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The effects of cytochalasin B, vinblastine and temperature on particle movement in the plasma membrane of several 3T3 mouse fibroblast lines were investigated. Preincubation of normal 3T3 cells for 24 h in 5–10 μg/ml cytochalasin B had no effect on the mean square relative displacement of marker particles in the membrane (motion constant), but preincubation for 4 h in 40 μg/ml vinblastine reduced the value of this constant by 70%. A 10 °C decrease in temperature decreased the motion constant in normal cells ( Q 10 = 4) more than in virus-transformed 3T3 cells ( Q 10 = 1.8). Interpreting the motion constant of the particles as an expression of the viscosity of the membrane material, values of 3 poise for normal 3T3 cells and 6 poise for the transformed cells are obtained for 37 °C and pH = 7.4. A method is suggested to quantitate aggregation of particles on the surface of cells. When this method is applied to gold particles on 3T3 cells, disaggregation of particles is seen to behave as an unordered process, whereas aggregation appears to express cellular control. This consideration and the effect of vinblastine indicate that the interpretation of particle movement as Brownian movement in a viscous membrane material does not cover all phenomena observed. The membrane movement of the flat revertant SVF1 101 [1] was investigated. This cell line occupies an intermediary position between normal 3T3 mouse fibroblasts and the polyoma and SV40 transformed 3T3 cell lines as judged by growth properties. Its membrane movement was found to occupy an intermediary position between the membrane movements of these cell lines, too.

1. The kinetics of the sintering of niobium carbide is largely determined by the presence in the latter of iron, which is picked up during milling in units with steel balls. Activated sintering was found to be exhibited by powder containing, in the starting condition, as little as 0.3 wt.% of iron. No upper limit of the activating action of iron has been established. 2. The activation of the shrinkage of specimens containing iron is induced by the formation of a liquid phase, which intensifies the processes of viscous and diffusional flow at the particle interfaces. 3. Powders of smaller particle size, too, being characterized by larger specific surface and greater particle structure defectiveness, exhibit intensified sintering.

An electro-optic birefringence technique was employed to study the orientation mechanism of montmorillonite in an electric field. The instantaneous reversal of the field polarity produced evidence of a low voltage permanent dipole and a high voltage induced dipole. This technique was used to study theeffect ofelectrolyte concentration on the rotational diffusion coefficient, a measure of the rate at which the particles rotate or relax, within the solution, from a preferred orientation. Thus, a measure of the immediate environment of the particles was obtained that is not an average effect for the whole system, yet allows for the full development of the clay-cation-water interactions under the experimental conditions. It was found that particle rotation could be accounted for using the measured particle size and normal water viscosity only when the double layer was fully developed, with no free ions or other perturbations. As soon as perturbations were applied, either by adding salts or applying an electric field, the measured particle size and normal viscosity would not account for the data. Either the rotating moiety has to be larger, that is, be a particle plus a water hull, or the viscosity greater, or in some cases both.

The distribution of the electrical charge and the charge‐to‐mass ratios of powder particles are related to the distribution of the particle radii. The latter distribution is assumed to be log‐normal and the particle charge is assumed to be quadratic in its radius. It is found that neither the microscopic average values nor the macroscopic average values are always good representations of the electrical properties of the powder sample. The variations of the average and the median values of the distributions as functions of the standard deviation of particle size are studied.

For batch emulsion polymerizations of vinyl chloride, the reaction rate can be well represented by the empirical expression dx/dt = k (1 + ax), where x is the polymer concentration, and k and a are constants dependent upon initiator concentration and particle number. A simple mathematical model for continuous stirred-reactor polymerizations has been derived from this expression. The model predicts that at short residence times, a steady state of low PVC concentration is reached quickly; with longer residence time, the system more slowly approaches a higher steady-state polymer concentration. Above a critical residence time, equal to 1/ak, the rate of monomer supply becomes the limiting factor. Experimental data on continuous polymerizations are in good qualitative accord with the predictions of the model using constants fitted to batch-charge data. Quantitative agreement is best when the particle number is large; discrepancies may be attributed to a broader particle size distribution in continuous runs. Particle size measurements show evidence of intermittent particle formation in unseeded continuous runs; continuous seeding narrows the particle size distribution, but it is still broader than in batch charges. The model seems sufficiently valid to yield a number of useful implications about practical aspects of continuous emulsion PVC polymerization.

A model of boron ignition treating the inhibiting effect of a boric oxide coating has been developed. Transient differential equations describing the generation and removal of the oxide and associated thermal effects along with heat transfer between the particle and surroundings have been derived, converted to difference form and programmed for computer solution for determination of ignition limits and ignition times. Predictions for particles studied by Macek in a flat-flame burner have been compared with experimental results—agreement is good for dry gas cases, but poor when the gas stream includes water. The program has been used to predict effects of initial oxide thickness, particle size, pressure, oxygen content, initial particle temperature, gas temperature and surroundings radiation temperature on ignition. In addition, the original differential equations have been treated by a stability analysis to determine ignition limits—excellent agreement is found between results obtained with the stability ...

