Thermal spray powder of dicalcium silicate and coating thereof and manufacture thereof

Description

[0001] This invention relates to thermal spray powders of dicalcium silicate, thermal spray coatings thereof, and a process for manufacturing such powders.

BACKGROUND

[0002] Thermal spraying involves the melting or at least heat softening of a heat fusible material such as a metal or ceramic, and propelling the softened material in particulate form against a surface which is to be coated. The heated particles strike the surface where they are quenched and bonded thereto. In a plasma type of thermal spray gun, a high temperature stream of plasma gas heated by an arc is used to melt and propel powder particles. Other types of thermal spray guns include a combustion spray gun in which powder is entrained and heated in a combustion flame, such as a high velocity, oxygen-fuel (HVOF) gun. Thermal spray coatings of oxide ceramics are well distinguished from other forms such as sintered or melt casted by a characteristic microstructure of flattened spray particles visible in metallographically prepared cross sections of coatings.

[0003] In one group of thermal spray materials, powders are formed of oxides for spraying coatings that are used for thermal insulation at high temperature such as on burner can surfaces in gas turbine engines. Coatings are also needed for erosion and wear protection at high temperatures, and require resistance against thermal cycle fatigue and hot corrosion in a combustion environment. Zirconium dioxide (zirconia) typically is used in such applications. Because of phase transitions, the zirconia is partially or fully stabilized with about 5% (by weight) 15% calcium oxide (calcia) or 6% to 20% yttrium oxide (yttria)

[0004] However, these coatings have limitations particularly in resistance to hot corrosion as they allow attack of the substrate or a bond coating

[0005] Dicalcium silicate (Ca₂SiO₄) is a ceramic conventionally used for cement and refractory applications. Excellent hot corrosion and heat resistance of dicalcium silicate based coatings also has been demonstrated in a high temperature combustion environment. However, it is polymorphic with at least five phases including three high temperature α modifications, an intermediate temperature monoclinic β phase (larnite) and an ambient temperature γ phase. The transformation from the β phase to the γ phase exhibits a volume increase of 12% leading to degradation in both the thermal spray process and the coatings in thermal cycling. The β phase may be retained by quenching or the use of a stabilizer such as sodium or phosphorous. Other suggested stabilizers include oxides (or ions) of sulphur, boron, chromium, arsenic, vanadium, manganese, aluminum, iron, strontium, barium and potassium. At least some of these have also been reported as unsuccessful, and therefore still questionable in stabilizing, including chromium, aluminum, iron, strontium and barium.

[0006] U.S. patent No. 4,255,495 (Levine et al.) discloses plasma sprayed coatings of thermal barrier oxides containing at least one alkaline earth silicate such as calcium silicate. U.S. patent No. 5,082,741 (Tiara et al.) and an article "Advanced Thermal Barrier Coatings Involving Efficient Vertical MicroCracks" by N.Nakahira, Y.Harada, N.Mifune, T.Yogoro and H.Yamane, Proceedings of International Thermal Spray Conference, Orlando FL, 28 May - 5 June 1992, disclose thermal spray coatings of dicalcium silicate combined with calcium zirconate (CaZrO₃) in a range of proportions.

[0007] A commercial powder of β phase dicalcium silicate for thermal spraying is sold by Montreal Carbide Co. Ltd., Boucherville CQ, Canada, indicated in their "Technical Bulletin MC-C₂S" (undated).

[0008] In a chemical analysis the present inventors measured less than 1% by weight of potential stabilizers such as phosphorous in Montreal Carbide powder.

[0009] A commercial powder of dicalcium silicate for thermal spraying also is sold by Cerac Inc., Milwaukee, Wisconsin. In a Certificate of Analysis for calcium silicate (October 20, 1997), Cerac reports major β phase and low levels of aluminum (0.12%), iron (0.1%) and magnesium (0.25%), and 0.02% or less of other elements.

[0010] An object of the present invention is to provide an improved powder of dicalcium silicate for thermal sprayed coatings for thermal barriers having resistance to hot corrosion and sulfidation in a combustion environment. A further object is to provide a novel process of manufacturing such a powder. Another object is to provide an improved thermal sprayed coating of dicalcium silicate for thermal barriers having resistance to hot corrosion and sulfidation in a combustion environment.

SUMMARY

[0011] The foregoing and other objects are achieved by a thermal spray powder comprising a substantially uniform powder composition consisting of dicalcium silicate, sodium, a further ingredient selected from the group consisting of phosphorous and zirconium, and incidental ingredients, such that the dicalcium silicate is stabilized in a larnite phase that is majority by volume. Acording to the invention the further ingredient comprises phosphorous, in which case, preferably, the sodium recited as disodium monoxide is present in an amount of 0.2% to 0.8%, and the phosphorous recited as phosphorous pentoxide is present in an amount of 2.5% to 4%. In a prefered embodiment the further ingredient comprises zirconium, in which case, preferably, the sodium recited as disodium monoxide is present in an amount of about 0.2% to 0.8%, and the zirconium recited as zirconium dioxide is present in an amount of 10% to 50%. These percentages are by weight of oxide based on the total composition. The zirconium, if present, should be at least partially in the form of zirconium dioxide containing calcium oxide as stabilizer of the zirconium dioxide, or yttrium oxide its stabilizer.

