Synchrotron Experiments in Polymers
With the synchrotron being built at Monash, a question that comes to mind is “ is this innovation to be of any benefit to materials research and teaching at Monash?”
The answer is that a number of Monash Materials research groups use synchrotrons for experiments even now, having to travel overseas to do this.
For some time now, various research groups in Materials Engineering at Monash have been making use of synchrotron light to conduct different experiments, looking at texture development in metals, phase transformations in intermetallics, morphology development in polymers related to processing, and so on. Graham Edward and Peng Wei Zhu have travelled numerous times to overseas synchrotrons to pursue research on the molecular morphology of injection moulded polymers, this research being done in a program supported by the CRC for Polymers. The use of the synchrotron facilities has been funded by the Australian Synchrotron Research Program (ASRP) which has funded trips and equipment usage utilising mainly the Australian National Beamline Facility located at the Photon Factory in Tsukuba Japan. The advantage offered by synchrotron light over conventional X-ray sources is that a fine beam of extreme intensity can be obtained, allowing detailed experiments to be done in a fraction of the time (and better than) what can be achieved in a standard laboratory. The work being done by Edward and Zhu is concerned with quantifying the fine-scale morphology gradients found in injection mouldings, with the aim of relating this to the processing conditions. The fine-scale of the microstructure gradients necessitates the use of synchrotron radiation to obtain a fine beam unobtainable in conventional laboratory X-ray sources. An understanding of the morphology distribution has the potential to allow prediction of moulding properties such as post-mould warping, which is determined by competing internal stresses from the different layers. The layers themselves arise from the different shear environments through the moulding thickness, from high shear near the mould walls to zero shear in the centre plane of the mould. The resultant morphologies range from isotropic ‘spherulitic’ structures in the centre to the evocatively named ‘shish-kebab’ structures with high molecular orientation near the walls.
A typical trip to use some funded beam-time at the Photon Factory by Dr Edward involves travelling to Tsukuba, setting up the experiment, doing up to 4 days of experiments (96 continuous hours of experiment - the beam-line is not turned off at night), then coming home. Sounds easy – try doing 4 days of continuous work with only limited rest periods!
Fortunately, 3 researchers usually go to the Photon Factory: Drs Edward, Zhu and often a student, either undergraduate or a higher degree researcher. These students benefit greatly from exposure the use of this advanced technology, and nearly ten different students have gained this experience in recent years. The work (continuous, has that been mentioned?) is split into shifts, and students with superior powers of endurance often work the shift from the evening to the morning, although this is not always feasible. Given the intensive time schedule, no time for tourism is generally available, and due to the trips usually coming in the middle of semesters, it is not convenient to tack on extra time to ‘do Japan’ to any reasonable extent with teaching obligations waiting back at Monash.
Graham Edward
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The Nano SPD (Severe Plastic Deformation) Group
The “NanoSPD” Group in the Department of Materials Engineering is known internationally for active research in the area of Ultra-Fine-Grained / Nano Materials by Severe Plastic Deformation (SPD). Among the many processes of SPD, Equal Channel Angular Extrusion (ECAE) has been shown to have great potential for producing large scale bulk ultrafine-grained materials (1) with novel mechanical properties. Almost all research projects taken by the NanoSPD group target industrial applications and involve international cooperation. Several projects on aluminium and titanium alloys have been supported by the US Airforce.
The international leadership of the group is based on the special ECAP with Back-Pressure equipment designed and manufactured under the supervision of Dr. Rimma Lapovok. The first rig for room temperature ECAP was designed and built in 1998, with two further modifications (2), including another rig for high temperature ECAP with Back-Pressure (3) and a new large scale rig for ECAP of Ti alloys is in design, as part of the LIEF grant involving several Universities in Victoria and NSW. The new equipment should be commissioned this year.
The unique features of Monash University equipment were a base for starting a series of projects on
superplasticity of magnesium alloys;
improvement of strength and ductility of aluminium automotive alloys;
improvement of fatigue life of aluminium aerospace alloys; and
compaction of metallic particles.
The results in superplasticity significantly exceed any data known up to date (4).
The first project on compaction of magnesium swarf (2002) has shown an increase of magnesium recovery rate after re-melting of ECAP produced compacts from 68 to 92% (5).
Since 2006 projects on compaction of metallic powders with especial emphasis on titanium powders have been carried out, for example the project on low temperature compaction of Ti-6Al-4V powder supported by DARPA. It was found that compaction of this powder to the density above 98% of theoretical one and 700 MPa of green strength can be obtained by ECAP with Back-Pressure at temperatures as low as 400ºC (6).
