CN113213973B - Method for controlling sintering atmosphere of high-emissivity thermal protection coating - Google Patents

Method for controlling sintering atmosphere of high-emissivity thermal protection coating Download PDF

Info

Publication number
CN113213973B
CN113213973B CN202110574298.7A CN202110574298A CN113213973B CN 113213973 B CN113213973 B CN 113213973B CN 202110574298 A CN202110574298 A CN 202110574298A CN 113213973 B CN113213973 B CN 113213973B
Authority
CN
China
Prior art keywords
temperature
furnace
coating
mixed gas
thermal protection
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.)
Active
Application number
CN202110574298.7A
Other languages
Chinese (zh)
Other versions
CN113213973A (en
Inventor
李明伟
孙宇雷
钟业盛
史丽萍
赫晓东
何飞
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Heilongjiang Deming Technology Development Co ltd
Original Assignee
Harbin Institute of Technology
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Harbin Institute of Technology filed Critical Harbin Institute of Technology
Priority to CN202110574298.7A priority Critical patent/CN113213973B/en
Publication of CN113213973A publication Critical patent/CN113213973A/en
Application granted granted Critical
Publication of CN113213973B publication Critical patent/CN113213973B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
    • C04B41/81—Coating or impregnation
    • C04B41/85—Coating or impregnation with inorganic materials
    • C04B41/87—Ceramics
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/0072—Heat treatment
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
    • C04B41/50—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials
    • C04B41/5053—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials non-oxide ceramics
    • C04B41/5062—Borides, Nitrides or Silicides
    • C04B41/5071—Silicides

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Turbine Rotor Nozzle Sealing (AREA)

Abstract

A method for controlling the sintering atmosphere of a high-emissivity thermal protection coating relates to the field of materials. The invention aims to solve the problems that key filler components are easy to oxidize in the sintering process of the high-emissivity thermal protection coating and a base material is oxidized and damaged in the sintering process. The rigid fiber heat-insulating tile coated with the radiation filler, which has no oxidation loss, and the dense high-emissivity heat-protective coating is obtained. The method is simple and convenient to operate, has low equipment requirement, and has important significance for reusable heat protection of the ultrahigh temperature zone on the surface of the hypersonic aircraft. The invention is applied to the field of rigid fiber heat insulation tiles.

