Effect of Crystallization Conditions

We can manipulate the properties of nylon products by changing the conditions under which we crystallize them. The degree of crystallinity is increased by slow cooling, annealing, and by crystallization from highly oriented melts. As we increase the crystallinity level, stiffness and yield strength increase at the expense of impact strength. 

We can nucleate crystallization from the melt by incorporating finely ground inorganic crystalline compounds such as silica. Nucleation of injection molded nylons has three primary effects it raises the crystallization temperature, increases the crystallization rate, and reduces the average spherulite size. The net effect on morphology is increased crystallinity. This translates into improved abrasion resistance and hardness, at the expense of lower impact resistance and reduced elongation at break. 

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Table 11.1 The effect of crystallization conditions on the polymorphic form of salmeterol xinafoate...

Fig. 2. Coordination modes in homoleptic, ionic LnCp3 derivatives (a belong to space group P2, b indication from a powder diffraction pattern c show additional the modifications Pbcm and P2i/n (contact dimer-effect of crystallization conditions [78b]) d belong to space group Pna2t and exhibit lengthened intermolecular Ln-C contacts)...

Monomers Consider first the behaviour of Synthes iieT monoraers of the ChMAA-n series at varying temperatures, as well as the effect of crystallization conditions on their structure. 

Many of the performance related properties (Table 3) in a given application (Table 4) depend upon the crystalline characteristics of the part. Interestingly, the content of defect structures determines the crystalline form in the range of 11-14% levels, the beta form develops, whereas the alpha predominates at either extreme of this range (71,73,106). A detailed review of the effects of crystallization conditions upon the phases and morphology includes a summary of crystallographic, infrared, and thermal studies as well as related scanning electron... 

Homo- and co-polymerization of ethylene were performed by using a catalyst system composed of TiCl4/THF/NgCla complex with AlEtj at TO C. In order to investigate the role of MgCla in the catalyst 6 catalysts with different composition (Mg/Ti - 0.42 -16.5) were characterized by means of elemental analysis, IR spectroscopy, x-ray powder diffraction, and SEM technique. The catalytic activity of polymerization increased linearly with the Ng/Ti ratio of catalyst within the experimental range. The activity of copolymerization with 1-hexene also increased with Hg/Ti ratio. The enhancement of polymerization rate by the addition of 1-hexene in the reaction medium was observed only for the catalyst of Mg/Ti ratio smaller than 2.5. The effect of crystallization conditions during the catalyst preparation on the chemical composition and physical structure of catalysts was discussed. The variation caused by different crystallization conditions had considerable influences on the rate profiles of homo-and copolymerization of ethylene. 

Effects of Rate Conditions. It is essential for commercial a-quartz crystals to have usable perfection growth at a high rate and at pressure and temperature conditions that allow economical equipment design. The dependence of rate on the process parameters has been studied (8,14) and may be summarized as follows. Growth rate depends on crystallographic direction the (0001) is one of the fastest directions. Because AS is approximately linear with AT, the growth rate is linear with AT. Growth rate has an Arrhenius equation dependence on the temperature in the crystallization zone ... 

Mathews and Rawlings (1998) successfully applied model-based control using solids hold-up and liquid density measurements to control the filtrability of a photochemical product. Togkalidou etal. (2001) report results of a factorial design approach to investigate relative effects of operating conditions on the filtration resistance of slurry produced in a semi-continuous batch crystallizer using various empirical chemometric methods. This method is proposed as an alternative approach to the development of first principle mathematical models of crystallization for application to non-ideal crystals shapes such as needles found in many pharmaceutical crystals. 

Spanos, N. and Koutsoukos, P.G., 1998. The transformation of vaterite to calcite effect of the conditions of the solutions in contact with the mineral phase. Journal of Crystal Growth, 191, 783-790. 

The orientational relationships between the martensite and austenite lattice which we observe are partially in accordance with experimental results In experiments a Nishiyama-Wasserman relationship is found for those systems which we have simulated. We think that the additional rotation of the (lll)f< c planes in the simulations is an effect of boundary conditions. Experimentally bcc and fee structure coexist and the plane of contact, the habit plane, is undistorted. In our simulations we have no coexistence of these structures. But the periodic boundary conditions play a similar role like the habit plane in the real crystals. Under these considerations the fact that we find the same invariant direction as it is observed experimentally shows, that our calculations simulate the same transition process as it takes place in experiments. The same is true for the inhomogeneous shear system which we see in our simulations. 

Firstly, they might be expected to have an effect when corrosion occurs under conditions of active (film-free) anodic dissolution and is not limited by the diffusion of oxygen or some other species in the environment. However, if the rate of active dissolution is controlled by the rate of oxygen diffusion, or if, in general terms, the rate-controlling process does not take place at the metal surface, the effect of crystal defects might be expected to be minimal. 

Figure 6.3 The effect of environmental conditions on the surface of a zinc phosphate cement (d) stable and undulating surface with no sign of crystallites observed under dry conditions, (b) crystal growth observed in an atmosphere of 100 % relative humidity, (c) extreme porosity observed in the bulk of the cement pores are 0-5 pm in diameter (Servais Cartz, 1971).

The first is the prediction of the Habitus made from the characteristics of the crystal structure, entirely neglecting the effect of growth conditions. We will call this the structural form or abstract form. The second logical approach is to predict the Habitus thermodynamically when the crystal reaches the equilibrium state. This may be called the equilibrium form. The third is a method of analyzing the factors that may have an effect by correlating the Habitus and Tracht shown... 

We shall start from an analysis of what sort of morphology we should expect for quartz crystals if we entirely neglect the effect of environmental conditions. 

In spite of its high specific gravity the apparent density of the needle-shaped crystals, according to Clark [15], is only 0.27 under a pressure of 240kg/cm2 it is 0.86. The crystals may be obtained in the form of pellets whose apparent density is about 0.8. The effect of the conditions of preparation have been thoroughly examined by Smolenski and Plucinski [13], They found that at a diazotization temperature as recommended by Clark, i.e. 15°C, the product pours with difficulty. Conversely, diazotization at a higher temperature (25-45°C) results in formation of a product with a density of about 0.82. 

Hartley, F. D., F. W. Lord and L. B. Morgan Crystallization phenomena in polymers. III. Effect of melt conditions and the temperature of crystallization on the course of the crystallization in polyethylene terephthalate. Phil. Trans. 247 A, 23-34 (1954). 

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