Crystalline particle, diameter size distribution

Coefficient of Variation One of the problems confronting any user or designer of crystallization equipment is the expected particle-size distribution of the solids leaving the system and how this distribution may be adequately described. Most crystalline-product distributions plotted on arithmetic-probability paper will exhibit a straight line for a considerable portion of the plotted distribution. In this type of plot the particle diameter should be plotted as the ordinate and the cumulative percent on the log-probability scale as the abscissa. 

Recently, the VLS growth method has been extended beyond the gas-phase reaction to synthesis of Si nanowires in Si-containing solvent (Holmes et al, 2000). In this case 2.5-nm Au nanocrystals were dispersed in supercritical hexane with a silicon precursor (e.g., diphenylsilane) under a pressure of 200-270 bar at 500°C, at which temperature the diphenylsilane decomposes to Si atoms. The Au nanocrystals serve as seeds for the Si nanowire growth, because they form an alloy with Si, which is in equilibrium with pure Si. It is suggested that the Si atoms would dissolve in the Au crystals until the saturation point is reached then they are expelled from the particle to form a nanowire with a diameter similar to the catalyst particle. This method has an advantage over the laser-ablated Si nanowire in that the nanowire diameter can be well controlled by the Au particle size, whereas liquid metal droplets produced by the laser ablation process tend to exhibit a much broader size distribution. With this approach, highly crystalline Si nanowires with diameters ranging from 4 nm to 5 nm have been produced by Holmes et al. (2000). The crystal orientation of these Si nanowires can be controlled by the reaction pressure. 

The effect of temperature on the size distribution of the Au nanocrystals can be readily seen from the TEM images in Figure 2. The mean diameters of the nanocrystals formed at 30, 45, 60, and 75 °C are 7, 10, 12, and 15 nm, respectively, but the interparticle separation remains nearly the same at 1 nm. X-ray diffraction measurements show that with increase in temperature, the crystallinity of the film increases (Figure 3). The films obtained at 45 and 60 °C exhibit prominent (111) peaks (d = 2.33 A), while those obtained at 30 °C show weak reflections, probably due to the small particle size. The growth of the (111) peak with temperature indicates an increase in the particle size. 

Moisture content slightly hygroscopic. A well-defined crystalline hydrate is not formed although surface moisture may be picked up or contained within small pores in the crystal structure. At relative humidities between about 15% and 65%, the equilibrium moisture content at 25°C is about 2.0%. At relative humidities above about 75%, tribasic calcium phosphate may absorb small amounts of moisture. Particle size distribution Tribasic calcium phosphate powder typical particle diameter 5-10 pm 98% of particles <44 pm. 

Particle Size and Crystallinity of Ferrite Crystals The particle size of ferrite crystals was measured because the larger particles are, of course, desirable for their easy separation from a suspension. The size was measured using Laser Diffraction Analysis (LDA). Just before the measurement, the suspension containing a small amount of ferrite crystals was sonicated to disperse the ferrite particles. The particle size distribution of the ferrite crystals formed from 400 mg-Se(IV) solution is shown in Figure 8-1. The distribution has two peaks at nearly 0.2 and 1.8 fim. The median, mode and average diameters were slightly smaller than those obtained from the ferrite crystals formed from only iron(II) sulfate solution. 

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