Platinum (Pt)
Platinum is one of the rarest and most valuable metals on Earth, prized for its extraordinary catalytic activity, exceptional corrosion resistance, and high-temperature stability. It is indispensable in automotive catalytic converters (accounting for ~40% of demand), petroleum refining, fuel cells, laboratory equipment, and jewelry. Its density of 21,450 kg/m³ makes it one of the heaviest stable elements.
Properties
- Density
- 21,450 kg/m³
- Melting Point
- 1,768 °C
- Boiling Point
- 3,825 °C
- Thermal Conductivity
- 71.6 W/(m·K)
- Electrical Resistivity
- 1.06 × 10⁻⁷ Ω·m
- Tensile Strength
- 125–240 MPa
- Yield Strength
- 50–130 MPa
- Hardness
- 50–80 HV (annealed)
- Elongation
- 30–40%
- Crystal Structure
- FCC
Common Grades
- Pt 999.5 (Pure): High-purity platinum for laboratory crucibles, thermocouples, and analytical standards.
- Pt-10% Rh: Platinum-rhodium alloy for high-temperature thermocouples (Type S) up to 1,600°C.
- Pt-30% Rh: High-rhodium alloy for glass fiber bushings and extreme-temperature sensors (Type B).
- Pt-5% Ir: Platinum-iridium alloy with improved hardness for spark plug electrodes and surgical instruments.
Applications
- Automotive: Catalytic converters (diesel oxidation catalysts), spark plug electrodes, oxygen sensors
- Chemical Processing: Catalysts for nitric acid production, silicone curing, petroleum reforming
- Laboratory: Crucibles, evaporation dishes, resistance thermometers (Pt100/Pt1000), electrodes
- Fuel Cells: PEM fuel cell catalyst layers, hydrogen economy electrolyzer electrodes
- Medical: Pacemaker electrodes, chemotherapy drugs (cisplatin), dental alloys
FAQ
Why is platinum used in catalytic converters?
Platinum's unique surface chemistry allows it to catalyze the oxidation of carbon monoxide and hydrocarbons into CO₂ and water at relatively low temperatures (250–400°C). Its resistance to poisoning by sulfur compounds and thermal stability at exhaust temperatures (up to 1,000°C) make it irreplaceable in diesel catalytic converters.
What is the difference between platinum and palladium in catalysts?
Platinum excels in diesel oxidation catalysts and is better at oxidizing CO and hydrocarbons under oxygen-rich (lean-burn) conditions. Palladium is preferred for gasoline three-way catalysts and is more effective at converting hydrocarbons under stoichiometric conditions. Palladium is also ~50% cheaper, driving substitution where possible.
Is platinum harder than gold?
Yes, platinum (50–80 HV annealed) is significantly harder than pure gold (25 HV). However, both are relatively soft metals. Platinum alloys like Pt-5%Ir achieve 90–120 HV, comparable to 18K white gold alloys. Platinum's higher density (21,450 vs 19,300 kg/m³) gives jewelry a noticeably heavier feel.