Determination of the Thermal Parameters of Geopolymers Modified with Iron Powder

Abstract

The paper presents the results of research concerning the influence of a metallic micromaterial on the thermal conductivity λ, specific heat Cp, and thermal diffusivity a of modified geopolymers. Iron oxide in the form of powder with an average granulation of 10 μm was used as the geopolymer-modifying material. The research concerned geopolymer composite samples with metakaolin (activated with potassium silicate) and the addition of iron in amounts ranging from 0.5% to 2.5% in relation to the weight of the metakaolin. Additionally, the samples were modified with sand and fireclay in two different amounts—1:1 and 1:1.2 in relation to the metakaolin. The addition of fireclay caused a decrease in the thermal conductivity of the composites by 30% when compared to the samples with the addition of sand. The lowest value of the thermal conductivity coefficient λ was obtained for the geopolymer with metakaolin and fireclay. When the ratio of these components in the composite was 1:1, the value of thermal conductivity was equal to 0.6413 W/(m·K), while in the case of their ratio being 1:1.2, it was equal to 0.6456 W/(m·K). In the samples containing fireclay, no significant influence of the added iron on the values of thermal conductivity was noticed. In the case of the geopolymer with sand, the effect was noticeable, and it was most visible in the samples containing metakaolin and sand in the ratio of 1:1.2. It was noticed that with an increase in the addition of Fe, the thermal conductivity of the composite increased.

Review on Geopolymers as Wellbore Sealants: State of the Art Optimization for CO2 Exposure and Perspectives

“…For these reasons, Fe is considered incompatible with GPs at elevated temperatures (above 800 °C). 49,51,198 GPs with higher iron oxide contents also show lower acid resistance, even when compared to OPCs. 199 With regards to mechanical properties, some recent studies have reported higher compressive, flexural, and tensile strengths of iron-bearing GPs, which has been ascribed to the filler effects of iron oxides and the combined action of polysialates, iron-silicates, and ferro-sialates (Fe(−Al)−S− H).…”

“…Only limited research exists regarding the effect of Si/Fe ratios on the properties of GPs. ,, In general, high concentrations of ferric oxide, apart from its impacts on the color of GPs, can give higher specific gravity, enhanced thermal conductivity, and increased thermal expansion of the setting material while also impacting the morphology of GPs after curing at elevated temperatures. For these reasons, Fe is considered incompatible with GPs at elevated temperatures (above 800 °C). ,, GPs with higher iron oxide contents also show lower acid resistance, even when compared to OPCs . With regards to mechanical properties, some recent studies have reported higher compressive, flexural, and tensile strengths of iron-bearing GPs, which has been ascribed to the filler effects of iron oxides and the combined action of polysialates, iron-silicates, and ferro-sialates (Fe­(−Al)–S–H). ,,− Other studies, however, have shown that iron can negatively impact GP properties through the rapid precipitation of Fe species due to the higher atomic size of Fe compared to Si or Al, causing more rapid consumption of OH – , which in turn results in deceleration of the dissolution of the remaining precursor and inhibition of the geopolymerization and thus reduced strength of the system. ,, However, as shown by Davidovits, these negative impacts of elevated Fe contents on GP properties may be suppressed, as they achieved improved mechanical durability of GPs even with extremely high quantities of iron.…”

“…Usually, lower porosities also give lower permeabilities and thus a system that can better resist chloride attack and CO 2 penetration. , The key factors affecting the porosity (and permeability) of a GP are as follows: Water to solid ratio: Increasing the water content in a GP system can cause an increase in porosity and permeability due to the enhanced mobility of ions, destabilization of Al tetrahedra, and increased susceptibility of the system to fracturing (as discussed in Section ). Conversely, a decrease in the water-to-solid ratio, for a given composition, can significantly decrease the porosity and permeability of the GP, leading to improved microstructures. , However, a decrease in water content beyond a certain point can result in drying shrinkage and the development of microcracks, ultimately resulting in increased permeability of the GP to aggressive chemical agents and susceptibility to corrosion-induced damage. , It is also important to note that GP activation and polymerization are sensitive to water content, which may lead to increased porosity at suboptimal water contents. − Alkali content: Recent studies clearly show the reduced porosity of GPs at increased reaction rates obtained through increasing the alkali content. However, as noted above, excess alkalinity can impact the charge balance of GPs and lead to long-term leaching and lower system durability .…”

“…Water to solid ratio: Increasing the water content in a GP system can cause an increase in porosity and permeability due to the enhanced mobility of ions, destabilization of Al tetrahedra, and increased susceptibility of the system to fracturing (as discussed in Section ). Conversely, a decrease in the water-to-solid ratio, for a given composition, can significantly decrease the porosity and permeability of the GP, leading to improved microstructures. , However, a decrease in water content beyond a certain point can result in drying shrinkage and the development of microcracks, ultimately resulting in increased permeability of the GP to aggressive chemical agents and susceptibility to corrosion-induced damage. , It is also important to note that GP activation and polymerization are sensitive to water content, which may lead to increased porosity at suboptimal water contents. − …”

“…Although the modern development of AAMs goes back to 1959, the study of GPs as green alternatives to OPC started coming into focus approximately 40 years ago. − Since then, the notable features of GPs have attracted the attention of academic and industrial sectors, resulting in increasing research intensity as well as progressively extensive application of GPs, such as in concrete, coating applications, refractory materials, insulation, and fire-resistant materials. , GPs have also been recognized as suitable candidates for zonal isolation of CCS wellbores mainly because of their lower permeability and lower Ca content compared to OPC-based sealants. ,− However, serious challenges to the use of GPs in zonal isolation of CCS wells do exist and need to be dealt with. Key issues noted in the literature include the sensitivity of GP activation and polymerization to water content, the viscosity profile, controlling thickening time, efflorescence (alkali leaching) and/or carbonation, and the low tensile strength of GPs. − Moreover, due to the system complexity caused by the wide range of parameters involved in GP synthesis, development of standard mix designs is still in its primary stage (laboratory scale). The need for liquid alkali-based activators with high pH imposes further challenges due to safety issues, and studies working on reducing the need for such activators are broadly welcomed. , Finally, while GPs have been recognized as potential wellbore sealant materials, and despite the extensive research conducted on the development of GP systems and a noticeable number of reviews published on various aspects of these materials, ,,,− the zonal isolation potential of GP systems in CCS operations has not been addressed as thoroughly.…”