The mechanisms and kinetics of the reduction of powdered Fe2O3 and Fe3O4 samples have been investigated under nonisothermal conditions to provide a detailed insight into the processes occurring. Both conventional linear heating temperature-programmed reduction (TPR) and constant rate temperature-programmed reduction (CR-TPR) techniques were utilized. Fe2O3 was found to reduce to Fe in a two-step process via Fe3O4. The mechanism of the prereduction step of Fe2O3 to Fe3O4 was found to follow an nth order expression where nucleation or diffusion was not the rate-controlling factor while the main reduction step to metal was described by a model involving the random formation and growth of nuclei. A CR-TPR rate perturbation method, “rate-jump”, was applied to the measurement of variations in apparent activation energy throughout the reduction processes, under near-equilibrium conditions and the activation energy measurements are compared with those obtained under conventional linear heating conditions.

A new system has been developed for the study of both bulk and surface metal oxides by temperature programmed reduction (TPR) under both conventional linear heating and constant rate thermal analysis (CRTA) conditions. It is shown that constant rate temperature-programmed reduction (CR-TPR) is capable of producing higher resolution of overlapping events, provides more insight into reduction mechanisms, and allows easier quantification of reduction processes than conventional TPR. The CR-TPR curves for both bulk and supported copper oxides confirmed that reduction followed a nucleation or autocatalytic mechanism. Bulk nickel oxide was found to reduce via a similar mechanism. Advantages of the CR-TPR “rate-jump” technique to determine reaction energetics are illustrated by investigation of the apparent activation energy (E a) of CuO reduction, and the results are compared with those obtained under linear heating conditions. Both approaches yield reasonable values of E a under the appropriate experimental conditions employed. However, the CR-TPR “rate-jump” technique allows variations in E a to be measured as a function of the extent of reduction, revealing changes in the reaction mechanism or kinetics. Our results suggest it is possible to estimate the apparent activation energy of both the nucleation and growth stages involved in reduction. The validity of the “rate-jump” technique employed is confirmed using the thermal decomposition of CaCO3, a widely investigated process. The TPR system uses a hygrometer cell to monitor the production of H2O as the sample is reduced. The sample temperature is controlled by a computer in such a way that the production of H2O, i.e., the rate of reduction, can be maintained at a constant preselected value for CR-TPR experiments. Important instrumental features include a fast response furnace, direct temperature measurement, a sensitive specific detector, and control and data analysis software developed specifically for this work.

Thermally induced reactions are of great importance in the manufacture and characterization of a very wide range of increasingly complex materials covering areas as diverse as ceramics and heterogeneous catalysts. Subsequently, there is a need for improved thermoanalytical methods that can provide enhanced resolution and a greater understanding of the energetics and mechanisms involved. This paper describes a new solid insertion probe mass spectrometer (SIP-MS) system that is designed to meet these needs by operating high vacuum with small sample masses. The SIP-MS system supports both conventional linear heating and a range of sample-controlled thermal analysis (SCTA) techniques including constant rate thermal analysis (CRTA). Its ability, in conjunction with the latter technique, to obtain reliable apparent activation energy measurements throughout a process under near-ideal experimental conditions is demonstrated. In addition, the system can discriminate between different reaction mechanisms and provide information on the often complex solid-state reactions found in calcination processes.

Cadaver dogs are routinely used internationally by police and civilian search organisations to locate human remains on land and in water, yet little is currently known about the volatile organic compounds (VOCs) that are released by a cadaver underwater; how this compares to those given off by a cadaver deposited on land; and ultimately, how this affects the detection of drowned victims by dogs. The aim of this study was to identify the VOCs released by whole porcine (Sus scrofa domesticus) cadavers deposited on the surface and submerged in water using solid phase microextraction gas chromatography mass spectrometry (SPME GC-MS) to ascertain if there are notable differences in decomposition odour depending on the deposition location. For the first time in the UK, the volatile organic compounds (VOCs) from the headspace of decomposing porcine cadavers deposited in both terrestrial and water environments have been detected and identified using SPME-GCMS, including thirteen new VOCs not previously detected from porcine cadavers. Distinct differences were found between the VOCs emitted by porcine cadavers in terrestrial and water environments. In total, seventy-four VOCs were identified from a variety of different chemical classes; carboxylic acids, alcohols, aromatics, aldehydes, ketones, hydrocarbons, esters, ethers, nitrogen compounds and sulphur compounds. Only forty-one VOCs were detected in the headspace of the submerged pigs with seventy detected in the headspace of the surface-deposited pigs. These deposition-dependent differences have important implications for the training of cadaver dogs in the UK. If dog training does not account for these depositional differences, there is potential for human remains to be missed. Whilst the specific odours that elicit a trained response from cadaver dogs remain unknown, this research means that recommendations can be made for the training of cadaver dogs to incorporate different depositions, to account for odour differences and mitigate the possibility of missed human remains operationally. 1.1. VOCs from the decomposition of carbohydrates Carbohydrates are broken down into their constituent sugars and

Acid treatment of Ca2+ montmorillonite has been shown to increase significantly its effectiveness as a support for ZnC12 Friedel-Crafts alkylation catalysts; optimum treatment conditions have been established and evidence is reported for a synergistic interaction between absorbed salt and acid-activated clay.

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A new, high-resolution system for analyzing and characterizing materials is described. Based on evolved gas analysis (EGA), it can perform both controlled transformation rate thermal analysis and stepwise isothermal analysis as well as conventional (linear temperature program) EGA. Features include a fastresponse furnace, direct temperature measurement, sensitive specific detector, and sophisticated temperature control. The system permits, for the first time, a comparison of the three modes of operation under an identical sample environment. The advantages and limitations of each are illustrated using a sample chosen to model a type of reaction often found in the preparation of catalysts by calcination, the thermal decomposition of hydroxides. It is shown that these methods used with our system have potential advantages in analysis and in the study of complex thermal decomposition processes, by increasing the resolution of consecutive events and providing a more closely controlled sample environment.In conventional thermal analysis the sample is made to follow a predetermined, usually linear, temperature program while one or more of its properties, e.g., mass loss, energy change, or gas evolution, is measured. To improve resolution and provide better conditions for kinetic studies, a number of workers have developed techniques in which variable heating rates are used.1-1 1 2 These differ from normal thermoanalytical procedures in that the heating rate is not predefined but is altered as a consequence of some change in a monitored parameter of the sample, e.g., in TG it would be the reaction rate as determined from the rate of change of sample mass.