Expansive properties of the mixture C4ASH12 − 2CS III. Effects of temperature and restraint

The effects of temperature and restraint upon the hydration and the expansion of $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}\text{? 2}\text{C}\text{S}$ mixture compacts in different contact solutions have been investigated. Temperatures above 20°C do apparently hinder the formation of an impervious felt-like layer of ettringite around the $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}$ particles, thus greatly reducing the retarding effect of the lime. An uniaxial restraint of 1 Kg/cm² is enough to reduce sensibly the expansions which remain however high (about 100%). The results can be satisfactorily interpreted by the reaction and expansion mechanism hypothesized in our previous papers.     

Participation of lewis base on vinyl chloride polymerization with Al(C2H5)3CCl4 catalyst system

The polymerization of vinyl chloride has been investigated using an $\text{Al}\text{(}\text{C}{}_2\text{H}{}_5\text{)}{}_3\text{CCl}{}_4$ catalyst system in the presence of various Lewis bases. Effective Lewis bases are γ-butyrolactone, diglyme and diethylenetriamine which are multidentate. The rate of polymerization is dependent not only on the basicity of the Lewis base used but also on a coordination number of one. The latter is the predominant factor. For the effect of polymeric amines, a tentative hypothesis is discussed.     

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 metal-support interactions on the hydrogenation of CO over PdSiO2 and PdLa2O3

A study of CO hydrogenation over $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$ has been carried out for the purpose of identifying the effects of Pd dispersion, Pd morphology, and support composition on the catalytic activity of supported Pd. The specific activity of each catalyst for methanol and methane synthesis was determined from microreactor studies carried out at a fixed set of reaction conditions. Palladium dispersion was measured by H₂O₂ titration, and the morphology of the Pd crystallites, as expressed by the distribution of Pd(100) and Pd(111) planes, was determined from in situ infrared spectra of adsorbed CO. The crystallite morphology of the $\text{Pd}\text{SiO}{}_2$ catalysts is the same, independent of Pd weight loading: 90% of the surface is comprised of Pd(100) planes and 10% of the surface is comprised of Pd(111) planes. By contrast, the crystallite morphology of the $\text{Pd}\text{La}{}_2\text{O}{}_3$ catalysts changes with Pd loading. Primarily Pd(100) planes are exposed at low-weight loadings while Pd(111) planes are exposed at high-weight loadings. The Pd dispersion has little effect on the methanol turnover frequency over both $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$, for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over $\text{Pd}\text{SiO}{}_2$, but increases with decreasing dispersion over $\text{Pd}\text{La}{}_2\text{O}{}_3$. It is further observed that the Pd morphology influences the specific activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ is a factor of 7.5 greater than that of $\text{Pd}\text{SiO}{}_2$.     

Stabilization effect of Co for Mo phase in CoMoAl2O3 hydrodesulfurization catalysts studied with X-Ray photoelectron spectroscopy

The promotional effects of Co in $\text{CoMo}\text{Al}{}_2\text{O}{}_3$ hydrodesulfurization (HDS) catalysts were studied by means of X-ray photoelectron spectroscopy. The higher MoO₃-content $\text{Mo}\text{Al}{}_2\text{O}{}_3$ catalysts (10 and 20 wt% MoO₃) contain mobile Mo, which migrates from the pores to the outermost surface layers of the catalysts and segregates to form less active crystalline MoS₂ during the HDS reaction, while in the case of $\text{Mo}\text{Al}{}_2\text{O}{}_3$ (5 wt% MoO₃) catalyst: no migration of Mo was observed. It is revealed that the Co in $\text{CoMo}\text{Al}{}_2\text{O}{}_3$ catalyst inhibits the migration and segregation of Mo and that it keeps Mo effective for the HDS reaction, since no surface enrichment of Mo was observed. It is concluded that stabilization of the Mo monomolecular layer is the main role of Co. The active species of Mo is suggested to have the composition of S/Mo(IV) = 1 on the basis of the sulfur contents of the catalysts under the mild HDS reaction conditions.     

Adsorption mechanism of Boscan porphyrins on MoO3' Co3O4and CoMoAl2O3

The adsorption of Boscan porphyrins on $\text{Co-Mo}\text{Al}{}_2\text{0}{}_3$ and molybdenum and cobalt oxides was studied with the aim of establishing the mechanism of vanadium elimination during the hydrodemetallization (HDM) of heavy oils. The results show a change in the e.p.r. signal of V0²⁺ and in the u.v.-visible bands of the porphyrins adsorbed on the catalyst. This change is not observed on the support alone. Under the hydrotreating conditions used, only the $\text{Co-Mo}\text{Al}{}_2\text{0}{}_3$ catalysts show a high demetallization activity. As the support alone does not show HDM activity, the cobalt and molybdenum species on the surface, are the demetallization agents.     