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Materials Research Goes Green
The development of renewable energy sources that are alternative to fossil fuels is a burgeoning scientific area. Solar cells convert the energy of the sun to electricity with little or no emission to the environment. Reducing the cost of converting solar energy into electricity is a global endeavor that is attracting the attention of researchers worldwide. A vibrant team consisting of researchers at the Department of Materials Engineering and the School of Chemistry, Monash University is at forefront of research for dye-sensitised solar cells, a new type of solar energy devices that is now recognised as the most significant alternative photovoltaic technology to silicon wafer-based solar cells.
The nanocrystalline dye-sensitised solar cell (DSSC) incorporates an inorganic nanostructured semiconductor film (usually a 10 to 20 micron porous TiO2 layer) that is coated with a monolayer of a photoactive dye, and a conducting electrolyte that contains a redox couple (1). In DSSCs, the main charge-transfer processes take place at the semiconductor/dye/electrolyte interfaces. When a photon of light is absorbed by the dye an electron is excited and injected into the TiO2 semiconductor. The electrons migrate through the TiO2 nanoparticles to the external load and to the counter electrode which is a conductive coated glass, and rejuvenate the original state of the dye through the electrolyte. The repeating process generates an electron current. High incident photon to electron conversions efficiencies (IPCE >70 %) and overall cell efficiencies of over 10% have been achieved with this novel device.
The dye-sensitised solar cells have a number of features that distinguish them from silicon based solar cells. A major component of the cell, titanium dioxide (TiO2), is an industrial material widely used as a pigment in paints and as an additive in toothpaste and cosmetic products, and thus is available at low cost. The cost of the dye is not prohibitive since only a monolayer coating of the titania surface is required. The simplicity of the cell design and low cost of the materials used offer promise of drastically reduced production costs, lighter weight devices and easier fabrication into large sizes when compared to the silicon-based solar cells. Another important feature of the DSSCs is their superior performance than silicon cells in low incident light, making them more suitable for indoor applications. In contrast to devices based on silicon wafers, where flat assemblies are preferred, the DSSC has the potential to be made into flexible devices on polymer substrates that can fit on surfaces with intricate contours. A great attraction of this flexibility is that they may be “painted” on any appropriate surface, such as car roofs and roof tiles, or be “printed” and molded into any shape.
The development of dye sensitised solar cells is still at the research stage at the present time. Major technical issues remain to affect the efficiency, lifetime and processibility of the devices. A multi-disciplinary approach for materials development, device fabrication and optimization has been taken at Monash through collaborations between Professors Maria Forsyth, Yi-Bing Cheng of Materials Engineering and Doug Macfarlane, Leone Spiccia of Chemistry. The research team is further strengthened by the joining of Dr Udo Bach, an experienced DSSC researcher from Professor Michael Grätzel’s lab where the DSSC was originally invented. More than ten postgraduates and research fellows are working in a range of areas covering synthesis of solid state electrolytes, infrared sensitive dyes, novel nanostructures of TiO2 particles, monolithic and tandem cell devices. These activities are part of the research programs funded by the newly established ARC Centre of Excellence for Electromaterials Science (ACES). http://www.eng.monash.edu.au/mat/aces/index.html The DSSC research team at Monash is also a major partner in the Victorian Consortium for Organic Solar Cells (VICOSC) for winning a $6M grant from the Victorian Government recently to produce prototype organic solar cells printed on plastics within 3 years. http://www.vicosc.unimelb.edu.au/
Yi-Bing Cheng
PACRIM 2007
November 2007 saw a number of us from the Monash Materials Department make the trip to Korea for the 6th Pacific Rim International Conference on Advanced Materials and Processes. This conference was held on the beautiful island of Jeju off the southern coast of Korea with participation of researchers from over 30 countries contributing more than 900 papers. Amongst the symposiums at this conference was a dedicated symposium on the ‘Modeling and Simulation of Materials and Processes’. This is now a common occurrence at International meetings of both academia and industry and is illustrative of the growing popularity of the use of ‘Modeling’ in materials and process problems. The increase in popularity of materials modeling is partly due to the increase in computing power over the last ten years; it is now possible to do practically relevant calculations on a desktop computer instead of requiring access to very large and expensive workstations.
However, the recognition by industry that significant savings in time and money can be realized through the exploitation of modeling of materials and process development and monitoring is also contributing greatly to this popularity.
Examples abound in industry: the new generation of power stations in Denmark are now claimed to be the most efficient in the world, resulting in significant decreases in greenhouse gas emissions over previous stations. These advances are largely due to the higher operating temperatures at which they operate. In the past, such operating temperatures were not possible because of material degradation. This has now been remedied by the development of new steels that can operate at the higher temperatures. These steels were developed largely using new materials modeling techniques.
Materials and process modeling will never replace experiments; but they are not supposed to. The coupling of materials modeling and experiment are leading to large efficiencies in many areas of materials and process development and industry is taking note. For those of us involved in modeling it is an exciting time. The only way is up.
Christopher Hutchinson.