Near-infrared transmitting copper oxide nanoparticles

Abstract

Black IR-reflective or transmissive pigments from which LiDAR-responsive black coatings can be formed, wherein the pigments exhibit similar blackness M to non-IR-reflective carbon black y Values. The CuO particles exhibit small crystallites with a (−111) / (111) reflection intensity ratio of less than 18 nm and less than 1.2. The method of forming the CuO particles includes precipitating CuCO3 or CuCO3 / Cu(OH)2 using an alkaline carbonate as a precipitant and calcining the precipitate at about 300 °C to about 400 °C.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims the benefit of and priority to U.S. Patent Application Serial No. 16 / 929,414, filed July 15, 2020, entitled “Near Infrared Transmitting Copper Oxide Nanoparticles,” the contents of which are incorporated herein by reference in their entirety. TECHNICAL FIELD

[0003] The present disclosure generally relates to copper oxide-based pigments and pigment compositions for use in paint formulations featuring near infrared transmission and / or reflection for use in near IR light detection and ranging (LiDAR) applications. BACKGROUND

[0004] For purposes of presenting the context of the present disclosure generally, background description is provided herein. To the extent that the work of the current named inventors, and aspects of the description that can not otherwise qualify as prior art to the present technology, are described in this Background section, they are not to be construed as constituting prior art by virtue of being described in this section.

[0005] Autonomous vehicles use LiDAR light in the near IR, typically at 905 nm or 1550 nm, to detect objects. As explained in Figure 1 , white and many other colors exhibit near IR reflection, while traditional black pigments used in paints and coatings, typically based on carbon black, absorb near IR frequencies. This often makes objects with coatings having traditional black pigments virtually invisible to LiDAR sensors. Black and dark color paints are often encountered in traffic in Figure 2 , vehicles and other objects that reflect near IR in the manner explained in Figure 3 , it is desirable to use black and dark color paints on vehicles and other objects that reflect near IR in the manner explained in

[0006] Copper(ll) oxide (CuO) has been investigated for use as a black pigment, which has been used as a dark color pigment for ceramic glazes. Coating pigments generally require uniform particles of less than 3 microns. CuO powders exhibit different morphologies and properties depending on their method of preparation. Typically, commercial methods do not provide CuO particles that are readily used as coating pigments because these methods produce large particles or aggregates of fine particles. Typical precipitation methods provide CuO with an average particle size greater than 10 microns, although particles less than 10 microns with a narrow particle distribution of less than three are prepared by milling. For example, U.S. Patent No. 9,683,107 is directed to an infrared-reflective “black” pigment prepared by heating and milling at least 99% pure CuO at over 480°C to produce particles of about 1 to 3 microns (with crystallite size greater than 19 nm), although the “black” pigment is brownish in appearance with CIE-LAB values of about 28, 0.5, and -0.3.

[0007] For LiDAR applications, it is desirable to have a bandgap of about 1.2 to 1.7 eV with an energy band edge less than 700 nm (or 1.77 eV) to absorb the visible spectrum and transmit near-IR wavelengths that are active for LiDAR. As-is, typical bulk CuO has a bandgap of greater than 1.3 to 1.7 eV and an energy band edge greater than 1.77 eV and does not meet this requirement. There is a need for a CuO pigment having the appropriate size and composition that exhibits blackness approaching carbon black and is configured to selectively reflect near-IR radiation, particularly at 905 nm and / or 1550 nm wavelengths, for object detection by autonomous vehicles using LiDAR technology. SUMMARY

[0008] This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features.

[0009] In aspects, the present teachings provide a black pigment comprising near-IR transmitting and / or reflecting particles having CuO on at least a portion of the outer surface of the particles. The particles have a crystallite size of less than about 15 nm and a relative intensity of the (-111) / (111) planes of about 1.2 or less by X-ray diffraction analysis (XRD). The particles can have a diameter of less than about 10 nm to greater than about 10 pm. The particles enable reflection of LiDAR radiation at 905 nm and / or 1550 nm for object detection and exhibit a bandgap of 1.2 to 1.7 eV and a blackness M y value of at least about 132.

