Black Electrochemical Coatings for aerospace and allied Applications - Part 1

1 Introduction

The blackened surface facilitates attaining the ambient temperature faster due to enhanced radiative heat exchange with surroundings. It also assists in minimising the temperature gradient across the stack of components in an equipment panel owing to improved radiative coupling. However, there are selective black coatings which exhibit a high absorption in ultraviolet-visible light but low absorption in the infrared region (low IR emissivity). These coatings have widespread application in solar thermal applications, such as solar water heating, solar air conditioning, concentrated solar power plants etc. Solar selective coatings are envisioned for use on minisatellites, where solar energy is to be used to power heat engines or to provide thermal energy for remote regions in the interior of the spacecraft. The nature of the black coatings relies not only on the intrinsic properties of the material but also on the morphology and light-trapping ability.

Stray light is one of the most common criteria that cause optical devices to fail to produce accurate test results. It is therefore essential to find the correct and most effective way to minimize or block stray light completely to circumvent the inaccurate measurements and their adverse effects. Ultrahigh absorptance black coatings play a significant role in supressing the stray light in the optical systems. These surfaces are of paramount importance in the design of terrestrial and space-borne optical instruments and sensors used for measurements in ultra-violet, visible and infrared spectral regions. Spectrally selective black coatings exhibiting high solar absorptance and low infrared emittance in particular have been used as selective absorbers for solar collectors for quite a long time. On the other hand, the flat absorber black coatings have significant technological applications in thermal management of electronic instruments. A flat absorber coating absorbs almost all the energy incident upon it throughout the spectral range. These coatings are characterized by high solar absorptance and high infrared emittance. Almost all the internal electronic housings of equipment panels are coated with flat absorber black coatings to improve their heat radiation characteristics.

In this article the importance of minimising the unwanted stray light that interferes with the performance of an optical system’s intended functions are deliberated. The role of passive thermal control system utilizing the known optical properties of surfaces for thermal management of devices and spectrally selective black coatings in solar energy systems are outlined. The structural materials and their finishing requirements, the selection criterion of black coatings materials and processes for aerospace applications are conversed.

Black coatings can be applied to a variety of substrates by different set of techniques. Electrochemical finishing is employed as an ideal means for improving one or more surface properties, chemical, mechanical, electrical or optical. These are used for preventing corrosion, providing better adhesion for paints, lubricants, and adhesives; improving micro hardness; reducing friction on sliding surface, producing a solid film lubricant to prevent cold welding in space conditions, providing adequate optical surface for thermal control application, etc. [1–5].

This article presents a critical review of black electrochemical finishes, viz., black chromate, chrome-manganese, molybdate, permanganate, galvanic anodizing, chemical oxidation conversion coatings, black anodizing, black chrome, nickel and cobalt plating, black electroless Ni-P coating, black plasma electrolytic oxide films on the aerospace metallics. The process details, optical properties, relative advantages-disadvantages of black electrochemical coatings vis-a-vis carbon nanotube-based coatings and thermal control black painting for diverse functional applications are discussed. This will enable the user to make the right choice of substrate material and black coating for the specific application.

1.1 Stray Light in Optical Systems

The term “stray light” also known as optical noise within optical equipment, refers to any inadvertent light in an optical system. It can be from an unintended source or an intended source through an undesired path. Stray light can influence photometric precision and accuracy of the instruments in the form of higher signal to noise ratio (SNR) or thermal loading. The suppression of stray light is often overlooked until later in the design process. Even if stray light reduction is budgeted for in the initial design, there are subtle complexities that are often undetected. A simple solution to overcome this problem is to specify a high absorptance black finishing on specific surfaces. This is because most of the light energy incident on the black surface gets absorbed by the surface, converting that light energy into heat.

