Chromium carbide

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Chromium carbide [1]
Cr3C2structure.jpg
Chromium carbide Cr3C2.JPG
Names
IUPAC name
Chromium(II) carbide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.031.420
PubChem CID
Properties
Cr3C2
Molar mass 180.009 g/mol
Appearance gray orthorhombic crystals
Density 6.68 g/cm3
Melting point 1,895 °C (3,443 °F; 2,168 K)
Boiling point 3,800 °C (6,870 °F; 4,070 K)
reacts
Structure
Orthorhombic, oP20
Pnma, No. 62
Hazards
NFPA 704
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g., diesel fuelHealth code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentineReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calciumSpecial hazards (white): no codeChromium carbide
2
1
1
US health exposure limits (NIOSH):
PEL (Permissible)
 TWA 1 mg/m3 [2]
REL (Recommended)
 TWA 0.5 mg/m3 [2]
IDLH (Immediate danger)
 250 mg/m3 [2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Chromium carbide is a ceramic compound that exists in several different chemical compositions: Cr3C2, Cr7C3,and Cr23C6. At standard conditions it exists as a gray solid. It is extremely hard and corrosion resistant. It is also a refractory compound, which means that it retains its strength at high temperatures as well. These properties make it useful as an additive to metal alloys. When chromium carbide crystals are integrated into the surface of a metal it improves the wear resistance and corrosion resistance of the metal, and maintains these properties at elevated temperatures. The hardest and most commonly used composition for this purpose is Cr3C2.

Ceramic inorganic, nonmetallic solid prepared by the action of heat

A ceramic is a solid material comprising an inorganic compound of metal, non-metal or metalloid atoms primarily held in ionic and covalent bonds. Common examples are earthenware, porcelain, and brick.

Corrosion Gradual destruction of materials by chemical reaction with its environment

Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and stopping corrosion.

In metallurgy, refraction is a property of metals that indicates their ability to withstand heat. Metals with a high degree of refraction are referred to as refractory. These metals derive their high melting points from their strong intermolecular forces. Large quantities of energy are required to overcome intermolecular forces.

Contents

Related minerals include tongbaite [3] and isovite, (Cr,Fe)23C6, both extremely rare. [4] Yet another chromium-rich carbide mineral is yarlongite, Cr4Fe4NiC4. [5]

Tongbaite is a rare mineral that has the chemical formula Cr3C2, or chromium carbide.

Properties

There are three different crystal structures for chromium carbide corresponding to the three different chemical compositions. Cr23C6 has a cubic crystal structure and a Vickers hardness of 976 kg/mm2. [6] Cr7C3 has a hexagonal crystal structure and a microhardness of 1336 kg/mm2. [6] Cr3C2 is the most durable of the three compositions, and has an orthorhombic crystal structure with a microhardness of 2280 kg/mm2. [6] For this reason Cr3C2 is the primary form of chromium carbide used in surface treatment.

Synthesis

Synthesis of chromium carbide can be achieved through mechanical alloying. In this type of process metallic chromium and pure carbon in the form of graphite are loaded into a ball mill and ground into a fine powder. After the components have been ground they are pressed into a pellet and subjected to hot isostatic pressing. Hot isostatic pressing utilizes an inert gas, primarily argon, in a sealed oven. This pressurized gas applies pressure to the sample from all directions while the oven is heated. The heat and pressure cause the graphite and metallic chromium to react with one another and form chromium carbide. Decreasing the percentage of carbon content in the initial mixture results in an increase in the yield of the Cr7C3, and Cr23C6 forms of chromium carbide. [7]

Mechanical alloying

Mechanical alloying (MA) is a solid-state and powder processing technique involving repeated cold welding, fracturing, and re-welding of blended powder particles in a high-energy ball mill to produce a homogeneous material. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or pre-alloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. One consideration that should be avoided is powder contamination.

Chromium Chemical element with atomic number 24

Chromium is a chemical element with 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 boasts a high usage rate as a metal that is able to be highly polished while resisting tarnishing. Chromium is also the main additive in stainless steel, a popular steel alloy due to its uncommonly high specular reflection. Simple polished chromium reflects almost 70% of the visible spectrum, with almost 90% of infrared light being reflected. The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, because many chromium compounds are intensely colored.

Graphite allotrope of carbon, mineral, substance

Graphite, archaically referred to as plumbago, is a crystalline form of the element carbon with its atoms arranged in a hexagonal structure. It occurs naturally in this form and is the most stable form of carbon under standard conditions. Under high pressures and temperatures it converts to diamond. Graphite is used in pencils and lubricants. Its high conductivity makes it useful in electronic products such as electrodes, batteries, and solar panels.

