Highest Resolution Electrical Measurements

High-resolution Dielectric Characterization Of Minerals


Dr Tamara Monti received her PhD in Electromagnetics from Universita Politecnica delle Marche, Italy and she is currently working as Research Fellow in the Microwave Processing Group at the University of Nottingham, UK. Her primary research interest is in understanding the mechanisms of interaction between microwave and matter during microwave processing at a fundamental level and relating the macroscale effects with the microscale phenomenological explanation.


In the following International Journal of Mineral Processing paper, co-led by Dr Tamara Monti and Dr Alexander Tselev from ORNL’s Center for Nanophase Materials Sciences, an original approach for measuring the microwave conductivity of mineral phases in rocks, in situ and at microscale is introduced. The importance of this paradigm for understanding the complex interactions occurring in the microwave processing of rocks and minerals is highlighted. A summary of the paper is hereby reported:


High-resolution dielectric characterization of minerals: A step towards understanding the basic interactions between microwaves and rocks

By Tamara Monti et al. International Journal of Mineral Processing, 2016


Microwave energy has been demonstrated to be potentially beneficial for reducing the cost of several steps of mining and processing of raw materials. Understanding the interaction between microwaves and minerals at the fundamental level has found to be essential in order to elucidate the underlying physical processes that control the macroscale behaviour of mineral materials. Those are ascribed to the complexity of the involved physical phenomena associated with chemical and physical transformations, where electrical, thermal and mechanical forces play concurrent roles. The Scanning Microwave Microscopy represents a method, which is novel in the field of mineral processing, for characterization of dielectric properties of mineral samples at microwave frequencies down to sub-micrometre length scale. In particular, as opposed to conventional dielectric techniques, the method makes possible quantitative measurements of the dielectric constant, loss factor and conductivity of micrometre-sized mineral inclusions within a complex structure of natural rocks, with high resolution and accuracy.


In this exemplary work, this new characterization method is presented. The method is based upon the PrimeNano scanning impedance microwave microscope. Micrometric hematite inclusions were characterized at a microwave frequency of 3 GHz. Both dielectric constant and conductivity of the inclusions were obtained. The unique capability of the microwave microscope was combined with scanning electron microscopy/energy-dispersive x-ray spectroscopy and confocal micro Raman spectroscopy to determine the details of the physical structure as well as chemical and elemental composition of mineral samples on similar length scales and to relate them with the submicrometre-scale dielectric properties. sMIM data can be further used in multi-physics studies of the complex interactions between microwaves and rocks in order to accurately model the complex heterogeneity of the rocks in terms of dielectric and other physical properties, and to design and optimize the microwave processing of the mineral materials.

Fig.1: From left to right: SEM/EDX image of a complex mineral inclusion in a natural rock. The black box highlights the hematite inclusion under analysis. An image of the real part of the permittivity ε’ and an image of conductivity σ of the hematite inclusion.


To read the original publication of this paper, please visit International Journal of Mineral Processing or the University of Nottingham.


Dr. Tamara Monti’s Research

The recent research of Dr. Monti focuses on understanding the complex interaction between the electromagnetic field and samples under high-power microwave heating and materials processing. The Scanning Microwave Impedance Microscopy (sMIM) is the only instrument able to predict complex phenomena like the localization of the fields during the processing due to the sample heterogeneity at sub-micrometric scales.


A sample list of Dr. Monti’s recent publications:

  1. T. Monti, A. Tselev, O. Udoudo, I.N. Ivanov, C. Dodds, S.W. Kingman, “High-resolution dielectric characterization of minerals: A step towards understanding the basic interactions between microwaves and rocks”. International Journal of Mineral Processing, Volume 151, 10 June 2016, Pages 8-21, ISSN 0301-7516; http://dx.doi.org/10.1016/j.minpro.2016.04.003.
  2. T. Monti et al., “Near field microwave microscopy for nanoscale characterization, imaging and patterning of graphene”. Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO), 2014 International Conference on, Taipei, 2014, pp. 32-38; http://dx.doi.org/10.1109/3M-NANO.2014.7057298.
  3. T. Monti et al., “Graphene etching by a Near-Field Scanning Microwave Microscope”. Microwave Symposium Digest (IMS), 2013 IEEE MTT-S International, Seattle, WA, 2013, pp. 1-4; http://dx.doi.org/10.1109/MWSYM.2013.6697641.
  4. T. Monti, et al., “Near-Field Microwave Investigation of Electrical Properties of Graphene-ITO Electrodes for LED Applications“. J. Display Technol. 9, 504-510 (2013).
  5. M. Farina, et al. “Tomographic effects of near-field microwave microscopy in the investigation of muscle cells interacting with multi-walled carbon nanotubes”. Applied Physics Letters, 101, 203101 (2012); http://dx.doi.org/10.1063/1.4767518.


Contact the author: Dr. Tamara Monti.




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