Diffusion

Diffusion

It is not only important to have the correct quality of gases, it is equally important to handle the gases by using equipment most suited for the application.

Contamination of pure gases and calibration gases by inappropriate regulators, tubing, flow meters, valves and connections etc. through diffusion and out gassing is a known phenomenon. Consequently, in order to obtain calibration and high purity gases in the specified quality at the point of use all metal non contaminating and diffusion resistant gas handling equipment like regulators, valves, non return valves, tubing and fittings.

Sources of Error When Transferring Gases

Reduction in component concentrations - increase in Absorbent Surface Area.

• ERROR: Employment of unsuitable material
• IMPACT: Chemical Reaction, especially in the presence of moisture.
  
  

• ERROR: Ad/Desorption on surface area.
• IMPACT: Gas molecules are given off in the gas stream. Components adhere to surface area.
  
  

• ERROR: Line leaks.
• IMPACT: Partial pressure gradients between different gases forces gas molecules towards the side with lower partial pressure, regardless pressure.
  
  

• ERROR: Dead volume is not taken in account.
• IMPACT: Pressure drifts as well as the motion of the molecules themselves; contaminate the pure gas stream with foreign gases from the dead area.
  
  

• ERROR: Permeation through hose walls.
• IMPACT: Even after first purge, foreign gas molecules enter stream of gas ( H₂O, CO₂, HC etc)
  
  

• Material: Contamination of O₂
• Stainless Steel: 0 ppm
• Mylar: 0.02 ppm
• PTFE: 13 ppm
• PVC: 27 ppm
• Natural Rubber: 40 ppm