Optical instruments play a crucial role in technological enhancements, not only in the field of optics but in many others as well, from medicine to astronomy. Present-day achievements would not have been possible if it weren’t for microscopes, telescopes, spectrometers, and the list goes on. The precision of these instruments is directly related to the accuracy of test results, measurements and the decisions made based upon them. While working with these instruments, many factors are taken into consideration. For example, the external environment can drastically alter tests and their results. One of the most influential external factors that causes inaccurate test results is the phenomena of ‘stray light’. Any stray light signal can induce noise and fluctuations in sensor that may contribute to errors in the desired measurements. The following shows some of the examples of stray light effects:

The level of stray light is very critical for spectrometers as it can limit the ability of an instrument to measure the intensity of light. As a result, the test results of a spectrometer can have narrow and intense absorption bands. In medical microscopes, stray light can reduce image contrast. This produces a difference between the actual object and its microscopic image which is a matter of great concern.

In space telescopes, the glow of stray light from the sky can limit their ability to detect far away and faint objects. The detectors used in these optical instruments respond to all types of light that reaches them. Stray light is also responsible for a decrease in light absorbance ability and reducing the linearity of the instrument. In a small camera, stray light can cause a minor loss, but in a space telescope, it can result in the loss of a massive amount of data. It is therefore very important to prevent or minimize the stray light in optical instruments.

The ultra-high absorptance coatings are extremely useful to improve the absorptance of thermal detectors and to suppress the unwanted reflections or scattered light in optical systems, like telescope housing and baffles where stray light reduction is vital [6, 7]. The latter is of significance when it is necessary to reduce the physical size of the instrument whilst not compromising performance. These coatings have been successfully employed in the baffle instruments of many spacecrafts such as Laser Interferometric Gravitational Wave Observatory (LIGO), Cosmic Background Explorer (COBE), Hubble Space Telescope (HST), Extreme Ultraviolet Explorer (EUVE), and Ultra Violet Imaging Telescope (UVIT) of Astrosat. Baffles are frequently built into telescope designs to stop this unwanted light reaching to inside telescope tubes/detector.

The design of the baffle needs to very carefully weigh the benefits of diffuse versus specular vane surfaces [8, 9]. For example, diffuse surfaces tend to be more susceptible to outgassing and particulate contamination of nearby surfaces than do specular. However, with the specular approach slight design errors or manufacturing tolerances can be more critical. Specular reflection implies that angle between the reflected beam and the normal to the surface equals the angle made by the incident radiation with the same normal. Reflection from highly polished and smooth surfaces approaches specular characteristics. In a diffused reflection, the incident beam is reflected in all directions. Most of the engineering materials have rough surfaces, and these rough surfaces give diffused reflections. The specular and diffused reflections are illustrated in Figure 1.1.

Fig. 1.1: Specular and diffused reflections

1.2 Thermal Control Applications

We live in the world of the Earth’s atmosphere with ‘room temperature technology’. Equipment on the Earth having a tendency to run too cold or too hot may be readily brought back to acceptable operating temperature through heat exchange with atmosphere. A spacecraft operating in space, experiences extreme temperatures. It’s one side may get exposed to direct sun whereas the other side encounters deep cold space. Further, when the spacecraft dives into eclipse, some of its components that are non-operational, experience extremely low temperatures while those that are operational get heated to higher temperatures. This harsh thermal environment inflicts a temperature gradient of a few hundred degrees centigrade. However, the different components, and devices in spacecraft can perform at their fullest capacity only at a narrow temperature range. Because vacuum prevails, there is no heat convection in space and heat exchange is restricted to only radiation, which is a poor substitute for convection. Under these circumstances, the challenge in spacecraft thermal design is to ensure an optimum temperature range to all the sub-systems during the entire mission conditions (pre-launch, launch, transfer orbit, in-orbit phases) [10–12]. If we consider a spacecraft far away from Earth’s atmosphere, and assume that it does not have any internal power dissipation; the steady state temperature of spacecraft can be expressed by the following energy balance equation [13, 14].

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Where T is the absolute temperature of the spacecraft in K, S is the solar constant (mean value 1,353 Wm^-2), σ is the Stefan-Boltzmann constant (56.7×10^-9 Wm^-2K^-4), A_p is the projected area of the spacecraft in m² and A is the total surface area of the spacecraft in m², α is the solar absorptance, and ε is the thermal emittance of the exposed surface. Because S, σ, A_p and A are constant in this relationship, it can be seen that the temperature of a given area of the spacecraft is directly controlled by the α/ε ratio. Passive thermal control system utilizing the known optical properties {absorptance (α) and emittance (ε)} of the surface ensures a reliable thermal control of spacecraft components [15–17]. The thermo-optical properties of surface also play an important role in thermal management for ground applications, though not as effective as for space applications. This is because, in space, the radiation is the pre-dominant mode of heat transfer, while for ground operations in addition to radiation, other mode of heat transfer, i.e., conduction and convection, also contribute.

