Ceramic composite and production method thereof

Abstract

A black ceramic composite coating is presented. The ceramic composite coating comprises a ceramic matrix having embedded therein carbide nanoparticles (in particular metal carbide nanoparticles) and/or metal-carbon composite nanoparticles (with separate metal and carbon phases) embedded therein. The carbide nanoparticles are metastable and the metal-carbon composite nanoparticles are decay products of the metastable carbide nanoparticles. A further aspect of the invention relates to producing such a ceramic composite coating.

Claims

1. A black ceramic composite coating with a surface having a total hemispherical reflectivity of no more than 5% over the entire wavelength range from 400 nm to 1 m and for any incidence angle greater than 20, comprising a ceramic matrix distinct from a carbide matrix, wherein said ceramic matrix has at least one of carbide nanoparticles and metal-carbon composite nanoparticles embedded therein, the at least on of carbide nanoparticles and metal-carbon composite nanoparticles having an average size in the range from 5 to 500 nm, wherein said carbide nanoparticles are metastable and wherein said metal-carbon composite nanoparticles are decay products of the metastable carbide nanoparticles.

2. The ceramic composite coating as claimed in claim 1, wherein said ceramic matrix has metal-carbon composite nanoparticles embedded therein, said metal-carbon composite nanoparticles comprising metal cores with carbon shells.

3. The ceramic composite coating as claimed in claim 1, wherein said ceramic matrix is a metal oxide matrix.

4. The ceramic composite coating as claimed in claim 3, wherein said metal oxide matrix consists of an oxide selected from the group consisting of: VO.sub.2, Al.sub.2O.sub.3, SiO.sub.2, MgO, TiO.sub.2, ZrO.sub.2, Mn.sub.3O.sub.4, SnO.sub.2, ZnO, spinel having the general formula AB.sub.2O.sub.3 with A and B being metal cations having different valences, perovskite having the general formula ABO.sub.3 with A and B being differently sized metal cations, and mixtures thereof.

5. The ceramic composite coating as claimed in claim 1, wherein said carbide nanoparticles consist of carbides of metals selected from the group consisting of: Ni, Co, Fe, Cr, Mo, Pt, Pd, and mixtures thereof.

6. The ceramic composite coating as claimed in claim 5, wherein the density of said at least one of the carbide nanoparticles and the metal-carbon composite nanoparticles in said matrix is non-uniform across the thickness of the ceramic composite coating.

7. A method of producing a ceramic composite coating by chemical vapour deposition, the ceramic composite coating being a black ceramic composite coating with a surface having a total hemispherical reflectivity of no more than 5% over the entire wavelength range from 400 nm to 1 m and for any incidence angle greater than 20, comprising a ceramic matrix distinct from a carbide matrix, the ceramic matrix having at least one of carbide nanoparticles and metal-carbon composite nanoparticles embedded therein, the at least one of carbide nanoparticles and metal-carbon composite nanoparticles having an average size in the range from 5 to 500 nm, said carbide nanoparticles being metastable and said metal-carbon composite nanoparticles being decay products of the metastable carbide nanoparticles, said method comprising: introducing at least one first precursor for depositing the ceramic matrix into a reaction chamber; introducing second precursors for depositing the carbide nanoparticles into the reaction chamber, the second precursors comprising an inorganic, metalorganic or organometallic precursor and at least one of an alcohol and an aldehyde; transporting the precursors to a substrate maintained at a deposition temperature; and forming said ceramic matrix from the at least one first precursor and said embedded carbide nanoparticles from the second precursors.

8. The method as claimed in claim 7, wherein the at least one first precursor and the second precursors are introduced into the reaction chamber at respective times, the reaction chamber being purged there between, the introductions of the at least one first precursor and the second precursors being repeated plural times.

9. The method as claimed in claim 7, wherein the at least one first precursor and/or the second precursors comprise metalorganic or organometallic compounds.

10. The method as claimed in claim 7, wherein the ceramic matrix formed from the first precursor is a metal oxide matrix consisting of oxide selected from the group consisting of: VO.sub.2, Al.sub.2O.sub.3, SiO.sub.2, MgO, TiO.sub.2, ZrO.sub.2, Mn.sub.3O.sub.4, SnO.sub.2, ZnO, spinel having the general formula AB.sub.2O.sub.3 with A and B being metal cations having different valences, perovskite having the general formula ABO.sub.3 with A and B being differently sized metal cations, and mixtures thereof.

11. The method as claimed in claim 7, wherein said carbide nanoparticles formed from the second precursors consist of carbides of metals selected from the group consisting of: Ni, Co, Fe, Cr, Mo, Pt, Pd and mixtures thereof.

