DE102004039512B4 - Carbonaceous body and method of treating such - Google Patents

Abstract

carbonaceous body in the form of a bipolar plate of a fuel cell or a tribological claimed component in the form of a carbon brush, a bearing, a slider, a pump wing or a gasket in which the carbon is in a surface layer of the body with a thickness D of 100 nm ≤ D ≤ 5 μm chemically is bound to fluorine.

Description

The The invention relates to a carbonaceous body, in Shape of a bipolar plate of a fuel cell or a tribological claimed component in the form of a carbon brush, a bearing, a slider, a pump wing or a seal. Also, the invention makes reference to a method for treating a carbonaceous body having fluorine in its surface becomes chemically bound.

From the DE 197 54 411 A1 For example, a carbonaceous material sliding contact is known wherein the carbonaceous or graphitic material used is mixed with a bromine-containing resin. This can be achieved in the finished sliding contact a reduction of sparking and a reduction in wear.

Also It is known that an oxidation protection for carbon brushes by liquid impregnation to achieve. In contrast does not protect against oxidation, it can swell at high temperatures the carbon brush respectively. To avoid this, it is intended to use carbon brushes Subtolerance, so that the brushed bristles the desired Have sizing.

Further you can the starting materials of a carbon brush alkali and Erdalkalifluoride add to achieve a solid lubrication.

A bipolar plate of a fuel cell after the WO 2003/047016 A2 has a hydrophobic layer in the region of its channels through which liquid flows.

From the DE 29 05 366 C2 is a cathode with a solid intercalation compound of carbon and fluorine known. The intercalation compound is present in a first hydrophilic surface. Furthermore, the cathode has a second hydrophobic surface. The surfaces are applied to a current carrier to form an air cathode.

To produce electrodes, after the DE 100 38 800 A1 several carbon or platinum containing layers produced in a plasma and internally supported vacuum process, wherein some layers may have a few layers thick hydrophobic fluorinated hydrocarbon surface by changing the plasma conditions and with simultaneous introduction of fluorine.

In the DE 693 17 261 T2 For example, a process for producing carbon fluoride particles or themselves are described. The fluoride particles consist of a carbon core and a high carbon fluoride-containing shell. Corresponding carbon fluoride particles may be used, for example, as electrodes or composites.

Of the DE 697 04 231 T2 is a surface modification of magnetic heads refer. In order to achieve a high affinity for used lubricants while avoiding impurities, the outermost atomic layer contains organic, fluorinated groups.

Of the The present invention is based on the object, a carbon-containing body and further develop a method for treating such that specifically physical or chemical properties are changed can, without that it is a change the composition of the materials that make up the carbonaceous body will be produced.

According to the invention Task solved by that in the carbonaceous body of the carbon in a surface layer of the body with a thickness D of 100 nm ≤ D ≤ 5 microns chemically Fluorine is bound.

According to the invention, a fluorination of the carbonaceous body takes place by chemical reaction between a solid and a gaseous reactant. Thus, chemical bonds (C _x F _y ) occur, wherein atomic hydrogen attached to C is replaced by atomic fluorine. In the case of bipolar plates, approximately 75% of atomic hydrogen is likely to be replaced by atomic fluorine.

at The bipolar plate is formed by chemical reaction between solid and gaseous Reactants chemical fluorine compounds. For this purpose, fluorine-nitrogen mixtures or fluorine-air mixtures act on the carbonaceous body, wherein accumulated atomic hydrogen replaced by atomic fluorine becomes. Through this surface activation Hydrophilic properties are achieved, so that in channels of a Bipolar plate available liquid drain well can.

With increasing fluorine content can also be a barrier fluorination, whereby an oxidation protection for metal-containing carbonaceous bodies such as carbon brushes achieved which causes the otherwise known swell at high operating temperatures is prevented.

At the same time, in the case of a carbon brush as a carbon-containing body, which may be metal-containing or metal-free, the advantage is that fluorine is partially released during operation in order to influence or reinforce a patina formation in the region of the mating surface of the carbon brush running surface. This results in an improved radio interference Behavior and a lower brush wear, without it being necessary that the carbon brush is impregnated by liquid or by adding components in the starting materials of the carbon brush is changed. The mating surface may be formed by a commutator or slip ring.

The fluorination according to the invention also gets for made of carbon graphite materials, electrographic materials, carbon fiber reinforced plastics or carbon fiber reinforced Carbon tribological components such as bearings, pump shifter or seals for use, resulting in improved coefficients of friction, a reduced wear in particular under dry running conditions and a lower frictional heat can be achieved. As tribological components come slider or wing of Pumps such as rotary vane pumps, bearings or sealing rings in question, to name just a few examples.

One Process for treating a carbonaceous body in Shape of a bipolar plate of a fuel cell or a tribological claimed component in the form of a carbon brush, a bearing, a slider, a pump wing or a seal, with a halogen, characterized by that the carbonaceous body a halogen-gas mixture is exposed, causing the carbon in a surface layer of the body with a thickness D of 100 nm ≤ D ≤ 5 microns chemically Fluorine is bound.

