High Emissivity Cerium Oxide Coating

Abstract

The present invention relates to a coating composition comprising: 10 to 80 wt % of cerium oxide comprising a dopant based upon the total weight of the composition, wherein said dopant is selected from iron oxide, cobalt oxide, chromium oxide, lanthanum oxide, or mixtures thereof, and the atomic ratio of dopant metal to cerium is in the range 0.01:1 to 0.5:1; and 10 to 50 wt % of binder based upon the total weight of the composition.

Claims

1. A coating composition comprising: 10 to 80 wt % of cerium oxide comprising a dopant based upon the total weight of the composition, wherein said dopant is selected from iron oxide, cobalt oxide, chromium oxide, lanthanum oxide, or mixtures thereof, and the atomic ratio of dopant metal to cerium is in the range 0.01:1 to 0.5:1; and 10 to 50 wt % of binder based upon the total weight of the composition.

2. The coating composition according to claim 1, comprising 10 to 70 wt % of cerium oxide comprising a dopant, and 10 to 45 wt % of binder.

3. The coating composition according to claim 1, wherein the dopant is iron oxide and/or cobalt oxide.

4. The coating composition according to claim 1, wherein the atomic ratio of dopant metal to cerium is in the range 0.05:1 to 0.5:1.

5. The coating composition according to claim 1, wherein said binder is an aluminum phosphate inorganic binder.

6. The coating composition according to claim 1, further comprising an emissivity agent and/or a filler.

7. The coating composition as claimed in claim 6, wherein said emissivity agent is selected from titanium dioxide (TiO.sub.2), silicon carbide (SiC), chromium oxide (Cr.sub.2O.sub.3), silicon dioxide (SiO.sub.2), iron oxide (Fe.sub.2O.sub.3), boron silicide (B.sub.4Si), boron carbide (B.sub.4C), silicon tetraboride (SiB.sub.4), molybdenum disilicide (MoSi.sub.2), tungsten disilicide (WSi.sub.2), and zirconium diboride (ZrB.sub.2), or mixtures thereof

8. The coating composition according to claim 1, which produces a coating having an emissivity of 0.85 to 0.98 in the wavelength range 1-25 μm.

9. (canceled)

10. (canceled)

11. (canceled)

12. (canceled)

13. A method for preparing a coated substrate, comprising the steps of: a) providing a substrate, preferably selected from a silica insulating brick, ceramic fiber, ceramic module, refractory brick, plastic refractory, castable refractory, refractory mortar, fiberlite, ceramic tile, an array of fiber board, and metal; b) applying a coating composition as defined in claim 1 onto at least one surface of said substrate; and c) heating said coating composition to form the coated substrate.

14. The method according to claim 13, wherein step (c) heating is at a temperature of 500° C. to 1700° C. and/or wherein step (c) heating is for 1 to 5 hours.

15. The method according to claim 13, wherein the coating composition is applied in step (b) by a method selected from spray coating, brush coating, dip coating or combinations thereof, preferably spray coating (e.g. air spray coating).

16. The method according to claim 13, comprising the steps of: a) providing a substrate, preferably selected from a silica insulating brick, ceramic fiber, ceramic module, refractory brick, plastic refractory, castable refractory, refractory mortar, fiberlite, ceramic tiles, and array of fiber board, and metal; ai) applying a primer onto at least one surface of said substrate; aii) drying said primer to give a substrate having a primer coating; b) applying a coating composition as defined in claim 1 onto said primer coating of said substrate having a primer coating; and c) heating said coating composition to form the coated substrate.

17. The method according to claim 16, wherein said primer comprises a mixture of silicon oxide and silica aerogel, preferably a mixture of silicon oxide and silica aerogel in a weight ratio of 9:1 to 1:1.

18. The method according to claim 16, wherein the step (c) heating is at a temperature of 500° C. to 1700° C. and/or wherein step (c) heating is for 1 to 5 hours.

19. (canceled)

20. (canceled)

21. A coated substrate, preferably a coated refractory, wherein said coating comprises: 10 to 80 wt % of cerium oxide comprising a dopant based upon the total weight of the coating, wherein said dopant is selected from iron oxide, cobalt oxide, chromium oxide, lanthanum oxide, or mixtures thereof, wherein the atomic ratio of dopant to cerium oxide is in the range 0.01:1 to 0.5:1, preferably 0.05:1 to 0.5:1; and 20 to 55 wt % of binder based upon the total weight of the coating.

22. The coated substrate as claimed in claim 21, wherein said coating further comprises an emissivity agent.

23. The coated substrate as claimed in claim 21, wherein said dopant is iron oxide and/or cobalt oxide.

24. The coated substrate according to claim 18, in a furnace.

25. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0118] FIG. 1 is an optical photograph of the cross-section of the coated sample prepared according to the Example 4 described below.

[0119] FIG. 2 is an optical photograph of the top surface of the coated samples prepared according to Example 2 and Example 4 described below.

EXAMPLES

Materials

[0120] All starting materials were commercially available from Sigma Aldrich.

Measurement Methods

[0121] Emissivity was measured at temperatures of 600° C., 900° C., 1300° C. and 1600° C. using an FTIR infrared emissometer, modified to include a computer-controlled circular turntable equipped with a blackbody reference and an integrated axisymmetric heating system based on a CO.sub.2 laser. During measurement, a sample is heated by the CO.sub.2 laser, causing it to radiate. This radiation/emission is detected by the FTIR instrument. The spectral emissivity is determined by calculating the ratio of the sample spectral emittance intensity and the blackbody spectral emittance intensity.

