Why Are Chemicals Stored In Metal Containers?

Lucy Bell-Young

by Lucy Bell-Young

27th January 2021

While metal containers are reactive, they are a crucial element to any factory. The typical laboratory houses a considerable range of chemicals that require safe storage. As we mentioned in our earlier discussion about why chemicals are stored in plastic containers, every substance has unique properties and storage requirements.

Strong acids, for example, are best stored in PMP or HDPE containers. This is partly because these plastics are chemically inert and so won’t react with the substance. Metal containers, on the other hand, are significantly more chemically reactive than other materials like plastic or glass. For this reason, it is not suitable to store certain chemicals in metal containers as they are likely to corrode.

But if metal containers are so reactive, why do laboratories use them at all?

Flammable Solvent Storage Cabinets

A collection of bottled flammable substances

Flammable solvents include substances like alcohols, toluene, and hexane. These chemicals are liquids that have a flashpoint of approximately 37.8°C. This is the lowest temperature at which the flammable liquid releases enough vapour to ignite.

The vapour released by flammable solvents lingers above the liquid. This represents the main source of danger as vapour is prone to ignition by naked flames, or sparks produced by electrical switches such as thermostats.

Fire resistant metal cabinets are ideal for the storage of flammable solvents. This is because they have at least 30 minutes of fire resistance, and are robust enough to withstand any damage. Metal cabinets are also equipped with metal trays to contain spillages.

In this way, fire resistant metal containers  are ideal for flammable solvents as they protect them against naked flames. This is something plastic or glass containers could not facilitate.

Chlorinated Solvents

Naked flames and sparks in the workplace aren’t the only things metal containers protect against. Chlorinated solvents, such as chloroform, would have violent reactions with flammable solvents if the two were mixed. This is why chlorinated and flammable solvents should be kept separate.

While chlorinated solvents like trichloroethylene (TCE) do not have flashpoints, meaning that they are highly resistant to ignition, they do have flammable limits in air. These limits are measured in volume percent, and define the concentration of solvent vapours in the air under which a flame may occur. TCE, for example, has a flammable limit of 8% at 25°C.

While these concentrations are rare, they become more likely when solvents are stored in confined areas. Therefore, chlorinated solvents should be stored in well ventilated metal containers, cabinets, or bins to avoid ignition.

Reactivity of Metal Containers

As we have seen, metal containers are vital for storing different kinds of solvents. However, they do have certain drawbacks. Metal containers are not able to store most acids because of how they react together. You can see the general word equation for this reaction below:

Acid + Metal → Salts + Hydrogen Gas

When metal reacts with acid, salt and hydrogen gas are produced. This ultimately reduces the volume of the chemical being contained. As well as this, acid is a highly corrosive substance with the ability to eat away at most materials.

When acids and bases are stored in Teflon containers, for example, corrosion isn’t a problem because of the hydrophobic properties of PTFE. Since metal containers don’t have this slippery advantage, it means that they are more likely to corrode when storing particular chemicals.

Packaging Materials

Not all hope is lost for metal containers, though, as they provide excellent protection for the transportation of chemicals. At ReAgent, our 1000L IBCs (Intermediate Bulk Containers) are protected by an exterior metal cage; and our 200L drums give you the option of a stainless steel outer-skin for maximised protection.

An example of how ReAgent uses metal containers to protect IBCs
“At ReAgent, our 1000L IBCs are protected by an exterior metal cage.”

Which Group Of Elements Contains The Most Reactive Metals?

The most reactive metals in the periodic table are the elements in Group 1. These are alkali metals and include:

  • Lithium (Li)
  • Sodium (Na)
  • Potassium
  • Rubidium (Rb)
  • Cesium (Cs)
  • Francium (Fr)

Alkali metals are the most reactive metals because they have larger atomic radii and low ionisation energies. With only one electron in their outer shell, any one of these elements are also ready and raring to lose that electron when they ionically bond with other elements.

These metals get more reactive the further you go down the group, making francium the most reactive element in Group 1 while lithium is the least reactive. The reason this happens is because as the group descends, the atoms of each element get larger: lithium, for example, has a Van der Waals radius of 182pm, while francium’s is 348pm. Additionally, the further down an element is in the group, the further its outer electron gets from the nucleus, and the weaker the attraction becomes between the outer electron and the nucleus.

Alkali metals are so reactive, in fact, that they have to be stored under oil. This is because the hazards of alkali metals are that they are incredibly sensitive to air-borne moisture and, yes, air itself. When these elements react with water, they produce hydrogen gas, heat, and the corresponding metal hydroxide. Meanwhile, when these metals react with air, they form caustic metal oxides – and the heavier the metal, the more likely it is to ignite spontaneously at room temperature. Storing alkali metals in oil prevents these reactions by acting as a protective barrier between the metal and air or water.

Vector listing alkali metals in Group 1

Finding the right container for your product is like finding the right case for your phone. There are many characteristics that have to be considered: Is it shatterproof? Does it provide enough protection? Is it the right size and shape?

Luckily, at ReAgent we specialise in manufacturing and packaging a variety of chemicals so that we can meet the individual needs of your business. From HDPE bottles to 25,000L tankers, we’ve got the perfect packaging for you, whether it’s for corrosive acids, flammable liquids, or even deionised water.

Disclaimer

All content published on the ReAgent.ie blog is for information only. The blog, its authors, and affiliates cannot be held responsible for any accident, injury or damage caused in part or directly from using the information provided. Additionally, we do not recommend using any chemical without reading the Material Safety Data Sheet (MSDS), which can be obtained from the manufacturer. You should also follow any safety advice and precautions listed on the product label. If you have health and safety related questions, visit HSE.gov.uk.