SPACECRAFT, COATING AND METHOD

Abstract

A spacecraft, for example a satellite, or a part thereof having a coating comprising a 2D material on an outer surface thereof is described. The 2D material comprises one or more elements, excluding C, N and S, in an amount of at least 50 at. %; and respective oxides of the one or more elements of the 2D material have a vapour pressure of at most 10 Pa at a temperature of 323 K.

Claims

1. A spacecraft or a part thereof having a coating comprising a 2D material on an outer surface thereof, wherein the 2D material comprises one or more elements, excluding C, N and S, in an amount of at least 50 at. %; and wherein respective oxides of the one or more elements of the 2D material have a vapour pressure of at most 10 Pa at a temperature of 323 K.

2. The spacecraft or a part thereof according to claim 1, wherein the 2D material comprises the one or more elements, excluding C, N and S, in an amount of at least 66 at. %.

3. The spacecraft or a part thereof according to claim 1, wherein the 2D material is a transition metal dichalcogenide, TMD, having a chemical formula MX2, wherein M is a transition metal and X is a chalcogen.

4. The spacecraft or a part thereof according to claim 3, wherein X is Se or Te.

5. The spacecraft or a part thereof according claim 3, wherein M is a group 5 transition metal or a group 6 transition metal.

6. The spacecraft or a part thereof according to claim 4, wherein the TMD is MoSe.sub.2, WSe2 or NbSe.sub.2, preferably MoSe.sub.2 or WSe2.

7. The spacecraft or a part thereof according to claim 1, wherein the 2D material comprises flakes thereof, having a dimension, transverse to a thickness thereof, in a range from 5 nm to 390 nm, preferably in a range from 10 nm to 200 nm, more preferably in a range from 15 nm to 100 nm.

8. The spacecraft a or a part thereof according to claim 7, wherein the coating has a roughness average R_a in a range from 0 nm to 50 nm, preferably in a range from 10 nm to 40 nm, more preferably in a range from 15 nm to 35 nm.

9. (canceled)

10. A method of protecting, at least in part, a spacecraft, for example a satellite such as a Very Low Earth Orbit, VLEO, satellite, or a part thereof according to claim 1, the method comprising: exposing the coating to atomic oxygen incident thereupon, reacting the one or more elements of the 2D material with the atomic oxygen and producing respective oxides of the one or more elements.

11. A method of providing a coating on a substrate for a spacecraft, for example a satellite, or a part thereof, the method comprising: providing a 2D material, for example by liquid phase exfoliation, LPE; and depositing the 2D material on the substrate, for example by electrophoretic deposition, EPD, thereby providing the coating on the substrate; optionally wherein the 2D material is a transition metal dichalcogenide, TMD, having a chemical formula MX2, wherein M is a transition metal, preferably a second row or a third row transition metal, and X is a chalcogen.

12. The method according to claim 11, wherein providing the 2D material by LPE comprises dispersing a 2D material precursor in a liquid phase, exfoliating the 2D material precursor dispersed in the liquid phase, for example by sonication, and purifying the exfoliated 2D material, for example by centrifugation, thereby providing the 2D material.

13. The method according to claim 12, wherein exfoliating the 2D material precursor dispersed in the liquid phase by sonication comprises sonicating the 2D material precursor dispersed in the liquid phase at a power in a range from 25 W to 1 kW, preferably in a range from 50 W to 500 W, more preferably in a range from 75 W to 150 W, for example 100 W, 110 W or 120 W for 1 g of the 2D material precursor dispersed in 100 ml of the liquid phase, optionally at a frequency in a range from 20 kHz to 1174 kHz, preferably in a range from 25 kHz to 100 kHz, more preferably in a range from 30 kHz to 50 kHz, for example 35 kHz, 37 kHz or 40 kHz, optionally for a duration in a range from 0.5 hours to 12 hours, preferably in a range from 2 hours to 6 hours, for example 4 hours, optionally at a temperature in a range from 283 K to 313 K, preferably in a range from 288 K to 303 K.

