The Effects of Trace Metal Cations on the High Temperature Reactions of an Halloysite Mineral

<p>This thesis describes a kinetic study of the high temperature solid state reactions of a well characterized halloysite mineral and five of its cation-saturated forms, the cations used being sodium, calcium, manganese, copper and iron (Ill). The reaction sequence may be represented by the idealised equations: The formation of mullite from metakaolinite has been studied in the temperature range 1020° - 1200°C, by X-ray analysis. Comparison of the experimental data with several theoretical models suggests that up to 90% conversion the reaction takes place by exponential nucleation followed by crystal growth. There is, however, some evidence for diffusion occurring as a rate controlling process, especially at high degrees of conversion to mullite. The rate constants and experimental thermodynamic functions have been evaluated for all halloysite samples. The free energies of activation (111-128 k cal.mole-1) and the rate constants are independent of the starting materials, but the enthalpies of activation (51-118 k cal.mole-1) and the entropies of activation (0 to -50 cal.deg.-1 mole-1) are not.</p>

The Effects of Trace Metal Cations on the High Temperature Reactions of an Halloysite Mineral

<p>This thesis describes a kinetic study of the high temperature solid state reactions of a well characterized halloysite mineral and five of its cation-saturated forms, the cations used being sodium, calcium, manganese, copper and iron (Ill). The reaction sequence may be represented by the idealised equations: The formation of mullite from metakaolinite has been studied in the temperature range 1020° - 1200°C, by X-ray analysis. Comparison of the experimental data with several theoretical models suggests that up to 90% conversion the reaction takes place by exponential nucleation followed by crystal growth. There is, however, some evidence for diffusion occurring as a rate controlling process, especially at high degrees of conversion to mullite. The rate constants and experimental thermodynamic functions have been evaluated for all halloysite samples. The free energies of activation (111-128 k cal.mole-1) and the rate constants are independent of the starting materials, but the enthalpies of activation (51-118 k cal.mole-1) and the entropies of activation (0 to -50 cal.deg.-1 mole-1) are not.</p>

Archaeological applications of natural gold analyses

Compositional studies of natural gold usually have a geological focus, but are also important in archaeological provenancing. Both methodologies rely on compositional comparison of two sets of samples, one of which is geographically constrained. Here we describe how experiences in gold characterization resulting from geological studies are relevant to archaeology. Microchemical characterization of polished sections of natural gold identifies alloy compositions, alloy heterogeneity and mineral inclusions. Gold from all deposit types shows Cu and Sn values much lower than those recorded during numerous studies of artefacts. Inclusions in artefact gold include various Cu- and Sn-bearing compounds which indicate specific high temperature reactions that could ultimately illuminate the conditions of (s)melting. The use of LA-ICP-MS to generate a wide range of elemental discriminants for provenance studies may be compromised by alloy adulteration and/or unrepresentative analysis of natural/artefact alloys, which are commonly highly heterogeneous at the micron scale. Geological studies normally characterize only the earliest-formed (hypogene) alloy, whereas archaeology-focussed studies should entail analyses of bulk alloy compositions and impurities that may be incorporated during (s)melting. Isotopic-based provenancing alleviates many of these problems but, to date, generates regional rather than locality specific targets. A dual isotopic-compositional approach is recommended.

A Tracer Study on sCO2 Corrosion with Multiple Oxygen-Bearing Impurities

Several modern power production systems utilize supercritical CO2 (sCO2), which can contain O2 and H2O as impurities. These impurities may degrade the compatibility of structural alloys through accelerated oxidation. However, it remains unclear which of these impurities plays a bigger role in high-temperature reactions taking place in sCO2. In this study, various model and commercial Fe‐ and Ni‐based alloys were exposed in 300 bar sCO2 at 750 °C to low levels (50 ppm) of O2 and H2O for 1,000 h. 18O-enriched water was used to enable the identification of the oxygen source in the post-exposure characterization of the samples. However, oxygen from the water did not accumulate in the scale, which consisted of Cr2O3 in the cases where a protective oxide formed. A 2wt.% Ti addition to a Ni-22%Cr model alloy resulted in the formation of thicker oxides in sCO2, while a 1wt.% Al addition reduced the scale thickness. A synergistic effect of both Al and Ti additions resulted in an even thicker oxide than what was formed solely by Ti, similar to observations for Ni-based alloy 282.

