| HS Code | 647595 |
| Appearance | Colorless to pale yellow transparent liquid |
| Phenyl Content | ≥25% |
| Viscosity At 25 C | 200-500 mPa·s |
| Refractive Index At 25 C | 1.49-1.51 |
| Density At 25 C | 1.02-1.08 g/cm³ |
| Flash Point | ≥280°C |
| Volatile Matter | ≤1.0% (150°C, 3 h) |
| Acid Value | ≤0.05 mg KOH/g |
| Thermal Stability | Good high-temperature stability |
| Dielectric Strength | ≥30 kV/mm |
| Volume Resistivity | ≥1×10^14 Ω·cm |
| Pour Point | ≤-40°C |
As an accredited Phenyl Silicone Fluid RH-C256A factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Phenyl Silicone Fluid RH-C256A is packaged in 200 kg steel drums, sealed for safe storage and transport. |
| Container Loading (20′ FCL) | Phenyl Silicone Fluid RH-C256A loaded in a 20′ FCL container, securely palletized and strapped, with proper labels and shipping documents. |
| Shipping | Phenyl Silicone Fluid RH-C256A is shipped in sealed 200 L drums or IBC totes at ambient temperature. It is generally handled as a non-hazardous industrial chemical. Store in a cool, dry, well-ventilated area, keep containers closed, avoid spills, and follow the SDS. |
| Storage | Store Phenyl Silicone Fluid RH-C256A in a cool, dry, well-ventilated area away from direct sunlight, heat, sparks, and open flames. Keep containers tightly closed when not in use and protect from moisture and contamination. Store separately from strong oxidizing agents. Avoid freezing and extreme temperatures. Use appropriate secondary containment, and follow local regulations and the supplier’s SDS. |
| Shelf Life | Shelf life: typically 24 months from manufacture when kept in original sealed container, stored cool, dry, and away from direct sunlight. |
Closed-loop liquid-phase heat transfer systems that exceed the atmospheric oxidation threshold of mineral-based thermal oils—ordinarily set at approximately 280°C to 300°C for severely hydrotreated paraffinic grades—can be evaluated with Phenyl Silicone Fluid RH-C256A when the expansion tank is blanketed with dry nitrogen. The principal operational distinction derives from the phenyl-modified dimethylsiloxane backbone, which increases aromatic character and lowers evaporation loss relative to dimethyl silicone fluids of equivalent kinematic viscosity. The fluid is charged into a system equipped with a positive-displacement gear pump or a magnetically coupled centrifugal pump. Seal and gasket compatibility requires verification: FFKM or low-temperature fluoroelastomer is generally acceptable, while standard EPDM O-rings and nitrile rubber gaskets exhibit swelling or embrittlement after 500 h to 1000 h at 230°C to 260°C. Start-up after charging involves cold circulation at ambient temperature for 20 min to 30 min, followed by staged heat-up at 5°C/min to 10°C/min until 120°C, where dissolved water and low-boiling fractions are vented through a high-point bleed valve. The upper continuous service temperature in closed systems is generally limited by oxidative gelation rather than thermal cracking; typical phenyl silicone fluids in this class exhibit flash points in the range of 280°C to 330°C under ASTM D92, but air ingress at the expansion vessel can initiate viscosity increase after 400 h to 800 h. A nitrogen purge rate of 0.1 L/min to 0.5 L/min per cubic metre of vapour space is normally sufficient in service. Kinematic viscosity should be monitored at 40°C using ASTM D445; a viscosity increase above 25% to 30% from the fresh-fluid baseline signals either oxidation or contamination. The system charge volume should leave 25% to 30% of the expansion vessel capacity as vapour space to accommodate thermal expansion. For hot-oil units serving reactor jackets, press platens, or calender rolls, the fluid is circulated at 1.5 m/s to 3.5 m/s linear velocity in the heater tubes, and the heater surface watt density must not exceed 2.5 W/cm² to avoid film coking. A condition-monitoring matrix is shown below; each parameter is checked after initial 100 h of operation and then at 500 h intervals.