Thermal control techniques are broadly grouped into passive and active. Passive thermal control techniques are preferentially adopted for the thermal control of spacecraft. The passive system does not involve any relative movement of its parts and does not require external power for operation. This eliminates the possibility of its failure. The passive thermal control system utilizes coatings, multilayer insulation (MLI) and radiators of known optical properties to achieve the required thermal control. Active thermal control systems, on the other hand require external power for their operations and/or involve the moving parts, for example – electrical heaters, mechanical refrigerators, thermostatic louvers, pumped fluid loops, etc. The passive thermal control methods are used when simplicity, cost and reliability are the key design factors [4, 15, 18, 19].

1.3 Spectrally Selective Black Coatings

Although the absorptance (α) and emittance (ε) of surfaces are equal at a particular wavelength, but they can be different in the visible solar region than in the infrared. The ratio of solar absorptance and infrared emittance α(λ=VIS)/ε(λ=IR) or simply α/ε defines the solar selectivity of the coating. Solar selective coatings are extremely important for thermal control applications [20, 21]. The black coatings manifesting high solar absorptance and low thermal emittance are the core part for solar thermal technologies, such as solar water heaters, concentrated solar power plants, solar thermoelectric generators and solar thermo-photovoltaics.

1.3.1 Ideal Selective Absorber

The surface of an ideal selective absorber should follow black body principle that is completely absorbing in the solar spectrum region (0.3–2.5 μm), α=1. In order to reduce the thermal heat losses via emitted radiation, the surface should have a very low emissivity in the infrared spectrum region (2.5–30 µm), the wavelengths in that it emits, ε=0. Absorber surfaces are governed by the basic radiation principles [22]:

1. the absorptivity of a surface at a particular wavelength (i. e., the fraction of incident radiation that it absorbs) is equal to its emissivity at the same wavelength (the amount of radiation it emits expressed as a fraction of the amount that an ideal black body would emit)
2. all the radiation incident on a surface must either be absorbed, reflected or transmitted, so absorptivity, transmissivity and reflectivity must sum to 1.

The solar selective surface will absorb the incident radiations in the solar spectrum region and will emit at different wavelengths in infrared region. Whilst absorptivity must equal emissivity at each specific wavelength, they can and do vary with wavelength. As a consequence, the ideal reflectance function of a selective solar absorber is a step function between a minimum value of reflectance (hence high absorptivity) in the solar wavelength range and a high reflectance (hence low emissivity) in the infrared (IR) thermal radiation range. Ideally the lower reflectance limit would approach 0 % while the upper limit would be 100 %; however, in reality these values cannot be achieved. Perfect gold surfaces have reflectance values in the IR of nearly 98 % (ε = 0.2), whilst blackened surfaces with 98 % reflectance are also possible.

For lower temperatures there is no energetically significant overlap between the thermal emission spectrum of a body (with the blackbody spectrum according to Planck being the upper limit) and the solar spectrum. A critical wavelength (λcrit) for the step function can be defined which separates the two respective wavelength regions. For higher temperatures, however, the thermal emission spectrum is shifted towards shorter wavelengths which implies an increasing overlap of the spectra. Therefore, the critical wavelength has to be optimized with respect to solar absorptance and thermal emittance for different operating temperatures. The solar hemispherical blackbody radiation spectra at three different temperatures is presented in Figure 1.2.

Fig. 1.2: Solar hemispherical spectral irradiance for reference Air Mass of 1.5 (AM1.5) and blackbody radiation spectra calculated from Planck’s law for three different temperatures (300 °C, 400 °C, 500 °C) [22]

1.3.2 Flat Absorber Black Coatings

The flat absorber black coating exhibiting high absorptance throughout the solar spectrum from visible to infrared (α, ε ≈ 1) wavelengths are pivotal in improving the heat radiation characteristics [23]. These coatings are predominantly implemented on internal electronic housings of equipment panels. In an equipment some of the electronic components that are in operation generate lot of heat and may become extremely hot, while those are ideal may be cold. Owing to enhanced heat exchange as per Kirchhoff’s law of thermal radiation (α = ε) at a given temperature and wavelength, the flat absorber black coating helps to minimise the temperature gradient across the components providing the acceptable temperature limit [24–29].