Another method for the synthesis of chromium carbide utilizes chromium oxide, pure aluminum, and graphite in a self-propagating exothermic reaction that proceeds as follows: [7]

Exothermic reaction chemical reaction that releases energy by light or heat; opposite of an endothermic reaction

An exothermic reaction is a chemical reaction that releases energy through light or heat. It is the opposite of an endothermic reaction.

3Cr2O3 + 6Al + 4C → 2Cr3C2 + 3Al2O3

In this method the reactants are ground and blended in a ball mill. The blended powder is then pressed into a pellet and placed under an inert atmosphere of argon. The sample is then heated. A heated wire, a spark, a laser, or an oven may provide the heat. The exothermic reaction is initiated, and the resulting heat propagates the reaction throughout the rest of the sample.

Uses

Chromium carbide is useful in the surface treatment of metal components. Chromium carbide is used to coat the surface of another metal in a technique known as thermal spraying. Cr3C2 powder is mixed with solid nickel-chromium. This mixture is then heated to very high temperatures and sprayed onto the object being coated where it forms a protective layer. This layer is essentially its own metal matrix composite, consisting of hard ceramic Cr3C2 particles embedded in a nickel-chromium matrix. The matrix itself contributes to the corrosion resistance of the coating because both nickel and chromium are corrosion resistant in their metallic form. After over spraying the coating, the coated part must run through a diffusion heat treatment to reach the best results in matter of coupling strength to the basemetal and also in matter of hardness. Another technique utilizes chromium carbide in the form of overlay plates. These are prefabricated chromium carbide coated steel plates, which are meant to be welded onto existing structures or machinery in order to improve performance. Chromium carbide is used as an additive in cutting tools made out of cemented carbides, in order to improve toughness by preventing the growth of large grains. [8] The primary constituent in most extremely hard cutting tools is tungsten carbide. The tungsten carbide is combined with other carbides such as titanium carbide, niobium carbide, and chromium carbide and sintered together with a cobalt matrix. Cr3C2 prevents large grains from forming in the composite, which results in a fine-grained structure of superior toughness.

Thermal spraying materials processing technology

Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface. The "feedstock" is heated by electrical or chemical means.

Nichrome is any of various alloys of nickel, chromium, and often iron. The most common usage is as resistance wire, although they are also used in some dental restorations (fillings) and in a few other applications.

A metal matrix composite (MMC) is composite material with at least two constituent parts, one being a metal necessarily, the other material may be a different metal or another material, such as a ceramic or organic compound. When at least three materials are present, it is called a hybrid composite. An MMC is complementary to a cermet.

Related Research Articles

Carbide inorganic compound group

In chemistry, a carbide is a compound composed of carbon and a less electronegative element. Carbides can be generally classified by the chemical bonds type as follows: (i) salt-like, (ii) covalent compounds, (iii) interstitial compounds, and (iv) "intermediate" transition metal carbides. Examples include calcium carbide (CaC2), silicon carbide (SiC), tungsten carbide (WC; often called, simply, carbide when referring to machine tooling), and cementite (Fe3C), each used in key industrial applications. The naming of ionic carbides is not systematic.

Stainless steel steel alloy resistant to corrosion

In metallurgy, stainless steel, also known as inox steel or inox from French inoxydable (inoxidizable), is a steel alloy, with highest percentage contents of iron, chromium, and nickel, with a minimum of 10.5% chromium content by mass and a maximum of 1.2% carbon by mass.

Group 6 element group of chemical elements

Group 6, numbered by IUPAC style, is a group of elements in the periodic table. Its members are chromium (Cr), molybdenum (Mo), tungsten (W), and seaborgium (Sg). These are all transition metals and chromium, molybdenum and tungsten are refractory metals. The period 8 elements of group 6 are likely to be either unpenthexium (Uph) or unpentoctium (Upo). This may not be possible; drip instability may imply that the periodic table ends around unbihexium. Neither unpenthexium nor unpentoctium have been synthesized, and it is unlikely that this will happen in the near future.

Brazing metal-joining technique by high-temperature molten metal filling

Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the adjoining metal.

Chromite spinel, oxide mineral

Chromite is a mineral and can be described as an iron chromium oxide, with a chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite (MgCr2O4). A substitution of the element aluminium can also occur, leading to hercynite (FeAl2O4). Chromite today is mined particularly to make stainless steel through the production of ferrochrome (FeCr), which is an iron-chromium alloy.

Plating is a surface covering in which a metal is deposited on a conductive surface. Plating has been done for hundreds of years; it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solderability, to harden, to improve wearability, to reduce friction, to improve paint adhesion, to alter conductivity, to improve IR reflectivity, for radiation shielding, and for other purposes. Jewelry typically uses plating to give a silver or gold finish.