Effects of TiB2 and TiAl3 particles, smaller than 15μ and 600μ, respectively, on grain refining of cast structure of 99.75% and 99.99% aluminum were studied. The results obtained are as follows:1) Grain size of cast aluminum decreased when 0.01 to 0.10%TiB2 was added. This effect became more pronounced as the particle size decreased. Further, it was found that the refinement effect due to TiB2 was more effective when the temperature of molten aluminum was raised to 900°C and 0.006%Ti was added in advance.2) Similarly, grain refining effect due to TiAl3 became more pronounced as the content of TiAl3 increased from 0.07% to 0.54% and the particle diameter decreased. This effect was further noted when the holding time and the temperature of the molten metal containing TiAl3 particles increased.3) When 0.05%TiB2 and 0.016%TiAl3 were added together to the molten metals, the refinement effect was very pronounced if the particle sizes of TiB2 and of TiAl3 were less than 2μ and 100μ, respectively. This observation was consistent with the refinement effect of the Al-5%Ti-1%B master alloy on the cast structure of pure aluminum.

The accuracy of particle size distributions determined from electron micrographs is examined from both theoretical and experimental points of view. Particle detectability and apparent size are found to be sensitive functions of defocus, and hence of elevation of particles in the specimen. Contrast is shown to vary with orientation of both particles and support material. Sources of contrast inherent in the support in the subnanometer range are illustrated. It is concluded that particle size distributions become increasingly subject to error as the fraction of particles with sizes below about 2.5 nm increases.

Employing a bench scale electrostatic precipitator, the particle collection efficiency as a function of particle size distribution was determined for different applied voltages. The collection efficiency was measured using an Andersen cascade impactor. The results were compared with theoretical calculations, field charging being the predominant mechanism. The data were compared with semi-empirical equations predicting the efficiency of single stage precipitators.

Microencapsulation of solid stearyl alcohol particles by complex coacervation was studied. Spherical particles of solid stearyl alcohol were prepared by the vibrating capillary method. Various size fractions of these particles were encapsulated by a modified technique described in an earlier report. Particle concentration and particle-size studies revealed that only a small fraction of the total amount of colloid was used in the formation of the capsule wall. Wall thickness decreased with increasing ratios of solid particles and increased as the particle diameters increased. Scanning electron micrograph observations of the surface showed that acacia was retained on the surface of particles melted and congealed in acacia solution and that the final encapsulated particles had a scaly surface appearance. The studies tended to confirm indications from earlier work that gelatin molecules interact directly with acacia on the surface of the stearyl alcohol particles to form the capsule.

A study is reported on the possibility to determine the influence of particle sizes of cement on the strength of cement mortars by taking into consideration all the particles in a set, under the presumption that apart of the independent effect of every particle in the course of hydration there is a simultaneous and intermediate effect of all the particles on the same physical property. The method has been applied to cement of identical chemical and phase composition but different particle size distributions.

The deposition rate of aerosol particles in turbulent flow has been measured in vertical pipes for nominal Reynolds numbers of 10,000 and 50,000 and for particle dia. of 1·4–21 μm using monodisperse aerosols generated by the vibrating orifice monodisperse aerosol generator. The experiments covered a τ+ range of 0·21–774, where τ+ is the dimensionless particle relaxation time. For small τ+ values, the deposition velocity was found to increase rapidly with increasing particle size, reaching a peak at τ+ = 30. Beyond τ+ = 30, the dimensionless deposition velocity, V+, showed only a moderate dependence on τ+, decreasing slightly at higher τ+ values. Below τ+ = 10. V+ was found to increase as the second power of particle relaxation time and as the fourth power of particle size. The experimental results are in good agreement with several of the existing theories in the region below τ+ = 30. However, the theories are inadequate to explain the results beyond τ+ = 30.

The efficiency of depth filtration of aerosols is shown to be enhanced in the presence of sound in the low sonic frequency range. A number of parameters were investigated, including sound intensity, sound frequency, face velocity through the filter and aerosol particle size, using monosized uranine-methylene blue aerosol particles deposited on a commercial fibrous filter. In the particle-size range 0·65–1·75 μm efficiency increased with particle size, whereas an increase in the face velocity through the filter resulted in a decreasing effect due to sound. It is postulated that the enhancement in deposition efficiency was due to increased inertial impaction and interception caused by sound induced vibration of the aerosol particles, and to an increase in particle diffusivity due to acoustically induced turbulence. A theory of acoustically enhanced aerosol filtration is presented which is in good agreement with the data.

