The method of deposition of pyrocarbon and device for its implementation

C23C16/26 - Deposition of carbon only

The invention relates to obtain a graphite material and can be used in chemical engineering, nuclear and electronic industries. The technical result consists in increasing the productivity of the deposition of pyrocarbon. Submit to the zone of deposition of the mixture of hydrocarbon and inert gas and vary the concentration of hydrocarbon in time. The flow rate of the hydrocarbon in time increase parabolically with the constant flow of inert gas according to the equation: G =₀+A

²where G₀- the initial flow of hydrocarbon, g/s; And a is a constant, g/s³determined from the preliminary experiment at G=G₀;

- time process, with. the Device contains a critical section for the feed hydrocarbon and the gear to regulate the pressure to the critical section. In the reduction gear drive mechanism is composed of a Cam with a parabolic profile and a screw pair. Auger screw pair is connected to the Cam through the Cam. Nut screw pair is connected to the arm of the gearbox through the grip. The Cam and the screw is made to move in mutually perpendicular of napravlennom and can be used in chemical technology, atomic and electronic engineering.

Graphite materials have high heat resistance and thermoresistance, and are reliable protective barriers for the diffusion of fission fragments in the fuel elements (cartridges) of nuclear reactors.

The highest density of the graphite material has a pyrocarbon obtained by the pyrolysis of hydrocarbons (acetylene, methane, ethane, butane, and others ) at a temperature of 1000-1100^o(See Amer. Ceram. Soc. Bull., 1974, v. 54, p. 270).

The main disadvantage of the method of deposition of carbon from the gas phase is the low deposition rate. This disadvantage becomes relevant when obtaining microtalon representing fuel cores with a diameter of 0.2-0.5 mm with shells of loose and dense pyrocarbon. A loose layer thickness of 80-100 μm is pressure compensator gaseous fission products, and a dense layer performs protective functions (see Chernikov A. S., fedyk, I. I., Kurbakov S. D. and other Fe-based spherical fuel particles with protective coatings for reactors with advanced security-Nuclear energy, 1999, I. 87, vol. 6, S. 451-460).

The disadvantage of this method is the dispersion characteristics of the coating due to the abrupt change in the size of custcene pyrocarbon coatings, including feed in a fluidized layer of a mixture of acetylene-propylene-argon with varying concentrations of acetylene and propylene in the total hydrocarbon concentration 39-80% vol. (see U.S. Pat. USA 4194027 from 18.03.80 year, NCI 427-249). The disadvantage of this method lies in the poor performance of the coating process.

The present of the invention is to improve the performance of the application process pyrocarbon coatings.

According to the invention the task is solved in that in the zone of deposition in a fluidized bed serves a mixture of hydrocarbon and inert gas and vary the concentration of hydrocarbon in time, the consumption of hydrocarbon increases parabolically according to the relation: G = G₀+A

²where G₀- the initial flow of hydrocarbon, g/s, And constant, g/s³determined from the preliminary experiment at G=G_o,

- time process, with.

The closest in technical essence to the tasks for the implementation of the proposed method is a device for dispensing gas flows (see and. C. 679951 from 15.08.79, Ál. G 05 D 7/01), including the critical section, providing a constant selected flow rate regardless of the device lies in the difficulty of adjusting the pressure before the critical section according to the parabolic law, so how does the pressure change step by step.

In the proposed device for implementing the method on the task of improving the performance of the coating process.

According to the invention the task is solved in that the dosing device of the hydrocarbon stream consists of critical section for gas supply and gear for regulating the pressure to the critical section, the pressure adjustment provides a drive mechanism consisting of a Cam with a parabolic profile, screw, and the screw coil pair is connected to the Cam through the Cam nut screw pair is connected to the crank gear through engagement, and Cam and the screw is made to move in mutually perpendicular directions.

The proposed method differs from the known parabolic feed hydrocarbons in a fluidized bed.

The proposed device is different from the known presence of the drive mechanism, allowing the parabolic flow of hydrocarbon on the proposed method.

The authors of the invention on the basis of the researches found that when applying the first layer of pyrocarbon on a spherical particle ratak as the process speed is proportional to the surface area of the particles, at the first stage of the coating process is the utilization of pyrocarbon small, and at the last stage of the hydrocarbon is not enough. In excess of the hydrocarbon coating thickness is proportional to the time process, i.e., the surface area of the particles is proportional to the square of time. It is experimentally shown that the dispersion characteristics of the coating decreases with the hydrocarbon feed in the fluidized bed according to the parabolic law in accordance with the increase in surface area of the particles.

