Research and preparation of nano silver layer coating on aluminum oxide Nguyen Van Canh

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Research and preparation of nano silver layer coating on aluminum oxide Nguyen Van Canh

^*

, Nguyen Tran Hung

Institute of Chemistry and Material, Academy of Military Science and Technology.

*Corresponding author: [email protected].

Received 01 January 2022; Revised 05 February; Accepted 14 February 2022.

DOI: https://doi.org/10.54939/1859-1043.j.mst.77.2022.86-92

ABSTRACT

Silver nanoparticles on the Al2O3 substrates have been employed in many applications in medical, biology, defense, etc. There are two main approaches to prepare the Al2O3-supported silver nanoparticles, which are chemical reduction and physical method with their own advantages and disadvantages. In this study, the chemical reduction approach was employed to fabricate the silver nanoparticles on the Al2O3 from the AgNO3 precursor with appropriate reaction conditions. The results showed that the silver nanoparticles were uniformly distributed on the surface of the Al2O3 with the silver nanoparticles loading of about 4.5 %w/w.

Keywords: Silver nanoparticles; Al₂O₃, Al₂O₃-supported silver nanoparticles; Thermal emission coefficient.

1. INTRODUCTION

In comparison to the conventional silver nanoparticles (Ag NPs) and Al2O3, the Al2O3- supported silver nanoparticles combine both advantages of the silver nanoparticles such as good thermal and electrical conductivity, low thermal reflection coefficient, high antimicrobial activity, and Al2O3 with low thermal emission coefficient, high chemical resistivity, good bonding capability, reasonable density [1-3]. Additionally, Al2O3-supported silver nanoparticles have the capability of releasing Ag ions for a long period of time. For example, Vitalija R. group successfully fabricated Al2O3/Ag NPs composite with Ag layer thickness of 0.1 μm, thermal emission coefficient of 0.4 in the wavelength region of 8 - 14 μm, and high antimicrobial activity [4]. Recently, several works have been intensively focused on the development of these materials (Ag, Al2O3, Au, Si, SiO2) [5-11]. However, the application of the Al2O3-supported silver nanoparticles in defense and oil exploitation still remains limited. In this work, the Al2O3- supported silver nanoparticles are prepared using the chemical reduction method of Ag ions on the Al2O3’s surface. The advantage of the protocol is to form a uniform Ag NPs layer with high Ag loading on the Al2O3.

Table 1. Thermal emission coefficient of some materials [11].

Surface Material

Thermal emission coefficient

Alloy 24ST Polished 0.09 Plaster 0.98

Alumina, Flame sprayed 0.8 Platinum, polished plate 0.054 - 0.104

Aluminum Commercial sheet 0.09 Pine 0.84

Aluminum Foil 0.04 Plaster board 0.91

Aluminum Commercial Sheet 0.09 Porcelain, glazed 0.92

Aluminum Heavily Oxidized 0.2 - 0.31 Paint 0.96

Aluminum Highly Polished 0.039 - 0.057 Paper 0.93

Aluminum Anodized 0.77 Plaster, rough 0.91

Aluminum Rough 0.07 Plastics 0.90 - 0.97

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Aluminum paint 0.27 - 0.67 Polypropylene 0.97

Antimony, polished 0.28 - 0.31 Polytetrafluoroethylene

(PTFE) 0.92

Asbestos board 0.96 Porcelain glazed 0.93

Asbestos paper 0.93 - 0.945 Pyrex 0.92

Black Silicone Paint 0.93 PVC 0.91 - 0.93

Black Epoxy Paint 0.89 Quartz glass 0.93

Cadmium 0.02 Roofing paper 0.91

Carbon, not oxidized 0.81 Rubber, foam 0.90

Carbon filament 0.77 Rubber, hard glossy plate 0.94 Carbon pressed filled surface 0.98 Rubber, natural hard 0.91 Cast Iron, newly turned 0.44 Rubber, natural oft 0.86

Cast Iron, turned and heated 0.60 - 0.70 Salt 0.34

Cement 0.54 Sand 0.9

Clay 0.91 Sandstone 0.59

Coal 0.80 Sapphire 0.48

Cotton cloth 0.77 Sawdust 0.75

Copper electroplated 0.03 Silica 0.79

Copper heated and covered

with thick oxide layer 0.78 Silicon Carbide 0.83 - 0.96 Copper Polished 0.023 - 0.052 Silver Polished 0.02 - 0.03

Copper Nickel Alloy, polished 0.059 Snow 0.96 - 0.98

Glass smooth 0.92 - 0.94 Soil 0.90 - 0.95

Glass, pyrex 0.85 - 0.95 Steel Oxidized 0.79

Gold not polished 0.47 Steel Polished 0.07

Gold polished 0.025 Stainless Steel, weathered 0.85 Granite, natural surface 0.96 Stainless Steel, polished 0.075

