Solid State NMR Characterisation of Disordered Inorganic Oxide Materials
Automobile Windscreen Borosilicate Glass Made by Conventional Methods; and Novel Non-Equilibrium Phases Formed by Flame Spray Pyrolysis
Solid state NMR is carried out on glass samples made at the Johnson Matthey Technology Centre at Sonning Common. The project involves the study of sodium borosilicate based glasses used for automobile windscreens and highly amorphous materials produced by flame spray pyrolysis.
Johnson Matthey produces a large amount of glass for automobile windscreens and automotive obscuration enamels used on rear windscreens. These enamels must pass a new industry acid test where a sheet of glass covered with enamel on one side is half submerged in 0.1N H2SO4 at 80˚C for 72 hours without the enamel losing its colour. The industrial supervisors of the project at Johnson Matthey are currently trying to develop glasses with compositions which allow the glass to pass this test whilst keeping a relatively low firing temperature of around 600˚C. The structural features of the glasses can be studied using NMR and together with knowledge of the compositions of the glasses and their properties it is hoped to find out which elements in the compositions affect the structural properties, and thereby how the compositions can be altered to achieve the required physical properties.
Flame spray pyrolysis (FSP) is a new technique for synthesising high purity, chemically homogeneous powders; but little is known about the structure of these materials, and so NMR will be a useful probe since they are potentially highly disordered. FSP can be used to make borosilicate glasses similar to those produced by conventional methods in the other part of the project as well as ceramic materials such as aluminium oxide, zirconium dioxide and cerium oxide.
Why Use NMR?
NMR can provide quantitive information about the structure of materials on the atomic scale. Other probes at this level such as X-ray absorption require long-range atomic order and so only NMR can probe the atomic environment of disordered systems.
Glass does not have long range, periodic atomic arrangement and is described as an amorphous solid with short range order at the atomic scale due to chemical bonding.
Borosilicate glasses have high strength and chemical durability which makes them technologically important materials for a wide variety of applications. The physical and chemical properties of the glasses depend on their compositions including the types of additives included in the glass. The nature of the structural units in the glass depends on the composition and these affect the physical properties of the glass. Borosilicate glasses have a low thermal expansion coefficient and a high resistance to chemical attack; for this reason they are used for laboratory and pharmaceutical glassware and nuclear waste glasses as well as for automobile windscreens.