[0010] In other aspects, the present teachings provide a coating composition comprising a fluid medium and a black pigment comprising near IR transmitting and / or reflecting particles having CuO disposed on at least a portion of the outer surface of the particles. The coating composition can be used as a black paint or coating.

[0011] In other aspects, the present teachings provide a method of making near IR transmitting and / or reflecting particles having CuO on at least a surface of the particles. The method comprises forming and precipitating CuCO3 or CuCO3 / Cu(OH)2 by reaction of an alkali metal carbonate with a water soluble copper (II) salt. The precipitation can be accompanied by deposition of CuCO3 onto a support particle when the aqueous solution has suspended particles (nanoparticles or microparticles). The support particle can be a core particle comprising CuO of the particle and can have a cross section of less than 300 nm to greater than 1.5 μΜ. When the deposition is on another constituent particle, the CuO portion of the particle is 50 nm or less. The nanoparticles or microparticles of CuCO3 / Cu(OH)2 are rinsed, filtered, dried and calcined to a temperature between about 300 and 400 °C.

[0012] In further aspects, the present teachings provide a black paint for application on the outer surface of a vehicle or other object capable of being detected by LiDAR technology. For example, LiDAR technology can assist in many functions of an autonomous vehicle by detecting reflections of 905 nm and / or 1550 nm wavelengths transmitted from the near IR laser of the LiDAR technology. The black pigments of the present technology can exhibit a blackness M y value of at least about 132, which results in an aesthetic quality of the carbon black pigment and also provides good reflection of infrared radiation.

[0013] Further areas of applicability of the above-coordinated technology and various methods of implementation will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

[0014] BRIEF DESCRIPTION OF DRAWINGS

[0015] The present teachings will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0016] Figure 1 A reflectance chart showing current white and black paints for vehicles is shown, illustrating that reflectance of near IR is insufficient for conventional black paints based on carbon black.

[0017] Figure 2 A reflectance chart showing target IR reflecting black paint versus current black paint is shown, where the goal is to achieve blackness similar to current paints but reflectance at near IR of 905 and / or 1550 nm.

[0018] Figure 3 "blackness" plot showing current automotive standard carbon black pigments and various commercially available near-IR reflecting pigments based on chromium iron oxides.

[0019] Figures 4A-4C Transmission electron micrographs of IR reflecting CuO particles according to an aspect of the technology are shown, where aggregated particles greater than 6 μm Figure 4A ) are aggregated particles less than about 40 nm Figure 4B ) and primarily about 20 nm particles Figure 4C ).

[0020] Figure 5 Blackness M value plots showing black touch-up paint, carbon black, CuO based IR reflecting paint (Cool Black 0912), commercially available CuO variants and CuO particles precipitated and calcined using various precipitants and calcination temperatures. y including particles according to an aspect of the technology.

[0021] Figures 6A-6E From left to right are photographs of: carbon black Figure 6A ), CuO precipitated with Na2CO3 calcined at 300°C according to an aspect of the technology Figure 6B ), CuO precipitated with (NH4)2CO3 calcined at 300°C Figure 6C ), CuO precipitated with NaOH calcined at 300°C Figure 6D ) and commercial CuO powder Figure 6E ).

[0022] Figures 7A-7C are X-ray micrographs of: CuO precipitated with NaOH calcined at 300°C Figure 7A ), CuO precipitated with (NH4)2CO3 calcined at 300°C Figure 7B ) and CuO precipitated with Na2CO3 calcined at 300°C according to an aspect of the technology Figure 7C where the size bar has a length of 1 μm.

[0023] Figure 8 is a plot of relative intensity of the (-111) / (111) reflection of CuO particles formed from different precipitates and calcined at different temperatures as indicated herein.