The overall rate of reaction of buffered gel-immobilized glucose oxidase particles is described by means of an enzyme rate equation which relates the overall reaction rate of a particle to the free solution characteristics of the enzyme, the effective diffusivity of the limiting substrate in the gel, the characteristic particle size, and the limiting substrate concentration adjacent to the gel surface. This equation accounts quantitatively for the limitation of the overall rate of reaction by substrate diffusion, and it is used to illustrate the influence of the system parameters, i. e., particle size, enzyme concentration, and pH, on the extent of the diffusional resistance associated with gel-immobilized glucose oxidase particles. The enzyme rate equation is generally applicable to those enzymes whose kinetics approximately follow Michaelis-Menten form when in free solution.

The dielectric constant has been measured on compressed Rochelle-salt powders of varying particle sizes under different conditions of humidity. The measurements were made at 100 kHz in a temperature range from −60 to +45 °C which covers the ferroelectric and both the paraelectric regions. Under normal conditions of temperature and humidity, both the para–ferro–paraelectric phase transitions in all the compressed powders up to 20 μm particle size were observed. The ferroelectricity in these powders were confirmed by observing the hysteresis loops. It was noticed that the lower transition temperature increased with decreasing particle size while the upper transition temperature remained almost unaffected, thus decreasing the ferroelectric temperature range with decreasing particle size. There was no change in the dielectric constant with particle size indicating that the surface layers as well as the depolarization field in the case of Rochelle salt have no significant effect up to 20 μm particle size. The experimental values of the dielectric constant were in reasonably good agreement with the values calculated by modified Bruggeman's formula. Es wurde die Dielektrizitatskonstante von komprimierten Seignettesalzpulverproben unterschiedlicher Teilchengrose bei verschiedenen Feuchtigkeitsbedingungen gemessen Die Messungen wurden bei 100 kHz im Temperaturbereich von −60 bis +45 °C durch gefuhrt, wobei der ferroelektrische und beide paraelektrischen Bereiche uberstrichen wurden. Unter den Normalbedingungen von Temperature und Feuchtigkeit wurden beide Phasenubergange, para–ferro–paraelektrisch, in allen komprimierten Pulvern bis zu 20 μm Teilchengrose beobachtet. Ferroelektrizitat in diesen Proben wurde durch die Beobachtung der Hystereseschleifen bestatigt. Es wurde beobachtet, das die untere Ubergangstemperatur mit abnehmender Teilchengrose zunimmt, wahrend die obere Ubergangstemperatur fast unbeeinflust bleibt und somit der ferroelektrische Temperaturbereich mit abnehmender Teilchengrose abnimmt. Die Tatsache, das keine Anderung der Dielektrizitatskonstante mit der Teilchengrose vorhanden ist, zeigt, das sowohl die Oberflachenschichten, als auch das Depolarisationsfeld im Falle des Seignettesalzes keinen wesentlichen Einflus bis zu 20 μm Teilchengrose haben. Die experimentellen Werte der Dielektrizitatskonstante befinden sich in ziemlich guter Ubereinstimmung mit den auf Grund der modifizierten Bruggemanschen Formel berechneten Werten.

Settling velocities have been measured for two particle fractions settling together through a liquid. The two fractions differed only in particle density but not in particle size. It is shown that the settling velocity of each fraction may be determined from the Richardson-Zaki equation, if the total particle concentration is used to correct the terminal fall velocity of the particles in each fraction. The concept of a critical concentration in binary sedimentation has been examined. At this concentration the two fractions appear to settle at the same velocity. Previous authors have attributed the effect to mechanical interlocking of the particles, but the present work shows that an alternative hydrodynamic argument can account for the phenomenon.

Five different fine powders with average particle size of about 100 microns or smaller were fluidized with air over their respective bubblefree ranges of fluidization. Photographs taken through the front transparent wall of the column showed that the beds contained cavities and microchannels whose sizes were of the same order of magnitude as the particle size. It is shown that interparticle van der Waals adn capillary forces play an important role in the bubble-free expansion of small particles. Measurements of bed expansion and average particle drag coefficients are consistent with the proposed role of interparticle forces.

Four grades of coamercially available microcrystalline cellulose have been examined and the appearance, particle size distributions, specific surface areas, pore size distributions and surface energies determined. The median Stokes diamsters ahow general correlation with published data, but Coulter counter results are larger by a factor of approximately 1.4. Correlation is also seen with values obtained from air permeametry experiments.Scanning electron-microscopy demonstrated the presence of two general types of particle, one roughly rod-like and the other an irregular mass. At higher magnifications, fully hydrolysed samples show a microfibrillar structure, the individual fibrils possessing a transparent longitudinal axis. The possibility that the fibrils are hollow is confirmed by analysis of the adsorption isotherms using mathematical models which indicate that the materials are porous, With a modal radius value of about 2.0 nm.

