Synthesis of High Near-Infrared Reflective Black Pigment Based on YMn2O5

Yamaguchi, Kazuki; Mochizuki, Satoru; Nagato, Yudai; Morimoto, Takuro; Masui, Toshiyuki

doi:10.3390/colorants2040036

Open AccessArticle

Synthesis of High Near-Infrared Reflective Black Pigment Based on YMn₂O₅

by

Kazuki Yamaguchi

,

Satoru Mochizuki

,

Yudai Nagato

,

Takuro Morimoto

and

Toshiyuki Masui

^*

Department of Chemistry and Biotechnology, Faculty of Engineering, and Center for Research on Green Sustainable Chemistry, Tottori University, 4-101, Koyama-cho Minami, Tottori 680-8552, Japan

^*

Author to whom correspondence should be addressed.

Colorants 2023, 2(4), 705-715; https://doi.org/10.3390/colorants2040036

Submission received: 14 September 2023 / Revised: 2 November 2023 / Accepted: 30 November 2023 / Published: 6 December 2023

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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Abstract

:

Y(Mn_0.95M_0.05)₂O₅ (M = Al, Fe, Ga, Ti, and Zr) samples were synthesized via a sol–gel method using citric acid to find a new near-infrared (NIR) reflective black pigment. Among these samples, the optical reflectance of Y(Mn_0.95Fe_0.05)₂O₅ and Y(Mn_0.95Ga_0.05)₂O₅ in the near-infrared region was found to be larger than that of YMn₂O₅. Then, the concentration of the dopant (Fe or Ga) was changed between 0 and 15%, and the resulting UV–Vis–NIR reflectance spectra were measured. As a result, the optical reflectance of the Fe-doped samples decreased in the near-infrared region, while that of the Ga-doped samples increased. Accordingly, Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.20) samples were synthesized, and the crystal structure, particle size, optical properties, and color of the samples were characterized. The single-phase samples were obtained in the composition range of 0 ≤ x ≤ 0.15, and the lattice volume decreased with increasing Ga³⁺ concentration. Optical absorption below 850 nm was attributed to the charge transfer transition between O_2p and Mn_3d orbitals, and the absorption wavelength of Y(Mn_1−xGa_x)₂O₅ shifted to the shorter wavelength side as the Ga³⁺ content increased, because of the decrease in the Mn³⁺ concentration. Although the sample color became slightly reddish black by the Ga³⁺ doping, the solar reflectance in the near-infrared region reached 47.6% at the composition of Y(Mn_0.85Ga_0.15)₂O₅. Furthermore, this NIR reflectance value was higher than those of the commercially available products (R < 45%).

Keywords:

black pigment; environmentally friendly; Mn⁴⁺ ion; yttrium manganate

Graphical Abstract

1. Introduction

As the need for power and energy conservation increases, there is a growing demand for thermal barrier coatings. A black color, in particular, usually causes a large rise in room temperature and requires a large amount of cooling energy when it is applied to roofing materials and automobiles. Therefore, black thermal barrier pigments with high performance are required. Existing black thermal barrier inorganic pigments such as iron titanate (Fe₂TiO₄) and iron–chromium mixed oxide ((Fe,Cr)₂O₃) have typically been used so far [1]. However, these materials are not pure black, and their solar reflectance is not sufficient. Furthermore, safety considerations have recently led to a demand for chromium-free materials, and new black thermal barrier materials are needed to replace existing materials [2,3,4,5].

Based on this situation, we focused on YMn₂O₅ as a base material with the aim of developing a novel environmentally friendly black heat-blocking pigment. YMn₂O₅ adopts an orthorhombic structure (space group: Pbam), where Mn³⁺ and Mn⁴⁺ ions are anti-ferromagnetically ordered; the former are coordinated with five O²⁻ ions and the latter are six coordinated [6,7]. Although this compound has been reported as a catalyst [8,9] and a ferroelectric material [10,11], there have been few studies on its color and optical properties. YMnO₃, which is composed of the same metallic elements but has a different composition, is already known as a black heat-blocking pigment [12,13]. However, this compound has a slightly bluish black color, and its solar reflectance in the wavelength range of 700–1300 nm, which is most involved in heat generation, is not so high. There are similar challenges with respect to other conventional black pigments, such as manganese–bismuth oxide and calcium–manganese–titanium oxide. Thus, the development of a black pigment with a higher solar reflectance in the wavelength range of 700–1300 nm is desired.

