During this project you will produce zeolite films by the paper-making technique varying the ratio of the constituent materials. Each film will have its own unique properties, in particular its own porosity. The films will then be characterized by PALS and potentially also electron microscopy.

Zeolite materials have been used for a wide range of practical processes as filters, catalysts, adsorbent and as molecular sieves. They consist mainly of alumina or silica structures that allow filtration or absorption at a molecular level. This makes them of great interest for purification of gas or liquids in particular the removal of NOx and SOx generated in a power station. A novel technique for producing zeolite films utilizes a paper making method and produces films that are well suited for removal of these gasses in a reaction tower but without the disadvantages of the bead and pellet type zeolites that are typically used. Unfortunately there is very little information on the size and fraction of pores in zeolites produced by this method and as such there is an ideal opportunity for the physical structure of these materials to be measured by PALS.

At the ANU two beamlines have been developed for experiments using positrons. The second of these two beamlines is dedicated to material analysis using positron annihilation spectroscopy (PALS). Positrons are emitted from a 22-Na sample, cooled, trapped then temporally compressed, producing a sub nanosecond pulse of variable energy positrons (0.5 - 20keV). The positrons are then implanted into a material, where the energy at which the positrons hit the material determines their mean penetration depth. Once implanted the positrons thermalise (in a few picoseconds), then diffuse inside the material. In the material the positrons can either annihilate with an electron producing two (511 keV) gamma rays or become trapped in vacancies or pores inside the material. As the electron density in the vacancies is significantly lower than that in the bulk material, the chance of annihilating with an electron in a pore is less and thus the lifetime of the positron is increased. By detecting the emitted gamma rays from many annihilation events we build a spectrum of positron decays which can be used to determine the size and density of pores in the material.

This project will enable the student to undertake materials science experiments from the ground up, making and characterising their own unique material. Along the way, they will develop skills in:

• Handling positron beams and gamma ray detection
• Preparation and handling of zeolite films
• High vacuum practice
• Working in a team environment
• Fast pulse processing and high speed data acquisition
• Data analysis and interpretation
• Computer control of experimental hardware