Acid-based geopolymers: Understanding of the structural evolutions during consolidation and after thermal treatments

Abstract

Materials such as ceramic matrix composites are developed for mechanical applications at high temperature, but their cost remains a limitation. Consequently, the use of acid-based geopolymer matrices may be an alternative to reduce costs. In this study, the sample was prepared from metakaolin and phosphoric acid. FTIR and NMR spectroscopies, XRD and thermal measurements were used to understand the structural evolution of acid-based geopolymers (binders) during consolidation and after thermal treatments. According to the results, the consolidation of the binder has been divided into four steps: the dissolution of the metakaolin, the polycondensation reactions forming AlPO 4 entities and hydrated phases, the breakdown of Si-O-Al bonds with formation of various hydrated silica *Manuscript Click here to download Manuscript: manuscript.docx Click here to view linked References

Control of the alumino-silico-phosphate geopolymers properties and structures by the phosphorus concentration

“…The synthesis of the reference geopolymer was described in a previous study [6], using a metakaolin produced by Imerys with a Si/Al ratio equal to 1 as the aluminosilicate source, whose characteristics and reactivity have been studied by Gharzouni et al [18], and a 85 wt% pure phosphoric acid produced by VWR. During the synthesis, the phosphoric acid has been first diluted in distilled water to reach the selected water content and mixed with the metakaolin until reaching an Al/P ratio equal to 1, this reactive mixture being then poured in a sealed container and cured at 70°C for 72 h.…”

“…In this study, the influence of the water content on the reactive mixture has been studied by synthetizing two series of samples. The first one has been obtained by adding water to the reference composition, originally containing 0.45 mol % of water, and called R [6], up to a maximum of 0.68 mol %. The notation of those samples has been defined as R-x, x being the ratio of the molar percentage of added water over the reference one.…”

“…This path seems promising as the resulting materials present improved mechanical properties [4,5]. An acid-based geopolymer formation starts with the dissolution of an aluminosilicate source into an acid (usually orthophosphoric acid) leading to the release of Al 3+ ions, which then polycondense with the phosphorous entities to form three-dimensional hydrated aluminophosphate networks [6]. The hydrated silica still remaining after the release of those Al 3+ ions can then form some additional silicate networks, that may react with some of the remaining phosphorous entities, thus forming Si-O-P bonds [6,7].…”

“…An acid-based geopolymer formation starts with the dissolution of an aluminosilicate source into an acid (usually orthophosphoric acid) leading to the release of Al 3+ ions, which then polycondense with the phosphorous entities to form three-dimensional hydrated aluminophosphate networks [6]. The hydrated silica still remaining after the release of those Al 3+ ions can then form some additional silicate networks, that may react with some of the remaining phosphorous entities, thus forming Si-O-P bonds [6,7]. As for geopolymers in alkali medium, previous studies were carried out to understand the influence of the aluminosilicate sources, the activation solution and the consolidation temperature on the structure and working properties of acid-based geopolymers [8,9].…”

Silico-Aluminophosphate and Alkali-Aluminosilicate Geopolymers: A Comparative Review

“…Recently, the AAS geopolymers have been investigated from multiple angles, such as the synthesis mechanism and chemistry (Provis, 2013;Provis and Bernal, 2014;Provis et al, 2015), properties and durability Arbi et al, 2016;Ding et al, 2016), life cycle analysis (Habert et al, 2011;Ouellet-Plamondon and Habert, 2015), and multi-field applications (MacKenzie, 2015;Rao and Liu, 2015;Luukkonen et al, 2019). Yet, the available review related to the SAP geopolymer is limited even though such type of geopolymer was termed as aluminosilicate phosphate cement (Khabbouchi et al, 2017;Katsiki, 2019), phosphoric acid-based geopolymer (Liu et al, 2012;Guo et al, 2016), phosphate-based geopolymer , acid-based geopolymers (Mathivet et al, 2019), and phosphate-bonded materials (MacKenzie, 2015). This paper mainly reviews the development of the SAP geopolymers in reference with the conventional AAS geopolymers.…”