The response characteristics of several commercially available optical particle counters have been studied experimentally using monodisperse aerosols generated by the vibrating-orifice generator. The particle diameters ranged from 0.5 to 10 μm and the particle refractive index from 1.4 to 1.6. Aerosol material used in the study included DOP (di-octyl phthalate) of 1.49 refractive index and Cargille index-of-refraction liquids of 1.4, 1.5 and 1.6 refractive index. The response of the forward scattering counters (Royco 245 and Bausch & Lomb 40-1) was found to be independent of the particle refractive index above 1 μm in particle diameter. The right-angle scattering counter (Royco 220) showed a more pronounced particle refractive index effect. The experimental results are in good agreement with theoretical predictions of counter response based on Mie-theory calculations. The resolution of the counter had been studied as a function of the particle size. The relative standard deviation of the pulse height distribution was found to increase with decreasing particle size due to the decreasing signal-to-noise ratio of the counter. A sheath-air inlet and a conical inlet are described. These new optical counter inlets improved significantly the resolution and the sampling efficiency of the counters. The use of the vibrating-orifice monodisperse aerosol generator as an aerosol concentration standard for evaluating sampling efficiencies of optical counters is described.

A simplistic study of the dynamics of a falling particle ensemble is described. It shows the effect created by the introduction of particle size distributions on precipitation onset and duration and compares it to the case where air motions or pressure fields triggered by the particles are neglected. The assumption of homogeneously sized raindrops seems adequate if precipitation rates and total rainfall are considered. As soon as timing is involved a more refined treatment is required.

From the engineering viewpoint, continuous operation of powder handling processer is based on solids flow theory and rate equations incorporated with the techniques of process measurement and control. Establishing these theories, and then giving fundamental items such as material properties of solids, structure of epuipments and operational conditions, it would be possible to predict various phenomena relating to powder and inversely to design proper equipments as well as to select optimum conditions. At the same time, development of measuring and controling instruments is essential to continuous processes.This article briefly presents systematic analyses on the mechanism of solids flow in relation to the unit operations of storage, supply, transport and sieving at first and then the kinetics of closed-circuit grinding, further followed by automatic detecting techniques of particle flowrate, mixing ratio and particle size.

Aluminum fine particles of free surfaces were made by the evaporation method in helium gas to investigate the relation between the superconducting transition temperature Tc of the fine particle and its size. The fine particles were collected without exposure to the air to obtain clean surfaces, however, this process introduced some undesirable weak contacts among the particles. The size distribution was determined by means of electron micrographs, and the average diameter ranged from 90 to 160 A. The superconducting transition temperature Tc was determined from the change of diamagnetic susceptibility with temperature. The present experiment shows that Tc rises with a decrease in , and becomes about 1.8 K for of 90 A, considerably higher than that of bulk aluminum 1.16 K.

The dielectric constant of compressed powders of KDP and Rochelle salt has been measured st 1 MHz as a function of particle sizes ranging from 20µ to 600µ over a wide temperature range to cover ferro and paraelectric phases. Dielectric anomalies indicating the ferroelectric behaviour in both KDP and Rochelle salt powders are observed upto 20µ particle size. The existence of ferroelectricity was further confirmed by observing ferroelectric hysteresis loops. The measured values of the dielectric constant in Rochelle salt were independent of particle size while in KDP they decreased with decreasing particle size. The experimental values are compared with the values calculated by modified Bruggeman's formula. It is found that the agreement in theoretical and experimental values in Rochelle salt was with in 25%. In KDP the agreement between experimental and theoretical values was poor and the measured values were less than 1/4th of the calculated values.