[0012] Objectives also are achieved by a process of manufacturing a thermal spray powder of dicalcium silicate having a stabilized crystal structure. An aqueous mixture is formed of calcium carbonate powder, silicon dioxide powder, and an organic binder containing as an integral constituent a stabilizing element in an amount sufficient to stabilize the dicalcium silicate in a larnite phase that is majority by volume. The aqueous mixture is spray dried to form a powder. The spray dried powder is heated, such as by sintering or plasma melting, such that the dicalcium silicate is formed with larnite phase that is majority by volume.

[0013] Preferably the stabilizing element is sodium, advantageously contained in an organic binder sodium carboxymethylcellulose. Further advantageously, the aqueous mixture further comprises a compound of phosphorous, preferably as hydrous aluminum phosphate in aqueous solution. Alternatively or in addition to phosphorous, the aqueous mixture further comprises stabilized zirconium dioxide powder with calcia or yttria stabilizer.

[0014] Objectives are further achieved by a thermal spray coating of a composition as described above for the powder. The coating has a web of interconnected, randomly oriented microcracks substantially perpendicular to the coating surface. The coating may include a bonding layer of a thermal sprayed nickel or cobalt alloy on a metallic substrate, and an intermediate layer of a thermal sprayed partially or fully stabilized zirconium oxide. The layer of dicalcium silicate composition is thermal sprayed onto the intermediate layer. The intermediate layer blocks reaction between the bonding layer and the layer of dicalcium silicate composition.

DETAILED DESCRIPTION

[0015] Dicalcium silicate compositions can be manufactured by agglomeration procedures such as spray drying as taught in U.S. patent No. 3,617,358 (Dittrich), incorporated herein in its entirety by reference, followed by sintering (calcination) or melting. Sodium is added as a stabilizing ingredient. A second added ingredient is phosphorous as a stabilizer. Alternatively to the phosphorous, the second additive is stabilized zirconia or, as another alternative, both phosphorous and zirconia may be added. In spray drying a water soluble organic or inorganic binder is used in an aqueous mixture or slurry containing the other ingredients. In a preferred embodiment, the sodium is added by way of containment in the binder formulation, advantageously sodium carboxymethylcellulose (sodium CMC) containing about 2% by weight sodium. Other ingredients and calculated formulae are listed in Table 1 for seven formulations.

Table 1

Spray Dry Menu (Quantities in units of weight)
Run #	CaCO3	SiO2	AP	CZ	YZ
1	154	46
2	150	50	25
3	150	50	10
4	154	46	25
5	154	46	10
6	154	46			33
7	154	46		33
AP- Al(H2PO4)3, 50% solution. CZ - ZrO2-5CaO-0.5Al2O3-0.4SiO2, in weight percents. YZ - ZrO2-7Y2O3, in weight percent.

[0016] Raw materials were precipitated calcium carbonate (CaCO₃, purity 98%, size 1-10 µm), ground silica (SiO₂, purity 99%, 2-15 µm), hydrous aluminum phosphate (AP), calcia stabilized zirconia (CZ, 98% purity, 0.4-20 µm) and yttria stabilized zirconia (YZ, 99% purity, 0.4-15 µm). The amounts of each ingredient are in units of weight, each formulation being in 60 liters of distilled water per unit of weight of the raw materials. The binder is present in an amount of 4% by weight of the raw materials. The Na₂O content was nearly constant around 0.45% as the binder remained constant. A surfactant such as sodium polyacrylate is added in an amount of 2% by weight. The mixture is atomized conventionally with compressed air upwardly through a nozzle into a heated oven region, as described in the aforementioned Dittrich patent, and the resulting agglomerated powder is collected.

[0017] Table 2 lists powders by lot numbers formulated (some in two sizes) from these compositions. All were subsequently sintered at 1200°C for 3 hours, except Lot 709 which was treated by feeding through a plasma gun as described in U.S. patent Nos. 4,450,184 (Longo et al.), the portions describing such process being incorporated herein by reference. Table 3 gives chemical compositions (from chemical analyses) and phases (from x-ray diffraction) for eight of the lots.

