Use of an open-ended coaxial cavity method to characterize powdery substances exposed to humidity

Abstract

The effect of moisture adsorption in the characterization of dielectric powders by an indirectly coupled open-ended coaxial cavity method operating at 4.5 GHz was analyzed. SiO2, Al2O3, and ZrO2 powders were exposed to 5% and 100% relative humidity levels and Bruggeman symmetric, Looyenga, and General Mixing Model equations were used to determine changes in permittivity and loss tangent of the inclusions. Low moisture adsorption (0.1–2.5 vol. %) induced only a small change in inclusion permittivity but had a pronounced impact on dielectric losses. Calculated moisture percentages based on responses of the resonator and the General Mixing Model correlated well with traditional mass based determination. The presented characterization method exhibited high sensitivity for the determination of dielectric properties of powders and their moisture content to be further utilized in, e.g., process and quality monitoring.

Low-loss dielectric ceramic materials and their properties

“…Tuhkala et al 52,53 estimated the microwave dielectric properties of several materials with reasonable accuracy by this technique. The method is shown to be useful for studying the properties of powders in several ways.…”

“…The method is shown to be useful for studying the properties of powders in several ways. They also reported estimation of humidity level of the powders, 53 effect of surfactant treatment, 54 evaluation of the amount of two powder phases 52 using the above method. 48…”

The effect of BaTiO 3 particle shape on complex permittivity of 0.98MgTiO 3 –0.02BaTiO 3 composite powders at GHz frequencies

“…2). These equations had previously been found to have good correlation in the characterization of dielectric properties of particles reported by Tuhkala et al, Conger et al and Nelson et al [12,13,[15][16][17][18].…”

“…4) the power α determines the mixing model, i.e., -1 = serial, 0 = logarithmic and 1 = parallel and the subscript i refers to the volume fraction and dielectric loss tangent of the i th material. The parallel mode was shown to have good correlation in the determination of dielectric loss and molar ratios of composite powders reported by Tuhkala et al, Huang et al and Fukuda et al [13,15,22,23].…”