| Condition parameter | Test standard | Action threshold |
|---|---|---|
| Kinematic viscosity at 40°C | ASTM D445 | +25% vs fresh-fluid baseline |
| Flash point, Cleveland open cup | ASTM D92 | decrease > 30°C |
| Water content | ASTM E203 | > 200 mg/kg |
| Acid number | ASTM D664 | > 0.2 mg KOH/g |
| Total insolubles by membrane filtration | ASTM D4055 | > 0.1 wt% |
In optoelectronic device assembly, RH-C256A is applied at the interface between a high-brightness LED die package and a glass or acrylic secondary optic. Phenyl substitution raises the refractive index of the siloxane fluid into the typical range of 1.50 to 1.55 at 589 nm and 25°C, as determined by ASTM D1218. The fluid is dispensed as a layer of 0.05 mm to 0.2 mm; thicker layers increase optical shear loss and may cause pump-out under thermal cycling. For high-power LED modules, the coupling layer is subjected to continuous junction temperatures around 120°C to 150°C. Haze formation after 1000 h at 150°C indicates insufficient phenyl concentration or residual catalyst carryover from upstream assembly. The product can be diluted with toluene or xylene for spray or capillary filling, but residual solvent must be removed by vacuum drying at 60°C to 80°C for 30 min to 60 min before the secondary optic is clamped. Silicone coupling fluids for this use require a dielectric breakdown strength above 14 kV/mm when tested according to IEC 60243-1. In fiber-optic splice closures, the fluid is injected into a refractive index matching chamber; void formation is controlled by filtering through a 1 μm absolute membrane prior to filling. Reflow soldering after optical coupling is not recommended if the fluid contains volatile fractions above 0.5 wt% at 150°C. The selected fluid viscosity must permit air escape during assembly; fluids below 100 mm²/s at 25°C tend to migrate along lead frames and contaminate wire-bond pads, while fluids above 1000 mm²/s may retain bubbles. Published data for this specific grade in 200 mm wafer-level optical assembly is limited, so production qualification should include a 1000 h damp-heat test at 85°C/85% RH and a 500-cycle thermal shock test from -40°C to 125°C before release.
Phenyl Silicone Fluid RH-C256A is filled into automotive viscous fan drives and torsional vibration dampers at a fill ratio of 75% to 90% of the shear chamber volume, depending on the viscosity grade and clutch geometry. The fluid is degassed at 5 mbar to 20 mbar before filling to prevent air entrainment, which manifests as low-frequency shudder during cold start. After filling, the assembly is sealed and rotated at 1000 min⁻¹ to 3000 min⁻¹ for 15 min to verify absence of internal leakage through the bimetallic valve. High-temperature viscosity retention is evaluated by rotational viscometry under ISO 3219, with failure in fan clutch applications usually expressed as a viscosity drop greater than 15% after 200 h at 150°C under air. Silicone fluids with phenyl substitution generally show a lower viscosity-temperature slope than dimethyl fluids, but published data for this specific grade is limited; fixture-level qualification is required before production fill. In passenger-car viscous couplings, a fluid viscosity between 10,000 mm²/s and 60,000 mm²/s at 25°C is common, and the fill mass is controlled to ±0.1 g for repeatable torque transmission. Overfilled clutches exhibit elevated chamber pressure and hump at high speed, while underfilled clutches lose torque after 20 h to 50 h of sustained slip. The elastomer O-ring must be selected from fluorosilicone or hydrogenated nitrile; phenyl silicone fluid can extract plasticizers from standard nitrile seals within 300 h at 120°C. On production lines, the filling station is calibrated by gravimetric dispensing pumps, and the fluid reservoir is kept under nitrogen to minimize moisture uptake. Finished assemblies are leak-tested at 0.5 bar to 1.0 bar differential pressure for 5 s to 10 s before shipment.
Molding release for high-Tg epoxy transfer molding and phenolic compression tooling operates effectively with RH-C256A only when the material is applied as a dilute semisacrificial film rather than as an internal additive. The fluid is typically diluted in an aliphatic hydrocarbon or light mineral spirit to a concentration of 2 wt% to 10 wt%, with the exact dilution set by the tool surface finish and the demolding draft angle. The solution is applied to tool steel at 80°C to 120°C using a non-aerosol spray head or a lint-free cloth, then cured at 180°C to 230°C for 20 min to 45 min to form a thin phenyl silicone film. High-temperature resistance prevents release-film degradation during phenolic molding cycles at 160°C to 190°C; dimethyl silicone fluids often fail by forming siliceous deposits above 220°C. The release layer must be refreshed every 5 to 20 shots because phenyl silicone fluid alone does not form a durable semi-permanent network unless combined with an alkoxy-functional silicone resin or a hydroxyl-terminated phenyl silicone. Transfer of the release film to the molded part is assessed by Fourier-transform infrared microscopy on the surface; a detectable Si-O-Si absorbance ratio above the tool baseline indicates overapplication. For epoxy molding compounds containing amine hardeners, the release film must be fully cured before material contact because free silicone fluid can plasticize the epoxy surface and reduce adhesion of subsequent coatings or inks. Tool temperature uniformity should be maintained within ±3°C across the cavity to avoid selective release failure. In multi-cavity tooling with deep ribs or zero-draft surfaces, an additional spray pass after 3 to 5 shots is common. The finished molded parts include electronic connector housings, ignition coils, and phenolic commutator rings where surface contamination must remain below the detection limit of dyne-pen testing at 34 mN/m.
