DE1950066A1 - Coated item and process for its manufacture - Google Patents

Description

Patent attorneys Dfpl.lng.F.WcfctaEnn, 1950066

Oipl. Ing.F-LlVCiSkXiUR, üfl. Chain. ilHuber
8 Munich 27, USbUtr. 22

Case 2Ö616-7

GULP GENERAL ATOMIC INC.

aasai "a" s33b & * Maasaias "iai3at

San Diego / CALIFORNIA, USA Coated object and Bsaaaxiaaaaesasssaaasassaa Process for its manufacture

The invention relates to the coating of objects and in particular processes for coating objects with pyrolytic carbon, as well as those according to these processes manufactured products »

The coating of objects with pyrolytic carbon is a well-known coating process, ßr is generally carried out so that pyrolytic carbon on objects deposited by decomposition at high temperature (Pyrolysis) of carbonaceous substances, such as volatile or gaseous hydrocarbons, is formed · From the Various specific examples of achieving such a deposition are known in U.S. Patent 3,290,921. The types of crystalline formed are pyrolytic Carbon. A preferred overspray process in accordance with this patent is a fluidized bed process in which the hydrocarbon gas or a mixture

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of the hydrocarbon gas is used with a carrier gas to move a bed of objects to be coated in To keep levitation.

With coating in a fluidized bed and with other known ones possible processes for the deposition of pyrolytic carbon are used for the production of the decomposition of the carbon » hydrogen gas uses high temperatures »Such Decomposition temperatures vary between, for example öoo ° C and 23oo ° C. At such high temperatures the hydrocarbon gas and settles on the objects elemental carbon is deposited "

By suitable choice of temperature, the carbon-containing one Substance and other operational variables one obtains various different types of pyrolyctic carbon " As stated in the above patent? can have at least three different carbon structures be achieved, namely laminar carbon, isotropic carbon and granular carbon · The strengths of these Types of pyrolytic carbon vary. If you are at If the deposited pyrolytic carbon wants to achieve high strength properties, one uses stronger types of carbon, d. H. isotropic or laminar carbon.

The object of the present invention is to provide a method for depositing pyrolytic carbon, whereby a high structural strength is achieved. Another goal. Is to create solid objects that go with are coated with pyrolytic carbon

According to the invention, the conditions of the pyrolytic Carbon deposition carefully controlled to be pyrolytic To deposit or deposit carbon, which releases heat

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Has expansion coefficient which is less than the coefficient of thermal expansion of the object to be coated, so that the pyrolytic carbon, after the coated object has cooled to room temperature, is under a tangential compressive stress is caused, the structural strength of the coated object is increased and that the resulting resistance of the coated object is greater, the greater the amount of tangential compressive stress ± nt _t up to "an upper limit", as mentioned later _{f is} reached. Di · coals "materials on which the main interest is located, are isotropic carbon · _t are deposited at temperatures of about I5oo ° C or below" These carbons have up to a modulus of rupture in the range of 21 _{1 kg / mm (3o ooo psi)

49 _r 2 kg / now (70,000 psi) and are therefore well able to withstand these tangential pressure loads.

In particular, pyrolytic carbon has greater structural strength under compressive stress than under tension » tension. Taking advantage of this higher compressive strength, it is possible to use a coated object to produce high structural strength * The use of these relatively high temperatures necessary for achieving pyrolysis of the hydrocarbon gas and the subsequent deposition are required on the object to be coated, facilitate the achievement of this purpose due to the large, available temperature difference.

Because of the high temperatures _t in which the pyrolysis is carried out _t the materials "from which the article to be coated. Items can be made somewhat limited. Such a substance, which is sometimes used as a base material or substrate, should not suffer any significant loss of strength at the pyrolysis temperatures.

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. . BADORiGlNAL

and do not chemically react with the substances in the pyrolysis zone. Examples of suitable substrate materials include carbon, in particular graphite, tantalum, tungsten, molybdenum, alloys thereof and refractory materials in general, such as mullite. The coefficient of thermal expansion of possible substrate materials is usually known or, if not known, easily determined. Usually substrates are chosen with thermal expansion coefficients between etvra 6 and 9 χ Ιο ^"6/00 for the purposes of the present application.

The object to be coated is placed in the zone in which the pyrolysis is to be carried out, and in heated to a preselected temperature. This temperature, as will be explained later, is functional of the type dee carbon to be deposited, the desired coefficient of thermal expansion of the deposited carbon and on the size of the final tangential compressive stress that when the cold coated object is reached, depending on the temperature and the other coating conditions chosen accordingly to the particular crystalline type of carbon desired and one previously chosen Coefficient of thermal expansion of carbon, the lower is than the coefficient of thermal expansion of the substrate material a, to accomplish.

