Energy storage systems are paramount in enabling progress towards a zero-emission future. The structural integrity of a latent heat thermal energy storage system for transport of refrigerated food has been investigated for the first time. Fatigue failure is a critical issue for tubes made from aluminium alloys containing phase change material at low temperatures, due to random vibration loads induced by trucks moving on rough roads. Random vibration fatigue life analysis was conducted for tubes with nominal diameters of 50 mm and 32 mm, and thicknesses of either 1.6 mm and 3 mm, using ANSYS Mechanical. The results of the modal analyses showed that the natural frequencies of the tube-PCM systems are higher than 136 Hz. This is outside the frequency domain induced by driving on rough roads, which is between 1 and 100 Hz. Tube-PCM behaves as one solid body when filled with PCM and it is bonded to tube wall resulting in balanced deformation and stress on both sides of a middle support. However, tube filled partly with PCM bonded to tube wall showed an unbalanced distribution of stress concentrated to the side with confined PCM. During cyclic melting and solidification processes, contact between tube and PCM changes where PCM can slide or form a gap. This reduces the maximum stress while still unbalanced between the two sides of tube with and without confined PCM. Tube-PCM with larger ratio of diameter to thickness (Di/t) are more sensitive to contact type, for instance tube diameter of 50 mm and 1.6 thickness compared with tube 32 mm and 3 mm thickness with no sensitivity. The minimum fatigue life was found 2.6 million hours for tube-PCM size 50 mm with 1.6 mm tube thickness. This was assuming a full cycle with minimum to maximum stress ratio equal to one. The lifetime reduced to 2.8 million hours under random vibration cycles with stress ratio equal to 0.5. These results indicate that aluminium tube sizes of 50 and 32 mm with a thickness of 1.6 mm are satisfactory for an expected life of 20 years. Aluminium is well-suited for thermal energy storage in refrigeration due to its low density, excellent corrosion resistance, and high thermal conductivity. The optimal size and thickness depend on the expected lifetime and specific design criteria.

The objective of this project was to further develop new composites and a testing program for the performance-based specification for natural Amazonian geopolymer (GP) for use in ceramics and construction. While fly ash-based alkali activated materials are now an established technology, metakaolin-based GPs still need to be developed and optimized regarding the knowledge of the specific characteristics and properties of local resources. Amazonian kaolin was calcined into metakaolin (AMK). AMK particle size reduction for better reactive material was evaluated by means of dry and wet ball milling and sieving. Three types of metakaolin were analyzed for particle size distribution, and their size d50 ranged from 7.9 to 2.8 mu m. Further GP characterization followed physical and mechanical properties in flexural strength tests. In addition, scanning electron microscopy and energy dispersive spectroscopy were used to investigate the microstructure of the materials. Energy dispersive X-ray fluorescence was used to measure the GP material composition. Analysis of the results revealed that the strength and stiffness of sodium-metakaolin-based GP were inversely proportional to particle size. All distinct particle size GPs showed, in general, some increase in strength and stiffness within curing times ranging from 3 to 28 days.

Geopolymers represent a distinct class of materials characterised by their X-ray amorphous nature and nanoporous, nanoparticulate structure. Geopolymers can be conveniently mixed, poured, and cured under ambient conditions. This makes this class of materials an interesting alternative to ordinary Portland cement for structural processes. Additionally, the addition of alumina can improve mechanical properties, while the addition of glass can form an impermeable glaze which could be useful for molten salt containment. Therefore, in this investigation, potassium metakaolin-based geopolymer composites with varying proportions of glass particles and alumina platelets were fabricated, cured, heat-treated, and analyzed to study the effects of composition on material properties. Various attributes including rheological properties, densities, mass loss, shrinkage, and porosities were compared. It was observed that certain compositions exhibited high viscosities, making high shear mixing challenging, while also displaying significant permeability that would hinder their ability to contain liquids without leakage. Additionally, certain samples showed reduced densities, suggesting potentially weaker mechanical properties; however, the investigation did not include a direct assessment of mechanical properties. The most promising candidates for containing liquids at high temperature contained 50 wt% KGP, 25 or 35 wt% glass powder, and 25 or 15 wt% alumina platelets, respectively. ASH-G slurries required a minimum of 65 vol% KGP to produce a homogenous material compatible with additive manufacturing. The minimum amount of glass phase to form surface glazes was 16 vol%. Only samples containing more glass phase than alumina phase produced glazed composites.