Especially it is possible, the carbonaceous body a halogen-gas mixture with a halogen content F with F ≤ 5 Vol .-% suspend, whereby a surface activation of the carbonaceous body he follows. This means that there is a functional thin film in the nano- to micro-range forms. In bipolar plates can thereby a hydrophilization take place.

Becomes the halogen content increases, and except for preferably a maximum of 25 vol .-%, the result is a Sealing of the body surface against z. B. Air and water and a passivation against z. For example, air. When used with carbon brushes as the carbonaceous body then results in particular the advantage that the patina formation between carbon brush and mating surface is influenced so that a better Kommutierungsverhalten as well as a temperature reduction. The radio interference behavior is improved (spark-extinguishing properties) and reduces brush wear.

One correspondingly higher Halogen content of preferably at most 25% by volume is for improvement the material properties, d. H. to improve the coefficients of friction, Reduction of wear and achieving low frictional heat also with tribological components of advantage, consisting of a Carbon graphite material, electrographite material, carbon fiber reinforced plastics or carbon fiber reinforced Carbon exist.

In particular, according to the invention for sliding contacts by acting in the carrier gas existing halogen, in particular fluorine, achieved a depot effect, due to the dependent from the use or the degree of utilization of the carbonaceous body fluorine released on the wear surface will be desired physical properties such as wear reduction, brush fire reduction to reach.

A corresponding depot effect is also with tribological components advantageous.

is the carbonaceous body a bipolar plate, a depot effect is not required.

at metal-containing carbon bodies In particular, when using fluorine as halogen, the swelling tendency reduced in the pressing direction.

at carbon brushes as carbonaceous bodies Furthermore, there is the advantage that the fluorination to a Oxidation protection emanating from the carbon brush or with this connected strand or fitting takes place. The fluorinated non-carbon ingredients of the carbon material such. B. Ashes cause lubricant properties.

In particular, it is provided that the carbon-containing body is exposed in a reactor to a pressure P _{1 of} 10,000 Pa (100 mbar) ≦ P ₁ ≦ 100 Pa (1 mbar) for a time t ₁ , which is then followed by the reactor with the halogen gas. Mixture flooded and then the halogen-gas mixture on the body over a time t ₂ acts.

In this case, the carbon-containing body can be exposed to the negative pressure over time t ₁ with t ₁ ≥ 10 min. The halogen-gas mixture acts on the carbon-containing body in particular over a period of time t ₂ with t ₂ ≦ 1.5 h. In order to improve the chemical bonding of the halogen, the carbonaceous body should be exposed to the halogen-gas mixture at a temperature T of 20 ° C ≦ T ≦ 80 ° C.

The Invention will be explained below with reference to exemplary embodiments.

example 1

A carbon brush of composition 63 % By weight of graphite and 37% by weight of copper with a porosity of 10% was placed in a reaction vessel. The reaction vessel was then pumped down to a pressure of 100 Pa. At this pressure, the carbon brush was held for about 10 minutes. Then, the reaction vessel was purged with nitrogen under normal pressure. Both processes were carried out at room temperature. Subsequently, a reaction gas mixture in the form of fluorine (F ₂ ) and nitrogen (N ₂ ) was fed to the reaction vessel, wherein the volume fraction of fluorine was 10% and that of nitrogen was 90%. The temperature was adjusted to about 35 ° C. The effect of the fluorine-air mixture on the carbon brush lasted up to 50 minutes. This was followed by another rinsing with nitrogen (N ₂ ). The carbon brush was then subjected to heating tests in a drying oven. It could be determined that a swelling tendency in the pressing direction was greatly reduced. Also, in running tests showed a reinforced patina formation between the carbon brush and the mating surface.

Example 2

A bipolar plate of resin-bonded graphite-filled polymer or graphite with a C content of more than 80% was arranged according to Example 1 in a reactor, which was then evacuated accordingly. After purging with nitrogen (N ₂ ), an F ₂ / N ₂ / O ₂ mixture was introduced as the reaction gas, the vol .-% fraction of F _{2 being} 5%, N _{2 being} 90% and O _{2 being} 5%. amounted to. The bipolar plate was the reaction gas over a period of max. Exposed for 30 minutes at a temperature of 35 ° C.

scanning electron micrographs the bipolar plate have then revealed that a functional thin formed in the micro range, in which the fluorine was chemically bound. Wetting of the bipolar plate with water showed hydrophilization, which was determined by contact angle measurement.

Example 3

A carbon brush in the form of a carbon-graphite material with a porosity of 15% by volume was fluorinated according to Example 1. Then the carbon brush in a 2000 W universal motor tested. It could lower the operating temperature of 15 ° C be measured. Also according to Example 1 was a resin-bonded Graphite material in the form of a carbon brush fluorinated, wherein the porosity was 10 vol .-%. A use with a universal motor with a capacity of 2000 W has resulted in an operating temperature reduction of 10 ° C.