Preparatory Example: Preparation of a Primer Coating

[0122] Silicon oxide and silica aerogel were mixed together in a weight ratio of 8:2. Then, a primer was prepared by mixing 50 wt % of the silicon oxide/silica aerogel mixture with 50 wt % of an aluminium phosphate solution containing 50% v/v aluminium phosphate.

[0123] A plastic refractory, which was prepared by mold casting to a size of 115×76×25 mm, was used as a substrate. Before being coated with the primer, the substrate was dried under atmospheric conditions overnight and was then heat-treated at 1500° C. for 2 hours. The substrate was then cooled to room temperature before coating.

[0124] The coating solution was sprayed on the cooled substrate by spray coating to a thickness of 300 μm. It was then dried at room temperature for 30 minutes to obtain the primer-coated substrate.

Preparation of Non-Doped Cerium Oxide

Comparative Example 1

[0125] A coating solution was prepared by mixing 50 wt % of cerium oxide (CeO.sub.2) powder with 50 wt % of an aqueous aluminium phosphate solution containing 50% v/v aluminium phosphate.

[0126] The non-doped cerium oxide coating solution was directly sprayed to 300 μm thickness on a primer-coated substrate prepared according to the Preparatory Example. The coated specimen was then sintered for 3 hr at 1200° C. with heating rate of 1° C./min.

[0127] The emissivity of the coated substrate was measured according to the method described above.

[0128] The non-doped CeO.sub.2 coating was found to show high emissivity in the range of 0.8-0.98 in mid-infrared wavelengths (i.e. 5-25 μm) at both 1300° C. and 1600° C.; however, in near-infrared wavelengths (i.e. below 5 μm), the emissivity dropped to around 0.22 at both temperatures.

Preparation of Doped Cerium Oxide

Example 2

[0129] A mixture of 84.3 wt % cerium oxide (CeO.sub.2) powder and 15.7 wt % iron oxide (Fe.sub.2O.sub.3) (i.e. an atomic ratio of 1:0.2) was prepared, wherein the wt % values are based upon the total weight of the mixture. The mixed composition was grinded and mixed by ball milling. Then, the ball was removed and the composition was dried at 110° C. overnight to obtain the mixed composition in powder.

[0130] A coating solution was prepared by mixing 50 wt % of the powder with 50 wt % of an aqueous aluminium phosphate solution containing 50% v/v aluminium phosphate.

[0131] The Fe.sub.2O.sub.3-doped cerium oxide coating solution was directly sprayed to 300 μm thickness on a primer-coated substrate prepared according to the Preparatory Example. The coating specimen was then sintered for 3 hr at 1200° C. with heating rate of 1° C./min.

[0132] The emissivity of the coated substrate was measured according to the method described above.

[0133] The Fe.sub.2O.sub.3-doped CeO.sub.2 coating was found to show an increased emissivity with increasing temperature. The emissivity of the Fe.sub.2O.sub.3-doped CeO.sub.2 coating at 600° C. increased by 45% based on the emissivity at 300° C. and reached the emissivity value of 0.90-0.98 at temperatures of 1300° C. and 1600° C. across the whole wavelength range (1-25 μm).

Example 3

[0134] A mixture of 92.0 wt % cerium oxide powder and 8.0 wt % cobalt oxide (CoO) (i.e. an atomic ratio of 1:0.2) was prepared, wherein the wt % values are based upon the total weight of the mixture. The mixed composition was grinded and mixed by ball milling. Then, the ball was removed and the composition was dried at 110° C. overnight to obtain the mixed composition in powder.

[0135] A coating solution was prepared by mixing 50 wt % of the powder with 50 wt % of an aqueous aluminium phosphate solution containing 50% v/v aluminium phosphate.

[0136] The CoO-doped cerium oxide coating solution was directly sprayed to 300 μm thickness on a non-coated substrate. The coating specimen was then sintered for 3 hr at 1200° C. with heating rate of 1° C./min.

[0137] The emissivity of the coated substrate was measured according to the method described above.

[0138] The emissivity of the CoO-doped CeO.sub.2 coating at 900° C. increased by 50% based on the emissivity at 600° C. and reached a saturation value at an emissivity of around 0.9 across the whole wavelength range (1-25 μm).

Example 4

[0139] A mixture of 72.5 wt % cerium oxide (CeO.sub.2) powder and 27.5 wt % lanthanum oxide (La.sub.2O.sub.3) (i.e. an atomic ratio of 1:0.2) was prepared, wherein the wt % values are based upon the total weight of the mixture. The mixed composition was grinded and mixed by ball milling. Then, the ball was removed and the composition was dried at 110° C. overnight to obtain the mixed composition in powder.

[0140] A coating solution was prepared by mixing 50 wt % of the powder with 50 wt % of an aqueous aluminium phosphate solution containing 50% v/v aluminium phosphate.

[0141] The La.sub.2O.sub.3-doped cerium oxide coating solution was directly sprayed to 300 μm thickness on a primer-coated substrate prepared according to the Preparatory Example. The coating specimen was then sintered for 3 hr at 1200° C. with heating rate of 1° C./min.

[0142] The appearance of all Examples was checked after sintering and in all cases it was found that the coating appeared dense and without cracks on the surface.