If silicone oil turns black, thickens or forms carbon deposits after only a few days, the problem may be product selection rather than temperature alone. A stated “maximum temperature” may refer to short-term use or a closed system—not continuous operation in air.

Silicone oils resist heat because their Si–O backbone has a bond energy of approximately 452 kJ/mol, higher than the roughly 347 kJ/mol of C–C bonds. However, side groups determine the practical temperature limit.

Methyl silicone oil (PDMS) offers good thermal stability, but prolonged exposure to air near 200°C can cause oxidation. Phenyl silicone oil generally provides better high-temperature stability because phenyl groups modify intermolecular forces and thermal degradation behaviour.

Selection by Temperature

Around 200°C: IOTA BJ100

Suitable for heat transfer, pressure transmission and dielectric fluids.

• Viscosity at 25°C: 100–150 mm²/s

• Flash point: approximately 260°C

• Volatility at 250°C for two hours: <1.5%

• Dielectric strength: approximately 20 kV/mm

• Recommended range: −35 to 200°C

BJ100 combines heat resistance with electrical insulation, making it suitable for capacitors and transformers.

Around 280°C: IOTA BJ400

Suitable for high-temperature heat transfer, release and lubrication where a thicker oil film is required.

• Viscosity at 25°C: 400–450 mm²/s

• Density: 1.073 g/cm³

• Flash point: 300°C

• Stated range: −30 to 280°C

Confirm whether 280°C is a continuous temperature or only a short-term peak.

Around 300°C: BJ550 or IOTA255-500

IOTA BJ550

• Viscosity: approximately 125 mm²/s

• Flash point: 300°C

• Pour point: −50°C

• Open-system range: −40 to 230°C

• Closed-system range: −40 to 315°C

BJ550 provides good flow and wide-temperature performance. Its 315°C rating applies to suitable closed systems—not continuous operation in open air.

IOTA255-500

• Viscosity: 450–500 mm²/s

• Flash point: 300°C

• Refractive index: 1.495–1.505

• Stated range: −30 to 300°C

Its higher viscosity is suitable for thicker lubricating films and high-viscosity heat-transfer applications. It may be evaluated as an alternative for AP-500 or TSF433 applications, but replacement must be confirmed through testing.

Key Selection Rules

• Distinguish continuous temperature from short-term peak temperature.

• Confirm whether the system is open, closed or protected by inert gas.

• Do not treat flash point as the maximum service temperature.

• Lower viscosity improves circulation and heat transfer; higher viscosity provides a thicker lubricating film.

• Acids, alkalis, water, mineral oil, metal salts and metal oxides can accelerate degradation.

• For 350–400°C, consider a customised fluid or redesign of the heat-transfer system.

Quick guide: choose BJ100 around 200°C, BJ400 around 280°C, and BJ550 or IOTA255-500 for suitable 300°C applications.

For complete TDS documents or sample testing, visit www.siliconeoil.net or contact Iota Silicone Oil Anhui Co., Ltd. Select by temperature duration, system type, viscosity and application—not by the maximum-temperature claim alone.