The tensile strengths of single powders and binary mixtures

A theory of tensile strength for single powders and binary mixtures has been developed by means of equations incorporating the particle size parameters and the compositions of binary mixtures.New concepts of using ‘reduced tensile strength’ and choosing a reference state are introduced. These, together with the law of corresponding states, enable the tensile strengths of powders and binary mixtures to be calculated with an accuracy of about ± 15%.     

Effects of combined humidity and temperature on the friction of non-compacted iron,copper and hydroscopic powders

The effects of humidity and temperature on the interparticle friction of iron, copper, Portland cement and plaster of Paris powders have been investigated using a torsional apparatus. It is found that at ambient temperature (22 ± 2 °C), the interparticle friction of iron and copper powders, of a given particle shape, size distribution and size, first decreases then increases and again decreases with increasing humidity. At a constant relative humidity of ～30%, the friction of iron and copper powders is relatively insensitive to temperatures up to ～20 °C and then increases slowly but approximately linearly with increasing temperature. At 22 ± 2 °C, the interparticle friction of Portland cement and plaster of Paris powders increases gradually and then decreases with increasing humidity.     

The effect of large particles on the flow properties of powders

This paper is presented to fill a gap in the knowledge of the effect of larger particles on the flow behaviour of finer powders. Very little has appeared in the literature on the matter and the study is justified in that it is common practice to remove coarse particles before testing on a shear tester. The assumption is made in removing larger particles that they do not affect behaviour and that it is the fines which cause the binding and hence the flowability problems.Four different dry fine powders, a fine white sand, an electrostatic precipitator dust, a mixture of zircon and pyrophyllite (ZAP75) and a local steaming coal were investigated. No generalisation can be made about the addition of various volumetric percentages of spheres of varying sizes or of irregular particles. Thus, with fine sand, balls had little effect on the shear strength whereas irregular coal particles produced marked effect increasing consistently with the relative amount added. On the other hand, with the ZAP75, an increase in strength at low normal loads was exhibited but a decrease (over strength of powder alone) was found at higher normal loads.Experiments were conducted on a whole coal with varying limits of upper size (and also with varying limits of lower size) and the shear strength was found to be strongly dependent on those size limits. It is concluded that whereas much more experimental work is necessary before generalisation can be made of the effect of the presence (or absence, depending on the viewpoint) of large particles on the flowability of a powder, such an effect cannot be ignored.     

Influence of temperature on the reactivity of limestone particles with sulfur dioxide

A modified version of the grain theory was used to analyse the effect of temperature on the sulfation reaction. The theory combines the influence of temperature on the grain size, its effect on the rate of transport of SO₂ and the chemical reaction. An efficient numerical procedure is presented for solving the model equations which take into account the radial gradient of the effective diffusivity in a particle.     

The effect of catalyst temperature zoning on hydrotreating a coal-derived liquid

The effect of catalyst temperature zoning on hydrotreating reactions, coke formation, and changes in catalyst surface area and pore volume was examined. A coal liquid was hydrotreated with the top zone operated in the range of 400–500° C (752–932° F) while the lower zone was maintained at 400° C (752° F). Increasing the top zone from 400° C (752° F) to 450° C (842° F) had beneficial effects on hydrogenation, HDN, and HDM at no cost of increased catalyst coke content. A further temperature increase was detrimental because of excessive coking and possible thermodynamic equilibrium limitations.     

Studies of the Effects of Particle Size Distribution on the Packing Efficiency of Particles

In the studies of pigment volume effects in paint films, particle packing has been shown to be very important. The effects of particle size distribution on this packing has been known but has received little quantitative consideration. In this paper we consider the packing of real and model continuous distributions of particle sizes. An extension of an algorithm for the calculation of random densest packing is given which applies to continuous distributions. Using a log-normal distribution as a model, the effect of the width of a single distribution on packing is considered. Mixtures of distributions are also considered with the calculation of packing efficiency as a function of mean size ratio and distribution widths. Maxima are shown to occur in the packing efficiency of mixtures of distributions as a function of the volume fractions of the individual distributions. The implications of these packing variations in real systems are then discussed.     