1.4 Structural Materials and Finishing for Aerospace Applications

Aerospace materials, the materials used in construction of aircrafts, spacecrafts, launch vehicles can be broadly classified into four categories: metallics, non-metallic (or polymeric materials), composites and ceramics [30]. Metallics are the most commonly used structural materials in building the aerospace systems today. Metallic materials are inorganic substances, usually combinations of metallic elements which may also contain small amounts of non-metallic elements, such as carbon, nitrogen, and oxygen. Metals are rarely used as a pure element but are mixed with other elements to form an alloy. This is usually necessary to acquire the required properties of the material. There are several advantages offered by metallic materials over non-metallics, such as ductility, malleability, adequate hardness, ease of forming (machining and castability), high specific strength, excellent thermal and electrical conductivity, impact capability (vibration and shock absorption), weldability, low friction, self-lubricating qualities. In the present context our discussion is confined to the metallic materials.

Aerospace and space industries have traditionally been a pacemaker for development and introduction of advanced engineering materials and production technologies. The key driving forces for materials development are weight reduction, application-specific performance improvement, and cost reduction. Application of advanced engineering materials has significant impact on both economic and ecological issues [31, 32]. Mass reduction is an important criterion in design of aerospace and automobile parts to reduce the fuel cost [1, 33]. Hence, there are constant efforts to reduce the structural mass. Reduction in structural mass leads to fuel saving or increase in payload capability or loading of higher fuel mass. The latter has great significance in space industry as it leads to an increase in life span of spacecraft. Hence, there are constant efforts to reduce the structural mass. Aluminium alloys are the front runner structural material in the aerospace industry. The other light metal alloys include magnesium and titanium alloys. In addition, many other materials e.g., various type of steels, superalloys, copper alloys, etc. are employed for specific functional requirements. Galvanized steel products are often utilized in fabrication of landing gear components, fasteners, and interior fittings. The selection of materials is made on the basis of functional requirements, design for manufacturing and environmental effects on materials performance. Structural properties such as elastic modulus, tensile strength, ductility and damage tolerance (fatigue and fracture) are emphasized since they are major considerations in design. The heritage or long-term reliability, compatibility, electrical and thermal requirements, safety and cost, etc. are some of the other parameters to be contemplated. Much of the materials processing technology developed for use on Earth is applicable to material processing in space, but there are fundamental differences in gravity and environment during flight, on-orbit and re-entry phase, which can have profound effects on materials properties. The hardware exposed to space must withstand the harsh space environment. This includes vacuum, thermal cycling, charged particle radiation, ultraviolet radiation, and in some environments, plasma effects and atomic oxygen. Micrometeoroids and space debris particles may impact at high velocities. All of these may have significant effects on material properties either alone or in synergism.

The finishing used in space technology, requires higher standards and better control than those used for ground applications, because space conditions are harsh and an on-orbit spacecraft is not approachable for repair. The coatings designed for space missions have to withstand extreme aerodynamic heating, acceleration, shock, vibration and acoustic noise during space flight. They must have good resistance to physical and optical properties when exposed to atomic oxygen, ultraviolet radiation, bombardment of high energy particles (electrons and protons), extreme temperature cycling, ultrahigh vacuum, and collective effects of these environments [34]. The application of defective coatings not only seriously affects the performance of a particular subsystem but also increases the probability of the failure of the entire mission by damaging it permanently. The space worthiness of the coating is evaluated by the simulated environmental tests, viz, humidity, thermal cycling, thermovacuum and radiation tests. Further evaluation of coating is carried out by outgassing test, measurement of optical, electrical properties and any other test based on the functional requirements.