Table 2

Powders
Lot #	Run #	Size	Additives	Heat Treat
307	1	Std	Na	Sinter
309	1	Fine	Na	Sinter
403	2	Std	Na, P	Sinter
414	3	Std	Na, P	Sinter
429	4	Std	Na, P	Sinter
506	5	Std	Na, P	Sinter
513	6	Std	Na, CZ	Sinter
515	6	Fine	Na, CZ	Sinter
520	7	Std	Na, YZ	Sinter
709	1	Std	Na	Plasma
821	Blend of Run 1 & CZ 75/25 Wt%
Std = Standard - predominantly 30 to 125 µm Fine - predominantly 22 to 88 µm. Na - sodium; P - phosphorous

Table 3

Powder compositions (Volume Percents)
Lot#	CaO	SiO2	MgO	Al2O3	P2O5	Na2O	Y2O3	ZrO2	Phases
307	62.23	36.28	0.42	0.29	0.03	0.49			100% β
309	64.48	43.03	0.40	0.29	0.09	0.41			100% β
403	56.92	33.62	0.35	1.80	6.67	0.39			75% β, CA
414	58.83	36.66	0.37	0.89	2.73	0.42			75% β, CA
429	57.67	33.30	0.38	1.72	6.17	0.45			75% β, CA
506	61.96	32.58	0.40	0.95	3.09	0.49			75% β, CA
513	49.19	29.09	0.33	0.47	0.01	0.40	0.04	19.71	75% β, CZ
515	51.04	27.63	0.33	0.47	0.01	0.41	0.03	19.25	75% β, CZ
520	47.37	28.84	0.28	0.42	0.02	0.40	1.53	20.62	75% β, YZ
CA is calcium aluminate, Ca3Al2O6. β - larnite

[0018] The powders were thermal sprayed with a Sulzer Metco model F4 plasma gun with a model Twin 10 (TM) powder feeder, using an 8 mm nozzle, argon primary gas at 30 standard liters/minute (slpm) flow, hydrogen secondary gas at 12 slpm, argon powder carrier gas at 3 slpm, 550 amperes, 63 volts, 12 cm spray distance and 3 kg/hr powder feed rate. Several types of substrates included cold rolled steel, Fe-13Cr-44Mo alloy and a Ni alloy of 1.5Co-18Fe-22Cr-9Mo-0.6W-0.1C-max1Mn-max1Si. The substrates were prepared conventionally by grit blasting. Coatings having a thickness of 650 to 730 µm were effected. The finer powders were sprayed with the same gun and parameters except at a spray rate 1.2 kg/hr. Table 4 shows detected phases in the coatings.

Table 4

Plasma Sprayed Coating Phases
Lot/Coating #	Detected Phases
307	β
309	β
403	α ortho
414	β (+), α ortho
429	α ortho
506	β (+)
513	α ortho, cubic zirconia
515	α hex, cubic zirconia
520	α hex, cubic zirconia
709	β
821	β, cubic zirconia

(+) after β designates disordered lattice.

[0019] A more important feature of the preferred coatings is a web of interconnected, randomly oriented microcracks substantially perpendicular to the coating surface. Such cracks relieve stresses in thermal cycling. These microcracks were observed particularly in a coating from lot 506 which is stabilized at 75% β phase (larnite) with disodium monoxide and phosphorous pentoxide, and contains aluminum oxide bound with the calcia as Ca₃Al₂O₆. However, the x-ray diffraction pattern indicated a disordered lattice. Similar microcracking was observed in a coating from lot 515 containing sodium and calcia stabilized zirconia (CZ). Compositional inhomogeneity was visible in coatings with high amounts of silica or phosphorous (lots 403, 429), and inhomogeneity for lot 414. Lot 429, low in phosphorous, was most uniform. The microcracking is considered to be important for stress relief in thermal cycling. In the coatings, there should be between about 1 and 5 microcracks per cm² of coating surface.

[0020] After a heat treatment at 1200°C for 48 hours, only three coatings appeared stable against dusting, 506 (low phosphorous) and 515 (CZ), and 414 which completely detached. The only coating to retain the β phase was 506. Coating 515 exhibited a mechanical stable appearance. It is concluded that the coatings that dusted would not be stable in hot environments. Coating 414 was "superstabilized" in a high temperature α phase formed in the heat treatment. A significant amount of calcium zirconate (CaZrO₃) was formed in the heat treated coating 515. After a second heat treatment of coatings 506 and 515 at 1300°C for 48 hours, only the β phase was detected in the coatings. These coatings remained stable.

[0021] Further long term cyclic corrosion testing was performed with coatings 414, 506 (both low phosphorous) and 515 up to 900°C, with V₂O₅, (85 wt%) / Na₂SO₄ (15 wt%) ash as a corrosive agent. These coatings efficiently protected the underlying bond coat and substrate from attack from the agent which did not penetrate the coatings. Reference yttria stabilized zirconia coatings were damaged and partly spalled, and the corrosive agent penetrated the coating.

[0022] More broadly, the disodium monoxide should be present in an amount of 0.2% to 0.8%. If phosphorous pentoxide is the second stabilizer, it should be present in an amount of 2.5% to 4%. Alternatively, if zirconium dioxide (zirconia) is the second additive, it should be present in an amount of 10% to 50% by weight. The powder should have a size distribution generally within a range between about 10 and 100 µm. Alternatives to the aluminum phosphate as a raw material are sodium phosphate and zirconium phosphate.

[0023] As indicated above for, a preferred aspect of the invention, the organic binder for the spray dry process contains the stabilizing element sodium as an integral constituent of the binder compound. More broadly, other stabilizing elements such as potassium or any of the other stabilizing elements set forth above for dicalcium silicate may be used. The stabilizing element is in an amount sufficient to stabilize the dicalcium silicate in a larnite phase that is at least majority or, preferably, substantially fully stabilized larnite.

