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Simon Clark

Macquarie University, School of Engineering in the Faculty of Science and Engineering, Faculty Member

Macquarie University, Department of Earth and Planetary Sciences, Faculty Member

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I am a highly successful scientific leader with an international focus who has bridged academe and national laboratories throughout my career. I am widely recognized for my expertise in developing and strengthening collaborative research programs around the world.Since 2012 I have been at Macquarie University, Sydney, where I have contributed through a number of roles including Deputy Head of the Department of Earth and Planetary Sciences, leading the successful bid for the cooperative research centre SmartCrete CRC and helping to establish a new Civil Engineering program.My specialties include: leading community research initiatives, managing major research facility developments, collaborative research, Earth science, materials engineering, synchrotron, and neutron scattering and imaging, high-pressure science and technology, cement and concrete research.

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Papers by Simon Clark

The Kinetics of Aragonite Formation from Solution via Amorphous Calcium Carbonate

Nanomaterials

Magnesium doped Amorphous Calcium Carbonate was synthesised from precursor solutions containing v... more Magnesium doped Amorphous Calcium Carbonate was synthesised from precursor solutions containing varying amounts of calcium, magnesium, H2O and D2O. The Mg/Ca ratio in the resultant Amorphous Calcium Carbonate was found to vary linearly with the Mg/Ca ratio in the precursor solution. All samples crystallised as aragonite. No Mg was found in the final aragonite crystals. Changes in the Mg to Ca ratio were found to only marginally effect nucleation rates but strongly effect crystal growth rates. These results are consistent with a dissolution-reprecipitation model for aragonite formation via an Amorphous Calcium Carbonate intermediate.

format_quoteStudy showed a linear correlation in Mg/Ca ratios between ACC and precursor solutions with a distribution coefficient of 0.12.format_quote

The nano- and meso-scale structure of amorphous calcium carbonate

Scientific Reports

Understanding the underlying processes of biomineralization is crucial to a range of disciplines ... more Understanding the underlying processes of biomineralization is crucial to a range of disciplines allowing us to quantify the effects of climate change on marine organisms, decipher the details of paleoclimate records and advance the development of biomimetic materials. Many biological minerals form via intermediate amorphous phases, which are hard to characterize due to their transient nature and a lack of long-range order. Here, using Monte Carlo simulations constrained by X-ray and neutron scattering data together with model building, we demonstrate a method for determining the structure of these intermediates with a study of amorphous calcium carbonate (ACC) which is a precursor in the bio-formation of crystalline calcium carbonates. We find that ACC consists of highly ordered anhydrous nano-domains of approx. 2 nm that can be described as nanocrystalline. These nano-domains are held together by an interstitial net-like matrix of water molecules which generate, on the mesoscale, ...

Axial ratio anomalies and electronic topological transitions in Cd0.80Hg0.20 at high pressures

Journal of Physics and Chemistry of Solids, 2008

High-pressure angle-dispersive X-ray diffraction measurements show that Cd 0.80 Hg 0.20 alloy rem... more High-pressure angle-dispersive X-ray diffraction measurements show that Cd 0.80 Hg 0.20 alloy remains in the hcp structure up to 50 GPa. We observe subtle anomalies in the pressure variation of the lattice parameters and their ratio, and in normalized stress versus strain. Electronic-structure calculations, as well as experimental and theoretical results for Cd, suggest that these anomalies are related to the occurrence of electronic topological transitions. Our results support Lifshitz's prediction that electronic phase transitions can cause anomalies in structural and elastic properties of materials.

High-pressure behavior of osmium: An analog for iron in Earth’s core

Journal of Applied Physics, 2012

ABSTRACT High-resolution x-ray diffraction with diamond-anvil cells, using argon as a quasi-hydro... more ABSTRACT High-resolution x-ray diffraction with diamond-anvil cells, using argon as a quasi-hydrostatic pressure medium, documents the crystal structure and equation of state of osmium to over 60 GPa at room temperature. We find the zero-pressure bulk modulus in fair agreement with other experiments as well as with relativistic electronic band-structure calculations: Osmium is the densest but not the most incompressible element at ambient conditions. We also find no evidence for anomalies in the ratio of unit-cell parameters, c/a, or in the compressibility of osmium as a function of pressure. This is in agreement with other experiments and quantum mechanical calculations but disagrees with recent claims that the electronic structure and equation of state of osmium exhibit anomalies at pressures of similar to 15-25 GPa; the discrepancies are may be due to the effects of texturing. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4726203]

