Luminescent pigments and paints, and methods of manufacturing and applying the same

Abstract

A doped pigment for application to an object can be used for measurement of thermal history of the object. In addition, a paint comprising a doped pigment and a doped binder, wherein the pigment and the binder have luminescent profiles which provide for resolution over first and second, different temperature ranges can be used for measurement of thermal history of the object. The pigment can be fabricated by a method which comprises the steps of gelling host precursors in a solvent to form a pigment gel; drying the pigment gel; and calcining the dried pigment gel; and the paint can be fabricated by fabricating a pigment by the above-described method; blending the pigment into water; and blending the blended pigment into a binder.

Description

[0001] LUMINESCENT PIGMENTS AND PAINTS, AND METHODS OF MANUFACTURING AND APPLYING THE SAME

[0002] The present invention relates to luminescent pigments and paints, and methods of manufacturing and applying the same.

[0003] Summary of the Invention

[0004] In one aspect the present invention provides a paint for application to an object for measurement of thermal history of the object, the paint comprising a doped pigment and a doped binder, wherein the pigment and the binder have luminescent profiles which provide for resolution over first and second, different temperature ranges.

[0005] In another aspect the present invention provides a doped pigment for application to an object for measurement of thermal history of the object.

[0006] In a further aspect the present invention provides a method of fabricating a pigment for application to an object for measurement of thermal history of the object, the method comprising: gelling host precursors in a solvent to form a pigment gel; drying the pigment gel; and calcining the dried pigment gel.

[0007] In a yet further aspect the present invention provides a method of fabricating a paint for application to an object for measurement of thermal history of the object, the method comprising: fabricating a pigment by the above-described method; blending the pigment into water; and blending the blended pigment into a binder.

[0008] Brief Description of the Drawings

[0009] Preferred embodiments of the present invention will now be described hereinbelow by way of example only with reference to the accompanying drawings, in which:

[0010] Figure 1 illustrates calibration curves for a luminescent pigment and a luminescent binder in accordance with an embodiment of the present invention; Figure 2 illustrates calibration curves for paints including Y2SiO5(YSO), apatite (YAS) and a mixture of YSO / YAS in accordance with embodiments of the present invention;

[0011] Figure 3 illustrates the luminescent intensity for the pigment (EuxYi-^SiOsx at different concentrations of the rare earth Eu;

[0012] Figure 4 illustrates a calibration curve of a paint sample comprising Y2SiO5:Tb and a potassium silicate binder heat treated at different temperatures;

[0013] Figure 5 illustrates a calibration curve for a Y2SiOs pigment sample in accordance with an embodiment of the present invention;

[0014] Figure 6 illustrates calibration curves for lithium silicate and potassium / lithium silicate binders in accordance with embodiments of the present invention;

[0015] Figure 7 illustrates X-ray diffraction plots of pigments for the paint of Example #1 synthesised at room temperature and at 90 °C;

[0016] Figure 8 illustrates calibration curves for the paint of Example #1 where the pigment was calcined at temperatures of 300 °C, 350 °C, 400 °C, 450 °C and 500 °C;

[0017] Figure 9 illustrates the total monotonic, temperature-sensing range as a function of the pigment calcination temperature for the paint of Example #1;

[0018] Figure 10 illustrates calibration curves for the paint of Example #1 as a function of applied thickness;

[0019] Figure 11 illustrates calibration curves for the paint of Example #1 obtained using bandpass filters with centre wavelengths of from 592 nm to 694 nm;

[0020] Figure 12 illustrates calibration curves for the paint of Example #1 obtained using different starting-fit points; and Figures 13(a) and (b) illustrate emission spectra for the paint of Example #1 where heat treated at different temperatures and the calibration curve derived therefrom.