[0024] The powder size distribution generally should be in a range of 10 µm to 200 µm, for example predominantly 30 to 125 µm for thicker coatings or 22 to 88 µm for thinner coatings. The zirconia, when used, should be partially or fully stabilized with 5% to 15% by weight of calcia or 6% to 20% by weight of yttria. At least some stabilization of the zirconia is desired because some zirconia phase is in the powder particles. Stabilized zirconia is distinguished from calcium zirconate which contains substantially more calcia. Other known or desired stabilizers for the zirconia such as magnesium oxide may be used. In an alternative embodiment, phosphorous is used along with the sodium in powder and coatings containing the stabilized zirconia.

[0025] Proportions should be the same as for the individual cases.

[0026] Plasma gun melting of spray dried powder in place of sintering, is an alternative. Also, lot 821 tested a blend of lot 307 dicalcium silicate with a partially stabilized zirconia powder. Although lot 307 was stabilized only with sodium which was less effective, the testing suggested that powders of the present invention may be blended with other compatible high temperature powders for tailored results. Advantageously, the zirconium oxide is blended in an amount of 10% to 50% by weight of the total powder, preferably 15% to 25%, for example 20%.

[0027] Preferably the dicalcium silicate is applied over a conventional bonding layer of alloy, such as Ni-22Cr-10Al-1.0Y (by weight)., or Ni-20Cr or Ni-50Cr, thermal sprayed on an alloy substrate. However, at high temperature the dicalcium silicate may react with the bonding alloy. Zirconia is less prone to such a reaction. Therefore, an advantageous coating is formed of a bonding layer of a thermal sprayed nickel or cobalt alloy on a metallic substrate, and an intermediate layer of a thermal sprayed partially or fully stabilized zirconium oxide. The layer of dicalcium silicate composition is thermal sprayed onto the intermediate layer, the bonding layer being between about 100 µm and 200 µm thick, and the intermediate layer preferably being between about 50 and 200 µm thick. The intermediate layer thereby blocks reaction between the bonding layer and the layer of dicalcium silicate composition.

[0028] Applications for the coatings include burner cans, heat shields, blades, vanes and seals in gas turbine engines, rocket nozzles, piston crowns and valve faces in diesel engines, and contast rolls and tundish outlets in steel mills.

[0029] While the invention has been described above in detail with reference to specific embodiments, various changes and modifications which fall within the spirit of the invention and scope of the appended claims will become apparent to those skilled in this art. Therefore, the invention is intended only to be limited by the appended claims or their equivalents.

Claims

1. A thermal spray powder comprising a substantially uniform powder composition consisting of dicalcium silicate, sodium, a further ingredient selected from the group consisting of phosphorous and zirconium, wherein the further ingredient comprises phosphorous, and incidental ingredients, such that the dicalcium silicate is stabilized in a larnite phase that is majority by volume, wherein the sodium recited as disodium monoxid is present in an amount of about 0.2% to 0.8%, and the phosphorous recited as phosphorous pentoxide is present in an amount of about 2.5% to 4%, the percentage being by weight of oxide based on the total composition.

2. The powder of claim 1 wherein the incidental ingredients comprise aluminum recited as aluminum oxide up to 2%.

3. The powder of claim 1 wherein the incidental ingredients comprise magnesium recited as magnesium oxide up to 0.5%.

4. The powder of claim 1 wherein the further ingredient comprises zirconium.

5. The powder of claim 4 wherein the sodium recited as disodium monoxide is present in an amount of about 0.2% to 0.8%, and the zirconium recited as zirconium dioxide is present in an amount of 10% to 50%, the percentages being by weight of oxide based on the total composition.

6. The powder of claim 4 wherein the zirconium is at least partially in the form of zirconium dioxide containing calcium oxide as stabilizer of the zirconium dioxide.

7. The powder of claim 4 wherein the zirconium is at least partially in the form of zirconium dioxide containing yttrium oxide as stabilizer of the zirconium dioxide.

8. The powder of claim 1 having a size distribution within a range between 10 and 100 µm.

9. The powder of claim 1 further comprising a powder of stabilized zirconium oxide in an amount of 10% to 50% blended with the powder composition of dicalcium silicate, based on the total weight of the powder.

10. A process of manufacturing a thermal spray powder of dicalcium silicate having a stabilized crystal structure, comprising steps of:

forming an aqueous mixture comprising calcium carbonate powder, silicon dioxide powder, and an organic binder containing as an integral constituent a stabilizing ingredient in an amount sufficient to stabilize the dicalcium silicate in a larnite phase that is majority by volume; wherein the stabilizing ingredients comprises sodium and a further ingredient selected from the group consisting of phosphorous and zirconium, wherein the further ingredient comprises phosphorous and incidental ingredients, wherein the sodium recited as disodium monoxid is present in a amount of 0.2% to 0.8%, and the phosporous recited as phosphorous pentoxide is present in an amount of 2.5% to 4%, the percentage being by weight of dried oxide, spray drying the aqueous mixture to form a spray dried powder; and

heating the spray dried powder such that the dicalcium silicate is formed with larnite phase that is majority by volume.

