The Kinetics of Aragonite Formation from Solution via Amorphous Calcium Carbonate.

Magnesium doped Amorphous Calcium Carbonate was synthesised from precursor solutions containing varying amounts of calcium, magnesium, HO and DO. 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.

Assessment of Alkali-Silica Reaction Potential in Aggregates from Iran and Australia Using Thin-Section Petrography and Expansion Testing.

The alkali-silica reaction can shorten concrete life due to expansive pressure build-up caused by reaction by-products, resulting in cracking. Understanding the role of the aggregate, as the main reactive component, is essential for understanding the underlying mechanisms of the alkali-silica reaction and thereby reducing, or even preventing, any potential damage. The present study aims to investigate the role of petrographic studies along with accelerated tests in predicting and determining the potential reactivity of aggregates, including granite, rhyodacite, limestone, and dolomite, with different geological characteristics in concrete.

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

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.

Determining the water content of nominally anhydrous minerals at the nanometre scale.

The amount and distribution of water in nominally anhydrous minerals (NAMs) are usually determined by Fourier-transform infrared spectroscopy. This method is limited by the spot size of the beam to the study of samples with dimensions greater than a few micrometers. Here, we demonstrate the potential of using photoinduced force microscopy for the measurement of water in NAMs with samples sizes down to the nanometer scale with a study of water concentration across grain boundaries in forsterite.

Characterizing concrete corrosion below sewer tidal levels at chemically dosed locations.

Unexplainable concrete softening below the water line has been observed by Sydney Water in their gravity sewer network, some of which is subjected to corrosion control methods using chemical ferrous chloride (FeCl) dosing of the wastewater. We applied a combination of physical and chemical tools to determine the properties of the top 20 mm of concrete cores recovered from sewer pipes. These techniques consist of neutron tomographic imaging, scanning electron microscopy, hardness mapping, and pH profiling.

Unravelling the mechanism of pressure induced polyamorphic transition in an inorganic molecular glass.

The atomic structure of a germanium doped phosphorous selenide glass of composition GePSe is determined as a function of pressure from ambient to 24 GPa using Monte-Carlo simulations constrained by high energy x-ray scattering data. The ambient pressure structure consists primarily of PSe molecules and planar edge shared phosphorus rings, reminiscent of those found in red phosphorous as well as a small fraction of locally clustered corner-sharing GeSe tetrahedra. This low-density amorphous phase transforms into a high-density amorphous phase at ~6.

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

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.

Hydrogen bonding induced distortion of CO3 units and kinetic stabilization of amorphous calcium carbonate: results from 2D (13)C NMR spectroscopy.

Systematic correlation in alkaline-earth carbonate compounds between the deviation of the CO3 units from the perfect D3h symmetry and their (13)C nuclear magnetic resonance (NMR) chemical shift anisotropy (CSA) parameters is established. The (13)C NMR CSA parameters of amorphous calcium carbonate (ACC) are measured using two-dimensional (13)C phase adjusted spinning sidebands (PASS) NMR spectroscopy and are analyzed on the basis of this correlation. The results indicate a distortion of the CO3 units in ACC in the form of an in-plane displacement of the C atom away from the centroid of the O3 triangle, resulting from hydrogen bonding with the surrounding H2O molecules, without significant out-of-plane displacement.

Pressure induced separation of phase-transition-triggered-abrupt vs. gradual components of spin crossover.

The application of pressure on [Co(II)(dpzca)2], which at ambient pressure undergoes abrupt spin crossover (SCO) with thermal hysteresis, gives unique insights into SCO. It reversibly separates the crystallographic phase transition (I41/a↔P21/c) and associated abrupt SCO from the underlying gradual SCO, as shown by detailed room temperature (RT) X-ray crystallography and temperature dependent magnetic susceptibility studies, both under a range of 10 different pressures. The pressure effects are shown to be reversible.

A proposed method for retrospective eye dose assessments for the purposes of resolving cataract compensation claims.

The 2011 International Commission on Radiological Protection (ICRP) statement on tissue reactions suggested a significant reduction in the threshold dose for radiation induced cataracts. This, combined with the potential for a long delay between exposure and cataract diagnosis, may result in an increased requirement to evaluate eye dose from past exposures in order to settle current compensation claims. This article highlights how compensation claims relating to radiation exposure are assessed within the UK legal system and suggests that in vivo Electro Paramagnetic Resonance (EPR) dosimetry of teeth has utility for the retrospective quantification of radiation doses to the eye.

Pressure-dependent structures of amorphous red phosphorus and the origin of the first sharp diffraction peaks.

Characterizing the nature of medium-range order (MRO) in liquids and disordered solids is important for understanding their structure and transport properties. However, accurately portraying MRO, as manifested by the first sharp diffraction peak (FSDP) in neutron and X-ray scattering measurements, has remained elusive for more than 80 years. Here, using X-ray diffraction of amorphous red phosphorus compressed to 6.

A beamline for high-pressure studies at the Advanced Light Source with a superconducting bending magnet as the source.

A new facility for high-pressure diffraction and spectroscopy using diamond anvil high-pressure cells has been built at the Advanced Light Source on beamline 12.2.2.

Osmium diboride, an ultra-incompressible, hard material.

The need for wear- and scratch-resistant materials drives the quest for new superhard materials. In this work, we apply two design parameters to identify ultra-incompressible, superhard materials-high valence electron density and high bond covalency. Our first example of such a material is OsB2.