Phenyl Silicone Fluid RH-C256A is added as a processing plasticizer and internal release agent in selected high-consistency silicone rubber and fluorosilicone compounds. Typical addition levels range from 1 phr to 5 phr, depending on filler surface area and cure system. In silica-filled silicone rubber, the fluid is added after the reinforcing fumed silica has been wetted and dispersed, because simultaneous addition with untreated silica can trap hydroxyl groups at the filler-polymer interface and reduce green strength. Mixing is performed in a 25 L to 75 L internal mixer with ram pressure and finished on a two-roll mill, maintaining compound temperature below 120°C to avoid premature acid-catalyzed condensation. The phenyl-modified fluid contributes to reduced compression set after post-cure; post-cure at 200°C for 4 h to 8 h is required to volatilize low-molecular-weight silanol species and stabilize the network. In fluorosilicone compounds, the fluid is used at lower levels, 0.5 phr to 2 phr, and must be evaluated for interaction with peroxide curatives. Phenyl silicone fluids are generally not compatible with tin-catalyzed condensation systems because residual silanol groups can interfere with catalyst activity. Factory-scale batch-to-batch variation in the fluid’s volatile content above 200°C is a relevant processing parameter; a thermogravimetric loss at 250°C exceeding 2.0 wt% under ASTM E1131 can cause porosity in compression-molded seals. Molded goods produced from such compounds include fluorosilicone diaphragm check valves, high-temperature silicone gaskets for commercial baking ovens, and O-rings for fuel cell humidifier plates. Production-scale extrusion of phenyl-silicone-modified profiles requires a vented single-screw extruder with an L/D ratio of 24:1 to 30:1 and a screw temperature profile increasing from 40°C at the feed throat to 100°C at the die. If moisture is present, pre-drying of the compound for 2 h to 4 h at 80°C to 100°C is required before extrusion.
Conveyor chains in paint curing ovens and powder-coating furnaces operate with pinned joints that reach 200°C to 260°C during normal excursions. Conventional mineral and ester chain oils generate carbonaceous residue and volatile organic emissions, while RH-C256A is used as a high-temperature carrier fluid in formulated chain lubricants. The phenyl modification raises oxidation resistance and reduces the rate of dry-film deposition. A typical compounded lubricant contains 70 wt% to 90 wt% phenyl silicone fluid, 5 wt% to 20 wt% polytetrafluoroethylene fine powder, and 1 wt% to 5 wt% of a thermally stable anti-wear additive such as an aryl phosphate ester or a sulfurised fatty acid, though the additive package must be verified for solubility and thermal stability. The lubricant is applied by centralised drip-feed systems at a dosage of 0.2 mL to 0.8 mL per chain link per hour, depending on chain speed and furnace temperature. Ash content should be less than 0.5 wt% according to ASTM D482 to prevent residue accumulation on slider guides. In anti-seize pastes, phenyl silicone fluid functions as a high-flash-point carrier for graphite, molybdenum disulfide, or calcium fluoride thickeners at 30 wt% to 50 wt% of the paste mass. The paste is brushed onto bolts subjected to 340°C to 450°C cyclic heating; published data for this specific product is limited above 400°C, and components must be validated by torque-tension testing after thermal exposure. Avoid use in oxygen-enriched atmospheres; silicone fluids can form silica deposits if oxidation is not excluded. Application to stainless steel fasteners should be preceded by degreasing and abrasive cleaning to prevent galling. The resulting finished assemblies are used on exhaust flanges, turbine housing studs, and paint-line chain pins where disassembly after 500 h to 1000 h at elevated temperature is required.
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Phenyl Silicone Fluid RH-C256A is supplied as a clear, mobile phenylmethylpolysiloxane fluid in which a controlled fraction of dimethylsiloxane units is replaced by phenyl-substituted siloxane units. The model designation RH-C256A identifies a nominal viscosity grade near 256 mm²/s at 25 °C, distinguishing it from lower-viscosity dimethyl silicone fluids and from higher-phenyl-content optical resins. The product is intended for high-refractive-index thermal media, optoelectronic coupling, and elastomer lubrication where dimethyl silicone oil is limited by evaporation, silica formation, or refractive index mismatch. The phenyl substitution raises refractive index to 1.49–1.52 and density to 1.04–1.08 g/cm³ at 25 °C. Published data for this specific configuration is limited; the following technical evaluation is based on class-level phenylmethyl silicone fluid data and should be verified against the supplier certificate of analysis before use.
