Rhenium

Embark on a journey to explore the chemical properties of Rhenium, a rare and highly valuable metal known for its exceptional characteristics and versatility. This guide provides detailed examples and insights into the world of Rhenium, showcasing its role in modern technology and industry. With its unique ability to withstand extreme temperatures and corrosive environments, Rhenium has carved out a niche in aerospace, electronics, and catalysis. Delve into the intricacies of its chemical behavior, compounds, and reactions that make Rhenium an indispensable element in advanced scientific research and applications.

What is Rhenium?

Rhenium is a metallic element with the chemical symbol Re and atomic number 75. It is extracted from molybdenite and other ores where it occurs in low concentrations. Rhenium is one of the rarest elements in the Earth’s crust and has the third-highest melting point of all elements, making it highly valued for its strength and resistance to wear and corrosion in extreme environments. The discovery of rhenium was significant in the field of chemistry for its unique properties among the transition metals in the periodic table. Its exceptional ability to withstand high temperatures and its catalytic properties make it crucial in the manufacturing of high-performance engines and catalysts.

Rhenium Formula

• Formula: Re
• Composition: Consists of a single rhenium atom.
• Bond Type: Rhenium forms both covalent and ionic bonds, enabling a wide range of complex compound formations, especially with halogens and oxygen.
• Molecular Structure: In its elemental form, rhenium adopts a hexagonal close-packed structure, which contributes to its high density and melting point. The compounds of rhenium, including rhenium heptoxide (Re₂O₇) and rhenium carbide (ReC), exhibit diverse molecular structures.
• Electron Sharing: Rhenium participates in electron sharing to form covalent bonds and is known for its ability to form ionic bonds in compounds such as ammonium perrhenate (NH₄ReO₄).
• Significance: Rhenium’s unparalleled melting point and resistance to wear make it indispensable in jet engines, gas turbines, and catalysis, demonstrating its critical role in high-performance applications.
• Role in Chemistry: Rhenium’s impact on chemistry is profound, with its compounds used in high-temperature superalloys and as efficient catalysts in chemical reactions.

Atomic Structure of Rhenium

Exploring the atomic structure of Rhenium reveals the foundations of its exceptional characteristics and wide application range.

• Atomic Level: Every atom of Rhenium is characterized by 75 protons, establishing it as atomic number 75 on the periodic table. The electron configuration of Rhenium, [Xe]4f¹⁴ 5d⁵ 6s², with a full 4f orbital, five electrons in the 5d orbital, and two in the 6s orbital, is critical to its chemical behavior and bonding capacity.
• Molecular Formation: Rhenium’s ability to form stable molecules results in consistent molecular structures across its compounds. Its compounds, notably rhenium heptoxide (Re₂O₇) and rhenium carbide (ReC), are vital in numerous applications requiring high strength and resistance to extreme conditions, reflecting Rhenium’s essential role in the development of durable materials and catalysts.

The behavior and stability of Rhenium under different temperatures and pressures have been extensively studied, showcasing its solid state under standard conditions. Its extraordinary melting point and durability at elevated temperatures underscore its utility in demanding environments, such as in the aerospace, defense, and chemical industries, solidifying Rhenium’s contribution to advancing modern science and industrial capabilities.

Properties of Rhenium

 

Physical Properties of Rhenium

Physical Property	Detail
Appearance	Silvery-white, with a metallic luster
Density	21.02 g/cm³ at 20°C, making it one of the densest elements
Melting Point	3186°C, one of the highest of all elements
Boiling Point	5596°C, which is also among the highest
State at 20 °C	Solid, due to its high melting point
Thermal Conductivity	48 W/(m·K), indicating good ability to conduct heat
Electrical Resistivity	193 nΩ·m at 20°C, showcasing its relatively high resistivity compared to other metals
Heat of Fusion	33.2 kJ/mol, the energy required to change from solid to liquid state without changing temperature

Chemical Properties of Rhenium

Rhenium stands out for its remarkable resistance to heat and wear, making it invaluable in high-temperature applications. Its most noteworthy chemical properties include:

• Oxidation States: Rhenium exhibits a wide range of oxidation states, from -1 to +7, with +4, +6, and +7 being the most common in its compounds. The versatility in oxidation states contributes to Rhenium’s reactivity and ability to form diverse compounds.
• Compounds and Reactions:
  • Rhenium Heptoxide: This compound demonstrates Rhenium’s highest oxidation state (+7). It is used in the preparation of other Rhenium compounds.
  • Perrhenic Acid: Produced from Rhenium heptoxide and water, it’s a precursor to many other Rhenium compounds.
  • Rhenium Carbonyl: Illustrates Rhenium’s ability to form complex covalent compounds.
• Catalysis: Rhenium is a potent catalyst, especially in hydrogenation and dehydrogenation reactions. Its catalytic properties are exploited in refining crude oil into gasoline, leveraging its ability to resist poisoning by sulfur and nitrogen compounds.

Thermodynamic Properties of Rhenium

Property	Value
Melting Point	3186 °C
Boiling Point	5596 °C
Heat of Fusion	33 kJ/mol
Heat of Vaporization	704 kJ/mol
Specific Heat Capacity	0.137 J/g·K
Thermal Conductivity	48 W/m·K

Material Properties of Rhenium

Property	Value
Density	21.02 g/cm³
Mohs Hardness	7.0
Tensile Strength	800 MPa
Young’s Modulus	463 GPa
Poisson’s Ratio	0.30
Vickers Hardness	2450 MPa

Electromagnetic Properties of Rhenium

Property	Value
Electrical Resistivity	193 nΩ·m
Magnetic Susceptibility	-0.0008

Nuclear Properties of Rhenium

Property	Value
Atomic Number	75
Atomic Mass	186.207
Stable Isotopes	Re-185, Re-187
Natural Abundance (Re-185)	37.4%
Natural Abundance (Re-187)	62.6%
Cross Section for Thermal Neutrons	90 barns (for Re-187)

Preparation of Rhenium

Rhenium is predominantly obtained as a by-product of molybdenum and copper mining. The preparation process involves:

1. Extraction from Molybdenite Ores: Rhenium is primarily obtained as a by-product of the copper and molybdenum mining industries. Molybdenite (MoS₂) is processed for molybdenum.
2. Roasting of Molybdenum Concentrates: The initial step involves roasting molybdenum concentrates containing molybdenite.
3. Leaching Process: The collected material from roasting, containing rhenium, is subjected to a leaching process, often with alkaline solutions.
4. Solvent Extraction and Ion Exchange: The solution obtained from leaching is then treated through solvent extraction and ion exchange techniques to separate and concentrate rhenium compounds.
5. Reduction to Metallic Rhenium: The purified rhenium compound, typically ammonium perrhenate (NH₄ReO₄), is then reduced with hydrogen in high-temperature furnaces to produce for various applications.

Chemical Compounds of Rhenium

Rhenium Heptoxide

Rhenium heptoxide is one of the most well-known oxides of rhenium and a key compound in its chemistry.

Equation: Re+7O₂​→Re₂​O₇

Perrhenic Acid

Perrhenic acid is a strong acid formed from the hydration of rhenium heptoxide and is of significant importance due to its role in the preparation of other rhenium compounds.

Equation: Re₂​O₇​+H₂​O→2HReO₄

Rhenium Carbide

Rhenium carbide is a compound that demonstrates rhenium’s ability to form stable compounds with non-metals other than oxygen.

Equation: Re+C→ReC

Rhenium Trifluoride

Rhenium trifluoride showcases the halide chemistry of rhenium, indicating its ability to form stable halide compounds.

Equation:32Re+3F₂→2ReF₃

Rhenium Pentachloride

Rhenium pentachloride demonstrates rhenium’s ability to form complex halides, which are pivotal in synthetic chemistry and serve as precursors to a wide array of organometallic compounds.

