Calcium hydride is widely used as a desiccant for alkaline solvents


Jul 26, 2023

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What is Calcium Hydride? Calcium hydride, also known as CaH2, is a compound that has the chemical symbol CaH2. It is therefore an alkaline-earth metal hydride. This gray powder (sometimes pure white, but usually gray) reacts violently to water and releases hydrogen. CaH2 has been used for desiccant.

CaH2 has a structure similar to that of salt. During the Battle of the Atlantic German subs used calcium hydroide as a decoy sonar called bold. Alkali metals, alkaline earths metals, and beryllium are all heavier than each other and produce hydrogen halides. The sodium hydride master mold is a well-known example. They are insoluble with all solvents which do not react. Crystals of CaH2 have a structure similar to PbCl2 or perovskite.
Why is calcium hydrolith called Hydrolith
CaH2 (brine hydride) is known as hydrolith because it has a structure similar to that of salt. Sodium hydride can be formed from both alkali and alkaline Earth metals.

What is calcium hydride used for?
It is more safe to use than more aggressive reagents. It is used widely as a desiccant in alkaline solvants such as amines, pyridine and sodium metal. It is used to dry alcohol.

Reduced metal oxide
CaH2 is used as a reducer to produce metals out of metal oxides Ti, V., Nb., Ta. and U. Decomposition into Ca metal is recommended for operation.
TiO2 + two CaH2-Ti plus two CaO + two H2

Hydrogen source
CaH2 was used to make hydrogen. In the 1940s it was used to produce hydrogen under the name “Hydrolith”.

Hydrolith is the trade name for this compound. In an emergency it can be used to fill up the airship with portable hydrogen. This usage is expensive.

This may be a reference for wartime. The compound is used as a convenient, safe, and easy way to inflate the weather balloons for many decades. In the lab, small amounts are produced to conduct experiments.
CaH2 and water react as follows.
CaH2 + 2 H2O-Ca(OH)2 + 2 H2
The dry solvent can be easily separated into two hydrolysis products: H2 gaseous and Ca(OH).

It may not be as efficient as molecular Sieves. It is safer than using more reactants like sodium metal or a sodium-potassium alloy. It is used widely as a dehydratant for alkaline solvants such as amines, pyridine and sodium metal. It is used to dry alcohol.

CaH2 can be a convenient material, but it has its own disadvantages.
As a result, its drying rate may be slower than LiAlH4. CaH2 has a similar appearance to Ca(OH), so its quality is not readily apparent.

What happens if you add water and calcium hydride together?
Calcium hydride reacts violently (CaH2) with water, releasing hydrogen. The hydrolysis of CaH2 by ethanol in solution has a lower energy activation than other reactions.

How can you make calcium hydroxide?
Calcium hydride may be made by combining dry hydrogen with calcium metal and heating the mixture between 300degC and 400degC.
One way to prepare calcium hydroide is by heating calcium chloride, hydrogen and sodium. The reaction is triggered by:
CaCl2+H2 + 2 na-CaH2+2 NaCl
This reaction involves the formation of sodium chloride molecules from sodium atoms, hydrogen (H), and calcium (Ca).

Magnesium (Mg) can be reduced with calcium oxide (CaO), resulting in the production of calcium hydride. The reaction occurs in the presence hydrogen. This reaction produces also magnesium oxide. The chemical formula is:
CaO + H2-CaH2+ MgO

What is the type of bond that calcium hydride has?
The ionic hydroide reacts violently to remove the hydrogen (H2). The dihydrohydrides consist of only hydrogen, one other element, and water. They are usually in the form MH2 (or MH3), such as magnesium hydride, sodium hydride, lithium hydride, calcium hydride, or calcium hydride.

Unstable calcium hydroide as a high-temperature thermal cell with promise
CaH2 is a candidate that has a high energy density (thermal batteries), and a low price. Its high operating temperature and low cycle stability have been the major factors in its failure to be developed and implemented as a CSP factory thermal cell. In this study, alumina was used at a 1:1 molar ratio to thermodynamically stabilise CaH2, releasing hydrogen with a lower temperature.
Temperature-programmed desorption measurements show that compared with the decomposition of pure CaH2 to about 1000degC under 1 bar of hydrogen pressure, the addition of Al2O3 will lower the decomposition temperature to ~600degC, thereby making the reaction thermodynamically unstable for the release of hydrogen from CaH2. The experimental entropy and enthalpy of the CaH2 system is determined by measuring the pressure component’s isotherm between 612degC to 636degC.
Enthalpy and entropy are measured using DHdes=100+-2 kJ mol-1, respectively. Ca12Al14O33 was confirmed by the XRD after TPD. SEM and XRD confirmed that a system capacity loss was observed during the hydrogen-cycle at 636degC. The cause of this loss was the excess Al2O3. Hydrogen cycle capacity has improved significantly by reducing initial Al2O3 and achieving a CaH2:Al2O3 molar proportion of 2:1. This is a high-temperature, thermal battery that has great potential for the next CSP generation.
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