Aluminium Nitride (AlN): The Complete Guide

Aluminium nitride is a highly advanced technical ceramic distinct from typical aluminium halide salts. It appears as a white or pale yellow powder in its raw form and is engineered for its remarkable ability to conduct heat extremely well while acting as an effective electrical insulator. This rare combination makes it a cornerstone in optoelectronics, semiconductor manufacturing, and high‑performance LED technology.

1. Basic Identification

• Chemical Formula: AlN
• Alternative Names: Aluminium nitride
• Molecular Weight: 40.99 g/mol
• CAS Number: 24304-00-5
• Appearance: White to pale yellow powder; sintered parts are gray or off‑white

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2. Physical Properties

Property	Aluminium Nitride
Melting Point	~2200 °C (3992 °F) under N₂ pressure
Boiling Point	Sublimes/decomposes ~2000 °C at normal pressure
Density	3.26 g/cm³
Thermal Conductivity	140 – 320 W/m·K (purity dependent)
Electrical Resistance	>10¹³ Ohm·cm (excellent insulator)
Solubility	Insoluble in water; slowly hydrolyzes in moist air

AlN is a covalently bonded material. As a powder, it is fine and slightly moisture‑sensitive. Sintered components are hard, heat‑resistant ceramics.

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3. Chemical Behavior & Synthesis

3.1 Slow Hydrolysis

Fine AlN powder slowly degrades in high humidity:

AlN + 3 H₂O → Al(OH)₃ + NH₃ ↑

This is a slow, non‑violent reaction that releases ammonia gas (detectable by its sharp smell in humid storage).

3.2 Synthesis – Carbothermal Reduction

Al₂O₃ + 3 C + N₂ → 2 AlN + 3 CO

Alumina is heated with carbon in pure nitrogen at >1600 °C. Alternatively, pure aluminum powder can be directly nitrided at high temperatures.

3.3 Reaction with Alkalis

AlN is attacked by hot concentrated alkaline solutions, completely dissolving and releasing ammonia.

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4. Industrial Applications

4.1 High‑Power Microelectronics

AlN ceramic substrates pull heat away from silicon chips faster than most metals while remaining electrically insulating – essential for:

• High‑power LED arrays
• Electric vehicle motor controllers
• Military and aerospace radar systems

4.2 Deep‑UV LEDs

With a wide bandgap (6.01 eV), AlN alloys with gallium nitride (AlGaN) to produce deep ultraviolet LEDs for water sterilization and biomedical sanitization.

4.3 Telecommunications (RF Filters)

AlN is piezoelectric, used in surface acoustic wave (SAW) sensors and RF filters in mobile phones.

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5. Safety & Hazard Management

GHS Symbol	Meaning
❗ GHS07	Irritant

Critical Warning: Sintered solid pieces are harmless unless cut (dust hazard). Raw powder is irritating and releases ammonia when wet.

5.1 Health Effects

Route of Exposure	Effect
Inhalation	Powder causes throat/lung irritation; ammonia from hydrolysis damages respiratory tract.
Skin Contact	Slightly irritating; ammonia may cause redness if trapped against sweat.
Eye Contact	Mechanical irritation, redness, pain.
Ingestion	Possible digestive distress; less toxic than aluminum halides.

5.2 PPE

• Respiratory: N95 or P100 for powder or machining
• Hands: Standard lab gloves
• Eyes: Safety glasses with side shields
• Body: Lab coat

5.3 First Aid

• Skin: Wash with soap and water
• Eyes: Flush 15 minutes; ensure no abrasive particles remain
• Inhalation: Move to fresh air if ammonia fumes cause distress

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6. Storage & Handling

• Container: Sealed, moisture‑proof
• Atmosphere: Dry storage critical
• Location: Cool, dry shelf
• Incompatibles: Strong acids, strong bases, water/humidity

6.1 Disposal

• Solid ceramic waste → standard industrial waste
• Bulk powder → slow hydrolysis outdoors (vent ammonia), then discard inert Al(OH)₃ sludge

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7. Environmental Impact

AlN slowly hydrolyzes to aluminum hydroxide (common soil component) and ammonia (disperses or acts as nitrogen source). No significant bioaccumulation or water toxicity.

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8. Comparison with Other Aluminium Compounds

Compound	Formula	Primary Nature	Primary Use
Aluminium Oxide	Al₂O₃	Ceramic / abrasive	Smelting ore, sandpaper, generic insulators
Aluminium Nitride	AlN	Advanced ceramic	Thermal management, RF filters, LEDs
Aluminium Chloride	AlCl₃	Reactive acid catalyst	Plastics, petrochemical refining
Aluminium Phosphide	AlP	Reactive solid	Agricultural fumigant

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9. Frequently Asked Questions

Q: Why use AlN instead of cheaper aluminium oxide (alumina) for electronics?
A: AlN conducts heat nearly ten times better than alumina, preventing chips from overheating while remaining electrically insulating.

Q: Is aluminium nitride the same as aluminium metal?
A: No. Aluminium metal is silvery and conductive. AlN is a ceramic compound that looks and behaves like crushed stone or a ceramic dish.

Q: Can I smell it?
A: Dry AlN is odorless. But if powder is left open, it reacts with humidity to produce ammonia, giving a sharp “window cleaner” smell.

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10. Summary Data Sheet

Property	Value
Chemical Name	Aluminium Nitride
Formula	AlN
Appearance	White/yellow powder or gray ceramic
Density	3.26 g/cm³
Key Attribute	High thermal conductivity + electrical insulation
Primary Hazard	Dust inhalation; ammonia release when wet
Storage	Dry, sealed environment