14. The method according to claim 11, wherein the 2D material comprises flakes thereof, having a dimension, transverse to a thickness thereof, in a range from 5 nm to 390 nm, preferably in a range from 10 nm to 200 nm, more preferably in a range from 15 nm to 100 nm.

15. The method according to claim 11, wherein depositing the 2D material on the substrate by EPD comprises preparing a suspension of the 2D material, immersing the substrate in the suspension and applying a voltage in a range between 5 V and 30 V, preferably between 10 V and 20 V between the immersed substrate and a counter electrode.

16. The method according to claim 15, wherein applying the voltage comprises applying the voltage for a duration in a range from 0.5 hours to 6 hours, preferably in a range from 1 hour to 3 hours.

17. (canceled)

18. The spacecraft or a part thereof according to claim 1, wherein the spacecraft is a satellite.

19. The spacecraft or a part thereof according to claim 2, wherein the 2D material comprises the one or more elements, excluding C, N and S, in an amount of at least 75 at.%.

20. The spacecraft or a part thereof according to claim 3, wherein M is a second row or a third row transition metal.

21. The spacecraft or a part thereof according to claim 4, wherein M is Nb or Ta.

22. The spacecraft or a part thereof according to claim 4, wherein M is Mo or W.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0170] For a better understanding of the invention, and to show how exemplary embodiments of the same may be brought into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:

[0171] FIG. 1 schematically depicts the upper and lower altitudes (dashed black times) that define VLEO. How atmospheric density varies with altitude at high (purple line) and low (gold line) solar flux is also displayed. Finally, the percentage contributions of the four major components of the LEO atmosphere, He (green), 0 (pale blue), N.sub.2 (dark blue) and O.sub.2 (red) to the overall atmospheric density, as a function of altitude are displayed in the graph background. Data used to generate this figure are representative and were obtained from the NRLMSISE model.

[0172] FIG. 2 schematically depicts elastic specular (left) and thermal diffuse (right) reemission patterns for a nominal one-sided flat plate geometry, wherein v.sub.i and v.sub.r are the incident and re-emitted particle velocities, .sub.i and .sub.r the corresponding incidence angles with respect to the surface normal n, and D and L are representative drag and lift forces.

[0173] FIG. 3 schematically depicts drag and lift coefficients as a function of incidence angle derived from the Schaaf and Chambre GSI model for a one-sided flat panel. Fully diffuse and complete specular reflection cases presented.

[0174] FIG. 4 schematically depicts the interaction potential /eV (blue curve) experienced by an O(.sup.3P) (red sphere) as a function of the distance r/ from the surface of a satellite (grey cuboid).The attractive regime is defined as the range of distances for which the interaction potential is <0; the repulsive regime is defined as the range of distances for which the interaction potential is >0.

[0175] FIG. 5 schematically depicts drag (top curve) and lift (bottom curve) coefficients as a function of incidence gas particle mass derived from Sentman's equations for a one-sided flat panel at three different incidence angles .

[0176] FIG. 6 schematically represents monoatomic reaction steps (left) and diatomic reaction steps (right). A: Chemisorption; B: Physisorption; C: Desorption; D: Surface diffusion; E: Surface diffusion to an active site; F: Langmuir-Hinshelwood recombination; and G: Eley-Rideal recombination. O(3P) atoms are represented by blue spheres, the surface by the grey cuboid and defect sites on the surface by the pair of X.

[0177] FIG. 7 schematically depicts a process of LPE.

[0178] FIG. 8 schematically depicts a process of EPD.

[0179] FIG. 9 shows particle size distributions, obtained by DLS, for 2D materials according to exemplary embodiments.

[0180] FIG. 10 shows particle size distributions, obtained by DLS, for 2D materials according to exemplary embodiments.

[0181] FIG. 11 shows particle size distributions, obtained by DLS, for 2D materials according to exemplary embodiments.