The band structure of YMn₂O₅ is composed of a valence band consisting of O_2p orbitals and a conduction band consisting of Mn_3d orbitals [14]. Accordingly, it is considered that YMn₂O₅ strongly absorbs visible light (300~700 nm) due to the O_2p–Mn_3d charge transfer transition and reflects near-infrared (NIR) light (700–2500 nm). In this study, we synthesized Y(Mn_0.95M_0.05)₂O₅ (M = Al, Fe, Ga, Ti, and Zr) samples and characterized their NIR reflectance property to obtain a new environmentally friendly pigment that possesses high thermal barrier performance and a sufficient black color. Among these samples, the optical reflectance of Y(Mn_0.95Fe_0.05)₂O₅ and Y(Mn_0.95Ga_0.05)₂O₅ in the near-infrared region was improved compared with that of YMn₂O₅. Accordingly, Y(Mn_1−xM_x)₂O₅ (M = Fe or Ga, 0 ≤ x ≤ 0.15) samples were synthesized, and it was found that Ga³⁺-doping was more effective than Fe³⁺ in enhancing the NIR reflectivity. In this study, therefore, Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.20) samples were synthesized, and the crystal structure, particle size, optical properties, and color of the samples were characterized. From the viewpoint of practical application, a color comparison with YMnO₃ and commercially available black pigments and an evaluation of chemical stability were carried out. As a result, we found that the Y(Mn_0.85Ga_0.15)₂O₅ pigment exhibits higher solar reflectance in the wavelength range of 700–1300 nm compared to conventional black pigments and has the potential to become a new NIR-reflective inorganic black pigment.

2. Materials and Methods

2.1. Synthesis

The Y(Mn_0.95M_0.05)₂O₅ (M = Al, Fe, Ga, Ti, and Zr) samples were synthesized using a citrate sol–gel method. Y(NO₃)₃·6H₂O (Kishida Chemical, Osaka, Japan, 99.9%), (CH₃COO)₂Mn·4H₂O (FUJIFILM Wako Pure Chemical, Osaka, Japan, 99.9%), Al(NO₃)₃·9H₂O (FUJIFILM Wako Pure Chemical, 98.0%), Fe(NO₃)₃·9H₂O (FUJIFILM Wako Pure Chemical, 99.9%), Ga(NO₃)₃·8H₂O (Kishida Chemical, 99.0%), [(CH₃)₂CHO]₄Ti (FUJIFILM Wako Pure Chemical, 95.0%), ZrO(NO₃)₂·2H₂O (FUJIFILM Wako Pure Chemical, 97.0%), and citric acid (FUJIFILM Wako Pure Chemical, 98.0%) powders were weighed as shown in Table 1. [(CH₃)₂CHO]₄Ti was dissolved in a mixed solution of 5 cm³ of deionized water, 10 cm³ of nitric acid, and 45 cm³ of ethanol. ZrO(NO₃)₂·2H₂O was dissolved in a mixed solution of 50 cm³ of deionized water and 5 cm³ of nitric acid, and the other nitrates were dissolved in 50 cm³ of deionized water. Each raw material solution was mixed and stirred homogeneously; then, citric acid (CA) powder was added as a chelating agent. The mixed solution was stirred at 90 °C until a gel was obtained, and the gel was dried at 120 °C in an oven for 24 h. The dried gel was placed in an alumina crucible and calcined at 500 °C in air for 6 h. After calcination, the samples were again heated at 1100 °C in air for 12 h. Before characterization, the samples were ground in an agate mortar.

