如何处理对空气敏感的金属粉末?

哪些金属粉末是空气敏感的

对水敏感的金属粉末涵盖相当广泛的类别。

1) 首先是碱金属和碱土金属锂（Li）、钠（Na）和钾（K）就是典型的例子。它们不仅对空气敏感，还具有与水反应的特性，即会剧烈与水反应，产生热量和氢气，从而引发严重的火灾和爆炸危险。粉末状的镁（Mg）、钙（Ca）和锆（Zr）也属于此类。

2) 一些细小的颗粒 过渡金属也对空气敏感。 当金属被研磨成细粉时，其表面积急剧增大，在空气中容易迅速氧化，甚至可能自行着火。典型的例子包括兰尼镍、铝粉（Al）和锌粉（Zn）。其中，自燃性铝粉一旦接触空气或潮湿环境便会自发燃烧，同时与水反应时还会释放可燃的氢气。

3) 一些在先进制造中广泛应用的合金粉末也对空气敏感。以FGH95超合金粉末为例，其氧含量与操作环境密切相关。在户外加工的粉末比在惰性气体保护下处理的粉末吸收的氧气量高出115%以上。而且粉末越细，氧含量越高，因为细小颗粒具有更大的表面积，有利于氧化和吸附反应的发生。

4) 氢气储存合金粉末是另一个值得关注的领域。 在实际应用中，当氢气中含有CO、O₂或CO₂等杂质时，La-Ni-Al系列储氢合金可能发生表面钝化现象。这些杂质会形成氧化物和氢氧化物层，阻碍进一步的氢气吸收，这种现象被称为“中毒”。此外，在经过多次吸脱氢循环后，由于反复的体积膨胀与收缩，这些合金粉末往往会发生进一步的粉化。

金属粉末在空气中对什么特别敏感

金属粉末通常对空气中的两种成分较为敏感。

第一个主要因素是氧气（O₂）。空气中的氧气会氧化大多数活泼金属。对于细小的金属粉末而言，这可能导致自燃。研究表明，当FGH95合金粉末在空气中加热时，其含氧量会随温度升高而增加，一旦温度超过150°C，这种增加现象就会显著加剧。

2) 水蒸气（H₂O）是另一个关键因素。空气中的湿气与水反应性材料接触时会产生氢气和热量，可能引发火灾或爆炸。即使某些粉末反应不剧烈，湿气仍可能降低其性能或加速腐蚀。

Common Handling Practices for Air-Sensitive Metal Powders

When working with air-sensitive metal powders, the name of the game is complete exclusion of air and moisture. Here's what that looks like in practice:

1) Storage: Store them in sealed, dry containers under an inert gas atmosphere (like argon). The storage area should be cool, well-ventilated, and moisture-proof. Many of these materials come from the manufacturer already packaged under inert gas, submerged in mineral oil, or dissolved in a solvent. As a rule of thumb, only buy what you can use up within a year.

2) Work Environment: The safest approach is to handle them inside an inert-gas glovebox. If you absolutely have to work in a fume hood, keep the sash as low as possible to provide a barrier in case of a violent reaction, and make sure all your glassware is completely dry.

Transfer Techniques: For liquid pyrophoric reagents, you can use a double-tipped needle (cannula method) to transfer them under inert gas protection. If the syringes have to be used to withdraw smaller quantities, ensure they are dry and purged with an inert gas.

3)Personal Protective Equipment (PPE): Always use proper PPE while working with these chemicals, and this should include closed-toed boots made of non-penetrating material (a good example would be leather), face shield and chemical splash goggles, quick removal lab coat or an apron, and solvent-resistant gloves with a fire-resistant outer surface. One should never work alone and should always ensure that someone can see and hear them.

4) Choice of Inert Gas: Nitrogen is the usual gas, but it does not react well with all the chemicals. Always refer to the Safety Data Sheet of the material used.

FAQ

Q: Can I use nitrogen as a blanket gas for all air-sensitive metal powders?

A: No, nitrogen is an inert gas that is often used; however, it does not suit all kinds of materials. Before starting work, always check your material's SDS. SAFETY DATA CENTER: Search the SDS database by product name or CAS for downloading PDF files.

Q: What should I do if a spill happens?

A: Firstly, remove all potential sources of ignition and leave the work area. If the spill is small, then it may be covered with dry sand or lime to retard the process of reacting with air and moisture. It is important not to touch the spilled substance and to call professionals immediately.

Q: What type of fire extinguisher should I use in case of a fire?

A: Use a Class D metal fire extinguisher (such as Met-L-X) or have dry lime on hand. Never use ABC-rated or CO₂ extinguishers—they can actually make some pyrophoric materials react more violently. Also, absolutely do not use water or foam.

Q: What if I get pyrophoric powder on myself?

A: If your clothing or skin catches fire, immediately drop to the ground and roll to smother the flames (if a safety shower is nearby, head straight for it). Flushing with large amounts of water can help carry away the heat from the reaction. If you have a large amount of dry active compound on you, and it's not reacting yet, brush off as much as possible before rinsing with water.

Final Thoughts

Handling air-sensitive metal powders takes specialized knowledge, a meticulous mindset, and thorough preparation.

For research and industrial applications that call for high-quality metal powders, Stanford Advanced Materials (SAM) is a supplier worth looking into. SAM offers a wide range of spherical metal powders for 3D printing, including tantalum-based, aluminum-based, nickel-based, and cobalt-based powders, as well as high-entropy alloys andthermal spray powders. SAM's powders feature tight particle size distribution and good flowability, and they offer customized solutions to meet specific requirements.