Siliziumnitridkeramik (Si₃N₄)

Silicon nitride (Si₃N₄) ceramics are high-performance non-oxide structural ceramics formed by strong covalent bonds between silicon and nitrogen atoms. With high hardness, hohe Festigkeit, excellent fracture toughness, low density and exceptional thermal shock resistance, Si₃N₄ can withstand rapid temperature changes above 1000 °C without cracking. It is widely recognized as one of the toughest and most reliable advanced ceramics for extreme mechanical and thermal environments.

Crystalline forms of Silicon Nitride (Si₃N₄)

Silicon nitride (Si₃N₄) is known to exist in two main crystalline structures: α-Si₃N₄ and β-Si₃N₄, as well as an amorphous phase. Unter diesen, α-Si₃N₄ is a low-temperature metastable phase, while β-Si₃N₄ is the high-temperature stable phase. These different forms of silicon nitride exhibit significant differences in structure and properties, die ihre jeweiligen Einsatzgebiete bestimmen.

α-Si₃N₄

α-Si₃N₄ has a trigonal crystal system with a complex, tightly packed structure. It is typically formed during low-temperature synthesis and is metastable at high temperatures. During sintering, α-Si₃N₄ readily transforms into β-Si₃N₄, promoting grain growth and densification. It has a high specific surface area and is often used as a raw material for producing high-performance β-Si₃N₄ ceramics.

β-Si₃N₄

β-Si₃N₄ has a hexagonal crystal system with a long columnar, interlocking grain structure. It is the thermodynamically stable phase at high temperatures, featuring high strength, excellent fracture toughness, superior thermal shock resistance, and good oxidation resistance. It is the primary crystalline phase in all high-performance silicon nitride ceramics.

Silicon nitride ceramics, with β-Si₃N₄ as the sole main crystalline phase, possess high strength, high toughness, and excellent thermal shock resistance, making them the preferred material for engine parts, high-speed bearings, and cutting tools.

Vorteile

High strength & Zähigkeit: Flexural strength 600–1000 MPa; excellent resistance to mechanical impact.
Superior thermal shock resistance: Withstands ΔT >800 °C; ideal for rapid heating/cooling cycles.
High wear & Korrosionsbeständigkeit: Resists most acids, alkalis and oxidation; long service life.
Low density & high-temperature stability: Leicht; maintains strength up to 1200–1300 °C.

Anwendungen

Engine & Automobilteile: Turbocharger rotors, valve seats, Brennkammerauskleidungen.
Bearings & sealing: High-speed bearings, mechanical seal rings, pump components.
Cutting & forming tools: Ceramic cutting inserts, dies, wear-resistant guides.
Halbleiter & Luft- und Raumfahrt: Wafer carriers, high-temperature jigs, heat exchangers.