Ice smooth 0.966 Stainless Steel, type 301 0.54 - 0.63

Ice rough 0.985 Steel Galvanized Old 0.88

Inconel X Oxidized 0.71 Steel Galvanized New 0.23

Iron polished 0.14 - 0.38 Thoria 0.28

Iron, plate rusted red 0.61 Tile 0.97

Iron, dark gray surface 0.31 Tin unoxidized 0.04

Iron, rough ingot 0.87 - 0.95 Titanium polished 0.19

Lead Oxidized 0.43 Tungsten polished 0.04

Magnesia 0.72 Tungsten aged filament 0.032 - 0.35

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Magnesite 0.38 Water (0 - 100^oC) 0.95 - 0.963

Magnesium Oxide 0.20 - 0.55 Wood Beech, planned 0.935

Mercury liquid 0.1 Wood Oak, planned 0.885

Mild Steel 0.20 - 0.32 Wood, Pine 0.95

Molybdenum polished 0.05 - 0.18 Wrought Iron 0.94

Mortar 0.87 Zinc Tarnished 0.25

Nickel, elctroplated 0.03 Zinc polished 0.045

Nickel, polished 0.072 Oak, planed 0.89

Nickel, oxidized 0.59 - 0.86 Oil paints, all colors 0.92 - 0.96

Nichrome wire, bright 0.65 - 0.79 Paper offset 0.55

2. EXPERIMENTAL 2.1. Materials

- Instruments and glasswares: beakers, flasks, vacuum filter, stirrers, vacuum drier, etc.

- Materials: AgNO3 solution, Al2O3 (Sigma Aldrich) (99.9%), sodium citrate (99.5%) (China), and glucose (99.5%), NaOH (>98%) (China), distilled water.

2.2. Fabrication of Al2O3/Ag NPs composite

Al2O3-supported Ag NPs was prepared as following procedure:

Figure 1. Fabricating scheme of Al2O3-supported silver nanoparticles composite.

0.12 ml AgNO3 solution with an estimated Ag concentration of 600 ppm was mixed with glucose 1% and water to obtained 2000ml (solution A). Solution A was heated to 90 ^oC on a heater plate with a heating speed of 5 ^oC/min and stirring at a speed of 500-600 cycles/min.

Sodium citrate 10% solution was gradually added to solution A with the ratio of 1/10 solution A.

The temperature and stirring speed were remained as above for 60 minutes. The mixture colour changed from incolor to grey. At this stage, the concentration of Ag NPs was determined to be approximately 600 ppm. Al2O3 powder was introduced to the mixture and continued stirring 60 minutes at a temperature of 80 ^oC. Because the Al2O3 has a high density, controlling stirring speed is necessary. After the reaction, the mixture was naturally cooled down to room temperature. The product was filtered, thoroughly washed with distilled water, and dried in vacuum drier at 105 ^oC for 8 hours to obtained final product. The colour of the Al2O3 changed from white to grey, indicating that the Al2O3’s surface was successfully cover with Ag layer.

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Mixing Al2O3/Ag NPs with different weight ratios and polyester fabrics to make samples for measuring the coefficient of thermal emissivity. The Al2O3/Ag NPs composite loadings in the textile (%w/w) were 0% (VNTAN0), 11% (VNTAN), 12% (VNTAN1), 13% (VNTAN2), 14%

(VNTAN3).

2.3. Characterization

- Scanning electron microscopy (SEM) (Jeol JSM - 7500F and JSM - LA650, Japan) was employed to investigate the morphology structure of the Al2O3/Ag NPs composite;

- The elemental composition of the Al2O3/Ag NPs was determined using Electron Diffractive X-ray microscopy (EDX) (Jeol JSM - 7500F and JSM - LA650, Japan) and X-ray diffraction (XRD) (D8 - Advance and Sciencce D5005, Germany).

- The thermal emission coefficient was measured followed the QTTN 11.005:2011 standard

“IR radiation source/experimental procedure” in the wavelength range of from 2.5 to 14 μm and some other measurement methods [12-14].

3. RESULTS AND DISCUSSION 3.1. Morphology and structure of the Al2O3/Ag NPs composite

Figure 2. SEM image of the Al2O3/Ag NPs composite.

Figure 2 shows SEM image of the prepared Al2O3/Ag NPs composite. It can be clearly seen from the figure that the resultant Al2O3/Ag NPs composite is in a spherical shape with particle size ranging from 100 - 200 nm. It is visibly observed that the size of Al2O3/Ag NPs composite is not uniform; however, the Ag NPs layer is well-covered on the whole surface of the Al2O3. The coverage of the Ag NPs will be a decisive factor for the thermal emission property and antimicrobial activity of the Al2O3/Ag NPs composite.

3.2. Crystallinity investigation of the Al2O3/Ag NPs composite

The crystallinity of the prepared Al2O3/Ag NPs composite was studied using the XRD pattern as shown in figure 3. The diffraction peaks that appeared on the XRD pattern of the Al2O3/Ag NPs composite are well-assigned to the crystalline phases of Al2O3 and Ag (in the form of Ag2O). The presence of Ag2O is attributed to the oxidation of the Ag metal in the XRD measuring condition. The average particle size of Al2O3/Ag NPs composite was also determined using the Debye-Sherrer formulation: D = 0.9 λ/β cosθ, where λ is the X-ray diffraction wavelength, β is the maximal width of the diffraction peak, and θ is the diffraction angle. The result showed that the Al2O3/Ag NPs composite has particles size in a range of 100 - 200 nm, which is consistent with the size observed in SEM image.