[0021] Detailed Description of the Invention

[0022] It will be appreciated that aspects, embodiments and preferred features of the invention have been described herein in a way that allows the specification to be written in a clear and concise way. However, unless circumstances clearly dictate otherwise, aspects, embodiments and preferred features can be variously combined or separated in accordance with the invention. Thus, preferably, the invention provides a product or method having features of a combination of two or more, three or more, or four or more of the aspects described herein. In a preferred embodiment, a product or method in accordance with the invention comprises all aspects of the invention.

[0023] Within the context of this specification, the word "about" means preferably plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2%.

[0024] Within the context of this specification, the word "substantially" means preferably at least 90%, more preferably 95%, even more preferably 98%, most preferably 99%.

[0025] Within the context of this specification, the word "comprises" means "includes, among other things" and should not be construed to mean "consists of only".

[0026] Within the context of this specification a dopant (also called a doping agent) is a trace of impurity element that is introduced into a chemical material to alter its original electrical or optical properties. The amount of dopant necessary to cause changes is typically very low. When doped into crystalline substances, the dopant's atoms get incorporated into its crystal lattice.

[0027] The present invention utilizes luminescent dopants. The luminescent properties of materials incorporating luminescent dopants depends upon the material, and in particular the specific material structure. As a material is exposed to higher temperatures, the structure of the material will change, resulting in a change in the luminescent properties. Through calibration, the luminescence of a material can be correlated to its past temperature of exposure.

[0028] For temperature sensing, the present invention encompasses a combination of a pigment and a binder. Dopants (luminescent centres) can be provided to either the pigment or the binder, providing different measurement regimens.

[0029] As represented in Figure 1, a doped binder shows measurement resolution at lower temperatures, in this embodiment <600 °C, and a doped pigment shows measurement resolution at higher temperatures, in this embodiment >600 °C.

[0030] The present inventors have recognized that the mixing of a doped pigment and a doped binder allows for the two luminescent behaviours to be exploited, and for measurement resolution over a wider range of temperature, in this embodiment starting at about 150 °C, and extending to temperatures of at least 1200 °C.

[0031] The mixing of the pigment into the binder yields a liquid that can be sprayed as a coating. Moreover, the measurement resolution can be tailored by modifying the mixture primarily to include doped binder, for resolution at lower temperatures, doped pigment, for resolution at higher temperatures, or a combination of doped binder and doped pigment, allowing for a wide range of temperature resolution.

[0032] In one embodiment, as described in more detail hereinbelow, the relationship between the doped binder and the doped pigment can be tailored by changing the pigment calcination temperature.

[0033] In one, primary aspect the paint comprises a pigment and a binder.

[0034] In one embodiment the pigment is Y:Si. In one embodiment the Y:Si pigment includes not more than 0.5 mol% Si. A SiO2mol° / o of 0.5 results in Y2SiOs, and a range of 0-0.5 SiO2mol% yields a mixture of Y2SiO5, Y2O3and possibly apatite 4.67(SiO4)3O. Outside this range, impurities were found, such as Y2Si2O?, which hindered performance.

[0035] Figure 2 illustrates calibration curves, in this embodiment represented by lifetime decay, for paints including Y2SiOs (YSO), apatite (YAS) and a mixture of YSO / YAS.

[0036] In one embodiment the pigment includes Eu, which has been found to encourage the formation of the apatite phase.

[0037] In one embodiment the pigment includes one or both of a rare earth dopant and a transition metal dopant.

[0038] In one embodiment the pigment is (REAYi-y)2SiO5x, where RE is a rare earth or transition metal dopant.

[0039] In one embodiment the dopant is Eu3+.

[0040] Figure 3 illustrates the intensity for the pigment, where including an Eu dopant concentration (x) of 0.005, 0.02, 0.04, 0.08, 0.1, 0.16, 0.2, 0.25 and 0.32. As will be seen, a maximum intensity is achieved at a concentration (x) of about 0.16.

[0041] In one embodiment the dopant concentration in the pigment is from about 0.05 to about 0.25, optionally from about 0.1 to about 0.2.

[0042] In another embodiment the dopant is Tb3+.