12. The method as claimed in claim 7, comprising annealing the ceramic matrix with said embedded carbide nanoparticles so as to convert at least part of said carbide nanoparticles into metal-carbon composite nanoparticles.

13. The method as claimed in claim 7, wherein the chemical vapour deposition is pulsed spray evaporation chemical vapour deposition, wherein the at least one first precursor is injected into the reaction chamber as a first precursor solution and wherein the second precursors are injected into the reaction chamber as a second precursor solution.

14. The method as claimed in claim 7, wherein the at least one first precursor and the second precursors are introduced into the reaction chamber at respective times, the reaction chamber being purged there between, the introductions of the at least one first precursor and the second precursors being repeated plural times; wherein the at least one first precursor and/or the second precursors comprise metalorganic or organometallic compounds; wherein the ceramic matrix formed from the first precursor is a metal oxide matrix consisting of oxide selected from the group consisting of: VO.sub.2, Al.sub.2O.sub.3, SiO.sub.2, MgO, TiO.sub.2, ZrO.sub.2, Mn.sub.3O.sub.4, SnO.sub.2, ZnO, spinel having the general formula AB.sub.2O.sub.3 with A and B being metal cations having different valences, perovskite having the general formula ABO.sub.3 with A and B being differently sized metal cations, and mixtures thereof; wherein said carbide nanoparticles formed from the second precursors consist of carbides of metals selected from the group consisting of: Ni, Co, Fe, Cr, Mo, Pt, Pd and mixtures thereof; wherein said method comprises annealing the ceramic matrix with said embedded carbide nanoparticles so as to convert at least part of said carbide nanoparticles into metal-carbon composite nanoparticles; wherein the chemical vapour deposition is pulsed spray evaporation chemical vapour deposition, wherein the at least one first precursor is injected into the reaction chamber as a first precursor solution and wherein the second precursors are injected into the reaction chamber as a second precursor solution; and wherein the first precursor solution comprises vanadium oxy-tri-isopropoxide dissolved in an organic solvent and wherein the second precursor solution comprises cobalt acetylacetonate and/or nickel acetylacetonate dissolved in an alcohol.

15. The method as claimed in claim 14, wherein the at least one first precursor or the second precursors comprise metal alkoxides or metal -diketonates.

16. The method as claimed in claim 7, wherein the at least one first precursor or the second precursors comprise metal alkoxides or metal -diketonates.

17. A black ceramic composite coating with a surface having a total hemispherical reflectivity of no more than 5% over the entire wavelength range from 400 nm to 1 m and for any incidence angle greater than 20, comprising a ceramic matrix distinct from a carbide matrix; wherein said ceramic matrix has at least one of carbide nanoparticles and metal-carbon composite nanoparticles embedded therein; wherein the at least one of the carbide nanoparticles and the metal-carbon composite nanoparticles have an average size in the range from 5 to 500 nm, wherein said carbide nanoparticles are metastable; wherein said metal-carbon composite nanoparticles are decay products of the metastable carbide nanoparticles; wherein said ceramic matrix has metal-carbon composite nanoparticles embedded therein, said metal-carbon composite nanoparticles comprising metal cores with carbon shells; wherein said ceramic matrix is a metal oxide matrix.

18. The ceramic composite coating as claimed in claim 17, wherein said metal oxide matrix consists of VO.sub.2 and wherein said metastable carbide nanoparticles comprise carbides of metals selected from the group consisting of: Ni, Co, Fe, Cr, Mo, Pt, Pd, and mixtures thereof.

19. The ceramic composite coating as claimed in claim 18, wherein said metastable carbide nanoparticles comprise CoC.sub.x nanoparticles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) By way of example, preferred, non-limiting embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which:

(2) FIG. 1: is a transversal cross-sectional schematic of an advanced cermet with metastable carbide nanoparticles;

(3) FIG. 2: is a transversal cross-sectional schematic of the advanced cermet of FIG. 1, wherein a part of the metastable carbide nanoparticles have decayed to their stable form;

(4) FIG. 3: is a transversal cross-sectional schematic of the advanced cermet of FIG. 1, wherein substantially all of the metastable carbide nanoparticles have decayed to their stable form;

(5) FIG. 4: is a schematic drawing of a CVD reactor equipped for pulsed-spray evaporation CVD;

(6) FIG. 5: is flow chart of an example of a pulsed-spray evaporation CVD process in accordance with a preferred embodiment of an aspect of the invention;

(7) FIG. 6: is a diagram comparing the THRs of advanced cermets according to the invention with that of a metal oxide coating;

(8) FIG. 7: is a diagram comparing the THRs of the advanced cermets of FIG. 6 in the near UV and visible wavelength range.

