Tungsten carbide

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Tungsten carbide
A-WC-polyhedral.png
Names
IUPAC name
Tungsten carbide
Other names
Tungsten(IV) carbide
Tungsten tetracarbide
Identifiers
3D model (JSmol)
ECHA InfoCard 100.031.918
EC Number 235-123-0
PubChem CID
Properties
WC
Molar mass 195.85 g·mol−1
AppearanceGrey-black lustrous solid
Density 15.63 g/cm3 [1]
Melting point 2,785–2,830 °C (5,045–5,126 °F; 3,058–3,103 K) [2] [3]
Boiling point 6,000 °C (10,830 °F; 6,270 K)
at 760 mmHg [3]
Insoluble
Solubility Soluble in HNO
3
, HF [2]
1·10−5 cm3/mol [2]
Thermal conductivity 110 W/(m·K) [4]
Structure
Hexagonal, hP2 [5]
P6m2, No. 187 [5]
6m2 [5]
a = 2.906 Å, c = 2.837 Å [5]
α = 90°, β = 90°, γ = 120°
Trigonal prismatic (center at C) [6]
Thermochemistry
39.8 J/(mol·K) [4]
32.1 J/mol·K
Related compounds
Other anions
Tungsten boride
Tungsten nitride
Other cations
Molybdenum carbide
Titanium carbide
Silicon carbide
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

Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through a process called sintering for use in industrial machinery, cutting tools, abrasives, armor-piercing rounds, other tools and instruments, and jewelry.

A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than are chemical names and structural formulas.

Chemical compound Substance composed of multiple elements

A chemical compound is a chemical substance composed of many identical molecules composed of atoms from more than one element held together by chemical bonds. A chemical element bonded to an identical chemical element is not a chemical compound since only one element, not two different elements, is involved.

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.

Contents

Tungsten carbide is approximately twice as stiff as steel, with a Young's modulus of approximately 530–700 GPa (77,000 to 102,000 ksi), [4] [7] [8] [9] and is double the density of steel—nearly midway between that of lead and gold. It is comparable with corundum (α- Al
2
O
3
) in hardness and can only be polished and finished with abrasives of superior hardness such as cubic boron nitride and diamond powder, wheels, and compounds.

Steel alloy made by combining iron and other elements

Steel is an alloy of iron and carbon, and sometimes other elements. Because of its high tensile strength and low cost, it is a major component used in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons.

Young's modulus or Young modulus is a mechanical property that measures the stiffness of a solid material. It defines the relationship between stress and strain in a material in the linear elasticity regime of a uniaxial deformation.

Lead Chemical element with atomic number 82

Lead is a chemical element with symbol Pb and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, lead is silvery with a hint of blue; it tarnishes to a dull gray color when exposed to air. Lead has the highest atomic number of any stable element and three of its isotopes each include a major decay chain of heavier elements.

Naming

Historically referred to as Wolfram, Wolf Rahm, wolframite ore discovered by Peter Woulfe was then later carburized and cemented with a binder creating a composite now called "cemented tungsten carbide". [10] Tungsten is Swedish for "heavy stone".

Wolframite intermediate mineral variety between hübnerite and ferberite

Wolframite, (Fe,Mn)WO4, is an iron manganese tungstate mineral that is the intermediate between ferberite (Fe2+ rich) and hübnerite (Mn2+ rich). Along with scheelite, the wolframite series are the most important tungsten ore minerals. Wolframite is found in quartz veins and pegmatites associated with granitic intrusives. Associated minerals include cassiterite, scheelite, bismuth, quartz, pyrite, galena, sphalerite, and arsenopyrite.

Colloquially among workers in various industries (such as machining and carpentry), tungsten carbide is often simply called carbide, despite the imprecision of the usage. Among the lay public, the growing popularity of tungsten carbide rings has also led to consumers calling the material tungsten.

Machining process in which a piece of raw material is cut into a desired final shape and size by a controlled material-removal process; manufacturing process

Machining is any of various processes in which a piece of raw material is cut into a desired final shape and size by a controlled material-removal process. The processes that have this common theme, controlled material removal, are today collectively known as subtractive manufacturing, in distinction from processes of controlled material addition, which are known as additive manufacturing. Exactly what the "controlled" part of the definition implies can vary, but it almost always implies the use of machine tools.