Equation:Re+5Cl₂→2ReCl₅

Rhenium Diboride

Rhenium diboride is a compound known for its extraordinary hardness and high electrical conductivity,

Equation:Re+2B→ReB₂

Isotopes of Rhenium

Isotope	Natural Abundance	Half-life	Notes
^185Re	37.4%	Stable	Commonly used in rhenium-osmium dating
^187Re	62.6%	4.12 × 10^10 years	Decays to ^187Os; used in geological dating
^186Re	Synthetic	3.7186 days	Used in radiopharmaceuticals for therapy
^188Re	Synthetic	17 hours	Applied in cancer treatment and research
^189Re	Synthetic	24.3 hours	Utilized in nuclear science for research

Uses of Rhenium

1. Super Alloys: Rhenium is a key component in superalloys, materials that are essential for high-temperature turbine engines in jet aircraft and industrial gas turbines.
2. Catalysis in Petroleum Refining: Rhenium is used as a catalyst in the petroleum industry, particularly in the catalytic reforming process which is crucial for converting petroleum refinery naphthas into high-octane gasoline.
3. Electrical Contacts: Due to its high melting point and good wear resistance, rhenium is used in electrical contacts and filaments. These applications benefit from rhenium’s durability and ability to withstand arcing.
4. Thermocouples: Rhenium-alloyed thermocouples, particularly tungsten-rhenium and molybdenum-rhenium alloys, are used for measuring temperatures up to 2200°C.
5. X-ray Equipment: Rhenium is used in the anodes of X-ray machines. Its high melting point makes it an ideal material for X-ray sources.
6. Medical Applications: Rhenium-186 and Rhenium-188 isotopes are used in radioactive pharmaceuticals for the treatment of liver cancer and rheumatoid arthritis.
7. Filament Material: Rhenium is used in filaments for mass spectrometers and ion gauges. Its stability under high-temperature conditions makes it suitable for these precision instruments.
8. Spacecraft Engines: The high melting point and resistance to heat make rhenium suitable for use in rocket engines, including thrusters and other components exposed to extreme temperatures during space missions.
9. Nuclear Reactors: Rhenium is used in nuclear reactor fuel rods as an alloying element with tungsten, enhancing their stability and resistance to high-temperature deformation.

Production of Rhenium

1. By-product of Copper and Molybdenum Mining: Most Rhenium production is from the processing of molybdenite concentrate from copper ores.
2. Extraction from Flue Dusts: Capturing Rhenium from the flue dusts of molybdenum roasters.
3. Purification Processes: Including solvent extraction and ion exchange to isolate Rhenium compounds like ammonium perrhenate.
4. Reduction to Metal: Pure Rhenium is produced by reducing ammonium perrhenate with hydrogen.
5. Recycling: Spent platinum-rhenium catalysts are recycled to recover Rhenium, contributing to the supply.

Applications of Rhenium

Rhenium has several critical applications across various high-tech and industrial fields:

• Aerospace and Defense: As an alloying element in superalloys used for jet engine components, offering unmatched resistance to high-temperature corrosion and thermal fatigue.
• Catalysis: In the petrochemical industry, rhenium is used as a catalyst for hydrogenation and the production of lead-free, high-octane gasoline. Its catalytic properties are essential for the efficient functioning of high-temperature reactors.
• Electronics and Electrical: Due to its high melting point and good wear resistance, rhenium is used in electrical contacts and filaments. Its thermal stability makes it ideal for thermocouples in high-temperature measurements.
• Medical: The radioactive isotopes ^186Re and ^188Re are utilized in the treatment of liver cancer and other types of cancers, exploiting their beta-emitting properties for targeted radiotherapy.
• Research and Development: Rhenium’s unique properties stimulate ongoing research in material science, especially in the development of new superalloys, and its isotopes are used in nuclear medicine and metallurgical research.

Rhenium, a metal of extremes, commands attention for its rarity and remarkable properties. From jet engines to cancer treatment, its uses span diverse fields, marking its significance in modern technology. This article delves into Rhenium’s fascinating world, exploring its chemical behavior, preparation methods, and versatile applications, showcasing its invaluable contribution to advancements in science and industry.