DE1667026A1 - Process for the pyrolytic deposition of carbon - Google Patents

Description

Process for the pyrolytic deposition of carbon

The invention relates to methods for the pyrolytic deposition of carbon or other substances from a Gias or steam,

The invention relates mainly to the production of coated particles, especially from nuclear fuel, Es it is known to apply a coating of pyrolytic carbon to nuclear fuel particles. That at high Temperature carbon from a carbon-containing gas these particles are deposited. In production processes for carrying out this process, it is known to use a fluidized bed device to use, in each of which a certain amount of nuclear fuel particles is treated. The application a tumble furnace has also been proposed.

A desirable feature of the pyrolytic coating is that it must be of high density in order for the coated

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Particles can be effective in operation, i.e., to allow them to diffuse out of the fuel during operation Delay or prevent the formation of fission products. To a To achieve high density in the layer within acceptable production times, the deposition temperature must be high.

In a high temperature process to carry out the pyrolytic Deposition of a substance from a gas that has been introduced into a device through an injection opening According to the invention, an oxidation reaction or another comparable, exothermic reaction is stimulated.

In one embodiment, the invention can include introducing an oxidizing component through the injection opening or Injection nozzle together with the process gas and the excitation Provide an exothermic zone adjacent to the opening or the nozzle, thereby reducing the risk of sooting or nozzle clogging is reduced and at the same time the fluidized bed temperature is increased.

Optionally, the oxidizing ingredient can be based on another Way, the main objective being to develop exothermic heat on a part of the device that is exposed to away from the injection port, i.e. closer to the actual substances involved in the process, and the reaction can be controlled in such a way that a required

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Part of the heat of reaction is supplied.

In addition, an oxidizing component can both through the injection port together with the reaction gases as well be introduced into the device via a different route.

When the reaction gases include a gas containing a component that is to be deposited pyrolytically on the process material in the high temperature fluidized bed apparatus or other device, it may be desirable _for both a Oxydierungskomponente into the apparatus together with the coating / Aufwirbelungsgas and a Inject the oxidizing component into the fluidized bed through a separate opening. The oxidizing constituent, for example carbon dioxide, oxygen, air or water vapor, is preferably introduced into the device together with the reaction gas or gases. A high concentration of the coating agent in the reaction gases can then be used and high amounts of precipitation result. The presence of the oxidizing component leads to a lower risk of sooting and enables very high coating temperatures without the nozzle being clogged.

Of course, the areas adjacent to the opening will depend on the nature of the oxidizing ingredient used, as required It is adapted in an appropriate manner, for example in some cases there is a special nozzle design around the opening required to prevent backburning, an "ubetance" is preferably used as the oxidizing component,

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which only increases at the high temperature reached at the opening such an oxidizing component.

In a special case, i.e. the pyrolytic deposition of carbon on particles in a fluidized bed, the Carbon-containing gas is added as an oxidizing component, preferably CO 2 or what is known as a coating gas. this has the additional advantage that it increases the partial pressure of the CO when particles containing oxides are coated and in this way suppresses the formation of carbides,

Example I.

A 200 g quantity of refractory carbide particles, each about 4-500 µm in diameter, was placed in a fluidized bed furnace. The amount was swirled in a gas mixture containing argon, methane and, as an oxidizing component, carbon dioxide in a volume ratio of 4: 5: 1, for 15 minutes. During this time the temperature of the oven was increased at 2150 ⁰ C and the partial pressure of methane was increased by adjustment of the gas streams, wherein the final Gaszusarnmensetzung was 95% methane and 5% carbon dioxide. The coating process began and carbon was deposited on the particles from the methane. The process was continued under these conditions for 1 3/4 hours; after this time the particles were 133 microns thick. The weight of the batch showed an increase of 196 g. The pyrolytically deposited carbon layer had a high density,