[0182] FIG. 12 shows particle size distributions, obtained by DLS, for 2D materials according to exemplary embodiments.

[0183] FIG. 13 shows Raman shift for 10V 1 h deposition, for 2D materials according to exemplary embodiments.

[0184] FIG. 14 shows Raman microscope images for 10V 1 h deposition, for 2D materials according to exemplary embodiments.

[0185] FIGS. 15A to 15D show AFM images for 10V 1 h deposition, for 2D materials according to exemplary embodiments.

[0186] FIGS. 16A to 16D show SEM EDS data for 10V 1 h deposition, for 2D materials according to exemplary embodiments.

[0187] FIG. 17 show EDS spectra for 10V 1 h deposition, for 2D materials according to exemplary embodiments.

[0188] FIGS. 18A to 18B show Raman shift and Raman microscope images for 10V 2 h deposition, for 2D materials according to exemplary embodiments.

[0189] FIGS. 19A to 19D show AFM images for 10V 2 h deposition, for 2D materials according to exemplary embodiments.

[0190] FIGS. 20A to 20B show SEM EDS data for 10V 2 h deposition, for 2D materials according to exemplary embodiments.

[0191] FIGS. 21A to 21B show Raman shift and Raman microscope images for 10V 3 h deposition, for 2D materials according to exemplary embodiments.

[0192] FIGS. 22A to 22D show AFM images for 10V 3 h deposition, for 2D materials according to exemplary embodiments.

[0193] FIGS. 23A to 23B show SEM EDS data for 10V 3 h deposition, for 2D materials according to exemplary embodiments.

[0194] FIGS. 24A to 24B show Raman shift and Raman microscope images for 15V 1 h deposition, for 2D materials according to exemplary embodiments.

[0195] FIGS. 25A to 25D show AFM images for 15V 1 h deposition, for 2D materials according to exemplary embodiments.

[0196] FIGS. 26A to 26B show Raman shift and Raman microscope images for 20V 1 h deposition, for 2D materials according to exemplary embodiments.

[0197] FIGS. 27A to 27D show AFM images for 20V 1 h deposition, for 2D materials according to exemplary embodiments.

[0198] FIGS. 28A to 28B show Raman shift and Raman microscope images for 10V 1 h deposition after baking, for 2D materials according to exemplary embodiments.

[0199] FIGS. 29A to 29D show AFM images for 10V 1 h deposition after baking, for 2D materials according to exemplary embodiments.

[0200] FIGS. 30A to 30E show SEM EDS data for 10V 1 h deposition after baking, for 2D materials according to exemplary embodiments.

DETAILED DESCRIPTION OF THE DRAWINGS

[0201] Materials and Chemicals

[0202] All the materials and chemicals in this experiment were commercially provided and used without further purification: Boron Nitride, 99.5% (metals basis) 325 mesh powder (Alfa Aesar). Molybdenum (IV) selenide, 99.9% trace metals basis, 325 mesh (Aldrich). Tungsten (IV) selenide, 99.8% metals basis, 10-20 m powder (Alfa Aesar). Niobium selenide, 99.8% metal basis, 5 m powder (Alfa Aesar). IPA, 2-propanol, 99.5% (GC), (Sigma-Aldrich). Indium tin oxide coated PET, surface resistivity 600/sq.

[0203] Exfoliation

[0204] In this study, there are four materials to be exfoliated.