[0024] Figures 9A-9D From left to right are photographs of different milled pigments: carbon black Figure 9A ), CuO precipitated with Na2CO3 calcined at 300°C according to an aspect of the technology Figure 9B ), CuO precipitated with Na2CO3 calcined at 400°C according to an aspect of the technology Figure 9C) and 500°C calcined Na2C03 precipitated CuO Figure 9D

[0025] Figure 10 is a plot of the (-111) / (111) relative intensity versus crystallite size for Na2C03 precipitated CuO calcined at temperatures of 300, 400, 500, and 600°C.

[0026] Figure 11 is a composite reflectance spectrum of various coatings including carbon black, commercially available CuO, a common commercially available NIR reflective coating, and a NIR reflective CuO according to embodiments.

[0027] Figure 12 is a schematic cross-section of a typical layered painted substrate.

[0028] Figure 13 is a plot of the reflectance intensity versus LiDAR detected rotation angle for a mirror, a red pigment, a green pigment, and a black pigment according to an aspect of the technology.

[0029] It should be noted that the drawings set forth herein are intended to exemplify the general manner of the methods, algorithms and apparatuses set forth in the various aspects. These drawings can not precisely reflect the specific characteristics of any given aspect and are not necessarily intended to limit or limit the specific embodiments within the scope of the technology. In addition, some aspects can include features from combinations of the drawings. DETAILED DESCRIPTION

[0030] The technology generally provides black pigments containing near-IR transmitting and / or reflecting particles having CuO disposed on at least a portion of the outer (i.e., exposed) surface of the particles. The entire particle can be CuO. The CuO provides strong absorption of visible light in most of the visible spectrum, but shows significant reflection in the near-IR. In aspects, the crystalline size, as indicated by the (-111) reflected size, can have a maximum dimension of less than about 18 nm, and the relative intensity of the (-1,1,1) / (1,1,1) plane is about 1.2 or less. The particles can have a diameter dimension of less than about 40 nm. The particles enable reflection of LiDAR radiation at 905 nm and / or 1550 nm for object detection, and the particles show a band gap of 1.2 eV to 1.7 eV and exhibit a blackness M y value of at least about 132. The particles can have a nanoscale dimension of less than 40 nm to a microscale dimension of greater than 10 pm. The small crystalline size of the CuO particles provides near-IR transmission or reflection without significant visible light reflection characteristic of black pigments. Reflection of LiDAR radiation at 905 nm and / or 1550 nm can be used in detection of the particles.

[0031] ​In one aspect of the technology, incorporating black pigments into a coating composition such that the composition, when applied to a surface, retains, provides, or enhances the near-IR reflectance of the black pigments. The black pigments can exhibit a blackness M y value of about 132 or greater, thereby resulting in a black coating having similar black color quality as provided by traditional black coatings based on carbon black, which are coatings lacking reflectance or transmittance capabilities in the IR. The coating composition can include a fluid medium that allows for the application of the black pigments at a particle loading that achieves the desired aesthetic on the desired surface. The fluid medium is preferably a fluid that allows for coating by common techniques such as spraying or dipping.

[0032] In another aspect, the present teachings provide a method of making a near-IR transmissive and / or reflective particle having CuO on at least the surface of the particle. The method includes forming and precipitating CuCO3 from an aqueous solution by the reaction of an alkali metal carbonate with a water-soluble copper (II) salt, such as copper (II) nitrate. The precipitation can be accompanied by deposition of the CuCO3 onto a carrier particle. The carrier particle can be a nanoparticle of mica, synthetic mica, glass, quartz, alumina, or any other particle that enhances the reflection and / or transmission of IR radiation while maintaining the aesthetic of a black pigment. The particle cross-section can be less than 300 nm, and wherein the CuO portion of the particle is 50 nm or less. The particles can be formed into particle aggregates, which can be milled to form nanoparticles or aggregated nanoparticles, such as particles less than 300 nm. Milling can include ball milling, jet milling, or any other technique that facilitates the formation of particles of the desired size. The particles can generally be less than 300 nm or greater than 10 μιη, while maintaining a small crystallite size, such as about 15 nm or less.