DETAILED DESCRIPTION OF ONE OR MORE PREFERRED EMBODIMENTS

(9) An advanced cermet 10 according to a preferred embodiment of the invention is schematically depicted in FIGS. 1-3. The advanced cermet 10 is applied as a black coating on substrate 12. The advanced cermet 10 comprises a metal oxide matrix 14 with embedded nanoparticles 16-1, 16-2 (together referred to as 16). The nanoparticles 16-1 (FIGS. 1 and 2) are metastable metal carbide nanoparticles. The nanoparticles 16-2 (FIGS. 2 and 3) are the stable decay products of the metastable carbide nanoparticles 16-1. FIGS. 1 to 3 illustrate different states of the same advanced cermet 10.

(10) In FIG. 1, 100% or close to 100% of the embedded nanoparticles are in the metastable carbide state. Such an advanced cermet may be obtained by depositing the nanoparticles at moderate temperatures, such that the transition from the carbide phase to the metal-carbon phase is thermodynamically improbable.

(11) FIG. 2 shows the situation in which a certain amount of the carbide nanoparticles 16-1 have decayed so as to yield the metal-carbon composite nanoparticles 16-2. An advanced cermet in that state may be obtained by incompletely annealing the advanced cermet of FIG. 1 or by growing the nanoparticles 16 under conditions where the deposition of the carbide is followed with a certain probability by the annealing thereof.

(12) Finally, FIG. 3 shows the completely annealed advanced cermet 10, in which all carbide nanoparticles have been transformed into the metal-carbon composite nanoparticles 16-2 with separate metal and carbon phases. As shown in FIGS. 2 and 3, the metal-carbon composite nanoparticles 16-2 have a core-shell configuration, the core 18 being formed by the metal phase whereas the shell 20 is formed by the carbon phase.

(13) FIG. 4 illustrates a CVD reactor 22 for carrying out pulsed-spray evaporation CVD of an advanced cermet. The CVD reactor comprises a main chamber 24 having arranged therein a substrate holder 26 with a substrate heater 28. The substrate (not shown in FIG. 4) may be placed on the substrate heater 28 by a manipulator (not shown). A vacuum pump 30 is connected to the main chamber, as well as a trap for the carrier gas (not shown). The precursors and the carrier gas may be introduced into the main chamber through a tubular evaporation and transport chamber 32. The evaporation and transport chamber 32 is equipped with heaters (not shown) allowing it to be brought to sufficiently high temperatures for the evaporation of the precursor solutions and the transport of the resulting vapour. The liquid precursor solutions are injected by respective injectors 34 into an evaporation zone 36 of the evaporation and transport chamber 32. In the evaporation zone 36, precursor vapours are then formed, which are transported by the carrier gas through a so-called transport zone 38 leading into the main chamber 32. The carrier gas (represented by arrow 40) may be introduced at a controlled flow rate through carrier gas inlet 42.

(14) FIG. 5 shows a flow chart illustrating pulsed-spray evaporation CVD (PSE-CVD) according to a preferred embodiment of the invention. The sequence used and the numerical values in FIG. 5 are illustrative only and may be varied depending on the composition of the coating to deposit. In a first step (S51), the various parts of the reactor that is used to produce a black composite coating are heated to the desired temperatures. A first deposition phase of the ceramic matrix material from the first precursor(s) is then started. In the illustrated case, a first precursor solution containing the first precursor(s) is injected into the evaporation zone (step S52) at a predefined rate (4 Hz in the example) and with predefined opening times of the injector (2 ms for each injection in the example). The precursor vapour formed in the evaporation zone is transported by the carried gas into the main chamber of the reactor, where the ceramic matrix is deposited on the substrate. The injection regime of the first precursor solution is maintained for a predefined amount of time (10 minutes in the example), before the injections of the first precursor solution are stopped and the reactor is purged using the flux of carrier gas (step S53) during a first purge time (30 s with nitrogen in the illustrated example). A second precursor solution containing the precursors for the carbide nanoparticles is then injected into the evaporation zone (step S52) at a predefined rate (4 Hz in the example) and with predefined opening times of the injector (2 ms for each injection in the example). The vapour formed from the second precursors is transported into the main chamber, where the carbide nanoparticles are deposited from the second precursors. The injection regime of the second precursor solution is maintained for a predefined amount of time (20 minutes in the illustrated example), whereupon the reactor is again purged. The deposition steps are repeated a certain number of times. The injection parameters may be varied in accordance with the desired deposition profile. It should also be noted that the last deposition is not necessarily a deposition of the carbide nanoparticles but could be one of the ceramic matrix. When the growth of the advanced cermet has completed, the reactor is cooled down and the grown samples are taken out of the reactor.