Effect of pressure on the crystal structure of ettringite

Cement and Concrete Research, 2008

X-ray diffraction and infrared data have been collected from a sample of ettringite from ambient ... more X-ray diffraction and infrared data have been collected from a sample of ettringite from ambient pressure to 6.4 GPa. The sample was found to reversibly transform to an amorphous phase at 3 GPa. The isothermal bulk modulus of ettringite was found to be 27(7) GPa and the incompressibilities of the lattice parameters were found to be 71(30) GPa along a and 108(36) GPa along c.

High-Pressure Elasticity and Stability of Osmium: An Analog for Iron in Earth's Core

ABSTRACT Osmium - a hexagonal close-packed (hcp) transition metal - is an analog for iron at high... more ABSTRACT Osmium - a hexagonal close-packed (hcp) transition metal - is an analog for iron at high pressures, and provides key information about the properties of the metal alloy making up Earth&#39;s core. High-resolution x-ray diffraction with diamond-anvil cells, using synchrotron-based angular-dispersive methods and argon as a quasi-hydrostatic pressure medium, documents the crystal structure and equation of state of Os to 65 GPa at room temperature. We confirm that the zero-pressure bulk modulus is 405 (± 8) GPa, in agreement with other experiments as well as with theoretical electronic band-structure calculations: osmium is the densest but not the most incompressible element at ambient conditions. We find no evidence for anomalies in the ratio of unit-cell parameters, c/a, or in the compressibility of Os as a function of pressure. This is in agreement with other experiments and quantum mechanical calculations, but disagrees with recent claims that the structure or equation of state of osmium exhibit anomalies at pressures of ~ 15-25 GPa; the discrepancies are apparently due to spurious effects of non-hydrostaticity. The stability of hcp Os is similar to that of hcp Fe, suggesting that a systematic characterization of analog metals at high pressures may clarify the properties of Earth&#39;s core despite uncertainties in its chemical composition.

Structural Phase Transitions in AuIn2 at High Pressure

ABSTRACT

White phosphorous: the equation of state and pressure-induced transitions

Acta Crystallographica Section A Foundations of Crystallography, 2005

Thermal equations of state for B1 and B2 KCl

American Mineralogist, 2002

Compressibility of solids generally drops as compression proceeds. Bonds shorten and stiffen with... more Compressibility of solids generally drops as compression proceeds. Bonds shorten and stiffen with density increase in the same structure. However for the B1-B2 phase transition in many measured alkali halides, bond lengths increase in going to the denser phase. And IR mode frequencies decrease (Hofmeister 1997), leading to the counter-intuitive expectation that compressibility should increase in going to the denser B2 phase. Past volume measurements have been equivocal at best in recognizing any such compressibility increase. New thermal equations of state for B1 and B2 KCl from in-situ X-ray diffraction measurements of phase volumes on Station 16.4 of the CLRC Daresbury Laboratory are no less equivocal about the issue of whether compressibility increases or decreases across the transition. In contrast, the new volume measurements show an easily resolved thermal expansion increase in going from B1 to B2 KCl. The product a•K, which is better known than either a or K, increases from 0.0195 ± 0.0005 kbar/∞C in B1 to 0.0275 ± 0.0009 kbar/∞C in B2 KCl. Yagi (1978) demonstrated a similar increase for KF, also supported mainly by increases in a. This increase can also be seen in RbCl (Walker et al. 2001). Bond weakening indicated by the thermal expansion increase is consistent with the elusive compressibility increase that is expected across the B1-B2 transition but which is not resolved from volume measurements. The thermal effects are more visible than the compressional effects on a•K across the transition. Bond tightening upon decompression reduces a, increases solid viscosity, and hence decreases the Rayleigh number. An upwelling of material undergoing a decompression phase change with decrease of coordination number may have its convective friskiness damped at such a transition.