[0033] As detailed herein, the present teachings are directed not only to the development of black pigments in a coating composition, but also to the application and use of the coating composition as a paint that cures on the exterior surface of a vehicle or other object capable of being detected by LiDAR technology. LiDAR detection can allow for the normal operation of an autonomous vehicle by detecting the reflection of 905 nm and / or 1050 nm wavelengths transmitted from the near-IR laser of LiDAR technology, while the coating composition retains the blackness typical of carbon black IR absorbing pigments.

[0034] In one aspect of the technology, the CuO portion of the nanoparticle can be 50 nm or less and have a band gap of less than 1.7 eV, such as 1.2 to 1.6 eV. The size results from the synthesis of the nanoparticle by precipitating CuCO3 or CuCO3 / Cu(OH)2 nanoparticles, followed by drying and subsequent calcination of the particles at a temperature between about 300 and about 400 °C, thereby decomposing the CuCO3 or CuCO3 / Cu(OH)2 nanoparticles into CuO nanoparticles having a cross-section of less than 40 nm to a cross-section of up to 10 μιη. Figures 4A-4CExemplary CuO nanoparticles are shown in the TEM images, where aggregated particles greater than 6 μm (4A), where aggregated particles are less than about 40 nm (4B) and primarily about 20 nm particles (4C).

[0035] In another aspect of the present technology, the method of making nanoparticles is by a precipitation method, in which an aqueous solution of Cu(N03)2or other highly soluble Cu(ll) salt such as CuBr2, CuCl2, Cu(CI03)2or CuS04is combined with an aqueous solution of a precipitating agent, which can be Na2C03, K2C03, Li2C03, Rb2C03, Cs2C03, Fr2C03or any combination thereof. The basic precipitating agent can be added to the Cu(N03)2solution until the pH reaches a level of 9 to 10. The resulting precipitate is then isolated and rinsed with water to effectively result in suspended solid CuC03or CuC03 / Cu(OH)2particles free of basic nitrate and basic carbonate. The CuC03 / Cu(OH)2particles are those with CuC03, Cu(OH)2and mixed anions of CO3 -2 and OH"anions, similar to malachite. After filtration and drying, the aggregated CuC03particles are ground to a fine powder appropriate for formulating a coating composition, and the particles are calcined at a temperature between about 300 and about 400 °C to form black CuO particles.

[0036] The rinsed CuC03particles or CuC03 / Cu(OH)2are dried. The drying can occur in air, under nitrogen, inert atmosphere, oxygen-rich atmosphere, or under vacuum. The drying can occur at a temperature from ambient to about 120 °C, depending on the pressure used during drying. The dried CuC03-containing particles can be ground to a fine or ultra-fine powder. The grinding can be performed in any mill appropriate for the hardness of the material. For example, the mill can be, but is not limited to, a ball mill, jet mill, high compression roller mill, roller mill, or general purpose mill. Subsequently, the dried particles are calcined at a temperature between about 300 and 400 °C to convert the CuC03-containing particles to CuO-containing particles exhibiting a band gap of about 1.7 eV or less. As an alternative to making the particles by precipitation, CuO particles can be formed from ground malachite, such as using CuC03-Cu(OH)2(Sigma), in which the calcination is performed in the manner described above for the Na2C03precipitated particles to produce a black pigment with similar properties of LIDAR activity. Thus, by appropriate calcination temperature and precursor composition, the resulting black pigment can exhibit a blackness M y value greater than about 132.

