Comparative assessment of calcium aluminate cement and potassium-metakaolin-based geopolymer as binders in high-alumina refractoriesAbstract
This investigation demonstrated the effects of calcium aluminate cement’s total or partial replacement with a potassium-metakaolin-based geopolymeric binder (K-GP) in high-alumina castables. Experimental measurements were conducted to analyze the produced samples’ processing, microstructure, and properties after curing and firing (800-1400 °C). The results highlighted K-GP as a viable binder option for producing cement-free refractories. After firing at 1100-1400 °C, the improved properties of geopolymer-bonded refractories were attributed to their complex resultant microstructure, comprising alumina particles strongly adhered by a glassy phase and contained randomly distributed clusters of kaliophilite and/or leucite grains within the ceramic matrix. After firing at 1250 °C, the samples exhibited a promising set of properties: high thermal shock resistance, modulus of rupture of 17.01 MPa, Young’s modulus of 67.15 GPa, porosity of 16.85%, density of 2.87 g/cm³, and linear shrinkage of 0.33%. These properties are suitable for applications at intermediate temperatures (i.e., petrochemical and non-ferrous industries).
Keywords:
Geopolymer; Binder; Castable; Metakaolin; Alumina
INTRODUCTION
The development of advanced refractory monolithics has seen significant progress in recent years. These ceramic materials are characterized by complex compositions, comprising coarse aggregates, fine and ultrafine components, binders, specific additives, and other constituents 1)-(4. Binders are critical for facilitating the solidification of fresh compositions, promoting cohesion among microstructural elements, and ensuring the mechanical integrity of the final products. In refractory castable production, the strategic selection of binder systems is vital for enhancing initial mechanical strength and promoting the in-situ formation of robust ceramic bonds at elevated temperatures 2), (4), (5. Efforts to improve binder systems have been closely aligned with the Sustainable Development Goals (SDGs) of the United Nations 2030 Agenda, prioritizing carbon footprint reduction, energy efficiency, and circular economy practices 1)-(4), (6.
Calcium aluminate cements (CACs) are widely used as binders in refractory materials due to their rapid setting properties, which provide high green mechanical strength (after curing but before sintering) and excellent performance at elevated temperatures 3), (7)-(9. However, the drying process for CAC-based materials requires careful and gradual heating to effectively remove free water and decompose hydrated phases (e.g., CAH10, C2AH8, C3AH6, and AH3, where C = CaO, A = Al2O3, and H = H2O) present in the consolidated microstructure. This process often increases porosity in the refractory matrix, potentially compromising mechanical strength within the temperature range of 110 °C to 1000 °C, before sintering 3), (7)-(9. Moreover, the drying step typically involves slow heating rates to prevent catastrophic failure of ceramic linings, resulting in significant energy consumption and high operational costs 10), (11. Additionally, CAC production poses environmental challenges, including substantial consumption of natural resources, high energy demands, and considerable CO2 emissions.
To address these limitations, research has increasingly focused on reducing or replacing CACs with alternative materials (1, 4, 11). Geopolymers, or inorganic polymers, have emerged as promising alternatives, offering environmental, technical, and economic advantages 12)-(14. These binders can be synthesized at near-ambient temperatures via different approaches (alkaline or acidic 15) and methodologies (“one-part” or “two-part” 16). Geopolymers are typically formed by alkalinizing amorphous aluminosilicate precursors (e.g., calcined clays, metakaolin, fly ash, biomass ash) with highly alkaline solutions (e.g., alkali silicates or hydroxides). This process drives the polycondensation of inorganic monomers (e.g., Al(OH)4 -, Si(OH)4, SiO(OH)3 -, and SiO2(OH)2²-), forming rigid three-dimensional aluminosilicate networks stabilized by alkali cations (e.g., Li+, Na+, K+, Cs+, or Ca²+) 12), (17)-(19. The resulting geopolymeric materials often contain nanoparticles (5-40 nm in size) and exhibit properties typical of ceramics 12. Applications of geopolymers range from civil construction 20 and hazardous waste management 21 to water treatment 22), (23, catalysis 24, heat-resistant components 25), (26, refractory ceramics 27, and soil stabilization 28.