Thermal energy storage is increasingly needed in a sustainable world because of its potential of capturing waste heat and being incorporated in solar power plants. For power generation, in particular, as turbine technology advances, a demand for higher temperature thermal energy storage materials also grows. For this purpose, latent thermal energy storage fits in well since it uses phase change materials (PCMs) which generally have a higher energy density compared to their sensible heat counterparts. In the present study, a eutectic Na2CO3(41.69%)-(33.1%)KCl-(25.21%)NaCl phase change material (PCM) with a melting temperature of 569 degrees C was chosen as the storage material to experimentally assess the performance benefit of using a readily available stainless steel (ss304) wire mesh (as the periodic structure) to enhance heat transfer within the domain. In addition, for discharging, a numerical model was developed and compared with the experimental results. Furthermore, for discharging, a numerical investigation of the influence of the heat transfer fluid (HTF) flow-rate to the rate of heat transfer was performed. Overall, it was experimentally observed that the charging time for the composite case was shortened by about 35%, compared to the pure PCM case. For discharging, in the axial direction, the composite solidification time when compared to the pure PCM case was on average 10% shorter. Regarding the radial discharging performance of the composite, there was only about 5% improvement compared to the pure PCM case, which was expected due to the thermal contact resistance in the radial direction. Discharging experimental results were used to validate a discharging numerical model. Discharging results from the model showed that increasing the flow rate of the heat transfer fluid (HTF) reduced the time for solidification. It was observed that for the HTF flow rate of 5 L/min, 10 L/min, 20 L/min and 30 L/min, the discharge time was shortened by 23%, 30%, 33% and 35%, respectively.

Geopolymers (GP) are a class of X-ray amorphous, nanoporous, nanoparticulate materials that can be mixed, poured, and cured under ambient conditions. Typically, geopolymers are made using a Group 1 (G1) alkali activator such as sodium or potassium metasilicate and an aluminosilicate precursor. An analogous material to GPs is ordinary Portland cement because of the similarities in processing, however, the resulting microstructure is more similar to that of a glass. Geopolymers are more thermally stable than OPC and can therefore be used in a variety of thermal energy storage systems, as energy storage is an increasing global concern. In this study, potassium metakaolin-based geopolymer composites containing glass particles and alumina platelets were manufactured, heated in air, and exposed to molten sodium chloride or potassium chloride under an air atmosphere. Results showed the formation of an amorphous self-healing geopolymer composite (ASH-G) that could contain molten G1 chlorides for over 200 h without signs of macro or microscopic chemical degradation. The filling of cracks by glass particles in the composite after heating to 850 °C makes this material self-healing. It was found that the morphology of ASH-G composites was more affected by temperature and duration than contact with corrosive molten chlorides in air. Future works include investigating the effect of molten salt on mechanical properties during initial heating, after prolonged heating, and the material compatibility with other molten Group 1 chloride eutectics.

In this work, melting of a high-temperature inorganic phase change material (PCM) eutectic (with a melting point of 569 °C) within a vertical cylindrical tank has been experimentally investigated. To promote the heat transfer rate, a periodic structure that is constructed by a commercial SS-304 mesh screen has been considered and immersed into the PCM tank. Thermal characteristics of the PCM-periodic structure tank under different initial temperatures (450, 490 and 546 °C) and wall temperatures (620, 640, 660, 680 and 700 °C), are then investigated and reported. The presented experimental data can facilitate practical engineers to find the best operating condition of similar PCM tanks; meanwhile, it can also be employed for the investigation of thermal response of transient heat conduction before melting starts.