(15) The growth process of FIG. 5 may be greatly varied depending on the desired end product and the chemistry involved. For instance, while it may be preferable for practical reasons to have all first precursors necessary for the deposition of the ceramic matrix in one solution, separate precursor sources could also be used. The same holds for the second precursors. The deposition sequence may also be modified so as to lead to the incorporation of other (non-carbide) nanoparticles into the ceramic matrix, to result in the inclusion of two or more types of different carbide nanoparticles or to compounds of two or more metal carbides. By varying the deposition sequence, more complicated ceramic matrices may be grown, e.g. mixed oxide matrices, multi-layered matrices, etc.

(16) The flux of the carrier gas may be held constant throughout the entire growth process. Alternatively, the flux of carrier gas could be varied so as to adjust or optimize the deposition conditions.

(17) The temperature of the evaporation and transport chamber is also preferably held constant while the deposition goes on. If necessary or deemed advantageous, however, that parameter could also be changed over time. The same is true for the temperature of the substrate.

EXAMPLE

(18) An advanced cermet with a VO.sub.2 matrix having metastable CoC.sub.x nanoparticles embedded therein was grown on a silicon substrate using a CVD reactor of the Luxembourg Institute of Science and Technology (LIST), equipped with a PSE unit for the controlled injection of liquid feedstock. The precursors selected for this example were metal acetylacetonates and metal alkoxides that are easy to handle, store and implement. These precursors are soluble in ethanol and a large number of other solvents. In this example, ethanol was used for both the first and second precursors due to its reactivity with cobalt acetylacetonate (Co(acac).sub.2) above 220 C. to form metallic or carbide deposits depending on the temperature used. The first precursor solution was a 5 mM (5 mmol/l) solution of vanadium oxy-tri-isopropoxide (VO(O.sup.iPr).sub.3) in ethanol. The second precursor solution was a 5 mM solution of Co(acac).sub.2 in ethanol. The precursor solutions were injected as pulsed sprays into an evaporation tube maintained at 220 C. under vacuum. The precursors' delivery was performed by 2 ms opening of the injector with a frequency of 4 Hz, which yielding respective feeding rates of 2.5 ml/min. The carrier gas was nitrogen introduced with a flow rate of 40 sccm (standard cubic centimeters per minute) maintained constant through the entire deposition process.

(19) The deposition conditions are summarised in the following table:

(20) TABLE-US-00001 Pressure during deposition 5 mbar Carrier gas: nitrogen 40 sccm Precursor 1: VO(O.sup.iPr).sub.3 in ethanol 0.005 mol/l Delivery of the precursor 1 4 Hz, 2 ms opening time Precursor 2: Co(acac).sub.2 in ethanol 0.005 mol/l Delivery of the precursor 2 4 Hz, 2 ms opening time Temperature of evaporation and transport 220 C. Deposition temperature 450-600 C.

(21) The deposition cycle was the following:

(22) 1. Precursor solution 1 during 10 minutes

(23) 2. Purge with nitrogen during 30 s,

(24) 3. Precursor solution 2 during 20 minutes,

(25) 4. Purge with nitrogen during 30 s.

(26) The deposition cycle was carried out three times, followed by a deposition from precursor solution 1 lasting 22 minutes. After the total deposition time of 115 minutes, a film thickness of 1.1 m was reached, which corresponded to an average growth rate of 9.5 nm/min.

(27) To obtain an advanced cermet with stable metal-carbon composite nanoparticles, the metastable carbide nanoparticles embedded in the VO.sub.2 matrix were converted into metal-carbon composite nanoparticles by annealing the advanced cermet obtained from the CVD in an inert atmosphere at 600 C. during 60 minutes.

(28) FIG. 6 shows a comparison of the THRs observed in the wavelength range of 300 to 2500 nm with an incidence angle of 8 for a pure VO.sub.2 matrix, an advanced cermet with metastable CoC.sub.x nanoparticles embedded in a VO.sub.2 matrix and an advanced cermet with stable CoC composite nanoparticles embedded in a VO.sub.2 matrix. The THR measurements were carried out using PerkinElmer Labsphere equipment, which covers the 250-2500 nm spectral range and which is equipped with an integration sphere. FIG. 7 is a close-up showing the comparison of the THRs of the advanced cermets in the near UV and visible light wavelength range.

(29) While specific embodiments have been described herein in detail, those skilled in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.