Mineralogical Analysis of Bentonite from the ABM5 Heater Experiment at Äspö Hard Rock Laboratory, Sweden

The present study reports on the analysis of all blocks of the ABM5 test, which is a medium scale bentonite buffer deposition test. In contrast to similar tests, the ABM5 was conducted at higher temperature (up to 250 °C). The aim of the study was to characterize the chemical and mineralogical reactions and to identify the effect of the extraordinarily high temperature. Reactions observed were similar to those observed in previous and/or similar tests covering cation exchange, anion inflow, dissolution and precipitation of C- and S-phases, Fe corrosion, and Mg increase at the heater. Neither the type nor the extent of the different reactions could be related to the significantly higher temperature. However, due to the absence of lubricant used between heater and bentonite, it could be proved that the calcite previously present was dissolved and precipitated as siderite at the contact, pointing towards the importance of the presence of carbonate when considering different Fe corrosion products. Moreover, for the first time, a decrease of the Mg content at the heater was observed, which was probably because a Mg-rich clay was used. The reasons for Mg increase or decrease are still not completely understood.

Surface Properties and Morphology of Boron Carbide Nanopowders Obtained by Lyophilization of Saccharide Precursors

The powders of boron carbide are usually synthesized by the carbothermal reduction of boron oxide. As an alternative to high-temperature reactions, the development of the carbothermal reduction of organic precursors to produce B4C is receiving considerable interest. The aim of this work was to compare two methods of preparing different saccharide precursors mixed with boric acid with a molar ratio of boron to carbon of 1:9 for the synthesis of B4C. In the first method, aqueous solutions of saccharides and boric acid were dried overnight at 90 °C and pyrolyzed at 850 °C for 1 h under argon flow. In the second method, aqueous solutions of different saccharides and boric acid were freeze-dried and prepared in the same way as in the first method. Precursors from both methods were heat-treated at temperatures of 1300 to 1700 °C. The amount of boron carbide in the powders depends on the saccharides, the temperature of synthesis, and the method of precursor preparation.

On improving the controllability of low-temperature combustion by building two-stage sequential high-temperature reactions in an ethanol/diesel dual-fuel engine using multiple injections

Low-temperature combustion (LTC) has advantages in reducing emissions and improving efficiency, at the expense of hard controllability. To improve its controllability, this paper proposes a two-stage stratified compression ignition (TSCI) strategy, which aims to decouple ignition and the following combustion as two-stage sequential high-temperature reactions, and couple them to external events like multiple injections, supercharge, etc. A trace amount of high reactivity fuel (HRF) is injected near the top dead center (TDC) and auto-ignited, initiating the combustion process, which controls ignition. The highly premixed charge (HPC), whose equivalent ratio, temperature, reactivity can be tuned as needed, control the combustion course after ignition. Based on the TSCI concept, one demonstrative multiple-injection strategy is suggested and tested on a single-cylinder ethanol/diesel dual-fuel engine. It is concluded from the experimental results that the TSCI combustion process presents two-stage sequential high-temperature reactions, which is different from any other LTC strategies. This sequential combustion shows good controllability. Within a certain range, the ignition phase is directly and linearly related to the ignition-oriented injection (IOI) event. With the advance of IOI timing, the ignition is advanced consequently. Increasing IOI quantity has the same tendency. As for HPC, when HPC reactivity is increased, the maximum pressure raising rate (MPRR) is increased and the whole combustion process is more concentrated.

Overview

It is an indisputable observation, beyond climate change: that the urgent development of simple new technologies, to ensure the supply of quality fresh water for cities and towns, industry and agriculture, presents an existential challenge for humanity. Several novel technologies that fill that need show that the job is not impossible. They are summarized in this volume. They are environmentally friendly and inexpensive. They include techniques for seawater desalination, wastewater sterilization –including viruses-, selective removal of heavy metals from industrial wastewater, efficient concentration of wastewater slimes to recycle water, and the prevention of water cavitation for much cheaper transport. Other new techniques like high temperature reactions achieved in low temperature water, and low energy desalination are in the wings. Borrowing from biology , new and edible class of surfactants is environmentally friendly, and can replace standard surfactants in present useage. The new technologies are cheap and scalable.