The Y(Mn_1−xFe_x)₂O₅ (0 ≤ x ≤ 0.15) and Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.20) samples were synthesized via the same procedure described above for the Y(Mn_0.95M_0.05)₂O₅ (M = Fe or Ga) samples. The starting materials were weighed as listed in Table 2 and Table 3.

2.2. Characterization

Crystalline phases and structures were identified by means of X-ray powder diffraction (XRD; Rigaku, Ultima IV). The diffraction patterns were measured using Cu Kα radiation at 40 kV and 40 mA. The XRD data were collected by scanning in the 2θ range of 20–80°. The sampling width was 0.02°, and the scan speed was 6° min⁻¹. The lattice volumes were calculated from the XRD peak angles refined using CellCalc Ver. 2.20 software with α-Al₂O₃ as a standard. Optical reflectance spectra were recorded using an ultraviolet–visible–near-infrared (UV–Vis–NIR) spectrometer (JASCO, Hachioji, Japan, V-770 with an integrating sphere attachment) using a standard white plate as a reference. The step width was 1 nm, and the scan rate was 1000 nm min⁻¹. Electron micrographs of the sample particles were taken using a Hitachi H-7650 transmission electron microscope (TEM) operating at 100 kV. The sample particles were dispersed ultrasonically in ethanol and then supported on amorphous carbon film on a copper TEM grid. The color properties of the powder samples were evaluated in the Commission Internationale de l’Éclairage (CIE) L*a*b*C system using a color chromatometer (Konica-Minolta, CR-400). The L* parameter indicates brightness or darkness on a neutral gray scale. The a* and b* values represent the red–green and yellow–blue axes, respectively. The chroma parameter (C) represents saturation and is calculated by the formula C = [(a*)² + (b*)²]^1/2. The standard deviation of all values in the L*a*b*C color coordinate data was less than 0.1. The NIR solar reflectance (R) was calculated using the following equation [15]:

R = \frac{\int_{700}^{2500} r (λ) i (λ) d λ}{\int_{700}^{2500} i (λ) d λ}

where r(λ) is the spectral reflectance obtained from experiments and i(λ) is the standard solar spectrum (W m⁻² nm⁻¹). The NIR reflectance value (R) is expressed as the integral of the product of the observed spectral reflectance and the solar irradiance divided by the product of the solar radiation, both integrated over the range of 700 to 2500 nm.

3. Results and Discussion

3.1. Y(Mn_0.95M_0.05)₂O₅ (M = Al, Fe, Ga, Ti, and Zr)

3.1.1. X-ray Powder Diffraction (XRD)

Figure 1 shows the XRD patterns of the Y(Mn_0.95M_0.05)₂O₅ (M = Al, Fe, Ga, Ti, and Zr) samples. In the samples with Al, Fe, Ga, and Ti, the target YMn₂O₅ phase was obtained as a single phase. On the other hand, in the sample with Zr, the target YMn₂O₅ phase was obtained as the main phase, but YMnO₃ and ZrO₂ peaks were detected as impurities, resulting in a mixed phase.

3.1.2. Ultraviolet–Visible–Near-Infrared (UV–Vis–NIR) Reflectance Spectra

The UV–Vis and NIR reflectance spectra of YMn₂O₅ and Y(Mn_0.95M_0.05)₂O₅ (M = Al, Fe, Ga, and Ti) obtained with a single target phase in Section 3.1.1 are shown in Figure 2a,b, respectively. In the visible region, the optical absorption around 700 nm due to the O_2p–Mn_3d charge transfer transition [14] was weakened by the doping of Al, Fe, and Ga. The O_2p–Mn_3d charge transfer transition of the Mn³⁺-doped sample was weaker than that of the host material because Mn³⁺ in the host lattice was partially replaced by Al³⁺, Fe³⁺, and Ga³⁺, resulting in a lower Mn³⁺ concentration. On the other hand, the Ti⁴⁺-doped sample showed enhanced optical absorption around 700 nm. The O_2p–Mn_3d charge transfer transition was not inhibited because Ti⁴⁺ should have replaced the Mn⁴⁺ sites. The ionic radius of Ti⁴⁺ (ionic radius at the six-coordination site: 0.0605 nm [16]) is larger than that of Mn⁴⁺ (ionic radius at the six-coordination site: 0.053 nm [16]), suggesting that the MnO₆ octahedron is distorted by Ti⁴⁺ doping. As a result, the spin-forbidden ⁴A_2g → ²E_g, ²T_1g transitions of Mn⁴⁺ were enhanced [17]. These are the reasons for the enhanced optical absorption around 700 nm due to Ti⁴⁺ doping.