1.5 Black Coatings Materials and Coating Processes

A wide range of black coating materials are available, e.g., polymeric, sol-gel, inorganic. Some of the materials and coatings outgas in particular in the vacuum / space environment. The outgassing materials may escape, forming a cloud of charged molecules in the vicinity of the spacecraft, or may recondense on the surfaces at a lower temperature. Although the total mass loss (TML %) could render a material unsuitable for flightworthy applications, it is the collected volatile condensable material (CVCM %) that is of much concern because it may result in a drastic change in electrical, thermal, and optical properties of the exposed surfaces. Hence, it is imperative to use only those materials and coatings that have low outgassing. The outgassing test is performed as per ASTM E 595-83 standard. For a material to be considered for general flight usage, the maximum % TML and % CVCM values are specified as < 1 and < 0.1, respectively. When applications for space-based instruments and optical systems are considered the outgassing properties becomes extremely important. Hence, for specific critical applications, e.g., baffles, optical systems and sensors these values are specified far lower.

Thermal stability of organic polymeric materials such as paints are quite limited, making them unsuitable for absorbing high-intensity light [35]. Moreover, they have a general tendency for outgassing. Among the polymeric materials, the black carbon paints provide excellent thermal radiation properties, but release a high percentage of condensable volatile materials particularly in space. Hence, these coatings are generally not recommended on critical optical assemblies [36–38]. Another problem associated with paints is their limited shelf-life.

The black coatings can be obtained with varieties of deposition processes, physical vapour deposition, chemical vapour deposition, sol-gel process, wet electrochemical and electroless deposition, etc. Physical and chemical vapour deposition techniques are generally adopted for deposition of thin films. The sol-gel process is a chemical method widely used in the solar selective coating preparation. In the process of sol-gel, the colloidal solution is obtained from some metal alkoxides and metal salts by various forms of hydrolysis and polycondensation reactions. This is then deposited to form a coating. The coatings fabricated by sol-gel process are uniform but easily damaged [39–40]. For higher thermal stability, one may use black inorganic coatings. These coatings are often metal/metal oxides and can be obtained at a low cost by various wet electrochemical methods; chemical conversion, anodic oxidation, plating, etc. Most of these inorganic black coatings are highly stable, but have a restricted range of properties in comparison to organic coating materials. Further, there are black carbon nanotubes containing coatings, where a very low reflectance, far below 1 % over a substantial wavelength range can be achieved.

The present article describes the various methods of black coatings on metallics by wet electrochemical and electroless processes for aerospace and allied applications. Spectral irradiance measurements and degradation of black surfaces are discussed and reviewed elsewhere [4, 7, 41, 42]. It has been established that the emittance of coatings does not change significantly from environment exposure. On the other hand, low absorptance always increases with contamination and/or exposure to the space environment [4]. -to be continued-

