IP Library › Granted Patent US 12,345,243
Granted Patent B2
US 12,345,243 · App. 18/238,101 · Granted Jul 1, 2025

Graphite/hexagonal boron nitride bimaterials for electric propulsion

Inventors: Celia S. Chari (Pasadena, CA); Katherine T. Faber (Pasadena, CA); Bryan W. McEnerney (Pasadena, CA); Richard R. Hofer (Pasadena, CA); James A. Wollmershauser (Pasadena, CA); Edward P. Gorzkowski, III (Severna Park, MD)
Assignees: California Institute of Technology; The Government of the United States of America, as represented by the Secretary of the Navy
F03H1/0006C01B32/21B64G1/413
View Patent ↗
Loading inventors, assignments & file history…
Monitor This Case
Get email alerts when status or documents change.
Order Certified Copies
Most orders are placed with the USPTO same day — all within 24 business hours.
Order via The Patent Place →
Pre-filled with this patent's details
Quick Facts
Patent No.
US 12,345,243
App. No.
18/238,101
Granted
Jul 1, 2025
Kind
B2
Abstract

Aspects disclosed herein include graphite and hexagonal boron nitride bimaterials, methods of making these bimaterials, and electric propulsion devices or thrusters with these bimaterials. Aspects disclosed herein include electric propulsion devices comprising: at least one portion comprising or formed of a monolithic bimaterial; wherein the monolithic bimaterial comprises a graphite material and a hexagonal boron nitride material; and wherein the graphite material and hexagonal boron nitride material are monolithically integrated in the bimaterial.

Claims (65)

1. An electric propulsion device comprising:

at least one portion comprising or formed of a monolithic bimaterial;

wherein the monolithic bimaterial comprises a graphite layer material and a hexagonal boron nitride layer ;

wherein the graphite layer and hexagonal boron nitride layer are monolithically integrated in the bimaterial; and

wherein the hexagonal boron nitride layer comprises less than 0.001 mol/cm 3 of boron carbide.

2. The device of claim 1 , wherein the hexagonal boron nitride layer provides a function of being an electrically insulating layer in the electric propulsion device.

3. The device of claim 1 , wherein the hexagonal boron nitride layer electrically isolates:

a first electrically conductive portion or component of the device from a second electrically conductive portion or component,

at least one electrically conductive portion or component of the device from a cathodically-biased portion of the device,

an anodically-biased portion from a cathodically-biased portion of the device;

a portion of an anode or an anodically-biased portion from a magnetic circuit of the device; and/or

a wall of a discharge chamber or a portion of the wall from the magnetic circuit of the device.

4. The device of claim 1 , wherein the hexagonal boron nitride layer electrically isolates the graphite layer from at least one other electrically conductive portion or component of the device.

5. The device of claim 1 comprising a discharge chamber having a plasma maintained therein;

wherein the discharge chamber comprises a wall having a first surface facing the plasma and a second surface opposite the first surface;

wherein at least a portion of a wall of the discharge chamber comprises or is formed of the bimaterial; and

wherein (i) at least a portion of the first surface of the wall comprises the graphite layer such that the graphite layer of the bimaterial faces the plasma and/or ii) at least a portion of the first surface of the wall comprises the hexagonal boron nitride layer such that the hexagonal boron nitride layer of the bimaterial faces the plasma.

6. The device of claim 5 , wherein the hexagonal boron nitride layer undergoes secondary electron emission due to interaction with the plasma within the discharge chamber.

7. The device of claim 5 , wherein at least a portion of the second surface of the wall comprises the hexagonal boron nitride layer.

8. The device of claim 5 , wherein the second surface of the wall comprises the hexagonal boron nitride layer; and wherein the hexagonal boron nitride layer is configured to electrically isolate the graphite layer from an electrically conductive portion of another component of the device.

9. The device of claim 8 , wherein the another component is a magnetic circuit or a portion of the magnetic circuit of the device.

10. The device of claim 5 , wherein the device is characterized as a magnetically shielded conductive wall thruster or wherein the first surface of the wall of the discharge chamber is electrically conductive and the device comprises magnetic shielding to minimize erosion of the wall of the discharge chamber.

11. The device of claim 1 comprising a hollow cathode and wherein a plasma comprises ions of a gaseous propellant.

12. The device of claim 1 being a solar electric propulsion (SEP) device, an ion thruster, a Hall-effect thruster, a gridded ion thruster, a magnetoplasmadynamic (MPD) thruster, any variation thereof, or any combination thereof.