Semicontinuous emulsion copolymerization of butyl methacrylate and butyl acrylate with a monomer emulsion feed has been investigated. The distribution of a constant amount of anionic emulsifier between the initial reactor charge and the emulsion of monomers was varied. The surface tension during the feeding of the monomer emulsion as well as the size distribution and average particle size in the final latices were measured. It was found, that the distribution of emulsifier affected the mechanism of the particle growth and the final particle size. At a high content of emulsifier in the initial reactor charge a large number of small particles appeared, which underwent extensive limited flocculation during the later stages of polymerization. The extent of the flocculation was controlled by the overall amount of emulsifier. In case of a very low content of emulsifier in the initial reactor charge no flocculation occured and even a nucleation of new particles took place towards the end of the monomer emulsion feeding. Es wurde die semikontinuierliche Copolymerisation von Butylmethacrylat/Butylacrylat in Emulsion bei allmahlichem Zuflus einer Monomer-Emulsion untersucht. Die Verteilung einer konstanten Menge des anionischen Emulgators zwischen dem Anfangsansatz im Reaktor und der zulaufenden Monomeremulsion wurde variiert. Die Oberflachenspannung wahrend der Zugabe der Monomeremulsion sowie die Grosenverteilung und die Durchschnittsgrose der Partikel in den hergestellten Latices wurden gemessen. Es wurde gefunden, das die Verteilung des Emulgators den Mechanismus des Partikelwachstums und die Endgrose der Partikel beeinflust. Bei hohem Gehalt an Emulgator im Ausgangsansatzdes Reaktors bildeten sich viele kleine Partikel, die in spateren Polymerisationsphasen stark, aber im Umfang beschrankt, agglomerierten. Der Bereich der Agglomeration wurde durch die Gesamtmenge des Emulgators bestimmt. Im Falle eines sehr kleinen Gehalts an Emulgator im Ausgangsansatz kam es zu keiner Agglomeration. und es wurde sogar die Entstehung neuer Partikel am Ende der allmahlichen Zugabe der Monomeremulsion beobachtet.

The air filtration theory demonstrates the existence of a minimum efficiency value for some aerosol particle sizes and velocities. Through experiments, many laboratories have sought to prove this efficiency minimum while using industrial filter pads. Generally used methods, involving monodisperse aerosol generation, are difficult to implement. The authors describe a laboratory experiment ready for semi-industrial application, thanks to the use of a new type of particle counter. A lightly poly dispersed soda-fluorescein (uranin) aerosol is used.

Large soil particles (predominantly montmorillonite) shed small (submicron- and micron-sized) particles when collected in water or on membrane filters or upon collision with an obstacle. Small particles present in large numbers in the interstices of a large soil particle are released into air or water and form an independent aerosol or hydrosol colloidal suspension leaving the parent particles practically unchanged. The shed particles did not originally belong to the aerosol or hydrosol population but are released in the sampling apparatus; consequently the determined concentration of aerosol particles is not representative of the aerosol concentration in air. Da- and h-μm aerosol particles act as accretion centers for cloud droplets when ingested by a cloud; they form large drops which shatter and form numerous fragments. The shed hydrosol particles in water drops formed on those fragments provide additional freezing nuclei that freeze these water drops. Studies of natural aerosol particles must include not only their size, surface structure and chemical composition, but also the function those aerosol particles perform in nature as condensation and ice-forming nuclei.

By the addition of KOH solution to FeSO4-Cr2(SO4)3 mixed solution, Fe(OH)2 was formed and it was oxidized to Fe3O4 by air. The heat treatment of formed Fe3O4 precipitate was carried out in vaccum (10-5 Torr) and in H2-H2O mixed gas (H2O/H2=2) at 200-500 C for 5 hrs.The effects of the heating temperatureon particle size, surface area and pore structure (pore distribution, pore diameter, pore volume) were investigated by means of X-ray diffraction, electron microscopy and gas adsorption.Addition of Cr(III) suppressed the particle growthof Fe3O4 and also increased the surface area remarkably.By the heat treatment of the precipitate; 1) The particle growth of Fe3O4 occurred slightly at temperatures above 400 C, 2) The surface area changed with rise in temperature, that is, the area increased with temperature up to about 300 C and showed a maximum at this temperature. Above 300 C, however, the area decreased. The increase in surface area was caused by micropore (diameter lt 50 A) resulting from the removalof water contained, and the decrease was caused by the pore-widening process resulting from sintering of the precipitate at temperatures above 400 C, 3) The changes of particle size, surface area and pore structure were also affected by heating atmosphere.

1. The most objective data upon the size of particles in dispersion-strengthened alloys are provided by electron diffraction microscopy. 2. The method of extraction and subsequent electron microscopical examination of particles ensures high reliability in determinations of particle size parameters and enables analysis to be carried out at any stage of alloy preparation. 3. The x-ray method of determination of mean particle sizes gives reliable results when few inclusions more than 1000 A in size are present. The method can also be recommended for the evaluation of relative changes in the size of strengthening phase particles under the action of various factors. In investigations of this type, the presence of a large number of coarse particles is not an obstacle.

The theory of transient electric light scattering is extended to larger particles, fulfilling the restrictions of the Rayleigh-Debye-Gans approximation. The equations derived are valid for rigid, strongly elongated, monodisperse particles, orientated under the simultaneous action of both their permanent and induced dipole moments. The equation for the rise of the effect gives the possibility the particle electric moments to be determined. The equation describing the decay of electric light scattering differs from the one given by Wippler. It offers a method for obtaining the particle rotational diffusion coefficient. For small particles the equations derived coincide with the formulas of Nishinari-Yoshioka, Benoit, and Tinoco, describing transient electric birefringence. The dependence of the coefficient on particle size in the formulas presented shows the limits of application of the small particle theory.

