Kinetic control of MgO hydration in refractory castables by using carboxylic acids

Santos, T.D. de Souza; Santos, Joelma dos; Luz, A.P.; Pagliosa, C.; Pandolfelli, V. C.

doi:10.1016/j.jeurceramsoc.2017.11.046

Cited by 38 publications

(34 citation statements)

References 39 publications

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“…Different strategies can be considered for having a better control of Mg(OH)2 formation during the refractory processing steps, such as: (i) adding organic compounds (acetate, acids, etc. ) to the prepared mixtures in order to change the morphology of the formed brucite crystals to better fit their growth in the resulting microstructure [13,14], and (ii) using hydrating agents (i.e., carboxylic acids) to favor a faster Mg(OH)2 nucleation rate on a magnesia surface, which can limit its crystal growth [8,15]. Both alternatives focus on inducing brucite formation in the developed formulations, instead of inhibiting the hydration reaction [16,17], because the fresh Decrease in the hydration susceptibility molded MgO-bonded castables could still present enough room to accommodate stresses before their setting time.…”

Section: Introductionmentioning

confidence: 99%

Aluminum lactate role in improving hydration and drying behavior of MgO-bonded refractory castables

Fini

Miguel

Pinto

et al. 2020

Ceramics International

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Developing MgO-bonded castables is still an important subject for refractory producers and end-users based on the expansive character of the in-situ Mg(OH)2 formation. Considering that magnesia undergoes hydration when exposed to water and the generated hydrated phase needs to be properly accommodated in the resulting microstructure to inhibit the generation of cracks, it is very important to find out alternatives to control/change the MgO hydration reaction rate, which may help to optimize the permeability and green mechanical strength of the castables. Therefore, fast and safer drying of such refractories can be carried out when adjusting Mg(OH)2 generation with proper additives. This research investigated the use of aluminum lactate (AL) as a likely additive to change the hydration and drying behavior of vibratable castables bonded with different MgO sources (dead burnt, caustic or fumed one). Firstly, XRD, TG and DSC measurements of magnesia-based aqueous suspensions were evaluated to identify the AL effect on changing the hydration reaction products during the curing and drying steps. After that, Al2O3-MgO refractories were prepared and their flowability, curing behavior, cold flexural strength, apparent porosity, permeability and explosion resistance were evaluated. The results indicated that, instead of Mg(OH)2, Mg6Al2(OH)16(OH)2.4.5H2O/ Mg6Al2(OH)16(CO3).4H2O was the main hydrated phase identified in the AL-containing compositions. Due to this change in the hydration behavior of the refractories, the mixtures prepared with dead-burnt or magnesia fumes plus organic salt presented a longer setting time. Besides that, crack-free samples with improved permeability and green mechanical strength could be obtained when adding 0.5 wt.% or 1.0 wt.% of aluminum lactate to the tested castable compositions. Consequently, 1.0 wt.% of the selected additive favored the design of refractories with enhanced properties and greater spalling resistance, as no explosion could be observed even when subjecting the prepared samples to severe heating conditions (20°C/min).

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Section: Introductionmentioning

confidence: 99%

Aluminum lactate role in improving hydration and drying behavior of MgO-bonded refractory castables

Fini

Miguel

Pinto

et al. 2020

Ceramics International

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“…In order to better control the kinetic of the brucite nucleation and growth, a pre-activation step of the MgO particles is required as suggested by Santos Jr. [12,13]. Hence, the selected dead-burnt magnesia was mixed with distilled water and formic acid in a lab stirrer for 2 minutes.…”

Section: -Refractory Castables Containing Different Drying Agentsmentioning

confidence: 99%

“…On the other hand, MgO-H2O, MgO-AcF and MgO-SM compositions dried at 110°C for 24h and then subjected to the TG measurements ( Fig. 1b) did not show the presence of free-water in their structure, whereas the mixtures comprised by MgO plus the organic aluminum salt (OAS) or the permeability enhancing active compound (MP) still presented a small mass change around 80-200°C, which might be related to the decomposition of gel-like phases [33,35] or the release of inter-lamellar water contained in hydrotalcite-like compounds [12], both of them derived from the action of these additives (as will be pointed out when discussing the XRD results). In fact, organic additives, such as OAS, may undergo hydrolysis in the first contact with water [43] and also favor the complexation of magnesium ions [20].…”

