## Common ground
All options are crucible support plates, used to hold crucibles in high-temperature industrial processes like metal melting or crystal growth.
## Options at a glance
**3926.90 – Plastic material**
- **Defining trait:** Made from synthetic polymer; not suitable for high heat.
- **Typical examples:** Polypropylene or PTFE supports for low-temp lab use.
- **Best fit when:** The application involves low temperatures (below 150°C) and chemical resistance, not high heat.
**6903 – Refractory ceramic**
- **Defining trait:** Engineered for extreme heat and thermal shock; typically aluminum oxide or silicon carbide-based.
- **Typical examples:** Kiln shelves, furnace linings, high-temp crucible stands.
- **Best fit when:** Used in industrial furnaces or kilns with temperatures above 1000°C.
**6909.1X – Ceramic**
- **Defining trait:** General ceramic material; may include non-refractory types.
- **Typical examples:** Porcelain, stoneware, or glazed ceramics for moderate heat.
- **Best fit when:** Moderate temperature use (up to ~800°C), often in labs or small-scale processes.
**7017 – Glass**
- **Defining trait:** Made from silica-based glass; transparent and chemically inert but fragile under thermal stress.
- **Typical examples:** Glass crucible supports in chemical labs, borosilicate trays.
- **Best fit when:** Low to moderate heat (up to ~500°C), transparency or chemical purity is needed.
## Key differences
| Feature | 3926.90 (Plastic) | 6903 (Refractory ceramic) | 6909.1X (Ceramic) | 7017 (Glass) |
|---------------------|-------------------|----------------------------|------------------|--------------|
| Max temperature | <150°C | >1000°C | ~800°C | ~500°C |
| Thermal shock resistance | Poor | Excellent | Moderate | Poor |
| Transparency | No | No | No | Yes |
| Chemical resistance | High (plastic) | Very high | High | Very high |
## How to choose
- Does it need to withstand temperatures above 800°C? → 6903
- Is it used in a lab with moderate heat and transparency needed? → 7017
- Is it for general ceramic use at medium heat (e.g., pottery kiln)? → 6909.1X
- Is the temperature below 150°C and chemical resistance key? → 3926.90
## Overlaps & pitfalls
- **Overlaps:** A refractory ceramic plate may also be classified as "ceramic" (6909.1X), but 6903 is more specific. Use 6903 if high-temp performance is the main feature.
- **Pitfall:** “Ceramic” (6909.1X) includes non-refractory types; don’t assume it’s heat-resistant unless specified.
- **Priority rule:** If a product is designed for extreme heat, prioritize 6903 over 6909.1X. Otherwise, choose based on material function and temperature range