Example 4

A slider of a rotary vane pump measuring 96 × 59 × 6 mm ³ consisting of a carbon-graphite material having a porosity of 10% by volume was placed in a reaction vessel. The reaction vessel was then pumped down to a pressure of 100 Pa. At this pressure, the slider was held for about 10 minutes. Then, the reaction vessel was purged with nitrogen under normal pressure. The prevailing temperatures were in the room temperature range. Subsequently, a reaction gas mixture in the form of fluorine (F ₂ ) and nitrogen (N ₂ ) was fed to the reaction vessel, wherein the volume fraction of fluorine was 10% and that of nitrogen was 90%. The temperature was adjusted to about 35 ° C. The action of the fluorine-air mixture on the slide took about 50 minutes. This was followed by another rinsing with nitrogen (N ₂ ). The corresponding slide was then inserted into a rotary vane pump and tested under dry running conditions. It was found that there is an improvement in the coefficient of friction, a reduced wear and a lower frictional heat compared to sliders that have not been fluorinated.

Example 5

Corresponding In example 3, slides made of electrographite material were fluorinated. There was also an improvement in friction, a reduction the frictional heat and wear.

Claims (14)

Carbon-containing body in the form of a bipolar plate a fuel cell or a tribologically stressed component in the form of a carbon brush, one Bearings, a slide, a pump sash or a gasket that the carbon in a surface layer of the body with a thickness D of 100 nm ≤ D ≤ 5 μm chemically is bound to fluorine. Carbonaceous body according to claim 1, characterized characterized in that the carbonaceous body having a porosity P with 5% by volume ≦ P ≦ 20% by volume. Method for treating a carbon-containing body in the form of a bipolar plate of a fuel cell or a tribologically stressed component in the form of a carbon brush, a bearing, a slider, a pump wing or a gasket, with a halogen, characterized in that the carbon-containing body is a halogen gas Mixture is suspended, causing the Carbon in a surface layer of the body with a thickness D of 100 nm ≤ D ≤ 5 microns is chemically bonded to fluorine. Method according to claim 3, characterized that the carbonaceous body exposed to a fluorine-nitrogen mixture. Method according to claim 3, characterized that the carbonaceous body exposed to a fluorine-air mixture. Method according to claim 3, characterized that the carbonaceous body in the form of a bipolar plate a fluorine gas mixture with a halogen content F with F ≤ 5 vol.% is suspended. Method according to claim 3, characterized that the carbonaceous body in the form of a tribologically stressed component in the form of a Carbon brush, a bearing, a slider, a pump sash or a gasket Exposed to fluorine gas mixture with a halogen content F with 5% <F ≤ 20% becomes. Method according to at least one of claims 3 to 7, characterized in that the carbonaceous body is exposed in a reactor to a pressure P over a time t ₁ , then that the reactor is flooded with a fluorine-gas mixture and the body the fluorine gas Is exposed for a time t ₂ , wherein the time t ₁ is t ₁ ≥ 10 min and / or the time t ₂ is t ₂ ≤ 1.5 h, wherein during the time t _2, the carbonaceous body at atmospheric pressure the fluorine Gas mixture is exposed. Method according to at least Claim 8, characterized that the carbonaceous body is exposed to the fluorine gas mixture at a temperature T with 30 ° C ≤ T ≤ 40 ° C. A method according to claim 3, characterized by the steps of introducing a carbon brush or a tribological component with a porosity between 5 and 25 vol .-% in a reaction vessel, pumping down the reaction vessel to a pressure P with 100 Pa ≤ P, holding the pressure P over a time t _{1 of} 5 min ≦ t ₁ ≦ 15 min, purging the reaction vessel with nitrogen at atmospheric pressure, introducing a reaction gas mixture containing about 10% by volume of F ₂ and about 90% by volume of N ₂ into the reaction vessel of the reaction gas mixture to the carbon brush over a time t ₂ with 40 min ≤ t ₂ ≤ 60 min, rinsing of the reaction vessel with N ₂ and removal of the carbon brush from the reaction vessel. Method according to at least claim 10, characterized that the reaction gas mixture on the carbon brush at a temperature T with 30 ° C ≤ T ≤ 40 ° C acts. Method according to claim 3, characterized that as a carbonaceous body used is one made of carbon-graphite material, Electrographite material, carbon fiber reinforced plastic (CFRP) or made of carbon fiber reinforced Carbon (CFC) exists. A method according to claim 3, characterized by the steps of introducing a bipolar plate containing resin bound graphite having a carbon content of more than 80% into a reaction vessel, pumping the reaction vessel down to a pressure P of 100 Pa ≤ P, maintaining the pressure P over a time t ₁ with 5 min ≦ t ₁ ≦ 15 min, purging the reaction vessel with nitrogen at atmospheric pressure, introducing one in about 5 vol.% F ₂ , about 90 vol.% N _2, and about 5 vol.% O ₂ containing reaction gas mixture to the carbon brush over a time t ₂ with 25 min ≤ t ₂ ≤ 35 min, rinsing of the reaction vessel with N ₂ and removal of the carbon brush from the reaction vessel. Method according to at least Claim 15, characterized that the reaction gas mixture on the carbon brush at a temperature T with 30 ° C ≤ T ≤ 40 ° C acts.