11. The process of claim 10 wherein the organic binder is sodium carboxymethylcellulose.

12. The process of claim 11 wherein the compound of phosphorous is hydrous aluminum phosphate in aqueous solution.

13. The process of claim 11 wherein the compound of phosphorous is hydrous aluminum phosphate in aqueous solution.

14. The process of claim 10 wherein the aqueous mixture further comprises stabilized zirconium dioxide.

15. The process of claim 14 wherein the zirconium dioxide contains calcium oxide as stabilizer.

16. The process of claim 14 wherein the zirconium dioxide contains yttrium oxide as stabilizer.

17. The process of claim 10 wherein each powder in the aqueous mixture has a size less than 20 µm.

18. The process of claim 10 wherein the step of heating comprises sintering the powder.

19. The process of claim 10 wherein the step of heating comprises feeding the powder through a plasma gun.

20. A thermal spray coating comprising a layer of a substantially uniform coating composition consisting of dicalcium silicate, sodium, a further ingredient selected from the group consisting of phosphorous and zirconium, and incidental ingredients, the coating having a coating surface and a web of interconnected, randomly oriented microcracks substantially perpendicular to the coating surface.

21. The coating of claim 20 wherein the further ingredient comprises phosphorous, and the dicalcium silicate is stabilized in a larnite phase that is majority by volume.

22. The coating of claim 21 wherein the sodium recited as disodium monoxide is present in an amount of about 0.2% to 0.8%, and the phosphorous recited as phosphorous pentoxide is present in an amount of about 2.5% to 4%, the percentages being by weight of oxide based on the total composition.

23. The coating of claim 21 wherein the incidental ingredients comprise aluminum recited as aluminum oxide up to 2%.

24. The coating of claim 20 wherein the incidental ingredients comprise magnesium recited as magnesium oxide up to 0.5%.

25. The coating of claim 20 wherein the further ingredient comprises zirconium.

26. The coating of claim 25 wherein the sodium recited as disodium monoxide is present in an amount of 2% to 0.8%, and the zirconium recited as zirconium dioxide is present in an amount of about 10% to 50%, the percentages being by weight of oxide based on the total composition.

27. The coating of claim 25 wherein the zirconium is at least partially in the form of zirconium dioxide containing calcium oxide as stabilizer of the zirconium dioxide.

28. The coating of claim 25 wherein the zirconium is at least partially in the form of zirconium dioxide containing yttrium oxide as stabilizer of the zirconium dioxide.

29. The coating of claim 20 wherein the coating contains between one and five microcracks per cm of coating surface.

30. The coating of claim 20 wherein the layer of dicalcium silicate composition is between 50 µm and 200 µm thick.

31. The coating of claim 20 further comprising a bonding layer of a thermal sprayed nickel or cobalt alloy on a metallic substrate, and an intermediate layer of a thermal sprayed partially or fully stabilized zirconium oxide, the layer of dicalcium silicate composition being thermal sprayed onto the intermediate layer, the bonding layer being between about 100 µm and 200 µm thick, and the intermediate layer being between about 50 µm and 200 µm thick, whereby the intermediate layer blocks reaction between the bonding layer and the layer of dicalcium silicate composition.

Ansprüche

1. Ein thermisches Spritzpulver umfassend eine im wesentlichen gleichmässige Pulverzusammensetzung bestehend aus Dikalziumsilikat, Natrium, einem weiteren Bestandteil aus der Gruppe bestehend aus Phosphor und Zirkon, wobei der weitere Bestandteil Phosphor umfasst und weitere Bestandteilen, so dass das Dikalziumsilikat in einer larniten Phase stabilisiert wird, die den Grossteil des Volumens einnimmt, wobei das erwähnte Natrium als Dinatrium Monoxid vorliegt in einer Menge von ungefähr 0.2% bis 0.8% und der Phosphor erwähnt als Phosphorpentoxid in einer Menge von 2.5% bis 4% vorliegt, wobei die Prozentangaben Gewichtsprozent in Bezug auf die gesamte Zusammensetzung sind.

2. Das Pulver gemäss Anspruch 1, wobei die weiteren Bestandteile Aluminium, erwähnt als Aluminiumoxid, bis zu 2% umfassen.

3. Das Pulver gemäss Anspruch 1, wobei die weiteren Bestandteile Magnesium, erwähnt als Magnesiumoxid, bis zu 0.5% umfassend.

4. Das Pulver nach Anspruch 1, wobei die weiteren Bestandteile Zirkon umfassen.

5. Das Pulver nach Anspruch 4, wobei das als Dinatriummomoxid erwähnte Natrium in einer Menge von ungefähr 0.2% bis 0.8% vorliegt, und das erwähnte Zirkon, erwähnt als Zirkondioxid, in einer Menge von ungefähr 10% bis 50% vorliegt, wobei die Prozentangaben Gewichtsprozent des Oxids in Bezug auf die gesamte Zusammensetzung sind.