[0037] The precipitation method according to aspects of the present technology can be a deposition-precipitation method. A solution of Cu(NO3)2may be combined with nanoparticles, e.g., mica, synthetic mica, glass, quartz, or alumina, as core material to form a suspension on which CuCO3may be deposited during reaction with a precipitant to form a shell. The shell can be continuous or discontinuous, e.g., provided as CuO islands on the core particles. Upon washing and calcination, the core-shell nanoparticles are those having a core covered or modified by a CuO shell. In one aspect, the core cross-section is less than or equal to 10 μm, and the shell thickness is less than 50 nm and can be a continuous or discontinuous shell. In another aspect, the core particle cross-section can be equal to or less than 300 nm, with CuO surface features having a dimension less than 50 nm.

[0038] For the combination of the precipitant solution and the solution or suspension including Cu(NO3)2, the precipitation or deposition-precipitation method can be carried out as a batch or continuous process. Slow addition of the basic precipitant solution can be carried out using at least one dropping funnel or its equivalent, or at least one pump, with the distribution profile of the addition maintained at a desired rate, which can be constant, accelerated, or decelerated, such that the quality and yield of the CuCO3-containing precipitated particles can be optimized. Suitable agitation can be provided by at least one agitator or other mixer. A continuous mixing loop can be constructed using at least one active or passive in-line mixer through which the flow of the suspension passes. Alternatively or additionally, mixing can be carried out or enhanced by cavitation, which can be facilitated by ultrasound, piezoelectric, or other means.

[0039] After the formation of the precipitated CuCO3- or CuCO3 / Cu(OH)2-containing particles, the resulting aqueous solution can be removed from the particles by filtration or centrifugation. Filtration can be carried out by applying pressure on the side of the filter adjacent to the particles or reducing the pressure on the side of the filter away from the particles. Subsequently, the particles are washed to remove the water-soluble salts. Washing can be carried out in batch mode, in which the particles are suspended in pure water and filtered again or centrifuged again; or the particles can be washed in continuous mode by passing water through the filter bed or centrifuge bed. The water can be distilled water, ion-exchange water, or reverse osmosis purified water, as desired.

[0040] The use of alkali metal carbonates as precipitants provides small crystallite sizes of less than about 18 nm and favorable (-111) / (111) ratios, with excellent blackness when calcination is carried out at temperatures of about 300-400°C to convert the carbonate / hydroxide particles to CuO particles without any significant visible light reflection. Other precipitants and methods of grinding or otherwise reducing particle size do not provide high quality black IR reflecting pigments, as indicated in U.S. Patent No. 6,680,071, for example. As can be seen in Table 1 of U.S. Patent No. 6,680,071, the use of Na2CO3as a precipitant provides a CuO particle with a (-111) / (111) ratio of 0.5, which is not as good as the ratio of 0.3 provided by the use of NaHCO3as a precipitant. The use of Na2CO3as a precipitant also provides a CuO particle with a crystallite size of 22 nm, which is not as small as the crystallite size of 18 nm provided by the use of NaHCO3as a precipitant. Figure 5 Figure 5 y ​​It can be seen that, similar to non-IR reflective repair paints, the required blackness, similar to that of carbon black, cannot be achieved by grinding commercially available CuO or by forming nanoparticles from CuO. The precipitation method used to obtain the black pigment of this invention using NaCO3 as a precipitate yields sufficient blackness upon calcination at 300°C, but not at 450°C. Similarly, using ammonium carbonate as a precipitate provides sufficient blackness upon calcination at 300°C, but not at 450°C, while using NaOH as a precipitate does not allow for sufficient blackness. Figures 6A-6E The study explains that commercially available CuO (6E) produces poor blackness, similar to Cu(OH)₂ (6D) precipitated from NaOH calcined at 300°C. In contrast, using CuCO₃ to precipitate from sodium carbonate (6B) or ammonium carbonate (6C) and calcining at 300°C produces a black pigment similar to carbon black (6A), although the ammonium carbonate-derived CuO has some reddish hue.

