Looking back to guide us on how to move forward for geopolymers

Making geopolymers and alkali activated materials with specific properties requires skill and a thorough understanding of the process. The trial and error approach used by many researchers may result in an acceptable product but there is little or no understanding of why it worked and how to improve or optimise the product. It also leaves potential producers without quality control of feedstock hence limited quality assurance on product. This presentation will look back at how the geopolymer group at Curtin University improved its understanding of geopolymer technology via development of XRD, SEM and related analytical techniques. Examples on how geopolymers were made with very high compressive strength on one hand and on the other hand with impressive fire resistance will be described. However, this is not the end of the story. Ultimately the goal is to commercialise geopolymers and for this to happen we must conduct rigorous life cycle analysis and embodied energy assessments to be confident that these materials are competitive and sustainable. One way to ensure low embodied energy is to explore alternate activators and sources of alumina and silica. When alternate precursors such as Bayer liquor have been used to manufacture geopolymers they prove to have a very low embodied energy and are potentially less expensive. The use of Bayer liquor for geopolymers will be described in detail and examples provided on how this approach may be viewed as a way forward for the field of geopolymers for specific products

In situ elevated temperature testing of fly ash based geopolymer composites

In situ elevated temperature investigations using fly ash based geopolymers filled with alumina aggregate were undertaken. Compressive strength and short term creep tests were carried out to determine the onset temperature of viscous flow. Fire testing using the standard cellulose curve was performed. Applying a load to the specimen as the temperature increased reduced the temperature at which viscous flow occurred (compared to test methods with no applied stress). Compressive strength increased at the elevated temperature and is attributed to viscous flow and sintering forming a more compact microstructure. The addition of alumina aggregate and reduction of water content reduced the thermal conductivity. This led to the earlier onset and shorter dehydration plateau duration times. However, crack formation was reduced and is attributed to smaller thermal gradients across the fire test specimen

The first 20 hours of geopolymerization: An in situ WAXS study of flyash-based geopolymers

This study followed the first 20 h of flyash geopolymerization at 70 °C using time resolved Wide Angle X-ray Scattering (WAXS). The extent of dissolution of the amorphous phase of the flyash was determined to range from 29% to 54% for the different formulations trialed. The dissolution rate of the flyash significantly reduced after the first 5 h for all samples. During the formation stage of the geopolymer there were significant temporal variations in the chemistry of the dissolved solution due to the rate of flyash dissolution, with a relative standard deviation of 20%, 57% and 24% for the Si/Al, Na/Al and H/Si ratios, respectively. Utilizing the Power Law, scattering in the low angle region of the WAXS pattern combined with the geopolymer peak area yielded a measure which correlated with the compressive strength-providing a new method to measure the flyash dissolution and geopolymer formation processes independently. The evolution of several zeolite-like phases was followed, noting there are different formation mechanisms involved even within the same sample. Four samples were examined with compressive strengths ranging from 14(2)-50(9) MPa, each was synthesized with flyash from Collie Power Station (Western Australia) activated with sodium silicate solution of varying concentrations

Quantitative analysis of turbostratically disordered nontronite with a supercell model calibrated by the PONKCS method

Two calibration-based quantitative X-ray diffraction (XRD) models for turbostratically disordered Bulong nontronite, the PONKCS (partial or no known crystal structure) approach and the supercell structural model, were compared in terms of the accuracy and refinement error from Rietveld quantitative phase analysis. The PONKCS approach achieved improved nontronite quantitative results with synchrotron diffraction patterns compared with those achieved with laboratory XRD data as a result of better data quality and the use of Debye–Scherrer geometry with significantly reduced preferred orientation effects. The introduction of a peak shape modifier (spherical harmonics) to correct the quantification result is mainly useful for laboratory XRD patterns containing nontronite collected from Bragg–Brentano geometrywith appreciable preferred orientation effects. A novel calibration approach for the nontronite supercell model was developed, based on the Rietveld quantitative formula in the TOPAS symbolic computation system. The calibrated supercell model achieved better accuracy (deviation within 1 wt%) and lower refinement error than the PONKCS approach because the physically based description of turbostratic disorder requires fewer refinable parameters than the PONKCS approach. The drawbacks and limitations of the supercell approach are also discussed

A comparison between different foaming methods for the synthesis of light weight geopolymers