6. Das Pulver nach Anspruch 4, wobei das Zirkon mindestens teilweise in Form von Zirkondioxid,enthaltend Kalziumoxid als Stabilisierer des Zirkondioxids, vorliegt.

7. Das Pulver nach Anspruch 4, wobei das Zirkon zumindest teilweise in Form von Zirkondioxid enthaltend Yttriumoxid als Stabilisierer des Zirkondioxids,vorliegt.

8. Das Pulver nach Anspruch 1, mit einer Grössenverteilung innerhalb eines Bereichs zwischen 10 und 100µm.

9. Das Pulver nach Anspruch 1, umfassend weiterhin ein Pulver aus stabilisiertem Zirkonoxid in einer Menge von 10% bis 50% vermischt mit der Pulverzusammensetzung aus Dikalziumsilikat, bezogen auf das gesamte Gewicht des Pulvers.

10. Ein Verfahren zur Herstellung eines thermischen Spritzpulvers aus Dikalziumsilikat mit einer stabilisierten Kristallstruktur, umfassend die Schritte:

Herstellung einer wässrigen Lösung umfassend Kalziumkarbonatpulver, Siliziumdioxidpulver und einen organischen Binder enthaltend als einen integralen Bestandteil ein stabilisierendes Element in einer Menge, die ausreichend ist, das Dikalziumsilikat in einer larniten Phase zu stabilisieren, die den grössten Teil des Volumens einnimmt; wobei die stabilisierenden Elemente Natrium und Phosphor und Zirkonium umfassen, und wobei die weiteren Elemente Phospor und zufällige Beimischungen umfassen, wobei das als Dinatriummonoxid erwähnte Natrium in einer Menge von 0.2% bis 0.8% und er als Phosphorpentoxid erwähnte Phosphor in einer Menge von 2.5% bis 4% vorhanden ist, wobei die Prozentangaben Gewichtsprozent des getrockneten Oxids sind;

Sprühtrocknen der wässrigen Lösung um ein sprühgetrocknetes Pulver herzustellen;

und Aufheizung des sprühgetrockneten Pulvers so dass das Dikalziumsilikat in einer larniten Phase ausgebildet wird, die den Grossteil des Volumens einnimmt.

11. Das Verfahren nach Anspruch 10, wobei der organische Binder Natrium carboxymethylcellulose ist.

12. Das Verfahren nach Anspruch 11, wobei der Phosphorbestandteil wasserhaltiges Aluminiumphosphat in wässriger Lösung ist.

13. Das Verfahren nach Anspruch 11, wobei der Phosphorbestandteil wasserhaltiges Aluminiumphosphat in wässriger Lösung ist.

14. Das Verfahren nach Anspruch 10, wobei die wässrige Lösung weiterhin stabilsiertes Zirkondioxid enthält.

15. Das Verfahren nach Anspruch 14, wobei das Zirkondioxid Kalziumoxid als Stabilisierer enthält.

16. Das Verfahren nach Anspruch 14, wobei das Zirkondioxid Yttriumoxid als Stabilisierer enthält.

17. Das Verfahren nach Anspruch 10, wobei jedes Pulver eine Grösse von weniger als 20µm hat.

18. Das Verfahren nach Anspruch 10,wobei der Schritt des Aufheizens ein Sintern des Pulvers umfasst.

19. Das Verfahren nach Anspruch 10, wobei der Schritt des Aufheizens das Durchführen des Pulvers durch eine Plasmapistole umfasst.

20. Eine thermische Spritzschicht umfassend eine Schicht einer im wesentlichen gleichförmigen Schichtzusammensetzung bestehend aus Dikalziumsilikat, Natrium, einer weiteren Beimischung aus der Gruppe bestehend aus Phosphor und Zirkon, und eines weiteren Bestandteils, wobei die Beschichtung eine Beschichtungsoberfläche und ein Netz aus miteinander verbundenen, zufällig orientierten Mikrorissen umfasst, die im wesentlichen senkrecht zur Beschichtungsoberfläche orientiert sind.

21. Die Beschichtung nach Anspruch 20, wobei die weiteren Bestandteile Phosphor umfassen, und das Dikalziumsilikat in einer larniten Phase stabilisiert ist, die den grössten Teil des Volumens einnimmt.

22. Die Beschichtung nach Anspruch 21, wobei Natrium erwähnt als Dinatriummonoxid in einer Menge von 0.2% bis 0.8% und der Phosphor erwähnt als Phosphorpentoxid in einer Menge von 2.5% bis 4% vorliegt,wobei die Prozentangaben Gewichtsprozent des Oxids in Bezug auf die gesamte Zusammensetzung sind.

23. Die Beschichtung nach Anspruch 21, wobei die weiteren Bestandteile Aluminium, erwähnt als Aluminiumoxid, bis zu 2% umfassen.