Ensembling and monolayer parameters for the dehydrogenation of cyclohexane over PtAl2O3 catalyst

The ensembling and the monolayer parameters, such as the number of atoms in an active center (n), the absolute efficiency of an active center (r_n), the number of migration regions (Z₀), average area of migration regions (Δ), fractional surface coverage (θ_c), and the average number of atoms in a region (v), were evaluated for the dehydrogenation of cyclohexane over $\text{Pt}\text{Al}{}_2\text{O}{}_3$ catalyst in vapor phase. The reaction was studied using alumina of two types in the temperature range 225–350 °C at two contact times. Monoatomic ensemble is the active center in the system studied. Dependence of probability of formation of atomic ensemble (P_n) on the average number of atoms in a migration region is also given.     

Surface interactions in the system RhAl2O3

Under oxidizing conditions Rh is easily dispersed on γ-Al₂O₃ up to a saturation concentration of > 10% of the support area. The average oxidation state of the dispersed phase is Rh³⁺. Excess Rh is present in the three-dimensional Rh₂O₃ particles. The interaction with the support in air is weak at <600 °C and both the dispersed and three-dimensional phases are easily reduced. Multiple chemisorption of CO, NO, and H is noted on the dispersed phase. In the limit two adsorbate molecules reside on the surface Rh in very dilute samples. The multiplicity is a strong function of Rh concentration and invalidates the measurement of accessible metal area in dilute samples. H₂-O₂ titration, with proper precautions, gives more reliable results, due to a constant surface oxide stoichiometry. In heat treatment (>600 °C), Rh-oxide interacts with both γ-Al₂O₃ and γ-Al₂O₃, diffusing into the subsurface region and the bulk. This process can only be partially reversed by reduction in H₂ (>550 °C). Thus, the measured value of surface Rh will depend also on the prereduction procedure. Exposure of $\text{Rh}\text{Al}{}_2\text{O}{}_3$ catalysts to high temperature under oxidizing conditions will cause loss of active area by both particle growth and by diffusion into the bulk of the support. In concentrated samples one can distinguish among the three Rh states: dispersed on surface, particulate, and dissolved in the support.     

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.     

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.     

Mechanisms and kinetics of C4AF hydration with gypsum

The mechanisms and kinetics of early stage C₄AF hydration with gypsum was studied by measuring the heat of hydration with a conduction calorimeter. The heat of the reaction was 173 cal/ g-C₄AF. The reaction equation was estimated to be

$\text{C}{}_4\text{AF}\text{+ 4}\text{CaSO}{}_4\text{·2}\text{H}{}_2\text{O}\text{+ 35}\text{1}\text{3}\text{H}{}_2\text{O}\text{→}\text{4}\text{3}\text{C}{}_3\text{(}\text{A}{}_{0.75}\text{,}\text{F}{}_{0.25}\text{)·3}\text{C}\text{S}\text{H}{}_{31}\text{+}\text{2}\text{3}\text{FH}{}_3$

The equation for rate of hydration was ζ = 0.25t as the thickness (ζ) or hydrated C₄AF increased from 0 to 0.6 μm.     

The measurement of very early hydration reactions of portland cement clinker by a thermoelectric conduction calorimeter

The heat evolved from very early hydration reactions of portland cement can be measured with the isothermal thermoelectric conduction calorimeter. The cement compounds involved in these reactions are primarily C₃A, NC₈A₃, KC₈A₃, C₄AF, $\text{C}{}_4\text{A}{}_3\text{S}$, CaSO₄, C₃S, and CaO. This paper will describe design, operation and applications of the thermoelectric conduction calorimeter.     

Conversion of bituminous coal in COH2O systems: 3. Soluble metal catalysis

The oxyanions of the highest oxidation states of several transition metals, including W, Mo, Cr and Mn, were found to catalyse the liquefaction of Illinois No. 6 coal in $\text{CO}\text{H}{}_2\text{O}$ systems at 400°C. Unlike the high pH (s> 12) required in the base-catalysed system, the effective range for these metal-mediated conversions extend down to pH < 5.0. The benzene-soluble product was found to have a higher $\text{H}\text{C}$ ratio than the starting coal, and the metals were reduced to water-insoluble, lower oxidation states during conversion. A chain scheme is suggested as an explanation for the data.     

Ce4+Ce3+ redox equilibrium in Na2O-B2O3 melts by linear sweep voltammetry

New semi-empirical equations were presented to study the redox equilibria of transition metal ions in molten oxides by linear sweep voltammetry. These equations gave the relation between the peak potential and the polarographic half-wave potential, and contained the Randles-Sevcik equation as an extreme case. The measurements of $\text{Ce}{}^{\mathrm{4+}}\text{Ce}{}^{\mathrm{3+}}$ equilibrium in several Na₂O-B₂O₃ melts were used to verify the equations. The agreement between the electrochemically estimated value of the equilibrium and the other estimated from the chemical analysis of the quenched sample was quite satisfactory. The relation between the $\text{Ce}{}^{\mathrm{4+}}\text{Ce}{}^{\mathrm{3+}}$ equilibrium and the composition of the melt was discussed as the functions of the basicity.     

