Environmental cell

The Carbon-IR cell is a cooper cylindrical box able to contain samples 10 cm in diameter and 7 cm high (8 x 6cm for the old version). The total effective volume of this cell is 550 cm³ (312 cm³ for the old version). It has an aperture in its side for injection or outlet of gas. A sapphire window encircled by a metallic flange composes the cover.

Two diametrically opposed 3.4 cm diameter glass windows are located through the vertical cell wall. They make possible to follow the vertical evolution of the sample. A 18.0 megapixel digital single-lens reflex camera with 70-300 mm lens enables to monitor it through one of those windows.

Vacuum chamber

The environmental cell is placed inside a bigger metal chamber that can be hermetically closed and bound to a vacuum pump to create high vacuum inside (about 1×10^-6 mbar). It is closed by a second sapphire window.

Cryostat and temperature

We use a cryostat that can cools down to -210°C by means of a helium compressor. The cryostat power is about 45 W. The temperature of the chamber is controlled by a Si diode and a heating resistance (model Lakeshore HTR-50) inserted inside the copper under the environmental cell, at the bottom centre. This 25 ohm resistance is connected to an high accuracy temperature controller where the required temperature value can be configured to 0.1°C. It allows to measure and control the temperature down to -210°C . This temperature controller also displays the temperature measured by a second Si diode also located under the cell but near the cylinder edge. This second probe helps to measure the thermal gradient along a radius of the cell. The temperatures are displayed with +/- 0.2°C uncertainty.

Pressure

The thermodynamic system of the SERAC cell is also used here. It is composed of a glass container that acts as a reservoir for 10 liters of gas, connected to a gas bottle, a primary pump and a turbo pump and an absolute pressure sensor MKS Baratron 390HA series, 100 Torr type. It measures pressures between 10^-4 mbar and 133 mbar. Operating and display are done on an electronic box with 0.08% uncertainty. Valves between all the components enable to isolate them when required by the experimental protocols.

A mass flow controller can be inserted between the thermodynamic system and the CARBON-IR cell. It enables to measure the gas injection rate towards the cell. Real-time graphic display and record of the measured mass flow and the absolute pressure values are possible, at a chosen frequency, using a LabView interface.

Characteristics

– minimum temperature: 63K, -210°C (a room T°)
– maximum temperature: 290K (+17°C)
– stabilisation time (new sample holder):

• to 160K: 2h
• to 100K: 3h
• to 65K: 4h

– vacuum: < 1 10^-6 mb
– Sample size:
– cylindrical, d = 80 mm, h = 60 mm: up to 312 cm³ (old version)
– cylindrical, d = 100 mm, h = 70 mm: up to 550 cm³ (new version)

Sample holders (aluminum), to be inserted in the cooper cell:

Cylindrical:
– d = 68 mm, h = 58 mm
– d = 48 mm, h = 20 mm
– d = 48 mm, h = 10 mm
– d = 48 mm, h = 5 mm
– d = 48 mm, h = 2 mm
– d = 48 mm, h = 1 mm
– d = 40 mm, h = 8mm
– d = 39 mm, h = 7mm
– d = 38 mm, h = 6mm
– d = 37 mm, h = 5,5mm
– d = 36 mm, h = 5mm
– d = 35 mm, h = 4,5mm
– d = 34 mm, h = 4mm
– d = 33 mm, h = 3,5mm
– d = 32 mm, h = 3mm
– d = 31 mm, h = 2,5mm
– d = 30 mm, h = 2mm
– d = 29 mm, h = 1,5mm
– d = 28 mm, h = 1mm

For the ‘Gognito mode’:
– d = 20 mm, h= 5 mm
– d = 18 mm, h= 4.5 mm
– d = 16 mm, h= 4 mm
– d = 14 mm, h= 3.5 mm
– d = 12 mm, h= 3 mm
– d = 10 mm, h= 2.5 mm