CN101775590A - Graphite base with protective coating layer and preparation method thereof - Google Patents
Graphite base with protective coating layer and preparation method thereof Download PDFInfo
- Publication number
- CN101775590A CN101775590A CN201010011510A CN201010011510A CN101775590A CN 101775590 A CN101775590 A CN 101775590A CN 201010011510 A CN201010011510 A CN 201010011510A CN 201010011510 A CN201010011510 A CN 201010011510A CN 101775590 A CN101775590 A CN 101775590A
- Authority
- CN
- China
- Prior art keywords
- gas
- graphite base
- reaction chamber
- sicl
- sic coating
- 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.)
- Granted
Links
Images
Abstract
The invention provides a graphite base with a protective coating layer and a preparation method thereof. The invention prepares a silicon carbide coating layer on the surface of the porous graphite base through combining the in-situ chemical gas-phase reaction permeation and the chemical gas-phase deposition two-step method. The preparation method is carried out according to the following steps: placing the a base body of the graphite base in a reaction chamber, introducing SiCl4 gas and H2 gas into the reaction chamber according to the volume ratio that SiCl4/H2 equals to 1/5 to 50 under the condition of the reaction chamber temperature between 1300 and 1600 DEG C and the vacuum between 200 and 500 Pa, wherein the hydrogen flow rate is between 200 and 1000 ml/min, the gas introduction time is between 0.5 and 2 hours, and a primary SiC coating layer is permeated on the base body of the graphite base through the in-situ gas-phase reaction; and then b, introducing CH3SiCl3 gas and H2 gas into the reaction chamber according to the volume ratio that CH3SiCl3/H2 equals to 1/5 to 100, controlling the hydrogen flow rate to be in a range between 200 and 1000 ml/m and the gas introduction time between 1 and 50 hours, and depositing a secondary SiC coating layer outside the surface of the primary SiC coating layer after schizolysis.
Description
Technical field:
The present invention relates to high purity graphite pedestal technical field, further say graphite base that relates to a kind of SiC of having (silicon carbide) supercoat and preparation method thereof.
Background technology:
The research of GaN material is the forward position and the focus of present global semiconductor research with using, it is the novel semiconductor material of development microelectronic device, opto-electronic device, for the growth of the preparation of monocrystalline GaN material, silicon epitaxial single crystal generally all adopt vapor phase epitaxial growth (be chemical vapour deposition, method CVD).At preparation GaN monocrystalline, in the process of silicon epitaxial single crystal material, must guarantee the high cleaning of reaction environment.At present, in the process of epitaxy monocrystal material, the reaction pedestal/crucible of use all is a graphite material, because corrosion dry linting phenomenon can take place under high temperature, corrosive gas environment graphite material, thereby powder impurity is incorporated in the monocrystal material.The best measure that solves graphite base/graphite plate etching problem is that graphite base/graphite plate is applied whole dense coating.
High-purity carborundum (SiC) material has that density is low, thermal property is stable, high-temperature oxidation resistant, anti-ly wash away, excellent properties such as anticorrosive, be the ideal material system of graphite base top coat.Solve the difficult problem that the graphite base preparation method exists some to be difficult to overcome: 1, density, adopt the SiC material of traditional prepared to be difficult to fine and close fully.2, surface finish, because the graphite base used of single crystal growing requires surface finish very high, the essential original planeness of pedestal that keeps after coating preparation finishes, promptly coat side must uniformity, and traditional preparation technology is difficult to accomplish.3, full parcel, graphite base integral body all will be in corrodibility, 1000～1800 ℃ of Working environments, and whole surface must adopt coating to wrap up entirely, and traditional preparation process technology all has the point of suppon defect problem.4, bonding strength: because the coefficient of expansion of graphite substrate and SiC there are differences, the SiC coating of traditional technology preparation tends to cracking, causes coating to lose efficacy.5, thermal conduction: because SiC has higher thermal conductivity (120W/mK), so thermal conduction is even fast.
Summary of the invention:
One of purpose of the present invention provide a kind of have complete densification, evenly, full the parcel and the high graphite base of graphite base bonding strength with supercoat; Two of purpose provides this preparation method with graphite base of supercoat.