In the case of M = Fe and Ga, the reflectance in the near-infrared region from 700 nm to 2500 nm was slightly improved compared to that of YMn₂O₅. This is probably due to the partial substitution of Mn³⁺ with trivalent Fe³⁺ and Ga³⁺, which reduced the concentration of Mn³⁺ and weakened the charge transfer absorption between Mn³⁺ and Mn⁴⁺ [18].

On the other hand, for M = Al, the reflectance in the near-infrared region was lower than for YMn₂O₅. This is considered to be because of the ionic radius of Al³⁺ (ionic radius: 0.048 nm at five-coordination sites [16]), which distorts the crystal structure significantly and increases lattice defects. For M = Ti, the reflectance in the near-infrared region was significantly lower than that of YMn₂O₅. This is considered to be due to the partial substitution of Ti⁴⁺ for Mn⁴⁺, which strengthens the d-d transition absorption attributed to the ⁵E_g to ⁵T_2g transition of Mn³⁺ [19].

3.1.3. Color Properties

The L*a*b*C color coordinate data and NIR solar reflectance (R) of the YMn₂O₅ and Y(Mn_0.95M_0.05)₂O₅ (M = Al, Fe, Ga, and Ti) powder samples are summarized in Table 4. All the Y(Mn_0.95M_0.05)₂O₅ samples exhibited lower L* values than the YMn₂O₅ sample. However, the C value of the Al-doped sample increased, and its R value decreased. In the case of M = Ti, although the C value was lower compared to that of the host material, the R value also declined significantly. Only the samples with Fe or Ga additions exceeded the solar reflectance of YMn₂O₅. Thus, some Fe- or Ga-doped samples with different compositions were additionally synthesized, and their optical properties are evaluated in the next section.

3.2. Y(Mn_1−xFe_x)₂O₅ (0 ≤ x ≤ 0.15)

Figure 3 shows the XRD patterns of the Y(Mn_1−xFe_x)₂O₅ (0 ≤ x ≤ 0.15) samples. In the x range of 0 to 0.10, the YMn₂O₅ phase was obtained as a single phase. However, in the case of x = 0.15, the target phase and some impurities were detected. Therefore, the solid solubility limit of Y(Mn_1–xFe_x)₂O₅ is less than 15%. Figure 4a shows the UV–visible reflectance spectra of the Y(Mn_1−xFe_x)₂O₅ samples, where x is from 0 to 0.15. All samples absorbed visible light at wavelengths shorter than 700 nm, due to the O_2p–Mn_3d charge transfer transition [14]; as a result, these samples were black. However, as shown in Figure 4b, the reflectance at wavelengths of 700 nm to 2500 nm was decreased with increasing Fe³⁺ content, because of the d-d transition attributed to the ⁶A₁ to ⁴T₁ transition of Fe³⁺ [20].

The L*a*b*C color coordinate data and NIR solar reflectance (R) of the Y(Mn_1−xFe_x)₂O₅ powder samples, where x is from 0 to 0.15, are summarized in Table 5. Similarly to the results in Figure 4, the NIR reflectance value decreased with increasing Fe³⁺ content. Unfortunately, we found that increasing the amount of iron doping degraded performance, so we decided to study the Ga-doped samples in detail.