REFERENCES

[1] A.K. Sharma: Surface engineering for thermal control of spacecraft, Surf. Eng., 21(2005)3, 249–253, Doi: 10.1179/174329405X50118
[2] A.K. Sharma: Role of chemical coatings in space applications: Recent trends in finishing of light metal alloys, Trans. Soc. Adv. Electrochem. Sci. Technol. (SAEST), India, 30(1995)12, 1–13
[3] A.K. Sharma: Metal Finishing for thermal control of spacecraft, Trans. Met. Finish. Assoc. India, 11(2002), 133–140
[4] A.K. Sharma; N. Sridhara: Degradation of thermal control materials under a simulated radiative space environment, Adv. Space Res., 50(2012), 1411–1424, Doi: 10.1016/j.asr.2012.07.010
[5] A.K. Sharma; R. Uma Rani; K. Giri: Studies on anodization of magnesium alloys for thermal control applications, Met. Finish., 95(1997)3, 43–46, 48–51, Doi: 10.1016/S0026-0576(97)86772-4
[6] S.R. Meier: Methods to suppress stray light in black materials, Proc. SPIE, 5526(2004)1, 195–207, www.deepdyve.com/lp/spie/methods-to-suppress-stray-light-in-black-materials-IcQwccXBwi 
[7] T. Kralik; D. Katsir: Black surfaces for infrared, aerospace, and cryogenic applications, Proc. SPIE, 7298, Infrared Technology and Applications XXXV, (2009), 729813, Doi: 10.1117/12.819277
[8] G.L. Peterson; S.C. Johnston: Specular baffles, Proc. SPIE, 1753(1993)1, 65–76, Doi: 10.1117/12.140692
[9] M.J. Persky: Review of black surfaces for space-borne infrared systems, 70(1999)5, 2193–2217, Doi: 10.1063/1.1149739
[10] A.D. Kraus; A. Bar-Cohen: Thermal Analysis and Control of Electronic Equipment, McGraw-Hill, New York, (1983)
[11] G. Barg; N. Djordjevic; S. Hall.: The development of Prometheus: An expert system tool for preliminary design of spacecraft thermal control systems, Proc. 1st Int. Conf. Industrial and Engineering applications of Artificial Intelligence and Expert Systems, ACM Press, New York, (1988), 380–387
[12] G. Joseph: Journey from Ground to Space from a System Engineer’s Guide to Building an Earth Observation Camera, CRC Press, Florida, (2015), 303–325
[13] B.N. Agarwal: Design of Geosynchronous Spacecrafts, Prentice Hall, Englewood, (1986), 281
[14] A.K. Sharma; H. Bhojaraj; V.K. Kaila; H. Narayanamurthy: Thermal control coatings on Mg-Li alloys, SAE Technical Paper 932123, 1993; SAE Int. J Aerospace, Section-1, 102(1993), 865–872, Doi: 10.4271/932123
[15] D.G. Gilmore: Spacecraft Thermal Control Handbook, 2nd Edition, The Aerospace Corporation Press, El Segundo, California, (2002)
[16] R.D. Karam: Satellite Thermal Control for System Engineers, Progress in Astronautics and Aeronautics, AIAA, Cambridge, Vol.181 (1998)
[17] J. Meseguer; I. Pérez-Grande; A. Sanz-Adréz: Spacecraft Thermal Control, Woodhead Publishing, Elsevier, (2012), 1–382
[18] F. Anvari; F. Farhani; K.S. Niaki: Comparative study on space qualified paints used for thermal control of a small satellite. Iranian J Chem. Eng., 6(2009)2, 50–62, www.ijche.com/article_10361_3e7db599f47c97944b269467141aeb1a.pdf 
[19] L. Kauder: Spacecraft Thermal Control Coatings References, NASA/TP-2005-212792, (2005)
[20] Heinz Scholz; Hans Jungk: Philips Corporation, Method of producing coatings having a high absorption in the range of the solar spectrum, U.S. Patent 4,080,269, (1978)
[21] Toshio Shikata; Shigetomo Ueda; Masakazu Inagaki: Solar heat absorber and a method of manufacturing the same, U.S. Patent 4,262,060, (1981)
[22] W. Platzer; C. Hildebrandt: Absorber materials for solar thermal receivers in concentrating solar power (CSP) systems (Chapter 15), Concentrating Solar Power Technology Principles, Developments and Applications, Keith Lovegrove; Wes Stein (Editors), Woodhead Publishing, Elsevier, (2012), 469–494
[23] K.A.J. Doherty; C.F. Dunne; A. Norman; T. McCaul; B. Twomey; K. T. Stanton: Flat Absorber Coating for Spacecraft Thermal Control Applications, J Spacecraft Rockets, 53(2016)6, 1035–1042, Doi: 10.2514/1.A33490