One of purpose of the present invention can realize by following technical measures:
Graphite base matrix surface exosmosis has elementary SiC coating, at elementary SiC coating external sediment one deck secondary SiC coating is arranged.
Two of purpose of the present invention can realize by following technical measures:
The present invention prepares coat of silicon carbide in conjunction with in-situ chemical gas-phase reaction infiltration+two-step chemical gas-phase deposition at the porous graphite base-plates surface, and concrete preparation method carries out as follows:
A. the graphite base matrix is inserted in the reaction chamber, when reaction chamber temperature is that 1300～1600 ℃, vacuum are under 200～5000Pa condition, according to SiCl
4: H
2=1: 5～50 volume ratios feed SiCl in reaction chamber
4Gas and H
2Gas, hydrogen flowing quantity are 200-1000ml/min, and aeration time is 0.5～2 hour, and the original position gas-phase reaction is permeated the elementary SiC coating of one deck on the graphite base matrix; Then
B. according to CH
3SiCl
3: H
2=1: 5～100 volume ratios feed CH in reaction chamber
3SiCl
3Gas and H
2Gas, control reaction chamber in temperature and pressure constant, hydrogen flowing quantity is 200-1000ml/min, aeration time is 1～50 hour, after the cracking in elementary SiC coatingsurface external sediment one deck secondary SiC coating.
The present invention is at the indoor feeding SiCl of pyroreaction
4Gas and H
2Gas, SiCl
4Pintsch process discharges silicon when being adsorbed onto the graphite base surface, silicon and the direct combination of top layer graphite carbon, thus graphite base is wrapped up, original position forms elementary SiC coating, and the elementary SiC coating that reaction in forms is tied firmly on graphite base; Stop to feed SiCl
4Behind the gas, change feeding CH
3SiCl
3Gas and H
2Gas, CH
3SiCl
3On elementary SiC coating, deposit one deck secondary SiC coating after the cracking.
The present invention compares the SiC coating that adopts prepared of the present invention with background technology, form Chemical bond with graphite base, since graphite surface in advance in-situ chemical reaction prepared the elementary SiC coating of one deck, alleviated the thermal mismatching of direct employing CVD technology when graphite base surface preparation SiC coating, improved bonding strength, coating and graphite base form the combination of Si-C chemical bond, and the bonding strength height is unstressed.Adopt the coat of silicon carbide of the present invention's preparation, all be made up of high-purity beta-SiC, density of material is at 3.20g/cm
3About.This SiC coating graphite base-plates surface densification, smooth, imporosity, high temperature resistant, anti-corrosion, anti-oxidant.The present invention measures composition, structure and the performance of the SiC coating of preparation.As following table:
The performance of table 1 in-situ chemical gas-phase reaction+CVD SiC coating
| Performance class | Crystal formation | Density gcm -3 | Thermal conductivity W/mk | Thermal expansivity (RT) 10 -6·k -1 | Elastic modulus G Pa |
| Performance data | ??β-SiC | ??3.15-3.20 | ??120 | ??4.0 | ??460 |
Description of drawings:
Fig. 1 is the structural representation of the embodiment of the invention, and number in the figure is: 1, graphite base matrix 2, elementary SiC coating 3, secondary SiC coating;
Fig. 2 is the fracture apperance SEM photo of the graphite base of the present invention with supercoat; By the photo of Fig. 2 as can be seen, coating and graphite are in conjunction with very firm, and flawless, primary coating partly are penetrated in the graphite matrix, form " pinning " effect.Secondary SiC coating combines well with elementary SiC coating, middle no interface.
Fig. 3 is the surface topography SEM photo of the sedimentary SiC coating of the present invention;
Fig. 4 is the XRD figure spectrum of the sedimentary SiC coating of the present invention;
The SiC Bulk coat graphite base of the diameter 67mm of Fig. 5 the present invention preparation.
