形成气体是一个复杂的话题，因此我将在本节提供一些初步的背景知识，然后在下一次介绍焊接部分。
你是说 "甲酸 "吗？
Forming gas is a mixture of hydrogen (H2) and an inert gas (usually nitrogen, N2) that is used to reduce oxides on metal surfaces to water. Please don’t confuse this with formic acid (HCO2H), which I hope to touch on in another posting later this year.
安全
用惰性气体稀释氢气的原因是要将氢气含量控制在 5.7%（体积比）以下，因为超过这个浓度，氢气就会自燃。林德（Linde）和空气产品（Air Products）等气体公司认为，低于这一水平的成型气体是惰性混合物，因此气瓶附件使用的接头是氮气、氩气、氦气等使用的标准 CGA580 型接头。根据气体供应商的不同，他们可能会允许最大 5.0% 或 4.0% 的氢气，以确保在安全范围内。
尽管如此，100% 的氢气炉在世界各地的各种不同工艺中都有使用，我还在世界各地看到过使用 10% 甚至 20% 氢气/氮气的焊接工艺。我并不是说 >5% 的 H2/N2 不能安全使用，但使用时必须小心。
燃气供应
有三种方法可为气基焊接工艺提供气体：
1/ Mixing hydrogen and nitrogen in a special panel. Sometimes this may also incorporate a catalytic reactor that reacts ppm traces of oxygen, with hydrogen to form water: the water is then removed by adsorption. This process makes a very "clean" forming gas that will have optimal reducing properties. Usually, the nitrogen source is from vaporised cryogenic N2, and the hydrogen is from a cylinder or "tube"-based sources.
2/气瓶供应。可使用单个气瓶或多组气瓶提供混合气体。通常情况下，这种气体无需净化即可直接使用。
3/ Ammonia cracking. Basically, NH3 -> 3N2 + H2. This is feasible, but results in a fixed 3:1 ratio of N2 to H2, and is never used (to my knowledge) in soldering. It is also massively inefficient in terms of costs and power usage to make the ammonia, plus the ammonia usually has a much higher moisture content than a nitrogen plus hydrogen gas mixture.
它对焊接有什么作用？我下次再讲：我会讲热力学和动力学，而且会有一个测试。
干杯安迪