Geopolymers exhibit several advantageous properties that make them suitable for refractory ceramic formulations, including rapid setting capabilities 29; reduced risks of damage or explosion during drying, enabling faster processing compared to CAC-based compositions 30; extended lifespan of refractories, with optimized mechanical behavior over a wide temperature range 31), (32; enhanced sustainability and cost-efficiency 33. While alkali oxide content in refractory ceramics is typically controlled to maximize refractoriness and minimize liquid phase formation, studies have demonstrated the potential for refractory phase crystallization (e.g., nepheline 34)-(36, leucite 37)-(39, pollucite 40), (41, mullite 42)-(44, cordierite 38) within geopolymeric matrices when exposed to elevated temperatures.
The crystallization of these phases depends on several factors, such as: (i) chemical composition, particularly Si/Al and Si/M ratios (M = Cs, K, Na, Ca, etc.); (ii) reactivity of aluminosilicate precursors and alkaline reagents; (iii) binder content and overall ceramic formulation; (iv) mixing and curing conditions; (v) geopolymeric network structure; (vi) thermal treatment parameters (e.g., temperature, duration, heating and cooling rates); and (vii) thermochemical interactions between the geopolymer gel and other ceramic constituents (e.g., fine powders, aggregates, impurities, and additives) during heating 39), (45)-(55.
Limited research has investigated the incorporation of geopolymers into complex refractory formulations 30), (56)-(58. A significant barrier to more extensive exploration in this area lies in the justified concerns surrounding the use of raw materials with elevated levels of alkali oxides, such as Na2O or K2O, which may adversely affect the refractoriness of the resulting ceramics. Nevertheless, Beimdiek and colleagues 30 reported that bauxite-based formulations containing 75 wt.% Al2O3 demonstrated several notable advantages compared to analogous compositions prepared with calcium aluminate cement (CAC), including the absence of chemically bound water, ensuring adequate permeability and facilitating the drying process; robust hot mechanical strength with minimal variation in properties across the temperature range of 1000 °C to 1400 °C, as indicated by a hot modulus of rupture ranging from 5 to 20 MPa; the ability to accommodate mechanical stresses due to their thermoelastic behavior; exceptional chemical resistance, as evidenced by the absence of reactions when the samples were exposed to a highly acidic aqueous solution (99% H2SO4) at pH = 0 and 20 °C for seven days; and extended service life. Additionally, the authors noted deformation exclusively in samples subjected to refractoriness-under-load tests at temperatures exceeding 1400 °C. Moreover, the study validated the practical feasibility of geopolymer-bonded refractory castables for industrial applications, including their use in rotary kiln linings within the cement industry.
Previous research 57 by the current authors demonstrated that high alumina (96 wt.%) refractories bonded with a combination of 2.7 wt.% CAC and 1.3 wt.% metakaolin (as a precursor for geopolymer formation) exhibited a flexural strength of 39.1 MPa and high thermal shock resistance (∆T~1000 °C) after firing at 1400 °C for 2 hours. This performance surpassed that of the reference composition, which contained only CAC as a binder. In this case, geopolymerization of the precursors within the composition was induced using a NaOH and colloidal silica-based liquid reagent (SiO2/Na2O molar ratio ~ 1.4).
Studies have indicated that the lower viscosity of the liquid phase in the K2O-Al2O3-SiO2 system, compared to the Na2O-Al2O3-SiO2 one, and the crystallization potential of the K-geopolymer gel into leucite within the ceramic matrix, can enhance the refractoriness and thermomechanical performance of composites containing such binders 38), (59), (60. Additionally, since KOH-based alkaline solutions exhibit lower viscosity than those prepared with NaOH, a smaller amount of caustic liquid can be managed during the mixing step 44), (52), (58), (61), (62. These factors may lead to the design of low-alkali-containing compositions and user-friendly methods for crafting geopolymer-based materials.
Considering the advances achieved to date and aiming to gradually reduce the calcium aluminate cement (CAC) content in refractory compositions, this study evaluated the effects of the total or partial replacement of CAC with a potassium-metakaolin-based geopolymeric binder in high-alumina refractory castables. The performance of the prepared ceramics was analyzed after curing and firing within the temperature range of 40 °C to 1400 °C.