13. The electric propulsion device of claim 1 , wherein a plurality of distinct portions of the electric propulsion device comprises said monolithic bimaterial.

14. The device of claim 1 , wherein:

the bimaterial comprises a first surface formed of the graphite layer and a second surface formed of the hexagonal boron nitride layer, the first surface being opposite of the second surface; or

the bimaterial comprises a first surface formed of the hexagonal boron nitride layer and a second surface formed of the hexagonal boron nitride layer, the first surface being opposite of the second surface, wherein the graphite layer is between the first and second surfaces.

15. The device of claim 1 , wherein the graphite layer and the hexagonal boron nitride layer are connected via a continuous atomic structure;

wherein the graphite layer and the hexagonal boron nitride layer are connected via a monolithic heterointerface; and/or

wherein an interface between the graphite layer and the hexagonal boron nitride layer is coherent or semicoherent.

16. The device of claim 15 , wherein the graphite layer and the hexagonal boron nitride layer are connected via an interface layer therebetween; wherein the interface layer comprises C, B, and N.

17. The device of claim 16 , wherein the interface layer:

comprises a combination of graphite and boron nitride;

has a thickness less than or equal to 100 μm;

is free of oxide materials and carbide compositions or comprises less than 0.005 mol/cm 3 of oxide and carbide compositions; and/or

is free of boron carbide or comprises less than 0.005 mol/cm 3 of boron carbide.

18. The device of claim 1 , wherein the hexagonal boron nitride layer covers or encapsulates at least a portion of the graphite layer such that:

the graphite layer is not in electrical communication with a magnetic circuit of the electric propulsion device; and/or

the graphite layer is not exposed to a propellant gas, a vacuum, air, oxygen gas, or a combination thereof.

19. The device of claim 1 , wherein the hexagonal boron nitride layer:

has a thickness selected from the range of 40 μm to 5000 μm;

is free of oxide and carbide compositions or comprises less than 0.001 mol/cm 3 of oxide and carbide compositions; and/or

has an electrical resistivity greater than or equal to 1·10 14 Ωcm at 25° C.

20. The device of claim 1 , wherein the graphite layer:

has a molar and/or mass purity greater than or equal to 98%;

has an electrical conductivity selected from the range of 400 Ω −1 cm −1 to 3000 Ω −1 cm −1 ;

has a density selected from the range of 1.6 g/cm 3 to 2.26 g/cm 3 ; and/or

has a thickness selected from the range of 0.5 cm to 100 cm.

21. The device of claim 1 , wherein the at least one portion of the device comprising or formed of the monolithic bimaterial has at least one dimension greater than or equal to 1 cm and/or the at least one portion of the electric propulsion device comprising or formed of the monolithic bimaterial has a volume greater than or equal to 0.1 cm 3 .

22. The device of claim 1 , wherein the at least one portion of the electric propulsion device comprising or formed of the monolithic bimaterial is free of macrofractures and microfractures after at least 5 thermal cycles between 25° C. and 250° C. at a rate of 3.75° C./min with 30 minute hold time at 250° C.

23. A method of making a monolithic bimaterial, the method comprising:

converting a portion of a graphite layer into a hexagonal boron nitride layer via a carbothermic reaction;

wherein the monolithic bimaterial comprises the graphite layer and the hexagonal boron nitride layer;

wherein the hexagonal boron nitride layer comprises less than 0.001 mol/cm 3 of boron carbide; and

wherein the carbothermic reaction occurs at a temperature greater than or equal to 1500° C.

24. The electric propulsion device of claim 1 , further comprising:

a cathode;

an anode; and

a discharge chamber containing a plasma of a gaseous propellant;

wherein at least a portion of a wall of the discharge chamber comprises or is formed of the monolithic bimaterial.

