Noble metals (aka precious metals) refer to silver (Ag), gold (Au), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). Except Ag and Au, the others are collectively called platinum metals. Noble metals are widely used in petroleum, chemical, electronic, electrical, marine, and aviation industry.
Definition according to DIN EN 10052: „Annealing carried out in a medium that allows the original metallic surface finish to be maintained by preventing oxidation of the metal.“
Annealing is a „heat treatment consisting of heating and soaking at a suitable temperature followed by cooling under conditions such that, after return to ambient temperature, the metal will be in a structural state closer to that of equilibrium.“
A medium is an „environment in which the product is placed during a heat treatment operation. The medium can be solid, liquid or gaseous. “
Pure metals are typically annealed in air or steam, but annealing of alloys should be done in protective atmosphere. Depending on the alloy, the protective gas consists of nitrogen, hydrogen or nitrogen/hydrogen mixtures.
The exact and consistent composition of the protective gas is vital for the quality of metal surfaces. Any unwanted chemical reactions with the metal must be reliably prevented. The solution is the Neutrotherm process, which is based on a neutral gas mixture containing less than 5 % hydrogen.
With minimal investment in hardware, the process provides excellent protection against oxidation of the metal, ensuring the surface remains clean.
Messer process = "Neutrotherm"
The Hydrotherm process is based on a gas mixture containing up to 100 % hydrogen. Here, the hydrogen has not only a chemical action, but - thanks to its high thermal conductivity - also performs a physical function.
Messer process = "Hydrotherm"
BRAZING AND HIGH-TEMPERATURE BRAZING
Brazing is a joining process wherein metals are bonded together using a filler metal with a melting temperature greater than 450 °C, but lower than the melting temperature of the base metal.
High-temperature brazing is flux-free brazing under exclusion of air (vacuum, protective gas) with filler metals whose melting temperature is above 900 °C.
Depending on the base material, two different types of gas atmospheres are used in furnace brazing using flux and inert gas and in high-temperature brazing:
- Chemically inert atmospheres, which protect the parts being brazed from coming into contact with other gaseous elements, which might react with the metals being joined thereby producing surface films that might inhibit flowing of, and wetting by the molten brazing alloy.
- Chemically active atmospheres, which will react, during the brazing cycle, with any surface films present on either the parts to be joined, or the brazing alloy preform, removing them in the process.
Messer processes = "Neutrotherm, "Hydrotherm"