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Element · Mg

Magnesium

The lightest structural metal in common use, and one that burns with a light bright enough to have been used for photography.

Construction material

Magnesium is about two thirds the density of aluminium and a quarter that of steel, which makes it attractive wherever mass is the binding constraint. Cast magnesium alloys appear in gearbox housings, laptop shells and aircraft components.

Its drawback is corrosion: magnesium is anodic to almost every other structural metal, so a magnesium part in contact with steel or aluminium in a wet environment corrodes preferentially. That same property is deliberately exploited in sacrificial anodes.

Extraction

Extracted from seawater as much as from ore. Magnesium is the third most abundant element dissolved in the ocean, and precipitating it as hydroxide then reducing it electrolytically is a mature route that is effectively unlimited in feedstock.

Uses

Magnesium's use is structural and depends entirely on being light: it is the lightest structural metal, which puts it in car and aircraft components, laptop casings and power-tool housings where every gram is argued over.

It is also a strong reducing agent, used to extract titanium and to strip oxygen from molten metals. Alloyed in small amounts into aluminium it improves strength and weldability, and a large share of magnesium production ends up there rather than in magnesium parts.

Medium confidence Weak evidence

How we know: 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.

is used as

  • Corrosion protection — application · as a sacrificial anode, corroding in place of the metal it protects

is found in

  • Olivine — mineral
  • Forsterite — mineral Wikidata
  • Asbestos — material · chrysotile is a magnesium silicate, the same composition as the serpentine around it and a different habit
  • Seawater — material · the most abundant metal in the sea, and the one extracted from it directly — the resource is effectively unlimited
  • 5000 series aluminium alloy — alloy · 0.5–5.5% · the alloying element, and the whole of the family's identity — more magnesium is more strength and, above about four per cent, a stress corrosion limit on service temperature
  • 6000 series aluminium alloy — alloy · 0.4–1.4% · half of the magnesium silicide that precipitates on ageing
  • 7000 series aluminium alloy — alloy · 1–3% · with the zinc, forming the precipitate that does the hardening
  • Zinc die-casting alloy — alloy · 0.02–0.06% · a trace, and it is there to suppress the intergranular corrosion that impurities cause
  • Peridot — mineral variety · an essential constituent rather than an impurity
  • Precious coral — material · several per cent, substituting for calcium in the calcite lattice, and the reason the material is harder and denser than reef aragonite
  • Talc — mineral PubChem

is an input to

  • Kroll process — process · the reducing agent, recovered afterwards by electrolysing the magnesium chloride by-product
  • Metallothermic reduction — process · the reducing metal where aluminium would contaminate the product, which is why titanium and zirconium go the magnesium route

is produced by

  • Molten salt electrolysis — process · from molten magnesium chloride, including the chloride returned by the Kroll process
  • Brine evaporation — process · from seawater and from salt-lake brine, precipitated as the hydroxide before reduction — the ocean is an effectively unlimited magnesium resource

is a component of

  • Duralumin — alloy · 0–2% · under a per cent, and enough to change how fast and how far the alloy ages

is sourced from

  • Seawater — material · extracted directly from the sea, precipitated as the hydroxide with lime before reduction — the one metal with no resource constraint worth discussing

is an alternative to

  • Aluminium — element · where weight is the binding constraint: magnesium is a third lighter again, and burns, corrodes and creeps in ways that keep it to castings rather than structure

Sources

  • Material World
    Our own writing
  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
  • PubChem
    US National Library of Medicine · Mixed — aggregated third-party content, rights retained by depositors
  • NIST — National Institute of Standards and Technology
    United States Department of Commerce · US Government work — public information, credit requested

Questions this page answers

Where it comes from, and what it becomes

Follow Magnesium 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

  • 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 (mined as rock salt from bedded deposits, or dissolved in place and pumped up as brine — which is what the chemical industry wants anyway) → Evaporite → is sourced from (what is left when a body of seawater evaporates faster than it is replenished — the salts come out in order of solubility, which is why the sequence is readable) → 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
  • Magnesium → is produced by (from molten magnesium chloride, including the chloride returned by the Kroll process) → Molten salt electrolysis → takes as input (after concentration, as one of the two routes to lithium chloride) → Lepidolite
  • Magnesium → is sourced from (extracted directly from the sea, precipitated as the hydroxide with lime before reduction — the one metal with no resource constraint worth discussing) → 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
  • 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 (the feedstock for solar salt and, in the salars, for the far stronger brines that lithium comes from) → 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
  • 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
  • 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 (mined as rock salt from bedded deposits, or dissolved in place and pumped up as brine — which is what the chemical industry wants anyway) → Evaporite → is composed of (precipitated early, when the water has reduced to roughly a fifth of its volume) → Gypsum

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

Downstream — what it becomes

  • Magnesium → is an input to (the reducing agent, recovered afterwards by electrolysing the magnesium chloride by-product) → Kroll process → produces (as sponge, which must then be crushed, melted and cast before it is usable metal) → Titanium → is a component of (the other half of the strengthening phase) → Nickel superalloy → is associated with (the jet engine created the industry, because no existing material survived the turbine inlet) → The wartime materials programmes complete chain
  • Magnesium → is an input to (the reducing metal where aluminium would contaminate the product, which is why titanium and zirconium go the magnesium route) → Metallothermic reduction → produces (magnesium reducing boron oxide, which gives an impure amorphous boron — the crystalline element needs a different route entirely) → Boron → is a component of (about one per cent, and structurally essential — the compound is Nd₂Fe₁₄B, and without the boron it does not form) → Neodymium magnet → is used as (the strongest in commercial use, and the reason a motor, a hard drive and an earbud can be small) → Permanent magnets
  • Magnesium → is a component of (under a per cent, and enough to change how fast and how far the alloy ages) → Duralumin → is used as (aircraft structure, which it was developed for and dominated for half a century) → Structural engineering
  • Magnesium → is used as (as a sacrificial anode, corroding in place of the metal it protects) → Corrosion protection
  • Magnesium → is an input to (the reducing metal where aluminium would contaminate the product, which is why titanium and zirconium go the magnesium route) → Metallothermic reduction → produces (magnesium reducing beryllium fluoride, and the reason beryllium is expensive before anyone accounts for how carefully it has to be handled) → Beryllium → is used as (copper-beryllium alloys, for non-sparking and spring applications) → Alloying
  • Magnesium → is an input to (the reducing metal where aluminium would contaminate the product, which is why titanium and zirconium go the magnesium route) → Metallothermic reduction → produces (aluminium reducing barium oxide under vacuum, the barium distilling off as vapour) → Barium → is used as (barium sulfate for gastrointestinal X-ray contrast) → Medical imaging

These are the most distinct paths onward. Magnesium ends up in others besides.