From 2001 to 2008 Isothermal Technology offered a Carbon Dioxide fixed point cell (-56.588°C). The cell was easy to use and could be maintained in a commercial liquid bath. Sales were low and due to the lack of demand we withdrew the product from our catalogue. Most users chose to stay with Mercury Cells, as a point on the ITS-90 the mercury point is important for the calibration on SPRTs.
The mercury point is not perfect, below the water triple point (0.01°C) mercury is the first ITS-90 point before the triple point of argon at -189.3442°C. It might be helpful to have an extra point somewhere in between. Mercury is hazardous and harmful to the environment – there is a move to find a new calibration point and interest in alternatives to the mercury cell is increasing.
So we found our own Carbon Dioxide cell at the back of the cupboard – and tested it. The first time we used the cell after some years we got a plateau length of 14.5 hours, within 1mK of the ITS-90 value. So we are currently assessing demand to determine if, 15 years after having first introduced a CO2 Fixed Point Cell, there is a demand for it today?
Original Data Sheet
If you would like to learn more, or have any interest please contact us.