Development of a microwave calorimeter for simultaneous thermal analysis,

An instrument has been developed for monitoring cure processes under microwave heating conditions. The main function of the instrument was a calorimeter for performing microwave thermal analysis. A single model resonant cavity was used as the heating cell in the microwave calorimeter. Thermal analysis measurements were obtained by monitoring the variation in the microwave power that was required to maintain controlled heating of the sample. The microwave thermal analysis data were analogous to conventional differential scanning calorimetry measurements. The dielectric properties of the sample, as a function of the extent of cure, have been obtained using perturbation theory from the changes in resonant frequency and quality factor of the microwave cavity during heating. Additionally, remote sensing fibre-optic probes have been employed to measure real time in situ infrared spectra of the sample during the cure reaction. In this paper, we describe the design and operation of the microwave calorimeter. Examples of experimental results are also presented

In situ analysis of cadmium sulphide chemical bath deposition by an optical fibre monitor

The CdS window layer in thin film solar cells is frequently grown by chemical bath deposition (CBD). Deposited films are typically less than 100 nm thick and the inability to identify the exact start of the deposition can make CBD an imprecise process. This paper describes the construction and testing of a simple optical fibre sensor that detects the start of the deposition process and also allows for its mechanism to be studied. The in situ optical fibre monitoring technique utilises the change in optical reflectance off the glass/deposited film/precursor solution interfaces at an operating wavelength of 1550 nm. A theoretical expression for the reflection of light from the interface is discussed and compared with experimental results. The monitoring technique shows the presence of two different deposition mechanisms. This result is confirmed by film densities calculated by Rutherford backscattering spectrometry and an optical model for ellipsometry measurements which indicates that the deposited CdS films consist of a double layer structure with a porous layer on top of a dense under layer. The application of the theoretical expression is optimised by assuming the refractive index of the CdS layer to be 2.02. The ellipsometry model shows that the refractive index of the CdS deposited is 2.14 for a two layer model of the film that included a porous upper layer through the effective medium approximation

Comparison of the Curing Kinetics of the RTM6 Epoxy Resin System Using Differential Scanning Calorimetry and a Microwave-Heated Calorimeter

The cure of a commercial epoxy resin system, RTM6, was investigated using a conventional differential scanning calorimeter and a microwave-heated calorimeter. Two curing methods, dynamic and isothermal, were carried out and the degree of cure and the reaction rates were compared. Several kinetics models ranging from a simple nth order model to more complicated models comprising nth order and autocatalytic kinetics models were used to describe the curing processes. The results showed that the resin cured isothermally showed similar cure times and final degree of cure using both conventional and microwave heating methods, suggesting similar curing mechanisms using both heating methods. The dynamic curing data were, however, different using two heating methods, possibly suggesting different curing mechanisms. Near-infrared spectroscopy showed that in the dynamic curing of RTM6 using microwave heating, the epoxy-amine reaction proceeded more rapidly than did the epoxy-hydroxyl reaction. This was not the case during conventional curing of this resin

Comparison of the curing kinetics of the RTM6 epoxy resin system using differential scanning calorimetry and a microwave-heated calorimeter

The cure of a commercial epoxy resin system, RTM6, was investigated using a conventional differential scanning calorimeter and a microwave-heated calorimeter. Two curing methods, dynamic and isothermal, were carried out and the degree of cure and the reaction rates were compared. Several kinetics models ranging from a simple nth order model to more complicated models comprising nth order and autocatalytic kinetics models were used to describe the curing processes. The results showed that the resin cured isothermally showed similar cure times and final degree of cure using both conventional and microwave heating methods, suggesting similar curing mechanisms using both heating methods. The dynamic curing data were, however, different using two heating methods, possibly suggesting different curing mechanisms. Near-infrared spectroscopy showed that in the dynamic curing of RTM6 using microwave heating, the epoxy-amine reaction proceeded more rapidly than did the epoxy-hydroxyl reaction. This was not the case during conventional curing of this resin