EXPERIMENTAL
Four high-alumina vibrated refractory castables were developed based on the Alfred particle packing model 3 and considering distribution modulus (q) = 0.26. The evaluated compositions consisted of mixtures of tabular alumina particles (d ≤ 6 mm, Almatis, Brazil), calcined and reactive aluminas (CL370 and CT3000SG, Almatis, Brazil), and 4 wt.% binder (Table I). The selected binder was either calcium aluminate cement (CAC, Secar 71, Imerys Aluminates, France) or a geopolymer (GP). The GP was formed in-situ during the processing of the monolithics through the reaction between metakaolin (MK) - derived from commercial kaolin (MCP-400, Minasolo, Brazil), which was calcined at 800 °C for 2h (8) - and an alkaline liquid reagent with SiO2/Na2O = 1.40 and H2O/Na2O = 15 (molar ratio). KOH aqueous solution (12M) was mixed with a colloidal silica suspension (SiO2 = 40 wt.%, Levasil CS40-125, Nouryon, Brazil). The silica suspension was added to the KOH aqueous solution, and they were mixed using a mechanical stirrer. This procedure was carried out for approximately 5 h, when the silica was completely dissolved, and a homogeneous and clear liquid was obtained.
The castable mixtures were processed in a planetary mixer (Solotest, Brazil), according to the protocol outlined in 57. 0.2 wt.% of a polymeric dispersant (Castament FS60, BASF) was added to the mixtures to reduce liquid demand and adjust the rheology of the monolithics. The compositions were prepared using varying amounts of a potassium alkaline solution (AS, SiO2/K2O ≈ 1.4, H2O ≈ 66 wt.%, pH 13-14), aiming to achieve mixtures with vibratable flow (VF) values around 130% (Table I, measured according to ASTM C1445-13). Prismatic samples (150 mm x 25 mm x 25 mm) were subsequently molded under vibration. The prepared molds were covered with plastic film and maintained in an oven at 40 °C for 24 hours. The cured specimens were then dried in an oven at 110 °C for 24 hours and subjected to thermal treatment at 800 °C, 1100 °C, 1250 °C, and 1400 °C for 2 hours with heating and cooling rates of 2 °C/min.
The performance of the refractories was characterized using several techniques: 1) three-point bending tests (model DL10000, Instron - EMiC, USA, following ASTM C133-97 guidelines); 2) apparent porosity and density measurements based on the Archimedes principle, using water as the immersion liquid (ASTM C830-00); 3) elastic modulus determination at room temperature (~25 °C) utilizing the impulse excitation technique (Sonelastic, ATCP, Brazil, ASTM E1876-15); and 4) linear dimensional variation assessment (ASTM C113-14). The results presented are the average values and standard deviations obtained from five samples. Additionally, samples of selected compositions previously fired at 1250 °C and 1400 °C for 2 hours were evaluated for thermal shock damage resistance (∆T ~ 1000 °C, ASTM C1171-91), following the procedure described in 57.
Powder samples of the matrices of the studied castables (fine components of the formulations, d < 200 µm) after curing at 40 °C for 24 hours and firing at 1400 °C for 2 hours were analyzed using X-ray diffraction (Bruker D8 Focus, CuKα radiation [λ = 1.5418 Å], with a nickel filter, 40 mA, 40 mV, and a step size of 0.02°) and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR, PerkinElmer Spectrum 3, 4000-400 cm-1, 20 scans, and a resolution of 4 cm-1).
The fracture surface and the matrix region of the best-performing compositions (which were previously treated at 1100 °C or 1400 °C for 2 hours), were further analyzed using Field Emission Gun - Scanning Electron Microscopy (FEG-SEM) with a Tescan Mira microscope, equipped with energy dispersive spectrometry (EDS) utilizing a Bruker e-FlashFS spectrometer.
RESULTS AND DISCUSSION
The castable compositions were processed to achieve comparable rheological characteristics. Consequently, the demand for alkaline solution (AS) increased as the proportion of calcium aluminate cement (CAC) replaced by metakaolin rose from 9.3 wt.% to 11.3 wt.% (Table I). Accordingly, the AS/MK mass ratio required to process these refractories also increased, changing from 2.33 to 2.83. Due to the lower viscosity of the potassium-based alkaline solution (11.5 mPa.s, compared to 23.5 mPa.s for NaOH-based solution 44), approximately 20% less AS was required for processing the designed castables compared to equivalent systems containing NaOH instead of KOH 57. Handling a smaller amount of caustic liquid during the mixing stage can simplify the preparation of these ceramics and reduce the content of alkaline oxides (e.g., Na2O or K2O), which induce liquid phase formation in the Al2O3-SiO2 system when exposed to temperatures above 800 °C. This fact can enhance the thermal stability of the prepared compositions.