24. Die Beschichtung nach Anspruch 20, wobei die weiteren Bestandteile Magnesium, erwähnt als Magnesiumoxid bis zu ca. 0.5% umfasst.

25. Die Beschichtung nach Anspruch 20, wobei die weiteren Bestandteile Zirkon umfassen.

26. Die Beschichtung nach Anspruch 25, wobei das als Dinatriummonoxid erwähnte Natrium in einer Menge von ungefähr 0.2% bis 0.8% enthalten ist und das als Zirkondioxid erwähnte Zirkon in einer Menge von 10% bis 50% enthalten ist, wobei die Prozentangaben Gewichtsprozent des Oxids in Bezug auf die gesamte Zusammensetzung sind.

27. Die Beschichtung nach Anspruch 25, wobei das Zirkon zumindest teilweise in Form von Zirkondioxid, enthaltend Kalziumoxid als Stabilisierer für das Zirkondioxid, vorliegt.

28. Die Beschichtung nach Anspruch 25, wobei das Zirkon zumindest teilweise in Form von Zirkondioxid, enthaltend Yttriumoxid als Stabilisierer für das Zirkondioxid, vorliegt.

29. Die Beschichtung nach Anspruch 20, wobei die Beschichtung zwischen einem und fünf Mikrorissen pro cm der Beschichtungsoberfläche enthält.

30. Die Beschichtung nach Anspruch 20 wobei die Schicht der Dikalziumsilikat Zusammensetzung zwischen 50µm und 200µm dick ist.

31. Die Beschichtung nach Anspruch 20, weiter enthaltend eine auf ein metallisches Substrat thermisch gespritzte Verbindungsschicht aus einer Nickel oder Kobalt Legierung und einer thermisch gespritzten, teilweise oder vollständig stabilisierten Zirkonoxid Zwischenschicht, wobei die Schicht aus der Dikalziumsilikat Zusammensetzung thermisch auf die Zwischenschicht gespritzt ist, Die Verbindungsschicht ungefähr zwischen 100µm und 200µm dick ist und die Zwischenschicht ungefähr zwischen 50µm und 200µm dick ist, wobei die Zwischenschicht Reaktionen zwischen der Verbindungsschicht und der Schicht aus der Dikalziumsilikat Zusammensetzung blockiert.

Revendications

1. Poudre pour pulvérisation thermique comprenant une composition de poudre substantiellement uniforme consistant en silicate dicalcique, sodium, un autre ingrédient sélectionné parmi le groupe consistant en phosphore et zirconium, où l'ingrédient supplémentaire comprend le phosphore, et des ingrédients éventuels, de manière à ce que le silicate dicalcique soit stabilisé en une phase larnite qui est majoritaire en volume, où le sodium sous forme de monoxyde disodique est présent à une teneur de 0,2% à 0,8%, et le phosphore sous forme de pentoxyde phosphoreux est présent à une teneur de 2,5% à 4%, le pourcentage étant en poids d'oxyde basé sur la composition totale.

2. Poudre selon la revendication 1, dans laquelle les ingrédients éventuels comprennent l'aluminium sous forme d'oxyde d'aluminium jusqu'à 2%.

3. Poudre selon la revendication 1, dans laquelle les ingrédients éventuels comprennent le magnésium sous forme d'oxyde de magnésium jusqu'à 0,5%.

4. Poudre selon la revendication 1, dans laquelle l'ingrédient supplémentaire comprend le zirconium.

5. Poudre selon la revendication 4, dans laquelle le sodium sous forme de monoxyde disodique est présent à une teneur d'environ 0,2% à 0,8%, et le zirconium sous forme de dioxyde de zirconium est présent à une teneur de 10% à 50%, le pourcentage étant indiqué en poids d'oxyde par rapport à la composition totale.

6. Poudre selon la revendication 4, dans laquelle le zirconium est au moins partiellement sous la forme de dioxyde de zirconium contenant de l'oxyde de calcium comme agent stabilisant du dioxyde de zirconium.

7. Poudre selon la revendication 4, dans laquelle le zirconium est au moins partiellement sous la forme de dioxyde de zirconium contenant de l'oxyde d'yttrium comme agent stabilisant du dioxyde de zirconium.

8. Poudre selon la revendication 1 ayant une distribution de taille dans une plage entre 10 et 100 µm.

9. Poudre selon la revendication 1 comprenant en outre une poudre d'oxyde de zirconium stabilisé à une teneur de 10% à 50% mélangée avec la composition de poudre de silicate dicalcique, par rapport au poids total de la poudre.

