One-Dimensional NMR Imaging of High-Temperature First-Drying in Monolithics

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.

Direct observation of the moisture distribution in calcium aluminate cement and hydratable alumina‐bonded castables during first‐drying: An NMR study

“…The most plausible explanation for this discrepancy in the experimental and fitted values of the permeability is that the materials were dried at 110°C for 24 hours before the measurements were carried out at room temperature via the Air Permeability Test. As already reported in a previous study, the pore system of RC undergoes structural transformation from 20°C to 110°C. This means that over the course of 24 hours the pore network has changed.…”

“…This initial rise (I) corresponds to the transforming pore structure upon initial heating. During this initial heating stage, of up to 70°C, dehydration will occur, where chemically combined water is released, resulting in an increase in the moisture content.…”

“…[6][7][8] Recently, a high-temperature nuclear magnetic resonance (NMR) setup was developed and characterized demonstrating that the moisture distribution can be directly measured for regular castables (RC). 9,10 As NMR is a resonance technique, it can be specifically made sensitive to hydrogen and therefore to moisture as well. Hence, the moisture profiles can be nondestructively measured with a high spatial resolution on the order of 2-3 mm.…”

Moisture transport in pine wood during one-sided heating studied by NMR

“…The setup, schematically shown in Fig. 3, was specifically designed for performing non-isothermal moisture measurements on building materials, and will be introduced here briefly; a more extensive description can be found elsewhere [27,28].…”

“…concrete and refractories, possess the risk of explosive spalling when heated, requiring additional safety measures. Such a custom-built NMR setup has been developed to assess the non-isothermal moisture transport in concrete [23,24], fired-clay brick [25], gypsum [26], and refractory materials [27]. Here, we will employ the setup to explore the moisture transport in wood during heating.…”