Foaming to reduce the density of geopolymeric materials is increasingly being reported in the literature as it has been shown to be effective in improving their insulating properties. However, there is no consistency in foaming methods and as such this study was performed to compare methods in order to better understand their effect on the properties of geopolymers. A surfactant and two chemical foaming agents (hydrogen peroxide and aluminium powder) were added to a fly ash based geopolymer matrix. Surfactant was also combined with each of the chemical foaming agents in order to stabilise the foam in the geopolymer matrix and to reduce coarse pores. The physical, mechanical and microstructural properties of the low density geopolymers are presented and the effects of the foaming agents’ characteristics on the hardened product is discussed, as well as the relative merits of the different procedures to synthesise the foamed geopolymer. It was found that homogeneous microstructures with small pores can be obtained by adding surfactant and hydrogen peroxide. The combination of hydrogen peroxide (0.1 wt%) and surfactant (1.0 wt%) produced geopolymer foams with density and compressive strength values of 0.94 g/cm3 and 4.6 MPa, respectively

Nanoscale gold clusters in arsenopyrite controlled by growth rate not concentration: Evidence from atom probe microscopy

Auriferous sulfides, most notably pyrite (FeS2) and arsenopyrite (FeAsS), are among the most important economic minerals on Earth because they can host large quantities of gold in many of the world's major gold deposits. Here we present the first atom probe study of gold distribution in arsenopyrite to characterize the three-dimensional (3D) distribution of gold at the nanoscale and provide data to discriminate among competing models for gold incorporation in refractory ores. In contrast to models that link gold distribution to gold concentration, gold incorporation in arsenopyrite is shown to be controlled by the rate of crystal growth, with slow growth rate promoting the formation of gold clusters and rapid growth rate leading to homogeneous gold distribution. This study yields new information on the controls of gold distribution and incorporation in sulfides that has important implications for ore deposit formation. More broadly this study reveals new information about crystal-fluid interface dynamics that determine trace element incorporation into growing mineral phases

Optimising ambient setting Bayer derived fly ash geopolymers

The Bayer process utilises high concentrations of caustic and elevated temperature to liberate alumina from bauxite, for the production of aluminium and other chemicals. Within Australia, this process results in 40 million tonnes of mineral residues (Red mud) each year. Over the same period, the energy production sector will produce 14 million tonnes of coal combustion products (Fly ash). Both industrial residues require impoundment storage, yet combining some of these components can produce geopolymers, an alternative to cement. Geopolymers derived from Bayer liquor and fly ash have been made successfully with a compressive strength in excess of 40 MPa after oven curing. However, any product from these industries would require large volume applications with robust operational conditions to maximise utilisation. To facilitate potential unconfined large-scale production, Bayer derived fly ash geopolymers have been optimised to achieve ambient curing. Fly ash from two different power stations have been successfully trialled showing the versatility of the Bayer liquor-ash combination for making geopolymers

Benefits of sealed-curing on compressive strength of fly ash-based geopolymers

There is no standardized procedure for producing geopolymers; therefore, many researchers develop their own procedures for mixing and curing to achieve good workability and strength development. The curing scheme adopted is important in achieving maximum performance of resultant geopolymers. In this study, we evaluated the impact of sealed and unsealed curing on mechanical strength of geopolymers. Fly ash-based geopolymers cured in sealed and unsealed moulds clearly revealed that retention of water during curing resulted in superior strength development. The average compressive strength of sealed-cured geopolymers measured after 1 day of curing was a modest 50 MPa, while after 7 day curing the average compressive strength increased to 120~135 MPa. In the unsealed specimens the average compressive strength of geopolymers was lower; ranging from 60 to 90 MPa with a slight increase as the curing period increased. Microcracking caused by dehydration is postulated to cause the strength decrease in the unsealed cured samples. These results show that water is a crucial component for the evolution of high strength three-dimensional cross-linked networks in geopolymers

Individual particle morphology, coatings, and impurities of black carbon aerosols in Antarctic ice and tropical rainfall

© 2016 American Geophysical Union. All Rights Reserved. Black carbon (BC) aerosols are a large source of climate warming, impact atmospheric chemistry, and are implicated in large-scale changes in atmospheric circulation. Inventories of BC emissions suggest significant changes in the global BC aerosol distribution due to human activity. However, little is known regarding BC's atmospheric distribution or aged particle characteristics before the twentieth century. Here we investigate the prevalence and structural properties of BC particles in Antarctic ice cores from 1759, 1838, and 1930 Common Era (C.E.) using transmission electron microscopy and energy-dispersive X-ray spectroscopy. The study revealed an unexpected diversity in particle morphology, insoluble coatings, and association with metals. In addition to conventionally occurring BC aggregates, we observed single BC monomers, complex aggregates with internally, and externally mixed metal and mineral impurities, tar balls, and organonitrogen coatings. The results of the study show BC particles in the remote Antarctic atmosphere exhibit complexity that is unaccounted for in atmospheric models of BC