GB2264617A - Porous heating element - Google Patents
Porous heating element Download PDFInfo
- Publication number
- GB2264617A GB2264617A GB9220324A GB9220324A GB2264617A GB 2264617 A GB2264617 A GB 2264617A GB 9220324 A GB9220324 A GB 9220324A GB 9220324 A GB9220324 A GB 9220324A GB 2264617 A GB2264617 A GB 2264617A
- Authority
- GB
- United Kingdom
- Prior art keywords
- coating
- carbon
- titanium
- heating element
- precursor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 238000010438 heat treatment Methods 0.000 title description 11
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 28
- 238000000576 coating method Methods 0.000 claims abstract description 21
- 239000011248 coating agent Substances 0.000 claims abstract description 19
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 17
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 11
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 11
- 239000010703 silicon Substances 0.000 claims abstract description 11
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims abstract description 9
- 238000005485 electric heating Methods 0.000 claims abstract description 9
- 239000000463 material Substances 0.000 claims abstract description 9
- 239000010936 titanium Substances 0.000 claims abstract description 9
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 8
- 239000007833 carbon precursor Substances 0.000 claims abstract description 5
- 230000003647 oxidation Effects 0.000 claims abstract description 4
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 4
- 239000002243 precursor Substances 0.000 claims description 20
- 238000000034 method Methods 0.000 claims description 19
- 230000008569 process Effects 0.000 claims description 18
- 238000000151 deposition Methods 0.000 claims description 12
- 230000008021 deposition Effects 0.000 claims description 10
- 238000000623 plasma-assisted chemical vapour deposition Methods 0.000 claims description 5
- 239000012530 fluid Substances 0.000 abstract description 7
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 abstract description 7
- 229910010271 silicon carbide Inorganic materials 0.000 abstract description 7
- 238000005137 deposition process Methods 0.000 abstract description 4
- 229910021341 titanium silicide Inorganic materials 0.000 abstract description 3
- MTPVUVINMAGMJL-UHFFFAOYSA-N trimethyl(1,1,2,2,2-pentafluoroethyl)silane Chemical compound C[Si](C)(C)C(F)(F)C(F)(F)F MTPVUVINMAGMJL-UHFFFAOYSA-N 0.000 abstract description 3
- 239000007789 gas Substances 0.000 description 28
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 12
- 229910002804 graphite Inorganic materials 0.000 description 8
- 239000010439 graphite Substances 0.000 description 8
- 229910052786 argon Inorganic materials 0.000 description 6
- 238000005229 chemical vapour deposition Methods 0.000 description 5
- 229910001220 stainless steel Inorganic materials 0.000 description 5
- 239000010935 stainless steel Substances 0.000 description 5
- XJDNKRIXUMDJCW-UHFFFAOYSA-J titanium tetrachloride Chemical compound Cl[Ti](Cl)(Cl)Cl XJDNKRIXUMDJCW-UHFFFAOYSA-J 0.000 description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 4
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 3
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000000376 reactant Substances 0.000 description 3
- 229910000077 silane Inorganic materials 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 239000000377 silicon dioxide Substances 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- 229910010066 TiC14 Inorganic materials 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000001564 chemical vapour infiltration Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 239000002019 doping agent Substances 0.000 description 1
- 239000002657 fibrous material Substances 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 239000012466 permeate Substances 0.000 description 1
- 229920002239 polyacrylonitrile Polymers 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000005215 recombination Methods 0.000 description 1
- 230000006798 recombination Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/02—Induction heating
- H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
- H05B6/105—Induction heating apparatus, other than furnaces, for specific applications using a susceptor
- H05B6/108—Induction heating apparatus, other than furnaces, for specific applications using a susceptor for heating a fluid
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/01—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes on temporary substrates, e.g. substrates subsequently removed by etching
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/04—Coating on selected surface areas, e.g. using masks
- C23C16/045—Coating cavities or hollow spaces, e.g. interior of tubes; Infiltration of porous substrates
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
- C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F11/00—Chemical after-treatment of artificial filaments or the like during manufacture
- D01F11/10—Chemical after-treatment of artificial filaments or the like during manufacture of carbon
- D01F11/12—Chemical after-treatment of artificial filaments or the like during manufacture of carbon with inorganic substances ; Intercalation
- D01F11/125—Carbon
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F11/00—Chemical after-treatment of artificial filaments or the like during manufacture
- D01F11/10—Chemical after-treatment of artificial filaments or the like during manufacture of carbon
- D01F11/16—Chemical after-treatment of artificial filaments or the like during manufacture of carbon by physicochemical methods
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
- H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- General Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Textile Engineering (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Chemical Vapour Deposition (AREA)
Abstract
A porous electric heating element is made by coating a fibrous carbon precursor with carbon, silicon and titanium by a vapour deposition process, preferably a plasma activated vapour deposition process. The coating comprises silicon carbide, titanium carbide and titanium silicide, and its temperature coefficient of resistance can be less negative than that of known silicon carbide elements, or even be positive. The carbon precursor may then be removed by oxidation to leave hollow tubular fibres of the coating material. The element may be used to heat a fluid electrically. <IMAGE>
Description
Porous Heating Element
This invention relates to a fluid-permeable fibrous electric heating element, and to a process for making such elements.
