Ceramics and ceramic matrix composites as solar thermal receivers: recent advances

Introduction

It is beyond argument that Solar thermal energy conversion has emerged as a prominent pathway towards sustainable and renewable power generation, offering a viable solution to the global energy challenge while reducing greenhouse gas emissions. Solar thermal technology, which utilizes solar energy to produce electricity or supply heat for industrial processes, has garnered substantial attention for its efficiency and versatility. ¹

Concentrated solar power (CSP) systems, a leading solar technology, utilize solar thermal receivers to capture and convert concentrated sunlight into high-temperature heat. ² This heat is then utilized for a variety of applications, including electricity production via steam turbines or supplying thermal energy for industrial processes such as desalination and chemical manufacturing. ³ The efficiency and durability of these receivers directly influence the overall performance of CSP systems. Currently, CSP accounts for approximately 0.5% of global electricity generation. However, projections suggest a significant increase, with its contribution expected to reach 11% by 2050, highlighting its importance in the renewable energy landscape.^4,5

A significant body of research has focused on improving the materials used in solar thermal receivers to enhance their performance and durability. Traditional metallic components, while widely used, are prone to thermal fatigue and oxidation at elevated temperatures, which limits their operational lifespan. ³ Recent studies have turned to advanced ceramic materials and ceramic matrix composites (CMCs), which offer superior thermal stability, corrosion resistance, and mechanical properties under extreme conditions.^4,5 For instance, ceramics like silicon carbide and alumina demonstrate exceptional resistance to high temperatures, thermal cycling, and high thermal conductivity, making them ideal for solar thermal applications. ⁶ Additionally, their corrosion resistance and compatibility with high-temperature environments make them widely used in solar radiation. Also, it possess good optical properties, enabling efficient absorption of solar radiation across a broad spectrum of wavelengths. ⁷

Furthermore, the development of ceramic matrix composites has unlocked new possibilities for improving the performance of solar thermal receivers. Ceramic matrix composites combine the desirable properties of ceramics with enhanced mechanical strength, toughness, and fracture resistance, thanks to the incorporation of reinforcing fibers or particles within a ceramic matrix. This enables the design of lightweight, high-performance components capable of withstanding the rigors of solar thermal energy conversion.^8,9

Despite these advancements, challenges remain in optimizing ceramic and CMC materials to maximize heat absorption and minimize energy losses. This review aims to explore the latest innovations in ceramic and CMC technologies for solar thermal receivers, with a focus on their properties, performance metrics, and potential for scaling CSP systems. By analyzing recent developments, the review seeks to provide a comprehensive overview of the role of advanced materials in advancing solar thermal energy conversion and contributing to global renewable energy goals.

This alignment between material innovation and technological advancement underscores the role of ceramics in shaping CSP's evolution. The durability and performance of ceramic components have proven essential in ensuring the reliability and longevity of solar thermal receivers, thus contributing to the broader adoption of CSP technology in renewable energy applications.

Concentrated solar power technology (CSP)

Solar thermal receiver technology

Solar thermal receivers in CSP systems concentrate sunlight into heat for steam generation, turbines, or industrial heating. These systems operate at 500–1000 °C, necessitating materials capable of withstanding extreme thermal loads and cyclic heating conditions. So, Understanding the fundamental principles and types of solar thermal receivers is vital for comprehending their role in renewable energy systems. ²⁵

Ceramics and ceramic matrix composites as solar thermal receiver

Ceramics have high temperature capability with nonstrategic nature and potentially low cost which make them promising candidates for solar applications. ³⁸ In order to feed a gas turbine at operating temperatures (900–1300 °C); the temperature of the receiver wall should reach at least 1000 °C. ³⁹ Ceramics can be applied in metallic solar receivers as a high temperature absorber coating and also can be applied directly in bulk ceramic solar receivers. Specific properties of ceramic materials are required to be used as solar receivers. They are required to have (1) high thermal conductivity to enhance the heat transfer to the fluid and to limit internal gradients; (2) appropriate optical behavior to maximize the absorption of solar flux; (3) low expansion coefficient that minimizes deformations, fracture toughness and creep resistance; and (4) higher corrosion and oxidation resistance. ⁴⁰

Recent research and development efforts focused on utilizing ceramics and ceramic matrix composites in solar thermal receiver

The development a novel solar absorber material with favorable characteristics, emphasizing high efficiency and cost-effectiveness.