25. The electric propulsion device of claim 24 , wherein the anode is an annular anode.

26. The electric propulsion device of claim 24 , wherein the cathode is a hollow cathode.

27. The electric propulsion device of claim 1 , wherein the hexagonal boron nitride layer is free of boron carbide.

28. The method of claim 23 , wherein the hexagonal boron nitride layer is free of boron carbide.

Assignments (3)
ASSIGNMENT OF ASSIGNOR'S INTEREST Recorded Dec 7, 2023
From: GORZKOWSKI, III, EDWARD P.; WOLLMERSHAUSER, JAMES A.
To: THE GOVERNMENT OF THE UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF THE NAVY
Reel/Frame 065803/0378 →
ASSIGNMENT OF ASSIGNOR'S INTEREST Recorded Dec 6, 2023
From: CHARI, CELIA S.; FABER, KATHERINE T.; MCENERNEY, BRYAN W.; HOFER, RICHARD R.
To: CALIFORNIA INSTITUTE OF TECHNOLOGY
Reel/Frame 065779/0085 →
ASSIGNMENT OF ASSIGNOR'S INTEREST Recorded Aug 29, 2023
From: GORZKOWSKI, EDWARD P., III; WOLLMERSHAUSER, JAMES A.
To: THE GOVERNMENT OF THE UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF THE NAVY
Reel/Frame 064738/0323 →
Continuity (2)
Provisional Application 63401226 · Aug 26, 2022
Related Publication 20240068453A1 · Feb 29, 2024
References Cited (65)
US 7624566B1 · Manzella et al. · 2009 [cited by applicant]
US 8143788B2 · Hofer et al. · 2012 [cited by applicant]
US 8407979B1 · Hofer · 2013 [cited by applicant]
US 9591741B2 · Larigaldie · 2017 [cited by applicant]
US 9874202B2 · Goebel et al. · 2018 [cited by applicant]
US 10480493B2 · Hofer et al. · 2019 [cited by applicant]
US 10919649B2 · Conversano et al. · 2021 [cited by applicant]
US 11690161B2 · Daykin-Iliopoulos et al. · 2023 [cited by applicant]
US 20180226217A1 · Martinez · 2018 [cited by examiner]
US 20230136486A1 · Keidar et al. · 2023 [cited by applicant]
US 20230213024A1 · Simmonds et al. · 2023 [cited by applicant]
Alkoy et al. (1997) “Crystallization behavior and characterization of turbostratic boron nitride,” Journal of the European Ceramic Society. 17. 1415-1422. https://doi.org/10.1016/S0955-2219(97)00040-X. [cited by applicant]
Aydoǧdu et al. (2003) “Carbothermic formation of boron nitride,” Journal of the EuropeanCeramic Society. 23(16):3153-3161. https://doi.org/10.1016/S0955-2219(03)00092-X. [cited by applicant]
Bartnitskaya et al. (1993) “Formation of highly disperse boron nitride in carbothermal reduction in the presence lithium compounds,” Powder Metallurgy and Metal Ceramics. 32(1):63-72.https://doi.org/10.1007/BF00559737. [cited by applicant]
Bartnitskaya et al. (1995) “Effect oflithium on structure formation of graphite-like boron nitride with carbothermal synthesis,” Powder Metallurgy and Metal Ceramics. 33(7-8):335-340.https://doi.org/10.1007/BF00559576. [cited by applicant]
Çamurlu et al. (2006) “Role of boron carbide in carbothermic formation ofhexagonal boron nitride,” Journal of Materials Science. 41(15):4921-4927.https://doi.org/10.1007/s10853-006-0339-6. [cited by applicant]
Chari (2023) “Degradation of Ceramic Surfaces and its Mitigation: From Electric Propulsion to Cultural Heritage,” Dissertation (Ph.D.), California Institute of Technology. DOI: 10.7907/22st-q436. [cited by applicant]
Chari et al. (Dec. 2022) “High-temperature carbothermal synthesis and characterization of graphite/h-BN bimaterials,” J Am Ceram Soc., 106, 4, 2225-2239. [cited by applicant]
Chari et al. (Jul. 2022) “Oxidation resistance of AIN/BN via mullite-type Al18B4O33,” Journal ofthe European Ceramic Society. 42(8):3437-3445.https://doi.org/10.1016/j.jeurceramsoc.2022.02.037. [cited by applicant]
Choueiri (2001) “Plasma oscillations in Hall thrusters,” Phys. Plasmas, vol. 8, No. 4, 1411-1426. [cited by applicant]
Combat® (accessed Jul. 25, 2022) “Boron Nitride Solids Product Data Sheet,” (2022). https://www.bn.saint-gobain.com/sites/hps-mac3-cma-boron-nitride/files/2022-06/combat-bn-solids-ds.pdf. [cited by applicant]
Crofton et al. (Dec. 2021) “Low energy Xe + sputter yields for alumina, Hiperco 50, and boron nitride,” American Institute of Physics Advances. 11. 125126. https://doi.org/10.1063/5.0067346. [cited by applicant]
