Metals

EDXD detector on Module 2 of Large Detector Table 2 (LDT2) on our I12 beamline. The second collimator (detector slits) is placed just in front of the detector front-plate and is hidden behind lead shielding.

In the periodic table, the post-transition metals sit between the transition metals on their left, and the metalloids on their right. These metallic elements include aluminium, gallium, indium, tin, thallium, lead, and bismuth. Most are soft or brittle, with poor mechanical strength, and have melting points lower than the transition metals.

Lead is a heavy metal, with the highest atomic number of any stable element. Soft and malleable, it has a relatively low melting point. A freshly cut lead surface is silvery blue, but it tarnishes to dull grey on exposure to air. Notable uses include bullets, and radiation shielding.

Lead is one of the seven metals of antiquity that humans identified and made use of in prehistoric times (the other six are gold, silver, copper, tin, iron, and mercury). Lead is now used in alloys, solder, and roofing. Gallium and indium are semiconductors, and thallium is highly toxic and has been used as a pesticide.

Piezoelectric materials can generate an electric charge in response to applied mechanical stress. They have a lot of applications, finding their way into many everyday items from cigarette lighters and easy-light barbecues to quartz watches and scientific instruments. The market for piezoelectric materials is worth more than $10 billion a year, and the primary material used is the ceramic lead zirconate titanate (PZT), which contains up to 60% by weight of lead. Given the environmental and health issues associated with lead, there is increasing interest in developing lead-free piezoelectric ceramics. Researchers used the high-energy synchrotron radiation available on the Extreme Conditions Beamline (I15) to demonstrate an electric-field-induced phase transformation in the lead-free piezoelectric KNBT. Read more here.

Could worm poo hold the key to cleaning up toxic metals in contaminated soils? Diamond's intense X-rays were used to probe the tiny granules of calcium carbonate excreted by earthworms that had been living in lead-contaminated soil. Although tiny to us, the granules scaled up would be like a human excreting a spikey football!

The research team found that the excreted calcium carbonate granules contained a substantial amount of lead. When the earthworms ingest the lead, it associates with the calcium carbonate granules and is excreted out as insoluble metal carbonates. This could immobilise the metal, making it less available to plants. Read more here.

Painted in 1876, Edgar Degas' 'Portrait of a Woman' is a striking example of French Impressionism. It's also an intriguing success story for science. Observers first noticed that something wasn't quite right with the shadowy, black-clothed subject of Degas' painting back in the 1920s, but to work out what was going on, scientists needed to explore beneath the surface layer of paint. Using X-ray Fluorescence Microscopy at the Australian synchrotron, they were able to identify the elemental make-up of the painting and revealed the presence of an older image underneath.

Degas had painted over the original portrait using layers of lead-based paint, unknowingly initiating long-term chemical reactions. Over time, traces of lead reacted with oils and rose to the surface, leaving the painting tarnished by white blisters. If we can track the migration of lead within the painting and uncover more about how the process works, it might be possible to prevent it. A group of experts using spectroscopy beamline I18, are using chemical tomography to image the composition of paintings. They hope to learn exactly how the white blisters form and whether a chemical intervention could counteract the process and save these masterpieces.

Read more about 'Portrait of a Woman' here, or the team investigating the white lead deposits on Old Master paintings here.

Altarpieces from the 15th century AD often have silver areas created by the application of a thin foil of metal. Treatises from the period describe the addition of small amounts of lead white to the drying oil to help its polymerisation and the drying process. Over time, the silver can blacken or disappear altogether, but the causes of degradation are not well understood, and this limits conservation efforts. A group of researchers used several analytical techniques to analyse samples, including µSR-FTIR for the glues, varnishes and binding media, and µSR-XRD to determine the alteration to the silver compounds.

Their results showed that the conservation state of the silver foil is directly related to contact with the atmosphere. A paint layer or a well-preserved resin coating preserves the silver foil in a good conservation state. Where the protective layer is damaged or absent, leaving the silver surface exposed to the atmosphere, the silver alteration products are all that is left.

Read more here.