[0043] Figure 4 illustrates the calibration curve, in this embodiment represented by the lifetime decay, here at 543 nm, of a paint comprising an Y2SiOs:Tb pigment and a potassium silicate binder heat treated at different temperatures. As will be seen, the dynamic range is 700-1200 ps, which compares to 800-2000 ps for the counterpart paint utilizing an Eu dopant over the same temperature range.

[0044] In one embodiment the pigment can be used alone, in the absence of a binder.

[0045] In this embodiment the pigment can be used in powder form, and applied to a surface.

[0046] In an alternative embodiment the pigment can be pelletized, and the pellets inserted, fixed or applied at a desired location.

[0047] Figure 5 illustrates the calibration curve, in this embodiment represented as the lifetime decay, for a Y2SiOs pigment, which exhibits a measurement resolution over the range of from about 400 °C to at least 1200 °C.

[0048] In one embodiment the paint has a composition of pigment to binder of from about 5 wt% to about 25 wt%, optionally about 5 wt% to about 15 wt%.

[0049] In one embodiment the binder is an aqueous silicate solution, optionally metal silicate solutions, for example, aqueous alkali metal silicate solutions.

[0050] In one embodiment the binder is an aqueous solution which includes one or more of sodium silicate, potassium silicate, lithium silicate and magnesium aluminium silicate.

[0051] For potassium silicate solutions, the preferred composition is within the phase diagram between K2Si2O5and K2Si4O9.

[0052] Figure 6 illustrates calibration curves, in this embodiment represented as the lifetime decay, for lithium silicate and potassium / lithium silicate binders.

[0053] In one embodiment the binder has a mole fraction of SiO2of from about 0.5 to about 0.70, optionally from about 0.50 to about 0.60, optionally about 0.55 + / - 10%. The melting point of the binder, and hence the paint, can be tailored by changing the mole fraction of SiO2, with lower mole fractions giving higher melting points, for example, 1045 °C for 0.5 as compared to 771 °C for 0.7.

[0054] In one embodiment the composition of binder to water is from about 5 wt% to about 30 wt%, optionally from about 5 wt% to about 20 wt%, optionally about 12 wt% + / - 10%.

[0055] The amount of water in the mixture affects the viscosity and pH of the paint, with higher water content lowering the pH of the paint.

[0056] In one embodiment the paint has a solid content of from about 35 wt% to about 42 wt%, optionally from about 36 wt% to about 39 wt%.

[0057] Examples

[0058] Fabrication of exemplary pigments will now be described with reference to the following non-limiting Examples.

[0059] Example #1

[0060] In a first step, the pigment is formed by gelling of host precursors yttrium nitrate hexahydrate Y(NO3)3.6H2O, TEOS Si(OC2H5)4 and dopant precursor rare earth nitrate hexahydrate RE(NO3)3.6H2O, in a solvent.

[0061] Precursors are added in the ratio 1:20:2.79 for TEOS: Solvent: Water. Water is added in the ratio for TEOS:Water of up to 1:20:5. The amount of water affects the time of synthesis, but does not impact the quality of the pigment once fabricated. For synthesis, stoichiometric amounts of nitrate powders are dissolved separately in distilled water, and then combined and allowed to mix for 1 hour. The solvent is then added, and the mixture is allowed to spin for 1 hour. TEOS is then added dropwise. A gelating / chelating agent, such as citric acid, may be used. In this embodiment the dopant precursor is europium nitrate hexahydrate EU(NO3)3.6H2O. Other precursors include rare earth chlorides, such as EuCI3, and rare earth acetates, such as Eu(CH3CO2)3xH2O.

[0062] In this embodiment the solvent is ethanol (C2H6O), but other solvents can be used, including isopropyl alcohol (IPA).

[0063] In this embodiment gelling of the precursors is performed for at least 24 hours. Longer gelling times at room temperature have not been observed to affect the resulting pigment.

[0064] In this embodiment gelling is performed at room temperature. Whilst roomtemperature gelling is optimal, gelling can be done at temperatures between about 20 °C and about 150 °C.