Section: -Physical-chemical Transformations Derived From the Interactmentioning

confidence: 99%

“…Formic acid was incorporated into the castables preparation, as this compound may adsorb on MgO particles and decrease the energetic barrier for the interaction of this oxide with water, resulting in a greater likelihood for nuclei formation and, consequently, leading to a more controlled growth of the brucite crystals [12]. Despite the influence of this organic compound in the behavior of the RefM refractory, its action was not efficient enough to prevent cracking at 110°C.…”

Section: -Cold Flexural Strength and Apparent Porositymentioning

confidence: 99%

“…Usually, the main castable systems that present higher likelihood to undergo spalling or explosion during their drying step are the ones containing hydraulic binders (calcium aluminate cement, hydratable alumina or among the coarse and fine particles of the refractory. However, considering the density mismatch between MgO (ρMgO = 3.5 g/cm 3 ) and brucite (ρMg(OH)2 = 2.3 g/cm 3 ), this reaction can result in an expressive volumetric expansion, leading to the generation of cracks in the molded samples during curing and drying steps [12,15]. (1) Aiming to take advantage of the MgO hydration and optimize the bonding potential of this material, some approaches are suggested in the literature, such as: (i) inducing faster Mg(OH)2 formation before the composition setting time, when the molded castable still has enough room and some freedom to accommodate stresses [14,17], (ii) changing the morphology of the hydrated phase to better fit the crystal growth in the designed microstructure [18][19][20], and (iii) using hydrating agents (i.e., carboxylic acids, and others) to activate a higher number of sites and increase the Mg(OH)2 nucleation rate on MgO surface, which might limit the crystal growth [12,13].…”

Section: Introductionmentioning

confidence: 99%

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Fast drying of high-alumina MgO-bonded refractory castables

Pinto

Fini

Miguel

et al. 2020

Ceramics International

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Refractory producers face many challenges in terms of producing MgO-containing castables due to the high likelihood of magnesia to hydrate in contact with water, resulting in Mg(OH)2 generation. The expansive feature of this transformation affects the performance of such refractories, as (i) if this hydrated phase is not accommodated in the formed microstructure, ceramic linings with cracks and low green mechanical strength will be obtained; and (ii) if crack-free pieces are prepared, they should present low porosity and reduced permeability, which require special attention when heating these materials. In both cases, spalling/explosion may be favored during the drying step of MgO-containing compositions. Hence, this work investigated the ability of various additives in the optimization of the drying behavior of Al2O3-MgO castables. Vibratable compositions were tested after incorporating polymeric fibers (PF), an organic salt (OAS), SiO2-based additive (SM) or permeability enhancing active compound (MP) into the dry-mixtures. Various experimental measurements were performed to infer the role of the drying agents to prevent the samples' explosion and whether they would also influence other properties of the castables. As observed, OAS and MP helped to inhibit the MgO-bonded samples' explosion even under severe heating conditions (2-20°C/min) and increased their green mechanical strength and slag infiltration resistance when compared to the additive-free composition. On the other hand, the addition of polymeric fibers (PF) or silica-based compound (SM) to the formulations was not able to prevent the castables' explosion when using a high heating rate and other side effects (samples' cracking during drying at 110°C, high linear expansion and increased slag penetration during corrosion tests) could also be observed when testing these materials. Thus, the selection of suitable drying 2 agents is a key issue, as they may allow the development of MgO-bonded castables with enhanced properties and lower spalling risk during their first thermal treatment.

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Carboxylic acid-assisted hydration for the preparation of mesoporous magnesium hydroxide/magnesium oxide with ultra-high adsorption performance and selective adsorption: Experiments and DFT investigations

Li,

Zhang

et al. 2025

Applied Surface Science

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Kinetic control of MgO hydration in refractory castables by using carboxylic acids

Cited by 38 publications

References 39 publications

Aluminum lactate role in improving hydration and drying behavior of MgO-bonded refractory castables

Aluminum lactate role in improving hydration and drying behavior of MgO-bonded refractory castables

Fast drying of high-alumina MgO-bonded refractory castables

Carboxylic acid-assisted hydration for the preparation of mesoporous magnesium hydroxide/magnesium oxide with ultra-high adsorption performance and selective adsorption: Experiments and DFT investigations

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