Beryllium hydroxide (Be (OH) 2) structure, properties and uses

The beryllium hydroxide It is a chemical compound made up of two hydroxide molecules (OH) and one beryllium molecule (Be). Its chemical formula is Be (OH)_two and it is characterized by being an amphoteric species. In general, it can be obtained from the reaction between beryllium monoxide and water, according to the following chemical reaction: BeO + H_twoO → Be (OH)_two

On the other hand, this amphoteric substance has a linear molecular configuration. However, various structures of beryllium hydroxide can be obtained: alpha and beta form, as a mineral and in the vapor phase, depending on the method used..

Article index

• 1 Chemical structure
  • 1.1 Alpha beryllium hydroxide
  • 1.2 Beta beryllium hydroxide
  • 1.3 Beryllium hydroxide in minerals
  • 1.4 Beryllium hydroxide vapor
• 2 Properties
  • 2.1 Appearance
  • 2.2 Thermochemical properties
  • 2.3 Solubility
  • 2.4 Exposure risks
• 3 Uses
• 4 Obtaining
  • 4.1 Obtaining metallic beryllium
• 5 References

Chemical structure

This chemical compound can be found in four different forms:

Alpha beryllium hydroxide

Adding any basic reagent such as sodium hydroxide (NaOH) to a beryllium salt solution gives the alpha (α) form of beryllium hydroxide. An example is shown below:

2NaOH (diluted) + BeCl_two → Be (OH)_two↓ + 2NaCl

2NaOH (diluted) + BeSO₄ → Be (OH)_two↓ + Na_twoSW₄

Beta beryllium hydroxide

The degeneration of this alpha product forms a meta-stable tetragonal crystalline structure, which after a long period of time has passed, transforms into a rhombic structure called beta (β) beryllium hydroxide..

This beta form is also obtained as a precipitate from a sodium beryllium solution by hydrolysis under conditions close to the melting point..

Beryllium hydroxide in minerals

Although it is not usual, beryllium hydroxide is found as a crystalline mineral known as behoite (named in this way referring to its chemical composition).

It is produced in granitic pegmatites formed by the alteration of Gadolinite (minerals of the silicate group) in volcanic fumaroles.

This relatively new mineral was discovered for the first time in 1964, and currently they have only been found in granite pegmatites located in the states of Texas and Utah in the United States..

Beryllium Hydroxide Vapor

At temperatures above 1200 ° C (2190 ° C), beryllium hydroxide exists in the vapor phase. It is obtained from the reaction between water vapor and beryllium oxide (BeO).

Similarly, the resulting vapor has a partial pressure of 73 Pa, measured at a temperature of 1500 ° C..

Properties

Beryllium hydroxide has an approximate molar mass or molecular weight of 43.0268 g / mol and a density of 1.92 g / cm³. Its melting point is at a temperature of 1000 ° C, at which it begins its decomposition.

As a mineral, Be (OH)_two (behoite) has a hardness of 4 and its density ranges between 1.91 g / cm³ and 1.93 g / cm³.

Appearance

Beryllium hydroxide is a white solid, which in its alpha form has a gelatinous and amorphous appearance. On the other hand, the beta form of this compound is constituted by a well-defined, orthorhombic and stable crystalline structure..

It can be said that the morphology of the mineral Be (OH)_two it is varied, because it can be found as reticular, arborescent crystals or spherical aggregates. In the same way, it comes in white, pink, bluish and even colorless colors and with a greasy vitreous luster..

Thermochemical properties

Enthalpy of formation: -902.5 kJ / mol

Gibbs energy: -815.0 kJ / mol

Formation entropy: 45.5 J / mol

Heat capacity: 62.1 J / mol

Specific heat capacity: 1,443 J / K

Standard enthalpy of formation: -20.98 kJ / g

Solubility

Beryllium hydroxide is amphoteric in character, so it is capable of donating or accepting protons and dissolves in both acidic and basic media in an acid-base reaction, producing salt and water..

In this sense, the solubility of Be (OH)_two in water is limited by the solubility product Kps_(H2O), which is equal to 6.92 × 10^-22.

Exposure risks

The legal permissible human exposure limit (PEL or OSHA) of a beryllium hydroxide substance defined for a maximum concentration between 0.002 mg / m³ and 0.005 mg / m³ is 8 hours, and for a concentration of 0.0225 mg / m³ a maximum of 30 minutes.

These limitations are due to the fact that beryllium is classified as a type A1 carcinogen (human carcinogen, based on the amount of evidence from epidemiological studies)..

Applications

The use of beryllium hydroxide as a raw material for the processing of some product is very limited (and unusual). However, it is a compound used as the main reagent for the synthesis of other compounds and obtaining metallic beryllium..

Obtaining

Beryllium oxide (BeO) is the most widely used high-purity beryllium chemical compound in industry. It is characterized as a colorless solid with electrical insulating properties and high thermal conductivity.

In this sense, the process for its synthesis (in technical quality) in primary industry is carried out as follows:

1. Beryllium hydroxide dissolves in sulfuric acid (H_twoSW₄).
2. Once the reaction is carried out, the solution is filtered, so that in this way insoluble oxide or sulfate impurities are eliminated..
3. The filtrate is subjected to evaporation to concentrate the product, which is cooled to obtain crystals of beryllium sulfate BeSO₄.
4. The kiss₄ calcines at a specific temperature between 1100 ° C and 1400 ° C.

The final product (BeO) is used to manufacture special ceramic pieces for industrial use..

Obtaining metallic beryllium

During the extraction and processing of beryllium minerals, impurities are generated, such as beryllium oxide and beryllium hydroxide. The latter is subjected to a series of transformations until obtaining the metallic beryllium.

Be (OH) is reacted_two with an ammonium bifluoride solution:

Be (OH)_two + 2 (NH₄) HF_two → (NH₄)_twoBeF₄ + 2 h_twoOR

The (NH₄)_twoBeF₄ is subjected to an increase in temperature, undergoing thermal decomposition:

(NH₄)_twoBeF₄ → 2NH₃ + 2HF + BeF_two

Finally, reducing beryllium fluoride at a temperature of 1300 ° C with magnesium (Mg) results in metallic beryllium:

BeF_two + Mg → Be + MgF_two

Beryllium is used in metal alloys, production of electronic components, manufacture of screens and radiation windows used in X-ray machines..

References

1. Wikipedia. (s.f.). Beryllium hydroxide. Recovered from en.wikipedia.org
2. Holleman, A. F .; Wiberg, E. and Wiberg, N. (2001). Beryllium Hydroxide. Obtained from books.google.co.ve
3. Publishing, M. D. (s.f.). Behoite. Recovered from handbookofmineralogy.org
4. All Reactions. (s.f.). Beryllium Hydroxide Be (OH)_two. Retrieved from allreactions.com
5. PubChem. (s.f.). Beryllium Hydroxide. Recovered from pubchem.ncbi.nlm.nih.gov
6. Walsh, K. A. and Vidal, E. E. (2009). Beryllium Chemistry and Processing. Obtained from books.google.co.ve