The melting curve of FeSi to 150 GPa: Implications for D

The FeSi phase diagram to 150 GPa

Journal of Geophysical Research, 2010

The melting curve of FeSi has been determined to 150 GPa in the laser-heated diamond anvil cell (... more The melting curve of FeSi has been determined to 150 GPa in the laser-heated diamond anvil cell (LH-DAC) on the basis of discontinuities in the power versus temperature function. A multianvil experimental cross-check at 12 GPa using textural criteria as a proxy for melting is in good agreement with our LH-DAC results. The melting point of FeSi reaches ∼4000 K at the core mantle boundary and an extrapolated value of 4900 K at the inner-core boundary (ICB). We also present the melting curve as determined by the Lindemann melting law; this agrees well with our experimental curve to 70 GPa and then diverges to higher temperatures, reaching 6200 K at the ICB. These temperatures are substantially higher than previous LH-DAC determinations. The boundary of the "-FeSi → CsCl-FeSi subsolidus transition has also been determined by synchrotron-based X-ray diffraction at high pressures, and the results confirm a negative Clapeyron slope for the transition. We conclude that if present, FeSi is likely to be solid within the D″ layer and is unlikely to be present within the inner core for any plausible bulk core silicon content.

High-pressure phase transitions and equations of state in NiSi. I.Ab initiosimulations

Journal of Applied Crystallography, 2012

First-principles calculations have been used to determine the equation of state and structural pr... more First-principles calculations have been used to determine the equation of state and structural properties of NiSi up to pressures equivalent to that in the Earth's inner core. At atmospheric pressure, the thermodynamically stable phase is that with the MnP structure (as found experimentally). At high pressures, NiSi shows phase transformations to a number of high-pressure polymorphs. For pressures greater than ∼250 GPa, the thermodynamically stable phase of NiSi is that with the CsCl structure, which persists to the highest pressures simulated (∼500 GPa). At the pressures of the Earth's inner core, therefore, NiSi and FeSi will be isostructural and thus are likely to form a solid solution. The density contrast between NiSi and FeSi at inner-core pressures is ∼6%, with NiSi being the denser phase. Therefore, if a CsCl-structured (Fe,Ni)Si alloy were present in the inner core, its density (for the commonly assumed nickel content) might be expected to be ∼1% greater than that o...

X-ray absorption contrast images of binary chemical reactions

Chemical Geology, 2009

Low-divergence synchrotron-sourced X-rays enable a radiographic imaging scheme for full character... more Low-divergence synchrotron-sourced X-rays enable a radiographic imaging scheme for full characterization of binary chemical reactions and characterization by type of more complex reactions, in situ, in diamond anvil cells (DAC). Spatially resolved reactants are induced to react by laser heating of their interface. The spatially intermediate products are observed through X-ray absorption contrast. Limits to the technique include the ability to maintain controlled experiment geometry during compression and the ability to resolve chemical differences between reactants and products by X-ray absorption. The ability to make in situ observations at experimental pressure and temperature obviates the problem with quenching techniques for capturing liquid compositions in experiments with dimensions smaller than the diffusion length during quenching time. Partially molten Fe-alloy systems, of poor quenchability, are examined at DAC pressures and temperatures for relevance to Earth's core constitution and evolution. Determinations of eutectic melting in Fe-FeS match known results. Of the probable light elements that may alloy with Fe in the Earth's liquid outer core, Fe-FeS experiments show only modest quenching problems, but C and Si alloy experiments are highly vulnerable to quenching artifacts. The observed reactivity of FeS, Fe3C, FeSi, and FeO(OH) with Fe in DAC makes the observed non-reactivity between Fe and FeO more significant, reducing the probability that oxygen alone is the major alloy in Earth's molten outer core.

Compression mechanisms in quasimolecularXI3 (X=As,Sb,Bi)solids

Physical Review B, 1998

We explore the structural, vibrational, and electronic properties of a prototypical family of qua... more We explore the structural, vibrational, and electronic properties of a prototypical family of quasimolecular layered solid of the type XI 3 where (XϭAs,Sb,Bi) under compression. We use a combination of angledispersive powder x-ray diffraction and Raman spectroscopy to study the structural and vibrational response to pressure. We also perform first-principles density functional pseudopotential calculations using both the local density approximation and gradient-corrected techniques for the description of electron exchange and correlation to further examine the electronic properties under pressure. We find that an unusual nonmonotonic variation of the symmetric X-I stretch frequency can be unambiguously attributed to the formation of intermolecular bonds and that compression results in a sequence of transitions from hexagonal molecular to hexagonal layered to monoclinic. The pressure dependence of the ambient pressure hexagonal structure is given as a full structural determination of the high-pressure phase. The structural and vibrational response ͑including the complex pressure dependence of the bond-stretch frequency͒ is well accounted for by quantum mechanical simulation. We further find that gradient corrections are necessary for an appropriate description of equilibrium structure, bonding, vibrational properties, and compression mechanisms and that the local density approximation appears to fail badly. ͓S0163-1829͑98͒07445-1͔