Fluid heating systems in which heat is generated by an electric current flowing through a fluid-permeable electrically conductive element, and is transferred to a fluid permeating and flowing through the element, are known. Where the element is a fibrous material with the voids between the fibres providing the fluid path the element can provide high power densities in excess of 1 kW/cm3, combined with little resistance to the fluid flow as a result of high voidages of between 50 and 98 percent, for example. Such an element has low thermal capacity, so that it can provide a rapid response time where a change of heater power is desired.
UK patent GB 1 600 253 describes a method of making one such element, in which a body is formed of randomly disposed carbonisable fibres (for example of polyacrylonitrile) to which a latent solvent is applied, the solvent is then activated to bond the fibres together, and the fibres are then carbonised. The element so produced consists of a rigid structure of carbon fibres.
As described in GB 2 111 809 this fibrous carbon element may be used as a precursor in the manufacture of other types of elements, the carbon fibres being coated by a plasma assisted vapour deposition process with a material comprising silicon or silicon and carbon (primarily as silicon carbide). The original fibrous carbon precursor may either be retained, or removed by oxidation so that a structure of tubular fibres of the deposited material remains. A suitable heat treatment may be used to adjust the electrical conductivity and the temperature coefficient of resistance of the deposited material to desired values.
The fibrous carbon elements and the fibrous silicon or silicon carbide elements, made by the processes described in these two patents, can provide the advantages of high power density, low fluid pressure drop, and rapid response, as outlined above, but have a negative temperature coefficient of resistance. Consequently their resistance decreases as their temperature rises, so that controlling the electrical current through them in operation is more complex than with conventional metallic heating elements.
According to the present invention there is provided a process for making a fluid-permeable fibrous electric heating element, the process comprising depositing from the gas phase onto a fibrous carbon precursor a coating comprising silicon, titanium and carbon.
Preferably the deposition is performed by plasmaassisted chemical vapour deposition (PACVD), as this enables the deposition to be performed at lower temperatures than are necessary for chemical vapour deposition (CVD), for example between 700 and 900"C for
PACVD compared to over 900"C for CVD. This is because the plasma assists the breakdown of the reactant gases to form radicals or ions. Desirably deposition is continued until the coating is between 0.1 and 30 micrometres thick, preferably between 1 and 5 micrometres thick. The coating may also comprise a dopant material to modify its electrical resistivity. The electrical properties of the element can be controlled by adjusting the proportions of silicon, titanium and carbon which are deposited, and by heat treatment.The elemental proportions determine the proportions of the various deposited phases, which are primarily silicon carbide, titanium carbide, and one or more titanium silicides, while the heat treatment affects the grain structure of the coating. The carbon fibre precursor can be removed by an oxidation process to leave tubular fibres of the coating material.
The deposition process may rely on diffusion to ensure the reactant gases permeate the precursor and deposit the coating throughout the thickness of the precursor.
Alternatively the reactant gases may be caused to flow through the precursor by a pressure difference between opposite surfaces; where the precursor is of annular or tubular form, the gases may be supplied to the bore of the precursor and caused to flow radially outward to the outer surface of the precursor (or vice versa). The process is substantially the same as those referred to as plasmaassisted or isothermal chemical vapour infiltration, although in the process of the invention the deposition is preferably terminated while the voidage is high. As deposition proceeds the pressure difference increases, and the process may be monitored by monitoring the pressure difference.The degree of uniformity of the coating thickness through the element may be controlled by controlling the temperature of the precursor, the gas flow rate, and the pressure at the inlet suface of the precursor; a more uniform coating is generally obtained if the chemical reactions occur at a slower rate, and this can be achieved by reducing the temperature (so the sticking coefficient increases), by increasing the gas flow rate (so the residence time decreases), or by increasing the internal pressure (to increase the recombination rate in the gas phase).
The present invention also provides a fluid-permeable fibrous electric heating element comprising a structure constituted by fibres of a material comprising silicon, titanium and carbon, the fibres either having a carbon core or being hollow tubes.
The element of the invention which may be made by the above-defined process, depending on the proportions of the deposited phases and on the grain structure, may have a temperature coefficient of resistance either less negative than that of the silicon carbide elements of the prior art, or even positive. Consequently it is much easier to use, especially in high-power or high-temperature applications, as it is relatively easy to control the electric current through it. Hence the power supply needed, where such an element is used to heat a fluid, can be simpler and cheaper than with previously known fibrous heating elements.
