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Chemical Name: Hexamethyldisilane
Synonyms: Bis(trimethylsilyl), HMDS
Formula: C6H18Si2
Molecular Weight: 146.37 g/mol
Description: This compound looks like a clear, colorless liquid most of the time. It often carries a sharp, ether-like odor. Many people working with electronics, silicon-based materials, or specialty labs know it for its use in chemical vapor deposition or as a reducing agent.
Physical Hazards: Flammable — it catches fire with surprising ease, and can form explosive mixtures with air. Vapors could travel and ignite far from where the liquid got spilled.
Health Hazards: Skin or eye contact causes pain, redness or burns. Breathing in the vapor provokes headaches, coughing or shortness of breath. Prolonged exposure might irritate the lungs.
Environmental Concerns: It breaks down in water but silicon-based byproducts linger. Spilled liquid harms aquatic life if not contained.
Constituent: Hexamethyldisilane
Concentration: >95 percent by weight
Impurities: Byproducts from synthesis show up as trimethylsilanol or siloxanes in trace amounts, depending on source and process condition quality.
Inhalation: Get into fresh air at once, loosen any tight clothing, and support breathing as needed. If symptoms get worse, seek a doctor—respiratory effects sometimes lag.
Skin Contact: Take off contaminated clothing and wash skin with soap and lots of water. Chemical burns require medical attention.
Eye Contact: Rinse eyes steadily with water for at least fifteen minutes, making sure lids get pulled wide. Seek medical care quickly.
Ingestion: Never try to make someone vomit. Rinse mouth with water and get medical help at once since signs might not show up right away.
Suitable Media: Use dry chemical or carbon dioxide. Water might cause dangerous splashing or spattering with this liquid.
Hazards During Fire: Heavy, irritating vapors form under heat; silicon oxides, formaldehyde, and even explosive mixtures develop if the substance breaks down.
Fire-fighter Protection: Use self-contained breathing equipment and full gear because of toxic fumes and reaction risks.
Personal Precautions: Put on gloves, goggles, and a lab coat or apron right away. Only trained workers should handle a spill.
Environmental Steps: Keep liquid away from drains or open soil, and build small dikes using sand or inert absorbents to contain spreading. Chemicals should never leak into sewers or open waterways.
Cleanup Methods: Scoop absorbed material into non-sparking, sealable drums for hazardous disposal. Air the area out to clear vapors.
Handling: Avoid splashing or inhaling vapors, and don’t eat or drink anywhere nearby. Handle containers with care, using tools designed for flammable liquids.
Storage: Keep in tightly sealed steel containers, away from heat, sparks, or open flames. Temperature should stay cool and storage sites need good airflow. Never store with oxidizers or acids, which can trigger hazardous reactions.
Engineering Controls: Good local exhaust ventilation helps keep airborne forms below limits and pulls away fumes at the source.
Personal Protective Equipment: Chemical goggles and butyl rubber gloves reduce skin and eye risks. A flame-resistant lab coat limits hazardous exposure. Respiratory protection may be needed in poorly ventilated work areas—use full masks or supplied-air units. Always wash up after handling chemicals like this.
Appearance: Clear, colorless liquid
Odor: Ether-like or sweet
Boiling Point: Near 100–101°C
Melting Point: About −81°C
Flash Point: Flammable below room temperature
Vapor Pressure: Significant enough to form dangerous levels in the air
Density: Close to 0.76 g/cm³ at 20°C
Solubility: Insoluble in water, mixes well with organic solvents; reacts with moisture over time
Autoignition Temperature: Can ignite around 270°C
Evaporation Rate: Evaporates quickly in open air, adding risk by creating invisible vapors lower than air.
Chemical Stability: Stable under cool, dry conditions away from oxygen sources.
Incompatible Materials: Water, acids, oxidizing agents set off quick reactions; avoid heat, flames, and open spark sources.
Hazardous Decomposition: Heat or fire breaks this compound into silicon oxides, methane, formaldehyde, and hydrogen—mixes that can explode or smother oxygen in a small room.
Acute Effects: Breathing the vapor stings the respiratory tract and aggravates preexisting asthma; splashes burn skin or eyes.
Chronic Exposure: Regular exposure weakens lung or skin tissue over months, especially in poorly controlled labs. No strong links to cancer have surfaced in workers, but limited data keeps risk unclear.
Sensitization: Low odds of turning someone sensitive, yet every lab should stay cautious.
Aquatic Impact: Dissolves slowly, builds up siloxanes in the environment, and harms fish or aquatic bugs if spills reach water bodies.
Breakdown: Eventually reacts with air, sun, and water forming silicon oxides, but doesn’t break down quickly enough to avoid immediate environmental harm.
Waste Treatment: Burn only in approved incinerators with scrubbers; never pour down drains or on soil. Container remains hazardous after emptying, must get cleaned or destroyed by chemical waste handlers.
Disposal Laws: Most areas treat hexamethyldisilane as hazardous—disposal routes follow special legal rules for organosilicons.
UN Classification: Listed as a flammable liquid under international law.
Transport Instructions: Keep separate from foodstuff, oxidizers, and acids. Use sealed, upright containers held in well-ventilated vehicles, and never ship with unknown or incompatible cargo. Handling crews must know fire and spill actions in advance.
Workplace Limits: No universal exposure limit exists, though safety guidelines recommend keeping vapor levels as low as possible—usually under 1 part per million.
Labeling Rules: Most authorities require flammable and health risk labels, along with warnings about water reactivity.
Reporting: Large spills and accidental releases usually get reported under major chemical safety laws. Each country holds different requirements, but the burden falls on the user to check and comply before storage or use.