By the photo of Fig. 2 as can be seen: coating and graphite are in conjunction with very firm, and flawless, primary coating partly are penetrated in the graphite matrix, form " pinning " effect; Secondary SiC coating combines well with elementary SiC coating, middle no interface.By the SEM photo of Fig. 3 as can be seen: the coating densification, smooth.XRD figure by Fig. 4 is composed as can be seen: coating all is made up of polycrystal Beta-SiC, does not have other impurity.As seen from Figure 5: Bulk coat is smooth, fine and close, smooth, flawless, has presented the full parcel protection to graphite base.
Embodiment:
Embodiment 1:
A. graphite base matrix 1 is inserted in the reaction chamber that vacuum is 200Pa, when reaction chamber temperature rises to 1600 ℃, according to SiCl
4: H
2=1: 5 volume ratios feed SiCl in reaction chamber
4Gas and H
2Gas utilizes H
2Gas as carrier gas with SiCl
4The band of gas goes out, control carrier gas H
2Airshed is 1000ml/min, and aeration time is 0.5 hour, and the original position gas-phase reaction is permeated the elementary SiC coating 2 of one deck on graphite base matrix 1; Then
B. change into and feed CH
3SiCl
3Gas and H
2Gas is under the situation that temperature and pressure is constant in reaction chamber, according to CH
3SiCl
3: H
2=1: 100 volume ratios feed CH in reaction chamber
3SiCl
3Gas and H
2Gas utilizes H
2Gas as carrier gas with SiCl
4The band of gas goes out to utilize H
2Gas bell is with CH
3SiCl
3The band of gas goes out, control carrier gas H
2Airshed is 200ml/min, and aeration time is 1 hour, in elementary SiC coating 2 surperficial external sediment one deck secondary SiC coatings 3, takes out and is product after the cracking.
Embodiment 2:
A. graphite base matrix 1 is inserted in the reaction chamber that vacuum is 5000Pa, when reaction chamber temperature rises to 1300 ℃, according to SiCl
4: H
2=1: 50 volume ratios feed SiCl in reaction chamber
4Gas and H
2Gas utilizes H
2Gas as carrier gas with SiCl
4The band of gas goes out, control carrier gas H
2Airshed is 200ml/min, and aeration time is 2 hours, and the original position gas-phase reaction is permeated the elementary SiC coating 2 of one deck on graphite base matrix 1; Then
B. change into and feed CH
3SiCl
3Gas and H
2Gas is under the situation that temperature and pressure is constant in reaction chamber, according to CH
3SiCl
3: H
2=1: 5 volume ratios feed CH in reaction chamber
3SiCl
3Gas and H
2Gas utilizes H
2Gas as carrier gas with CH
3SiCl
3The band of gas goes out, control carrier gas H
2Airshed is 1000ml/min, and aeration time is 50 hours, in elementary SiC coating 2 surperficial external sediment one deck secondary SiC coatings 3, takes out and is product after the cracking.
Embodiment 3:
A. graphite base matrix 1 is inserted in the reaction chamber that vacuum is 3000Pa, when reaction chamber temperature rises to 1400 ℃, according to SiCl
4: H
2=1: 30 volume ratios feed SiCl in reaction chamber
4Gas and H
2Gas utilizes H
2Gas as carrier gas with SiCl
4The band of gas goes out, control carrier gas H
2Airshed is 600ml/min, and aeration time is 1 hour, and the original position gas-phase reaction is permeated the elementary SiC coating 2 of one deck on graphite base matrix 1; Then
B. change into and feed CH
3SiCl
3Gas and H
2Gas is under the situation that temperature and pressure is constant in reaction chamber, according to CH
3SiCl
3: H
2=1: 20 volume ratios feed CH in reaction chamber
3SiCl
3Gas and H
2Gas utilizes H
2Gas as carrier gas with CH
3SiCl
3The band of gas goes out, control carrier gas H
2Airshed is 600ml/min, and aeration time is 30 hours, in elementary SiC coating 2 surperficial external sediment one deck secondary SiC coatings 3, takes out and is product after the cracking.