The invention will now be further described, by way of example only, and with reference to the accompanying drawings in which:
Figure 1 shows a diagrammatic perspective view of an
apparatus for making a fluid-permeable
fibrous electric heating element; and
Figure 2 shows a longitudinal sectional view of part
of the apparatus of Figure 1.
Referring to Figure 1 an apparatus 10 includes an upright silica tube 12 sealed at each end, which can be evacuated by a vacuum pump 14. Around a central portion of the tube 12 is a multi-turn coil 16 of water-cooled copper tube whose ends are connected to terminals of a high voltage high frequency signal generator 18 (8kV, 345 kHz, up to 45 kW). Between the coil 16 and the tube 12 is a water-cooled, thin copper electrode 20 of cylindrical form, but with a longitudinal slot 21 to minimize eddy current heating. Two stainless steel gas lines 22, 23 enable gases to be supplied to one end of the tube 12. One gas line 22 connects to a mixing manifold 24 to which are connected supplies 26 of argon, hydrogen, silane, and ethene gas via respective metering valves 28.The other gas line 23 is trace-heated along its length to 80"C, and is connected to a heated boiler 30 via a switch-over valve 31 and a vapour source controller 32; the boiler 30 generates titanium tetrachloride vapour. The switch-over valve 31 enables the vapour to be supplied either to the gas line 23, or to a bypass line 33 which connects to a chamber 34 supplied with a bleed of argon gas from a source 35, hence to a cold trap 36 for condensing the titanium chloride, and hence to a vacuum pump 37. Pressure gauges 38 enable the pressures at the gas lines 22 and 23, the chamber 34, and at the duct connected to the vacuum pump 14 to be monitored. One end of the coil 16 is earthy (i.e. earthed within the generator 18, at least as regards ac), and the gas lines 22 and 23 are earthed.
Referring now to Figure 2 there is shown to a larger scale a sectional view of the central portion of the tube 12. The gas lines 22 and 23 both communicate with a stainless steel mixing chamber 40; the line 23 communicates directly with the lower half of the chamber 40 whereas the line 22 communicates through a perforated stainless steel plate 42. The chamber 40 has an external flange 44 by which it is clamped to two graphite coated alumina support rods 46 fixed at their top ends to the means sealing the upper end of the silica tube 12. The bottom ends of the rods 46 are connected by a stainless steel bar 48.An annular or tubular carbon fibre precursor 50 (which may be made as described in GB 1 600 253, as outlined above) is clamped between the bar 48 and the bottom of the mixing chamber 40: the lower end of the precursor 50 is blocked by a graphite end plate 52 supported on a graphite-coated alumina tube 54, while the upper end of the precursor 50 mates with an annular graphite ring 56 spaced apart, by a graphite-coated alumina tube 58, from a similar graphite ring 60 locating in an aperture in the bottom of the mixing chamber 40 to which it forms a gas-tight seal.
An annular graphite plate 62 is supported by the rods 46 above the bar 48, to provide a support for two cylindrically tubular components which surround the precursor 50. These components are a graphite tube or susceptor 64, outside which is a thin stainless steel heat shield 66; the shield 66 has a longitudinal slot to minimize eddy current heating. By virtue of the earth connection to the gas line 23, and the graphite coating on the alumina rods 46 and tubes 54 and 58, all the components within the tube 12 are earthed.
In operation, the apparatus 10 is assembled as shown in the Figures, and by means of the pumps 14 and 37 the tube 12 and the chamber 34 are evacuated. Argon is bled into the chamber 34 and the pump 37 arranged to hold the pressure at 7.5 torr (1 kPa). The titanium chloride boiler 30 is energised, and the valve 31 arranged so the vapour is supplied to the by-pass line 33 and so to the chamber 34 (this gives time for operation of the boiler 30 to stabilize). Argon and hydrogen are supplied to the gas line 22 and the pump 14 arranged to hold the pressure in the tube 12 at 3.5 torr (0.47 kPa). The signal generator 18 is energised, with the electrode 20 connected electrically to the mid-point of the coil 16.The graphite susceptor 64 is heated inductively to for example 750"C (this temperature might be between say 700C and 1000 C), and plasma is generated in the vicinity of the precursor 50 which leads to reduction of surface oxides, and can improve adhesion of the coating. The precursor 50 is heated by radiation from the susceptor 64 to substantially the same temperature as the susceptor 64.