Oa one of the goals of the enrobing process is to provide a Manufacture of product with high structural strength should be the pyrolyctic carbon used complete this goal. In general, the density of the deposited pyrolytic carbon should be at least about 1.5 g / cm2, since porous carbons do not have as high a resistance to pressure as denser carbons. Oa good one. Structural strength a criterion for the resulting

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Product, the pyrolytic carbon coating should likewise be strong enough to provide such strength To produce "accordingly, the pyrolytic" carbon is at least about 23M thick and usually has a thickness of 100 microns or more. Although both laminar as well as isotropic carbons for the production of coatings · » objects with good structural strength are used » den can, isotropic carbon is preferred because it does not contain any Has a tendency to split and in the isotropic coatings on non-uniform outlines in places where small Radii of curvature occur, no stresses arise as a result of anisotropic expansion «In general, isotropic

Carbon, which has an apparent crystallite size, is preferred

ο of about 50 A or less and at temperatures between about 1200 C and 1500 C is deposited

The cooling of the coated object from the high deposition temperature leads to a shrinkage or contraction of both the substrate material and the coating. In order to achieve the desired tangential compressive stress, the preliminary bond between the carbon coating and the substrate must be sufficiently strong and the coefficient of thermal expansion of the pyrolytic carbon coating should not differ so much from the coefficient of heat exchange of the substrate that the bond breaks or tears is put under tension, which would make it more prone to tearing. The coefficient of thermal expansion of the pyrolytic carbon coating is selected to be less than that of the substrate material so that after the coated article has cooled, the substrate material contracts more than the coating and the coating are subjected to tangential compressive stress. The difference in the coefficients should be

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however, not so large that the compressive fracture of the coating is reached after cooling, resulting in a . Destruction of the coating, or that the Severing substrate from coating at the interface therebetween.

The size of the tangential compressive stress in the coating * material after cooling does not only depend on the difference in the coefficients of thermal expansion of the respective materials. but also from the temperature difference between the deposition temperature and the ambient temperature. The expected temperature difference is therefore taken into account when determining the desired coefficient of thermal expansion for the pyrolytic carbon to be deposited. Due to the various interrelated variables that have to be taken into account, no fixed numerical value can be given definitively. However, the coefficient of thermal expansion of the substrate is usually no more than about 50 % greater than that of the carbon coating.

If the coated article is used at temperatures different from the ambient temperature, then the temperature of the intended use will also be taken into account. Preferably, the coating should both ambient temperature and at the use temperature _t when al "under rope ·! Dan, are under pressure tangantialen" stress.

The modulus of rupture of pyrolytic carbon deposited at about 150 ° C or below is said to exceed 21.1 kg / mm () o, ooo psi). In the case of coatings made of pyrolytic carbon, tangential compressive loads between about 3 (52 kg / mm ² (5,000 psi) and 21.1 kg / mm Oo, ooo psi)

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achieved, the resulting Coated Articles have high structural strengths. Sine tangential pressure *, load with at least a height of l (t, i kg / mm (20,000 psi) can be achieved using a graphite substrate with which the pyrolytic carbon forms an excellent bond. An actual one The upper limit for the tangential compressive strength is not has been determined and is very likely at least hanging depends in part on the substrate material and how tightly a bond is achieved thereto. Generally occurs when this upper limit is exceeded if the carbon layer is relatively thick, a loosening of the bond, and If the carbon coating is thin, it will be destroyed the carbon layer through pressure "

According to the invention, objects with various geometric shapes can be coated. Usually is the largest Dimension of the coated articles at least equal to 12.7 mm (1/2 inch) as the strength of the article is one desired benefit is. For some special purposes, however, smaller items may be desired. Balls, bars and even pipes are examples of such items that can be made with good structural strength »

The following examples illustrate two procedures for the production of solid, with pyrolytic carbon coated objects. Both examples use the generally preferred methods of depositing isotropic Carbon at temperatures below about 15oo ° C. For the The purpose of further explanation is if a pyrolytic Deposition process used, not significantly more difficult, isotropic carbon at temperatures below about I5oo ° C to be deposited as laminar carbon or isotropic carbon deposited at a higher temperature *

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Since such low edri gteiap era tur ~ i sot rope carbons with a BAF of 1 ₍ 1 or less, apparent crystallites

