Dissolution speed

Validation parameter Confirmation of the identity of pure substances Determination of identity of unknown substances Amount single pure substance Amount active substance Limit test (semi- quantitiative) Amount impurities/ degradation products (quantitative) Dissolution speed of substances Bioequivalence studies... 

The dissolution rate does not exhibit significant differences between Methocel E4M CR, Methocel K4M and Metolose 60SH4000 (formula 8) the respective t50 values are 1.78 h, 1.86 h and 1.75 h. Dissolution speed is higher with Metolose 90SH4000 (t50=1.06 h) (Fig. 5) and... 

The dissolution speed of the precipitate is usually not regarded as an important factor in batch procedures, as long as the dissolution could be completed in a few minutes or even somewhat longer time. For extremely slow dissolutions, the rate of dissolution may be accelerated by increasing the temperature. For on-line precipitate dissolutions, the speed of dissolution must be much faster, especially if the objective is to achieve sensitivity enhancements. Elevated temperatures are of limited use in on-line dissolution systems as this may produce undesirable gas bubbles in the system conduits and deteriorate precision. 

Their solubility in water is 0.1-0.2 %, which is just above the applied concentration of 0.1-0.15 %. During preparation the dissolution speed can be increased by heating. Fast... 

Cooling is most effectively accompHshed with a tandem arrangement of two extmders, as shown ia Figure 12, whereia the first extmder ensures complete dissolution of the blowiag ageat, and the second extmder is operated at slow speed for optimum cooling. Additional information on extmsion of foams is contaiaed ia Reference 28 (see FoAAffiD plastics Insulation, thermal). 

However, it should be mentioned that the dissolution process of a solid, crystalline complex in an (often relatively viscous) ionic liquid can sometimes be slow. This is due to restricted mass transfer and can be speeded up either by increasing the exchange surface (ultrasonic bath) or by reducing the ionic liquid s viscosity. The latter is easily achieved by addition of small amounts of a volatile organic solvent that dissolves both the catalyst complex and the ionic liquid. As soon as the solution is homogeneous, the volatile solvent is then removed in vacuo. 

As can be seen in Fig. 3.67, the corrosion resistance of amorphous alloys changes with the addition of metalloids, and the beneficial effect of a metaU loid in enhancing corrosion resistance based on passivation decreases in the order phosphorus, carbon, silicon, boron (Fig. 3.72). This is attributed partly to the difference in the speed of accumulation of passivating elements due to active dissolution prior to passivation... 

By contrast, if additional electrons were introduced at the metal surface, the cathodic reaction would speed up (to consume the electrons) and the anodic reaction would be inhibited metal dissolution would be slowed down. This is the basis of cathodic protection. 

Hot Dipped Coatings Major attempts have been made to improve the quality of aluminised steel strip. Requirements on coating thickness and uniformity have been imposed. It is the speed of sheet movement, length of path in the molten bath, temperature and composition of the bath that control the thickness of the intermetallic layer which lies below the aluminium outer surface. The process of intermetallic alloy formation is diffusion controlled, and it is usual that some dissolution of iron into the molten aluminium does occur at a rate, Ac/At, which is given by... 

Kassner used a rotating disc, for which the hydrodynamic conditions are well defined, to study the dissolution kinetics of Type 304 stainless steel in liquid Bi-Sn eutectic. He established a temperature and velocity dependence of the dissolution rate that was consistent with liquid diffusion control with a transition to reaction control at 860 C when the speed of the disc was increased. The rotating disc technique has also been used to investigate the corrosion stability of both alloy and stainless steels in molten iron sulphide and a copper/65% calcium melt at 1220 C . The dissolution rate of the steels tested was two orders of magnitude higher in the molten sulphide than in the metal melt. 

Situation There are two vendors for a particular bulk chemical who meet all written specifications. The products are equally useful for the intended reaction as far as the chemical parameters are concerned both comply in terms of one physical parameter, the size distribution of the crystals, but on the shop floor the feeling prevails that there is a difference. Because the speed of dissolution might become critical under certain combinations of process variables, the chemical engineers would favor a more finely divided raw material. On the other hand, too many fine particles could also cause problems (dust, static charging). 

The speed of agitation governs the rate. The boundary layer thickness decreases at high speeds. A physical process such as the dissolution of an ionic salt in plain water is associated with an activation energy of the order of less than about 5 kcal mol-1. The influence of temperature on physical processes is less pronounced than that from agitation. 

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