Diborane

Description

Diborane is a colorless gas at room temperature and atmospheric pressure. It has an unpleasant, distinctive, sickly sweet odor. Diborane is a highly flammable gas that forms a flammable mixture with air over a range of 0.9 percent to 98 percent diborane (at 1 atm). Diborane bums in air (or oxygen) with a blue to green flame. Diborane is considered pyrophoric at room temperature. The gas is easily ignited by a spark or the heat of reaction with moisture in air.
Pure diborane is insensitive to mechanical shock; however, shock and thermally sensitive mixtures may be formed in the presence of impurities such as oxygen, water, halogenated hydrocarbons, and so on. Thermal decomposition of diborane to hydrogen can result in excessive pressure buildup. Vessels for containment of diborane should be designed to contain such resultant decomposition pressure.

Chemical Properties

Diborane is a compressed, colorless, and flam- mable gas. It has a nauseating, sickly sweet odor.

Uses

Diborane is used as a rocket propellant, in thevulcanization of rubber, as a polymerizationcatalyst, as a reducing agent, in the synthesisof trialkyl boranes, and as a doping agent(Merck 1996).

Uses

Diborane is commonly used in the electronics industry for semiconductor doping by mixing small concentrations with silane in the gas phase prior to decomposition. When reacted with silane and oxygen, diborane also produces the cladding layers of wave guides for fiber optics by chemical vapor deposition.
Other uses of diborane include the preparation of boron nitride by the reaction of diborane with ammonia, as a catalyst for polymerization, and for the conversion of olefins to trialkyl boranes. It is also used in the conversion of amines to amine boranes and as a selective reducing agent with carbonyl compounds such as aldehydes and ketones to form alcohols.

Uses

As catalyst for olefin polymerization; as rubber vulcanizer; as reducing agent; as flame-speed accelerator; in rocket propellants; in intermediate in preparation of the boron hydrides; in conversion of olefins to trialkylboranes and primary alcohols; as a doping gas.

Production Methods

Diborane now can be produced more easily and in larger quantities by the reaction of LiH, NaH or alkali borohydrides with BF3 diethyl etherate, To obtain good yields, the alkali hydrides must be very finely powdered.

Air & Water Reactions

Highly flammable. Ignites spontaneously in moist air (forms hydrogen and boric acid), [Haz. Chem. Data (1966)]. Oxygen and Diborane form spontaneously explosive mixtures, [J. Amer. Chem. Soc. 76, 1997(1954)].

Reactivity Profile

Diborane is a colorless, air and moisture-sensitive gas, highly toxic. Diborane ignites in air. Diborane is very explosive when exposed to heat or flame, on contact with moisture Diborane produces hydrogen gas. Explosive reaction with benzene vapor, chlorine, nitric acid and tetravinyllead [Bretherick, 5th ed., 1995, p. 77]. Explosive reaction with dimethyl sulfoxide [Shriver, 1969, p. 209], violent reaction with halocarbon liquids used as fire extinguishants (e.g., carbon tetrachloride). Reaction with Al or Li produces complex hydrides that may ignite spontaneously in air [Haz. Chem. Data, 1975, p. 114].

Hazard

Diborane is pyrophoric and will ignite upon exposure to air. The boiling point is ?135°F and the flammable range is 0.8%–88% in air. The ignition temperature is 100° (37°C) to 140°F (60°C), and the flash point is 130°F (54°C). Diborane will react violently with halogenated fire-extinguishing agents, such as the halons. The four-digit UN identification number is 1911. The NFPA 704 designation is health 4, flammability 4, and reactivity 3. The white section of the diamond has a W with a slash through it, indicating water reactivity.

Health Hazard

Animal studies indicate that exposure todiborane results in irritation and possibleinfection in respiratory passage. In additionto the acute poisoning of the lungs, this gasmay cause intoxication of the central nervoussystem. A 4-hour exposure to 60 ppm maybe lethal to mice, resulting in death frompulmonary edema.