[24] R. Luthier; F. Levy: TiAlOn black decorative coatings deposited by magnetron sputtering, Vacuum, 41(1990)7-9, 2205–2208, Doi: 10.1016/0042-207X(90)94225-F
[25] P.K.C. Pillai; R.C. Agarwal: Black cobalt coatings for photothermal conversion of solar energy: Preparation and characterization, Energy Convers. Manage., 22(1982)2, 111–116, Doi: 10.1016/0196-8904(82)90032-2
[26] B. Vitt: Characterization of a solar selective black cobalt coating, Solar Energy Mater., 13(1986)5, 323–350, Doi: 10.1016/0165-1633(86)90082-1
[27] E. Barrera; F. Gonzalez; E. Rodriguez; A.-R. Jose: Correlation of optical properties with the fractal microstructure of black molybdenum coatings, Appl. Surf. Sci., 256(2010)6, 1756–1763, Doi: 10.1016/j.apsusc.2009.09.108
[28] A. Amri; Z-T. Jiang; N. Wyatt; C-Y. Yin; N. Mondinos; T. Pryor; M. Mahbubur Rahman: Optical properties and thermal durability of copper cobalt oxide thin film coatings with integrated silica antireflection layer, Ceram. Int., 40B(2014)10, 16569–16575, Doi: 10.1016/j.ceramint.2014.08.012
[29] S.N. Patel; O.T. Inal: Optimization and microstructural analysis of black-zinc-coated aluminum solar collector coatings, Thin Solid Films, 113(1984)1, 47–57, Doi: 10.1016/0040-6090(84)90387-0
[30] B.N. Bhat: Aerospace Materials Characteristics (Chapter 2), Aerospace Materials and Applications, Progress in Astronautics and Aeronautics, The American Institute of Aeronautics and Astronautics (AIAA), Inc., Reston, VA, 255(2018), 11–208, Doi: 10.2514/5.9781624104893.0011.0208
[31] M. Peters; C. Leyens: Aerospace and space materials, Mater. Sci. Eng., 3(2009), 1–11, www.eolss.net/Sample-Chapters/C05/E6-36-05-03.pdf 
[32] J. Kandasamy; V.R. Kar; M.T.H. Sultan Mohamed; M. Rajesh: Materials selection for aerospace components (Chapter 1), Sustainable Composites for Aerospace Application, M. Jawaid; M. Thariq (Editors), Woodhead Publishing, Elsevier, (2018), 1–19, Doi: 10.1016/B978-0-08-102131-6.00001-3
[33] B. Piascik; J. Vickers; D. Lowry; S. Scotti; J. Stewart; A. Calomino: Draft Materials, Structures, Mechanical Systems, and Manufacturing Roadmap Technology Area 12, NASA, (November 2010), TA-12.1–31, www.nasa.gov/pdf/501625main_TA12-MSMSM-DRAFT-Nov2010-A.pdf 
[34] M.D. Griffin; J. R. French: Space Vehicle Design, 2nd Edition, American Institute of Aeronautics and Astronautics, Inc., Reston, Virginia, (2004)
[35] www.rp-photonics.com/black_coatings.html 
[36] A.C. William Jr.; R.S. Marriott: NASA RP 1124, Outgassing Data for Selecting Spacecraft Materials, Published by National Technical Information Service-NTIS, 4th Edition, (1997)
[37] L. Keesey: Ah, That New Car Smell: NASA Technology Protects Spacecraft from Outgassed Molecular Contaminants, NASA, (2012), www.nasa.gov/topics/technology/features/outgas-tech.html 
[38] J.T. Knipple: NASA - Outgassing Data for Selecting Spacecraft Materials, (2018), <outgassing.nasa.gov.>
[39] L. Kaluza; A.S. Vuk; B. Orel: Structural and spectroscopic analysis of sol-gel processed CuFeMnO4 spinel and CuFeMnO4/silica films for solar absorbers, J Sol-gel Sci. Technol., 20(2001), 61–83, Doi: 10.1023/A:1008728717617
[40] L. Kaluza; B. Orel; G, Drazic; M. Kohl: Sol-gel derived CuCoMnOx spinel coatings for solar absorbers: Structural and optical properties, Sol. Energy Mater. Sol. Cells, 70(2001)2, 187–201, Doi: 10.1016/S0927-0248(01)00024-1
[41] C.J. Zarobila; S. Grantham; S.W. Brown; J.T. Woodward; S.E. Maxwell; D.R. Defibaugh, T.C. Larason, K.R. Turpie: Optical and mechanical design of a telescope for lunar spectral irradiance measurements from a high-altitude aircraft, Rev. Sci. Instrum., 91(2020)9, 094505, Doi: 10.1063/5.0004848
[42] J. Dever; B. Banks; K. de Groh; S. Miller: Degradation of Spacecraft Materials, Chapter 23 in Handbook of Environmental Degradation of Materials, Myer Kutz (Editor), William Andrew Inc., Applied Science Publishers, (2005), 465–501, Doi: 10.1016/B978-081551500-5.50025-2