Halogens

The name "halogen" means "salt-producing", and halogens react with metals to produce a range of salts, including calcium fluoride, sodium chloride, silver bromide and potassium iodide. Elemental halogens are highly reactive and toxic, and chlorine, bromine and iodine, are often used as disinfectants. Organobromides are organic compounds containing carbon bonded to bromine, and are the most important class of flame retardants. Organofluorines are organic compounds that contain the carbon–fluorine bond, and have a wide range of applications, including oil and water repellents to pharmaceuticals, refrigerants, and reagents in catalysis. Some organofluorines (such as CFCs) are environmental pollutants, contributing to ozone depletion, global warming, and toxicity.

All over the world, plant samples dried and pressed onto sheets of paper are stored in herbaria. Some of the examples have been there for centuries, and it's easy to think that we've learned all we can from them. The truth, however, is that herbarium samples are crucial to modern research, and can help us discover (for example) how natural environments are changing over time.

The University of Manchester museum herbarium was founded in 1860 and contains over a million specimens from all over the world. Over the centuries, botanists have used a wide range of techniques to keep the plant samples safe from bacteria, fungi, insects and rodents.

Mercury salt solutions, such as mercury chloride, were used as a preservative from the 17th century until the 1980s. The question now is whether the mercury presents a health risk to herbarium staff? As well as the threat from handling the specimens directly, mercury vapour is released from the containers whenever they are opened.

A team of researchers from the university used beamline B18 to characterise the mercury in herbarium specimens and to identify ways of limiting the release of mercury vapour from contaminated specimen boxes. They incorporated filters impregnated with selenium nanoparticles into the specimen boxes, and then placed samples in the beam to understand how the mercury was trapped and to identify whether this is a suitable long term solution. They found was that the selenium efficiently sequestered the mercury vapour, reducing the level by around 47%. Read more here.

(a) k3- weighted c EXAFS Fourier transform of aqua regia prepared 1% Au/C catalyst and Au foil standard (b) Normalised white line intensity correlated with VCM productivity over the course of the reaction induction period.

Where safety is critical, such as in pipelines, aircraft and nuclear waste storage vessels, our infrastructure relies on "corrosion-resistant" metals. Ironically, these materials are vulnerable to a form of corrosion known as pitting. 

Corrosion pits can occur in metals such as stainless steel, and nickel. A highly concentrated acidic metal chloride solution develops inside these pits, from which a layer of salt crystals can precipitate. This affects the corrosion rate, but it's challenging to study the structure and chemistry of these layers.

Scientists from the University of Birmingham used beamline I18 to carry out in situ X-ray diffraction and X-ray absorption spectroscopy studies on salt layers and solutions in one-dimensional artificial corrosion pits designed to be characteristic of real pits. The results revealed that the phases present in salt films on dissolving iron, nickel and stainless steel surfaces can vary through their thickness and showed that the metal ions have different chemical coordination environments depending on their proximity to the dissolving metal surface.

By learning how these pits form and propagate, we can build more accurate models of corrosion to predict the lifetime of components and plan when they need inspecting or replacing.