ThermoQuest Sorptomatic 1990 Technical Specification


Gas Inlets
Adsorbate: Two gases selectable, maximum inlet pressure 2 bar
Liquid coolant transfer: N2 maximum inlet pressure 3 bar (relative)
Calibrated piston movement: N2 inlet pressure 4 bar (relative)

Accepted Adsorbates
Physisorption: N2, Kr, Ar, CO2, He,...
Chemisorption: H2, O2, CO CH4,...

Sample Holders

The sample holders are about 20 cm3 in volume and are equipped with high vacuum stopcocks to avoid any risk of contamination by the atmosphere. These stopcocks permits transfer of the sample after the degassing procedure from the degassing to the analytical port while keeping the sample under vacuum. The sample can also be weighed under vacuum. The inlet diameter is 8mm enabling relatively easy loading of the sample. It is possible to use customised sample holders because the blank run can measure the internal volume.


Vacuum system

A special two stage rotary vacuum pump with two inlets to keep analysis separate from sample pre-treatment, allows an ultimate vacuum of 5 x10-3 Torr to be achieved. To protect the sample from water vapor (active alumina) and pump oil (carbon) filters are used on the inlet of the rotary pump. A pressure of 0.1 Torr is used during the desorption analytical process.
The Turbomolecular vacuum pump allows an ultimate vacuum of 1 x 10-6 Torr to be achieved.

Pressure measurement

Two capacitance manometers in the range 0.1 to 1000 Torr are used one to monitor the injection pressure the second measures the equilibrium pressure over the sample. Both gauges are accurate to within 0.25% of the pressure.
The pressure at the vacuum pump inlet is measured using a digital vacuum gauge with a range of 0.1 Pa to 100 Pa.

Coolant Transfer System

The sample must be kept at a constant temperature during the adsorption experiment. The sample holder is therefore placed in a 1 l dewar filled with liquid N2 that is maintained at a constant level, detected using a PT100 resistance thermometer, by using an automated refilling system from a 3 l reservoir dewar. The continuous refilling minimizes the condensation of liquid O2 from the environment. The reservoir dewar can be refilled at any time, if required, even during the experiment, and hence there is no practical time limit for the experiment.

Saturation Pressure Measurement

The saturation pressure, displayed on screen during the analysis, is monitoring using a temperature sensor (with a resolution better than 10mK) that is placed beside the sample in the dewar. Coolant temperature changes during the measurement, due to changes in atmospheric pressure, are hence detected and the instrument calculates the liquid coolant saturation pressure, to better than 0.1 Torr, from the detected temperature and this is recorded for each data point. The software also provides a calibration procedure for the temperature sensor.

Sample pre-treatment

Two separate independent ovens and vacuum ports are available which can be used to separately degas two different samples. These are used to remove adsorbed material from the sample and holder prior to the physisorption measurement, this is essential to ensure correct pore volume and specific surface area is obtained. The procedure should be performed under vacuum and at the highest temperature which is compatible with the sample. The heating procedure must be carefully chosen as it may influence the final results. The oven specification is given below.

Temperature: From room temperature to 723 K (450 oC)

Accuracy: +/- 1 % of full scale

Heating Procedures    1) Ballistic temperature increment: the total time to reach the maximum temperature is about 60 minutes.

   2) Programmed temperature rate: from 0.1 to 5 K/min

   3) Step-wise temperature increment, the total time to reach the maximum temperature depends on the sample-degassing rate. The degassing is performed at constant pressure, which is selected from 0.1 to 99 Pa, and hence the temperature is automatically controlled.

Heating Time:      Manual - (no time limit) or Automatic - from 1 to 18 hours with automatic oven shut-off at the end of the selected time.

Measurement ranges

Specific Surface Area: from 0.2 m2/g (depending on the nature of the sample) with no upper limit.

Pore Volume: from 0.0001 cm3/g


Pore Radius:    This depends on the calculation model applied to the data, but the normal range is 2 to 50 nanometers. This can be extended to the gas molecular dimension (i.e. N2 = 3.5 Angstroms) and up to 1000 Angstroms.

Reproducibility:

The measurement reproducibility is between 1 to 3% depending on the sample nature and the calculation model.

Analysis Time

This depends on the number of data points that are to be acquired and the sample nature (as this clearly changes the time required to reach the equilibrium pressure). Generally it takes between 2hrs and 2 days to generate an isotherm.

 
Back to the instruments page