[0041] CuO formed by precipitation of CuCO3 or Cu(OH)2 exhibits different morphologies and aggregate sizes depending on the precipitate used, such as... Figures 7A-7C As shown, the aggregated elongated filaments formed from the NaOH precipitation of Cu(OH)₂ exhibit a more uniform appearance (7A), while the separated, roughly spherical particles of CuO are formed from carbonates, although those formed from ammonium carbonate (7B) have a smaller size than those formed from sodium carbonate (7C). Note that the CuCO₃ produced from ammonium carbonate results in a slightly reddish hue, and the difference in relative (-111) / (111) intensity and the crystallite size determined by the (-111) peak suggests that the best black has smaller values ​​for both characteristics. Figure 8 As shown, CuO forms an excellent black pigment, exhibiting a small (-111) size and a relative (-111) / (111) intensity, where for values ​​greater than approximately For particles of approximately 1.2, sufficient blackness has not been achieved.

[0042] When CuCO3 / Cu(OH)2 is calcined at 400℃, the calcination temperature allows the black CuO to remain close to black at a lower temperature, but when calcined at 500℃, a more brownish CuO is formed, such as... Figures 9A-9D As shown. Although the relative strength (-111) / (111) remains low and decreases from the highest value when calcined at 300°C, the crystallite size, as measured by the size of (-111), increases from approximately 15 nm when calcined at 400°C to nearly 40 nm when calcined at 600°C. Figure 10 As shown in the image.

[0043] The near-IR reflective CuO-containing particles can be configured to have the same properties as... Figure 11coatings compositions similar to those described in the'1 1 1 patent. These particles can be included in water-based or oil-based formulations, such as water-based acrylic polyurethane enamel primers. Such black near-IR reflective coating compositions can be used as a base coat positioned between a primer and a clear coat to which it is applied to a finished vehicle body panel, as shown in Figure 12 Figure 13 As shown in the'1 1 1 patent, the black near-IR reflective coating compositions can be used as a base coat positioned between a primer and a clear coat to which it is applied to a finished vehicle body panel, as shown in

[0044] The preceding description is intended primarily for regular patent application purposes only and is not meant to limit the disclosure, its application or uses. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using the non-exclusive logical OR word "or". It should be understood that different order of steps within the methods can be employed without altering the principles of the disclosure. The disclosure of ranges includes disclosure of all ranges including endpoints within the entire range and sub-ranges within the entire range.

[0045] The headings (e.g., "BACKGROUND" and "SUMMARY") and sub-headings, if any, are intended only for general organization of topics within the disclosure, and are not meant to limit disclosure of the technology or any aspect thereof. The use of section headings is not intended to limit the scope of the disclosure or any aspect thereof.

[0046] As used herein, the terms "comprises," "comprising," "includes," "including" and "has," "having" and variants thereof are to be construed as non-exhaustive, such that continuous lists of items or elements do not preclude other similar items or elements not expressly stated in a given method or apparatus. Similarly, the terms "can" and "could" and variants thereof are to be construed as non-limiting, such that an embodiment or implementation that can or can not contain some element or feature is not excluded from the technology.

[0047] The broad teachings of the disclosure can be implemented in various forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited as the same will become apparent to one of ordinary skill in the art upon a review of the specification and following claims. A recital of one or more aspects or embodiments herein is intended to mean that a particular feature, structure, or characteristic described in connection with the embodiment or a particular system is included in at least one embodiment or aspect. The appearance of the phrase "in one aspect" (or variations thereof) is not necessarily referring to the same aspect or embodiment. It is also to be understood that the various method steps discussed herein can be performed in a different order than as depicted in the figures and that each method step can not be required in every aspect or embodiment.