[0205] In general, 1 g molybdenum diselenide, tungsten diselenide, niobium diselenide or Hexagonal Boron Nitride was weighed then added into 100 ml IPA. Suspensions were put in the sonication bath set at 50% power output (100% power output is 220 W effective ultrasonic power, 880 W peak ultrasonic power) and 37 kHz to sonicate for 4 hours, after which a pipette was used to transfer the supernatant into centrifugation tubes, which was then centrifuged twice at 4500 rpm for 30 min. After each centrifugation cycle, the supernatant was separated from sedimented material and added to fresh centrifugation tubes for the next centrifugation cycle or for electrophoretic deposition. During all sonications, water bath temperature was controlled by flowing 5 C. water through a cooling coil submerged in the bath. Typical measured bath temperatures during sonication were 23-51 C. Other sonication conditions attempted, including increasing sonicator power output to 70%, decreasing precursor concentration to 0.5 g per 100 ml and allowing the sonication bath to run uncooled. Although these modified conditions did produce exfoliated flake suspensions, these suspensions were less suitable for electrophoretic deposition and were not carried forward.

[0206] Deposition

[0207] Both applied voltage and deposition time influence electrophoretic deposition. Therefore, several different combinations of applied voltage and deposition time were attempted, namely: 10V 1 h, 10V2 h, 10V3 h, 15V1 h, 20V1 h.

[0208] For electrophoretic deposition, two pieces of ITO-coated PET films of approximate dimensions 5 cm by 8 cm were used as the anode and cathode. These two sheets were placed parallel in a beaker with the ITO surfaces face to face, separated by approximately 1 cm. To the top of each sheet was attached a clip to allow electrical connection to a power supply. The 2D material suspension was then added into the beaker, with the submerged area of each sheet being approximately 5 cm by 7 cm.

[0209] Characterization

[0210] DLS measurements were conducted using a Zetasizer Nano-S(Malvern Instrument, UK) operated according to manufacturer's instructions.

[0211] SEM EDS was performed using a tandem FEI Quanta 250 (Environmental) Scanning Electron Microscope. AFM was performed using a Multimode 8 Atomic Force Microscope (Bruker, USA) with PeakForce QNM mode with ScanAssyst activated. MPP-21100-10 Sb (n) doped Si cantilevers were used. Confocal Raman spectroscopy was used to test 10 accumulations per 10 s. Instruments were operated according to manufacturers' instructions.

[0212] Results & Discussion

[0213] Results of Dispersion

[0214] Dynamic light scattering (DLS) was used to characterise the particle size of the exfoliated flake dispersions, reported below as hydrodynamic diameter.

[0215] As we can see in FIG. 9 the particle size of WSe.sub.2 and MoSe.sub.2 are on average 10 nm and 60 nm respectively, whilst NbSe.sub.2 exhibits a larger particle size at about 400 nm. The particle size of hBN is not given here since because the particle size of hBN was too large for DLS to measure reliably.

[0216] Electrophoretic Deposition Results

[0217] Electrophoretic deposition was conducted by applying a fixed voltage between the ITO-coated PET sheets for the required deposition time, After electrophoresis, the ITO-coated PET electrode onto which deposition had occurred was removed from the suspension, had drops of residual solvent blown away with a stream of nitrogen gas and allowed to dry in ambient air, After the process of deposition, Raman, AFM and SEM-EDS were used to ensure the presence of the materials on the ITO coated PET and to assess the quality of the coatings.

[0218] Several deposition times and voltages were applied to optimise the coating.

[0219] Deposition Conditions: 10 V 1 h

[0220] For the deposition at 10V for 1 h, Raman spectroscopy reveals the following peaks: By comparison to the Raman spectra of MoSe.sub.2 from literature [66], the peak between 238 and 246 cm.sup.1 is the range of MoSe.sub.2, and the peak of 241 cm.sup.1 represents the MoSe.sub.2. The WSe.sub.2 shows a peak at 255 cm.sup.1 and there is a wide peak at 373 cm.sup.1. According to the literature, the wide peak is probably due to Raman insensitivity for WSe.sub.2 or the bond of WO, which suggests WSe.sub.2 has been partially oxidised.

[0221] In the Raman spectra of hBN, there is a significant peak at 1363 cm.sup.1, which is the evidence of the existence of hBN flakes with the significant intensity suggesting the concentration on the surface is high.

