Characterisation of microstructural evolutions in refractory castables by in situ high temperature ESEM

Abstract

This paper deals with the characterisation of the microstructural evolutions during the first heating of two commercial refractory castables by dilatometry and by in situ high temperature environmental scanning electron microscopy (HT-ESEM) up to 1300 • C. Investigations have been made both on the castables and on their respective matrix. Effects of microstructural changes have been observed on dilatometric results. Four temperature domains could be defined, in which shrinkage is occurring. During in situ HT-ESEM observations, important microstructural changes could be seen in these four temperature domains. They deal first with microcrack initiation due to dehydration mechanisms. Microcrack opening then increases when increasing the sample temperature. An acceleration of these microcrack-opening mechanisms was observed when sintering starts in the 800-950 • C temperature range. Between 1000 and 1100 • C, liquid phases appear in the material and liquid phase sintering starts to occur. An increase of the liquid phase amount and of liquid phase sintering effects are observed when increasing temperature up to 1300 • C. Crystal growth was identified as occurring at this temperature too. Above 1100 • C, a competition between shrinkage mechanisms and expansion ones take place. The balance between these two types of mechanisms is not the same for the two studied refractory castables.

New advances in the laboratory characterization of refractories: testing and modelling

“…The material is an ultra-low cement bauxite matrix that is reinforced with bauxite aggregates and 2 wt.% of FeCrAl fibres. It is described in [17,18].…”

In Situ Experiments in the Scanning Electron Microscope Chamber

“…It is possible to work under vacuum (classical SEM) or under controlled atmosphere (H 2 O, O 2 , He+H 2 , N 2 , air...). Different types of studies have been reported, relative to corrosion of metals (Jonsson et al, 2011), oxidation of metals (Schmid et al, 2001a(Schmid et al, , 2001bOquab & Monceau, 2001 ;Schmid et al, 2002 ;Abolhassani et al, 2003 ;Reichmann et al, 2008 ;Jonsson et al, 2009 ;Mège-Revil et al, 2009 ;Quémarda et al, 2009 ;Delehouzé et al, 2011), reactivity at high temperature (Maroni et al, 1999 ;Boucetta et al, 2010), phase changes (Fischer et al, 2004 ;Hung et al, 2007 ;), hydrogen desorption (Beattie et al, , 2011, redox reactions (Klemensø et al, 2006), microstructural modifications (Bestmann et al, 2005 ;Fielden, 2005 ;Yang, 2010), magnetic properties (Reichmann et al, 2011), sintering (Sample et al, 1996 ;Srinivasan, 2002 ;Marzagui & Cutard, 2004 ;Smith et al, 2006 ;Subramaniam, 2006 ;Courtois et al, 2011 ;Joly-Pottuz et al, 2011 ;Podor et al, 2012), thermal decomposition (Gualtieri et al, 2008 ;Claparède et al, 2011 ;Goodrich & Lattimer, 2011 ;Hingant et al, 2011), crystallisation (Gomez et al, 2009 in melts (Imaizumi et al, 2003 ;Hillers et al, 2007) and study of self-repairing -self-healingproperties of materials …”

In situ X-ray diffraction studies of electroceramics

“…High temperature optical microscopy, TEM, and environmental SEM (among others) allow direct observation of sintering, wetting angles, dislocation motion, phase development, crystal growth, orientation relationships, and even electrical, mechanical, and field emission behavior [66][67][68][69]. Of course, complementing these techniques with in-situ XRD, and vice-versa, can be quite valuable in many cases.…”