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.     

Compositions of stable and metastable C3A solid solutions crystallized from simulated clinker melts

The crystallization of C₃A from melts which simulate the composition the liquid phase developed in Portland cement clinkers at ～1350°C has been studied. The liquid phase contained CaO, A?₂O₃, Fe₂O₃, SiO₂ and modifiers, typically 4% Na₂O or 5% MgO. Analyses made using an analytical electron microscope and powder X-ray diffraction disclosed that slowly-cooled or annealed preparations yield C₃A containing the least Fe and Si in solid solution whereas metastable crystallizations yield proto-C₃A solid solutions whose tetrahedral sites, normally occupied by A?, may contain up to ～30% Fe and 12% Si replacing A?. It is suggested that clinker C₃A solid solutions have the formula: $\text{[}\text{Ca,Mg}\text{)}{}_{\mathrm{<mtext>72?(</mtext><mtext>n\; +\; m</mtext><mtext>)</mtext>}}\text{)(}\text{Na}{}_{\mathrm{<mtext>2</mtext><mtext>n\; +\; m</mtext>}}\text{)]}{}_{\mathrm{<mtext>72\; +\; </mtext><mtext>n</mtext>}}\text{[(}\text{A}\text{?,}\text{Fe}\text{)}{}_{\mathrm{<mtext>48\; ?\; (</mtext><mtext>m\; +\; z</mtext><mtext>)</mtext>}}\text{(}\text{Si}{}_{\mathrm{<mtext>m</mtext><mtext>\; +\; </mtext><mtext>3</mtext><mtext>4</mtext><mtext>z</mtext>}}\text{)}{}_{\mathrm{<mtext>48\; ?\; </mtext><mtext>1</mtext><mtext>4</mtext><mtext>z</mtext>}}\text{]0}{}_{144}$.     

A calculation of the elastic constant c33 of a graphite crystal as a function of temperature

A calculation is presented of the elastic constant C₃₃ of a graphite crystal as a function of temperature up to 2500 K, taking into account the anharmonic contribution and the changes in interlayer interactions due to the large lattice thermal expansion. Parametric variations in the theory show that the anharmonic contribution to C₃₃ depends principally on the parameter ($\text{?}{}^2\text{C}{}_{33}\text{?e}{}^2{}_{\mathrm{zz}}$) Comparison of theoretical results with the experimental data, which is mainly from neutron scattering experiments, shows that the data can be accounted for if ($\text{?}{}^2\text{C}{}_{33}\text{?e}{}^2{}_{\mathrm{zz}}$) lies in the range 7–10 × 10¹³ dynes/cm². A theoretical estimate of ($\text{?}{}^2\text{C}{}_{33}\text{?e}{}^2{}_{\mathrm{zz}}$) based on Lennard-Jones potentials between atoms in adjacent basal planes gives a value of 9·07 × 10¹³ dynes/cm².     

Synthesis and solution properties of comb polystyrenes

A new method for the synthesis of comb shaped polystyrenes of predetermined structure is described. Silicon-chlorine bonds are introduced into the backbone polystyrene by reaction of SiMe₂Cl₂ with hydrolysed styrene/vinyl acetate copolymers and coupled with polystyryl-lithium in benzene. From a common backbone polymer a series of comb polymers are prepared that have a constant number of branches but vary in branch length. The $\text{M}{}_{\mathrm{w}}\text{M}{}_{\mathrm{n}}$ of the whole comb polymers is about 1.3. The comb polymers with high branch density show θ (A₂) temperatures lower than that for linear polystyrene. The radius of gyration at θ (A₂) [〈S²〉_{θ (A2)}] is always larger than calculated from random flight statistics. For comb polymers with 20–30 branches increases with λ^?0.46 where λ is the fraction of polymer in the backbone. The intrinsic viscosities of the comb polystyrenes at θ (A₂) are equal to that of the parent backbone polymer when λ > 0.25 and increase only little when λ becomes equal to 0.1. Similar behaviour is found in toluene. Intrinsic viscosities in cyclohexane at 35°C show a complex pattern because of the θ-temperature variation.     

Infrared spectroscopic studies of the hydration products of the system CaOAl2O3CaSO4SiO2

Hardened pastes in this system were studied by infrared spectroscopy. The anhydrous mixes, which had bulk compositions C₆A$\text{S}$₃S_0–4 and C_6–10A$\text{S}$₃S₂, contained C₄A₃$\text{S}$ and other phases. Addition of silica to the bulk composition C₆A$\text{S}$₃ inhibited ettringite formation, unless the lime content was also increased. These results confirm ones previously obtained by X-ray diffraction and thermal analysis.