Bimodal crystal size distribution

The significance of this novel attempt lies in the inclusion of both the additional particle co-ordinate and in a mechanism of particle disruption by primary particle attrition in the population balance. This formulation permits prediction of secondary particle characteristics, e.g. specific surface area expressed as surface area per unit volume or mass of crystal solid (i.e. m /m or m /kg). It can also account for the formation of bimodal particle size distributions, as are observed in many precipitation processes, for which special forms of size-dependent aggregation kernels have been proposed previously. 

The first process in all cases is the production of the oxidiser in a suitable fine crystal size. A bimodal particle size distribution, obtained by mixing very fine with slightly coarser particles, often gives the best product. The fuel/binder is frequently prepared as a prepolymer so as to assist mixing and also to reduce the time of the later curing process. 

Bimodal pore size distribution in MCM-4I has been observed by several groups in the last few years [22-24], However, the relation between two types of mesopores were never fully understood. In a recent TEM study of an MCM-41-type silicate with a bimodal mesopore system, a paint-brush like morphology of the particles was observed (Figure 7) [25], It was then proposed that the two types of pores with the pore diameters of 2.5 nm and 3.5 nm respectively coexist and are parallel to each other in the particles. Due to different rates of crystal growth, the lengths of these two groups of mesopores are different, resulting in such a novel structure only on the (001) surface. 

Several approaches towards the synthesis of hierarchical meso- and macro-porous materials have been described. For instance, a mixture that comprised a block co-polymer and polymer latex spheres was utilized to obtain large pore silicas with a bimodal pore size distribution [84]. Rather than pre-organizing latex spheres into an ordered structure they were instead mixed with block-copolymer precursor sols and the resulting structures were disordered. A similar approach that utilized a latex colloidal crystal template was used to assemble a macroporous crystal with amesoporous silica framework [67]. 

A typical super-rate burning of an HMX-GAP composite propellant is shown in Fig. 7-26. The lead catalyst is a mixture of lead citrate (LC PbCi), Pb3(C6Hs07)2-xH20, and carbon black (CB). The catalyzed HMX-GAP propellant consists of 19.4% GAP, 78% HMX, 2.0% LC, and 0.6% CB. GAP cured with 12.0% hexamethylene diisocyanate (HMDI) and crosslinked with 3.2% trimethylolpropane (TMP) is used to formulate GAP binder. The HMX particles are finely divided crystallized (3 HMX of bimodal particle size distribution (70% of 2 pm and 30 % of 20 pm in diameter). 

Because is less convex (positive) than, the compressive strength is negative, but it creates a tensile stress in the hoop direction around the pore. This tensile stress is the destructive "crystallization pressure" A high equilibrium aystallization pressure requires a confined crystal in a pore of any geometry with a very small pore entrance Therefore, the stones with a bimodal pore size distribution are extremely susceptible to salt attack Ii7-i9]... 

One of the steps in the preparation of a side chain in the synthesis of an antibiotic involves a reaction between two soluble reactants to form a product that crystallizes from the reaction solvent, toluene. The reaction itself is relatively straightforward, requiring no special consideration for scale-up once the reaction conditions are established in the laboratory. The problem on scale-up to the pilot plant proved to be the crystal size distribution of the product. The crystals were bimodal with fines mixed with very large crystals. The filtration rate proved to be impracticably slow, and severe occlusion of starting material was experienced. 

Coalescence progress is represented by the evolution of droplet size m and PJPs, assuming ms = me. A bigger m indicates a greater tendency for larger droplets to aggregate compared to smaller droplets, thereby leading to a bimodal droplet size distribution. The model predicts that the droplets least prone to partial coalescence will be the smallest droplets that contain the smallest crystals and as little solid fat as possible. 

The commercially available zeolite adsorbents consist of small microporous zeolite crystals, aggregated with the aid of a clay binder. The pore size distribution thus has a well-defined bimodal character, with the diameter of the intracrystalline micropores being determined by the crystal structure and the macropore size being determined by the crystal diameter and the method of pelletization. As originally defined, the term zeolite was restricted to aluminosilicate structures, which can be regarded as assemblages of SiC>2 and AIO2 tetrahedra. However, essentially... 

The analysis of the kinetics of crystallization of different types of zeolites from aluminosilicate gels points to the conclusion that the crystallization takes place by the simultaneous growth of the constant number N0 of nuclei-I present in the system at the very start of the crystallization process and the number Na of nuclei-II released from the gel disolved during the crystallization process. Some characteristics of the crystallization systems such as the duration of the "induction period", the shortening of the "induction period" and the increase of the crystallization rate, respectively, with the gel ageing and the bimodal size distributions in the specific cases have been discussed and explained in relation to the ratio Na/N0 of particles (nuclei)-II and particles (nuclei)-I present in the crystallizing systems. 

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