Health Hazard

Inhalation of diborane gas results in irritation of the respiratory tract and may result in headache, cough, nausea, difficulty in breathing, chills, fever, and weakness. The odor of diborane cannot be detected below the permissible exposure limit, so this substance is considered to have poor warning properties. Overexposure to diborane can cause damage to the central nervous system, liver, and kidneys. Death can result from pulmonary edema (fluid in the lungs) and/or from lack of oxygen. Exposure to diborane gas has not been found to have significant effects on the skin and mucous membranes, but high concentrations can cause eye irritation, and contact with the liquid can cause burns. Chronic exposure to low concentrations of diborane may cause headache, lightheadedness, fatigue, weakness in the muscles, and tremors. Repeated exposure may produce chronic respiratory distress, particularly in susceptible individuals. An existing dermatitis may also be worsened by repeated exposure to the liquid. Diborane has not been shown to have carcinogenic or reproductive or developmental effects in humans.

Health Hazard

Boranes are highly toxic by inhalation, skin absorption or ingestion. They may produce acute or chronic poisoning. Diborane is an irritant to the lungs and kidneys. The primary effect of Diborane poisoning is lung congestion caused by local tissue irritation produced by the exothermic reaction of hydrolysis.

Fire Hazard

Diborane will ignite spontaneously in moist air at room temperature. Also, Diborane reacts violently with vaporizing liquid-type extinguishing agents. Diborane hydrolyzes in water to hydrogen and boric acid. Incompatible with air, halogenated compounds, aluminum, lithium, active metals, oxidized surfaces, chlorine, fuming nitric acid, nitrogen trifluoride, oxygen, and phosphorus trifluoride. Avoid moist air, electrical sparks, open flames or any other heat source. Hazardous polymerization may occur.

Fire Hazard

Diborane is a flammable gas that ignites spontaneously in moist air at room temperature and forms explosive mixtures with air from 0.8% up to 88% by volume. Diborane reacts with halogenated hydrocarbons, and fire extinguishing agents such as Halon or carbon tetrachloride are therefore not recommended. Carbon dioxide extinguishers should be used to fight diborane fires. Fires involving diborane sometimes release toxic gases such as boron oxide smoke.

Flammability and Explosibility

Diborane is a flammable gas that ignites spontaneously in moist air at room temperature and forms explosive mixtures with air from 0.8% up to 88% by volume. Diborane reacts with halogenated hydrocarbons, and fire extinguishing agents such as Halon or carbon tetrachloride are therefore not recommended. Carbon dioxide extinguishers should be used to fight diborane fires. Fires involving diborane sometimes release toxic gases such as boron oxide smoke.

Materials Uses

Common metals are suitable as materials of construction. These include the following metals and metal alloys: chrome-molybdenum steel, Type 300 stainless steel, brass, lead, Monel, K-Monel, and nickel. Piping and appurtenances for undiluted diborane must be designed by experienced engineers and safety and fire protection specialists. Saran, polyethylene, Kel-F, Teflon, graphite, and high-vacuum silicone grease are satisfactory for use with diborane.
In addition to the ability of a material to withstand chemical attack, the evaluation of materials compatibility with diborane should also emphasize the effect of the material on diborane stability (as expressed by the decomposition rate). The use of the following materials is not recommended:
? Metal oxides
? Natural rubbers
? Neoprene
? Leak-lock
? Permatex
? Ordinary oil and grease
? Nordel 1145 RPT elastomer, unfilled and Si02-filled
? silicon elastomer, unfilled and SiOrfilled
? CIS-4 polybutadiene elastomer, unfilled and SiOrfilled