Fertilizers have been given significant attention due to their critical need for agriculture yield to meet the demand for food growth arising from population growth. The demand for potassium fertilizer (metric tons of K2O) has increased by 12% between 2015 and 2020. Therefore, the concern about the limited availability of soluble potassium resources in the southern hemisphere has become a key research focus for identifying alternative resources and technologies. This study presents a review of the fundamental knowledge of alternative technologies, such as acid leaching, hydrothermal and molten salt technology, as well as different alternative K-bearing silicate resources (ultrapotassic syenite, nepheline syenite, glauconitic sandstone and mica). Studies on fluxing agents proposed for the extraction of K+ based on different methods were analysed and compared. This paper offers a detailed overview of experimental kinetic analysis, kinetic and mechanism reactions, aims to improve the extraction technology and address relevant industry challenges. This review also reports on thermodynamic analysis of the mineral-salt/acid/alkaline systems, providing insights into the basis of industrial applications. Finally, the review provides opportunities and challenges of each technique and has shown that further techno-economic and process analysis are required to better identify the viability of each technique for large-scale industrial demonstration.

Abstract Geopolymer refers to a large group of nanoporous, nanoparticulate materials that are synthesized by dissolution and polycondensation of aluminosilicates in basic solutions and can be made from a variety of starting materials, such as industrial waste ash, volcanic rock, or calcined clay. Geopolymers are X‐ray amorphous, corrosion resistant, refractory, and made at ambient temperature and pressure similar to cements. In this study, potassium metakaolin‐based geopolymer (KGP) composites containing alumina platelets and glass frit were fabricated, and the impact of heating temperature, dwell time, and heating/cooling rate on the microstructure was studied. The composites, heat treated up to 900°C for up to 20 h using heating/cooling rates of up to 1°C/min, showed that the addition of alumina platelets prevented major microcracking and was also able to reduce linear shrinkage. Glass frit has been shown to heal microcracks formed during KGP dehydration and crystallization. The resulting material had an open porosity of less than 1% and a uniform surface glaze of 250 μm thickness, while Oswald ripening of round closed pores occurred due to the migration of molten glass in the system.

Characterization of an Amazonian, laterite-doped, kaolinitic soil (LK) or "lateritic soil" and laterite-doped metakaolin (LMK) calcined at two distinct rates, as well as granite-marble (GM) particulate industrial wastes was performed by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray fluorescence (XRF) spectrometry, and particle size and distribution analysis. In addition, an LMK geopolymer (GP) and a lateritic metakaolin-based GP reinforced with granite-marble composite (LMKGP-GM) were tested for water resistance and for mechanical strength. XRD and XRF were used to investigate the composition of the composite materials, while XRD confirmed the formation of GP. Just as in the case of highly reactive commercial metakaolin used in construction, according to this study, lateritic soil-based metakaolin presented similar characteristics. Therefore, it could be used in the development of more sustainable ceramics and construction materials, including the use of GM waste as a reinforcing phase/aggregate.

Potassium-based, geopolymer composites were made with BASF(R) metakaolin and Mymensingh clay-derived metakaolin from Bangladesh. Since the natural Mymensingh clay contained 40 wt.% quartz, this same amount of quartz particulates was added to the BASF(R) metakaolin to make a synthetic analog of the natural calcined clay. By analogy with bone china, bone ash or calcined hydroxyapatite (5CaO center dot 3P(2)O(5) or "HA") particles, having a Ca: P ratio of 3.3:1, were added to make the three types of geopolymer-based composites described above. For less refractory particulate additions, dicalcium phosphate (DCP) (2CaO center dot P2O5 or "DCP") particles, having a Ca: P ratio of 2:1, were also added to another set of geopolymers. The ambient temperature compressive and flexural strengths were measured for all of the geopolymer composites. The HA or DCP reinforced geopolymer composites were fabricated and heat-treated to 1150 degrees C/1 h, after which they were converted to their mineralogical analogs. Their mechanical properties of compressive and 3-point flexural strengths were again measured. Flexural strengths of 22.42 +/- 11.0 MPa and 31.97 +/- 8.3 MPa were measured in 1 x 1 x 10 cm(3) heat-treated geopolymer bars reinforced with 10 wt.% of DCP and in geopolymer reinforced with 10 wt.% DCP +40 wt.% quartz additions, respectively. Significant improvements to ambient temperature properties were observed due to the self-healing effect of the flowing amorphous DCP, whose presence was verified by SEM. The geopolymer samples exhibited reduced water absorption (WA) (on a percentage dry weight basis) of within 0.03-0.5% after being heated at 1100celcius/1 h and 1125celcius/1 h, as compared with those at room temperature, which varied between 2.56% and 7.89%.