Initially, the performance of the investigated compositions was evaluated after curing at 40 °C for 24 hours (Figure 1). The refractories containing geopolymer (prepared with MK or MK-CAC blends) emerged as promising candidates for the manufacture of cement-free or ultra-low cement refractory components. For instance, the cured samples of TA-1C-3MK and TA-4MK exhibited cold modulus of rupture (CMOR) of 9.57 MPa and 9.64 MPa, respectively, after the curing stage, comparable to the green performance of the reference refractory (TA-4C, CMOR = 9.79 MPa, Figure 1a). Furthermore, these ceramics demonstrated an increase in apparent porosity from 7.91% (TA-4C) to 10.65% (TA-4MK, Figure 1a) and a decrease in density from 3.15 g.cm-3 (TA-4C) to 2.92 g.cm-3 (TA-4MK) as a function of the MK content in the composition.
Physico-mechanical properties of the designed high-alumina refractory castables obtained after the curing step at 40 °C/24 h: (a) cold modulus of rupture (CMOR) and apparent porosity (AP), and (b) elastic modulus (E) evolution as a function of time.
Regarding the elastic modulus values (Figure 1b), the refractories containing geopolymer exhibited minimal changes in stiffness, attributable to the complete consolidation of the samples within 24 hours at 40 °C and the stability of the gel over 16 days: TA-3C-1MK (35.99-38.65 GPa), TA-1C-3MK (26.64-28.45 GPa), and TA-4MK (36.30-37.44 GPa). This behavior is ascribed to the high reactivity of the developed geopolymeric system, which provided appropriate reaction kinetics for an effective geopolymerization process under the specified curing conditions 44. In contrast, the reference composition experienced phase transformations in its microstructure, linked to the ongoing hydration process of the cement over time. As a result, variations in Young’s modulus were observed in TA-4C samples up to 16 days.
The physico-mechanical performance of the evaluated refractories results from the synergistic interaction of the formed phases, which promotes suitable adhesion between the aggregates and the fine components. XRD and ATR-FTIR analyses (Figure 2) revealed that the alumina ceramics were typically composed of corundum and β-Al2O3 phases (NaAl11O17, an impurity found in tabular alumina). These phases are associated with Al-O-T (T = Si or Al) and Al-O-Al bonds, characterized by bands in the ATR-FTIR spectrum around 1022-988 cm-1 and 635-539 cm-1 (Figure 2b), respectively. In line with a previous study 57, the CAC contributed to the geopolymerization process as a source of Ca2+ and Al(OH)- 4, which are consumed to form essentially amorphous gels established by T-O-T (T = Si or Al) bonds centered around 988-973 cm-1. These gels coexist with α-quartz (a residual and non-reactive phase from metakaolin), K2O residues (TA-1C-3G), and/or KAlSi3O8 (TA-4G, Figure 2a). Additional insights provided by ATR-FTIR reveal the presence of physically adsorbed water in the ceramic microstructure, indicated by bands located in wavelength ranges of 3461-3360 cm-1 and 1474-1403 cm-1, as well as the existence of CO2- 3 groups (1645 cm-1, Figure 2b) inherent to carbonate compounds (e.g., CaCO3 or K2CO3).
(a) XRD patterns and (b) ATR-FTIR spectra. Identified phases and their ICSD code: α = Corundum - Al2O3 (00-042-1468); β = β-Al2O3 - NaAl11O17 (01-076-0923); A = AH3 - gibbsite - Al2O3•3H2O (00-029-0041); C = C3AH6 - Ca3Al2O6•6H2O (01-079-1286); ♦ = Quartz - SiO2 (01-085-0335); p = Potassium oxide - K2O (01-077-2176); and M = Microline - KAlSi3O8 (01-076-1239).
