Microwave properties of carbon powders

• Main Author: Shkal, Fatma
• Published: Cardiff University 2018
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761312

Microwave techniques have been used in many applications due to the simplicity of the associated construction and use. They provide several advantages in contrast with traditional methods, including fast (almost instantaneous) measurements and their non-destructive nature, at least at low microwave power levels. Moreover, microwave methods provide an accurate and sensitive measurements of dielectric properties of carbon powders (in sp2 form) due to their strong interactions with microwave electric fields. The contributions to the state-of-the-art provided by the work presented in this thesis are novel applications of the microwave cavity and coaxial probe methods to differentiate between the types of carbon materials of industrial relevance by characterization of their dielectric properties. Measurements are typically carried out between 10 MHz to 10 GHz for the coaxial probe method, and between 2.5 GHz to 10 GHz for the cavity method, also as a function of temperature up to 150 0C. The results of this thesis show that microwave methods are sufficient to differentiate carbons materials by measuring the complex permittivity under different conditions. The industrial relevance arises from being able to identify different types of carbons in two groups: one for blast furnace dust, which is crucial to quantify the utilization of coal injected in the furnace and determine the efficiency of coal injection; the other for activated carbons, which are highly porous structures used for applications such as carbon dioxide capture in fossil fuel combustion Dielectric properties of different carbons (quantified by their complex permittivities) shown in this thesis are measured in-situ as frequency-dependent and temperature-dependent quantities and are different for different types of carbonaceous materials in the two groups of powders. Hence, the impact of this work is the realisation of simple and easy to use test methods that are robust enough to be applied in an industrial setting.