Preparation of Self-healing Additives for Concrete via Miniemulsion Polymerization: Formulation and Production Challenges

International Journal of Concrete Structures and Materials

Concrete structures undergo internal damage; this usually starts at the atomic level with defects... more Concrete structures undergo internal damage; this usually starts at the atomic level with defects that then grow and form cracks, which can propagate through the material. Here, a method of preparation of poly(methyl methacrylate) (PMMA) nanocapsules adhesive system via miniemulsion polymerization technique is reported, where MMA + DMA (resin + accelerator) and BPO (hardener) components are separately encapsulated by PMMA shells. The crack-healing potential of these nanocapsules was then investigated by embedding them into the mortar matrix. The prepared PMMA core–shell self-healing nanostructures survived the mixing and hardening processes, and the hardened mortar alkaline environment. The stress fields associated with propagating cracks (load‐induced cracking) broke the brittle/weak inert shell of these core–shell structures, resulted in releasing the healing agents to bridge the nascent and early-stage fractures (

Corrosion Inhibitory Effects of Mullite in Concrete Exposed to Sulfuric Acid Attack

Corrosion and Materials Degradation

Prolonged exposure to low pH conditions affects the durability of concrete. In this work, the eff... more Prolonged exposure to low pH conditions affects the durability of concrete. In this work, the effect of mullite, aluminum silicate, on the strength and the acid corrosion of mortar and concrete under induced accelerated conditions in sulfuric acid solutions at pH of 0.25 and 1 was studied. The characterization of physicochemical changes was performed using techniques including compressive strength, scanning electron microscopy, micro-X-ray fluorescence spectrometry, and the Vickers hardness test. The results indicate that the addition of mullite does not have any significant effect on the overall strength of mortar and concrete samples, while it significantly increases their resistance to corrosion caused by sulfate attack by 90%, therefore, it is expected to increase the life span and decrease the maintenance costs of concrete pipes subjected to acid corrosion in sewer environments. The inhibition efficiency is observed to be sensitive to acid concentration and was improved with in...

format_quoteNo significant strength improvement was observed with 5% and 10% mullite due to excess water and lack of superplasticizers.format_quote

Detection of Gaps in Concrete–Metal Composite Structures Based on the Feature Extraction Method Using Piezoelectric Transducers

Sensors

A feature extraction methodology based on lamb waves is developed for the non-invasive detection ... more A feature extraction methodology based on lamb waves is developed for the non-invasive detection and prediction of the gap in concrete–metal composite structures, such as concrete-filled steel tubes. A popular feature extraction method, partial least squares regression, is utilised to predict the gaps. The data is collected using the piezoelectric transducers attached to the external surface of the metal of the composite structure. A piezoelectric actuator generates a sine burst signal, which propagates along the metal and is received by a piezoelectric sensor. The partial least squares regression is performed on the raw sensor signal to extract features and to determine the relationship between the signal and the gap size, which is then used to predict the gaps. The applicability of the developed system is tested on two concrete-metal composite specimens. The first specimen consisted of an aluminium plate and the second specimen consisted of a steel plate. This technique is able to...

format_quoteThe first loading vector captured 300% more damage information than undamaged cases, indicating its significance in predictions.format_quote

Halite-sylvite thermoelasticity

Unit-cell volumes of four single-phase intermediate halite-sylvite solid solutions have been meas... more

A Kinetic of the B1B2 Phase Transition of Rubidium Iodide as a Function of Pressure

Materials Science Forum

The kinetics of the pressure-induced B1-B2 phase transformation of Rbl have been studied under hy... more

The effect of various nucleating agents upon the crystallisation of cordierite glass cermaic

Acta Crystallographica Section A Foundations of Crystallography