ο ■ - ■

sizes of 5ο A or less and a density up to about

3
20 g / cm2 can be deposited, are accordingly usually used, since they have greater strength and greater wear resistance. However, isotropic carbon deposited at temperatures above about 150 ° C, for example from methane, propane, or the like, can be used for many purposes. Likewise, laminar carbon, which when separated from methane at temperatures below 150 ° C, can have an apparent crystallite size of about

β ■

50 A or less and a density greater than or equal to approximately 1.5 g / cm2, _B has to meet the requirements of many applications accordingly _e

EXAMPLE 1

One chooses a generally spherical object _e made of graphite and has a coefficient of thermal expansion of about 8 χ lo ° / C. The spheroid has a diameter of approximately l8 _e 7 mm (3/4 inch) _r is sandblasted something to any loose particles _t be removed and disposed in a perpendicular "right graphite reaction tube · The tube has a diameter of about 6 _S 3 cm and will be on a. Tempera door of about lAoo ° C heated while a current passing through the pipe, helium gas flow is maintained "If it can be started with the coating the spheroid and an additional charge of loo g Zirkondioxydteilchen _(t be to provide an additional, available deposition surface as in U.S. Patent 3,399,969), which have an average particle size of about fcoo Ji, are filled into the reaction tube. Propane gas is mixed with helium by a partial pressure of about 3 atm. (Total pressure 1 atm). The entire gas throughput is on

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held about 4,000 corvrain. Propane is subject to pyrolysis and deposits carbon. »On the» spheroid, carbon is deposited in the form of isotropic pyro.ly.tisehen carbon with a color expansion coefficient of about 5 to "/ C» Your later investigation also shows that the carbon is a BAP (Bacon Anisotropy Factor) of about J.1 _{t has} an apparent crystallite size of about ko A and a density of about 1.7 g / cm "*. The deposition continues until a coating of isotropic pyrolytic carbon of about 150 microns. (6/1000 inch) thickness is reached, the time being about an hour «

The resulting coated ball can affect the surrounding environment. cool temperature and is removed from the reaction tube. The change in temperature of nearly 400 ° C between the deposition temperature and the ambient temperature causes a contraction of the carbon spheroid as the substrate, which is sufficiently larger than that of the coating of isotropic carbon so that there is a compressive stress in the circumferential direction of about 10.5 kg / mm in the coating (I5000 psi) »This stress is well below the set breaking compressive stress of the coating "

The obtained coated article is structurally highly »strong · For example, a control article which is similarly coated with pyrolytic isotropic several carbon breaks? which has a greater coefficient of thermal expansion than the carbon substrate so that its perimeter will be in tension when dropped from a height of about Im (3 feet). The above-described coated article, the outer coating of which is under pressure, can repeatedly drop from the same height without being damaged. Other tests show that the coated sparoid has not only good breaking resistance, but also good wear resistance.

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-Io ~

EXAMPLE 2 . .

Jr

A graphite spheroid similar to that coated in Example 1 is placed in the same reaction tube heated to a temperature of about 135 ° C. while maintaining a flow of helium gas therethrough. When coating can commence, a similar additional charge of 100 g of ZrO2 particles is added to the reaction tube. Propane gas is mixed with the helium so that a gas throughput, which has a partial pressure of propane of about 0.4 atm (total pressure 1 atm), of about 8,000 cnrvmin is achieved. All the helium is forced through methyltrichlorosilane in bubbles. The propane and methyltrichlorosilane undergo pyrolysis, so that a mixture of isotropic carbon and silicon carbide is deposited on the spheroid. The deposition is continued for a period of about one hour until a coating of about 2oo ρ (8 / loo inch) is achieved.

The resulting coated ball is allowed to cool to ambient temperature and is removed from the reaction tube. The examination of the coating of isotropic carbon-silicon "earbid shows that it has a Wärmeausdehnungekoeffizienten of about 6 χ Io / ⁰ C and a density of about 2 g / CTAR has · D ^ e coating contains about Io weight percent of silicon in the form of silicon carbide · The isotropic carbon had a BAF of about 1.1 and an apparent crystallite size of about 35 A. The change in temperature causes the substrate to contract spheroidally which is sufficiently greater than that of the coating that a Compressive stress in the longitudinal direction of about 7 t © 3 kg / mm (Io ooo psi) arises «The ·· stress is well below the estimated breaking compressive stress of the coating ··

