Abstract
In this study a specialized high-temperature nuclear magnetic resonance (NMR) setup is presented for measuring free moisture in monolithic refractory castables during one-sided heating (100–300 °C). This setup makes use of a high thermal-stability Birdcage-coil for measuring the quantitative moisture content at high-temperatures, while also utilizing a mini-coil for calibrating transverse relaxation changes, as a function of temperature and hydration state, taking place in the sample throughout a drying experiment. We employ a high-temperature correction scheme that calibrates the effects of rising temperatures on the NMR signal. With this configuration, we can non-destructively measure moisture and temperature profiles continuously and achieve a spatial resolution of 2–3 mm for samples as long as 74 mm. After applying the NMR correction, we can extract information about the physical and chemical components of water as they are released from the porous matrix during first heat up. As a model material, we demonstrate the capability of our setup with a conventional castable after it has been cast and cured for 48 h.
Highlights
In steel and iron processing plants, the hot ladles where these metals are transported must be lined with refractories
The goal of this paper is to demonstrate that the quantitative moisture content can be directly measured by Nuclear Magnetic Resonance (NMR) and is related to the drying behaviour for high-temperatures without compromising the sample
In this study we have demonstrated and presented the functionality of a high-temperature nuclear magnetic resonance (NMR) setup capable of performing non-destructive measurements on conventional castables during first-heat up
Summary
In steel and iron processing plants, the hot ladles where these metals are transported must be lined with refractories These materials are capable of withstanding physical, thermal and chemical stresses and strains over a wide range of temperatures [1, 2]. The conservative heating rates are necessary due to generated steam pressures within the pores that soar rapidly beyond the mechanical strength of the material (2–6 MPa), sometimes causing physical destruction via explosive spalling While these drying temperatures are quite high for laboratory measurements, it is known that the heightened risk of spalling is found in both the dangerous so-called ebullition stage (100–300 °C) and hydrate decomposition stage (250–300 °C). Increasing the heating rate, altering the drying behaviour through control of material inputs and minimizing service failure is of great economic concern for industrial producers
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