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Silicon Carbide Oscillators for Extreme Environments
Published in Sumeet Walia, Krzysztof Iniewski, Low Power Semiconductor Devices and Processes for Emerging Applications in Communications, Computing, and Sensing, 2018
Daniel R. Brennan, Hua-Khee Chan, Nicholas G. Wright, Alton B. Horsfall
Crystals for electronic circuits are typically manufactured from quartz. Quartz mechanical resonators typically have a very high Q-factor, resulting in high selectivity to the desired frequency in the feedback loop. In addition, the oscillator frequency shows a weak temperature dependence in comparison to tuned circuits. These two characteristics mean that crystal oscillators have significantly better frequency stability than either LC or RC oscillators. However, quartz is not suitable for the development of high-temperature oscillators because it undergoes a phase transition at 573°C, referred to as the quartz inversion [19]. Above this temperature, the crystals do not operate as electronic filters and the oscillator produces a wide range of frequencies simultaneously. At the current time, no other material has been identified that can demonstrate the mechanical properties of a quartz resonator and operate at temperatures beyond this temperature. While crystal oscillators provide greater frequency stability with variations in temperature, the availability and complexities associated with incorporating a high-temperature crystal component were viewed as a disadvantage in comparison with the simplicity of prototype high-temperature LC oscillator–based circuits. Hence, crystal oscillators have not been experimentally investigated further.
Ore Pretreatment Methods for Grinding: Journey and Prospects
Published in Mineral Processing and Extractive Metallurgy Review, 2019
Veerendra Singh, Prashant Dixit, R Venugopal, K Bhanu Venkatesh
The research studies carried out in this area were mostly focused on the optimization of process parameters, quantification of impact on energy efficiency of grinding, improvement in liberation, quenching techniques, and efficient heating methods. In 1918, Yates found that heating Cornish tin ores up to 800°C followed by water quenching can reduce the energy requirement during grinding. Holman showed that Brazilian quartz became brittle if heated above 575°C and quenched. Both studies were related to the utilization of quartz inversion phenomena to develop the cracks at mineral interfaces for a costly mineral. Jones and Fullard (1966) found that almost ideal liberation was possible when high carbonate rocks were heated, cooled to room temperature, and then immersed in water. This was attributed to the evolution of carbon dioxide along the grain boundaries at high temperatures, creating internal pressure and exerting stresses at appropriate sites. This study provided a basis for further research on the grindability of minerals during heating.