This study focuses on calcined kaolin, commercial sodium silicate, and Amazonian bamboo to make geopolymer. The durability of geopolymer matrix (GP) and bamboo fiber geopolymer composite (GPBF) materials was analyzed by studying the resistance to the exposure to sulfuric and hydrochloric acids at concentrations from 0 to 15 wt%, testing two different geometry of samples. The microstructure of the raw and composite materials was investigated by X-ray fluorescence and scanning electron microscopy. Geopolymer formation was confirmed by X-ray diffraction with a characteristic amorphous hump at 28 degrees two theta and a few crystalline peaks of quartz. Visual appearance, mass change, and compressive strength behavior of all GP and GPBF samples immersed in 0, 5, 15 wt% of H2SO4 and HCl for 7, 28, and 112 days were investigated. GP and GPBF did not change in appearance, and no mass loss was observed in 0% acid (100% water) solution pH 12, an alkali solution due to partial dissolution of NaOH from the GP matrix, denoting durability in water. GP mass loss increased with varying sulfuric acid concentrations from 5, 10, and 15 wt%, resulting in values of 2.7%, 3.5%, and 4.4%, respectively. In general, the GP and GPBF specimens experienced higher compressive strength degradation when exposed to H2SO4 than to HCl. GP and GPBF can safely be applied as construction materials in applications exposed up to 15 wt% sulfuric or hydrochloric acid environments, including in sewage systems.

Geopolymer composites containing refractory, chopped basalt fibers and low-melting glass were made and systematically heat-treated at higher temperatures. Potassium-based geopolymer of stoichiometric composition K2O center dot Al2O3 center dot 4SiO(2)center dot 11H(2)O was produced by high shear mixing from fumed silica, deionized water, potassium hydroxide, (i.e., water glass) and metakaolin. With the addition of low-melting glass (T-m similar to 815 degrees C) the flexure strengths of the composites increased to similar to 6 MPa after heat treatment above 900 degrees C to 1100 degrees C. A Weibull statistical analysis was performed showing how the amorphous self-healing effect of the glass frit significantly improved the flexure strength of the geopolymer and ceramic composites after high-temperature exposure. At temperatures up to 900 degrees C, the geopolymer-basalt composite remained amorphous and the low-melting glass frit flowed into the dehydration cracks in the geopolymer matrix. This type of composite could be described as amorphous self-healed geopolymer (ASH-G). At similar to 1000 degrees C, the geopolymer converted to primarily a crystalline leucite ceramic, but the basalt fiber remained intact, and the melted glass frit flowed and sealed the cracks developed at that temperature. This type of composite could then be described as amorphous self-healed ceramic (ASH-C). A temperature of 1150 degrees C was determined to be optimum as at 1200 degrees C the basalt fibers melted and the strength of the reinforcement was lost in the composites. The amorphous self-healing effect of the glass frit significantly improved the room temperature flexure strength of the heat-treated geopolymer-based composites.