Heating element converts electricity into heat through the process of resistive or Joule heating (electric current passing through the element encounters resistance, resulting in heating of the element; this process is independent of the direction of current flow)

A heating element converts electrical energy into heat through the process of Joule heating. Electric current passing through the element encounters resistance, resulting in heating of the element. Unlike the Peltier effect, this process is independent of the direction of current flow.

Titanium carbide chemical compound

Titanium carbide, TiC, is an extremely hard refractory ceramic material, similar to tungsten carbide. It has the appearance of black powder with the sodium chloride crystal structure. As found in nature its crystals range in size from 0.1 to 0.3mm.

Inconel trademark of nickel based superalloys

Inconel is a family of austenitic nickel-chromium-based superalloys.

Titanium nitride chemical compound

Titanium nitride (TiN) is an extremely hard ceramic material, often used as a coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface properties.

Superalloy alloy that exhibits excellent mechanical strength and resistance to creep at high temperatures; good surface stability; and corrosion and oxidation resistance

A superalloy, or high-performance alloy, is an alloy that exhibits several key characteristics: excellent mechanical strength, resistance to thermal creep deformation, good surface stability, and resistance to corrosion or oxidation. The crystal structure is typically face-centered cubic austenitic. Examples of such alloys are Hastelloy, Inconel, Waspaloy, Rene alloys, Incoloy, MP98T, TMS alloys, and CMSX single crystal alloys.

Intergranular corrosion

Intergranular corrosion (IGC), also known as intergranular attack (IGA), is a form of corrosion where the boundaries of crystallites of the material are more susceptible to corrosion than their insides.

Electroless nickel plating (EN) is an auto-catalytic reaction that deposits an even layer of nickel-phosphorus or nickel-boron alloy on the surface of a solid material, or substrate, like metal or plastic. The process involves dipping the substrate in a bath of plating solution, where a reducing agent, like hydrated sodium hypophosphite (NaPO2H2 · H2O), reacts with the material's ions to deposit the nickel alloy. The metallurgical properties of the alloy depend on the percentage of phosphorus, which can range from 2–5% (low phosphorus) to 11–14% (high phosphorus). Unlike electroplating, it is not necessary to pass an electric current through the plating solution to form a deposit. Electroless plating prevents corrosion and wear, and can be used to manufacture composite coatings by suspending powder in the bath. EN plating creates an even layer regardless of the geometry of the surface – in contrast to electroplating which suffers from flux-density issues as an electromagnetic field will vary due to the surface profile and result in uneven depositions. Depending on the catalyst, EN plating can be applied to non-conductive surfaces.

Alloy steel steel that is alloyed with a variety of elements

Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low alloy steels and high alloy steels. The difference between the two is somewhat arbitrary: Smith and Hashemi define the difference at 4.0%, while Degarmo, et al., define it at 8.0%. Most commonly, the phrase "alloy steel" refers to low-alloy steels.

Cobalt-chrome

Cobalt-chrome or cobalt-chromium (CoCr) is a metal alloy of cobalt and chromium. Cobalt-chrome has a very high specific strength and is commonly used in gas turbines, dental implants, and orthopedic implants.

References

  1. ↑ Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, Florida: CRC Press, pp. 4–52, ISBN   0-8493-0594-2
  2. 1 2 3 "NIOSH Pocket Guide to Chemical Hazards #0141". National Institute for Occupational Safety and Health (NIOSH).
  3. ↑ Tongbaite: Tongbaite mineral information and data
  4. ↑ Generalov ME, Naumov VA, Mokhov AV, Trubkin NV, "Isovite (Cr,Fe)23C6 - a new mineral from the gold-platinum bearing placers of the Urals", Zapiski Vserossiyskogo mineralogicheskogo obshchestva, vol. 127, pp.26-37, 1998.
  5. ↑ Mindat, http://www.mindat.org/min-35899.html
  6. 1 2 3 Chattopadhyay, R. (2001). Surface Wear: Analysis, Treatment, and Prevention. Materials Park, OH: ASM International. pp. 228–229. ISBN   978-0-87170-702-4.
  7. 1 2 Cintho, Osvaldo; Favilla, Eliane; Capocchi, Jose (1 July 2007). "Mechanical–thermal synthesis of chromium carbides". Journal of Alloys and Compounds. 439 (1–2): 189–195. doi:10.1016/j.jallcom.2006.03.102.
  8. ↑ Ellis, Jonathan; Haw, Michael (November 1997). "Chromium Carbides". Materials World. 5 (11).

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