Mechanism of fibrillation in the flow of molten polymer mixtures

Experiments on the flow of melts of mixtures of thermodynamically incompatible polymers show that ultra-fine fibrils of one of the polymers form in the matrix of the other in the entrance to the extrusion orifice.     

An alternative presentation of the design parameters for mass flow hoppers

The procedure for determining the critical hopper outlet dimension and wall slope for mass flow hoppers by the Jenike method is well established and documented. However, existing presentations relating the bulk solid flow properties of effective angle of internal friction and the kinematic angle of wall friction with the hopper wall slope and flow factor for mass flow are often inconvenient for manual use and present difficulties when included in design programs suitable for microcomputers.This paper details an alternative presentation of the original Jenike flow factor charts. These alternative charts have been abbreviated to display only the critical design values in the border region between mass flow and funnel flow. The charts eliminate the need for imprecise parameter interpolations by displaying the required design parameters in the form of contours of constant wall slope and critical flow factor as a function of the effective angle of internal friction and the kinematic angle of wall friction.An illustrative example is provided to demonstrate the inherent advantages of this presentation for the evaluation of mass flow hopper geometries.     

Viscous flow effects in the periodic pressure cycling of gas-phase catalytic reactions

The previous study of Hamer and Cormack[1], on the increased effectiveness of gas phase catalytic reactions under conditions of oscillating external pressure, is extended to include viscous flow effects. For this purpose, the full, time dependent equations of viscous flow, diffusion and chemical reaction for a first order, isothermal reaction in a porous catalyst are solved numerically.The inclusion of viscous effects results in a new dimensionless parameter, N. It is shown that in general the catalyst effectiveness factor is smaller for smaller N. It is concluded, however, that even though viscous effects might be very important for extremely low permeability catalysts, viscous effects can be neglected for operating conditions such that N > 1. For one example cited this corresponds to a permeability of 0.2 millidarcy.     

Heat transfer in laminar flow of non-Newtonian fluids

The main objective of this work is the consideration of local heat transfer coefficients for non-Newtonian power-law pseudoplastic liquid in laminar flow in circular conduits. The wall boundary conditions chosen are cases involving uniformly constant heat flux and step change in heat flux.Analytical solutions are developed for the wall temperature profile and compared with experimental data. Additionally, the experimental data have been correlated for comparison with existing relationships, hitherto not verified adequately. The limits of experimental data are:

     

Mott—Schottky analyses on n- and p-GaAs/room temperature chloroaluminate molten-salt interfaces

Mott—Schottky analyses were performed on n- and p-GaAs electrodes in room temperature molten-salt electrolytes comprising mixtures of AlCl₃ and n-butyl pyridinium chloride (BPC) in approx. the 2:1molar ratio. These analyses revealed that the two interfaces, n-GaAs/AlCl₃BPC and p-GaAs/ AlCl₃-BPC, conformed with the behavior expected from the simple depletion layer model after suitable etching of the electrode surfaces. The flat-band potentials (V_fb) thus determined for interfaces were: ?0.20 ± 0.03 V (vs Al^{$\text{0}\text{3}$+}) for n-GaAs and +1.22 ± 0.01 V (vs Al^{$\text{0}\text{3}$}+) for p-GaAs, respectively. The doping densities obtained from the slope of the Mott—Schottky plots, however, were 2–3 times higher than those predicted from the Hall data supplied by the manufacturer. Possible reasons for these discrepancies are discussed. The difference between the V_fb values for the n- and p-type GaAs correspond to the energy band-gap of the semiconductor—a behavior consistent with the absence of significant band-edge unpinning effects in the two cases. Alternatively, the data were seen to be consistent with a behavior such that the band-edges are fixed at the surface for n- and p-GaAs electrodes and all or most of the applied voltage drops across the depletion layer in the semiconductor. The present data are compared with results from cyclic voltammetry obtained in a previous study. In this study, photocurrents were sustained on n-GaAs at potentials significantly positive of the valence band-edge in the presence of certain electroactive species in the AlCl₃BPC electrolyte. This behavior may be understood in terms of accumulation at the interface such that the semiconductor band-edges no longer remain fixed, unlike in the situation above in the absence of redox species. The mechanisms underlying charge accumulation could involve the presence of either a high density of surface states or an inverted p-type surface region caused by hole injection from highly oxidizing redox species as discussed by previous authors.     