Carpentry skilled trade

Carpentry is a skilled trade and a craft in which the primary work for performed is the cutting, shaping and installation of building materials during the construction of buildings, ships, timber bridges, concrete formwork, etc. Carpenters traditionally worked with natural wood and did the rougher work such as framing, but today many other materials are also used and sometimes the finer trades of cabinetmaking and furniture building are considered carpentry. In the United States, 98.5% of carpenters are male, and it was the fourth most male-dominated occupation in the country in 1999. In 2006 in the United States, there were about 1.5 million carpentry positions. Carpenters are usually the first tradesmen on a job and the last to leave. Carpenters normally framed post-and-beam buildings until the end of the 19th century; now this old fashioned carpentry is called timber framing. Carpenters learn this trade by being employed through an apprenticeship training—normally 4 years—and qualify by successfully completing that country's competence test in places such as the United Kingdom, the United States, Australia and South Africa. It is also common that the skill can be learned by gaining work experience other than a formal training program, which may be the case in many places.

Synthesis

Tungsten carbide is prepared by reaction of tungsten metal and carbon at 1400–2000 °C. [11] Other methods include a patented lower temperature fluid bed process that reacts either tungsten metal or blue WO
3
with CO/CO2 mixture and H
2
between 900 and 1200 °C. [12]

Tungsten Chemical element with atomic number 74

Tungsten, or wolfram, is a chemical element with symbol W and atomic number 74. The name tungsten comes from the former Swedish name for the tungstate mineral scheelite, tung sten or "heavy stone". Tungsten is a rare metal found naturally on Earth almost exclusively combined with other elements in chemical compounds rather than alone. It was identified as a new element in 1781 and first isolated as a metal in 1783. Its important ores include wolframite and scheelite.

WC can also be produced by heating WO
3
with graphite: directly at 900 °C or in hydrogen at 670 °C following by carburization in argon at 1000 °C. [13] Chemical vapor deposition methods that have been investigated include: [11]

Chemical vapor deposition chemical process used in the semiconductor industry to produce thin films

Chemical vapor deposition (CVD) is a deposition method used to produce high quality, high-performance, solid materials, typically under vacuum. The process is often used in the semiconductor industry to produce thin films.

WCl
6
+ H
2
+ CH
4
→ WC + 6HCl
WF
6
+ 2H
2
+ CH
3
OH
→ WC + 6HF + H
2
O

Chemical properties

There are two well-characterized compounds of tungsten and carbon, WC and tungsten semicarbide, W
2
C
. Both compounds may be present in coatings and the proportions can depend on the coating method. [14]

At high temperatures WC decomposes to tungsten and carbon and this can occur during high-temperature thermal spray, e.g., in high velocity oxygen fuel (HVOF) and high energy plasma (HEP) methods. [15]

Oxidation of WC starts at 500–600 °C (932–1,112 °F). [11] It is resistant to acids and is only attacked by hydrofluoric acid/nitric acid (HF/HNO
3
) mixtures above room temperature. [11] It reacts with fluorine gas at room temperature and chlorine above 400 °C (752 °F) and is unreactive to dry H
2
up to its melting point. [11] Finely powdered WC oxidizes readily in hydrogen peroxide aqueous solutions. [16] At high temperatures and pressures it reacts with aqueous sodium carbonate forming sodium tungstate, a procedure used for recovery of scrap cemented carbide.

Physical properties

Tungsten carbide has a high melting point at 2,870 °C (5,200 °F), a boiling point of 6,000 °C (10,830 °F) when under a pressure equivalent to 1 standard atmosphere (100 kPa), [3] a thermal conductivity of 110 W·m−1·K−1, [4] and a coefficient of thermal expansion of 5.5 µm·m−1·K−1. [7]

Tungsten carbide is extremely hard, ranking about 9 on Mohs scale, and with a Vickers number of around 2600. [8] It has a Young's modulus of approximately 530–700 GPa, [4] [7] [8] [9] a bulk modulus of 630–655 GPa, and a shear modulus of 274 GPa. [17] It has an ultimate tensile strength of 344 MPa, [9] an ultimate compression strength of about 2.7 GPa and a Poisson's ratio of 0.31. [17]

The speed of a longitudinal wave (the speed of sound) through a thin rod of tungsten carbide is 6220 m/s. [18]

Tungsten carbide's low electrical resistivity of about 0.2 µΩ·m is comparable with that of some metals (e.g. vanadium 0.2 µΩ·m). [11] [19]

WC is readily wetted by both molten nickel and cobalt. [20] Investigation of the phase diagram of the W-C-Co system shows that WC and Co form a pseudo binary eutectic. The phase diagram also shows that there are so-called η-carbides with composition (W,Co)
6
C
that can be formed and the brittleness of these phases makes control of the carbon content in WC-Co cemented carbides important. [20]

Structure

a-WC structure, carbon atoms are gray. Alpha tungsten carbide crystal structure.png
α-WC structure, carbon atoms are gray.