[0222] For NbSe.sub.2, a minor peak is observed at 239 cm.sup.1, consistent with the E.sub.g.sup.1 mode. Low intensity of peaks from NbSe.sub.2 suggests the concentration is low. The other peaks not mentioned are characteristic peaks of PET.

[0223] Under conditions of 10V and 1 h, Raman shift shows confirms the existence of the deposited 2D materials.

[0224] FIG. 14 shows that that MoSe.sub.2 and WSe.sub.2 are evenly dispersed across the surface but NbSe.sub.2 and hBN contain large particles and the sample looks patchy.

[0225] FIGS. 15A to 15D show AFM images for 10V 1 h deposition.

TABLE-US-00001 TABLE 1 Sample roughness. Material Roughness R.sub.a (nm) MoSe.sub.2 15.4 WSe.sub.2 20.2

[0226] To estimate the step height of deposited flakes, line scans were extracted at three points in each image showing typical step heights.

[0227] The R.sub.a roughness of MoSe.sub.2 and WSe.sub.2 are 15.4 nm and 20.2 nm respectively. However, overall image R.sub.a roughness will be not be representative of the surface roughness experienced by impinging gas molecules, since coatings of deposited flakes will consist of flat plateaus on a flat background, with flake edge step height changes contributing to an apparently high R.sub.a roughness value (i.e. R.sub.a is expected to be high for a patchy deposition, such as where the flakes are not deposited uniformly, including regions having a single flake thickness deposited thereupon, some regions having no flakes deposited thereupon and some other regions including stacks of deposited flakes). That is, the impinged surfaces are atomically flat, even if the flakes are not uniformly deposited.

[0228] SEM EDS helps us analyze the surface of material and the elemental composition. From FIGS. 16A to 16D we can see the morphology and surface elemental maps of four materials. If can be seen that hBN and NbSe.sub.2 are patchy whereas MoSe.sub.2 and WSe.sub.2 are deposited evenly.

TABLE-US-00002 TABLE 2 Elemental composition ratio. MoSe.sub.2 WSe.sub.2 NbSe.sub.2 hBN Mo: 0.5 W: 1.6 Nb: 0.1 B: 2.4 Se: 0.9 Se: 1.2 Se: 0.2 N: 2.1

[0229] From Table 2 and FIGS. 16A to 16D, for MoSe.sub.2, NbSe.sub.2 and hBN, the elemental ratios are around the expected 1:2 or 1:1. For WSe.sub.2, the elemental ratio is not 1:2. The assumption is the materials experience oxidation, as the WO peak broadens at 300-400 cm.sup.1.

[0230] Deposition Conditions: 10V 2 h

[0231] FIGS. 18A and 18B show Raman shift and Raman microscope images for 10V 2 h deposition, for 2D materials according to exemplary embodiments. WSe.sub.2 and MoSe.sub.2 show a good deposition, the peak of WSe.sub.2 is at 250 cm.sup.1 and MoSe.sub.2 is at 241 cm.sup.1. There are wide peaks around 280 cm.sup.1 which still need to be identified. There is a small signal of NbSe.sub.2 at 238 cm.sup.1 and the intensity is weak. It can be seen that at 1364 cm.sup.1 is the peak of hBN. FIG. 18B shows the uniformity of coating. From the image of NbSe.sub.2 is clear that the material is patchy and that hBN deposits poorly, possibly in large chunks.

[0232] FIGS. 19A to 19D show AFM images and line scans for 10V 2 h deposition. The height range of MoSe.sub.2 and WSe.sub.2 are 254 nm and 209.3 nm respectively. These images further confirm that hBN deposits poorly. Roughness data is shown below in Table 3, again noting that R.sub.a roughness is expected for be high for a patchy deposition.

TABLE-US-00003 TABLE 3 Sample roughness. Material Roughness R.sub.a (nm) MoSe.sub.2 25.8 WSe.sub.2 22.7

[0233] FIGS. 20A to 20B show SEM EDS data for MoSe.sub.2.

