THE rhenium is a metal, from atomic number 75, which is two positions below manganese in the Periodic Table, that is, in Group 7, sixth period. Were predicted by Mendeleev in 1869, when he published the first version of his Periodic Table, and discovered only in the year 1925. It is rare and is found in nature in small samples of molybdenum minerals.
Rhenium is mainly used as a catalyst for oil refining and in metal alloys high performance, with great temperature resistance, as it is the second highest melting point metal in the Periodic table.
Such alloys can be used in the manufacture of thermocouples (sensors for measuring temperature), flash filaments photographs and also in mass spectrometers, a device used to detect, identify and quantify molecules through your mass.
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rhenium summary
- Rhenium is a metal which was predicted by Mendeleev in 1869.
- It is not very abundant, with only 1 mg for every ton of Earth's crust.
- It presents a wide variety of oxidation states, ranging from -1 to +7.
- It is commercially extracted from molybdenite.
- It is used in metallic superalloys, which participate in the manufacture, for example, of aircraft turbine blades.
- Its name refers to the River Rhine, an important watercourse on the European continent.
Rhenium properties
- Symbol: Re.
- Atomic number: 75.
- Atomic mass: 186.207 c.u.
- Electronegativity: 1,9.
- Fusion point: 3185°C.
- Boiling point: 5596°C.
- Density: 20.8 g.cm-3.
- Electronic configuration: [Xe] 6s2 5d5.
- Chemical series: Group 7; External transition metals; block d.
Rhenium characteristics
Rhenium is a silvery-white metal considered one of the rarest elements on the planet. Its abundance is estimated to be in the range of 1 ppb (parts per billion), the equivalent of 1 mg of rhenium for every ton of Earth's crust.
Chemically, rhenium has similarities with element chemical most famous of his group, the manganese, as, for example, in wide variety of oxidation states (nine in all), which range from -1 to +7.
Despite being less reactive than manganese, rhenium, when finely divided, is able to suffer combustion in the presence of oxygen, forming stable oxides, such as Re2THE7, ReO3 and the ReO2. Rhenium heptoxide, in contrast to the metallic form of the element, is quite volatile.
It can also be dissolved in water, forming HReO4, perremic acid. Such an acid can also be formed if the metal is dissolved in oxidizing acids, as is the case with acid nitric (HNO3).
Another characteristic of rhenium is its high melting point, considered the second largest of the Periodic Table among the metals, behind only the tungsten. It is also the metal of highest boiling point, a property widely explored in its uses.
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Where is rhenium found?
Rarely will metallic rhenium occur in nature, although it has already been found in igneous rocks in Ukraine. There are rhenium minerals in the form of sulfides, as is the case with reniita (ReS2), which has already been detected in volcanic zones (fumarolas).
A mineral rich in rhenium has also been reported, tarkianite, a mixed sulfide of rhenium, copper, iron and molybdenum. However, none of these minerals contain economically significant amounts of the element.
So, the main commercial source of rhenium is molybdenite, where the metal content can vary from 1 ppm (part per million, equivalent to 1 mg per kilogram of mineral) to 2000 ppm. During the heat treatment of molybdenite, Re2THE7 It is formed. As it is volatile, this oxide can be collected in chimneys. It is then dissolved in water and precipitated in the form of KReO4, perremato of potassium.
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Rhenium applications
Since the late 1980s, the main uses of rhenium have been in the manufacture of superalloys (high performance metal alloys) with high temperature resistance and in the manufacture of catalysts platinum-rhenium (Pd-Re). These superalloys in which rhenium is applied are used for the manufacture of turbine blades for jet aircraft engines.
On the other hand, Pd-Re catalysts are used in the petrochemical industry, in production of high-octane gasoline free from sulfur, during the catalytic reforming step. Rhenium catalysts are resistant to chemical attack by nitrogen, phosphor and sulfur, which allows them to be used in hydrogenation reactions in various industrial processes.
Among minor uses, rhenium can form alloys with tungsten or molybdenum for diverse applications, such as electronic artifacts, flash equipment, vacuum tubes, x-ray tubes and thermocouples, sensors for measuring the temperature, which are capable of measuring from a few negative tens to thousands of degrees Celsius.
Precautions with Rhenium
- Some rhenium compounds are reported to be irritating to eyes and skin, such as rhenium hexafluoride.
- Experiments with animals found a risk of pulmonary fibrosis through the inhalation of rhenium dust.
- Rhenium VII sulfide spontaneously ignites on contact with air, emitting toxic fumes.
However, the amount of rhenium in the environment is so low that its risks are still not widely known. to ground and human beings.
history of rhenium
When publishing his Periodic Table in 1869, Dmitri Mendeleev left two gaps for two elements to be discovered in Group 7. Subsequently, these gaps were filled by element 43, technetium (Tc), and by element 75, rhenium (Re).
THE rhenium was discovered in 1925, when Walter Noddack, Ida Tacke and Otto Berg managed to obtain, at great cost, a single gram of the metal after processing about 660 kg of molybdenite in Germany. The name Rhenius refers to the term Rhenius, the Latin name of the famous river Rhine, which crosses Europe from north to south.
Exercises solved on rhenium
question 1
Rhenium, symbol Re, is a rare metal whose existence was predicted by Dmitri Mendeleev in 1869. Analyzing the current Periodic Table, one can classify rhenium as:
A) alkali metal.
B) alkaline earth metal.
C) nonmetal.
D) external transition metal.
E) internal transition metal.
Resolution:
Alternative D
Rhenium is in Group 7 of the Periodic Table, headed by manganese. In this position, it should be classified as an outer transition metal, as it belongs to the d-block.
question 2
Note some information about the chemical element rhenium, symbol Re:
- Melting point: 3185°C.
- Boiling point: 5596°C.
- Density: 20.8 g.cm-3.
- Abundance in the Earth's crust: 1 mg/ton.
Evaluate the information and tick the correct option.
A) Rhenium is a volatile metal, appearing as a liquid at room temperature.
B) When placing a piece of rhenium in water, it floats.
C) Rhenium is an element of great abundance in the earth's crust.
D) Rhenium's high melting point allows it to be used in alloys to provide greater thermal resistance.
Resolution:
Alternative D
The high melting point of rhenium improves the thermal resistance of metal alloys, which can be exposed to extreme heat conditions. Rhenium, by the way, has the second highest melting point among metals.
By Stefano Araújo Novais
Chemistry teacher