3.3. Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.20)

3.3.1. X-ray Powder Diffraction (XRD)

Figure 5 shows the XRD patterns of the Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.20) samples. For x ranging from 0 to 0.15, the YMn₂O₅ phase was obtained as a single phase. In contrast, for x ≥ 0.17, the target phase was observed as the main phase, but an additional impurity indexed as Y₃Ga₅O₁₂ was also detected. The composition dependence of the lattice volume of the samples calculated from each XRD pattern is shown in Figure 6. The introduction of small Ga³⁺ (ionic radius: 0.055 nm, five-coordination site [16]) ions into the Mn³⁺ (ionic radius: 0.058 nm, five-coordination site [16]) sites resulted in a linear increase in lattice volume with increasing Ga³⁺ content in the x ≤ 0.15 range. The substitution of six-coordinated Mn⁴⁺ sites with Ga³⁺ is ruled out, because the ionic radius of hexacoordinated Ga³⁺ (0.062 nm [16]) is larger than that of Mn⁴⁺ (0.053 nm [16]), so the lattice volume should increase with increasing Ga³⁺ concentration. The cell volumes at x = 0.17 and 0.20 were almost equal to that at x = 0.15. Thus, Y(Mn_1−xGa_x)₂O₅ solid solutions were successfully synthesized in the x = 0 to 0.15 region.

Figure 7 shows TEM images of YMn₂O₅ and Y(Mn_0.85Ga_0.15)₂O₅ samples obtained as a single phase. In both samples, the primary particles were very small, about 500 nm. These primary particles aggregated to form secondary particles of about 3 µm in size. No effect of Ga doping on particle size was observed. Therefore, the improvement in NIR solar reflectance due to Ga doping, which is discussed in the next section, is not due to a difference in particle size.

3.3.2. Ultraviolet–Visible–Near-Infrared (UV–Vis–NIR) Reflectance Spectra

UV–visible–NIR reflectance measurements were performed for the Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.15) samples obtained as a single phase. The reflectance spectra in the 300–800 nm wavelength region and 700–2500 nm wavelength region are shown Figure 8a,b. All samples were found to strongly absorb visible light at wavelengths shorter than 700 nm, and this optical absorption was attributed to the O_2p–Mn_3d charge transfer transition [14]. The optical absorption was slightly weakened by the decrease in Mn concentration with increasing Ga content. Since the optical reflection in the visible light was low, these samples were black.

It was found that the reflectance at wavelengths of 700 nm to 2500 nm improved when Ga³⁺ was dissolved in YMn₂O₅. This is thought to be due to the partial substitution of Mn³⁺ with Ga³⁺, which decreased the Mn³⁺ concentration and weakened the charge transfer transition between O_2p and Mn_3d orbitals. Furthermore, the reflectance in the near-infrared region was improved by introducing Ga³⁺. This is probably because the reduction in the Mn³⁺ concentration also weakened the charge transfer absorption of Mn³⁺–Mn⁴⁺ [16] in the near-infrared region. In the case of x = 0.15, the reflectance of wavelengths between 700 and 1300 nm, which is most involved in heat generation, was significantly improved.

3.3.3. Color Properties

The L*a*b*C color coordinate data and NIR solar reflectance (R) of the Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.15) powder samples are listed in Table 6. Photographs of the samples are also shown in Figure 9. Although there was no regular change in brightness, the redness (a*), yellowness (b*), and chroma (C) values showed an increasing trend with the Ga³⁺ doping. As the Ga³⁺ content increased, the color of the samples gradually changed to reddish black; among the samples listed in Table 6, the darkest black color was obtained for Y(Mn_0.85Ga_0.15)₂O₅. As discussed in Figure 8, substituting some of the Mn³⁺ with Ga³⁺ increased the optical reflection in the near-infrared region (700–2500 nm), resulting in the increased R value. Among the samples in Table 6, Y(Mn_0.85Ga_0.15)₂O₅ showed the highest R value (47.6%). This sample is considered to be the best black pigment with good NIR reflectance properties.