There are two forms of WC, a hexagonal form, α-WC (hP2, space group P6m2, No. 187), [5] [6] and a cubic high-temperature form, β-WC, which has the rock salt structure. [21] The hexagonal form can be visualized as made up of a simple hexagonal lattice of metal atoms of layers lying directly over one another (i.e. not close packed), with carbon atoms filling half the interstices giving both tungsten and carbon a regular trigonal prismatic, 6 coordination. [6] From the unit cell dimensions [22] the following bond lengths can be determined: the distance between the tungsten atoms in a hexagonally packed layer is 291 pm, the shortest distance between tungsten atoms in adjoining layers is 284 pm, and the tungsten carbon bond length is 220 pm. The tungsten-carbon bond length is therefore comparable to the single bond in W(CH
3
)
6
(218 pm) in which there is strongly distorted trigonal prismatic coordination of tungsten. [23]

Molecular WC has been investigated and this gas phase species has a bond length of 171 pm for 184
W
12
C
. [24]

Applications

Cutting tools for machining

Cemented carbide drill and end mills Tungsten carbide.jpg
Cemented carbide drill and end mills

Sintered tungsten carbide - cobalt cutting tools are very abrasion resistant and can also withstand higher temperatures than standard high-speed steel (HSS) tools. Carbide cutting surfaces are often used for machining through materials such as carbon steel or stainless steel, and in applications where steel tools would wear quickly, such as high-quantity and high-precision production. Because carbide tools maintain a sharp cutting edge better than steel tools, they generally produce a better finish on parts, and their temperature resistance allows faster machining. The material is usually called cemented carbide, solid carbide, hardmetal or tungsten-carbide cobalt. It is a metal matrix composite, where tungsten carbide particles are the aggregate, and metallic cobalt serves as the matrix. [25] [26]

Ammunition

Tungsten carbide is often used in armor-piercing ammunition, especially where depleted uranium is not available or is politically unacceptable. However, it is also common to use powder metallurgic tungsten alloys (in which metallic tungsten powder has been cemented with a metallic binder). W
2
C
projectiles were first used by German Luftwaffe tank-hunter squadrons in World War II. Owing to the limited German reserves of tungsten, W
2
C
material was reserved for making machine tools and small numbers of projectiles. It is an effective penetrator due to its combination of great hardness and very high density. [27] [28]

Tungsten carbide in its monolithic sintered form, or much more often in tungsten carbide cobalt composite (in which fine ceramic tungsten carbide particles are embedded in metallic cobalt binder forming a metal matrix composite or MMC) can be of the sabot type. SLAP, or saboted light armour penetrator where a plastic sabot discards at the barrel muzzle is one of the primary types of saboted small arms ammunition. Non-discarding jackets, regardless of the jacket material, are not perceived as sabots but bullets. Both of the designs are, however, common in designated light armor-piercing small arms ammunition.

Discarding sabots like used with M1A1 Abrams main gun are more commonplace in precision high-velocity gun amunition. [29] [30]

Mining

A Tricone roller cone assembly from a raiseboring reamer, showing the protruding tungsten carbide buttons inset into the rollers Drill bit 2-italy.JPG
A Tricone roller cone assembly from a raiseboring reamer, showing the protruding tungsten carbide buttons inset into the rollers

Tungsten carbide is used extensively in mining in top hammer rock drill bits, downhole hammers, roller-cutters, long wall plough chisels, long wall shearer picks, raiseboring reamers, and tunnel boring machines. It is generally utilised as a button insert, mounted in a surrounding matrix of steel that forms the substance of the bit. As the tungsten carbide button is worn away the softer steel matrix containing it is also worn away, exposing yet more button insert.

