The 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)two.
Generally, 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)two and the process is described by the following chemical reaction:
2KOH + Sr (NO3)two → 2KNO3 + Sr (OH)two
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..
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In addition to the process previously explained, it can be said that once the reaction is carried out, Sr (OH)two precipitates out of solution. Then it is subjected to the washing and drying process, finally obtaining a very fine white powder..
An alternative method for obtaining strontium hydroxide is by heating strontium carbonate (SrCO3) or strontium sulfate (SrSO4) with steam at a temperature between 500 ° C and 600 ° C. The chemical reaction occurs as shown below:
SrCO3 + HtwoO → Sr (OH)two + COtwo
SrS + 2HtwoO → Sr (OH)two + HtwoS
Currently 3 forms of strontium hydroxide are known: octahydrate, monohydrate and anhydrous.
Strontium hydroxide precipitates in octahydrate form from solutions under normal conditions of temperature and pressure (25 ° C and 1 atm), whose chemical formula is Sr (OH)two∙ 8HtwoOR.
This compound has a molar mass of 265.76 g / mol, a density of 1.90 g / cm and precipitates as tetragonal crystals (with space group P4 / ncc) with a quadrangular and colorless prismatic appearance..
Likewise, strontium hydroxide octahydrate has the ability to absorb atmospheric moisture, since it is an easily deliquescent compound..
According to optical microscopy studies (carried out using the X-ray diffraction technique), by raising the temperature to about 210 ° C -at a constant atmospheric pressure- Sr (OH)two∙ 8HtwoOr it is dehydrated and transformed into strontium hydroxide monohydrate (Sr (OH)two∙ HtwoOR).
This form of the compound has a molar mass of 139.65 g / mol and its melting temperature is -73.15 ° C (375K). Due to its atomic configuration, it has less solubility in water than that described in its octahydrated form..
By continuing to increase the temperature of the system to about 480 ° C, the dehydration is prolonged until obtaining an anhydrous strontium hydroxide.
Unlike its hydrated forms, it has a molar mass of 121.63 g / mol and a density of 3.625 g / cm.3. Its boiling point is reached at 710 ° C (1,310 ° F or 983 K) while the melting point is at 535 ° C (995 ° F or 808 K).
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 has a solubility of 0.41 grams per 100 milliliters.
Similarly, this substance is considered insoluble in acetone and fully soluble in acids and ammonium chloride..
Strontium hydroxide is not 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..
In addition, it is a severely irritating compound if it comes into contact with the skin, respiratory tract or other mucous areas of the body..
Due to its hygroscopic characteristics and basic properties, strontium hydroxide is used for different applications in industry:
At the beginning of the 21st century, in Germany strontium hydroxide began to be used for the refining of sugar from beets through the process patented by Carl Scheibler in 1882.
This procedure consists of the mixture of strontium hydroxide and the sugar pulp of the beet, which results in an insoluble disaccharide. This solution is separated by decantation and once the refining process has been carried out, the sugar is obtained as a final product..
Despite the fact that this procedure is still used today, there are other methods with much more 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 Cal as an extracting agent..
They are lubricating greases that contain strontium hydroxide. They are capable of strongly adhering to surfaces with metallic characteristics, are resistant to water and withstand sudden changes in temperature..
Due to their good physical and chemical stability, these greases are used as industrial lubricants.
The vast majority of plastics, when exposed to climatic factors such as the sun, rain and atmospheric oxygen, modify their properties and deteriorate.
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..
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