The color coordinate data for the Y(Mn_0.85Ga_0.15)₂O₅ sample in this study were compared with those of YMnO₃ and commercially available NIR-reflective black pigments such as Black 6350 (iron and chromium oxide; Asahi Kasei), Black 6301 (manganese and bismuth oxide, Asahi Kasei), and MPT-370 (calcium, manganese, and titanium oxide, Ishihara Sangyo), as shown in Table 7. Photographs of these pigments are also displayed in Figure 10.

The Y(Mn_0.85Ga_0.15)₂O₅ sample synthesized in this study exhibited a reddish black color with a redness (a*) value higher than those of YMnO₃ and the commercial products, indicating that its black color was inferior. However, Y(Mn_0.85Ga_0.15)₂O₅ has high near-infrared reflectance, and its solar reflectance is higher than that of YMnO₃ and the commercial products, indicating that it has sufficient performance as a thermal barrier pigment.

3.3.4. Chemical Stability Test

The chemical stability of Y(Mn_0.85Ga_0.15)₂O₅ was evaluated using powder samples. The powder samples were soaked in 4% CH₃COOH and 4% NH₄HCO₃ aqueous solutions, assuming vinegar and baking soda. After 24 h at room temperature, they were washed with deionized water and ethanol. The samples were then dried at room temperature. The color coordinate data of the samples after the chemical stability tests are summarized in Table 8, and photographs of the samples are also shown in Figure 11. The color tone and NIR solar reflectance changed slightly after the leaching tests in acid and base solutions. Although the Y(Mn_0.85Ga_0.15)₂O₅ pigment was slightly less chemically stable, the R value of the sample still remained as high as those of commercial pigments.

4. Conclusions

Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.20) samples were synthesized as environmentally benign inorganic NIR-reflective black pigments. In the x range from 0 to 0.15, the samples were obtained in a single phase and the lattice volume decreased linearly. These results indicate that solid solutions were successfully obtained in this x region. The Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.15) samples exhibited optical absorption in the visible light region due to the charge transfer transition between O²⁻ and Mn³⁺ and were reddish black in color. Among the synthesized samples, Y(Mn_0.85Ga_0.15)₂O₅ showed the highest NIR reflectance (47.6%), which was also higher than that of conventional black pigments. In particular, this pigment exhibited higher solar reflectance in the wavelength range of 700–1300 nm, which is most involved in heat generation. Therefore, the Y(Mn_0.85Ga_0.15)₂O₅ pigment will provide cooler roofs and exteriors for applications such as energy conservation buildings, as compared with the case of using conventional black pigments. The chemical stability of this sample is sufficient, and it has the potential to become a new NIR-reflective inorganic black pigment.

Author Contributions

The following are the author contributions to this study: Conceptualization, T.M. (Toshiyuki Masui); methodology, K.Y., T.M. (Takuro Morimoto), and T.M. (Toshiyuki Masui); validation, K.Y. and T.M. (Toshiyuki Masui); investigation, K.Y., S.M, and Y.N.; data curation, K.Y, S.M., Y.N., and T.M. (Takuro Morimoto); writing—original draft preparation, K.Y.; writing—review and editing, T.M. (Toshiyuki Masui); supervision, T.M. (Toshiyuki Masui); funding acquisition, T.M. (Toshiyuki Masui). All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by JSPS KAKENHI, grant numbers JP22K04698 and JP20H02439.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. XRD patterns of the Y(Mn_0.95M_0.05)₂O₅ (M = Al, Fe, Ga, Ti, and Zr) samples.

Figure 2. (a) UV–Vis and (b) NIR reflectance spectra for YMn₂O₅ and Y(Mn_0.95M_0.05)₂O₅ (M = Al, Fe, Ga, and Ti).

Figure 3. XRD patterns of the Y(Mn_1−xFe_x)₂O₅ (0 ≤ x ≤ 0.15) samples.

Figure 4. (a) UV–Vis and (b) NIR reflectance spectra for the Y(Mn_1−xFe_x)₂O₅ samples, where x is from 0 to 0.15.

Figure 5. XRD patterns of the Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.20) samples.

