are the easiest to apply while heating. In the case of furnace brazing, the alloy is usually placed beforehand since the process is usually highly automated. Some of the more common types of filler metals used are Aluminium-silicon Copper Copper-silver Copper-zinc (brass) Copper-tin (bronze) Gold-silver Nickel alloy Silver Amorphous brazing foil using nickel, iron, copper, silicon, boron, phosphorus, etc. Atmosphere As brazing work requires high temperatures, oxidation of the metal surface occurs in an oxygen-containing atmosphere. This may necessitate the use of an atmospheric environment other than air. The commonly used atmospheres are Air: Simple and economical. Many materials susceptible to oxidation and buildup of scale. Acid cleaning bath or mechanical cleaning can be used to remove the oxidation after work. Flux counteracts the oxidation, but may weaken the joint. Combusted fuel gas (low hydrogen, AWS type 1, "exothermic generated atmospheres"): 87% N2, 11–12% CO2, 5-1% CO, 5-1% H2. For silver, copper-phosphorus and copper-zinc filler metals. For brazing copper and brass. Combusted fuel gas (decarburizing, AWS type 2, "endothermic generated atmospheres"): 70–71% N2, 5–6% CO2, 9–10% CO, 14–15% H2. For copper, silver, copper-phosphorus and copper-zinc filler metals. For brazing copper, brass, nickel alloys, Monel, medium carbon steels. Combusted fuel gas (dried, AWS type 3, "endothermic generated atmospheres"): 73–75% N2, 10–11% CO, 15–16% H2. For copper, silver, copper-phosphorus and copper-zinc filler metals. For brazing copper, brass, low-nickel alloys, Monel, medium and high carbon steels. Combusted fuel gas (dried, decarburizing, AWS type 4): 41–45% N2, 17–19% CO, 38–40% H2. For copper, silver, copper-phosphorus and copper-zinc filler metals. For brazing copper, brass, low-nickel alloys, medium and high carbon steels. Ammonia (AWS type 5, also called forming gas): Dissociated ammonia (75% hydrogen, 25% nitrogen) can be used for many types of brazing and annealing. Inexpensive. For copper, silver, nickel, copper-phosphorus and copper-zinc filler metals. For brazing copper, brass, nickel alloys, Monel, medium and high carbon steels and chromium alloys. Nitrogen+hydrogen, cryogenic or purified (AWS type 6A): 70–99% N2, 1–30% H2. For copper, silver, nickel, copper-phosphorus and copper-zinc filler metals. Nitrogen+hydrogen+carbon monoxide, cryogenic or purified (AWS type 6B): 70–99% N2, 2–20% H2, 1–10% CO. For copper, silver, nickel, copper-phosphorus and copper-zinc filler metals. For brazing copper, brass, low-nickel alloys, medium and high carbon steels. Nitrogen, cryogenic or purified (AWS type 6C): Non-oxidizing, economical. At high temperatures can react with some metals, e.g. certain steels, forming nitrides. For copper, silver, nickel, copper-phosphorus and copper-zinc filler metals.