[0048] ​The foregoing description of the implementations has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Various elements or features of a particular implementation are generally not limited to that particular implementation, but are interchangeable with each other, and / or can be used in selected implementations, even if not specifically shown or described herein. Modifications and changes can be made in the implementations in accordance with the above description, which is to be understood as illustrative only. Such modifications and changes are intended to fall within the scope of the disclosure, but to the extent there are any inequivalences, such should be provided for as if not explicitly presented herein.

Claims

1. A black pigment with near-IR transmission and / or reflection properties, the black pigment comprising Multiple CuO crystallites with a maximum size of 18 nm or smaller and an intensity ratio of (-111) / (111) less than 1.2, The black pigment exhibits a band gap of 1.6 eV or less.

2. The black pigment according to claim 1, wherein... CuO microcrystals exist on at least a portion of the outer surface of the particles, and The particle diameter ranges from 50 nm to 10 μm.

3. The black pigment according to claim 2, wherein the particles comprise a core portion, said core portion comprising one of mica, synthetic mica, glass, quartz or alumina.

4. The black pigment according to claim 3, wherein the outer surface portion containing CuO has a thickness of less than 50 nm.

5. The black pigment according to claim 3, wherein the outer surface portion comprising CuO is a continuous or discontinuous shell on the core.

6. The black pigment according to claim 1, wherein the microcrystals have a maximum size of 15 nm or less.

7. The black pigment according to claim 1, wherein the black pigment exhibits a band gap of 1.2-1.6 eV.

8. A coating composition comprising: Fluid carrier; and A black pigment with near-IR transmission and / or reflection properties suspended in a fluid carrier. The black pigment contains CuO microcrystals with a maximum size of 18 nm or smaller and an intensity ratio of (-111) / (111) less than 1.

2. The black pigment exhibits a band gap of 1.6 eV or less.

9. The coating composition according to claim 8, wherein... CuO microcrystals exist on at least a portion of the outer surface of the particles, and The cross-section of the particles ranges from 50 nm to 10 μm.

10. The coating composition according to claim 9, wherein the particles comprise a core portion, said core portion comprising one of mica, synthetic mica, glass, quartz, or alumina.

11. The coating composition according to claim 10, wherein the outer surface portion comprising CuO has a thickness of less than 50 nm.

12. The coating composition according to claim 8, wherein the microcrystals have a maximum size of 15 nm or less.

13. The coating composition according to claim 8, wherein the black pigment in the coating composition exhibits a blackness M of at least 132. y value.

14. Methods for forming near-IR reflective or transmissive CuO microcrystals, including: Provide a solution or suspension containing a water-soluble Cu(II) salt; Add a precipitant solution containing an alkali metal carbonate to the solution or suspension to form a precipitate containing CuCO3; Rinse the sediment with water; Separate the precipitate; and The precipitate was calcined at a temperature between 300 and 400 °C to form near-IR reflective or transmissive CuO crystals, wherein the CuO crystals have a maximum size of 18 nm or less, an intensity ratio of (-111) / (111) less than 1.2 and a band gap of 1.6 eV or less.

15. The method of claim 14, wherein the water-soluble Cu(II) salt comprises Cu(NO3)2.

16. The method of claim 14, wherein the suspension comprises a suspension of core-forming particles, wherein the precipitate comprises a shell on the core-forming particles.

17. The method of claim 16, wherein the particles forming the core comprise at least one of mica, synthetic mica, glass, quartz, or alumina.

18. The method of claim 14, wherein the step of separating the precipitate includes filtering or centrifuging the precipitate, and the method further includes drying the precipitate after separation to form a dry precipitate.

19. The method of claim 14 further comprises grinding the precipitate.

20. The method of claim 14 further comprises grinding near-IR reflective or transmissive CuO microcrystals.

21. The coating composition according to claim 8, wherein the coating composition exhibits a band gap of 1.2-1.6 eV.

22. The method of claim 14, wherein the CuO microcrystals exhibit a band gap of 1.2-1.6 eV.

Images