Microstructure evolution of hydration products and strength change of hydratable alumina‐bonded castables below 1250°C

Abstract

There have been reports that strength of hydratable alumina (HA)-bonded castables without silica fume drops significantly at 600°C and decreases substantially again at 1000°C. But the strength variation of the HA-bonded castables during the intermediate temperature range has not been investigated and elaborated from the perspective of phase evolution and microstructural change in the castables. In this work, the relationship between the change in the strength of castables and the microstructural characteristics of the HA-bonded castables was investigated. The phase and microstructure evolution of HA-bonded castables between 110°C and 1250°C were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TG). It has been found that strength drops of the HAbonded castables during heating process do not mainly happen at the temperature at which HA hydrates decompose, but at the temperature at which the structure of dehydrated HA hydrates disintegrates.

Controlling hydration of hydratable alumina via co‐grinding with Mg–Al hydrotalcite

“…The as‐prepared MAT‐bearing HA was used as a hydraulic binder. Notably, 2–6 wt% HA was introduced into castables in previous studies to examine the properties of HA‐bonded castables, such as corrosion resistance and thermomechanical properties 4,29,3,34,35 . This study mainly investigates the hydration behavior of HA by co‐grinding it with a Mg–Al hydrotalcite.…”

“…27 These newly in situ formed MA spinel particles contribute to the ceramic bonding of castables, 28 thereby moderating the deterioration of castable strength at medium temperatures. 29 In addition, the formation of the in situ MA spinel accompanied by 8 vol.% of expansion can offset the shrinkage of HA-bond castables. 30 Hence, HA particles were ground using various amounts of MAT sheets.…”

“…Notably, 2-6 wt% HA was introduced into castables in previous studies to examine the properties of HA-bonded castables, such as corrosion resistance and thermomechanical properties. 4,29,3,34,35 This study mainly investigates the hydration behavior of HA by co-grinding it with a Mg-Al hydrotalcite. To investigate the effect of MAT-doped HA on the properties of castables, 5 wt% HA was selected and introduced into castables in this study.…”

“…The theoretical weight loss of T4 was 22.92 wt%, which is approximately the experimental weight loss of T4 (22.30 wt%). Three peaks in the DTG curve of the starting HA appeared at approximately 67 , 244 , and 470 • C, which were likely related to the desorption of loosely bound or physisorbed water, 38 the decomposition of boehmite and bayerite, 5,17,20,29,39 and the decomposition of some residual boehmite, 5,29 respectively. In the DTG curve of MAT, three peaks appeared at approximately 215, 310, and 417 • C, which were associated with the dehydroxylation between the OH groups of contiguous layers, the dehydroxylation between the OH groups of contiguous layers, and a combination dihydroxylation-decarbonation reactions, respectively.…”

“…Additionally, magnesia–alumina (MA) spinel will be formed around 700°C by MAT during heating 27 . These newly in situ formed MA spinel particles contribute to the ceramic bonding of castables, 28 thereby moderating the deterioration of castable strength at medium temperatures 29 . In addition, the formation of the in situ MA spinel accompanied by 8 vol.% of expansion can offset the shrinkage of HA‐bond castables 30 .…”