Moving into a carbon constrained world it is imperative that new forms of energy generation and storage are implemented to replace the fossil-fuel driven economy. Additionally, this dependence on fossil-fuels has generated large amounts of waste material (such as fly ash and black slag) which currently occupies large amounts of landfill area. Therefore, this current study investigated the thermal performance and stability of a waste-based alkali-activated material (AAM) for use as a high temperature storage material. Samples contained fly ash from a coal fire power plant, slag from an iron refinery, and commercially available sodium silicate solution. Thermo- and physical properties such as density and heat capacity were measured showing excellent properties as a storage material. Microstructure analysis by scanning electron microscopy, energy dispersive x-ray spectroscopy (SEM/EDS), and x-ray diffraction (XRD) was also conducted. Starting waste material indicated high concentrations of iron oxides, aluminosilicates, calcium hydrates, and minimal alkali activators such as sodium or potassium. A sodium silicate solution provided the necessary alkali activator. The thermal stability of this material was measured using a simultaneous thermal analyser (STA) indicating that the material is stable until 800 °C while the formation of aegirine, a mineral with thermal stability up to 990 °C, was found in the thermally cycled AAM suggesting this value could be higher. Lastly, the thermo- and physical properties, as well as the microstructure and thermal stability, of the material were reassessed after 50, 100, and 200 thermal cycles (635–800 °C) showing minimal weight loss and chemical change after the initial heating cycle. The desirable thermo- and physical properties coupled with excellent thermal stability and sample repeatability, indicate that this material could provide an option for high temperature thermal storage in the future.

Potassium-based geopolymer was fabricated at room temperature by high shear mixing of potassium metasilicate and metakaolin, forming a composition of K2O center dot Al2O3 center dot 4SiO(2)center dot 11H(2)O. Dolomite dust waste product was used as a particulate reinforcement to form composites containing 0, 20, 30 and 40 wt % dolomite (CaMg(CO3)(2)). The composites were heat treated at 400, 800 and 1,000 degrees C for 1 hour at a slow ramp rate of 1 degrees C/min. While single phase geopolymer exhibited 3-pt flexural strengths of similar to 7MPa, geopolymer composites containing 20 wt % dolomite and cured at room temperature achieved similar to 16 +/- 3.5 MPa. In general, strengths drastically decreased due to dehydration, but began to recover after 1000 degrees C heat treatments. Dolomite particulates helped to dissipate crack energy and enhanced flexural strengths. The geopolymer composites experienced increased porosity due to water loss at 400 degrees C and liberation of CO2 gas from carbonates at >= 800 degrees C.

Composites of phlogopite mica platelets of composition KMg3AlSi3O10(F,OH)(2) dispersed in potassium-based potassium geopolymer were fabricated. The platelet additions of up to 25 wt% were achieved which increased the flexure strength and thermal conductivity of pure potassium-based geopolymer. A maximum 3-point flexure strength at room temperature was measured as 11.4 MPa with a standard deviation of 0.34 MPa for 25 wt% mica additions. Heat treatments caused chemical decomposition and water loss at temperatures up to 700 degrees C and eventual formation of glassy and crystalline leucite at 1000 degrees C. A maximum post-treatment strength of 10.7 MPa with a standard deviation of 0.52 MPa was obtained for the 1000 degrees C heat-treated samples. The thermal conductivity increased from 0.24 +/- 0.000 W/mK for pure K-based geopolymer to 0.30 +/- 0.008 W/mK, as a function of mica platelet additions up to 10 wt %.

Clay-based ceramics are used in a wide variety of applications and could benefit from the addition of a reinforcing fiber. Basalt fibers are similar to glass fibers in regards to their relatively high strength and low cost, but they have an additional advantage of improved refractory properties. The clay used was based on a powder mixture of (by weight) 45% Kentucky ball clay, 40% talc, and 15% Georgia kaolin. This powder was mixed with 28% of its own weight of 0.1 M sodium carbonate solution (for formability) and up to 20% (cumulative weight) of discontinuous basalt fibers. The basalt fibers used had a 14 mu m diameter and were either chopped (6 min long) or milled (similar to 150 mu m long). The samples were hand-formed into 1x1x10 cm bars using plastic molds. Bars were fired to temperatures ranging from 850 to 1250 degrees C for 2 hours. The addition of the chopped basalt caused warping after firing, and so was not studied further. It was concluded that chopped fibers should only be used if their orientation can be controlled. The addition of milled basalt fibers improved strength at all temperatures (up to about 40% higher strength) except for the 1250 degrees C firing where the basalt-reinforced samples melted. After firing to 1050 degrees C, there was a clear distinction between fiber and matrix when viewed with electron microscopy/spectroscopy, but this was not seen for the 1150 degrees C fired samples. This work demonstrates that milled basalt fibers may be used as a cost-effective reinforcement for clay-based ceramics.