Safety Profile

Poison by inhalation. An irritant to skin, eyes, and mucous membranes comparable to chlorine, fluorine, arsine, and phosgene. The liquid causes local inflammation, blisters, redness, and swelling. Injuries to central nervous system, liver, and hdneys have also been produced in experimental animals. Sirmlar observations have been reported in humans, resulting at times in a reaction resembling metal fume fever. Human exposure to pentaborane has produced signs of severe central nervous system irritation such as drowsiness, dlzziness, visual disturbances, muscle twitching, and in severe cases, painful muscle spasm. Dangerously flammable when exposed to heat or flame or by chemical reaction. On contact with moisture, hydrogen is usually evolved. Highly explosive when exposed to heat or flame. Explosive reaction with air, tetravinyllead, O2 above 165℃, octanol oxime + sodium hydroxide, benzene vapor, HNO3Cl2. Violent reaction with halocarbon liquids. Other boron hydrides evolve H2 upon contact with moisture or can propagate a flame rapidly enough to cause an explosion. Heat can cause these materials to decompose violently or at least to evolve H2. They also react with water or steam to evolve hydrogen. Reaction with Al or Li forms complex hydrides that may ignite spontaneously in air. Powerful oxidlzing agents, such as chlorine gas, etc., can react violently with boron hydrides. Pentaborane (stable) is spontaneously flammable in air. See also BORANES and HYDRIDES.

Potential Exposure

Diborane is used as the source of boron in the semiconductor industry; as a catalyst for olefin polymerization; a rubber vulcanizer; a reducing agent; a flame-speed accelerator; a chemical intermediate for other boron hydrides; as a doping agent; in rocket propel- lants, and in the conversion of olefins to trialkyl boranes and primary alcohols.

Physiological effects

ACGIH recommends a Threshold Limit Value-Time- Weighted Average (TLV-TWA) of 0.1 ppm (0.11 mg/m3 ) for diborane. The TLVTWA is the time-weighted average concentration for a normal 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect.
OSHA lists an 8-hour Time-Weighted Average- Permissible Exposure Limit (TWA-PEL) of 0.1 ppm (0.1 mg/m3 ) for diborane. TWAPEL is the exposure limit that shall not be exceeded by the 8-hour time-weighted average in any 8-hour work shift of a 40-hour workweek

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit.Medical observation is recommended for 2448 h afterbreathing overexposure, as pulmonary edema may bedelayed. As first aid for pulmonary edema, a doctor orauthorized paramedic may consider administering a corticosteroid spray.

storage

diborane should be used only in a fume hood free of ignition sources and should be stored in a cold, dry, wellventilated area separated from incompatible substances and isolated from sources of sparks and open flames.

Shipping

UN1911 Diborane, Hazard Class: 2.3; Labels: 2.3-Poisonous gas, 2.1-Flammable gas Inhalation Hazard Zone A. Cylinders must be transported in a secure upright position, in a well-ventilated truck. Protect cylinder and labels from physical damage. The owner of the compressed gas cylinder is the only entity allowed by federal law (49CFR) to transport and refill them. It is a violation of transportation regulations to refill compressed gas cylinders without the express written permission of the owner.

Incompatibilities

A strong reducing agent. Unstable above 8 C. The presence of contaminants may lower the autoigni- tion temperature; ignition may take place at, or below, room temperature. Diborane can polymerize, forming liquid pentaborane (See P:0190). It ignites spontaneously in moist air; and on contact with water, hydrolyzes exothermically forming hydrogen and boric acid. Contact with halogenated compounds (including fire extinguishers) may cause fire and explosion. Contact with aluminum, lithium and other active metals form hydrides which may ignite spontane- ously. Incompatible with aluminum, carbon tetrachloride; nitric acid; nitrogen trifluoride and many other chemicals. Reacts with oxidized surfaces. Attacks some plastics, rubber or coatings.

Waste Disposal

Return refillable compressed gas cylinders to supplier. Incineration with aqueous scrub- bing of exhaust gases to remove B2O3 particulates.

GRADES AVAILABLE

Diborane is sold in ambient or refrigerated cylinders with a purity of 99 percent or greater. It is commonly used in the electronics industry, mainly in the form of dilute mixtures.