Sulfidation (British spelling also sulphidation) is a process of installing

sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...

ions in a material or molecule. The process is widely used to convert oxides to sulfides but is also related to corrosion and surface modification.

Inorganic, materials, and organic chemistry

Sulfidation is relevant to the formation of

sulfide mineral The sulfide minerals are a class of minerals containing sulfide (S2−) or disulfide (S22−) as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, th ...

s. A large scale application of sulfidation is the conversion of molybdenum oxides to the corresponding sulfides. This conversion is a step in the preparation of catalysts for

hydrodesulfurization Hydrodesulfurization (HDS) is a catalytic chemical process widely used to remove sulfur (S) from natural gas and from refined petroleum products, such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils. The purpose of rem ...

wherein alumina impregnated with

molybdate In chemistry a molybdate is a compound containing an oxoanion with molybdenum in its highest oxidation state of 6. Molybdenum can form a very large range of such oxoanions which can be discrete structures or polymeric extended structures, altho ...

salts are converted to

molybdenum disulfide Molybdenum disulfide (or moly) is an inorganic compound composed of molybdenum and sulfur. Its chemical formula is . The compound is classified as a transition metal dichalcogenide. It is a silvery black solid that occurs as the mineral molybdeni ...

by the action of

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...

. In

organosulfur chemistry Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfur ...

, sulfiding is often called thiation. The preparation of

thioamide A thioamide (rarely, thionamide, but also known as thiourylenes) is a functional group with the general structure R–CS–NR′R″, where R, R′, and R″ are organic groups. They are analogous to amides but they exhibit greater multiple bond ch ...

s from

amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it i ...

s involves thiation. A typical reagent is

phosphorus pentasulfide Phosphorus pentasulfide is the inorganic compound with the formula (monomer) or (dimer). This yellow solid is the one of two phosphorus sulfides of commercial value. Samples often appear greenish-gray due to impurities. It is soluble in carbon d ...

(P₄S₁₀). The idealized equation for this conversion is: :RC(O)NH₂ + 1/4 P₄S₁₀ → RC(S)NH₂ + 1/4 P₄S₆O₄ This conversion where an oxygen atom in the amide function is replaced by a sulfur atom involves no redox reaction.

Sulfidation of metals

It is known that aluminum improves the sulfidation resistance of iron alloys. The sulfidation of

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

is a multiple step process. The first step is an

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...

reaction, converting the

to a tungsten bronze on the surface of the object. The tungsten bronze coating is then converted to a

. One commonly encountered occurrence of sulfidation in manufacturing environments involves the sulfidic corrosion of metal piping. The increased resistance to corrosion found in stainless steel is attributed to a layer of

chromium oxide Chromium oxide may refer to: * Chromium(II) oxide, CrO * Chromium(III) oxide, Cr2O3 * Chromium dioxide (chromium(IV) oxide), CrO2, which includes the hypothetical compound chromium(II) chromate * Chromium trioxide (chromium(VI) oxide), CrO3 * Chro ...

that forms due to

of the

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hard ...

found in the alloy. The process of liquid sulfidation has also been used in the manufacturing of

diamond-like carbon Diamond-like carbon (DLC) is a class of amorphous carbon material that displays some of the typical properties of diamond. DLC is usually applied as coatings to other materials that could benefit from such properties. DLC exists in seven diff ...

films. These films are generally used to coat surfaces to reduce the wear due to friction. The inclusion of sulfidation in the process has been shown to reduce the

friction coefficient Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...

of the diamond-like carbon film.

References

{{Reflist Corrosion Thermodynamics Chemical reactions