Embodiment 4:
A. graphite base matrix 1 is inserted in the reaction chamber that vacuum is 2000Pa, when reaction chamber temperature rises to 1500 ℃, according to SiCl
4: H
2=1: 20 volume ratios feed SiCl in reaction chamber
4Gas and H
2Gas utilizes H
2Gas as carrier gas with SiCl
4The band of gas goes out, control carrier gas H
2Airshed is 600ml/min, and aeration time is 1.5 hours, and the original position gas-phase reaction is permeated the elementary SiC coating 2 of one deck on graphite base matrix 1; Then
B. change into and feed CH
3SiCl
3Gas and H
2Gas is under the situation that temperature and pressure is constant in reaction chamber, according to CH
3SiCl
3: H
2=1: 30 volume ratios feed CH in reaction chamber
3SiCl
3Gas and H
2Gas utilizes H
2Gas as carrier gas with CH
3SiCl
3The band of gas goes out, control carrier gas H
2Airshed is 600ml/min, and aeration time is 15 hours, and in elementary SiC coating 2 surperficial external sediment one deck secondary SiC coatings 3, taking out and being product is product after the cracking.
Claims (2)
1. the graphite base with supercoat is characterized in that the surperficial exosmosis of graphite base matrix (1) has elementary SiC coating (2), has one deck secondary SiC coating (3) at elementary SiC coating (2) external sediment.
2. preparation method with graphite base of supercoat is characterized in that this preparation method carries out as follows:
A. graphite base matrix (1) is inserted in the reaction chamber, when reaction chamber temperature is that 1300～1600 ℃, vacuum are under 200～5000Pa condition, according to SiCl
4: H
2=1: 5～50 volume ratios feed SiCl in reaction chamber
4Gas and H
2Gas, the control hydrogen flowing quantity is 200-1000ml/min, and aeration time is 0.5～2 hour, and the original position gas-phase reaction goes up the infiltration elementary SiC coating of one deck (2) at graphite base matrix (1); Then
B. according to CH
3SiCl
3: H
2=1: 5～100 volume ratios feed CH in reaction chamber
3SiCl
3Gas and H
2Gas, the control hydrogen flowing quantity is 200-1000ml/min, aeration time is 1～50 hour, after the cracking in elementary SiC coating (2) surperficial external sediment one deck secondary SiC coating (3).
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2010100115100A CN101775590B (en) | 2010-01-08 | 2010-01-08 | Graphite base with protective coating layer and preparation method thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2010100115100A CN101775590B (en) | 2010-01-08 | 2010-01-08 | Graphite base with protective coating layer and preparation method thereof |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN101775590A true CN101775590A (en) | 2010-07-14 |
| CN101775590B CN101775590B (en) | 2011-08-10 |
Family
ID=42512174
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN2010100115100A Expired - Fee Related CN101775590B (en) | 2010-01-08 | 2010-01-08 | Graphite base with protective coating layer and preparation method thereof |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN101775590B (en) |
Cited By (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102277560A (en) * | 2011-08-23 | 2011-12-14 | 南京理工大学 | Method for improving oxidation resistance of graphite electrode by obtaining SiC/C gradient surface coating through chemical vapor deposition |
| CN102850087A (en) * | 2012-09-29 | 2013-01-02 | 西安超码科技有限公司 | Method for preparing silicon carbide coating on graphite surface |
| CN103435367A (en) * | 2013-08-20 | 2013-12-11 | 青岛云路新能源科技有限公司 | Preparation method of antioxidant coating on surface of graphite |
| CN104969332A (en) * | 2013-02-27 | 2015-10-07 | 东洋炭素株式会社 | Susceptor |
| CN106083192A (en) * | 2016-06-08 | 2016-11-09 | 中国人民解放军国防科学技术大学 | There is graphite material of SiC coating and preparation method thereof |
