Materials
Sapphire (Single-Crystal Al₂O₃)
Single-crystal aluminium oxide with hardness, chemical resistance, optical transmission potential, and high-temperature stability reviewed by grade and application.
What Is Sapphire?
Sapphire is the single-crystal form of aluminium oxide (Al₂O₃), also known as corundum. Unlike polycrystalline alumina ceramics, single-crystal sapphire exhibits isotropic (or near-isotropic) optical properties, exceptional surface smoothness after polishing, and far superior chemical resistance.
Its combination of properties makes it the material of choice for:
- Optical windows requiring wavelength-band review from UV through mid-infrared
- High-temperature viewports in semiconductor process chambers
- Plasma-facing components where chemical attack resistance is critical
- Wear-resistant components where hardness approaches diamond (9 Mohs)
Key Material Properties
| Property | Value | Notes |
|---|---|---|
| Crystal Structure | Hexagonal (R3̄c) | Single-crystal material source should be confirmed |
| Density | 3.98 g/cm³ | — |
| Hardness | Grade-dependent material reference | Confirm if critical |
| Young’s Modulus | Axis-dependent material reference | Confirm if critical |
| Flexural Strength | Grade-dependent material reference | Confirm if critical |
| Max Use Temperature (air) | Application-dependent | Review mounting and atmosphere |
| Melting Point | Material reference | Confirm if critical |
| Thermal Conductivity | Axis-dependent material reference | Confirm if critical |
| Thermal Expansion Coefficient | Axis-dependent material reference | Confirm if critical |
| Refractive Index (589 nm) | Material reference | Confirm if critical |
| Optical Transmission Range | Grade, thickness, and surface-finish dependent | Confirm by wavelength requirement |
| Dielectric Constant | Frequency and axis dependent | Confirm if critical |
| Chemical Purity | Confirm by material source | Certificate-dependent |
Optical Transmission
Sapphire transmits broadly across the ultraviolet, visible, near-infrared, and mid-infrared spectrum:
| Wavelength Band | Review Note |
|---|---|
| UV | Confirm grade, thickness, and surface finish |
| Visible / NIR | Confirm wavelength band and transmission requirement |
| Mid-IR | Confirm wavelength, thickness, and operating temperature |
This broad transmission potential makes sapphire a candidate for multi-wavelength process monitoring, pyrometry windows, and UV-process viewports after the exact optical requirement is reviewed.
Chemical Resistance
Sapphire can offer strong chemical resistance, but compatibility should be reviewed against concentration, temperature, and exposure time:
| Chemical | Resistance |
|---|---|
| HF (dilute) | Review concentration, temperature, and exposure time |
| HF (concentrated, hot) | Requires application review |
| H₂SO₄, HNO₃, HCl | Review process conditions |
| NaOH, KOH (dilute) | Review process conditions |
| NaOH, KOH (hot, concentrated) | Requires application review |
| Plasma (Cl₂, CF₄, O₂) | Review plasma chemistry and power |
| Water, steam | Review temperature and mounting |
Crystal Orientation Options
We supply and machine sapphire in standard and custom crystal orientations:
| Orientation | Description | Common Applications |
|---|---|---|
| C-plane (0001) | Basal plane; optical behavior should be confirmed by requirement | LED substrates, general windows |
| A-plane (11-20) | — | Special optics, substrates |
| R-plane (10-12) | — | Heteroepitaxy substrates |
| M-plane (10-10) | — | Specialized semiconductor |
| Random / Custom | Off-axis cuts available | Customer-specified |
Machining Capabilities on Sapphire
Sapphire’s high hardness requires diamond tooling and careful inspection planning. Machining requirements can include:
| Process | Achievable Specification |
|---|---|
| Core drilling (cylindrical blanks) | Diameter tolerance reviewed by drawing |
| Slicing (diamond wire) | Thickness and minimum section reviewed by material and geometry |
| Lapping | Flatness and parallelism specified per application |
| Optical polishing | Roughness and surface form reviewed case by case |
| Grinding (OD/ID) | Tolerance reviewed by geometry |
| Chamfering & edge grinding | As specified |
Typical Products
- Viewport windows — flanged or unmounted, for process chamber monitoring
- Optical flats & windows — wavelength and polishing requirements reviewed by specification
- Laser windows — bare or coating-reviewed designs for specified wavelengths
- Wear plates & bearing inserts — exploiting extreme hardness
- Custom shapes — discs, rectangles, prisms, rods — drawing-based fabrication
Related Sapphire and Hard-Brittle Components
Sapphire is often reviewed alongside fused quartz and technical ceramics when buyers compare window materials, optical access components, or wear-resistant hard-brittle parts. These related pages keep the product selection separate from the material properties described here:
- Sapphire window — retained product detail page for sapphire optical and viewport windows
- Quartz plates, discs, and windows — adjacent flat quartz window and plate component formats
- Custom precision components — drawing-based custom parts in quartz, sapphire, and technical ceramics
- Custom quartz glass fabrication — adjacent hard-brittle material fabrication workflow for fused quartz projects
Quality & Documentation
- Crystal orientation verification can be discussed for specified orientations
- Surface roughness measurement can be discussed based on drawing requirements
- Dimensional inspection records can be included for agreed critical features
- Optical transmission testing can be discussed for optical-grade components