HFC-134a use in Magnesium Casting
Magnesium is a highly reactive metal. As temperatures of up to 800 °C can occur during the casting process, the surface of the melt has therefore to be protected against ignition, oxidation and the formation of nitrides. In the early years of industrial magnesium production only salt fluxes or powdered sulphur were known as protective cover for this purpose. To prevent contamination of the cast products, the salt fluxes were replaced by protective gas mixtures.
Sulphur dioxide (SO2) was the first cover gas used in magnesium foundries to protect the molten metal and plays an important role still today. Due to its toxic and corrosive properties (especially humid SO2 enhances corrosion of steel equipment) it was replaced by SF6 in most foundries. Due to its very high GWP SF6 was banned in the EU from 2018.
As well as SO2 and dilute SO2 mixtures, HFC-134a is being used as a cover gas. A study has shown that in die casting, on average 79% of the HFC-134a is destroyed over the melt during processing, reducing emissions of HFC-134a, and further reducing the environmental impact when compared to SF6. For further information see the Öko-Recherche 2009 report for the European Commission.
Electronics Manufacturing Applications
Electronics Manufacturing industries that use fluorocarbon gases for etching and chamber cleaning include liquid crystal displays (LCDs), photovoltaic cells (PV), and semiconductors (including light-emitting diodes). A range of gases are used in two important steps of electronics manufacturing:
- plasma etching silicon containing materials and
- cleaning chemical vapour deposition (CVD) tool chamber-walls where silicon has deposited.
The fluorinated gases used include CH2F2 (difluoromethane, HFC-32). The use of fluorocarbon gases in these processes is crucial to the production of devices, as there are no effective substitutes that can be utilized. The majority of FC emissions results from limited utilisation efficiency (i.e., consumption) of the FC precursors during the etching or the cleaning process. Key measures that have contributed to substantially reduce fluorocarbon gas emissions are, among others, installation of dedicated post process abatement measures.
The World Semiconductor Council (WSC) and its affiliated associations, agreed to voluntarily reduce atmospheric emissions of PFCs and information on the progress of this commitment was reported in a 2017 Statement of the 21st Meeting of the World Semiconductor Council (WSC) and its Best Practice Guidance for Semiconductor PFC Emission Reduction sets out technical guidance In order to effectively and efficiently achieve the (WSC) emission voluntary reduction program.