ISO/TS 20177:2018 真空技術—真空計—ガス放出率を測定および報告する手順 | ページ 6

3.1

outgassing rate

rate of molecules that leave a surface in vacuum, in units of throughput, measured at 23 °C or calculated for a gas temperature T = 23 °C

Note 1 to entry: For scientific investigations, it is distinguished between desorption and outgassing. The first is a surface effect, the second a bulk (diffusion) effect. For many measurement procedures, however, it is not possible to distinguish between the two effects. To measure the true outgassing rate, all molecules from a surface are removed by a bake-out or a similar procedure. A bake-out, however, in particular in industrial applications, is not possible or not desirable. For this reason, in this document, the term"outgassing rate" includes both desorption and outgassing rate.

Note 2 to entry: The temperature of the sample or the measurement chamber may be different from 23 °C, but the measured outgassing value in units of throughput shall be calculated as if released gas would have temperature 23 °C. In this way, it is possible, to state a measured throughput (at 23 °C) for a sample at 150 °C.

Note 3 to entry: In vacuum applications, the unit of throughput is commonly used for outgassing rates, but for known outgassing gas species it is also possible to use the unit of mass flow, e.g. g/s.

Note 4 to entry: In some cases, when outgassing gas molecules of a certain species easily adsorb on the surrounding surfaces of the measurement system, it is distinguished between intrinsic and measured outgassing rate. The intrinsic outgassing rate is the outgassing rate that leave the sample surface. It is higher than the measured one, when no equilibrium of ad- and desorption on the surfaces of the walls has been reached. In this document, it is assumed that equilibrium is established, but this may not be true for absorbing gases like water vapour.

3.2

geometrical surface area

area of a surface determined from its geometrical dimensions, not including surface roughness

3.3

mass range of outgassing

mass range of QMS from 1 to the highest m/z of all measured or expected outgassing gas species

Note 1 to entry: For the scope of this document, the mass range of outgassing is 300.

3.4

nitrogen equivalent outgassing rate

outgassing rate (3.1) when all gases released from the sample are assumed to be nitrogen molecules

Note 1 to entry: To be consistent, all quantities involved in a physical equation (e.g conductance and pumping speed) need to be expressed for nitrogen, if pressure is measured in nitrogen equivalent. Otherwise, the same nitrogen reading of a vacuum gauge could lead to different quantities dependent on gas species (see the following example).

3.5

bake-out time

time for which a sample or chamber is maintained at a specified (bake-out) temperature

Note 1 to entry: Bake-out time does not include the warm-up and cool-down phase.