A new particle size analysis of latexes has been developed using a disc centrifuge allowing a very fast zonal sedimentation of particles followed by an automatic optical device. This method, which involves 5-10 minutes, permits the routine control of fabrication for emulsions of PVC. Linked to a computer, it permits accurate determinations of particle sizes in terms of weight, surface or number averages. The complete operation for one latex requires less than 15 minutes. This technique has been used to follow the growth of particles in seeding operations, i.e., monosized seed latex and the competitive growth of 2 populations of seed particles. Some results have also been obtained by comparing accurate particle size analyses of latexes with rheological properties of plastisols obtained from these latexes.

The rate of chlorination of Fe2O3, NiO, and NiFe2O4 by Cl2 (1073 to 1473 K) and by HCl (1073 to 1273 K) diluted with He or Ar has been measured. The rates were measured as a function of particle size, temperature, gas composition and internal surface area. In all cases gas diffusion influences the rate. During the chlorination of the oxides with Cl2 at low temperatures there was incomplete pore diffusion and the rate is restricted to the pore walls near the external surface. At high temperatures the rate is controlled by the diffusion of Cl2 through the gas film boundary layer around the oxide particle. During the chlorination by HCl the rate is controlled primarily by the counter current diffusion of HCl to the surface and of the reaction products away from the surface.

The knowledge of the smallest particle radius rL detectable in Condensation Nuclei Counters is very important after recent measurements have shown deviations from the classical shape of the size distribution in natural aerosols. Despite the lack of calibration aerosols in the important size range, the lower limit rL can be determined with gas-to-particle conversion in connection with coagulation processes. From numerical calculation, the equation r L = 1/c. r min , c = 1.45 ± 0.10 was derived. r min can be evaluated from direct particle counts and volume determination by means of an absolute particle filter.

Equations are developed which relate NMR linewidths for aggregates of macromolecules to the molecular motional parameters τ c (correlation time) and A (“anisotropy factor”). The effects of molecular motion can be isolated from those of Brownian tumbling of the aggregates by measuring linewidths at two solution viscosities or aggregate sizes. Where molecular motion is anisotropic ( A > 0), e.g., in membranes, aggregated proteins, and lipid dispersions, NMR linewidths are not simply related to τ c Systems with the same τ c but different values of A may exhibit different linewidths, as for the lecithin 31 P resonance above and below the chain melting transition. The reduced linewidths observed from sonicated, compared with unsonicated, lecithin dispersions can be explained solely by the increased particle tumbling rates. Any differences in molecular motion within the bilayers are only minor. All the linewidth behavior reported for lecithin dispersions, including variations with vesicle radius and the only slight dependence on solution viscosity, are predicted by the theory developed here. It is shown that changes in A are greater than changes in τ c both along lecithin chains, and for lecithin phosphate groups at the chain melting transition.

The effect of yttrium oxide dispersoid volume fraction and particle size on the 1400†F (1033 K) and 1900†F (1311 K) rupture strength of a dispersion strengthened nickel-base superalloy, made by mechanical alloying, was investigated. Yttrium oxide Contents ranged from 0 pct to 4.5 pct by volume, and average oxide particle sizes varied from about 150A (15 nm) to 580A (15 nm) to 580A (58 nm). High volume fractions and small particle sizes gave low grain aspect ratios and poor 1900†F (1311 K) and 1400†F (1033 K) stress rupture properties following heat treatment. Rupture strengths at 1400†F (1033 K) were otherwise relatively unaffected by dispersoid parameters. At grain aspect ratios less than 6.0, 1900†F (1311 K) rupture strength was controlled by grain geometry while at higher values rupture strength was directly influenced by dispersoid parameters.

The unsteady-state mass and energy equations have been set up for the case of a single particle of brown coal plunged into a hot gas stream. These equations have been solved, with the aid of a digital computer, to give temperature histories for particles 20, 100 and 1000 μm in diameter. Analysis of these histories reveals that although ignition sometimes occurs with an abrupt temperature-jump, it can also occur without it; the last may possibly be associated with ignition instability. Reduction of particle size and of oxygen partial pressure both render temperature-jump ignition less likely. Gas temperatures required for ignition of brown-coal particles are only 600–800 K, the larger particles igniting at lower temperatures; ignition times are typically 5 ms for a 20 μm particle and 50 ms for a 100 μm particle, and are more affected by gas temperature than by oxygen concentration. It is unlikely that radiation plays a major part in the ignition of pulverized brown coal; recirculation of hot combustion products probably dominates. It is concluded that the ignition stability of burners fired with pulverized brown coal could be improved by avoiding the dilution of the coal stream with water vapour or inert drying gas, and by promoting the recirculation of hot gases back to the burner inlets. While the methods used are general and applicable (with appropriate reaction rate data) to other materials, the results here given depend heavily on the high chemical reaction rates between brown coal and oxygen at relatively low temperatures and are specific.

