8 julio, 2024

Strontium hydroxide: what it is, chemical structure, properties and uses

What is strontium hydroxide?

He strontium hydroxide (Sr(OH)₂) is an inorganic chemical compound made up of a strontium ion (Sr) and two hydroxide ions (OH). This compound is obtained by combining a strontium salt with a strong base, resulting in an alkaline compound whose chemical formula is Sr(OH)2.

In general, for the preparation of strontium hydroxide, sodium hydroxide (NaOH) or potassium hydroxide (KOH) is used as a strong base. On the other hand, the strontium salt (or strontium ion) that reacts with the strong base is strontium nitrate Sr(NO3)2 and the process is described by the following chemical reaction:

2KOH + Sr(NO3)2 → 2KNO3 + Sr(OH)2

In solution, the strontium cation (Sr+) comes into contact with the hydroxide anion (OH–) forming a basic ionic salt of strontium. Since strontium is an alkaline earth metal, strontium hydroxide is considered a caustic alkali compound.

Obtaining strontium hydroxide

In addition to the previously explained process, it can be said that once the reaction has been carried out, Sr(OH)2 precipitates out of solution. This is then subjected to the washing and drying process, finally obtaining a very fine white powder.

An alternative method for obtaining strontium hydroxide is from heating strontium carbonate (SrCO3) or strontium sulfate (SrSO4), with steam at a temperature ranging between 500°C and 600°C. The chemical reaction occurs as shown below:

SrCO3 + H2O → Sr(OH)2 + CO2

SrS + 2H2O → Sr(OH)2 + H2S

Chemical structure and physicochemical properties

Currently, 3 forms of strontium hydroxide are known: octahydrate, monohydrate and anhydrous.

Strontium hydroxide octahydrate

From solutions under normal conditions of temperature and pressure (25°C and 1 atm), strontium hydroxide precipitates in the octahydrated form, whose chemical formula is Sr(OH)2∙8H2O.

This compound has a molar mass of 265.76 g/mol, a density of 1.90 g/cm, and precipitates as colorless tetragonal crystals (with space group P4/ncc) with a quadrangular prismatic appearance.

Likewise, strontium hydroxide octahydrate has the ability to absorb atmospheric moisture, since it is an easily deliquescent compound.

Strontium hydroxide monohydrate

According to optical microscopy studies (carried out using the X-ray diffraction technique), by raising the temperature to around 210°C -at constant atmospheric pressure- Sr(OH)2∙8H2O is dehydrated and transformed into hydroxide strontium monohydrate (Sr(OH)2∙H2O).

This form of the compound has a molar mass of 139.65 g/mol and its melting point is -73.15°C (375K). Due to its atomic configuration, it presents less solubility in water than that described in its octahydrate form.

anhydrous strontium hydroxide

By continuing to increase the temperature of the system to about 480°C, the dehydration is prolonged until anhydrous strontium hydroxide is obtained.

Unlike its hydrated forms, it has a molar mass of 121.63 g/mol and a density of 3.625 g/cm3. Its boiling point is reached at 710°C (1,310°F or 983K) while the melting point is at 535°C (995°F or 808K).

Solubility

Strontium hydroxide octahydrate has a solubility in water of 0.91 grams per 100 milliliters (measured at 0°C), while its anhydrous form at similar temperature conditions presents a solubility of 0.41 grams per 100 milliliters.

Similarly, this substance is considered to be insoluble in acetone and fully soluble in acids and ammonium chloride.

chemical reactivity

Strontium hydroxide is non-flammable, its chemical reactivity remains stable at moderate temperatures and pressures, and it is capable of absorbing carbon dioxide from atmospheric air, transforming it into strontium carbonate.

Furthermore, it is a severely irritating compound if it comes into contact with the skin, respiratory tract or other mucous membranes of the body.

Strontium Hydroxide Uses

Due to its hygroscopic characteristics and basic properties, strontium hydroxide is used for different applications in the industry:

Extraction of molasses and refining of sugar from beets.
Plastic stabilizer.
Greases and lubricants.

Extraction of molasses and refining of beet sugar

At the beginning of the 21st century, strontium hydroxide began to be used in Germany to refine sugar from beets, through the process patented by Carl Scheibler in 1882.

This procedure consists of mixing strontium hydroxide and sugar beet pulp, which results in an insoluble disaccharide. This solution is separated by settling and once the refining process has been carried out, sugar is obtained as the final product.

Despite the fact that this procedure is still used today, there are other methods that are much more in demand because they are cheaper, which are used in the vast majority of sugar refineries in the world. For example, the Barsil method, which uses barium silicate, or the Steffen method, using lime as an extracting agent.

strontium fats

They are lubricating greases that contain strontium hydroxide. These are capable of adhering strongly to surfaces with metallic characteristics, they are resistant to water and can withstand sudden changes in temperature.

Due to their good physical and chemical stability, these greases are used as industrial lubricants.

plastic stabilizer

The vast majority of plastics, when exposed to climatic factors such as sun, rain and atmospheric oxygen, modify their properties and degrade.

Due to its considerable resistance to water, strontium hydroxide is added to these polymers -during the melting phase- acting as a stabilizer in the manufacture of plastic products to prolong their useful life.

Other apps

In the paint industry it is used as an essential additive to speed up the drying process in commercial and industrial paints.
From strontium hydroxide, strontium salts or ions are obtained, which are used as raw material for the production of fireworks.

References

Wikipedia (n.d.). Strontium hydroxide. Retrieved from en.wikipedia.org
PubChem (nd). Strontium Hydroxide. Retrieved from pubchem.ncbi.nlm.nih.gov
Honeywell (nd). Strontium Hydroxide Octahydrate. Recovered from honeywell.com

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