The TA-4MK composition was selected for further investigation, providing a direct comparison with the reference material, which utilizes only cement as a binder. The results demonstrated high stability in the properties of the refractory containing geopolymer after firing at temperatures ranging from 800 °C to 1400 °C. The following values were measured: CMOR = 15.21-17.34 MPa (Figure 3a), AP = 16.68%-17.52% (Figure 3b), apparent density = 2.87-2.89 g.cm-3, E = 67.5-73.48 GPa (Figure 3c), and linear shrinkage = 0.26%-0.48% (Figure 3d). Consequently, a refractory with superior mechanical performance compared to the reference material (TA-4C) was achieved when the samples were fired up to 1250 °C (Figure 4a). This enhanced performance of the TA-4MK composition is primarily attributed to the formation of a liquid phase above 800 °C 51), (52. The presence of this molten phase within the microstructure at elevated temperatures promotes viscous sintering and densification of the specimens, potentially facilitating the transformation of the aluminosilicate gel into vitreous and/or ceramic phases 27), (30), (31. In contrast, the sintering and densification of the CAC-containing refractory predominantly occurs via solid-state sintering, requiring higher temperatures to complete phase transformations. Additionally, the TA-4MK samples exhibited flexural strength up to 43.31% higher than the values measured for sodium geopolymer-bonded refractories 57, equivalent to the compositions investigated in this study. These findings underscore the significant role of K-geopolymers in enhancing the physico-mechanical performance of various composites containing these binders 38), (58)-(60.
Physico-mechanical properties of the designed refractory castables obtained after firing steps (1100-1400 °C/2h): (a) flexural strength (CMOR = cold modulus of rupture); (b) apparent porosity; (c) elastic modulus and (d) permanent linear change.
(a,c) ATR-FTIR spectra and (b, d) XRD patterns of the refractory castables’ matrix after 1100°C and 1400°C for 2h. Identified phases and their ICSD code: α = Corundum - Al2O3 (00-042-1468); β = β-Al2O3 - NaAl11O17 (01-076-0923); Y = Kaliophilite - KAlSiO4 (00-011-0313); L = Leucite - KAlSi2O6 (01-085-1626); = Leucite - KAlSi2O6 (01-071-1147); ♣ = CA2 - CaAl4O7 (01-072-0767); and f = CA6 - CaAl12O19 (01-084-1613).
However, the TA-4MK castable requires further optimization to improve its performance at temperatures exceeding 1250 °C. For instance, specimens of this composition exhibited a CMOR of 16.32 MPa after firing at 1400 °C, corresponding to approximately 49.36% of the mechanical strength of the TA-4C (Figure 3a). To elucidate this behavior, ATR-FTIR and XRD analyses were conducted on castable samples fired at 1100 °C and 1400 °C. The ATR-FTIR spectra confirmed the presence of T-OT (T = Si or Al) bonds in the TA-4MK samples, with relatively unchanged band profiles between 1000-400 cm-1 following both thermal treatments (Figures 4a and 4c). XRD analyses revealed the partial transformation of the gel into grains of kaliophilite (KAlSiO4) and leucite (KAlSi2O6) after firing TA-4MK specimens at 1100 °C (Figure 4b). Increasing the thermal treatment temperature to 1400 °C promoted viscous sintering, facilitating the decomposition of kaliophilite, as evidenced by modifications in the Si-O-Si and Si-O-Al bonds (T-O-T bonds, T = Si or Al, Figure 4c), resulting in leucite becoming the predominant crystalline phase derived from the gel (Figure 4d).
In the TA-4C refractory fired at 1100°C, the FTIR spectrum revealed bands associated with Al-O-Al bonds at approximately 942 cm-¹, characteristic of the corundum phase, along with Al-O bonds in the wavelength range of 800-400 cm-1 (Figure 4a). These spectral features could also be attributed to the β-Al2O3 and CA2 (where C = CaO and A = Al2O3) phases, as corroborated by XRD analysis (Figure 4b). Upon exposure to a higher temperature of 1400°C, notable changes were observed in the FTIR spectrum. These included an increase in the density of Al-O bonds, evidenced by the shift of the band near 942 cm-1 to 1066 cm-1. Additionally, the disappearance of bands at approximately 639 cm-1 and 495 cm-1 was recorded. The bands centered at 740 cm-1 and 560 cm-1 transformed into a series of well-defined, lower-intensity bands within the ranges of 772-698 cm-1 and 586-528 cm-1, respectively (Figure 4c). Phase transformations were also identified in the TA-4C refractory matrix during this thermal treatment. The corundum and CA2 phases were consumed to form CA6 (Figure 4d), resulting in alterations in the coordination number of aluminum due to an increase in the number of Al-O-Ca bonds and a decrease in Al-O-Al bonds (Figure 4c). The presence of CA6 in the TA-4C samples justifies the outstanding mechanical performance of this composition after firing at 1400 °C (Figure 3a).
