- ▸ Safety Data Sheet (SDS) PDF · SDS
- ▸ Technical Data Sheet (TDS) PDF · TDS
- ▸ Typical Certificate of Analysis (CoA) PDF · COA
Values shown are typical for the current commercial grade. A lot-specific Certificate of Analysis accompanies every shipment; the grade-specific SDS is available on request.
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.
Request SDS →Silicone Transformer Oil (STO-50), product code RS-STO 50 (formerly 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.
Fire point >340°C
Breakdown 50 kV
Less-flammable (NEC 450.23)
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.
STO-50 — Typical Properties
Figures are subject to change; STO-50 values are typical and not a guaranteed specification. Customers should validate suitability for their specific application.
CAS 63148-62-9 (polydimethylsiloxane) · conforms to IEC 60836, ASTM D 4652 and IEEE C57.111 · qualifies as less-flammable under NEC 450.23. Supplied in North America with reduced lead times — specifications, samples, and certificates of analysis available on request.
Regulatory & registration requirements
- TSCA (US):
- REACH (EU): Not determined from public registry
- EC number: 687-578-3
TSCA Inventory flag XU: a substance exempt from reporting under the Chemical Data Reporting Rule (40 CFR 711) (EPA flag legend).
Source: EPA TSCA Inventory (July 2025 release) · ECHA CHEM — retrieved 2026-07-12
Silicone Transformer Oil (STO-50) — 50 cSt PDMS Dielectric Fluid — frequently asked
What is the CAS number of Silicone Transformer Oil (STO-50)?
The CAS number of Silicone Transformer Oil (STO-50) is 63148-62-9.
What is the molecular formula of Silicone Transformer Oil (STO-50)?
The molecular formula of Silicone Transformer Oil (STO-50) is (C2H6OSi)n.
Which CAS numbers cover polydimethylsiloxane fluids?
Methyl end-blocked PDMS fluids are registered under CAS 63148-62-9, which EPA's Substance Registry Services names 'Siloxanes and Silicones, di-Me', a UVCB substance with no single molecular formula, with the synonym 'Polydimethylsiloxane, methyl end-blocked'. CAS 9006-65-9 is indexed as dimethicone, and an ECHA record groups CAS 9016-00-6, 63148-62-9 and 68037-74-1 as organopolysiloxanes, linear or branched with methyl groups.
What are the dielectric properties of silicone transformer fluid?
ASTM D4652 covers polydimethylsiloxane of nominal viscosity 50 mm2/s at 25 °C with a fire point of 340 °C or greater, for use as an insulating or cooling medium in transformers. A manufacturer bulletin gives a dielectric strength of 400 volts/mil and a volume resistivity of 1.0 x 10^15 ohm-cm at 25 °C for the 50, 100 and 200 cSt grades, and a U.S. Bureau of Reclamation table lists typical new silicone oil at 40 kV dielectric breakdown (ASTM D-877).