Showing papers on "Particle-size distribution published in 1975"

Microparticles with bonded hydrocarbon phases for high-performance reverse-phase liquid chromatography

Abstract: Porous silica microspheres with bonded hydrocarbon phases have been prepared for high-performance reverse-phase liquid chromatography. These bonded-phase particles exhibit high efficiency because of their small size (∼7 μm), narrow particle size distribution, and excellent solute mass transfer characteristics. Slurry-packed 25 cm×0.32 cm i. d. columns of 7 μm particles modified with octadecyl groups (18% C) exhibit plate height of <0.005 cm with water/methanol mobile phases at 50°C. The high concentration of octadecyl, dimethylbenzyl and trimethyl groups that are introduced by reaction with chlorosilanes minimizes band tailing due to solute adsorption by residual silanol groups on the support surface. These small particles are prepared with different size pores, which determine the level of organic stationary phase and resultant chromatographic retention. These particles with various pore sizes permit optimum reverse-phase interaction with solutes of different molecular weight.

Magnetic dry developer for electrostatic photography and process for preparation thereof

Abstract: A magnetic toner for electrostatic photography consisting essentially of spherical particles of a composition comprising a fine powder of a magnetic material having an average particle size not exceeding 1000 mμ and being dispersed in a binder resin, said powdery magnetic material being present in an amount of 25 to 75% by weight based on the composition, spherical particles of said composition having such a particle size distribution that particles having a particle size larger than 44 μ occupy up to 10% of the total particles and particles having a particle size smaller than 2 μ occupy up to 10% of the total particles, wherein said fine powder of the magnetic material is distributed predominantly in the surface layer portion of each spherical particle and said spherical particles have a volume resistivity not higher than 1 × 10 11 Ω-cm as measured in a magnetic field of about 680 gauss under a voltage of 1000 V.

Fixation of tobacco smoke aerosols for size distribution studies

Abstract: Determination of the particle size distribution in the particulate phase of tobacco smoke is difficult due to the liquid nature and high coagulation rate of this aerosol. The use of methyl 2-cyanoacrylate vapor to “fix” smoke particles permits the study of the size distribution of the smoke particles as they exit from the cigarette. Vapors of methyl 2-cyanoacrylate monomer polymerize due to water in the smoke particles. This fixes the shape of the particles that may be collected on a carbon film supported by an electron microscope grid. Electron micrographs of a sufficient number of particles are taken to yield statistically significant data for a histogram. Differences in smoke particle size distribution have been observed for different cigarette filters. Particle size distributions of the methyl 2-cyanoacrylate fixed smoke were found to be essentially the same as those obtained from smoke frozen at liquid N 2 temperature and replicated with a freeze-etch equipment. Other types of liquid aerosols have been evaluated by this technique, and the same degree of success has been obtained as with tobacco smoke aerosols.

The size dependence of sublimation rates for interplanetary ice particles

Abstract: The sublimation rates for water ice have been computed as a function of particle size for various solar distances. Because of the size dependence of the absorption and emission properties of the particles, a sublimation-rate minimum evolves whose depth and position are sensitive to the spectral-absorption properties of the particle in combination with the spectral distribution of solar radiation. As a consequence, a quasistable size of interplanetary ice particles is predicted which is independent of solar distance.

Aerosol size spectrum analysis using relaxation time measurement

Abstract: An experimental method has been developed to measure the dynamic relaxation times of aerosol particles. The particle relaxation time (tau-p) is determined from the ratio of the velocity amplitude of an aerosol particle (v-p) to the velocity amplitude of the medium (u-g) while the aerosol is subjected to acoustic excitation of a known frequency. A differential laser Doppler velocimeter is used to measure v-p, while a microphone is used to measure u-g. From the value of tau-p, the aerodynamic diameter of the particle can be determined if the particle density is known. The method can be applied to real-time in situ measurement of size distribution of an aerosol containing both solid particles and liquid droplets in the range of 0.1-10.0-micron diameters.

Density, Chemistry and Size Distribution of Interplanetary Dust

Abstract: Depth/diameter ratios measured for 98 craters in lunar glass targets reveal a broad distribution with a single strong peaking between 055 and 08 The measured values indicate a mean meteoroid density greater than 1 g/cu cm and probably less than 4 g/cu cm Microprobe analyses show that typical glass pit liners on silicate targets contain only approximately 01% or less of meteoritic material The size-frequency distribution of meteoroids was analyzed for a fractured glass surface of 60095, and a very steep size distribution of submicron meteoroids is indicated As in the case of 15205, a dip at approximately 5 micron in the size-frequency distribution is detected

Pressure, Velocity, and Geometry Effect on A12O3 Produced During Aluminized Propellant Combustion

Abstract: The effect of A12O3 particles on rocket motor stability is critical, but the mechanisms of droplet formation and roles played therein by pressure, velocity, and geometry are not well characterized. An experimental study is reported which was designed to increase this understanding. Size distribution of A12O3 particles as a function of pressure and velocity along with the effects of flow geometry was determined. There was some effect on the particle size as a function of pressure. Moderate-to-low parallel flow velocity resulted in significant changes to smaller particle size distribution as did flow vortices across an otherwise perpendicular flow system. Upon quenching of combustion products as a function of distance from the end-burning propellant surface, it was found that only at quench distances less than about 1 in. was the size distribution affected. The trend was for less smoke (d<\ fim) to be collected after early quench.