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Figure 3. XRD pattern of the Al2O3/Ag NPs composite.

3.3. Elemental composition and distribution in Al2O3/Ag NPs composite

Figure 4. EDX spectrum of Al2O3/Ag NPs composite.

The elemental composition and distribution in the Al2O3/Ag NPs composite were investigated using EDX spectroscopy as shown in figure 4. It is obvious from the EDX spectrum that the presence of the Ag on the Al2O3 surface with the loading of approximately 4.5 %w/w. The similar Ag contents were also obtained at different points of EDX measurement, indicating the well-coverage of the Ag NPs on the Al2O3’s surface. This result is in well agreement the Ag NPs loadings on the Al2O3 powder reported from previous works such as Ero.S[15] and Trinh Ngoc Chau [16].

3.4. Thermal emission coefficient of Al2O3/Ag NPs composite

Various Ag NPs loading proportions on the Al2O3’s surface was investigated, which resulted in the optimized Ag loadings content on the Al2O3 was determined to be about 4.5 %w/w.

Several additives were mixed with the Al2O3/Ag NPs composite and coated on the textile before measuring the thermal emission coefficient. The QTTN 11.005:2011 process at the wavelength’s range of 2.5 to 14 μm was employed to measure the thermal emission coefficient at the Z176 company, and the result is shown in table 2.

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Table 2. Thermal emission coefficient of samples in the wavelength range of 2.5-14 μm.

Sample Appearance Al2O3/Ag NPs composite loadings in the textile (%w/w)

Thermal emission coefficient VNTAN0 Olive colour,

smooth

0 0.98

VNTAN Olive colour, smooth

11 0.76

VNTAN1 Olive colour, smooth

12 0.55

13 0.55

14 0.55

The appearance of the Al2O3/Ag NPs composite-integrated textile shows that the textile has good mechanical properties. The thermal emission coefficient decreases along with the increase of the Al2O3/Ag NPs composite content and reach a minimum of about 0.55% at the Al2O3/Ag NPs composite loading of 12%. Further increase of the Al2O3/Ag NPs composite loadings witnesses a negligible change in the thermal emission coefficient. Thus, the optimized Al2O3/Ag NPs composite loadings in the textile is determined to be 12%. In comparison with the previous work reported by Vitalija R., et al. [4] for the thermal emission coefficient of 0.4 in the wavelength’s region of 8 - 14 μm with the Ag-coated Al2O3 material (Ag thickness of 0.1 μm), the thermal emission coefficient of 0.55 in this work is slightly higher, however, this is still significant for the application for the defense purpose.

4. CONCLUSION

The Ag NPs layer has been successfully fabricated on the surface of the Al2O3 nanoparticles.

The Ag NPs uniformly and densely covered on the surface of Al2O3 particles with the Ag NPs loading of approximately 4.5 %w/w. The Ag/Al2O3 composite-integrated textile was also successfully prepared with a low thermal emission coefficient of 0.55 at the Ag/Al2O3 composite content of 12%, which is promising for the application in defense.

Acknowledgment: The authors acknowledge the fund from the project BQP (No.091/2020).

REFERENCES

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[2]. Chou K.-S., Lu Y.-C. “The application of nanosized silver colloids in far infrared low-emissive coating”. Thin Solid Films 515, 7217–7221, 2007.

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[4]. Vitalija R., Ingrida P., Sandra V.-Ž., Julija B. “Reduction of Thermal Signature Using Fabrics with Conductive Additives”. MATERIALS SCIENCE (MEDŽIAGOTYRA). Vol. 19, (4), 409 – 414, 2013.

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[10]. Zhang, Q. G., et al. "Influence of grain boundary scattering on the electrical and thermal conductivities of polycrystalline gold nanofilms." Physical Review B 74.13 (2006): 134109.

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[12]. Zharova, Irina, et al. "Technique of measuring the emissivity coefficient of solid materials surface." MATEC Web of Conferences. Vol. 194. EDP Sciences, 2018.

[13]. Arkhipov, V. A., et al. "Technique of measuring the emissivity coefficient." Journal of Physics:

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[14]. L. Ibos, M. Marchetti, A. Boudenne, S. Datcu, J.Livet, Y. Candau. “Infrared emissivity measurement device: Principle and applications”. sl: Meas. Sc. Tech., 2950, 2006.

[15]. Ero. S et al. “Nitric oxide reduction by propene over Silver/Alumina and Silvergold/Alumina catalyst: Effect of preparation methods”. Applied Catalysis, 183-189, 2019

[16]. Trịnh Ngọc Châu, Phan Anh Châu, Nguyễn Văn Hà. “Tổng hợp và ứng dụng vật liệu nano bạc trên chất mang nhôm oxit”. Tạp chí Hội KHKT Phân tích Hóa, Lý và Sinh học Việt Nam, trang 36-41, 2010 (in Vietnamese).

TÓM TẮT

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