The product should not be confused with diphenylsiloxane homopolymers or with phenylated silicone resins used as LED encapsulants. Phenyl substitution in RH-C256A is generally in the range of 5–10 mol% for this viscosity class, though the exact level is supplier-controlled. The C256A suffix denotes a kinematic viscosity grade rather than a fixed chemical composition; the phenyl content and molecular weight distribution must be defined by the supplier batch release documentation.
Relative to dimethyl silicone fluids of equal kinematic viscosity, RH-C256A offers higher refractive index, higher density, lower volatility, and better oxidative stability at 200–250 °C. Relative to fluorosilicone fluids, it provides better low-temperature fluidity and lower density but lower resistance to ester, ketone, and aromatic solvents. Relative to high-phenyl silicone resins with phenyl substitution above 30 mol%, RH-C256A maintains lower viscosity and better flow below −40 °C but has a lower thermal decomposition onset. The product is therefore selected when the dominant failure mode is cyclic siloxane evaporation or oxidative gelation, not solvent-induced depolymerization.
Dimethyl silicone fluids degrade at elevated temperature by a backbiting chain-scission mechanism that liberates cyclic siloxanes, producing measurable evaporation loss and hard silica deposits. At 150 °C, open-dish evaporation per ASTM D6375 can exceed 10 wt% over 1,000 h for a 250 mm²/s dimethyl fluid. Phenylmethyl fluids of the RH-C256A class interrupt the backbiting pathway because the phenyl side groups restrict ring formation at the active chain end; class-level evaporation losses under the same conditions are typically below 3 wt%. The aromatic groups also reduce the rate of methyl radical abstraction, delaying the formation of crosslinked silica gel. Oxidation products in phenyl fluids tend to remain soluble or suspended rather than depositing as hard scale. In closed-loop heat transfer systems with bulk oil temperatures of 200–250 °C, this shift is operationally significant. At temperatures above 300 °C, phenyl-silicon bond cleavage becomes measurable; nitrogen blanketing at 0.5–1.0 bar(g) is recommended. The flash point by ISO 2592 is generally above 300 °C, but flash point alone does not predict the onset of oxidative viscosity increase or acid generation.
Field observations from a continuous hot-oil unit using a brazed plate heat exchanger showed that a dimethyl silicone fluid of 250 mm²/s produced a pressure-drop increase after 800 h due to deposition on the plate surfaces. A phenylmethyl silicone fluid of similar initial viscosity extended the cleaning interval beyond 2,000 h in the same unit. Published data for RH-C256A in this exact configuration is limited; the observation is class-level and should not replace a pilot-scale fouling study for critical installations.
At −40 °C, dimethyl silicone fluids with a viscosity of 250 mm²/s at 25 °C can develop viscosities of 7,000–10,000 mm²/s, exceeding the cold-start torque limits of many positive displacement pumps. Phenyl silicone fluids of the RH-C256A class are formulated to balance phenyl content against low-temperature fluidity; typical pour points are −50 °C to −70 °C by ISO 3016. The viscosity at −40 °C does not decline linearly with phenyl content. Above approximately 10 mol% phenyl substitution, viscosity rises disproportionately due to increased intermolecular forces. RH-C256A is selected where a moderate refractive index increase is required without sacrificing low-temperature pumpability. In analytical instrumentation and outdoor camera systems, the fluid can serve as both damping medium and optical coupling fluid. Batch-to-batch variation in phenyl distribution should be monitored by refractive index; a shift of ±0.002 may indicate a phenyl-content change sufficient to alter −40 °C viscosity by 10–20%.
In optical coupling and index-matching applications, tolerances on refractive index and dispensability are tighter than in thermal applications. Phenyl Silicone Fluid RH-C256A can be used as a nonreactive index-matching medium between glass, polycarbonate, or silicone optical elements when the refractive index is matched to the adjacent media within ±0.005. The phenyl substitution shifts the optical absorption edge to longer wavelengths; thin films of 25 µm generally transmit more than 90% across the visible spectrum, while ultraviolet transmittance below 350 nm is reduced. In high-brightness LED assembly, volumetric piston dispensers maintain shot-weight tolerances of ±0.5%; a viscosity drift from 250 mm²/s to 275 mm²/s at 25 °C can alter dispensed shot volume by approximately 5% at constant backpressure, producing optical gaps or air entrapment. Optical-grade material should be deaerated under vacuum of 1–5 kPa for 30 min and filtered to 10 µm or finer. Published data for this specific configuration is limited; production-line validation remains necessary.
