Metals — Laboratorium

Ions in a sea of electrons

copper · 20 °C

Cu⁺ ions (atom without its valence electron)free electrons

Voltage across the wire0.00 V

Temperature20 °C

Wire: 1 m of copper, 1 mm²

Drude model

Current: —
Wire resistance: —
Resistance vs. 20 °C: —
Drift velocity: —

R = ρ · LA, R(T) ≈ R₂₀ · [1 + α · (T − 20 °C)] copper: ρ = 1.68·10⁻⁸ Ω·m, α ≈ 0.0039 K⁻¹

I = n · e · A · v_d n ≈ 8.5·10²⁸ electrons per 1 m³ of copper

Electrons creep along at about a millimeter per second, yet the lamp lights up instantly — because the electric field sets the whole “sea” moving at once, like water in a full garden hose.

Metals on the podium

Hammer a metal and a salt

blows: 0

metal ionelectron “glue”Na⁺Cl⁻

Record holders

0.53 g/cm³Lithium — the lightest metal, lighter than water (though it reacts with water while floating).

22.6 g/cm³Osmium — the densest element; iridium is a close second.

−38.8 °CMercury has the lowest melting point — it is a liquid at room temperature.

3422 °CTungsten has the highest melting point of all metals — hence light bulb filaments.

29.8 °CGallium melts in your hand but doesn't boil until above 2200 °C.

63 MS/mSilver conducts best; copper is close behind, then gold and aluminum.

Why can metal be forged while salt shatters?

In a metal, the bond is a shared sea of electrons, so it doesn't matter which ion sits next to which. Layers can slide by one position and stay bonded — that is malleability (it can be beaten into sheet) and ductility (it can be drawn into wire). In an ionic crystal, the same shift puts Na⁺ ions opposite Na⁺ and Cl⁻ opposite Cl⁻. They repel each other and the crystal cracks.

Where does metallic luster come from?

Free electrons oscillate in step with the light wave and immediately radiate it back out, so a metal reflects almost all the light. Gold and copper absorb some of the blue, which is why they look yellow and reddish.

Metals in the periodic table →Crystal lattices →Electric circuits →

Blast furnace cross-section

model time: 0 h

Furnace controls

simplified model

Coke per ton of pig iron480 kg

Blast temperature1000 °C

Pig iron in hearth: —
Output: —
CO₂ from furnace per 1 t: —
Ore (63% Fe) per 1 t: —
In hearth: —
Good pig iron: —

1
Drying the charge and first reduction: 3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂approx. 200–600 °C, throat and upper shaft
2
Fe₃O₄ + CO → 3FeO + CO₂ · flux decomposition: CaCO₃ → CaO + CO₂approx. 600–900 °C
3
Indirect reduction: FeO + CO → Fe + CO₂approx. 900–1100 °C; overall: Fe₂O₃ + 3CO → 2Fe + 3CO₂
4
Softening and melting · CO₂ + C → 2CO · FeO + C → Fe + CO · slag: CaO + SiO₂ → CaSiO₃approx. 1100–1450 °C, cohesive zone (inverted “V”)
5
In front of the tuyeres, coke burns in the hot blast: C + O₂ → CO₂, and right after that CO₂ + C → 2COover 2000 °C — this is where the gas that reduces the ore is made
6
Hearth: liquid pig iron (approx. 4% carbon) at the bottom, lighter slag on topapprox. 1450–1550 °C; tapped every few hours

How much CO₂ does a ton of steel cost?

t of CO₂ per ton of crude steel, approximate values

The world average is about 1.9 t of CO₂ per ton of steel (worldsteel, 2023). A blast furnace needs carbon not just as fuel — here carbon is the reducing agent that strips oxygen from the ore. That is why “green steel” needs a different reducing agent: hydrogen. The equation Fe₂O₃ + 3H₂ → 2Fe + 3H₂O gives about 54 kg of hydrogen per ton of iron, and making it by electrolysis takes about 2.5–3 MWh of electricity.

Aluminum: the Hall–Héroult process

since 1886

Cell current400 kA

Cell voltage4.2 V

Al per day: —
Energy per 1 kg: —
Charge per 1 kg: —

m = I · t · Mz · F · η z = 3 (Al³⁺ + 3e⁻ → Al), F = 96,485 C/mol, η ≈ 95%

Aluminum is everywhere, yet it was long a treasure

Aluminum is the most common metal in Earth's crust (about 8% of its mass), but it is locked up in aluminosilicates — feldspars and clays — from which it is hard to extract. The ore is bauxite: about 4–5 t of bauxite yields about 2 t of alumina Al₂O₃, and that in turn gives 1 t of aluminum.

Before Charles Hall (USA) and Paul Héroult (France) independently invented electrolysis in molten cryolite in 1886, aluminum was made chemically and cost more than gold. According to a popular anecdote, Napoleon III served his most important guests with aluminum cutlery, while the rest ate with gold.