Nuclear

Tungsten carbide is also an effective neutron reflector and as such was used during early investigations into nuclear chain reactions, particularly for weapons. A criticality accident occurred at Los Alamos National Laboratory on 21 August 1945 when Harry Daghlian accidentally dropped a tungsten carbide brick onto a plutonium sphere, known as the demon core, causing the subcritical mass to go supercritical with the reflected neutrons.

Sports usage

A Nokian bicycle tire with tungsten carbide spikes. The spikes are surrounded by aluminum. Nokian Gazza Extreme 294 29er.jpg
A Nokian bicycle tire with tungsten carbide spikes. The spikes are surrounded by aluminum.

Trekking poles, used by many hikers for balance and to reduce pressure on leg joints, generally use carbide tips in order to gain traction when placed on hard surfaces (like rock); carbide tips last much longer than other types of tip. [31]

While ski pole tips are generally not made of carbide, since they do not need to be especially hard even to break through layers of ice, rollerski tips usually are. Roller skiing emulates cross country skiing and is used by many skiers to train during warm weather months.

Sharpened carbide tipped spikes (known as studs) can be inserted into the drive tracks of snowmobiles. These studs enhance traction on icy surfaces. Longer v-shaped segments fit into grooved rods called wear rods under each snowmobile ski. The relatively sharp carbide edges enhance steering on harder icy surfaces. The carbide tips and segments reduce wear encountered when the snowmobile must cross roads and other abrasive surfaces. [32]

Car, motorcycle and bicycle tires with tungsten carbide studs provide better traction on ice. The tungsten carbide insert protruding from inside of a zinc or aluminium seating is commonly called a "soul" in the tire manufacturing business. These are generally preferred to steel studs because of their superior resistance to wear. [33]

Tungsten carbide may be used in farriery, the shoeing of horses, to improve traction on slippery surfaces such as roads or ice. Carbide-tipped hoof nails may be used to attach the shoes; [34] in the United States, borium – chips of tungsten carbide in a matrix of softer metal such as bronze or mild steel – may be welded to small areas of the underside of the shoe before fitting. [35] :73

Surgical instruments

Tungsten carbide is also used for making surgical instruments meant for open surgery (scissors, forceps, hemostats, blade-handles, etc.) and laparoscopic surgery (graspers, scissors/cutter, needle holder, cautery, etc.). They are much costlier than their stainless-steel counterparts and require delicate handling, but give better performance. [36]

Jewelry

Tungsten carbide ring Tungsten Carbide.jpg
Tungsten carbide ring

Tungsten carbide, typically in the form of a cemented carbide (carbide particles brazed together by metal), has become a popular material in the bridal jewelry industry due to its extreme hardness and high resistance to scratching. [37] [38] Even with high-impact resistance, this extreme hardness also means that it can occasionally be shattered under certain circumstances. [39] Some consider this useful, since an impact would shatter a tungsten ring, quickly removing it, where precious metals would bend flat and require cutting. Tungsten carbide is roughly 10 times harder than 18k gold. In addition to its design and high polish, part of its attraction to consumers is its technical nature. [37] Special tools, such as locking pliers, may be required if such a ring must be removed quickly (e.g. due to medical emergency following a hand injury accompanied by swelling). [40]

Other

Tungsten carbide is widely used to make the rotating ball in the tips of ballpoint pens that disperse ink during writing. [41]

Tungsten carbide is a common material used in the manufacture of gauge blocks, used as a system for producing precision lengths in dimensional metrology. [ citation needed ]

English guitarist Martin Simpson is known to use a custom-made tungsten carbide guitar slide. [42] The hardness, weight, and density of the slide give it superior sustain and volume compared to standard glass, steel, ceramic, or brass slides.

Tungsten carbide has been investigated for its potential use as a catalyst and it has been found to resemble platinum in its catalysis of the production of water from hydrogen and oxygen at room temperature, the reduction of tungsten trioxide by hydrogen in the presence of water, and the isomerisation of 2,2-dimethylpropane to 2-methylbutane. [43] It has been proposed as a replacement for the iridium catalyst in hydrazine-powered satellite thrusters. [44]

A tungsten carbide coating has been utilized on brake discs in high performance automotive applications to improve performance, increase service intervals and reduce brake dust. [45]

Toxicity

The primary health risks associated with tungsten carbide relate to inhalation of dust, leading to fibrosis. [46] Cobalt-cemented tungsten carbide is also anticipated to be a human carcinogen by the American National Toxicology Program. [47]

Related Research Articles

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.