Before charging a hot-oil system with phenyl silicone fluid, materials compatibility checks are required. Silicone fluids can swell or soften EPDM and many fluorocarbon elastomers; perfluoroelastomer seals and gaskets are preferred. Copper-containing alloys should be avoided at sustained temperatures above 150 °C because copper can catalyze siloxane gelation; stainless steel 316L or glass-lined vessels are standard. A nitrogen blanket at 0.2–0.5 bar positive pressure reduces atmospheric moisture ingression. At 250 °C, dissolved moisture above 100 ppm can hydrolyze siloxane bonds, increasing silanol concentration and subsequent condensation viscosity. Filtration with 5 µm absolute elements on a slipstream loop removes particulate oxidation products. Volatiles by ASTM D6375 should be below 0.5 wt% to avoid vapor lock in expansion tanks. Thermal conductivity measured by ISO 22007-2 is typically 0.15 W/(m·K) at 25 °C, lower than that of common mineral heat-transfer oils, and therefore requires higher flow rates to provide equivalent heat removal.
In elastomer lubrication and mold-release applications, the processing window for RH-C256A is narrow. Silicone migration can contaminate adjacent surfaces and disrupt downstream painting, printing, or adhesive bonding. In O-ring assembly, application rates of 0.5–2 mg/dm² are typically sufficient; higher film weights increase the risk of migration to electrical contacts. In four-ball testing per ASTM D2266, silicone fluids of this class typically exhibit wider wear scar diameters than polyol ester or polyalphaolefin oils under mixed lubrication. RH-C256A is therefore not a direct substitute for metal-on-metal sliding loads. It is better suited to rubber-to-metal and plastic-to-plastic contacts. In injection molding, phenyl silicone release sprays may be atomized at 0.5–1.5 wt% in a volatile carrier, but parts require corona or plasma treatment before coating to remove residual silicone. Without surface activation, paint adhesion failures are common.
Under nitrogen, thermogravimetric analysis reports a decomposition onset that does not predict service life in aerated oil baths. For phenylmethyl silicone fluids, isothermal TGA at 250 °C in air shows an induction period before mass loss; the induction period shortens by approximately half for each 20 °C increase above 220 °C. Oxidation stability should be evaluated by ASTM D4636 or ASTM D6375. In a class-level comparison at 220 °C for 168 h, a phenylmethyl fluid of 250 mm²/s exhibited a viscosity increase of 8–12%, while a dimethyl silicone fluid of equal initial viscosity exceeded 25% under identical conditions. Product-specific certification for RH-C256A is required before use in safety-critical thermal management equipment.
For compliance certification, jurisdiction-specific documentation must be obtained from the supplier. Absence of a supplier declaration should be treated as a restriction, not a compliance failure of the chemical class.
| Property | Test method | Typical range |
|---|---|---|
| Kinematic viscosity at 25 °C | ISO 3104 / ASTM D445 | 220–280 mm²/s |
| Density at 25 °C | ISO 12185 | 1.04–1.08 g/cm³ |
| Refractive index at 25 °C | ASTM D1218 | 1.490–1.515 |
| Flash point | ISO 2592 | >300 °C |
| Pour point | ISO 3016 | −50 °C to −65 °C |
| Volatility, 24 h at 150 °C | ASTM D6375 | <2 wt% |
| Water content | ASTM D6304 | <250 ppm |
| Requirement | Standard or regulation | Verification status |
|---|---|---|
| REACH registration | Regulation (EC) No 1907/2006 | Supplier declaration required |
| RoHS restricted substances | Directive 2011/65/EU, screening per IEC 62321 | Product-specific XRF required |
| Halogen content | IEC 61249-2-21 | Class-level data limited |
| Food-contact eligibility | 21 CFR 177.2600 | Not assumed; end-use approval required |
| Transport classification | UN model regulations | Flash point above 300 °C; confirm SDS |
When humidity exceeds 60% in open systems, moisture-catalyzed headspace polymerization can occur; dry nitrogen blanketing or sealed storage is required. The fluid should not be exposed to strong amines or alkali metal hydroxides at temperatures above 100 °C; these reagents cleave the siloxane backbone and can produce gelation within hours. The product is incompatible with strong oxidizing agents such as concentrated nitric acid and hydrogen peroxide; contact may generate exothermic reactions. In carbon dioxide-rich environments, use above 180 °C should be avoided unless venting is provided. Storage should be maintained between 5 °C and 40 °C in closed containers, and bulk transfer equipment should be grounded to avoid static charge accumulation. Disposal must follow local waste codes; aromatic silicone fluids may be classified differently from dimethyl silicone oils.
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