The efficacy of any additive in polymer systems, ceramics, or coatings is dictated by its intrinsic physical properties. These properties influence handling, dispersion, compatibility, and ultimately, the performance of the end product. A thorough grasp of these parameters allows for better formulation decisions and quality control.
The physical properties of Zinc Borate can vary slightly depending on its specific hydrate form and manufacturing process. The most common commercial grades are based on the 3.5 hydrate and 2.0 hydrate forms. The following list and table detail the standard properties you can expect from a typical high-quality product.
Primary Physical Characteristics:
Appearance: A fine, white, odorless powder.
Solubility: Very low solubility in water and most organic solvents. This insolubility is a key advantage for applications requiring long-term stability and leach resistance.
Density: Has a specific gravity that impacts loading and dispersion in compounds.
Particle Size: Available in various mesh sizes, which directly affects its rate of dispersion and the viscosity of compounded materials.
Thermal Stability: Exhibits high dehydration temperatures, making it suitable for processing in high-temperature polymers.
The following table provides a quantitative summary of these critical parameters for a standard grade.
Table: Typical Physical Property Specifications of Zinc Borate (3.5 Hydrate)
| Property | Value / Description | Standard Test Method |
|---|---|---|
| Chemical Formula | 2ZnO·3B₂O₃·3.5H₂O | — |
| Molecular Weight | 434.66 g/mol | — |
| Appearance | White, free-flowing powder | Visual |
| Zinc Oxide (ZnO) | 37 - 40% | Gravimetric |
| Boric Oxide (B₂O₃) | 45 - 48% | Gravimetric |
| Loss on Ignition (LOI) | 13.5 - 15.5% | ASTM D7348 |
| Specific Gravity | 2.67 - 2.72 | ASTM D854 |
| Bulk Density | 350 - 650 kg/m³ | ASTM B527 |
| Median Particle Size (D50) | 5 - 12 µm | Laser Diffraction |
| Dehydration Temperature | > 290 °C | TGA |
| Refractive Index | ~1.58 | — |
| Solubility in Water | < 0.28 g/100ml @ 20°C | ASTM E1148 |
The data presented above is not merely academic; each property has a direct impact on how Zinc Borate functions in real-world scenarios.
Low Solubility & High Dehydration Temperature: These properties are fundamental for its use as a flame retardant in engineering plastics (like nylons, PBT, PET) and elastomers that are processed at high temperatures. It ensures the additive does not degrade or dissolve during processing, maintaining its fire-inhibiting action.
Particle Size Distribution: A fine and consistent particle size ensures excellent dispersion within a polymer matrix or coating. This uniformity prevents defects and ensures consistent flame retardancy throughout the entire material, which is a critical performance factor for high-grade Zinc Borate.
Refractive Index: This optical property is important for applications where clarity or specific color matching is needed. A refractive index close to that of many polymers allows it to be incorporated without causing significant opacity or visual defects in the final product.
In conclusion, selecting the correct grade of Zinc Borate with the appropriate physical specifications is paramount for achieving desired performance in your formulation. By referencing these key properties, you can make an informed decision that ensures product efficacy, stability, and quality.
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