Arie van Riessen

Fly ash based geopolymer thin coatings on metal substrates and its thermal evaluation

Class F fly ash based Na-geopolymer formulations have been applied as fire resistant coatings on steel. The main variables for the coating formulations were Si: Al molar and water: cement weight ratios. We have determined that the adhesive strength of the coatings strongly depend on geopolymer composition. The ease with which geopolymer can be applied onto metal surfaces and the resultant thickness depend on the water content of the formulation. Adhesive strengths of greater than 3.5 MPa have been achieved on mild steel surfaces for compositions with Si:Al of 3.5. Microstructure evolution and thermal properties of the optimised coating formulations show that they have very promising fire resistant characteristics.

Intracrystalline Proteins and Urolithiasis: A Synchrotron X‐ray Diffraction Study of Calcium Oxalate Monohydrate

The existence of intracrystalline proteins and amino acids in calcium oxalate monohydrate was demonstrated by X‐ray synchrotron diffraction studies. Their presence has implications for the destruction of calcium oxalate crystals formed in the urinary tract and the prevention of kidney stones.

Determination of amorphous phase levels in Portland cement clinker

The existence of glass or amorphous component in Portland cement clinker has been questioned for a long time. However, besides the crystalline phases, there are reports in the literature of noncrystalline material in cement clinker, which is considered to be the residue of the melt that has failed to crystallize. Absolute phase abundances were determined in this study by Rietveld refinements with laboratory X-ray data, using both internal and external phase composition standards. The results clearly demonstrate the existence of an amorphous component in Portland cement clinker. The presence of an amorphous component was also apparent from diffraction data for clinker from which the silicate phases had been chemically removed, using both laboratory X-ray and synchrotron radiation patterns.

Impact of activator type on the immobilisation of lead in fly ash-based geopolymer.

Immobilisation of heavy metals in geopolymers has attracted attention as a potential means of treating toxic wastes. Lead is known to be effectively immobilised in a geopolymer matrix, but detailed explanation for the mechanisms involved and the specific chemical form of lead are not fully understood. To reveal the effect of the activator types on the immobilisation of lead in geopolymers, 0.5 and 1.0wt% lead in the form of lead nitrate was mixed with fly ash and alkaline activators. Different alkaline activators (either combined sodium hydroxide and sodium silicate or sodium aluminate) were used to achieve the target Si:Al ratios 2.0 and 5.0 in geopolymers. Zeolite was formed in aluminate-activated geopolymers having a Si:Al ratio of 2.0, but the zeolite crystallization was suppressed as lead content increased. No specific crystalline phase of lead was detected by X-ray diffraction, electron diffraction or FT-IR spectrometry. In fact, double Cs corrected TEM analysis revealed that lead was evenly distributed with no evidence of formation of a specific lead compound. A sequential extraction procedure for fractionation of lead showed that lead did not exist as an exchangeable ion in geopolymers, regardless of activator type used. Aluminate activation is shown to be superior in the immobilisation of lead because about 99% of extracted lead existed in the oxidizing and residual fractions.

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

Abstract 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.

Quantitative X-ray diffraction phase analysis of poorly ordered nontronite clay in nickel laterites

Studies of the extraction of nickel from low-grade laterite ores require a much better quantitative understanding of the poorly ordered mineral phases present, including turbostratically disordered nontronite. Whole pattern refinements with nontronite X-ray diffraction data from a Western Australian nickel deposit (Bulong) using a nontronite lattice model (Pawley phase) with two space groups (P3 and C2/m) and a peaks phase group model were performed to improve the accuracy of quantitative X-ray diffraction of nickel laterite ore samples. Modifications were applied when building the new models to accommodate asymmetric peak shape and anisotropic peak broadening due to the turbostratic disorder. Spherical harmonics were used as convolution factors to represent anisotropic crystal size and strain and asymmetric peak shape when using the lattice model. A peaks phase group model was also developed to fit the anisotropic peak broadening in the nontronite pattern. The quantitative results of the new Pawley phase and peaks phase group models were compared and verified with synthetic mixtures of nontronite, quartz and goethite simulating various West Australian laterite ore compositions. The models developed in this paper demonstrate adequate accuracy for quantification of nontronite in the synthesized reference materials and should be generally applicable to quantitative phase analysis of nontronite in nickel laterite ore samples.

Thermal Properties of Geopolymers

The physics and testing methodology of thermal properties are introduced prior to a review of OPC and geopolymer thermal properties. The amorphous inorganic structure of the geopolymers lends itself to good thermal resistance which leads to potential applications such as thermal insulation. Thermal expansion can generate destructive internal stresses when structural parts are heated and restrained from moving. The thermal expansion measuring techniques commonly utilised are dilatometry, interferometry and thermomechanical analysis (TMA). Thermal expansion measurements of metakaolin and fly ash based geopolymers show several distinct regions as the temperature increases. The extent of these regions varies from system to system and the changes are attributed to dehydration, dehydroxylation, densification and crystallisation. Fillers and aggregates can be added to geopolymers to reduce the thermal expansion of the composite and extend the usable temperature range. Thermal conductivity determination is required to assess geopolymers’ suitability for potential applications in thermal barriers and construction structural members. The two approaches to measuring thermal conductivity: steady state and transient (non-steady state) techniques are compared. The microstructure of geopolymer profoundly influences thermal conductivity; particularly porosity which if increased leads to a reduction in thermal conductivity. The addition of aggregate influences the thermal conductivity of OPC and geopolymer concrete and at the same time decreases thermal durability due to mismatch of thermal conductivity between aggregate and matrix. Some geopolymers with low initial strength have been shown to gain strength after exposure to high temperatures. It has been hypothesised that unreacted precursor levels can convert to geopolymer at high temperature and increase the strength. Once again the importance of the geopolymer microstructure is highlighted.

Mineralogy of Al-substituted goethites

The structural models of three synthetic Al-substituted goethite specimens have been refined from the neutron data, including crystallographic determinations of the Al levels and H positions. The d-I data were calculated for the final models. A relationship between the c unit cell parameter and Al content has been extended to the entire goethite-diaspore solid-solution system, which makes the regression equation procedure simpler and more accurate. A second prospective H site could not be confirmed because of the quality of existing neutron data. However, it is hoped that a further neutron powder diffraction study of a synthetic, fully deuterated goethite material may allow the existence of the site to be demonstrated.

Other Potential Applications for Alkali-Activated Materials

The focus of this chapter is the discussion of a variety of niche applications (other than as a large-scale civil infrastructure material) in which alkali-activated binders and concretes have shown potential for commercial-scale development. The majority of these applications have not yet seen large-scale AAM utilisation, except as noted in the various sections of the chapter. However, there have been at least pilot-scale or demonstration projects in each of the areas listed, and each provides scope for future development and potentially profitable advances in science and technology. In addition to the applications specifically discussed in this chapter, there are also commercial and academic developments in alkali-activation for specific applications including a commercial product which is being marketed as a domestic tiling grout showing some self-cleaning properties [1], as well as alkali-activated metakaolin binders as a vehicle for controlled-release drug delivery [2, 3]. Although undoubtedly promising and of commercial interest, these are rather specialised applications, and so the focus of this chapter is instead on broader categories of research and development rather than in providing detailed analysis of specific products. The areas to be discussed will include lightweight materials, well cements, fire-resistant materials, and fibre-reinforced composites.

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.