SEM analyses revealed extensive precipitation of elongated CA6 grains in the vicinity of tabular alumina aggregates within the TA-4C refractory fired at 1400 °C (Figures 5a and 5d). This precipitation resulted in the formation of a porous interfacial transition zone, which facilitated effective bonding between the matrix and the aggregates, thereby enhancing their adhesion. The CA6 grains exhibited variability in shape, thickness, and degree of elongation, with random alignment relative to both each other and the alumina grains. In contrast, the microstructure of TA-4MK samples fired at 1100 °C presented a markedly different morphology. The formation of liquid phases and the partial transformation of the gel into aggregated grains of kaliophilite (KAlSiO4) and leucite (KAlSi2O6) led to the development of a heterogeneous microstructure with randomly distributed grains on the surface of alumina particles (Figures 5b and 5e). Upon increasing the thermal treatment temperature to 1400 °C, isolated leucite grains were no longer distinctly observable in the SEM analysis. Instead, the resulting microstructure displayed a porosity gradient and was characterized by alumina matrix particles strongly bonded to one another through a glassy phase (Figures 5c and 5f).
SEM images of the fracture surface of the TA-4C and TA-4MK castables after firing at 1100°C and 1400°C for 2h.
Additional tests confirmed the good thermal shock resistance of the designed geopolymer-bonded refractory (Figure 6). After undergoing 10 thermal cycles at 1025 °C (ΔT ~ 1000°C), the TA-4MK samples, previously fired at either 1250 °C or 1400 °C, retained approximately 83.52% and 88.19%, respectively, of their initial elastic modulus (cycle 0, Figure 6b). Although the elastic modulus (E) values for TA-4MK samples were lower than those observed for TA-4C (Figure 6a), the remarkable performance of the geopolymer-bonded refractory can be attributed to the bond strength provided by the glassy phase, which effectively binds the alumina particles, along with the presence of kaliophilite and/or leucite grains within the microstructure 57),(58. Furthermore, the porosity evident in the microstructure (as observed in SEM images) likely played a critical role in enhancing the material’s ability to absorb and dissipate thermal stresses. This characteristic mitigates crack propagation, thereby preserving the structural integrity of the refractory during thermal cycling.
(a) Absolute elastic modulus values and (b) its decay of the refractory castables bonded with CAC (TA-4C) or the designed geopolymer (TA-4MK) as a function of thermal shock cycles at 1025°C (ΔT ~ 1000°C). The evaluated bar samples were pre-fired at 1250°C or 1400°C for 2h.
CONCLUSIONS
The results obtained demonstrate that the TA-4MK composition exhibited superior performance following firing in the temperature range of 800-1250 °C, surpassing the CAC-bonded reference refractory. Chemical-structural stability of the geopolymer-binder composition was confirmed through XRD and ATR-FTIR analyses. SEM analyses further revealed a gradient in porosity within the developed microstructure, with alumina particles firmly adhered by a glassy phase. Additionally, randomly distributed clusters of kaliophilite and/or leucite grains were observed within the ceramic matrix. These characteristics collectively contribute to the sustained physical and mechanical properties of the designed castable. The samples previously fired at 1250 °C exhibited high thermal shock resistance after 10 thermal cycles at 1025 °C (∆T ~1000 °C), cold flexural strength of 17.01 MPa, elastic modulus of 67.15 GPa, apparent porosity of 16.85%, density of 2.87 g.cm-3, and linear shrinkage of 0.33%.
This study underscores the feasibility of geopolymers as a promising pathway for developing innovative, high-performance refractory castables. These materials show significant potential for applications at intermediate temperatures (800-1250 °C), particularly in the petrochemical and non-ferrous metals industries.
ACKNOWLEDGMENTS
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. This work was carried out with the support of Conselho Nacional de Desenvolvimento Científico e Tecnológico, CNPq - Brazil (Process 304005/2023-1). The authors would like to thank Almatis (Brazil) and Nouryon (Brazil) for supplying the alumina and the colloidal silica suspension used in this study. The authors are also grateful to Prof. Dr. Oscar Peitl and LaMaV (Vitreous Materials Laboratory, DEMa-UFSCar) for the FTIR analyses performed in this study.
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Publication Dates
-
Publication in this collection
24 Mar 2025 -
Date of issue
2025
History
-
Received
13 Jan 2025 -
Reviewed
29 Jan 2025 -
Reviewed
26 Feb 2025 -
Accepted
26 Feb 2025
