Based in Athens, NCSR (National Centre for Scientific Research) Demokritos is one of Europe’s leading research establishments, undertaking work in a variety of fields. It comprises eight institutes, several of which have designed and built specialist apparatus incorporating microbalances from CI Precision in the UK.
Unlike other suppliers of microbalances, CI Precision offers the devices in kit form, which is especially useful in research applications where the microbalance needs to be built into bespoke apparatus. Most of the kits supplied to NCSR Demokritos contain, in addition to the microbalance head, components such as the DISBAL control unit, temperature control option, LabWeigh software package, cables and accessories. A popular option is PTFE coating for the microbalance head.
Typical of the microbalance applications is that of George Pilatos, a chemical engineer working in the MESL (Materials and Membranes for Environmental Separations Laboratory) within the Physical Chemistry Institute. The microbalance head is being used for carbon nanotube formation studies and has been adapted within the lab (following the detailed instructions supplied by CI Precision) to enable it to be used at pressures of up to 10 bar.
The chemical vapour deposition (CVD) apparatus in which the microbalance is used includes a flow system – with three mass flow controllers and a digital back-pressure controller – and a high-temperature stainless steel tube inside a vertical tubular oven. Readings from the microbalance indicate the exact time at which the carbon depositions begin to form and the rate of weight gain.
Within this application the sample outgassing takes place at 10-3 mbar at temperatures ranging from 650 to 1000 degrees C. Pressure for the CVD experiments is a few millibars above atmospheric. Throughout the experiments the microbalance head is supplied with a flow of helium at a rate of approximately 50ml/minute.
George Pilatos states:
“We have bought several microbalance kits from CI Electronics since 1997 because the purchase price is good, the heads are reliable and they are simple to integrate with other equipment such as flow systems, valves and ovens”.
“The original microbalance eventually started to show signs of oxidation so we asked CI Electronics to refurbish it. The price for this work compared favourably with the purchase price of a new head, and CI Electronics was very helpful. Since its refurbishment the head has proved totally reliable, despite operating in conjunction with a flow system that flows up to 500ml/minute.”
Dr Nick Kanellopoulos, who is also in the MESL, is using a microbalance in apparatus for measuring sorption isotherms on nano-porous materials such as carbon and zeolites. This work includes monitoring the activation of activated carbon, hence operating temperatures can be as high as 950 degrees C.
Dr Kanellopoulos comments:
“The reason why we use the CI microbalance is that it is the best of its type on the market.” Elsewhere within the Physical Chemistry Institute, Dr Merope Sanopoulou is studying the sorption of vapours – such as water and methanol vapours – in polymeric films.
“We have used other microbalances in the past, but the CI microbalances are very good, and the support we get from CI Precision is excellent. It is also an advantage that CI Precision is based in Europe.”
Another researcher in the Physical Chemistry Institute using a CI microbalance to study sorption isotherms is Fotios Katsaros. He has used the apparatus with a variety of substrates including polymers, carbon, glasses and other porous substances. His experiments are often unusually long, so he has developed specialist software to check for equilibrium by monitoring for pressure changes. The gases he deals with are often organic, such as hexane and benzene.
Dr Katsaros explains why he chooses to use CI microbalances:
“I bought a CI microbalance several years ago and was very happy with it. Although I have looked at others from alternative suppliers, either they are more expensive or their performance characteristics are not as good. The CI microbalances perform well, are a good price, they are very reliable and the technical support from CI Precision is always excellent.”
NCSR Demokritos has been buying CI microbalances for over 20 years, though the applications have evolved in that time to include current fields of research such as carbon nanotubes. However, for the reasons explained above, the researchers are continuing to choose CI microbalance kits over the alternatives.
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