Description

Method for controlling sintering atmosphere of high-emissivity thermal protection coating
Technical Field
The invention relates to the field of materials, in particular to a method for controlling sintering atmosphere of a high-emissivity thermal protection coating.
Background
In the process of high-speed flight of the reusable hypersonic aircraft, severe aerodynamic thermal environment is generated around the aircraft body due to severe friction between the aircraft body and the ambient atmosphere, the surface temperature of the aircraft rapidly rises to 1500 ℃, and parts of the aircraft even reach 1700 ℃, and reliable thermal protection is a precondition and a key for guaranteeing the safe service of the aircraft. At present, the surface thermal protection of the reusable aircraft mainly adopts passive radiation type thermal protection, and the surface thermal protection of the aircraft body is realized by virtue of a rigid fiber heat-insulation composite material and a surface high-emissivity thermal protection coating thereof. Wherein, the high emissivity coating in surface radiates the heat on fuselage surface out through infrared radiation's mode can greatly reduce organism surface temperature and alleviate the thermal protection burden of inside thermal insulation material.
The main components of the high-emissivity thermal protection coating are borosilicate glass powder and silicon tetraboride (SiB)4) Or silicon hexaboride (SiB)6) And two high emissivity refractory metal silicides, wherein the glass powder is binder and coating main body, SiB4And SiB6One of the two metal silicides can be used as a sintering aidPrimary and secondary coating radiation agents. The coating slurry is sprayed on the surface of the ceramic fiber or carbon fiber rigid heat insulation tile, and then the compact glass coating is obtained after drying and sintering. However, the existing sintering mode of the coating adopts a normal-pressure and rapid sintering method, and partial metal silicide and SiB can be caused in the sintering process4Or SiB6Thermal oxidation reaction occurs, and particularly if metal silicide is oxidized, the emissivity of the coating is reduced, and the overall thermal protection performance is affected. In addition, if the matrix is ceramic fiber, the influence is relatively insignificant by adopting a normal-pressure and rapid sintering method, and if the matrix is carbon fiber rigid composite material, the carbon fiber can be obviously oxidized, and the mechanical property of the material is serious.
Disclosure of Invention
The invention aims to solve the problems that key filler components are easy to oxidize and a base material is oxidized and damaged in the sintering process of a high-emissivity thermal protection coating, and provides a method for controlling the sintering atmosphere of the high-emissivity thermal protection coating.
The invention relates to a method for controlling the sintering atmosphere of a high-emissivity thermal protection coating, which comprises the following steps:
firstly, drying the rigid fiber heat insulation tile sprayed with the coating slurry at the temperature of 30-70 ℃ for 12-24 h, transferring the dried heat insulation tile into a high-temperature atmosphere furnace, vacuumizing, introducing inert gas or mixed gas of the inert gas and oxygen, and controlling the pressure in the furnace to be in a normal pressure state, wherein the oxygen content in the mixed gas is 0.01-5%;
and secondly, heating the furnace to 1100-1400 ℃ at a heating rate of 1-10 ℃/min, preserving the temperature for 10-60 min, stopping heating, cooling the furnace to 700-1000 ℃, taking out the rigid fiber heat-insulating tile, and cooling to room temperature to obtain the rigid fiber heat-insulating tile coated with the dense high-emissivity thermal protection coating without oxidation loss of the radiation filler.
Further, the rigid fiber heat insulation tile is a carbon fiber rigid fiber heat insulation tile or a ceramic rigid fiber heat insulation tile.
Further, the rigid fiber heat insulation tile is a carbon fiber rigid fiber heat insulation tile or a ceramic rigid fiber heat insulation tile.
Further, the coating slurry is borosilicate glass powder, silicide of tantalum or molybdenum, and SiB4Or SiB6Absolute ethyl alcohol; the mixture ratio is 30 percent of borosilicate glass powder, 60 percent of tantalum or molybdenum silicide and 5 percent of SiB4Or SiB6And the balance of absolute ethyl alcohol.
Further, the oxygen content in the mixed gas is 0.05-4%.
Further, the oxygen content in the mixed gas is 0.1-3%.
Further, the oxygen content in the mixed gas is 0.5-3%.
Further, the oxygen content in the mixed gas is 1-2%.
Further, the rigid fiber heat insulation tile sprayed with the coating slurry is dried for 18-24 hours at the temperature of 40-60 ℃.
Further, the furnace temperature is increased to 1200-1300 ℃ at the heating rate of 3-6 ℃/min, and the temperature is kept for 30-50 min.
Further, stopping heating until the furnace temperature is reduced to 800-900 ℃.
The invention has the following beneficial effects:
according to the invention, a compact glass coating with high emission capability is prepared on the surface of the ceramic fiber or carbon fiber rigid heat insulation tile by accurately regulating and controlling the sintering atmosphere composition of the coating, and the coating has stable performance and high emissivity under a high-temperature condition, and can prevent the invasion of outside air due to compactness. And can provide obvious enhanced antioxidation for the matrix material. The sintering of the key high-emissivity filler (mainly avoiding the oxidation of metal silicide of tantalum or molybdenum) of the coating and the matrix skeleton (carbon fiber-based skeleton) without oxidation damage is realized, and the stable performance of the composite material and the surface coating is ensured. The method is simple and convenient to operate, has low equipment requirement, and has important significance for reusable heat protection of the ultrahigh temperature zone on the surface of the hypersonic aircraft.
Drawings
FIG. 1 is a macro topography of the coating after 1250 ℃ sintering of example 1;
FIG. 2 is a microstructure of the sintered coating of example 1;
FIG. 3 is a microstructure of the coating after sintering at 1200 ℃ of comparative example 1;
FIG. 4 is a microscopic topography of the thermal protective coating of the carbon fiber based rigid fiber thermal insulating tile of comparative example 2.
Detailed Description
