Gary Bond

Development of a new instrument for performing microwave thermal analysis

This article describes the design and operation of a new thermal analysis instrument which uses microwaves to simultaneously heat and detect thermally induced transformations in samples with masses in the range of 50 mg to 0.5 g. The data acquisition and control software developed for the instrument support a range of experimental techniques including constant power, linearly ramped power, linearly ramped temperature, and various modulated methods. Microwave thermal analysis utilizes the fact that physical or chemical alterations in a material, caused by processes such as melting, decomposition, or solid-solid phase changes, cause variations in its dielectric properties. These can be revealed by a variety of means including changes in the sample temperature, the differential temperature, or the shape of the power profile during linear heating experiments. The scope of the instrument is demonstrated with the decomposition of basic copper carbonate. The large temperature increase (∼100 °C) observed on the f...

Qualitative and quantitative aspects of microwave thermal analysis

Thermally induced transformations in materials (e.g. melting, decomposition or solid‐solid phase changes) alter their dielectric properties and hence their ability to interact with a microwave field. This paper describes a new technique, microwave thermal analysis, where microwaves are used both to heat a material and as a means of detecting thermal transitions. Two approaches are described. The first is based on the changes in the temperature of a material when subjected to a constant microwave power and the second on the microwave power profile obtained when a material is heated in a controlled (linear) manner. Both approaches can provide qualitative and quantitative information on solid state processes. A classification is proposed for the different types of results found for various materials and transitions. The advantages and limitations of studying transitions and reactions using microwave energy are discussed. # 2000 Elsevier Science B.V. All rights reserved.

Microwave Thermal Analysis - A New Approach to the Study of the Thermal and Dielectric Properties of Materials

This paper describes a new instrument for performing thermal analysis using microwaves both as a form of heating and as a novel means of detecting thermally induced transformations in materials. Results are presented for a selection of processes including decompositions, dehydrations and phase changes. The capability of the instrument to be coupled with ancillary techniques such as EGA is also demonstrated.

Development of a novel instrument for microwave dielectric thermal analysis

The advantages of microwave heating in industrial processing are becoming more widely appreciated and the technique is of increasing commercial significance. However, knowledge of a material’s dielectric properties as a function of temperature is of considerable importance as they determine the efficiency with which the material converts microwave energy into heat. This article describes the development of a novel instrument for a new form of thermal analysis, microwave dielectric thermal analysis (MDTA) in which the sample is heated not conventionally but by microwaves, while its dielectric properties at microwave frequencies are determined quasisimultaneously using a network analyzer. A plot of the dielectric properties against temperature then gives the MDTA curve. The fundamental principle underlying the use of MDTA is that not only do a material’s dielectric properties (both the real and imaginary parts of the complex permittivity) alter (generally smoothly) as a function of temperature but dramatic ...

Dielectric Characterisation of Lipid Droplet Suspensions Using the Small Perturbation Technique

This work proposes a novel approach to differentiate biological cells based upon the total concentration of lipids. Lipid accumulation within cells is significant as it serves as a marker pertaining to the metabolism and oncologic state of the cell and organism. This is accomplished through dielectric characterisation of the sample. This chapter presents a preliminary proof of concept experiment using vegetable oils and cell culture media to model lipid droplets in biological cells. The experiment indicated that solutions of numerous different lipid suspensions at different concentrations can be differentiated based upon the dielectric characteristics of the sample. The dielectric constant of vegetable oils was calculated to be between 2.9 and 3.1. The dielectric constant of the suspensions reached up to 27 at a concentration of 0.5% (v/v).