1. It is shown that the application of pressure intensifies particle regrouping processes and enables nonporous materials to be produced in cases where this cannot be achieved by free sintering. 2. The effects have been determined of the volume content of the liquid phase and the particle size of the refractory component on the degree of densification attainable at various pressures. Critical pressures necessary for the production of nonporous specimens under the conditions investigated have been established. 3. An analysis is made of the influence that the grain size of the refractory component has on the degree of densification. It is demonstrated that the rate of densification and shrinkage in liquid-phase sintering under a pressure substantially exceeding the capillary pressure is totally or virtually independent of the particle size of the solid-phase component.

When colloidal materials are carried in aqueous suspension through packed beds of spherical particles, it has been observed that the rate of transport of the colloidal particles depends on such factors as the size of the colloid, the size of the packing and the ionic composition of the aqueous phase. From such observations, a chromatographic technique has been developed, called hydrodynamic chromatography, which can yield size information on a variety of colloidal materials in the submicron range. Several examples are provided that illustrate how the technique is applied in the study of polymer latexes to determine particle size, assess particle size distribution, follow emulsion polymerization kinetics and provide evidence for particle agglomeration. The origin of the various transport and separation phenomena is also discussed.

The results of experiments carried out to determine the flow behaviour of a pure fluid through a scaled-up model of the sizer helix are described. The particle behaviour suggested by the fluid velocity profiles was checked by means of high speed cine-films and found to be in good agreement. The motion of both fluid and particles through the sizer helix was shown to be controlled by the distribution of static pressure along the vertical walls of the channel.

The erosion of graphite-epoxy composites by solid (sand) particle impingement is correlated by the equation e = Ψd Γ [ V sin ( α + β )] γ where the system constants Ψ, β, Γ and γ are experimentally determined and d , V and α are the particle size, velocity and impact angle, respectively.

Serious inaccuracies and limitations are present in optical particle counter measurements as a result of pulse height analysis. It is shown that the mean particle size limits of the several pulse height analyzer channels (i.e. the “size windows”) vary with the spectrum of the aerosol being measured. A mathematical analysis illustrates that this variation is less than 7 per cent for a typical atmospheric measurement; such a correction is generally not of controlling importance for aerosol sampling and analysis. The loss of counts as a result of electronic pulse processing is also evaluated, and it is shown that these counting losses, and not those due to coincidence, limit the maximum aerosol concentration which can be measured. In a typical illustration, this maximum is found to be only 24 per cent of that which is derived from consideration of coincidence losses alone. This result demonstrates that dilution of the ambient sample is required for virtually all measurements of the atmospheric aerosol by optical particle counters.

Preparative methods have been developed in order to obtain monodisperse polystyrene latices in the absence of added surface active agents. By suitable adjustment of the ionic strength of the aqueous phase the initiator concentration and the polymerisation temperature it was found possible to obtain a range of particle sizes, ca. 0.1 to 1.0 ,um, by single-stage reactions. The total initial ionic strength of the aqueous phase was found to play a critical function in determining particle size. A formula has been derived from the experimental data which enables the preparative conditions required to form a latex, containing particles of a particular size, to be predicted.

Variations of I/Na, Br/Na, and Br/Cl ion ratios with particle size in Puerto Rican marine aerosols suggest behavior of I and Br in agreement with the results of previous studies, although Cl losses are shown to be a significant factor in modifying ion ratios, especially in the submicron particle range.

The growth of aqueous sulfuric acid droplets originating from a heteromolecular nucleation process is calculated for particle sizes up to 1000 A. Two cases are discussed: (1) there exists a given initial concentration of a condensable trace gas, and (2) there exists a constant production rate of a condensable trace gas. The particle growth and the final particle size are calculated as functions of relative humidity from 10 to 99 per cent. Our previous studies on heteromolecular nucleation (Kiang et al., 1973) as applied to gas to particle conversion are extended to the particle growth process and found to agree roughly with experiments by Cox (1973).

The dielectric constant of triglycine sulphate in the form of compressed powders of varying particle sizes ranging from 55 to 500 μm has been measured at 100 KHz from 0 to 90 °C. Dielectric anomalies indicating the existence of ferro-electricity were observed for particle sizes up to 55 μm. The dielectric constant decreases with decreasing particle size and is much lower than that expected theoretically. These results have been qualitatively explained by postulating the formation of a defective surface layer of low dielectric constant.

