Instruments dilatometry

Symbolize as y, the proportionality constant between species i and its contribution to the property (i.e., the partial molar volumes in dilatometry, molar absorptivities in spectrophotometry, etc.). Then at any time the instrument reading is... 

Most instruments are so precise that they can be used to measure the melting temperature of the material and, by using linear dilatometry, to measure the thermal expansion coefficients. The thermal expansion coefficient can be measured using... 

A convenient method for determining transition times and transition temperatures of polymeric materials is dynamic mechanical analysis. One type of instrument which is particularly suitable for polymeric solids is the freely oscillating torsion pendulum (TP). Advantages of the TP include its simplicity, sensitivity, relatively low frequency ( 1 Hz) which permits direct correlation of transition temperatures with static nonmechanical methods (e.g., dilatometry and calorimetry), and its high resolution of transitions A major disadvantage of the conventional TP is that test temperatures are limited by the inability of materials to support their own weight near load-limiting transition temperatures. 

Dilatometry is one of the older classic methods for the determination of transition points between solids (Drucker 1925). The dilatometer usually consists of a large bulb connected to a capillary and filled with an inert liquid. Volume changes as a function of temperature or resulting from a solid-solid transition may be determined by changes in the volume of the inert liquid. The recent advances in the miniaturization of chemical instrumentation (e.g. Jakeway ef a/. 2000 Krishnanefa/. 2001), and the high precision associated with that miniaturization may lead to a renaissance of the use of some of these classic techniques and their applications to the study of polymorphism. 

The crystal phases in the glass-ceramics were determined by XRD analysis. All instruments were precisely and identically set to ensure a high precision to obtain the integral peak area. The microstructure of the fresh fractured cross section of the glass-ceramics was observed by SEM. The thermal expansion coefficient (TEC) was calculated from room temperature to 500 °C at a heating rate of 5°C/min in the dilatometry analyser (NETZSCH, DIL402PC). The flexural strength was determined in a 3-point bend test at a constant strain ratio of 0.5mm/min. 

In one of the few reviews dedicated to STA the Paulik brothers claim to have been the first to build a true simultaneous TG-DTA, in 1955. Over many years they developed their instrument, the Derivatograph to incorporate dilatometry, and evolved gas analysis, and used it to pioneer the development of controlled rate methods. By modern standards, the instrument performance was pedestrian, and used samples of... 

Figure 4.67[A] shows a typical isothermal experiment carried out with a DSC. Similar experiments could be carried out with isothermal calorimeters, dilatometry and other teehniques sensitive to crystallinity changes. After attainment of steady state at point 0, the experiment begins. At point 1, the first heat flow rate is observed, and when the heat flow rate reaches 0 again, the transition is complete. The shaded area is the time integral of the heat flow rate, and if there is only a negligible instrument lag, it represents the overall kinetics. In case of an excessive heat flow-rate amplitude, lag calibrations with sharply melting substances of similar thermal conductivity may have to be made (see Figure 4.22). Processes faster than about 1 min...

Thermomechanical analysis (TMA) measures the deformation of a material contacted hy a mechanical prohe, as a function of a controlled temperature program, or time at constant temperature. TMA experiments are generally conducted imder static loading with a variety of probe configurations in expansion, compression, penetration, tension, or flexime. In addition, various attachments are available to allow the instrument to operate in special modes, such as stress relaxation, creep, tensile loading of films and fibers, flexural loading, parallel-plate rheometry, and volume dilatometry. The type of probe used determines the mode of operation of the instrument, the manner in which stress is apphed to the sample, and the amount of that stress. 

The TMA is an easy-to-use analytical instrument that measures dimensional changes in a material as a function of temperature or time under a controlled atmosphere. Its main uses in research and QC include accurate determination of coefficient of linear expansion of plastic materials. It also is used to detect transitions in materials (e.g., glass transition temperature, softening and flow information, delamination temperature, creep and stress relaxation, and melting phenomena). A wide variety of measurement modes are available (expansion, penetration, flexure, dilatometry, and tension) for analysis of solids, powders, libers, and thin film samples. 

Kraus and Gruver chose dilatometry as their main instrument see Figure 13.6 (6). Here, the glass transition appears as an increase in the expansion coefficient at the elbows in the data. The width of the glass transition region increased from 9 to 20°C for the elastomer, principally on the upper side of the transition. 

Thermomechanical analysis thus permits a quick comparison of different materials. As long as instrumental and measuring parameters are kept constant, quantitative comparisons are possible. In Sect. 6.5, some more detailed applications of dilatometry and thermomechanical analysis to melting and crystallization are collected, as well as a discussion of the analysis of materials under tension. 

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