Silicon nitride tube

1. ‌Chemical Structure and Physical Properties‌

• ‌Chemical Composition‌: Si₃N₄ is formed by covalent bonding between silicon (Si) and nitrogen (N), constructing a three-dimensional network of [SiN₄] tetrahedral units. It exhibits two coexisting crystalline phases: α-phase (kinetically stable) and β-phase (thermodynamically stable)34.

• ‌Physical Characteristics‌:

• Density: 3.1–3.3 g/cm³37

• Hardness: HV 1500–1800 (comparable to diamond)57

• Flexural strength: 800–1200 MPa (2–3× that of alumina)7

• Fracture toughness: 6–9 MPa·m¹/² (3× that of alumina)7.

2. ‌Core Performance Advantages‌

• ‌High-Temperature Resistance‌: Long-term usability in air up to 1200°C, short-term up to 1600°C. Low thermal expansion coefficient (3.2×10⁻⁶/K) and exceptional thermal shock resistance (ΔT critical value >800°C)34.

• ‌Mechanical Properties‌: Combines high strength and toughness. The interwoven columnar grain structure of β-Si₃N₄ enhances fracture resistance via crack deflection mechanisms57.

• ‌Chemical Stability‌: Resists acid/base corrosion (except concentrated H₂SO₄/HF), molten metal erosion (e.g., aluminum), and oxidation temperatures >1400°C37.

• ‌Electrical Properties‌: Low dielectric constant (ε≈8–9) and minimal loss (tanδ <0.001) at high frequencies, ideal for RF device packaging67.

3. ‌Manufacturing Processes and Technologies‌

The fabrication of silicon nitride ceramics involves three stages: powder synthesis, forming, and sintering.

• ‌Powder Synthesis‌: Methods include direct nitridation of silicon powder or chemical vapor deposition (CVD), with particle size control (≤3 μm for cold isostatic pressing; >3 μm requires dry grinding)13.

• ‌Forming Techniques‌:

• Tape casting (controllable green tape thickness)2

• Cold isostatic pressing (high-density green body formation)8.

• ‌Sintering Processes‌:

• Reaction sintering: Low cost but higher porosity7.

• Gas pressure sintering (GPS): Achieves >99% density and superior strength7.