Example Ii 109827 / U81 _ ₅ _

227 g hit-resistant carbide particles, each with a nominal diameter of 500 ifr were placed in a fluidized bed furnace » The particles were at 2300 ° C in a gas mixture of argon, methane and - as an oxidizing component - of carbon dioxide in the Volume ratio of 4: 6: 1 whirled up «

After a reaction time of 120 minutes, the particles became removed. During the investigation it was found that the applied Carbon layer had a high density,

Example III

40 g of particles of a heat-resistant oxide material, each with a nominal diameter of 400 μ, were placed in a fluidized bed furnace, the temperature of which had already been increased to 1500 C. The amount was in a gas mixture, au ;; Argon, methane and carbon dioxide were whirled up in a volume ratio of 3: 6: 1. The temperature of the furnace was later increased ^{to 2100 ° C.} After increasing the temperature, the oven was allowed to run for 20 minutes; to test the effectiveness of the carbon dioxide oxidizing component, the supply of this component was then stopped. The nozzle was clogged with deposited carbon within two minutes,

Example IV

22 .g of a heat resistant oxide was introduced into a fluidized bed furnace at a temperature of 1500 ⁰ C, after the

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Coating with a first coating of pyrolytically deposited carbon at 1500 ⁰ C, the particles were in one: whirled> tröm eines'Argon-methane gas mixture wobei.das methane was passed through water before entering the furnace in the form of bubbles. The introduction of the gas saturated with water vapor as the oxidizing component was continued for 90 minutes at an oven temperature of 2100 ° C. and then interrupted.

After cooling, the particles were removed from the oven. One Examination of the particles showed that, first, a dense layer of pyrolytically deposited carbon was deposited had that, second, no noticeable conversion of the oxide to carbide had taken place, and that third, when examined the device did not detect any significant separation in the area of the injection opening,

Example V

A quantity of particles from (Th ₁ U) Op was placed in a similar manner in a fluidized bed furnace at 1500 ⁰ C and swirled in a stream of a gas mixture containing argon, methane and carbon dioxide in a volume ratio of 3: 4: 1 »

The temperature of the fluidized bed was increased to 185O ° C. After 15 minutes the flow rates were changed so that the volume ratio A: CH ₄ : CO _{2 became} 3: 4: 2. The increased proportion of CO ₂ , which is used to remove the _{soot formed from the CPI 4} , enables the layer to be observed,

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After an hour, the particles were removed from the oven * and examined, it was found to be a density Possessed carbon layer and was still in the oxide form.

Example VI

A quantity of 20 g of heat-resistant particles was placed in a fluidized bed vessel heated to 180 ° C. and in a Gas mixture of methane and oxygen in a volume ratio of 7: 1 whirled up for 20 minutes. The particles were then removed and the fluidized bed furnace nozzle examined. No damage was found on the nozzle. On the particle there was a dense layer of pyrolytically deposited carbon,

Although in the examples described above, the oxidizing component was introduced through the injection opening together with the process gas, this component can also be transferred to others Because of being introduced. The processes described above can also be used in conjunction with other coating processes as desired be applied.

Claims;

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Claims (2)

Claims 1 «Process for the pyrolytic deposition of a substance a gas phase at high temperature, which is passed through an injection port is introduced into a device in which the method takes place, characterized in that within the Device an exothermic reaction is stimulated ».. 2. The method according to claim 1, characterized in that the Reaction an oxidation reaction i ': t, 3, The method of claim 2, characterized in that an agent ^(T Jirkstoff) is introduced through the Öfriumj in the apparatus to the reaction: · ;; bo ~ chl i-unigen, A ₉ method according to; j :: - p "rüch 1, 2 ode, - ^; ,;: ■. '. Irch marked that as an oxide ieruii.:.· component ■" ■ · 1 · ■■!; - · I <"iw, wUor- ·. Tof", Li ^p 1: or './a ^ serdai.ip: j - "Ί 1': '. I:'"