TABLE-US-00004 TABLE 4 Elemental composition ratio. MoSe.sub.2 Mo: 1.9 Se: 2.6

[0234] From FIGS. 20A to 20B and Table 4 we can find that the ratio of MoSe.sub.2 is close to 1:2, with the flakes being spread evenly across the surface. It was not possible to gather SEM measurements of other coatings under these deposition conditions.

[0235] Deposition Conditions: 10V 3 h

[0236] FIGS. 21A and 21B show Raman shift and Raman microscope images for 10V 3 h deposition, for 2D materials according to exemplary embodiments. WSe.sub.2 and MoSe.sub.2 show peaks at 250 cm.sup.1 and 241 cm.sup.1 respectively, the peak of hBN is at 1364 cm.sup.1, with all results similar to deposition at 10V 1 h. The intensity of hBN and NbSe.sub.2 are weak suggesting low concentration for the deposition.

[0237] FIGS. 22A to 22D show AFM images and typical line traces for 10V 3 h deposition, for 2D materials according to exemplary embodiments, with Table 5 showing R.sub.a roughness values.

TABLE-US-00005 TABLE 5 Sample roughness. Material Roughness R.sub.a (nm) MoSe.sub.2 33.4 WSe.sub.2 22.8

TABLE-US-00006 TABLE 6 Elemental composition ratio. MoSe.sub.2 WSe.sub.2 Mo: 2.6 W: 11 Se: 4.0 Se: 8.9

[0238] From FIGS. 23A to 23B and Table 6, the ratio of MoSe.sub.2 and WSe.sub.2 are close to the ratio of 1:2. NbSe.sub.2 and hBN were not able to be measured by SEM EDS under these conditions. Based on the results of 10V 1 hour, another attempt was made applying higher voltage to provide a greater electric field and so more electrophoretic force to move the nanoparticles. So, we choose 15V and 20V as the test voltage since high voltage may cause oxidation.

[0239] Deposition Conditions: 15 V 1 h

[0240] FIGS. 24A to 24B show Raman shift and Raman microscope images for 15V 1 h deposition, for 2D materials according to exemplary embodiments. It can be seen from the diagram that for MoSe.sub.2 and WSe.sub.2 the peaks at 241 cm.sup.1 and 252 cm.sup.1 in order, with intensity similar to deposition at 10V 1 h. The peaks of hBN and NbSe.sub.2 are 1364 cm.sup.1 and 280 cm.sup.1 respectively. The intensity of hBN and NbSe.sub.2 peaks are weak suggesting the concentrations are low. As can be seen from the microscope pictures, MoSe.sub.2 and WSe.sub.2 show even deposition. However, NbSe.sub.2 and hBN coatings are still patchy.

[0241] FIGS. 25A to 25D show AFM images and typical line scans for 15V 1 h deposition, for 2D materials according to exemplary embodiments.

TABLE-US-00007 TABLE 7 Sample roughness. Material Roughness R.sub.a (nm) MoSe.sub.2 35.1 WSe.sub.2 23.2

[0242] Deposition Conditions: 20V 1 h

[0243] FIGS. 26A to 26B show Raman shift and Raman microscope images for 20V 1 h deposition, for 2D materials according to exemplary embodiments. The peak of WSe.sub.2 and MoSe.sub.2 are 252 cm.sup.1 and 241 cm.sup.1 respectively. The identity of the peak between 284 cm.sup.1 and 304 cm.sup.1 for MoSe.sub.2 still needs further confirmation, but is not thought to be due to oxidation. The microscope pictures show the MoSe.sub.2 and WSe.sub.2 have good deposition. Compare to 10V, 1 h, hBN does not show a good deposition since the material is highly patchy.

[0244] FIGS. 27A to 27D show AFM images and line scans for 20V 1 h deposition, for 2D materials according to exemplary embodiments.

