Static high temperature conductivity

Figure 4.1 Alternating current static high temperature conductivity cell (Ho, P.C., Palmer, D.A. and Mesmer, R.E. (1994). J. Solution Chem. 23, 997 with permission from Elsevier).

Static high temperature and pressure conductivity cells... 

A number of static high temperature cells were developed later for electrical conductivity. Some of them have been used for measiuements at temperatures below the critical temperature of water. Thus, Khitarov et al. (1963), EUis... 

Since the significant majority of the published literature on high temperature crack growth under static and cyclic loads is predicated upon experiments conducted on alumina and alumina matrix composites, the examples cited in the present review have centered around oxide ceramics and their composites. However, the implications of the results to other classes of ceramics, intermetallics, and brittle matrix composites are also described, wherever feasible, along with any available information in an attempt to illustrate the generality of the concepts developed here. 

Here a is the bulk ionic or dc conductivity is the angular frequency (27rf) r is the dipole relaxation time is the relaxed dielectric constant or low frequency/high temperature dielectric constant (relative permittivity due to induced plus static dipoles) is the unrelaxed dielectric constant or high frequency/low temperature dielectric constant (relative permittivity due to induced dipoles only) o is the permitivity of free space E p is the electrode polarization term for permittivity and E"-p is the electrode polarization term for loss factor. The value of E p and E"p is usually unity, except when ionic conduction is very high (75). 

A refractory sample exposed to a temperature of 1300°C was mounted on a stainless steel shaft with a section of stainless steel tubing placed around the shaft which in turn served as a high temperature "sacrificial anode. Corrosion tests were conducted at rotation speeds of 60 and 120 rpm, along with a few under-static conditions. 

The first measurements of the electrical conductivity of aqueous electrolytes at high temperature were performed 100 years ago by Noyes and co-workers at MIT (Noyes et al., 1903, 1907, 1910a, 1910b) using a high-pressiue platimun-lined steel vessel. The body of the cell is one of the electrodes, while two others platimun electrodes were located in the upper and lower part of the vessel and insulated from it by mica and quartz washers. The solution is filled into the cell and it remains static diuing the measiue-ment performed near saturation with vapor phase. The platimun electrode on the vessel wall was in contact with the liquid and vapor phase and the conductivity of the solution was measured between this electrode and the electrode at the bottom vessel. The third electrode at the upper part of the cell was in contact with the vapor phase and it allowed determining the voliune of the sample. 

Ions are produced in air by high temperatures or ultraviolet radiation. The ionized air can be sufficiently conductive to reduce static hazards. The static charge is conveyed by tiie ionized air firom an object to a groimding electrode located nearby. When UV lamps are used, eye protection is required. 

Electrical and Thermal Conductivity these properties are strongly correlated, high thermal conductivity usually indicating high electrical conductivity. Materials with high conductivity should be used in situations that require fast response to temperature swings or rapid dissipation of static electricity. 

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