Method and means for determination of particle size distributions in a mass flow of a granular material

Abstract: Method and means for determining the particle size distribution in a flow of granular material in the particle size range of 1 μm to several millimeters by introducing into a constant velocity stream of a carrier medium, preferably transversely thereof, a stream of the material to be analyzed, said introduction being effected at a constant velocity within a measuring time period, and the velocities of said two streams being so coordinated as to cause the individual particle size classes to be carried along separate particle paths in a fan-shaped pattern while being subjected to an electromagnetic radiation, and determining the particle quantities corresponding to the individual particle size classes in the fan-shaped stream of material from the extinction or absorption of said electromagnetic radiation.

Stratospheric aerosol size distribution.

Abstract: On the basis of observational results with ruby laser radar (λ=6943 A) backscattering and data on small ions, we examined typical stratospheric aerosol size distribution so far proposed.Power law size distribution and bimodal size distribution can explain both the laser radar backscattering coefficient and small ion density if we take into account the existence of numerous Aitken particles. Thus we cannot determine aerosol size distribution uniquely at the present stage of the investigations. We will examine here bimodal size distribution in some detail by considering the elementary physical processes.Power law size distribution, we suppose, is produced by in situ sulfuric acid particle nucleation. This size distribution is modified by increased outer particle injection such as a meteor particle or a volcanic eruption.When meteor particles are undergoing sedimentation, eddy diffusion, and growing by attachment of sulfuric acid particles which have a mean radius 5×10-3μm, assuming the power law size distribution, then meteor particle size distribution is lognormal. Bimodal size distribution is formed by both the lognormal size distribution and the preexisting Aitken size sulfuric acid particles.

Effect of the Viscosity Ratio, μd/μc, on the Particle-size Distribution in Emulsions

Abstract: The object of this paper is to investigate the effect of the ratio of the viscosities of dispersed and continuous phases, μd⁄μc, on the particle-size distribution in o/w-type emulsions. The viscosity ratios (μd⁄μc) used were 0.836 : 1, 0.271 : 1, 0.0992 : 1, 0.0280 : 1, and 0.00133 : 1. The size of the dispersed liquid droplets was measured by the microphotographic method. The mean diameter and the particle-size distribution were determined, and, further, the specific interfacial energy was evaluated. When the viscosity ratio was much smaller than unity, the particle-size distribution showed a skewed curve. On the contrary, the specific interfacial energy increased remarkably as the viscosity ratio approached unity.

Particle Coarsening in Fused Salt Media

Abstract: The growth of particles of a dispersed phase in a solute saturated solid or liquid matrix has been the subject of much interest in recent years. The dispersion of particles coarsens in order to decrease their total surface energy by the transfer of material from the small to larger particles leading to a decrease in the number of particles.

Studies on carboxylate cement --relations of particle size, setting time and powder-liquid ratio to film thickness--.

Abstract: 1. Particle size distribution and setting timesExperimental results show that in the case of carboxylate cement the particle size distribution is centering on 4-12μ, and especially in the case of C, particles under 10μ amount to about 85%.Zinc phosphate cement is proved to be composed of coarse particles as compared with carboxylate cement.As shown in Fig. 2, C is quickest of the four kinds of carboxylate cement in setting time, showing 10 in hardness after 8 minutes and 100 after 11 minutes 30 seconds, followed by B, D and A in this order.It can be said that in general the setting reaction velocity of cement is quickened in case the particle size is small, supposing other factors such as temperature, kinds of solution, density and powder-liquid ratio are the same.Consequently, in the case of C, it can be presumed that because of the particles under 10 it amounting to about 85% as revealed by the measurement of particle size distribution, C is quick in the hardness-appearing time. But from the fact that A, which is composed of fine particles as compared with B, is delayed, approximately 2 minutes in the hardness-appearing time, it is presumed that there must be causes other than particle size.The main component of carboxylate cement powder is ZnO, which is usually sintered at around 1000°C to control its reactivity, while, its liquid, composed of polyacrylic acid, is also considered to be variable in the setting reaction velocity by such factors as the number of COOH per unit capacity, molecular weight and the degree of polymerization. So, the delay of A in setting as compared with B is presumably due to the facts above-mentioned.On the other hand, as revealed in Fig. 3, the setting time is varied to a great degree in accordance with the powder-liquid ratio. That is, in case the powder (g)/ liquid(g) ratio is 1.8/1.0, hardness appearing after 12 minutes becomes 100 after 20 minutes. Besides, the rising velocity of hardness is slow in this case. The length of setting time is presumably related to the density of powder in the cement mixture.

Determination of the Particle Size Distribution of Powders by Means of a Photosedimentograph

Abstract: : A method is described for determining the particle size distribution (1 - 40 micrometers) of small powdered samples (5 - 30 mg). The measurement is carried out with a photosedimentograph consisting of a Leitz-sedimentometer, a light source of constant intensity, a commercial recorder, a thermostat, and some other accessories. The analysis is semi-automatic, and leads to accurate results within only one hour.