TABLE-US-00008 TABLE 8 Sample roughness. Material Roughness R.sub.a (nm) MoSe.sub.2 36.6 WSe.sub.2 21.4

[0245] Post-Deposition Bake

[0246] To predict the statues of coatings after suffering space environment, we use a vacuum thermal chamber to test the coatings. Due to the time limitation, we only test the 10V 1 h sample.

[0247] Table 9 shows the maximum temperature (1) and minimum pressure (2) in the vacuum chamber when simulating the space environment.

TABLE-US-00009 TABLE 9 Pressures and temperatures in vacuum chamber. Current Temperature Pressure (mbar) (A) ( C.) 1 5.77 10.sup.7 1.152 101.2 2 9.38 10.sup.7 0.902 23

[0248] These temperature data attempt to simulate part of space temperature and pressure, meanwhile, it can clean the surface of the coatings for the further research.

[0249] Raman, AFM, SEM EDS were used to characterize the coatings again after this thermal vacuum bake out.

[0250] FIGS. 28A to 28B show Raman shift and Raman microscope images for 10V 1 h deposition after baking, for 2D materials according to exemplary embodiments. After the testing, these materials show stable properties and very similar morphology to that before baking. FIGS. 29A to 29D show AFM images and line scans for 10V 1 h deposition after baking, for 2D materials according to exemplary embodiments.

TABLE-US-00010 TABLE 10 Sample roughness. Material Roughness R.sub.a (nm) MoSe.sub.2 17.4 WSe.sub.2 21.6

[0251] FIGS. 23A to 30E show SEM EDS data for 10V 1 h deposition after baking, for 2D materials according to exemplary embodiments.

TABLE-US-00011 TABLE 11 Elemental composition ratio. MoSe.sub.2 WSe.sub.2 NbSe.sub.2 hBN Mo: 0.8 W: 2.2 Nb: 0.2 B: 3.1 Se: 1.8 Se: 1.7 Se: 0.2 N: 2.1

[0252] The MoSe.sub.2 is roughly close to the 1:2, whereas other samples show unexpected element ratios. Raman spectra show no unexpected features. The effect of low pressure baking on these coatings needs to be further studied.

Results Summary

[0253] In summary, among all these deposition conditions, MoSe.sub.2 and WSe.sub.2 show consistency good coating results, but NbSe.sub.2 and hBN are inconsistent, with hBN typically producing poor coatings. A possible reason is that hBN and NbSe.sub.2 have large particle size that are a result of incomplete exfoliatation.

[0254] The most likely condition to produce best quality deposition by electrophoretic is under 10V 3 hours from 50% power 1 g/100 ml dispersion.

[0255] Although a preferred embodiment has been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims and as described above.

SUMMARY

[0256] In order to realize the significant commercial desire for sustained satellite operation in VLEO, improved coating materials capable of minimizing atmospheric drag or improving aerodynamic lift production are a necessity. Such materials will need to combine both excellent atomic oxygen erosion resistance properties and atomic oxygen reflection properties. The fundamental material properties necessary to achieve these aims have been discussed in detail and the significant body of literature on the utilization of oxides in various forms as coatings to protect against erosion by atomic oxygen has been reviewed. The lack of significant literature into the atomic oxygen reflection properties of these coating materials is notable. Particularly as the limited results that have been obtained have led to the identification of layered van der Waals materials as the ideal surface structure for obtaining excellent atomic reflection properties. Despite their phenomenal atomic reflection properties, carbon based graphitic materials would appear to not be suitable for use in VLEO due to their well characterized chemical reactions with atomic oxygen, producing volatile oxide products that lead to the significant erosion and roughening of these materials. In comparison, hBN and MoSe.sub.2 have shown initial promise in combining the excellent atomic oxygen reflection properties of graphene with improved erosion resistance, whilst more novel, and as yet uninvestigated 2D materials may show even better performance.

[0257] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0258] All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at most some of such features and/or steps are mutually exclusive.

[0259] Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0260] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.