties of type K expansive cement of pure components I. Hydration of unrestrained paste of expansive component — Results

A mixture of $\text{C}{}_4\text{A}{}_3\text{S}\text{, C}\text{S}\text{H}{}_2\text{and CH}$, in stoichiometric ratio to form ettringite only was paste hydrated at temperatures between 20–50°C. Unrestrained specimens were tested for expansion, porosity, strength and hydration at different times. Expansions started at a critical degree of hydration α_cr, at which total porosity was minimum and strength was maximum. Raising curing temperature reduced α_cr and enhanced expansion and total porosity. Mercury intrusion porosimetry revealed a bimodal pore size distribution.     

Flow microcalorimetry on dilute polymer solutions

A flow microcalorimeter designed to measure the heat of mixing of dilute polymer solutions is described. The instrument is sensitive to steady state heating rates of ～10 μJ/sec. Measurements of heats of mixing of solutions of differing concentrations of n-hexane and cyclohexane are reported and are compared with recommended data of McGlashan and Stoeckli. Values of:

$\text{K}{}_1\text{=}\text{lim}\text{V}{}_2\text{→ 0}$

$\text{(}\text{H}\text{?}{}_1\text{?}\text{H}\text{?}{}^0{}_1\text{RTv}{}^2{}_2$ are obtained for four polymer—solvent systems: polyisobutylene—benzene, 0.22; polystyrene (PS)—cyclohexane, 0.33; PS—n-butyl acetate, ?0.06 all at 25°C; and PS—toluene, ?0.05 at 40°C. Various theoretical calculations of second virial coefficients A₂ made with use of the calorimetric data are compared with previously measured A₂ for the first two mixtures.     

Use of oxygen isotope exchange in CO2 to characterize active sites

The characterization of carbon surface activity in the absence of gasification was attempted using oxygen isotope exchange in CO₂ over spectroscopically pure natural graphite, the surface activity being characterized by the rate of approach to isotopic equilibrium. The probable mechanism of exchange is via the first step in the carbon-CO₂ reaction, the dissociation of CO₂ over a carbon free site: $\text{CO}{}_2\text{+}\text{C}{}_{\mathrm{f}}\text{?}\text{i}{}_1\text{j}{}_1\text{C(O)}\text{+}\text{CO}$. Assuming this mechanism to hold for isotopic exchange, the theoretical rate equation was derived. The rate constants i₁, and j₁, were obtained from previous studies. Theoretical calculations show that the exchange rate is negligible over natural graphite at temperatures much below gasification conditions. Experimental verification of the theoretical analysis was not possible due to the activity of the quartz boat, holding the graphite, for catalyzing the exchange reaction. The exchange reaction was successfully followed over the Pt and CaO supported on a graphitized carbon black, in which case the activity was much, much greater than that ovgr the empty quartz boat.     

Interaction parameters in the n-undecane/butanone/poly(dimethyl siloxane) system

Intrinsic viscosities, [η], second virial coefficients, A₂, preferential solvation coefficients, λ, and binary interaction potential as measured by light scattering, g₁₂, for the system n-undecane(1)/butanone(2)/poly(dimethylsiloxane) (3) have been determined at 20.0°C. The system shows cosolvent character, as the inversion in λ and the maxima in A₂ and in [η], at $\text{ø}{}_{10}\text{?0.65}$, seem to indicate. (g₁₃ – sg₂₃) and the ternary interaction potential, g_T, and its derivatives on system composition, and , have been evaluated. Global interaction parameters, χ_m3, have also been evaluated and a critical analysis on the approximations usually followed for χ_m3 calculations is undertaken.     

Effects of metal-support interactions on the synthesis of methanol over palladium

The synthesis of methanol and other products from CO and H₂ was studied over Pd catalysts prepared by adsorption of Pd(π-C₃H₃)₂ on MgO, ZnO, La₂O₃, γ-Al₂O₃, SiO₂, TiO₂, and ZrO₂ as well as over a SiO₂-supported Pd catalyst prepared from PdCl₂ and Pd black. Both the activity and selectivity of Pd were affected strongly by the nature of the support and the composition of the Pd precursor. The specific activity for methanol synthesis decreased in the order $\text{Pd}\text{La}{}_2\text{O}{}_3$ ? $\text{Pd}\text{SiO}{}_2$ [derived from PdCl₂] > $\text{Pd}\text{ZrO}{}_2$ > $\text{Pd}\text{ZnO}\text{≈}\text{Pd}\text{MgO}$ > PdTiO₂ > $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{≈}\text{Pd}\text{SiO}{}_2$ [derived from Pd(π-C₃H₅)₂] ? Pd black, while the specific activity for hydrocarbon synthesis decreased in the order $\text{Pd}\text{TiO}{}_2\text{?}\text{Pd}\text{ZrO}{}_2$ > $\text{Pd}\text{La}{}_2\text{O}{}_3$ > $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{≈}\text{Pd}\text{SiO}{}_2$ [derived from PdCl₂] ? $\text{Pd}\text{SiO}{}_2$ [derived from Pd(π-C₃3H₅)₂] ≈ Pd black ? $\text{Pd}\text{MgO}\text{?}\text{Pd}\text{ZnO}$. Dimethyl ether production was observed over four of the catalysts and the activity for formation of this product decreased in the order $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{?}\text{Pd}\text{TiO}{}_2\text{?}\text{Pd}\text{MgO}\text{≈}\text{Pd}\text{ZrO}{}_2$. The effects of support composition on the catalytic properties of Pd are discussed in the light of current ideas concerning metal-support interactions and the acid-base properties of the support.