[0065] Figure 7 illustrates X-ray diffraction plots of pigments synthesised at room temperature and at 90 °C. The higher-temperature gelling shows higher intensity peaks, corresponding to a secondary impurity phase (marked with stars).

[0066] In a second step, the pigment gel is dried.

[0067] In one embodiment the pigment is dried at a temperature of between 100 °C and 300 °C.

[0068] In this embodiment the pigment gel is dried at 250 °C.

[0069] In one embodiment the pigment gel is dried for between 12 hours and 24 hours, typically dependent on batch size.

[0070] In a third and final step, the pigment is calcined. In one embodiment the pigment is calcined at a temperature of between 150 °C and 750 °C.

[0071] In one embodiment the pigment is calcined for at least 1 hour.

[0072] Following this step, the pigment is mixed into water, and then mixed into the binder. The pigment and the binder, on mixing with water, interact to form a new mixture, with some dopant ions from the pigment being transferred into the binder. This dopant transfer yields the binder with the luminescent behaviour described above in relation to Figure 1, providing for resolution at lower temperatures. This mixing is critical for paint performance with wider measurement capabilities.

[0073] Figure 8 illustrates calibration curves, in this embodiment represented by the lifetime decay, for the paint of Example #1 where the pigment was calcined at temperatures of 300 °C, 350 °C, 400 °C, 450 °C and 500 °C before incorporating into the paint. As will be seen, the calcination temperature has a significant effect on the resolution of thermal history at different temperature ranges.

[0074] The calcination temperature can be used to tailor performance to specific temperature ranges:

[0075] • Lower pigment calcination temperatures (< 350 °C) provide good resolution at lower temperatures, typically starting at about 120 °C, but no resolution at higher temperatures, typically above 750 °C.

[0076] • Intermediate pigment calcination temperatures (about 400 °C) provide the widest dynamic range, with a temperature measurement resolution between about 200 °C and about 900 °C.

[0077] • Higher pigment calcination temperatures (>500 °C) do not provide measurement resolution at lower temperatures, but provide increased resolution at higher temperatures, typically at least 1000 °C.

[0078] The pigment calcination temperature thus allows for tailoring of the measurement range and performance. Measurement resolution arises not only due to crystallisation, but also from the interaction between the pigment and the binder. These two populations evolve differently with exposure to temperature, giving rise to measurement resolution. As shown in Figure 8, calcination of the pigment at about 400 °C is preferred when a wide temperature range is required. Other calcination temperatures can be selected when increased resolution is required over narrower ranges.

[0079] Figure 9 illustrates the total monotonic range (temperature sensing resolution) as a function of the pigment calcination temperature for the paint of Example #1.

[0080] The steps in mixing of the paint will now be described hereinbelow.

[0081] In a first step, the pigment is blended with water in a mixer, in this embodiment a ball mixer. In this embodiment, the mixer is an overhead stirrer with variable speed, but other mixers can be used, including horizontal bead mills.

[0082] In this Example, 2.5 g of pigment (Yo.84)2Si05:Euo.i6 and 6 g of water, here distilled water, were mixed using 58 g of 2 mm diameter zirconia beads and spun at 420 rpm for 10 minutes. In an alternative embodiment glass beads can be used.

[0083] In one embodiment the beads have diameters in the range of from about 1 mm to about 3 mm.

[0084] In one embodiment the mixer includes at least 20 g of beads.

[0085] In a second step, the mixed pigment is further mixed with the binder.

[0086] In this embodiment the pigment is mixed with 47 g of binder and spun at 550 rpm for 45 minutes.

[0087] In one embodiment the mixture is spun for at least 45 minutes. In a third step, the mixed paint is subjected to ultrasonication, in this embodiment for 180 s, using an ultrasonicator (50W, 42kHz ultrasonic frequency).

[0088] In one embodiment the paint can be applied to a surface by an applicator, such as a brush or a spray gun.

