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Material World
Application

Corrosion protection

Keeping a structural metal from returning to the oxide it was smelted from.

Corrosion is smelting in reverse: a metal reverting to the compound it was won from. Protecting against it takes one of three approaches — a barrier that excludes water and oxygen, a self-repairing oxide film grown by an alloying addition, or a sacrificial metal that corrodes preferentially.

The third is the interesting one, because it works even where the coating is damaged. Paint fails at a scratch; galvanising does not.

Medium confidence Weak evidence checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

uses

  • Argon — element · as a shielding gas that keeps oxygen away from hot metal during welding
  • Gold — element · as plating on contacts that must not tarnish
  • Chromium — element · the self-repairing oxide film that makes steel stainless
  • Fluorine — element · fluoropolymer linings resist chemicals that attack every metal
  • Magnesium — element · as a sacrificial anode, corroding in place of the metal it protects
  • Oxygen — element · as the element that both causes corrosion and forms the protective oxide films that prevent it
  • Titanium — element · its passive oxide film is why it survives seawater
  • Zinc — element · galvanising: zinc corrodes in the steel's place
  • Sodium hydroxide — compound · in the Bayer process and in metal cleaning before coating
  • Brass — alloy · in air rather than seawater — brass dezincifies in chloride
  • Stainless steel — alloy · by a self-repairing chromium oxide film rather than by a coating

Sources

  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Corrosion protection back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Corrosion protection → uses (as plating on contacts that must not tarnish) → Gold → is sourced from (a significant share of world gold arrives this way, recovered from copper anode slimes at no mining cost of its own) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
  • Corrosion protection → uses (the self-repairing oxide film that makes steel stainless) → Chromium → is produced by (as ferrochrome, reduced from chromite and added to steel without ever being separated as the pure metal) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation → takes as input (the feedstock, and an unusual one in being free, unlimited and available anywhere — the cost is entirely the energy to liquefy it) → Air
  • Corrosion protection → uses (as a sacrificial anode, corroding in place of the metal it protects) → Magnesium → is produced by (from seawater and from salt-lake brine, precipitated as the hydroxide before reduction — the ocean is an effectively unlimited magnesium resource) → Brine evaporation → takes as input (and the pond sequence is run so that the less soluble salts crystallise out first, leaving the sodium chloride to be harvested on its own) → Salt → is sourced from (by solar evaporation, which needs a dry sunny coast and is the cheapest route there is) → Seawater → is composed of (about 96.5 per cent by mass — seawater is 3.5 per cent dissolved solids and the rest of it is this) → Water
  • Corrosion protection → uses (its passive oxide film is why it survives seawater) → Titanium → is produced by (as sponge, which must then be crushed, melted and cast before it is usable metal) → Kroll process → takes as input (the inert atmosphere, without which the titanium would take oxygen from the air) → Argon → is produced by (drawn from an intermediate height in the column, between nitrogen and oxygen) → Air separation → takes as input (the feedstock, and an unusual one in being free, unlimited and available anywhere — the cost is entirely the energy to liquefy it) → Air
  • Corrosion protection → uses (in the Bayer process and in metal cleaning before coating) → Sodium hydroxide → is produced by (at the cathode, in fixed proportion to the chlorine whether demand agrees or not) → Chlor-alkali electrolysis → takes as input (the largest single use of salt, and the process the whole chlorine and caustic soda industry rests on) → Salt → is produced by (in the solar route — the same process, read from the other end) → Brine evaporation → takes as input (the feedstock for solar salt and, in the salars, for the far stronger brines that lithium comes from) → Seawater
  • Corrosion protection → uses (in air rather than seawater — brass dezincifies in chloride) → Brass → is composed of (the majority component) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation

These are the most distinct paths back. Corrosion protection can be traced through others besides.