It will be understood by those of ordinary skill in the art that the foregoing embodiments are specific examples for carrying out the invention, and that various changes in form and details may be made therein without departing from the spirit and scope of the invention in practice.
To make the objects, aspects and advantages of the embodiments of the present invention more apparent, the following detailed description clearly illustrates the spirit of the disclosure, and any person skilled in the art, after understanding the embodiments of the disclosure, may make changes and modifications to the technology taught by the disclosure without departing from the spirit and scope of the disclosure.
Example 1
The method for controlling the sintering atmosphere of the high-emissivity thermal protection coating is carried out according to the following steps:
firstly, coating slurry prepared by 30 mass percent of glass powder, 60 mass percent of tantalum silicide, 5 mass percent of silicon tetraboride and a proper amount of absolute ethyl alcohol is sprayed on the surface of a carbon fiber-based rigid fiber heat insulation tile, then the heat insulation tile with the coating is placed in a drying oven to be dried for 15 hours at the temperature of 60 ℃, then the dried heat insulation tile is transferred into a high-temperature atmosphere furnace, a vacuum pump is adopted to pump the atmosphere furnace to a high vacuum state (0.05Pa), and then Ar and O are introduced into the furnace2Mixed gas of (2), wherein O2The content of the heat insulation tile is 3 percent, the pressure in the furnace is controlled to be in a normal pressure state, the temperature of the furnace is increased to 1250 ℃ at the heating rate of 5 ℃/min, the heat preservation time is set for 30min after the temperature is increased to a preset temperature, the heating is stopped and the temperature is reduced to 850 ℃ along with the furnace, the atmosphere furnace is opened, the heat insulation tile is rapidly taken out, the temperature is reduced to the room temperature, and the radiation filler is obtainedA dense high emissivity thermal protective coating without oxidation loss.
Fig. 1 is a macro-topography of the dense high-emissivity thermal protection coating without oxidation loss of the radiation filler after sintering in the embodiment, and fig. 2 is a micro-topography of the dense high-emissivity thermal protection coating without oxidation loss of the radiation filler after sintering in the embodiment, and it can be seen from fig. 1 and fig. 2 that the coating is dense and defect-free and has the capability of blocking oxygen intrusion.
Comparative example 1
The preparation method of the thermal protection coating of the embodiment is carried out according to the following steps:
firstly, coating slurry prepared by 30 mass percent of glass powder, 60 mass percent of tantalum silicide, 5 mass percent of silicon tetraboride and a proper amount of absolute ethyl alcohol is sprayed on the surface of a carbon fiber-based rigid fiber heat insulation tile, then the heat insulation tile with the coating is placed in a drying oven to be dried for 15 hours at the temperature of 60 ℃, then the dried heat insulation tile is transferred into a high-temperature atmosphere furnace, a vacuum pump is adopted to pump the atmosphere furnace to a high vacuum state (0.05Pa), and then Ar and O are introduced into the furnace2Mixed gas of (2), wherein O2The content of the carbon fiber-based rigid fiber heat insulation tile is 7 percent, the pressure in the furnace is controlled to be in a normal pressure state, the temperature of the furnace is raised to 1200 ℃ at the heating rate of 5 ℃/min, the heat preservation time is set for 30min after the temperature is raised to the preset temperature, the heating is stopped, the temperature is reduced to 850 ℃ along with the furnace, the atmosphere furnace is opened, the heat insulation tile is taken out rapidly, and the temperature is reduced to the room temperature, so that the carbon fiber-based rigid fiber heat insulation tile heat protection coating is obtained.
FIG. 3 is a microscopic morphology of the thermal protective coating of the carbon fiber-based rigid fiber thermal insulating tile of the present comparative example. Therefore, after the upper limit of the oxygen content of 5% is exceeded, the obtained protective coating generates a serious oxidation phenomenon, generates a large number of holes and reduces the protective performance.
Comparative example 2
The preparation method of the thermal protection coating of the embodiment is carried out according to the following steps:
firstly, 30 percent of glass powder, 60 percent of silicide of tantalum, 5 percent of silicon tetraboride and a proper amount of silicon boride are mixed according to the mass percentSpraying coating slurry prepared by water and ethanol on the surface of a carbon fiber-based rigid fiber heat insulation tile, then drying the heat insulation tile with the coating in a drying oven at 60 ℃ for 15 hours, then transferring the dried heat insulation tile into a high-temperature atmosphere furnace, pumping the atmosphere furnace to a high vacuum state (0.05Pa) by adopting a vacuum pump, and then introducing Ar and O into the furnace2Mixed gas of (2), wherein O2The content of the carbon fiber-based rigid fiber heat insulation tile is 0.001 percent, the pressure in the furnace is controlled to be in a normal pressure state, the temperature of the furnace is raised to 1200 ℃ at the heating rate of 5 ℃/min, the temperature is kept for 30min after the temperature is raised to a preset temperature, the heating is stopped, the temperature is reduced to 850 ℃ along with the furnace, the atmosphere furnace is opened, the heat insulation tile is rapidly taken out, and the temperature is reduced to the room temperature, so that the carbon fiber-based rigid fiber heat insulation tile heat protection coating is obtained.
FIG. 4 is a microscopic morphology of the thermal protective coating of the carbon fiber-based rigid fiber thermal insulating tile of the present comparative example. Therefore, after the oxygen content is lower than the lower limit of 0.01 percent, the obtained protective coating still generates serious oxidation phenomenon, has a large number of holes and reduces the protective performance.
It can be seen from comparative examples 1 and 2 that neither exceeding nor falling below the oxygen content range given by the present invention gives an ideal thermal protective coating for carbon fiber based rigid fiber insulation tiles.

