Abstract: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 p… Show more
“…Reports in the literature suggest that the soluble salts could be replaced by reactive oxides as cation sources [17][18][19]. In these cases, hydration/hydrolysis reactions would provide the desired ions, excludi process [17-Authors' hydrotalcite and magnes alumina or c simply by c suspension, w steps [20] A n-A n-A n- According to the XRD results (Fig. 2), AL addition to the MgO-suspensions inhibited brucite formation.…”
Section: Materials and Techniquesmentioning
confidence: 99%
“…Authors' previous work has reported on the formation of hydrotalcite in some systems comprised by a blend of alumina and magnesia reactive sources (respectively, hydratable alumina or calcium aluminate cement and caustic magnesia), simply by combining these raw materials in an aqueous suspension, with no need of additional reactants or purification steps [20]. This paper presents and discusses this process route in order to produce hydrotalcite.…”
Section: -Aluminum Lactate Effects On Mgo Hydration Behaviormentioning
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).
“…Reports in the literature suggest that the soluble salts could be replaced by reactive oxides as cation sources [17][18][19]. In these cases, hydration/hydrolysis reactions would provide the desired ions, excludi process [17-Authors' hydrotalcite and magnes alumina or c simply by c suspension, w steps [20] A n-A n-A n- According to the XRD results (Fig. 2), AL addition to the MgO-suspensions inhibited brucite formation.…”
Section: Materials and Techniquesmentioning
confidence: 99%
“…Authors' previous work has reported on the formation of hydrotalcite in some systems comprised by a blend of alumina and magnesia reactive sources (respectively, hydratable alumina or calcium aluminate cement and caustic magnesia), simply by combining these raw materials in an aqueous suspension, with no need of additional reactants or purification steps [20]. This paper presents and discusses this process route in order to produce hydrotalcite.…”
Section: -Aluminum Lactate Effects On Mgo Hydration Behaviormentioning
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).
“…After the cooling step, the elastic modulus of 3.2CC and 3.2CC_0.5L (120 and 115 GPa, respectively) were higher than the reference composition 6CAC (~110 GPa). However, there are two differences between refractories 3.2CC and 3.2CC_0.5L that are relevant to point out: i) the presence of the aluminum lactate gel after the drying step explains the higher initial elastic modulus of the latter (70 versus 40 GPa); and ii) its decomposition at ~375 °C [14,25] increased the porosity content in the microstructure, causing a stiffness drop of the samples in the 300-400 °C range. Furthermore, Fig.…”
Section: Resultsmentioning
confidence: 99%
“…Although it was observed a drop in the HMOR values measured between 1200-1450 °C, the results obtained for 3.2CC and 3.2CC_0.5L were still similar to the ones of the reference 6CAC. Moreover, the aluminum lactate gel provided a better thermomechanical performance at 300 °C for 3.2CC_0.5L when compared to 3.2CC (5 versus 3 MPa), whereas its decomposition at ~375 °C [14,25] gave rise to pores in the resulting microstructure (Fig. 5b), which affected its hot modulus of rupture at higher temperatures (600-1450 °C).…”
Section: Resultsmentioning
confidence: 99%
“…Considering these aspects, a literature survey for additives that could induce a binding effect for alumina refractory castables containing calcium carbonate has been made. It was found out that the addition of aluminum lactate to high-alumina magnesia-bonded castables helped to inhibit the samples' explosion during drying and increased their green mechanical strength [13,14]. Moreover, some studies [15,16] reported a sol-gel aluminum lactate route to produce alumina glass, investigating the pH's effect over the hydrolysis and gelation of this organic salt.…”
Calcium aluminate cement (CAC) can induce the development of high green mechanical strength to refractory castables in a short period of time (24 h). However, the production of this hydraulic binder is energy-intensive and releases a large content of carbon dioxide (CO 2 ), which adds to global warming. Thus, aiming to develop an alternative binding system, this study investigated the combined addition of aluminum lactate (0.25-1.0 wt%) and calcium carbonate (3.2 wt%) to alumina castables. The prepared samples were analyzed using different experimental techniques, such as cold and hot modulus of rupture, hot elastic modulus, X-ray diffraction, and apparent porosity. According to the results, the lactate addition to the castables improved their green mechanical strength after drying at 110 °C/24 h (4.89 MPa) when compared to the one containing plain calcium carbonate (1.72 MPa). Furthermore, the carbonate-containing refractories presented cold and hot modulus of rupture similar or even superior to the castable containing cement in a wide temperature range (600-1500 °C).
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