A system to investigate the remediation of organic vapors using microwave-induced plasma with fluidized carbon granules

This article describes a system to investigate the parameters for the remediation of organic vapors using microwave-induced plasma on fluidized carbon granules. The system is based on a single mode microwave apparatus with a variable power (2.45 GHz) generator. Carbon granules are fluidized in a silica tube situated in the sample section of a waveguide incorporating two additional ports to allow plasma intensity monitoring using a light sensor and imaging with a digital camera. A fluoroptic probe is used for in situ measurement of the carbon granule temperature, while the effluent gas temperature is measured with a thermocouple situated in the silica tube outside the cavity. Data acquisition and control software allow experiments using a variety of microwave power regimes while simultaneously recording the light intensity of any plasma generated within the carbon bed, together with its temperature. Evaluation using two different granular activated carbons and ethyl acetate, introduced as a vapor into the fluidizing air stream at a concentration of 1 ppm, yielded results which indicated that significant destruction of ethyl acetate, as monitored using a mass spectrometer, was achieved only with the carbon granules showing high plasma activity under pulsed microwave conditions. The system is therefore suitable for comparison of the relative microwave activities of various activated carbon granules and their performance in microwave remediation and regeneration.

Monitoring and control system for tuneable high frequency microwave assisted chemistry

Microwave chemistry is an established technique in the synthesis of organic compounds at a frequency of 2.45 GHz. This is considered to be a result of the development of microwave ovens, rather than an objective solution, which maximises efficiency through careful selection of the operating frequency. To obtain a frequency for a dielectric, the complex permittivity should be determined as a function of frequency. If the correct heating frequency is found, superheating can occur when a liquid solvent reaches its boiling point and exceeds it. This paper presents sensor diodes and temperature sensors used in a mono-mode reactor, with computer control of an E-H tuner, frequency and incident power to control temperature and power, experimental results showing heating and reactions using ethanol are reported.

Low-Temperature Continuous Flow Synthesis of Metal Ammonium Phosphates

The synthesis of the high performance inorganic materials essential to the quality of modern day life is hindered by traditionalist attitudes and reliance on outdated methods such as batch syntheses. While continuous flow methods have been extensively adopted in pharmaceutical circles, they remain largely unexplored for the preparation of inorganic compounds, despite higher efficiency, safety and versatility. In this publication, we demonstrate a step-change for the synthesis of metal ammonium phosphates through conversion of the extant batch process to a low-temperature continuous regime, exhibiting a tenfold increase in throughput combined with a significant decrease in particle size.

The Impact of Alkaliphilic Biofilm Formation on the Release and Retention of Carbon Isotopes from Nuclear Reactor Graphite

Abstract14C is an important consideration within safety assessments for proposed geological disposal facilities for radioactive wastes, since it is capable of re-entering the biosphere through the generation of 14C bearing gases. The irradiation of graphite moderators in the UK gas-cooled nuclear power stations has led to the generation of a significant volume of 14C-containing intermediate level wastes. Some of this 14C is present as a carbonaceous deposit on channel wall surfaces. Within this study, the potential of biofilm growth upon irradiated and 13C doped graphite at alkaline pH was investigated. Complex biofilms were established on both active and simulant samples. High throughput sequencing showed the biofilms to be dominated by Alcaligenes sp at pH 9.5 and Dietzia sp at pH 11.0. Surface characterisation revealed that the biofilms were limited to growth upon the graphite surface with no penetration of the deeper porosity. Biofilm formation resulted in the generation of a low porosity surface layer without the removal or modification of the surface deposits or the release of the associated 14C/13C. Our results indicated that biofilm formation upon irradiated graphite is likely to occur at the pH values studied, without any additional release of the associated 14C.

Lipid droplet detection by the cavity perturbation method

There are currently no point-of-care diagnosis strategies available to indicate the presence of neoplasmic growth. This research aims to develop a novel diagnostic strategy based on detecting TAG accumulation in cells. This element of the research is a preliminary experiment to prove the concept of detecting TAG lipid droplets in YEPD media. It was found that a change in mono-unsaturated concentration can be detected by the frequency shift in a resonant cavity. The dielectric constant of TAG vegetable oils was calculated at 2.34-2.39. It was also found that concentrations of lipid droplet can be differentiated up to 5% (v/v).