Faber et al. (1981) “Quantitative Studies of Thermal Shock in Ceramics Based on a Novel Test Technique,” Journal of the American Ceramic Society, 64, 5, 296-301. [cited by applicant]
Garnier et al. (1999) “Investigation of xenon ion sputtering of one ceramic material used in SPT discharge chamber,” in: 26th International Electric Propulsion Conference, IEPC Paper 1999-083, Kitakyushu, Japan. [cited by applicant]
Garnier et al. (Nov. 1999) “Low-energy xenon ion sputtering of ceramics investigated for stationary plasma thrusters,” Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films. 17. 3246-3254. https://doi.or… [cited by applicant]
Goebel et al. (2015) “Conducting Wall Hall Thrusters,” IEEE Transactions on Plasma Science. 43. 118-126. https://doi.org/10.1109/TPS.2014.2321110. [cited by applicant]
Guo et al. (Jan. 2023) “Lateral Heterostructures of Graphene and h-BN with Atomic Lattice Coherence and Tunable Rotational Order,” Small, 19, 2207217. [cited by applicant]
Hatta et al. (2003) “High temperature crack sealant based on SiO2—B2O3 for SiC coating on carbon-carbon composites,” Advanced Composite Materials. 12(2-3):93-106. https://doi.org/10.1163/156855103772658498. [cited by applicant]
Hofer (2004) “Development and Characterization of High-Efficiency, High-Specific Impulse Xenon Hall Thrusters”, University of Michigan, Ph.D. Thesis. [cited by applicant]
Hofer et al. (2017) “The H9 Magnetically Shielded HallThruster,” 35th International Electric Propulsion Conference, IEPC-2017-232. Altanta, GA. [cited by applicant]
Hubáček et al. (May 1996) “Chemical reactions in hexagonal boron nitride system,” Journal of SolidState Chemistry. 123:215-222. https://doi.org/10.1006/jssc.1996.0171. [cited by applicant]
Hubáček et al. (Jul. 1996) “High-temperature behaviour of hexagonal boronnitride,” Thermochimica Acta. 282-283:359-367. https://doi.org/10.1016/0040-6031(96)02884-5. [cited by applicant]
Jacobson et al. (1999) “High-Temperature Oxidation of Boron Nitride: I, Monolithic Boron Nitride,” J. Am. Ceram. Soc., 82 [2] 393-98. [cited by applicant]
Johnson-Walls et al. (1985) “Evaluation of Reliability of Brittle Components by Thermal Stress Testing,” J. Am. Ceram. Soc., 68 [7] 363-67. [cited by applicant]
Kleer et al. (1991) “Interface crack resistance of zirconia base thermal barrier coatings,” High performance ceramic films and coatings. 329-328. [cited by applicant]
Lu et al. (1998) “The Thermal Shock Resistance of Solids,” Acta Materialia, 46 13, 4755-68. [cited by applicant]
Mashnitskii et al. (1971) “High-Temperature Graphite Protective Coatings,” Institute of Material Physics Problems of the Academy of Sciences of the Ukrainian SSR. Translated from Ogneupory, No. 11, pp. 41-44. [cited by applicant]
Medvedovski (2018) “Preparation of boron nitride-based coatings through thermal diffusion process,” Advances in Applied Ceramics. 117(4):221-230.https://doi.org/10.1080/17436753.2017.1397938. [cited by applicant]
Mikellides et al. (2014) “Magnetic shielding of a laboratory Hall thruster. I. Theory and validation”, Journal of Applied Physics 115, 043303. [cited by applicant]
O'Connor (1962) “Synthesis of boron nitride,” Journal of the American Chemical Society.84(9): 1753-1754. https://doi.org/10.1021/ja00868a065. [cited by applicant]
Opila et al. (2016) “Borosilicate glass-induced fiber degradation ofSiC/BN/SiC composites exposed in combustion environments,” International Journal of Applied Ceramic Technology. 13(3):434-442. https://doi.org/10.1111/… [cited by applicant]
Parida et al. (Mar. 2022) “Sputtering yield and nanopattern formation study of BNSiO2 (Borosil) at elevated temperature relevance to Hall Effect Thruster,” Nuclear Instruments and Methods in Physics Research Section B: … [cited by applicant]
Park et al. (2017) “Large-scale synthesis of uniformhexagonal boron nitride films by plasma-enhanced atomic layer deposition,” ScientificReports. 7(1):40091. https://doi.org/10.1038/srep40091. [cited by applicant]
Pikalov (1988) “Mechanism of formation of graphitelike boron nitride in the carbothermal process,” Soviet Powder Metallurgy and Metal Ceramics. 27:404-406. [cited by applicant]
