- Chemical structure
- Alpha beryllium hydroxide
- Beta beryllium hydroxide
- Beryllium hydroxide in minerals
- Beryllium Hydroxide Vapor
- Properties
- Appearance
- Thermochemical properties
- Solubility
- Exposure risks
- Applications
- Obtaining
- Obtaining metallic beryllium
- References
The beryllium hydroxide is a chemical compound formed by two molecules of hydroxide (OH) and one molecule of beryllium (Be). Its chemical formula is Be (OH) 2 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 2 O → Be (OH) 2
On the other hand, this amphoteric substance has a linear molecular configuration. However, various structures can be obtained from beryllium hydroxide: alpha and beta form, as a mineral and in the vapor phase, depending on the method used.
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 solution of beryllium salt gives the alpha (α) form of beryllium hydroxide. An example is shown below:
2NaOH (diluted) + BeCl 2 → Be (OH) 2 ↓ + 2NaCl
2NaOH (diluted) + BeSO 4 → Be (OH) 2 ↓ + Na 2 SO 4
Beta beryllium hydroxide
The degeneration of this alpha product forms a meta-stable tetragonal crystalline structure, which after a long period of time 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.
By Andif1, from Wikimedia Commons
Beryllium hydroxide in minerals
Although it is not usual, beryllium hydroxide is found as a crystalline mineral known as behoite (named after its chemical composition).
It is produced in granitic pegmatites formed by the alteration of Gadolinite (minerals from the group of silicates) 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 / cm 3. Its melting point is at a temperature of 1000 ° C, at which it begins its decomposition.
As a mineral, Be (OH) 2 (behoite) has a hardness of 4 and its density ranges between 1.91 g / cm 3 and 1.93 g / cm 3.
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 Be (OH) 2 mineral is varied, because it can be found as reticular, arborescent crystals or spherical aggregates. Similarly, it comes in white, pink, bluish, and even colorless colors and with a greasy vitreous luster.
Thermochemical properties
Formation enthalpy: -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) 2 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 / m 3 and 0.005 mg / m 3 is 8 hours, and for a concentration of 0.0225 mg / m 3 maximum a time 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:
- Beryllium hydroxide is dissolved in sulfuric acid (H 2 SO 4).
- Once the reaction is carried out, the solution is filtered, so that in this way insoluble oxide or sulfate impurities are removed.
- The filtrate is subjected to evaporation to concentrate the product, which is cooled to obtain crystals of beryllium sulfate BeSO 4.
- BeSO 4 is calcined 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 metallic beryllium.
Be (OH) 2 is reacted with a solution of ammonium bifluoride:
Be (OH) 2 + 2 (NH 4) HF 2 → (NH 4) 2 BeF 4 + 2 H 2 O
(NH 4) 2 BeF 4 is subjected to an increase in temperature, undergoing thermal decomposition:
(NH 4) 2 BeF 4 → 2NH 3 + 2HF + BeF 2
Finally, reducing beryllium fluoride at a temperature of 1300 ° C with magnesium (Mg) results in metallic beryllium:
BeF 2 + Mg → Be + MgF 2
Beryllium is used in metal alloys, the production of electronic components, the manufacture of screens and radiation windows used in X-ray machines.
References
- Wikipedia. (sf). Beryllium hydroxide. Recovered from en.wikipedia.org
- Holleman, AF; Wiberg, E. and Wiberg, N. (2001). Beryllium Hydroxide. Obtained from books.google.co.ve
- Publishing, MD (nd). Behoite. Recovered from handbookofmineralogy.org
- All Reactions. (sf). Beryllium Hydroxide Be (OH) 2. Retrieved from allreactions.com
- PubChem. (sf). Beryllium Hydroxide. Recovered from pubchem.ncbi.nlm.nih.gov
- Walsh, KA and Vidal, EE (2009). Beryllium Chemistry and Processing. Obtained from books.google.co.ve