Figure 6. Compositional dependence of the lattice volume for the Y(Mn₁₋_xGa_x)₂O₅ (0 ≤ x ≤ 0.20) samples.

Figure 7. TEM images of the YMn₂O₅ (left) and Y(Mn_0.85Ga_0.15)₂O₅ (right) samples.

Figure 8. (a) UV–Vis and (b) NIR reflectance spectra for the Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.15) samples.

Figure 9. Photographs of the Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.15) samples.

Figure 10. Photographs of Y(Mn_0.85Ga_0.15)₂O₅, YMnO₃, Black 6350, Black 6301, and MPT-370 pellets made from powder samples.

Figure 11. Photographs of Y(Mn_0.85Ga_0.15)₂O₅ samples before and after the chemical stability test.

Table 1. Amounts of reagents used to synthesize Y(Mn_0.95M_0.05)₂O₅ (M = Al, Fe, Ga, Ti, and Zr).

Sample	Y(NO₃)₃·6H₂O	(CH₃COO)₂Mn·4H₂O	Reagent of Dopant	CA
YMn₂O₅	1.3739 g	1.7582 g	—	4.1350 g
Y(Mn_0.95Al_0.05)₂O₅	1.3879 g	1.6872 g	Al(NO₃)₃·9H₂O 0.1360 g	4.1766 g
Y(Mn_0.95Fe_0.05)₂O₅	1.3735 g	1.6699 g	Fe(NO₃)₃·9H₂O 0.1448 g	4.1335 g
Y(Mn_0.95Ga_0.05)₂O₅	1.3666 g	1.6617 g	Ga(NO₃)·8H₂O 0.1426 g	4.1129 g
Y(Mn_0.95Ti_0.05)₂O₅	1.3775 g	1.6746 g	[(CH₃)₂CHO]₄Ti 0.1022 g	4.1455 g
Y(Mn_0.95Zr_0.05)₂O₅	1.3564 g	1.6489 g	ZrO(NO₃)₂·2H₂O 0.0946 g	4.0819 g

Table 2. Amounts of reagents used to synthesize Y(Mn_1−xFe_x)₂O₅ (0 ≤ x ≤ 0.15).

Sample	Y(NO₃)₃·6H₂O	(CH₃COO)₂Mn·4H₂O	Fe(NO₃)₃·9H₂O	CA
Y(Mn_0.95Fe_0.05)₂O₅	1.3735 g	1.6699 g	0.1448 g	4.0973 g
Y(Mn_0.90Fe_0.10)₂O₅	1.3729 g	1.5813 g	0.2895 g	4.1322 g
Y(Mn_0.85Fe_0.15)₂O₅	1.3725 g	1.4930 g	0.4343 g	4.1308 g

Table 3. Amounts of reagents used to synthesize Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.20).

Sample	Y(NO₃)₃·6H₂O	(CH₃COO)₂Mn·4H₂O	Ga(NO₃)·8H₂O	CA
Y(Mn_0.95Ga_0.05)₂O₅	1.3666 g	1.6617 g	0.1426 g	4.1129 g
Y(Mn_0.90Ga_0.10)₂O₅	1.3595 g	1.5658 g	0.2839 g	4.0914 g
Y(Mn_0.85Ga_0.15)₂O₅	1.3523 g	1.4710 g	0.4236 g	4.0702 g
Y(Mn_0.83Ga_0.17)₂O₅	1.3494 g	1.4335 g	0.4790 g	4.0616 g
Y(Mn_0.80Ga_0.20)₂O₅	1.3452 g	1.3773 g	0.5617 g	4.0489 g

Table 4. Color coordinates and NIR solar reflectance (R) of the YMn₂O₅ and Y(Mn_0.95M_0.05)₂O₅ (M = Al, Fe, Ga, and Ti) powder samples.