Readey (2017) “Chapter 14. Interdiffusion and Metals,” Kinetics in Materials Science and Engineering. Boca Raton, FL: CRC Press, Taylor & Francis Group; 479-517. [cited by applicant]
Satonik et al. (2014) “Effects of plasma exposure on boron nitride ceramic insulators for hall-effect thrusters,” Journal of Propulsion and Power. 30. 656-663. https://doi.org/10.2514/1.B34877. [cited by applicant]
Sawlani (2015) “Effects of Secondary Electron Emission on the Plasma Sheath and Local Electron Energy Distribution with Application to Hall Thrusters,” Dissertation (Ph.D.), University of Michigan. https://hdl.handle.ne… [cited by applicant]
Sheldon et al. (1996) “Oxidation of BN-coated SiC fibers in ceramic matrix composites,” Journal of the American Ceramic Society. 79(2):539-543.https://doi.org/10.1111/j.1151-2916.1996.tb08163.x. [cited by applicant]
Solozhenko et al. (1999) “Refined phase diagram of boron nitride,” TheJournal of Physical Chemistry B. 103(15):2903-2905.https://doi.org/10.1021/jp984682c. [cited by applicant]
Song et al. (2010) “Large scale growth and characterization of atomic hexagonalboron nitride layers,” Nano Letters. 10(8):3209-3215.https://doi.org/10.1021/nl1022139. [cited by applicant]
Tartz et al. (2009) “Measuring sputter yields of ceramic materials,” in: 31st International Electric Propulsion Conference, IEPC Paper 2009-240, Ann Arbor, Michigan, USA. [cited by applicant]
Thomas et al. (1963) “Turbostratic boron nitride, thermal transformation toordered-layer-lattice boron nitride,” Journal of the American Chemical Society. 84(24):4619-4622. https://doi.org/10.1021/ja00883a001. [cited by applicant]
Tondu et al. (2011) “Sputtering yield of potential ceramics for hall effect thruster discharge channel,” in: 32nd International Electric Propulsion Conference, IEPC Paper 2011-106, Wiesbaden, Germany. [cited by applicant]
Uberuaga et al. (2019) “Semicoherent oxide heterointerfaces: Structure, properties, and implications,” APL Mater. 7, 100904. [cited by applicant]
Wakasugi et al. (Apr. 1991) “The solubilities of BN in B203 bearing melts,” Journal of Non-Crystalline Solids, 135, 139-145. [cited by applicant]
Wakasugi et al. (Jul. 1991) “Thermodynamics of Nitrogen in B2O3, B203—Si02, and B203—CaO Systems,” J. Am Cerorn SOC., 74 [ 7 ] 1650-53. [cited by applicant]
Xiaowei et al. (2004) “Effect of temperature on graphite oxidation behavior,” Nuclear Engineering and Design. 227(3):273-280.https://doi.org/10.1016/j.nucengdes.2003.11.004. [cited by applicant]
Yates et al. (1975) “The anisotropic thermal expansion of boron nitride,” The Philosophical Magazine: A Journal of Theoretical Experimental and Applied Physics.32(4):847-857. https://doi.org/10.1080/14786437508221624. [cited by applicant]
Yim (2017) “A survey of xenon ion sputter yield data and fits relevant to electric propulsion spacecraft integration,” in: 35th International Electric Propulsion Conference, IEPC Paper 2017-060, Atlanta, Georgia, USA. [cited by applicant]
Yim et al. (2008) “Modeling low energy sputtering of hexagonal boron nitride by xenon ions,” Journal of Applied Physics. 104. 123507. https://doi.org/10.1063/1.2987090. [cited by applicant]
Yoon et al. (1995) “Vapour-phase reduction and the synthesis of boronbased ceramic phases,” Journal of Materials Science, 30, 607-614. [cited by applicant]
Yoon et al. (1996) “Vapour-phase reduction and the synthesis of boron-based ceramic phases,” Journal of Materials Science, 31, 2265-2277. [cited by applicant]
Zhang et al. (2019) “Preparation and anisotropic properties of textured structuralceramics: A review,” Journal of Advanced Ceramics. 8(3):289-332.https://doi.org/10.1007/s40145-019-0325-5. [cited by applicant]
Zhang et al. (May 2021) “Experiment and simulation analysis on thermal shock resistance of laminated ceramics with graphite and boron nitride interfaces,” CeramicsInternational. 47(9):11973-11978. https://doi.org/10.101… [cited by applicant]
Zidar et al. (2012) “Hall-effect thruster channel surface properties investigation,” Journal of Propulsion and Power. 28. 334-343. https://doi.org/10.2514/1.B34312. [cited by applicant]