RUTHENIUM

Name: Ruthenium

Symbol: Ru

Group: 8

Period: 5

Block: d

Category: Transition metals

Atomic number: 44

Atomic mass: 101.97 u

Electrons per shell: 2, 8, 18, 15, 1

Electronegativity: 2.2

Density: 12.37 g/cc

Melting point: 2334ºC

Boiling point: 4150ºC

Thermal conductivity: 120 W (m·K)

Electrical conductivity: 1.4 × 10^7 S/m

Magnetic order: Paramagnetic

Ordinary state: Solid

Oxidation states: -3, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8

Mohs hardness: 6.5

Vickers hardness: 2298 MPa

Brinell hardness: 2160 MPa

Most stable isotopes: Ru-96 (5.54%), Ru-98 (1.87%), Ru-99 (12.76%), Ru-100 (12.60%), Ru-101 (17.06%), Ru-102 (31.55%), Ru-104 (18.62%)

Discoverer: Karl Ernst Claus, Russian-German (1844)

Ruthenium, identified with atomic number 44, is a transition metal that belongs to the prestigious platinum group metals, known as PGMs. Classified as a precious and noble metal, its use in jewelry is limited due to its brittle nature, but its value shines in industrial applications thanks to its extraordinary hardness and corrosion resistance. Among the metals in its group, ruthenium stands out as the most affordable and the heaviest in period 5 of the periodic table, making it a unique element in the field of metallurgy.

Discovered in 1844 by the scientist Karl Ernst Claus in the Ural region, ruthenium owes its name to "Ruthenia", the Latin term for Russia, inspired by the ancient Rus confederation. Although Claus, of Germanic origin, worked in a context where the political boundaries of the Russian and German empires differed from current ones, his decision to name the metal reflected a deep connection with Russia, marking his scientific contributions with the identity of this country. This discovery came decades after the Englishmen William Wollaston and Smithson Tennant discovered other metals in the group, such as platinum and palladium, positioning ruthenium as a late but significant discovery.

In its pure state, ruthenium is a precious metal that captivates with its mirror-white color, a radiant luster that distinguishes it within the platinum group metals. Its high melting point makes it exceptionally resistant to extreme temperatures, but its brittle nature, even at high temperatures, makes it a complex material to work with. This fragility, along with its tendency to pulverize easily and its difficulty in melting, restricts its use in metallurgy and jewelry. With a density of 12.45 g/cm³, ruthenium is notably heavy, which reinforces its robustness, although it poses challenges in its manipulation.

In nature, ruthenium is commonly found alloyed with other metals of its group, such as platinum or palladium, but its extraction is an arduous and costly process due to its scarcity in the Earth's crust. Although it is less abundant than palladium, its price is more accessible compared to other metals in the group, probably due to its lower versatility. Its greatest attribute is its extraordinary hardness, which makes it a key hardener in specialized alloys. Ruthenium combines effectively with metals of its group and with ferrous elements such as iron, cobalt, and nickel, but its solubility with copper and gold is limited, and it does not fuse with silver at any temperature. Alloys with p-block metals, such as tin, are equally unviable.

Chemically, ruthenium does not form carbides or nitrides. Among its compounds, ruthenium dioxide (RuO₂) stands out as a black, volatile material of limited industrial utility. More unique is ruthenium tetroxide (RuO₄), which remains liquid at room temperature, a rarity among metallic compounds. Despite its limitations, ruthenium's hardness and resistance make it indispensable in technical applications, such as high-durability coatings and chemical catalysts, where its ability to strengthen materials is invaluable.

Ruthenium, a platinum group metal, exhibits corrosion resistance that distinguishes it as a noble material, albeit with surprising chemical characteristics. At room temperature, it remains unaltered by all acids, regardless of their concentration, including hydrofluoric acid, whose reaction with ruthenium remains a subject of debate and limited study. Even aqua regia, a corrosive mixture capable of dissolving metals like gold, fails to attack it, not even at high temperatures. However, this metal presents a fascinating paradox: it dissolves rapidly in common bases, such as household bleach (NaOCl), with a vigorous reaction that releases heat, an unusual behavior for a metal considered noble or semi-noble.

Ruthenium's reactivity with alkalis is particularly intense, especially when they are in a molten state, where the reaction rate increases significantly. Despite this vulnerability, its resistance in other environments makes it valuable in specialized applications. In industry, ruthenium is used as an alternative to rhodium in white gold plating, providing a bright and durable finish. Additionally, its exceptional hardness makes it an ideal hardener for platinum and palladium alloys, especially in white gold jewelry, where it reinforces the strength and quality of the materials.

Ruthenium is a platinum group metal with exceptional properties that have made it a very valuable resource in both jewelry and high-performance industrial applications. Despite not forming carbides, as is the case with some refractory metals with which it is often confused, it stands out for its ability to harden and significantly improve the performance of other alloys, especially those composed of noble metals. In the field of jewelry, its most known use is as an alloying agent in platinum pieces, where it is employed as a more affordable alternative to iridium, offering additional hardness without sacrificing the characteristic luster of this precious metal. It is also used as a coating for white gold, being more wear-resistant than rhodium, although its final tone is different. When incorporated into white gold, ruthenium is not added directly due to its limited solubility; instead, it is first combined with palladium in an approximate proportion of ninety-five percent palladium and five percent ruthenium. This intermediate alloy acts as a bridge that allows ruthenium to disperse uniformly in molten gold, resulting in a high-quality final piece that is more scratch-resistant and has superior toughness, though it is harder to work with due to its increased hardness.

In the industrial sector, ruthenium is highly valued for its high natural corrosion resistance, a property that is enhanced when added in small quantities, generally between 0.1% and 6%, to other alloys. Its interaction with titanium is a notable example: this metal already possesses excellent corrosion resistance, but doping it with a minimal amount of ruthenium achieves an extraordinary increase in this property even at elevated temperatures. Furthermore, because ruthenium does not form carbides, it does not cause embrittlement, allowing the alloy to retain its mechanical strength and original toughness.

Another field in which ruthenium plays a fundamental role is in the manufacture of nickel- or cobalt-based superalloys. These alloys, extremely costly and complex to produce, are indispensable for the construction of components subjected to extreme conditions, such as aircraft engines, gas turbines, high-precision rotors, and aerospace parts that must withstand temperatures of up to one thousand degrees Celsius without losing strength or oxidizing. In these types of materials, ruthenium can account for up to six percent of the total mass, increasing their stability and resistance to sudden temperature changes and surpassing the quality of other commonly used elements such as molybdenum, tungsten, or tantalum.

Ruthenium has also been used, though less frequently, in certain grades of highly specialized steel. In these cases, it provides greater oxidation resistance at extreme temperatures, improves structural stability, and reinforces protection against corrosion. However, its use in this sector is limited, as its high cost and scarce availability make it a resource reserved for applications where its added value justifies the investment, with superalloys being the most common destination. Thus, ruthenium is positioned as a metal whose relevance not only resides in its rarity but also in its ability to transform and optimize the performance of the materials with which it combines, both in the refined world of jewelry and in demanding cutting-edge engineering.