Physical changes, monitoring

The electrical resistance (ER) method to monitor physical changes in an electrically conducting material is well known(6). 10 cm x 2.5 cm coated iron foils of 10 micron thickness were electrically resistance monitored during exposure to various corrosive environments to follow metal thickness loss at the paint/metal interface. The circuit shown in Figure 1 allowed foil resistance increase AR, which is directly related to metal thickness loss Ad according to Equation (1), to be determined within 0.003 microns. 

Areas of application of reaction calorimetry include determination of calorimetric data for reactions and process design, for the kinetic characterization of chemical reactions and of physical changes, for on-line monitoring of heat release and other analytical parameters needed in subsequent process development as well as for the development and optimization of chemical processes with the objective, for instance, to increase yield or profitability, control the morphology or degree of polymerization and/or index of polydispersity, etc. 

TG/DTA was utilized to monitor changes in the crystal morphology and physical changes of a hydrated API in a granulation blend and in tablets compressed from the blend. The TG/DTA thermograms are shown in Figures 6 and 7, respectively. 

The manufacture of polymer matrix composites involves complex chemical and physical changes that must be adequately controlled to produce desirable products. Monitoring techniques and models to correlate monitoring data to improve processing are therefore key aspects to increasing production rates and product quality. 

Fabrication of hardware based on the types of resins discussed herein is obviously a chemical process. To control a chemical process the starting raw materials must be precisely defined, and the course of the chemical process must be followed. In the aerospace industry this means the starting resin formulations must be consistent and precisely defined, and the chemical and physical changes that take place as a thermoset resin cures must be monitored and controlled. 

In general, physical changes associated with moisture uptake, such as any changes in disintegration behavior of tablets, are relatively fast. The time for such moisture uptake to occur can be monitored by weight gain at different relative humidities, and it is generally complete within a couple of days. 

The electrical conductivity method is one of the very few experimental techniques that can be used for in situ monitoring of radiation-induced chemical and physical changes. Sensitive measuring equipment is easily kept outside the radiation field, while the parts that sustain radiation damage are relatively cheap and easily replaceable. A major drawback of the conductivity method is that it does not provide direct chemical information, but the problem can be solved by comparing to results obtained by other methods that cannot be used directly in the radiation field. 

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