A simple relationship between particle shape effects and density,flow rate and Hausner Ratio

A study has been made of the relative magnitudes of particle shape effects on three bulk solids properties. The bulk solids used in this study were small plastic pellets of regular shapes and sizes. Experimental results indicate that variations in particle normal and tangential not-roundness have marked effects on the apparent density, flow rate and Hausner Ratio of the bulk solids. The not-roundness is the standard deviation of the radial distribution of the particle profile. It is a particle shape characteristic derived from morphological analysis.A simple relation of the form P(bulk property) = P(ideal) + P(deviation) is proposed and tested, in which P indicates the property under test. P(ideal) indicates the value of the property for perfect spheres; P(deviation accounts for the effect of particle shape.     

Small-angle neutron scattering from polymer solutions: 3. Semi-dilute solutions near the lower critical solution temperature

Measurements of the radius of gyration and the screening lengths have been made for semi-dilute solutions of polystyrene near the lower critical solution temperature. From these data two regions of behaviour are clearly discerned. By analogy with similar data near the upper critical solution temperature, a ‘phase diagram’ has been drawn from the results around the lower critical solution temperature.     

Lateral mixing of solids in gas—solid fluidized beds with continuous flow of solids

Lateral mixing of solids in a gas—solid fluidized bed with continuous flow of solids can be adequately expressed by the dispersion model. An expression for estimating the lateral dispersion coefficient in such a bed is proposed.     

Small-angle neutron scattering from polymer solutions: 2. The semi-concentrated region near the upper critical solution temperature

Small-angle neutron scattering experiments have been made on solutions of polystyrene in cyclohexane. From these experiments the radius of gyration has been determined as a function of polymer concentration at a fixed temperature (60°C). Additionally, the screening length has been determined as a function of temperature for a fixed polymer concentration of 36% (w/v). The results support the notion of an additional region of solution behaviour, the semi-concentrated region, predicted by mean field-type theory.     

Extraction of coals through dilute alkaline hydrolytic treatment at low temperature and ambient pressure

Assam and Talcher (bituminous) coals have been subjected to batch aqueous alkali treatment followed by extraction. It has been shown that alkali treatment increased extractability and reactivity of coal. Use of 1.4% aqueous sodium hydroxide was found to be capable of rendering about 40–50% coal extractable in ethylene diamine in two alkali treatments followed by extractions. Semibatch operation yielded about 26–33% extractable coal, and extraction data were found to be comparable with those obtained in batch degradation via a single alkali treatment. Of the solvents studied, polar and basic solvents were found to be the most effective.     

Effect of temperature on the tensile strength of lactose coated with fatty acids. Part 2. Tablets

A study has been made of the changes produced in the tensile strengths of tablets made from powdered lactose coated with fatty acids when alterations are made to the temperatures employed during tableting, storage and testing.The strengths at a fixed packing fraction of 0.86 depend on the temperature at which they are measured: they decrease with the amount of acid employed; they initially increase as the temperature during compression is increased, then pass through minima. They also depend on the storage conditions and on the melting points of the fatty acids concerned.The results conform to the Arrhenius equation and are explained in terms of the masking of Van der Waals' forces between lactose particles and the formation of welded bonds by the coatings.