Showing papers by "DSM published in 1972"

Influence of Metal Particle Size in Nickel-on-Aerosil Catalysts on Surface Site Distribution, Catalytic Activity, and Selectivity

Abstract: Publisher Summary This chapter discusses the effect of the metal particle size on the properties of a metal-on-carrier catalyst. To relate the adsorptive and catalytic properties of metal crystals to the crystal size, the structure of the crystal surface on an atomic scale must be known. This information is obtained from studies on crystal models. A surface atom has a smaller number of nearest neighbors than an atom in the interior of the crystal. The chapter illustrates the infrared studies on the adsorption of N2, CO, and CO2. The infrared spectra were recorded with a Grubb–Parson single-beam grating spectrometer provided with a GS 4-type monochromator. From thermodynamic considerations, it is evident that bulk nickel cannot be oxidized by CO2. In addition, the reaction of benzene with deuterium is an excellent means for studying the influence of the particle size on the catalytic activity.

Relation between the refractive index increment and the density increment of binary mixtures: Application to the determination of partial specific volumes of polymers in solution

Abstract: Starting from the Lorentz-Lorenz equation, Heller, a few years ago, advanced a method for calculating the partial specific volume of a substance in a dilute solution from the refractive index increment of the solution and the specific refraction of the solute. It is shown that this method, based on graphical extrapolation, can be considerably simplified. Further, a method is indicated by which the partial specific volume of a substance over the whole range of concentrations can be calculated in an analogous manner. The method is checked and elucidated with reference to some experimental examples.

Thermodynamic parameters of polystyrene solutions in cyclohexane, determined from sedimentation—diffusion equilibria in the ultracentrifuge. dependence on concentration, temperature and molecular weight

Abstract: Determination of the sedimentation–diffusion equilibrium is one of the methods furnishing data on the thermodynamic parameters of polymer solutions. By means of this procedure measurements can be performed over a considerable range of concentrations. The equilibria in the ultracentrifuge have been determined for five polystyrene samples of narrow distribution covering the molecular weight range 2 × 104 to 2 × 106, at concentrations up to 40 wt-% and at temperatures of 30, 45 and 65 °C. The results are expressed in the data for the chemical potential of the solvent, the number-average chemical potential of the polymer and the interaction parameter ξ. The results are compared with those obtained from osmotic pressure, light scattering and critical miscibility measurements. At very low concentrations the molecular weight dependence of the interaction parameter is in agreement with literature values derived from osmotic pressure and light scattering figures. At higher concentrations this molecular-weight dependence decreases sharply but remains noticeable up to 40% concentration.

The crystallization of branched polymers. II. Substitutional solution of side chains

Abstract: The crystalline structure of bulk polyethylene containing short chain branches was investigated with the aid of small-angle and wide-angle x-ray scattering. The crystalline density obtained from measurements of the invariant, the crystallinity, and the overall density were compared with the crystalline density following from the lattice constants. Good agreement was found for linear and alkyl branched samples; however systematic differences were observed for copolymers containing ester and carboxylic acid side groups. These results are explained by assuming the side groups to enter into the crystalline lattice by substitutional solution rather than at interstitial positions. The chains around the side groups would have to show a kinked structure. This type of crystallization is in agreement with the principle of optimal space filling laid down by Kitaigorodskii [5].