[0089] In a first step, the prepared paint is applied to a surface and allowed to air dry for a drying period.

[0090] In one embodiment the drying period is at least 15 minutes. In this embodiment the drying period is 30 minutes.

[0091] In a second step, the paint is then cured at an elevated temperature for a curing period.

[0092] In one embodiment the curing period is at least 30 minutes. In this embodiment the curing period is 1 hour.

[0093] In one embodiment the curing temperature is at least 100 °C. In this embodiment the curing temperature is 150 °C.

[0094] In one embodiment the paint is applied with a thickness of less than 50 pm.

[0095] In one embodiment the paint is applied to a thickness of from about 30 pm to about 40 pm.

[0096] Figure 10 illustrates calibration curves, in this embodiment represented by the lifetime decay, for the paint of Example #1 as a function of the applied thickness. As will be seen, the thickness of the applied paint has a significant effect where the paint is subjected to temperatures greater than 600 °C. The lifetime decay parameter is measured by monitoring the temporal response of the luminescence, that is, intensity over time. This intensity can be measured at specific wavelengths, and is selected by fitting a bandpass filter. Figure 11 shows that bandpass filters with centre wavelengths between 592 nm and 694 nm all provide suitable calibration curves.

[0097] The lifetime decay parameter is obtained by fitting a single exponential curve to the curve of intensity versus time. The window of fitting can be used further to change the measurement resolution. As shown in Figure 12, changing the starting-fit point, that is, adding a delay to the fitting, can have a significant influence on the measurement. A full-fitting window, starting at 0 ps, provides widest range and best resolution at lower temperatures <500 °C. Shorter-fitting windows, typically starting at 2000 ps, provide higher resolutions at higher temperatures. Fitting windows can be varied, or used in combination, in order to maximise measurement resolution depending on the requirements.

[0098] The primary measurement process for the paint of the present invention is measurement of lifetime decay. However, an alternative measurement includes the measurement of an intensity ratio between two individual areas, as represented by Area 1 / Area 2 in Figure 13, which provides suitable measurement resolution for temperatures between about 150 °C and about 900 °C.

[0099] Finally, it will be understood that the present invention has been described in its preferred embodiments and can be modified in many different ways without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS1. A paint for application to an object for measurement of thermal history of the object, the paint comprising a doped pigment and a doped binder, wherein the pigment and the binder have luminescent profiles which provide for resolution over first and second, different temperature ranges.

2. The paint of claim 1, wherein the pigment is Y:Si, optionally the Y: Si pigment includes not more than 0.5 mol% Si.

3. The paint of claim 1 or 2, wherein the pigment includes one or both of a rare earth dopant and a transition metal dopant, optionally the pigment is (REyYi-xjzSiOsx, where RE is a rare earth or transition metal dopant, optionally the dopant concentration x is from about 0.05 to about 0.25, optionally from about 0.1 to about 0.2, optionally the dopant is Eu.

4. The paint of any of claims 1 to 3, wherein the binder is an aqueous silicate solution, optionally a metal silicate solution, optionally an aqueous alkali metal silicate solution, optionally one or more of a sodium silicate solution, a potassium silicate solution, a lithium silicate solution and a magnesium aluminium silicate solution, optionally a potassium silicate solution within a phase diagram between K2Si2O5and K2Si4O9, optionally the binder has a mole fraction of SiO2of from about 0.5 to about 0.70, optionally from about 0.50 to about 0.60, optionally about 0.55 + / - 10%.

5. The paint of any of claims 1 to 4, wherein the paint has a composition of pigment to binder of from about 5 wt% to about 25 wt%, optionally from about 5 wt% to about 15 wt%.

6. The paint of any of claims 1 to 5, wherein the paint has a composition of binder to water of from about 5 wt% to about 30 wt%, optionally from about 5 wt% to about 20 wt%, optionally about 12 wt% + / - 10%.