10. Procédé de fabrication d'une poudre pour pulvérisation thermique de silicate dicalcique ayant une structure de cristal stabilisé comprenant les étapes de:

formation d'un mélange aqueux comprenant de la poudre de carbonate de calcium,
de la poudre de dioxyde de silicone, et un liant organique contenant comme constituant intégral un ingrédient stabilisant à une teneur suffisante pour stabiliser le silicate dicalcique en une phase larnite qui est majoritaire en volume; où les ingrédients de stabilisation comprennent du sodium et un autre ingrédient sélectionné dans le groupe constitué de phosphore et de zirconium, où l'autre ingrédient comprend du phosphore et des ingrédients éventuels, où le sodium sous forme de monoxyde disodique est présent à une teneur de 0,2% à 0,8%, et le phosphore sous forme de pentoxyde phosphoreux est présent à une teneur de 2,5% à 4%, le pourcentage étant en poids d'oxyde sec ;

séchage par pulvérisation du mélange aqueux pour former une poudre pulvérisée à sec;
et

chauffage de la poudre séchée par pulvérisation de façon à ce que le silicate dicalcique soit formé avec une phase larnite qui est majoritaire en volume.

11. Procédé selon la revendication 10, dans lequel le liant organique est la carboxyméthylcellulose sodium.

12. Procédé selon la revendication 11, dans lequel le composé de phosphore est du phosphate d'aluminium hydraté en solution aqueuse.

13. Procédé selon la revendication 11, dans lequel le composé de phosphore est du phosphate d'aluminium hydraté en solution aqueuse.

14. Procédé selon la revendication 10, dans lequel le mélange aqueux contient en outre de l'oxyde de zirconium stabilisé.

15. Procédé selon la revendication 14, dans lequel l'oxyde de zirconium contient de l'oxyde de calcium comme agent stabilisant.

16. Procédé selon la revendication 14, dans lequel l'oxyde de zirconium contient de l'oxyde d'yttrium comme agent stabilisant.

17. Procédé selon la revendication 10, dans lequel chaque poudre dans le mélange aqueux a une taille inférieure à 20 µm.

18. Procédé selon la revendication 10, dans lequel l'étape de chauffage comprend le frittage de la poudre.

19. Procédé selon la revendication 10, dans lequel l'étape de chauffage comprend l'alimentation de la poudre à travers un canon à plasma.

20. Revêtement par pulvérisation thermique comprenant une couche d'une composition de revêtement substantiellement uniforme constitué de silicate dicalcique, de sodium, d'un autre ingrédient sélectionné parmi le groupe consistant en phosphore et zirconium, et d'ingrédients éventuels, le revêtement ayant une surface de revêtement et un réseau de microfissures interconnectées, orientées aléatoirement substantiellement perpendiculaires à la surface de revêtement.

21. Revêtement selon la revendication 20, dans lequel l'ingrédient additionnel comprend le phosphore, et le silicate dicalcique est stabilisé en une phase larnite qui est majoritaire en volume.

22. Revêtement selon la revendication 21, dans lequel le sodium sous forme de monoxyde disodique est présent à une teneur d'environ 0,2% à 0,8%, et le phosphore sous forme de pentoxyde phosphoreux est présent à une teneur d'environ 2,5% à 4%, le pourcentage étant en poids d'oxyde par rapport à la composition totale.

23. Revêtement selon la revendication 21, dans lequel les ingrédients éventuels comprennent l'aluminium sous forme d'oxyde d'aluminium jusqu'à 2%.

24. Revêtement selon la revendication 20, dans lequel les ingrédients éventuels comprennent le magnésium sous forme d'oxyde de magnésium jusqu'à 0,5%.

25. Revêtement selon la revendication 20, dans lequel l'ingrédient additionnel comprend du zirconium.

26. Revêtement selon la revendication 25, dans lequel le sodium sous forme de monoxyde disodique est présent à une teneur de 0,2% à 0,8%, et le zirconium sous forme de dioxyde de zirconium est présent à une teneur d'environ 10% à 50%, le pourcentage étant en poids d'oxyde par rapport à la composition totale.

27. Revêtement selon la revendication 25, dans lequel le zirconium est au moins partiellement sous forme de dioxyde de zirconium contenant de l'oxyde de calcium comme agent stabilisant du dioxyde de zirconium.

28. Revêtement selon la revendication 25, dans lequel le zirconium est au moins partiellement sous forme de dioxyde de zirconium contenant de l'oxyde d'yttrium comme agent stabilisant du dioxyde de zirconium.

29. Revêtement selon la revendication 20, dans lequel le revêtement contient entre un et cinq microfissures par cm de surface de revêtement.

30. Revêtement selon la revendication 20, dans lequel la couche de composition de silicate dicalcique est comprise entre 50µm et 200µm d'épaisseur.

31. Revêtement selon la revendication 20, comprenant en outre une couche de liaison d'un alliage de nickel ou de cobalt pulvérisé thermiquement sur un substrat métallique, et une couche intermédiaire d'un oxyde de zirconium partiellement ou totalement stabilisé pulvérisé thermiquement, la couche de composition de silicate dicalcique étant thermiquement pulvérisée sur la couche intermédiaire, la couche de liaison étant entre environ 100µm et 200µm d'épaisseur, et la couche intermédiaire étant entre environ 50 µm et 200 µm d'épaisseur, par quoi la couche intermédiaire bloque la réaction entre la couche de liaison et la couche de composition de silicate dicalcique.