Sample	L*	a*	b*	C	R
YMn₂O₅	28.2	+2.83	−0.44	2.86	42.9
Y(Mn_0.95Al_0.05)₂O₅	27.5	+4.95	+1.73	5.24	39.5
Y(Mn_0.95Fe_0.05)₂O₅	25.5	+3.24	+0.10	3.24	43.5
Y(Mn_0.95Ga_0.05)₂O₅	25.8	+3.93	+0.53	3.97	43.7
Y(Mn_0.95Ti_0.05)₂O₅	25.2	+2.58	+0.20	2.59	31.2

Table 5. Color coordinates and NIR solar reflectance (R) of the Y(Mn_1−xFe_x)₂O₅ powder samples, where x is from 0 to 0.15.

Sample	L*	a*	b*	C	R
YMn₂O₅	28.2	+2.83	−0.44	2.86	42.9
Y(Mn_0.95Fe_0.05)₂O₅	25.3	+3.24	+0.10	3.24	43.5
Y(Mn_0.90Fe_0.10)₂O₅	26.2	+2.07	−0.98	2.50	37.7
Y(Mn_0.85Fe_0.15)₂O₅	24.7	+1.58	+1.02	1.88	28.1

Table 6. Color coordinates and NIR solar reflectance (R) of the Y(Mn_1−xGa_x)₂O₅ (0 ≤ x ≤ 0.15) powder samples.

Sample	L*	a*	b*	C	R
YMn₂O₅	28.2	+2.83	−0.44	2.86	42.9
Y(Mn_0.95Ga_0.05)₂O₅	25.8	+3.93	+0.53	3.97	43.7
Y(Mn_0.90Ga_0.10)₂O₅	27.0	+4.30	+0.74	4.36	45.4
Y(Mn_0.85Ga_0.15)₂O₅	25.8	+4.82	+1.25	4.98	47.6

Table 7. Color coordinates and NIR solar reflectance (R) of various black pigments.

Sample	L*	a*	b*	C	R
Y(Mn_0.85Ga_0.15)₂O₅	25.8	+4.82	+1.25	4.98	47.6
YMnO₃	22.6	−2.17	−9.04	9.30	43.9
Black 6350	25.3	+1.20	+4.06	4.23	41.3
Black 6301	23.7	+0.43	+1.05	1.13	38.7
MPT-370	23.0	+0.67	−0.27	0.72	44.0

Table 8. Color coordinate data of Y(Mn_0.85Ga_0.15)₂O₅ samples before and after the chemical stability test.

Treatment	L*	a*	b*	C	R
As synthesized	25.8	+4.82	+1.25	4.98	47.6
4% CH₃COOH	25.2	+4.39	+1.07	4.52	42.8
4% NH₄HCO₃	24.3	+4.49	−1.20	4.65	42.2

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Yamaguchi, K.; Mochizuki, S.; Nagato, Y.; Morimoto, T.; Masui, T. Synthesis of High Near-Infrared Reflective Black Pigment Based on YMn₂O₅. Colorants 2023, 2, 705-715. https://doi.org/10.3390/colorants2040036

AMA Style

Yamaguchi K, Mochizuki S, Nagato Y, Morimoto T, Masui T. Synthesis of High Near-Infrared Reflective Black Pigment Based on YMn₂O₅. Colorants. 2023; 2(4):705-715. https://doi.org/10.3390/colorants2040036

Chicago/Turabian Style

Yamaguchi, Kazuki, Satoru Mochizuki, Yudai Nagato, Takuro Morimoto, and Toshiyuki Masui. 2023. "Synthesis of High Near-Infrared Reflective Black Pigment Based on YMn₂O₅" Colorants 2, no. 4: 705-715. https://doi.org/10.3390/colorants2040036

APA Style

Yamaguchi, K., Mochizuki, S., Nagato, Y., Morimoto, T., & Masui, T. (2023). Synthesis of High Near-Infrared Reflective Black Pigment Based on YMn₂O₅. Colorants, 2(4), 705-715. https://doi.org/10.3390/colorants2040036

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Synthesis of High Near-Infrared Reflective Black Pigment Based on YMn₂O₅

Abstract

1. Introduction