| CN107513698A (en) * | 2017-09-08 | 2017-12-26 | 武汉理工大学 | A kind of preparation method of cubic silicon carbide silicon coating |
| CN108707876A (en) * | 2017-12-27 | 2018-10-26 | 苏州能讯高能半导体有限公司 | A kind of restorative procedure of graphite plate |
| CN109020625A (en) * | 2018-09-03 | 2018-12-18 | 航天特种材料及工艺技术研究所 | A kind of preparation method of antioxidant coating |
| CN111074342A (en) * | 2019-12-27 | 2020-04-28 | 季华实验室 | Method for preparing carrier disc coating by utilizing silicon carbide epitaxial growth equipment |
| CN111118599A (en) * | 2019-12-27 | 2020-05-08 | 季华实验室 | Preparation method of coating for silicon carbide epitaxial growth equipment carrying disc |
| TWI696589B (en) * | 2018-12-21 | 2020-06-21 | 財團法人工業技術研究院 | Graphite mold for glass shaping and manufacturing method of the same |
| CN111410560A (en) * | 2020-04-02 | 2020-07-14 | 江苏嘉明碳素新材料有限公司 | Preparation method of silicified graphite with high-density SiC coating |
| CN111497364A (en) * | 2020-04-02 | 2020-08-07 | 江苏嘉明碳素新材料有限公司 | Silicified graphite with high-compactness layer |
| CN112374912A (en) * | 2020-11-13 | 2021-02-19 | 湖南中科顶立技术创新研究院有限公司 | Preparation method of graphite base with silicon carbide coating |
| CN112624797A (en) * | 2020-12-15 | 2021-04-09 | 湖南德智新材料有限公司 | Graphite surface gradient silicon carbide coating and preparation method thereof |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3925577A (en) * | 1972-11-24 | 1975-12-09 | Westinghouse Electric Corp | Silicon carbide coated graphite members and process for producing the same |
| JP2000319080A (en) * | 1999-05-07 | 2000-11-21 | Tokai Carbon Co Ltd | Graphite member coated with silicon carbide |
| CN1329553C (en) * | 2004-08-31 | 2007-08-01 | 北京科技大学 | Process for preparing large area high quality anti-crack on diamant film |
-
2010
- 2010-01-08 CN CN2010100115100A patent/CN101775590B/en not_active Expired - Fee Related
Cited By (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102277560B (en) * | 2011-08-23 | 2013-07-17 | 南京理工大学 | Method for improving oxidation resistance of graphite electrode by obtaining SiC/C gradient surface coating through chemical vapor deposition |
| CN102277560A (en) * | 2011-08-23 | 2011-12-14 | 南京理工大学 | Method for improving oxidation resistance of graphite electrode by obtaining SiC/C gradient surface coating through chemical vapor deposition |
| CN102850087A (en) * | 2012-09-29 | 2013-01-02 | 西安超码科技有限公司 | Method for preparing silicon carbide coating on graphite surface |
| CN102850087B (en) * | 2012-09-29 | 2014-10-29 | 西安超码科技有限公司 | Method for preparing silicon carbide coating on graphite surface |
| CN104969332A (en) * | 2013-02-27 | 2015-10-07 | 东洋炭素株式会社 | Susceptor |
| CN103435367A (en) * | 2013-08-20 | 2013-12-11 | 青岛云路新能源科技有限公司 | Preparation method of antioxidant coating on surface of graphite |
| CN103435367B (en) * | 2013-08-20 | 2015-10-07 | 青岛云路新能源科技有限公司 | A kind of preparation method of graphite surface oxidation resistant coating |
| CN106083192A (en) * | 2016-06-08 | 2016-11-09 | 中国人民解放军国防科学技术大学 | There is graphite material of SiC coating and preparation method thereof |
| CN107513698B (en) * | 2017-09-08 | 2019-03-08 | 武汉理工大学 | A kind of preparation method of cubic silicon carbide silicon coating |
| CN107513698A (en) * | 2017-09-08 | 2017-12-26 | 武汉理工大学 | A kind of preparation method of cubic silicon carbide silicon coating |
| CN108707876A (en) * | 2017-12-27 | 2018-10-26 | 苏州能讯高能半导体有限公司 | A kind of restorative procedure of graphite plate |
| CN109020625A (en) * | 2018-09-03 | 2018-12-18 | 航天特种材料及工艺技术研究所 | A kind of preparation method of antioxidant coating |
| TWI696589B (en) * | 2018-12-21 | 2020-06-21 | 財團法人工業技術研究院 | Graphite mold for glass shaping and manufacturing method of the same |