Cementite iron and carbon compound

Cementite (or iron carbide) is a compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe3C. By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. It is a hard, brittle material, normally classified as a ceramic in its pure form, and is a frequently found and important constituent in ferrous metallurgy. While cementite is present in most steels and cast irons, it is produced as a raw material in the iron carbide process, which belongs to the family of alternative ironmaking technologies. The name cementite originated from the research of Floris Osmond and J. Werth, where the structure of solidified steel consists of a kind of cellular tissue in theory, with ferrite as the nucleus and Fe3C the envelope of the cells. The carbide therefore cemented the iron.

Carbon steel steel in which the main interstitial alloying constituent is carbon

Carbon steel is a steel with carbon content up to 2.1% by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:

Tool steel

Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion and deformation, and their ability to hold a cutting edge at elevated temperatures. As a result, tool steels are suited for use in the shaping of other materials.

High-speed steel subset of tool steels

High-speed steel is a subset of tool steels, commonly used as cutting tool material.

Spark testing is a method of determining the general classification of ferrous materials. It normally entails taking a piece of metal, usually scrap, and applying it to a grinding wheel in order to observe the sparks emitted. These sparks can be compared to a chart or to sparks from a known test sample to determine the classification. Spark testing also can be used to sort ferrous materials, establishing the difference from one another by noting whether the spark is the same or different.

Tantalum carbide chemical compound

Tantalum carbides form a family of binary chemical compounds of tantalum and carbon with the empirical formula TaCx, where x usually varies between 0.4 and 1. They are extremely hard, brittle, refractory ceramic materials with metallic electrical conductivity. They appear as brown-gray powders, which are usually processed by sintering. Being important cermet materials, tantalum carbides are commercially used in tool bits for cutting applications and are sometimes added to tungsten carbide alloys. The melting points of tantalum carbides peak at about 3880 °C depending on the purity and measurement conditions; this value is among the highest for binary compounds. Only tantalum hafnium carbide may have a slightly higher melting point of about 3942 °C, whereas the melting point of hafnium carbide is comparable to that of TaC.

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.

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 some of those properties.

Chromium carbide chemical compound

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.

Zirconium carbide chemical compound

Zirconium carbide (ZrC) is an extremely hard refractory ceramic material, commercially used in tool bits for cutting tools. It is usually processed by sintering.

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.

Boriding, also called boronizing, is the process by which boron is introduced to a metal or alloy. It is a type of surface hardening. In this process boron atoms are diffused into the surface of a metal component. The resulting surface contains metal borides, such as iron borides, nickel borides, and cobalt borides, As pure materials, these borides have extremely high hardness and wear resistance. Their favorable properties are manifested even when they are a small fraction of the bulk solid. Boronized metal parts are extremely wear resistant and will often last two to five times longer than components treated with conventional heat treatments such as hardening, carburizing, nitriding, nitrocarburizing or induction hardening. Most borided steel surfaces will have iron boride layer hardnesses ranging from 1200-1600 HV. Nickel-based superalloys such as Inconel and Hastalloys will typically have nickel boride layer hardnesses of 1700-2300 HV.

Cold saw

A cold saw is a circular saw designed to cut metal which uses a toothed blade to transfer the heat generated by cutting to the chips created by the saw blade, allowing both the blade and material being cut to remain cool. This is in contrast to an abrasive saw, which abrades the metal and generates a great deal of heat absorbed by the material being cut and saw blade.

Cemented carbide

Cemented carbide is a hard material used extensively as cutting tool material, as well as other industrial applications. It consists of fine particles of carbide cemented into a composite by a binder metal. Cemented carbides commonly use tungsten carbide (WC), titanium carbide (TiC), or tantalum carbide (TaC) as the aggregate. Mentions of "carbide" or "tungsten carbide" in industrial contexts usually refer to these cemented composites.

Cemented carbide as a tool material has been increasingly used for cutting tools, wear-resistant tools, impact-resistant tools, and other products with special purpose. Cemented carbide was first used in stretching mold area and has gone through cast iron mold, alloy steel mold, diamond dies, cemented carbide dies, polycrystalline module die and other developmental stages. With the property of high wear resistance, good polishing performance, low friction coefficient, etc., cemented carbide drawing die has been a substitute of steel mold which is used to stretching steel and non-ferrous metal.

Cutting tool materials are materials that are used to make cutting tools that are used in machining but not other cutting tools like knives or punches.

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