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The thus obtained coated article applies emerged as the "outstanding structural strength The coated spheroid can be repeated from about 1 m (3 ft) fall _t without a Be" injury occurs. Other attempts ensure that the coated spheroid has not only good resistance to fracture but also good wear resistance. Applies to the coating of isotropic carbon "silicon carbide _t that he has all the advantages from the standpoint of strength and wear resistance such as the completely produced from carbon coating of Example 1 ο In addition, it holds that when the other stall variables generally kept equal to, a coating from isotropic carbon which has been deposited with a Siliciunicarbidzusatz, _f has a greater strength than the same isotropic carbon without additive. General that up to about 15 weight 'percent silicon, or an equivalent amount Chett a ehnli * applies, carbide-forming additive can be included _f can without the desired properties of the coatings of pyrolytischein carbon, vie described above, be affected "

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Claims (1)

PATENT CLAIMS le Coated object with high strength, characterized by an object made of a material with a known coefficient of thermal expansion _t by a coating of pyrolytic carbon surrounding this object, which is deposited thereon at a temperature well above ambient temperature and has a firm bond to the object below wherein the pyrolytic carbon has a coefficient of thermal expansion which is smaller than that of the material of the object, and is under substantially tangential compressive stress as a result of the thermal contraction which occurs during the cooling of the coated object from the separating device temperature to the ambient temperature «/ 2. Coated article according to claim 1, characterized in that shows that the tangential compressive stress is little » 2
is at least about 3.52 kg / mm (500 psi). 3 · Coated article according to claim I _1, characterized in that "the coefficient of thermal expansion of the material is between about 6 and 9 χ ίο" / ° C · k . Coated article according to one of Claims 1, 2 and 3, characterized in that the thickness of the carbon layer is at least about 25 ρ. 5 * Coated article according to any one of claims 1, 2 and 3, characterized “that the material is carbon is. 00981 5 / HS3 ! 950066 . 6. Coated article according to any one of claims 1, 2 and 3 »characterized in that the pyrolytic carbon coating consists of isotropic carbon. 7ο Coated article according to one of Claims _{1 1} 2 and 3 «characterized in that the pyrolytic carbon is isotropic carbon with a density of at least about 1.5 g / cm and an apparent Kriatallite size of about 50 Å or less. 8 "The coated article of any one of claims l _e 2 and 3, characterized in that the pyrolytic carbon is an isotropic Kohlenetoff with a BAP of about 1.1 or less. 9. Coated article according to any one of claims 1, 2 and 3 "characterized in that the pyrolytic carbon is laminar and has a density of at least about 1.5 g / cm and an apparent crystallite size of about 50 Å or has less Ioο coated object according to one of claims 1, 2 and 3 « characterized in that the carbon coating is a contains additive carbide dispersed therein. 11 »Coated article according to one of Claims 1, 2 and 3, characterized in that the carbon coating is a contains silicon carbide dispersed therein * 12. A method of coating an object made of a material with a known coefficient of thermal expansion with pyrolytic carbon to produce a coated object one of the preceding claims, which has high strength properties, characterized in that the 009815/145 3 - 1 * 1 - the object to be overlooked is heated to a preselected separation temperature such that the pyrolytic carbon is deposited on the object from a carbonaceous atmosphere at the preselected temperature under conditions which lead to the formation of carbon which has a preselected coefficient of thermal expansion, which is less than that of the material of the object, and that the coated object is cooled to ambient temperature, the difference between the coefficient of thermal expansion of the material of the object and the deposited pyrolytic carbon such and the bond therebetween being sufficiently strong that upon cooling from the Deposition temperature to ambient temperature, the pyrolytic carbon coating is placed under substantial tangential reverse stress. 13 · Method according to claim 12, characterized in that the A lies the ash temperature between about 1500 ° C and 12oo ° C Ik » method according to claim 12, characterized in that the coefficient of thermal expansion of the material is between approximately 6 to 9 * lo" ^ / ° C. 15 «Method according to one of claims 12 to 14, characterized marked that the. tangential compression is at least about 3 "52 kg / mm (Jjooo psi)" l6. Method according to one of Claims 12 to 15 «thereby characterized in that the thickness of the carbon layer is at least about 25 ρ » 00981 S / 1453 17 · Method according to one of Claims 12 to 16 »thereby characterized ^ that the carbon-containing atmosphere contains a hydrocarbon, an inert gas and a volatile compound, which in turn contains a carbide-forming element. 18 "Method according to one of claims 12 to 17" thereby characterized in that the object is made of carbon. 19. The method according to any one of claims 12 to l8, characterized characterized that the deposited pyrolytisch® carbon is isotropic carbon with a density of little- at least about 1.5 g / cm ^ and an apparent xristailite O size is about 5o A or less. 2oc method according to any one of claims 12 to l8, characterized in that _t the pyrolytic carbon, a laminar carbon having a density of at least about 1; 5 g / cm and an apparent ^J Krietallitgröße von.etwa 5o A or less · 0Q9815 / U53