Claims (10)

1. A method for controlling the sintering atmosphere of a high-emissivity thermal protection coating is characterized by comprising the following steps of:
firstly, drying a rigid fiber heat insulation tile sprayed with coating slurry at the temperature of 30-70 ℃ for 12-24 h, transferring the dried heat insulation tile into a high-temperature atmosphere furnace, vacuumizing, introducing mixed gas of inert gas and oxygen, and controlling the pressure in the furnace to be in a normal pressure state, wherein the oxygen content in the mixed gas is 0.01-5%;
and secondly, heating the furnace to 1100-1400 ℃ at a heating rate of 1-10 ℃/min, preserving the temperature for 10-60 min, stopping heating, cooling the furnace to 700-1000 ℃, taking out the rigid fiber heat-insulating tile, and cooling to room temperature to obtain the rigid fiber heat-insulating tile coated with the dense high-emissivity thermal protection coating without oxidation loss of the radiation filler.
2. The method of claim 1 wherein the rigid fibrous insulation tile is a carbon fiber rigid fibrous insulation tile or a ceramic rigid fibrous insulation tile.
3. The method of claim 1 wherein the coating slurry is borosilicate glass frit, tantalum or molybdenum silicide, and SiB4Or SiB6Absolute ethyl alcohol; the mixture ratio is 30 percent of borosilicate glass powder, 60 percent of tantalum or molybdenum silicide and 5 percent of SiB4Or SiB6And the balance of absolute ethyl alcohol.
4. The method according to claim 1, wherein the oxygen content in the mixed gas is 0.05-4%.
5. The method according to claim 1, wherein the oxygen content in the mixed gas is 0.1-3%.
6. The method according to claim 1, wherein the oxygen content in the mixed gas is 0.5-3%.
7. The method according to claim 1, wherein the oxygen content of the mixed gas is 1-2%.
8. The method for controlling the sintering atmosphere of the high-emissivity thermal protective coating according to claim 1, wherein the rigid fiber heat insulating tile sprayed with the coating slurry is dried at a temperature of 40-60 ℃ for 18-24 h.
9. The method for controlling the sintering atmosphere of the high-emissivity thermal protective coating according to claim 1, wherein the furnace temperature is increased to 1200-1300 ℃ at a temperature increase rate of 3-6 ℃/min, and the temperature is maintained for 30-50 min.
10. The method according to claim 1, wherein the temperature of the furnace is reduced to 800-900 ℃ after the heating is stopped.
CN202110574298.7A 2021-05-25 2021-05-25 Method for controlling sintering atmosphere of high-emissivity thermal protection coating Active CN113213973B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202110574298.7A CN113213973B (en) 2021-05-25 2021-05-25 Method for controlling sintering atmosphere of high-emissivity thermal protection coating

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202110574298.7A CN113213973B (en) 2021-05-25 2021-05-25 Method for controlling sintering atmosphere of high-emissivity thermal protection coating

Publications (2)

Publication Number Publication Date
CN113213973A CN113213973A (en) 2021-08-06
CN113213973B true CN113213973B (en) 2022-03-11

Family

ID=77098477

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202110574298.7A Active CN113213973B (en) 2021-05-25 2021-05-25 Method for controlling sintering atmosphere of high-emissivity thermal protection coating

Country Status (1)

Country Link
CN (1) CN113213973B (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114105681A (en) * 2021-11-03 2022-03-01 航天特种材料及工艺技术研究所 High-emissivity surface toughening coating and preparation method thereof

