Lithium hydride

This is a special kind of salt.

It is made of two things. It is made of lithium and hydrogen.

It is very light. It is the lightest kind of this salt. It is a soft material.

This salt can be tricky. It reacts with water. It can even catch on fire in wet air.

People have used it for rockets. It can also help in nuclear machines.

It is a very interesting substance to study.

Lithium hydride is a special kind of salt. It is made of two parts. It is made from lithium and hydrogen.

This salt is very light. In fact, it is the lightest ionic compound. An ionic compound is a type of salt.

Making this salt is a set of steps. Scientists treat lithium metal with hydrogen gas. This works fast if it is hot. It can happen at 29 °C. But it works much faster above 600 °C.

Lithium hydride can be tricky to use. It reacts very fast with water. It can even catch fire in moist air. This can happen if the air is humid. It can also catch fire from static electricity. If it catches fire, do not use water to stop it. You should cover it with a metal object or special powder.

This salt has many uses. It has a lot of hydrogen in it. This makes it good for storing hydrogen. It can also be used in nuclear reactors. Some types are used as fuel in thermonuclear weapons. These weapons use a process called fusion to make power.

Cracking can happen in some parts of the salt. Cast parts can be brittle. This means they break easily.

Lithium hydride is a special kind of salt called an inorganic compound. It is made of two parts: lithium and hydrogen. This substance is a colorless solid, but the samples sold for work are often grey. It is very light for a salt. In fact, it is the lightest ionic compound, which means it is the lightest salt-like substance known.

Because it is so light, scientists find it very interesting for many different jobs.

Making this substance is a specific way of working with metals and gases. Scientists create it by treating lithium metal with hydrogen gas. This process can happen at temperatures as low as 29 °C. However, the reaction works much faster when it is hot, especially above 600 °C. If you add a tiny bit of carbon, the yield can reach up to 98% in two hours.

Other ways to make it include breaking down different lithium compounds at high heat.

Lithium hydride can be quite difficult to handle safely. It reacts very quickly with water and can even catch fire in moist air. If the air is humid, the powder might ignite all on its own. It can even catch fire from a tiny spark of static electricity. If a fire starts, you must not use water or carbon dioxide to put it out. Instead, you should smother the fire with a metal object or special powders like graphite.

This substance is useful in several high-tech fields. It has a very high hydrogen content. This makes it a candidate for storing hydrogen fuel, though it is hard to get the hydrogen out. It is also used to make other important chemicals. In the world of nuclear science, it can be used as a shield for reactors. Some types of lithium hydride are even used as fuel in thermonuclear weapons.

When scientists shape this material, they must be careful. They can make it into small pellets or even large crystals. Large crystals can be about 80 mm long and 16 mm wide. These crystals sometimes look blue because of tiny bits of lithium inside. If you try to cut or machine cast lithium hydride, it can be very brittle. This means it might crack easily during the work.

Lithium hydride (LiH) is an inorganic compound made of lithium and hydrogen. It is classified as an alkali metal hydride. This substance is a colorless solid, though commercial samples often appear grey. LiH is an ionic compound, meaning it has a salt-like structure. It is also the lightest ionic compound known, with a molar mass of only 7.95 g/mol. This light weight makes it a subject of great interest in various scientific fields.

Scientists produce lithium hydride through several different chemical processes. The most common method involves treating lithium metal with hydrogen gas. While this reaction can occur at temperatures as low as 29 °C, it is much faster at temperatures above 600 °C. Adding a tiny amount of carbon, between 0.001% and 0.003%, can increase the yield up to 98% within two hours. Other less common methods include the thermal decomposition of compounds like lithium aluminium hydride at 200 °C or lithium borohydride at 300 °C.

The physical properties of LiH depend heavily on its temperature and form. It is a soft material with a Mohs hardness of 3.5. As it heats up, it undergoes compressive creep, which is a slow deformation under pressure. At 350 °C, this creep is less than 1%, but it rises to over 100% at 475 °C. This means LiH cannot provide mechanical support when it is hot. Its thermal conductivity also changes based on whether it is in crystal form or a compact form.

Creating specific shapes of lithium hydride requires careful handling of the material. LiH can be made into a lumped powder that is compressed into pellets. It can also be cast from a melt to create more complex shapes. Large single crystals can be grown using the Bridgman–Stockbarger technique. These crystals can reach about 80 mm in length and 16 mm in diameter. They often appear bluish due to the presence of colloidal lithium. This color can be removed by a process called annealing at approximately 550 °C.

Lithium hydride is highly reactive, which requires strict safety protocols. It reacts rapidly with air of low humidity to form lithium hydroxide (LiOH). In moist air, the powder can ignite spontaneously. It is also highly reactive with water, which produces hydrogen gas and caustic LiOH. Because of these risks, LiH fires cannot be put out with water or carbon dioxide. Instead, they must be smothered with metal, graphite, or dolomite powder. Sand is often unsuitable because it can explode if it is not completely dry.

This compound has several important applications in energy and chemistry. Because it has a hydrogen content three times that of sodium hydride (NaH), it is studied for hydrogen storage. However, releasing the hydrogen requires temperatures above 700 °C, which is expensive to maintain. LiH is also used as a precursor to create other complex metal hydrides. For example, the Sundermeyer process uses LiH and silicon tetrachloride to produce silane. It is also used to synthesize reagents like lithium aluminium hydride and lithium borohydride.

In the field of nuclear science, lithium hydrides serve critical roles. Lithium-6 isotopes can be used for shielding nuclear reactors. Lithium-7 deuteride (7LiD) is used as a moderator because it has a low neutron absorption cross-section. Most notably, lithium deuteride is used as a primary fusion fuel in thermonuclear weapons. In these designs, a fission trigger produces neutrons that react with the lithium to create tritium. The resulting tritium then undergoes fusion with the deuterium. This process is much more energy-dense than nuclear fission, providing about 50 kilotons of energy per kilogram of material.