Neutron Cells for Liquid Samples

Cells used for high-temperature measurements in furnaces often consist of silica sample tubes, supported by thin vanadium sleeves. The key to the analysis is whether it is possible to have a container that scatters in a sufficiently predictable way, so that its background contribution can be subtracted. With the current neutron flux available from both pulsed and reactor sources, sample volumes of 

Neutron diffraction has been used extensively to study a range of ionic liquid systems however, many of these investigations have focussed on high-temperature materials such as NaCl, studied by Enderby and co-workers [3]. A number of liquid systems with relatively low melting points have been reported, and this section summarizes some of the flndings of these studies. Many of the salts studied melt above 100 °C, and so are not room-temperature ionic liquids, but the same principles apply to the study of these materials as to the lower melting point salts. 

Neutron diffraction has been used extensively to study a range of ionic liquid systems however, many of these investigations have focused on high temperature 

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In order to obtain comparable data from such complex systems we have developed a cell with the ability of use for measurements both in reflection and small-angle neutron scattering geometry. This cell allows studies of adsorbed surface layers and the equilibrium bulk structures for one sample in the same experiment by simple rotation of the cell. This is a particular advantage when smdying surfactants above the cmc or liquid crystals which may show one type of order at a surface and another in the bulk. 

The sample is mounted in a small cylinder containing a fluid, and the cylinder is, in turn, mounted in a piston cylinder cell. Load is applied to the piston until the desired pressure is reached inside the cell. The piston is then clamped with a locking nut. The advantage of the piston cylinder device is that it may break but not explode since a liquid does not expand dramatically. The drawback is that changing the pressure requires dismounting the cell to load it again. Steel or copper-beryllium clamps can be used for neutron structure studies since they allow almost three-dimensional studies. Clamps capable of higher pressures are made with an alumina... 

The DAC is unsuitable for an ordinary neutron experiment, because the latter requires much larger samples. Alternative means of compression, such as liquid- and gas-pressure cells, " or even sapphire anvils (specially designed for use with He cryostats), are but poor substitutes in the magnitudes of pressure. However, encouraging results have been obtained by using DACs in conjunction with high-power neutron sources and optimizing the diffraction instrument itself... 

In the experiments described here the volume of liquid adsorbate which was injected was sufficient to saturate the intra-granular mesopores. This volume was calculated from a knowledge of the sample meiss in the cell and the mesopore volume, derived from the nitrogen adsorption isotherms, (eg for the kinetic measurements with the S2M silica, this mass was 42mg for each of the two samples and the injected volume was 40 pi.) This volume was injected via the hypodermic needle, to the base of the cell which was below the zone of the incident neutron beam. The transmissions for the different samples was in a range of 0.7 to 0.9, being typieal for such porous silicas in these standard quartz neutron scattering cells. 

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