7. The paint of any of claims 1 to 6, wherein the paint has a solid content of from about 35 wt% to about 42 wt%, optionally from about 36 wt% to about 39 wt%.

8. The paint of any of claims 1 to 7, where applied to a surface, the paint having a thickness of less than 50 pm, optionally from about 30 pm to about 40 pm.

9. A doped pigment for application to an object for measurement of thermal history of the object.

10. The pigment of claim 9, wherein the pigment is Y:Si, optionally the Y: Si pigment includes not more than 0.5 mol% Si.

11. The pigment of claim 9 or 10, including one or both of a rare earth dopant and a transition metal dopant, optionally (REyYi-y)2SiO5x, where RE is a rare earth or transition metal dopant, optionally the dopant concentration x is from about 0.05 to about 0.25, optionally from about 0.1 to about 0.2, optionally the dopant is Eu.

12. The pigment of any of claims 9 to 11, wherein the pigment is (i) a powder or (ii) a pellet.

13. A method of fabricating a pigment for application to an object for measurement of thermal history of the object, the method comprising: gelling host precursors in a solvent to form a pigment gel; drying the pigment gel; and calcining the dried pigment gel.

14. The method of claim 13, wherein the host precursors comprise an yttrium precursor, a silicon precursor and a dopant precursor, optionally the yttrium precursor comprises yttrium nitrate hexahydrate Y(NO3)3.6H2O, optionally the silicon precursor comprises TEOS Si(OC2H5)4, optionally the dopant precursorcomprises (i) a nitrate hexahydrate RE(NO3)3.6H2O, where RE is a rare earth or transition metal, optionally europium nitrate hexahydrate Eu(NO3)3.6H2O, (ii) a rare earth or transition metal chloride, optionally EuCI3, or (iii) a rare earth or transition metal acetate, optionally Eu(CH3CO2)3xH2O, optionally the solvent is ethanol (C2H6O) or isopropyl alcohol (IPA).

15. The method of claim 13 or 14, wherein gelling of the host precursors is performed for at least 24 hours.

16. The method of any of claims 13 to 15, wherein gelling of the host precursors is performed at room temperature or at a temperature of between about 20 °C and about 150 °C.

17. The method of any of claims 13 to 16, wherein drying of the pigment gel is performed at a temperature of between about 100 °C and about 300 °C.

18. The method of any of claims 13 to 17, wherein drying of the pigment gel is performed for between about 12 hours and about 24 hours.

19. The method of any of claims 13 to 18, wherein calcining of the dried pigment gel is performed at a temperature of between about 150 °C and about 750 °C.

20. The method of any of claims 13 to 19, wherein calcining of the dried pigment gel is performed for at least 1 hour.

21. A method of fabricating a paint for application to an object for measurement of thermal history of the object, the method comprising: fabricating a pigment by the method of any of claims 13 to 20; blending the pigment into water; and blending the blended pigment into a binder.

22. The method of claim 21, wherein the binder is an aqueous silicate solution, optionally a metal silicate solution, optionally an aqueous alkali metal silicate solution, optionally one or more of a sodium silicate solution, a potassium silicate solution, a lithium silicate solution and a magnesium aluminium silicate solution, optionally a potassium silicate solution within a phase diagram between K2Si20s and K2Si40g, optionally the binder has a mole fraction of SiO2of from about 0.5 to about 0.70, optionally from about 0.50 to about 0.60, optionally about 0.55 + / - 10%.

23. The method of claim 21 or 22, wherein the paint has a composition of pigment to binder of from about 5 wt% to about 25 wt%, optionally from about 5 wt% to about 15 wt%.

24. The method of any of claims 21 to 23, wherein the paint has a composition of binder to water of from about 5 wt% to about 30 wt%, optionally from about 5 wt% to about 20 wt%, optionally about 12 wt% + / - 10%.

25. The method of any of claims 21 to 24, wherein the paint has a solid content of from about 35 wt% to about 42 wt%, optionally from about 36 wt% to about 39 wt%.

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