In addition, with the growth of the particle size change characteristics boiling particles that are described by the criterion of Archimedes:

where g = 9.8 m²with the acceleration of free fall,

_t,

_grespectively the density of the particles and gas, g/cm³d - size solid particles, see,

- kinematic viscosity, cm²/s
(see Garbis H. R. Heat transfer and dynamics of dispersed flow, Meters, Energy, 1978, S. 7). From the expression it follows that the velocity of the gas flow, which is directly linked with Hypertension, should increase even parabolic, and cubic law in time (Ah

d³for obespecheniya density of 1.0-1.8 g/cm³the density of the particles over time, the process falls (Ar

_td³and the result is to maintain a stable fluidized bed to increase the flow of hydrocarbons to the extent of 2.0, while the total flow rate of the gas phase increases to the extent of 1.5-1.7.

The constant value And in the proposed law of supply is determined from experiments at G=G_o. So, for a particle of d=0.2 mm,

=10 g/cm³the total mass m=30 g at t= 1500^oWith a coating thickness of 90 μm with a density pyrocarbon 1.0 g/cm³get when filing a mixture of argon (40% vol.) and acetylene (60%) within 250 with a volumetric flow of a mixture of 0.4 DM³/s, which corresponds to the mass flow of acetylene 0.3 g/S. this end, the mass of particles is 46 g, i.e. the mass of carbon is 16, this mass grows in time of the process according to the parabolic law m_c= A

², i.e., A=16 g/6,25

1,04²=2,5

10^-4g/s².

As the flow rate of acetylene is growing in time, the total expense method prototype G= 0, 3 g/

250=75 g in the proposed method achieved during 110-120 s, i.e. the process ematichesky shown in Fig.1, where: 1 - Cam, 2, 3 - screw pair, 4 - Cam, 5 - grip, 6 - arm reducer, 7 - cylinder hydrocarbon, 8 - critical-section 9 - reducer, 10 - valve, 11 - key, 12 - bearing.

For the implementation of the parabolic mode of growth of consumption over time Cam 1 move uniformly down the worm 2 and the worm wheel 3 is moved with a parabolic acceleration, and the profile of the Cam corresponds to the formula A

²of the proposed method, with the same acceleration rotates the crank gear, setting a parabolic increase in the pressure of the hydrocarbon before the critical section.

The flow rate and the gas pressure in the critical flow regime are related by the expression (see Daly, J., Harleman D. Mechanics of fluids, Meters, Energy, 1971, 362 S.)

where K= C_p/s_v- the ratio of specific heats of the gas at constant pressure and volume,

_g- gas density at pressure P, g/cm³,
S - the area of the bore holes of the critical section, cm².

When the linear pressure increase consumption increases linearly, because the density also grows linearly with parabolic growth of consumption grows parabolically.

The creature before the Rami.

Example 1. Put a layer of pyrocarbon on spherical particles with a total mass of 30 g in the prototype method with the following parameter values for the process:
d=0.2 mm,

_TV=10 g/cm³t=1500^oC, the initial costs G_Ar=0.3 g/s, G_C2H2= 0.15 g/s, G_C3H6= 0.15 g/s (volumetric concentration of hydrocarbons was 60%),

=250 C. For a time with 250 consumption (G_C2H2linearly increased to 0.3 g/l, and consumption, G_C3H6reduced to zero. In Fig. 2A shows the structural defects of the outer layer of the coating, due specifically to the stability of the fluidized bed when a significant change of the initial particle size in the last stage of the coating process.

Example 2. The parameters of the coating process similar to example 1 by the method prototype with the exception of two parameters: the flow rate of acetylene and process time. The flow of acetylene was changed by the dependence (value And was 2.5

10 g/s):
G_C2H2= (0,3+2,5

10^-4

²g/c
and the value of

was 110 C. the coating Structure shown in Fig.2B.

Example 3. The parameters of the coating process similar to example 2 except

2. Improves the structure of the coating due to the stabilization of the fluidized bed in the whole time interval of the process.

Claims

1. The method of deposition of pyrocarbon in a fluidized bed, comprising applying to the area of deposition of the mixture of hydrocarbon and inert gas, and varying the concentration of hydrocarbon in time, characterized in that the flow rate of the hydrocarbon in time increase parabolically with the constant flow of inert gas according to a ratio
G = G₀+A

²,
where G₀- the initial flow of hydrocarbon, g/s,
A - constant, g/s³determined from the preliminary experiment at G=G₀,

- time process, with.

2. A dosing device for the deposition of pyrocarbon, including critical section for the feed hydrocarbon and the gear to regulate the pressure to the critical section, characterized in that it comprises a drive mechanism consisting of the Cam is IKE coil pair is connected to the crank gear through engagement, moreover, the Cam and the screw is made to move in mutually perpendicular directions.

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