A grade-specific Safety Data Sheet (SDS) — with the complete hazard classification, handling precautions, and transport information — is supplied with every shipment and available on request. Confirm all safety and regulatory details against the SDS for your specific grade.
Silicone Transformer Oil (STO-50), also supplied as RawSil HT-50, is a 50 cSt polydimethylsiloxane (PDMS) fluid engineered as a low-moisture dielectric and heat-transfer fluid for electrical and thermal-management service. Its wide liquid range, high fire point, and stable dielectric properties make it a less-flammable alternative to mineral oil in transformers and a clean heat-transfer medium where thermal stability and non-conductivity matter.
Applications
- Power & distribution transformers — dry-type and liquid-filled; a less-flammable dielectric coolant meeting IEC 60836 and ASTM D 4652-92, with acceptance per IEEE C57.111.
- Silicone heat-transfer fluid — thermal-management and process heat-transfer service over a wide temperature range, with low volatility and oxidative stability.
- Electronics & data-center thermal management — dielectric, non-conductive fluid for cooling sensitive equipment.
Functional Equivalent to PMX-561 — Direct Drop-In
STO-50 matches Dow/XIAMETER™ PMX-561 specifications across all critical parameters, making it a direct drop-in replacement requiring no system modifications.
| Parameter | STO-50 (RawSource) | PMX-561 (Dow Inc.) |
|---|---|---|
| Chemical composition | PDMS | PDMS |
| Viscosity @ 25°C | 50 cSt | 50 cSt |
| Density @ 25°C | 0.96 g/cm³ | 0.96 g/cm³ |
| Specific heat | 1.51 kJ/kg·K | 1.51 kJ/kg·K |
| Thermal conductivity | 0.151 W/m·K | 0.151 W/m·K |
| Breakdown voltage | 50 kV | 50 kV |
| Volume resistivity @ 25°C | 1.0 × 10¹⁴ Ω·cm | 1.0 × 10¹⁴ Ω·cm |
| Flash point (open cup) | > 285°C | > 300°C |
| Fire point (open cup) | 370°C | ~350°C |
| IEC 60836 / ASTM D 4652-92 | Meets | Meets |
PMX-561 is a trademark of Dow Inc. RawSource is not affiliated with, endorsed by, or sponsored by Dow Inc. Specifications cited are from publicly available technical data sheets. IEC 836 and ASTM D 4652-92 are recognized industry standards for silicone-based dielectric fluids in transformer applications. Customers should validate suitability for their specific application.
This linear PDMS fluid is identified under CAS 63148-62-9 and, as the commercial mixture, CAS 63148-62-9 — both commonly cited on silicone-oil SDS/TDS. Relevant standards: IEC 60836 (unused silicone insulating liquids), ASTM D 4652 (silicone liquid for electrical insulation), and IEEE C57.111 (acceptance of silicone insulating fluid). It qualifies as a less-flammable fluid under NEC 450.23 (fire point >300°C) for indoor/vault installation.
Supplied in North America with reduced domestic lead times. Specifications, samples, and certificates of analysis available on request.