Recycling: 5% of the energy

Remelting aluminum scrap takes about 5% of the energy needed to make the metal from bauxite. A can can come back to the shelf as a new can — and since October 1, 2025, Poland has had a deposit of 50 grosz (about 12 US cents) on cans up to 1 L.

Electrolysis and cells →Where does electricity come from? →Plastic recycling →

Copper from Poland: electrorefining

cathode: 0 kg

Oreshales, sandstones and dolomites with about 1.5% copper, from the Lubin, Rudna and Polkowice-Sieroszowice mines

Flotationair bubbles carry grains of copper sulfides to the top — producing a concentrate

Smeltingat the Głogów and Legnica smelters: crude (blister) copper, about 98–99% Cu

Anodesfire refining and casting into anode plates

Cathodeselectrorefining: 99.99% copper — for cables and sheet

The Legnica–Głogów Copper District

KGHM Polska Miedź, Poland's copper company, mines ore from depths of about 600–1300 m and produces about 0.5–0.6 million t of electrolytic copper a year. Poland is also one of the world's leading producers of silver (about 1.3–1.4 thousand t a year in recent years) — silver, gold, selenium and the platinum metals end up in the anode slime, from which they are recovered.

anode: Cu → Cu²⁺ + 2e⁻ cathode: Cu²⁺ + 2e⁻ → Cu

The cell voltage is only about 0.3 V, so 1 kg of pure copper costs about 0.25–0.3 kWh — dozens of times less than a kilogram of aluminum.

Cell current: 20 kA
Copper per day: —

Alloy mixer

copper 100%

Base metal:

Result

bronze ✗ · brass ✗

copper

Hardness vs. base: —
Melting (approx.): —
Density (approx.): —
Corrosion resistance: —

Why an alloy is harder: dislocations

slips: 0

Shear stress0%

alloying atoms (larger and smaller)

Dislocations — “a ruck in the rug”

You can't move a heavy rug by pulling on its edge. But if you make a ruck in it and push the ruck to the other end, the rug moves with no effort. In the same way, a metal deforms not by sliding whole layers at once, but by the travel of dislocations — extra half-planes of atoms. Without them, metals would be hundreds or thousands of times stronger, but also brittle.

The added atoms are larger or smaller than the atoms of the base metal. They push apart or pull in the lattice, and the dislocation “snags” on them. That is why bronze is harder than copper and tin, and steel is harder than iron.

How grains form

A cooling metal solidifies in many places at once. Tiny crystals grow until they meet their neighbors — that is how grains form, visible under a microscope after etching. Grain boundaries also hold back dislocations, so a fine grain means a stronger metal.

Tension and strength →Crystals →

From the Bronze Age to duralumin

dates approximate

c. 9000 BCENear East: the first ornaments of native copper, cold-hammered.
c. 5000 BCEBalkans and Near East: smelting copper from ore in fire.
c. 3300 BCENear East: the Bronze Age begins. Copper with about 10% tin is harder and easier to cast.
c. 2300 BCEThe first bronze objects appear in what is now Poland, both imported and cast locally.
c. 1200 BCEAnatolia and Near East: iron spreads. Iron ores are everywhere; tin is found in only a few places.
8th c. BCEThe Lusatian culture fortified settlement at Biskupin, Poland (timber felled mostly around 738–737 BCE, according to tree-ring dating) — a time of transition: bronze still dominates, iron is only just appearing.
1856Henry Bessemer: a converter in which a blast of air burns excess carbon out of pig iron — cheap steel on a mass scale.
1886Hall and Héroult: aluminum electrolysis. The price of the metal drops fast.
1906–1909Alfred Wilm discovers precipitation hardening of an Al–Cu–Mg alloy — duralumin goes into airships, and later into airplanes.
1913Harry Brearley in Sheffield: steel with about 13% chromium that doesn't rust — stainless steel.
todayPolish coins: 1, 2 and 5 grosz — brass-plated steel (since 2014); 10, 20, 50 grosz and 1 złoty — cupronickel (Cu with 25% Ni); 2 and 5 złoty — bimetallic, cupronickel plus a golden Cu–Al–Zn–Sn alloy.

Test rack: 50 years outdoors

year 0

Time outdoors0 years

A qualitative model with approximate corrosion rates (for steel and zinc, based on the atmospheric corrosivity categories of ISO 9223). The full experiment with nails in test tubes, the electrochemical series and cathodic protection is in Electrochemistry, and the rusting race in Reaction Rates.

Reactivity series of metals

most reactive first

The aluminum paradox: it ranks high in the series, yet it doesn't corrode — because it instantly covers itself with a tight film of Al₂O₃ a few nanometers thick. This is passivation. Stainless steel protects itself in a similar way (Cr₂O₃), while rust on ordinary steel is porous and flakes off, so it protects nothing.

