Experimental techniques, ceramics

While necessary, the property measurements alone do not provide all the necessary information about the functionality of the seal material. However, material screening and evaluation using stack tests are not practical. In this section experimental techniques to evaluate the seal material in addition to property measurements are discussed. While discussions focus on glass or glass-ceramic composite seal materials, many of the techniques apply to other types of seal materials. 

Experimental Techniques of Glass Science, C. J. Simmons and O. H. El-Bayoumi, eds., American Ceramic Society, Westerville, OH, 1993. 

A major factor determining the importance of ceramics lies in their usefulness at high temperatures. Two types of experimental techniques are generally used in order to determine the minimum shock required to nucleate fracture (cracking), and the amount of the damage caused by thermal shock 83 the number of quenching cycles, and strength as a function of quench temperature and crack patterns. 

Conventional two-electrode dc measurements on ceramics only yield conductivities that are averaged over contributions of bulk, grain boundaries and electrodes. Experimental techniques are therefore required to split the total sample resistance Rtot into its individual contributions. Four-point dc measurements using different electrodes for current supply and voltage measurement can, for example, be applied to avoid the influence of electrode resistances. In 1969 Bauerle [197] showed that impedance spectroscopy (i.e. frequency-dependent ac resistance measurements) facilitates a differentiation between bulk, grain boundary and electrode resistances in doped ZrC>2 samples. Since that time, this technique has become common in the field of solid state ionics and today it is probably the most important tool for investigating electrical transport in and electrochemical properties of ionic solids. Impedance spectroscopy is also widely used in liquid electrochemistry and reviews on this technique be found in Refs. [198 201], In this section, just some basic aspects of impedance spectroscopic studies in solid state ionics are discussed. 

Wright AC (1993) Neutron and X-ray amorphography. In Sirmnons CJ, El-Bayoumi OH (eds) Experimental Techniques of Glass Science. Ceramic Trans, Am Ceram Soc, Westerville, p 205-314 Wright AC (1997) X-ray and neutron diffraction In Thorpe MF, Mitkova Ml (eds) Amorphous Insulators and Semiconductors. Kluwer, Dordrecht, The Netherlands, p 83-131... 

Bendow, B., 1993, in Experimental Techniques in Glass Science, eds. C.J. Simmons and O.H. El-Bayoumi (The American Ceramic Society, Ohio) p. 33. 

As mentioned previously, potentiometric titration is the most widely used experimental technique to study the electrical double layer on insoluble ceramic... 

We need to understand what controls the rate of a phase transformation. We can monitor both chemical and structural changes to address the sometimes subtle question— which change (chemistry or structure) occurs first The answer depends on why the phase change itself occurs. The experimental techniques we use are those given in Chapter 10, so we just give some specific illustrations here. The classical approach used to study the kinetics of solid-state reactions between two ceramic oxides is to react a bulk diffusion couple in much the same way as, for example, when studying the Kirkendall effect in metals. 

Figure 10.21 Data from Simmons, C. J. and El-Bayoumi, O.H., eds (1993) Experimental Techniques in Glass Science, The American Ceramic, Society, Westerville, OH, p. 88.

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