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United States Department of Agriculture

Agricultural Research Service

Title: Determining Dielectric Properties of Coal and Limestone by Measurements on Pulverized Samples

Author
item Nelson, Stuart

Submitted to: Journal of Microwave Power and Electromagnetic Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 21, 1996
Publication Date: N/A

Interpretive Summary: In coal mining operations, combustible mixtures of coal dust and air constitute explosive hazards. For this reason, the Code of Federal Regulations requires that the incombustible content of combined coal dust, rock dust, and other dust shall not be less than 65 percent in coal mines. Thus, there is need for rapid test methods to determine the rock dust component. Electrical properties, called dielectric properties, of coal an rock dust may possibly provide a means for these measurements. Because of our unique laboratory equipment and experience, we were asked by scientist of the U. S. Bureau of Mines (now Department of Energy) for assistance in determining the microwave properties of coal and limestone samples. Measurements of the dielectric properties of pulverized Pittsburgh coal and limestone samples were made at a frequency of 11.7 GHz with different sample compactions producing a range of bulk densities. Analysis of the data showed excellent linearity of the cube root of the dielectric constan of the pulverized samples with their bulk density. This straight-line relationship permitted the use of a dielectric mixture equation to accurately calculate the dielectric properties of the solid coal and solid limestone from these laboratory data. Significant differences were found in the properties of coal and limestone. Further studies are indicated. The data are being made available for the benefit of scientist working with new techniques involving coal and minerals.

Technical Abstract: Estimates for the permittivities of solid coal and limestone at 11.7 GHz and 20 C are obtained from measurements of the permittivities and bulk densities of pulverized samples and the particle material density. Linear regressions of the cube root of the dielectric constant on sample bulk density provide estimates of the dielectric constants of the solid materials. Since linearity with bulk density of the cube root of the dielectric constant is consistent with the Landau & Lifshitz, Looyenga dielectric mixture equation, that equation provides estimates for both the dielectric constant and loss factor when the relative complex permittivities are used for the calculation.

Last Modified: 10/22/2014
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