Patina, tarnish and anodizing

Silver turns black from trace amounts of hydrogen sulfide (from eggs, rubber, exhaust): 4Ag + 2H₂S + O₂ → 2Ag₂S + 2H₂O. The sulfide film is thin and can be removed.
Copper first turns brown (oxides), then darkens, and after a decade or several decades turns green: patina is mostly basic copper sulfates and carbonates. The Statue of Liberty (1886) started out the color of a new penny and turned green within about 20–30 years.
Anodized aluminum: an electric current thickens the oxide layer to a few to several dozen micrometers. The layer is porous, so it soaks up dye, and is then sealed — that is how colorful casings and carabiners are made.
Galvanizing: zinc corrodes ten to several dozen times more slowly than steel and gives up its electrons instead of the steel, even when the coating is scratched.

When metal burns — demonstrations only

never at home

Thermite

Once ignited, a mixture of aluminum powder and iron oxide reacts violently: 2Al + Fe₂O₃ → Al₂O₃ + 2Fe. Aluminum takes the oxygen from the iron because it binds to it more strongly, and the heat released melts the iron (over 2000 °C). This is how railroad rails are welded — in special molds, by trained welders.

Burning magnesium

A magnesium ribbon burns with a blinding white light (2Mg + O₂ → 2MgO) that must not be looked at without eye protection. Water must not be used to put it out: hot magnesium reacts with it, releasing hydrogen. Such experiments are shown by a teacher in the lab, with shields and a metal-fire extinguisher. More about flames in Combustion.

How does it work?

Metallic bonding

Metal atoms have few valence electrons and give them up easily. In a piece of metal these electrons don't belong to any single atom — they form a shared “sea of electrons” that holds together the lattice of positive ions. Hence electrical and thermal conductivity (electrons can flow and carry energy), metallic luster, and malleability and ductility.

Reduction: how to take oxygen away from ore

Most metals occur in nature as oxides or sulfides. To get the metal, it has to be reduced. In a blast furnace the reducing agent is carbon monoxide from coke:

Fe₂O₃ + 3CO → 2Fe + 3CO₂ 159.7 g of ore gives 111.7 g of iron → about 1.43 t of Fe₂O₃ per 1 t of Fe

More reactive metals — aluminum, magnesium, sodium — hold on to oxygen too strongly for carbon to take it. They need electricity. Faraday's law tells us how much metal a given charge produces:

m = Q · Mz · F 1 kg Al: Q ≈ 1.07·10⁷ C ≈ 2980 A·h; at 4.2 V that is about 12.5 kWh (at 100% current efficiency)

Steel: iron plus a pinch of carbon

Pig iron from a blast furnace has about 4% carbon and is brittle. In a converter, oxygen burns out most of the carbon, usually leaving 0.05–1%. With slow cooling, the carbon forms plates of hard cementite Fe₃C in pearlite. With rapid cooling (quenching) it gets trapped in the iron lattice — forming very hard and brittle martensite. Tempering, i.e. reheating to 150–650 °C, reduces hardness and brittleness.

Alloys and karats

gold fineness = K24 · 1000 18 K = 750 ‰, 14 K ≈ 583 ‰ (hallmarked as 585), 9 K = 375 ‰

Simplifications: all the simulations are models with approximate numbers. The sea of electrons is the classical Drude model (real electrons in a metal are described by quantum mechanics). The blast furnace has a simplified heat balance, the microstructures are for slowly cooled carbon steel, and the blacksmith game is based on typical charts for steel with about 1% C. The year of the data is given next to numbers that change over time.

Metalsfrom ore to alloy

Ions in a sea of electrons

Wire: 1 m of copper, 1 mm²

Metals on the podium

Hammer a metal and a salt

Record holders

Why can metal be forged while salt shatters?

Where does metallic luster come from?

Blast furnace cross-section

Furnace controls

How much CO₂ does a ton of steel cost?

Aluminum: the Hall–Héroult process

Aluminum is everywhere, yet it was long a treasure

Recycling: 5% of the energy

Copper from Poland: electrorefining

The Legnica–Głogów Copper District

Steel under the microscope

Properties

Forge: quenching and tempering

Hardness vs. toughness

Glow colors

Temper colors

Alloy mixer

Result

Why an alloy is harder: dislocations

Dislocations — “a ruck in the rug”

How grains form

From the Bronze Age to duralumin

Test rack: 50 years outdoors

Reactivity series of metals

Patina, tarnish and anodizing

When metal burns — demonstrations only

Thermite

Burning magnesium

Take a phone apart

Metals in a phone

Urban mining

Where from and where to

How much goes back into use?

How does it work?

Metallic bonding

Reduction: how to take oxygen away from ore

Steel: iron plus a pinch of carbon

Alloys and karats

Challenges

Did you know…?

Stay safe

Keys

Sources of the numbers