| CN111074342A (en) * | 2019-12-27 | 2020-04-28 | 季华实验室 | Method for preparing carrier disc coating by utilizing silicon carbide epitaxial growth equipment |
| CN111118599A (en) * | 2019-12-27 | 2020-05-08 | 季华实验室 | Preparation method of coating for silicon carbide epitaxial growth equipment carrying disc |
| CN111074342B (en) * | 2019-12-27 | 2021-11-09 | 季华实验室 | Method for preparing carrier disc coating by utilizing silicon carbide epitaxial growth equipment |
| CN111410560A (en) * | 2020-04-02 | 2020-07-14 | 江苏嘉明碳素新材料有限公司 | Preparation method of silicified graphite with high-density SiC coating |
| CN111497364A (en) * | 2020-04-02 | 2020-08-07 | 江苏嘉明碳素新材料有限公司 | Silicified graphite with high-compactness layer |
| CN112374912A (en) * | 2020-11-13 | 2021-02-19 | 湖南中科顶立技术创新研究院有限公司 | Preparation method of graphite base with silicon carbide coating |
| CN112624797A (en) * | 2020-12-15 | 2021-04-09 | 湖南德智新材料有限公司 | Graphite surface gradient silicon carbide coating and preparation method thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| CN101775590B (en) | 2011-08-10 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN101775590B (en) | Graphite base with protective coating layer and preparation method thereof | |
| CN102850087B (en) | Method for preparing silicon carbide coating on graphite surface | |
| CN102770582B (en) | Tantalum carbide-coated carbon material and manufacturing method for same | |
| EP2044244B1 (en) | Method of manufacturing substrates having improved carrier lifetimes | |
| CN106757324B (en) | A kind of manufacturing method of silicon epitaxial wafer | |
| CN111029246B (en) | Method for reducing triangular defects in SiC epitaxial layer | |
| CN101798223B (en) | Preparation method of compact silicon carbide ceramic | |
| CN110144567B (en) | Method for preparing super-thick silicon carbide gradient coating on silicon substrate by adopting chemical vapor deposition process | |
| JPH01162326A (en) | Manufacture of beta-silicon carbide layer | |
| JP2015083538A5 (en) | ||
| CN104412362A (en) | Silicon carbide epitaxial wafer, and preparation method thereof | |
| JP2013047181A5 (en) | ||
| CN105244255B (en) | A kind of silicon carbide epitaxy material and its production method | |
| CN104233222B (en) | A kind of method directly growing hexagonal boron nitride two-dimensional film on a si substrate | |
| CN107849730A (en) | Extension 3C SiC are grown on the monosilicon | |
| CN105731825B (en) | A method of preparing aluminium nitride film using Graphene glass low-cost large-area | |
| JP5910430B2 (en) | Method for manufacturing epitaxial silicon carbide wafer | |
| CN104451886A (en) | Preparation method of composite seed tray for growing A1N single crystals by PVT method | |
| CN105525277A (en) | Silicon carbide ceramic boat for plasma enhanced chemical vapor deposition and preparation method thereof | |
| CN105347799A (en) | Preparation method of large-particle-diameter Diamond/SiC composite | |
| KR101936171B1 (en) | Method for fabrication silicon carbide epi wafer and silicon carbide epi wafer | |
| Harris et al. | Growth Characteristics of Alpha‐Silicon Carbide: I. Chemical Vapor Deposition | |
| CN116259534A (en) | Silicon carbide epitaxy method | |
| Liu et al. | Fabrication and characterization of SiC thin films | |
| CN105732044A (en) | High-purity silicon carbide ceramic manufacturing method and ceramic base material |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| C06 | Publication | ||
| PB01 | Publication | ||
| C10 | Entry into substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| C14 | Grant of patent or utility model | ||
| GR01 | Patent grant | ||
| CF01 | Termination of patent right due to non-payment of annual fee |
Granted publication date: 20110810 Termination date: 20210108 |
|
| CF01 | Termination of patent right due to non-payment of annual fee |