Two night eruptions of the volcano Stromboli were studied through 70-mm photography. Single-camera techniques were used. Particle sphericity, constant velocity in the frame, and radial symmetry were assumed. Properties of the particulate phase found through analysis include: particle size, velocity, total number of particles ejected, angular dispersion and distribution in the jet, time variation of particle size and apparent velocity distribution, averaged volume flux, and kinetic energy carried by the condensed phase. The frequency distributions of particle size and apparent velocities are found to be approximately log normal. The properties of the gas phase were inferred from the fact that it was the transporting medium for the condensed phase. Gas velocity and time variation, volume flux of gas, dynamic pressure, mass erupted, and density were estimated. A CO2-H2O mixture is possible for the observed eruptions. The flow was subsonic. Velocity variations may be explained by an organ pipe resonance. Particle collimation may be produced by a Magnus effect.

V-I curves of compressed CdSe powders are studied experimentally. It is found that the current is well proportional to the product of the voltage dependent term; V+βexp (α√V), and the temperature dependent term; exp (-E/kT), in the measured temperature range (153 K~ 403 K), where α and β are constants, k the Boltzman constant, T the temperature and E the activation energy ranging from 0.096 eV to 0.44 eV depending on the temperature and the method of preparing samples. The effects of the applied pressure and particle size on the V-I curves are also studied experimentally. Transport mechanisms are discussed according to the phenomenological V-I curve obtained. It is shown that the presence of the surface layer, having different electrical properties from bulk, and of a particle and particle-to-particle contacts play an important role in the electrical conduction in compressed CdSe powders.

A series of lactose granulations made with various amounts of starch paste and water was subjected to milling through different screens and the particle sizes were determined. The distributions were log-normal when the size of the coarse material was determined by sieve analysis and the size of the fine material was determined microscopically. An equation was developed to describe the increase in surface area, ΔO, when material is milled through a screen with n holes of diameter d; this equation takes the form: log[n(ΔO)] =-q(log d) + p, where q and p are constants.

In aerosol exposures, it is important to determine the concentrations of deposited particles in the respiratory tract and correlate that with various factors describing the aerosol. Using a four-compartment lung model (with specified clearance times from each compartment), we have derived expressions and written Fortran IV programs to calculate particle retentions. Three exposure patterns were considered: continuous chronic, acute pulse, and 40-hour work week exposures. Particle concentrations in each compartment at any time and integrated exposure over any period were calculated for each pattern. Results show that changes in particle size and solubility can alter retention and integrated exposure in some compartments by orders of magnitude, even when identical masses of aerosol are inspired. Thus, air quality standards must take size distribution and solubility of the particle into account.

The formation of precipitate particles in solid solutions is studied by regarding the process as comprising chain reactions, where the collision of two single solute atoms initiates the clustering. Calculations are greatly simplified if back-reactions, i.e. the decomposition of once-formed particles, are completely neglected. The reaction constant for particle growth are considered to be dependent on the size of particles, and the dependence is different for different growth mechanisms. The kinetics are examined for the two cases, size-independent and size-dependent (proportional to the number of solute atoms in the respective particle) reaction constants; the behaviour of actual systems may be inferred from the results of these two imaginary cases. The resultant distribution of particle size is very different for the two cases, especially when the rate for the initiation of the chain reactions is slow in comparison to those for subsequent reactions; for the latter case (size-dependent) the distr...

The use of column packing with particle sizes of 10 μ in different modes of column chromatography, liquid—solid (LSC), bonded phase (BPC) and gel permeation (GPC), was investigated. LSC columns of very high efficiency, 10 effective plates/sec. and high reproducibility were produced by packing μPorasil, a silica gel with a surface area of 400 m 2 /g and an average particle size of μ, into drilled stainless-steel tubes. Bonded phases were prepared by the reactionof monomeric organosilanes with μPorasil to form monomolecular bonded layers. Octadecyl, aminopropyl and cyanopropyl groups were bound to the surface. Packed columns of the monomolecular, bonded phases gave very high efficiencies. More than 300 theoretical plates and 10 effective plates/sec can easily be obtained on a single 30-cm-long column at a carrier velocity of 0.7 cm/sec. High-speed GPC was performed by using packed columns of μStyragel 2 , a porous polymer of styrene and divinylbenzene, with average particle sizes of 20 μ. Columns packed with μStyragel ( dp ??? 10μ) gave 4000–10,000 theoretical plates/30 cm of column, depending upon the carrier velocity. Molecular-weight distributions of many polymers can be obatined in 10–15 min. In addition, the columns were also run at lower carrier velocities to separate small molecules which differ by as little as one methylene group.