Silane and ethene are then supplied to the gas line 22, and the pump 14 arranged to hold the pressure in the gas line 22 to 7.5 torr (1kPa), and the valve 31 is switched over so the titanium tetrachloride vapour is supplied to the gas line 23, so as to mix with the other gases in the mixing chamber 40. The molecules in the gases are broken down (into radicals or ions) as a result of both the high temperature and the plasma. Carbon, silicon and titanium atoms are consequently deposited onto the fibres which constitute the precursor 50. The resultant coating is believed to consist principally of silicon carbide, titanium carbide, and titanium silicide, although the exact formulae of the phases are not known.The thickness of the coating depends on how long the coating process is continued, as a coating deposition rate of around 0.1 micrometres/minute can be achieved. The process can be monitored by monitoring the pressure difference between the inside and the outside of the precursor 50. By way of example the gas flow rates, measured in standard cubic centimetres per minute, might be as follows: argon 1000, hydrogen 300, silane 10, ethene 10, and titanium tetrachloride vapour 15.
The energy provided to the plasma can be adjusted by moving the electrical connection between the coil 16 and the electrode 20. However, if the electrode 20 is connected to a good earth, then although the susceptor 64 will still be heated inductively no plasma will be formed, and only CVD will occur. It has been found that the PACVD process produces more deposition of titanium than CVD, so the method of the invention preferably utilizes a plasma.
After the coating process has been completed the coated precursor 50 is removed from the apparatus 10.
Usually the carbon fibres are then burnt out by heating in air to 770"C, in a furnace whose temperature is raised at 1.5 C/min, and then held at tht temperature for 16 hours.
After cooling, the resulting ceramic fibrous element may then be heat treated, for example it may be annealled in argon at 1300"C for 48 hours to reduce its resistance to a desired value.
It will be appreciated that the gases supplied to the apparatus 10 to bring about deposition of silicon, titanium and carbon as specified above are by way of example only, and that alternative gases may be used. For example
Ti(OCH3)3 might be used as an alternative to TiC14.
Claims (7)
1. A process for making a fluid-permeable fibrous electric heating element, the process comprising depositing from the gas phase onto a fibrous carbon precursor a coating comprising silicon, titanium and carbon.
2. A process as claimed in Claim 1 wherein the deposition is performed by plasma-assisted chemical vapour deposition.
3. A process as claimed in Claim 1 or Claim 2 wherein the deposition is continued until the coating is between 0.1 and 30 micrometres thick, preferably between 1 and 5 micrometres thick.
4. A process as claimed in any one of the preceding
Claims also comprising a subsequent step of removing the precursor by oxidation to leave tubular fibres of the coating material.
5. A fluid-permeable fibrous electric heating element comprising a structure constituted by fibres of a material comprising silicon, titanium and carbon, the fibres either having a carbon core or being hollow tubes.
6. A process for making a fluid-permeable fibrous electric heating element substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.
7. A fluid-permeable fibrous electric heating element made by a process as claimed in any one of Claims 1 to 4 or
Claim 6.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9220324A GB2264617A (en) | 1991-10-08 | 1992-09-25 | Porous heating element |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB919121312A GB9121312D0 (en) | 1991-10-08 | 1991-10-08 | Porous heating element |
| GB9220324A GB2264617A (en) | 1991-10-08 | 1992-09-25 | Porous heating element |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9220324D0 GB9220324D0 (en) | 1992-11-11 |
| GB2264617A true GB2264617A (en) | 1993-09-01 |
Family
ID=26299653
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9220324A Withdrawn GB2264617A (en) | 1991-10-08 | 1992-09-25 | Porous heating element |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2264617A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004031438A1 (en) * | 2002-09-28 | 2004-04-15 | Ludwig Hiss | Internally coated hollow body, coating method and device |
| DE102004062553A1 (en) * | 2004-12-24 | 2006-07-06 | Aixtron Ag | CVD reactor with RF heated process chamber |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1386551A (en) * | 1972-01-05 | 1975-03-05 | United Aircraft Corp | Silicon carbide surfaced filaments with titanium carbide coating |
| GB2111809A (en) * | 1981-12-14 | 1983-07-06 | Atomic Energy Authority Uk | An improved fluid permeable porous electric heating element |
-
1992
- 1992-09-25 GB GB9220324A patent/GB2264617A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1386551A (en) * | 1972-01-05 | 1975-03-05 | United Aircraft Corp | Silicon carbide surfaced filaments with titanium carbide coating |
| GB2111809A (en) * | 1981-12-14 | 1983-07-06 | Atomic Energy Authority Uk | An improved fluid permeable porous electric heating element |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004031438A1 (en) * | 2002-09-28 | 2004-04-15 | Ludwig Hiss | Internally coated hollow body, coating method and device |
| DE102004062553A1 (en) * | 2004-12-24 | 2006-07-06 | Aixtron Ag | CVD reactor with RF heated process chamber |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9220324D0 (en) | 1992-11-11 |
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