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1336559A (en) * 1970-05-20 1973-11-07 Triplex Safety Glass Co Metal oxide coatings
KR100454715B1 (en) * 2002-03-14 2004-11-05 한국과학기술연구원 MoSi2-Si3N4 COMPOSITE COATING AND MANUFACTURING METHOD THEREOF
CN107904544A (en) * 2017-11-08 2018-04-13 宝鸡文理学院 A kind of preparation method of refractory metal surfaces antioxidant coating
CN109467457B (en) * 2018-12-25 2020-05-29 北京交通大学 Composition, high-emissivity antioxidant coating prepared from composition and used for porous carbon fiber heat-insulating material surface and preparation method of high-emissivity antioxidant coating
CN110653136B (en) * 2019-10-08 2022-07-22 航天特种材料及工艺技术研究所 Surface oxidation-resistant high-emissivity coating of porous fibrous carbon-based heat-insulating material and preparation method thereof

Also Published As

Publication number Publication date
CN113213973A (en) 2021-08-06

Similar Documents

Publication Publication Date Title
US20220009838A1 (en) Long-term ablation-resistant nitrogen-containing carbide ultra-high temperature ceramic with ultra-high melting point and application thereof
CN113213973B (en) Method for controlling sintering atmosphere of high-emissivity thermal protection coating
CN106966753B (en) Preparation method of C/Al-Si-X ablation-resistant composite material
CN110653136B (en) Surface oxidation-resistant high-emissivity coating of porous fibrous carbon-based heat-insulating material and preparation method thereof
CN106673709B (en) Porous heat insulation material surface refractory high emissivity silicide-glass-hybrid coating and preparation
CN106565262A (en) Preparation method for low-density refractory and antioxidative carbon-ceramic composite material
CN113387724A (en) High-temperature-resistant long-life composite coating on surface of carbon/carbon composite material and preparation method thereof
CN110950681B (en) Preparation method of graphite oxidation-resistant coating
CN107473761B (en) Heat-proof and load-bearing integrated carbon aerogel/ceramic layered composite material and preparation method and application thereof
CN107353041A (en) SiC/SiC composite material surface coating systems and preparation method thereof
CN104945013B (en) A kind of C/C composite and the preparation method of surface oxidation-resistant composite coating thereof
Qian et al. Corrosion behavior of Y2O3-doped mullite-ZrSiO4 coatings applied on C/C–SiC composites in the presence of moisture at temperatures of 1373–1773 K
CN115636692B (en) High-temperature-resistant and oxidation-resistant ceramic coating and preparation method and application thereof
CN112010656B (en) Hafnium oxide fiber, preparation method thereof and application thereof in oxidation-resistant coating
CN105908043B (en) A kind of Mo ZrB2SiC AlN composites and preparation method thereof
CN105459564B (en) Interface is from toughening Si3N4The preparation method of/SiC lamella ceramic materials
CN117209299A (en) High-temperature-resistant ceramic material based on hafnium boride and preparation method thereof
CN113817946A (en) HEA-SiC high-temperature wave-absorbing material and preparation method thereof
KR100520436B1 (en) Method for Making Oxidation Protective Double Coating for Carbon/Carbon Composite
CN113981381B (en) Light material surface coating for fuselage of low-altitude flight rescue unmanned aerial vehicle for fire disaster and preparation method thereof
CN106966764B (en) High-temperature oxidation-resistant composite coating of thermal structure composite material and preparation method thereof
CN105506331A (en) Mo-Si-B-Ti-Zr-Al-Nb composite material and preparation method thereof
CN105503265A (en) Method for preparing SiC coating on graphite thermal field surface in graphite heating furnace
CN114315390A (en) Carbon/carbon composite material surface wide-temperature-range long-life antioxidant coating and low-temperature preparation method
CN110499078B (en) Preparation method and application of radar antenna housing or antenna window compressive stress coating

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant
TR01 Transfer of patent right

Effective date of registration: 20220527

Address after: 150029 Building 1, Kechuang headquarters, Shenzhen (Harbin) Industrial Park, No. 288, Zhigu street, Songbei District, Harbin, Heilongjiang Province

Patentee after: HEILONGJIANG DEMING TECHNOLOGY DEVELOPMENT Co.,Ltd.

Address before: 150001 No. 92 West straight street, Nangang District, Heilongjiang, Harbin

Patentee before: HARBIN INSTITUTE OF TECHNOLOGY

TR01 Transfer of patent right