First study by Besisa et al.. ⁷⁰ consequently, they offered a comparative analysis of the densification behavior, microstructure features, thermal emissivity, and thermal conductivity of two new high-temperature solar absorbers Oxide ceramics: ZrO₂/Fe₂O₃ and Al₂O₃/CuO ceramics. Ceramic composites of ZrO₂/(10–30 wt%) Fe₂O₃ and Al₂O₃/(10–30 wt%) CuO were synthesized via pressureless sintering at 1700 °C for 2 h. Evaluation of the solar-to-thermal efficiency of the composites was based on measured thermal emissivity, while thermal efficiency and heat transfer homogeneity were assessed through thermal conductivity and diffusivity measurements. The composites displayed homogeneous microstructures with complete interdiffusion and bonding of different phases resulting from solid solution reactions. Both Al₂O₃/CuO and ZrO₂/Fe₂O₃ composites exhibited similar densification trends with increasing CuO and Fe₂O₃ ceramic contents, although ZrO₂/Fe₂O₃ ceramics achieved a higher level of densification. However, excessive additions of CuO and Fe₂O₃ ceramics were found to be detrimental, leading to grain growth in alumina, and creation of the FeMnO₃ with low density which increased porosity in both systems, and degradation of their thermal and solar-to-thermal properties. ⁷⁰

Thus, Alumina composites with varying CuO content demonstrated superior thermal conductivity of 15.4 W/m·K and exceptional thermal emissivity of 0.561, compared to zirconia composites with varying Fe₂O₃ content. Therefore, Al₂O₃/CuO composites offer exceptional properties at a significantly lower cost than their competitive counterparts. These findings strongly position Al₂O₃/CuO composites as promising high-temperature solar absorber materials, surpassing ZrO₂ and other carbide and nitride ceramics. ⁷⁰

Another study introduced a novel composite material using Al₂O₃/CuO ceramics with assured durability and thermal performance. Various Al₂O₃/CuO composites with CuO content ranging from 10% to 40% were synthesized through a straightforward and cost-effective pressureless sintering method at 1700 °C for 2 h. All resulting ceramics exhibited dense and homogeneous microstructures. It was observed that incorporating a lower amount of CuO into Al₂O₃ ceramics significantly enhanced their properties and efficiency in absorbing solar energy. ⁵¹ This enhancement can be attributed to the uniform diffusion of CuO within alumina and the complete solid-state reaction between the two materials. However, higher CuO content was found to be undesirable as it led to the growth of alumina grains and degradation of other properties. Notably, the composite containing 10% CuO demonstrated the best thermal expansion, thermal conductivity, thermal emissivity, thermal shock resistance, and mechanical durability. Consequently, these Al₂O₃/CuO ceramics exhibit potential as promising high-temperature solar receiver materials with exceptional thermal efficiency and durability. ⁴⁶

In another research study, Ahmed et al.. ⁴⁴ synthesized Al₂O₃/TiC composites from a blend of TiO₂, Al, and graphite powders Utilizing self-propagating high-temperature synthesis in conjunction with direct consolidation, with the incorporation of either zirconia or iron metal powder. The findings indicate that addition of 1.0 mol of zirconia significantly improved both the physical and mechanical properties of the composites, as represented in Table 1. This was evidenced by a substantial reduction in sample porosity from 7.0 to less than 1.0 vol%, along with notable enhancements in microhardness (from 6.0 to 11 GPa) and fracture toughness (from 3.5 to 6.0 MPa m1/2), as well as to a microstructure that is more uniform and finely grained. ⁴⁴ Also, the same trend occurred with 5.0 wt% iron additions led to a significant reduction in porosity to less than 1.0 vol% with increases in microhardness to 12 GPa and fracture toughness to 4.5 MPa m^1/2, as shown in Table 2. This is due to the total liquid phase fraction (molten alumina and molten iron). While samples both with and without iron contain approximately the same total liquid amount, in the case of samples with iron, some of this liquid consists of molten iron, which possesses a lower viscosity compared to molten alumina. This lower viscosity liquid aids in decreasing the porosity in samples containing iron. However, increasing the zirconia addition to 2.0 mol resulted in higher porosity and reduced hardness and toughness. ⁴⁹

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Table 1.

Display the influence of zirconia additions on the physical and mechanical properties of the samples. ⁴⁴

Sample type	Sample with 0% mol zirconia	Sample with 1% mol zirconia	Sample with 2% mol zirconia
Micro-hardness, GP	6.35	11.22	4.79
Apparent porosity %	7.0	0.141	6.38
Fracture toughness, MPa m1/2	3.5	6.10	3.49

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Table 2.

The micro-hardness and fracture toughness were evaluated for samples containing varying additions of iron metal. ⁴⁴

Sample type	Micro-hardness, GPa	Fracture toughness, MPa m1/2
10 wt % iron	10.99	7.2
5 wt % iron	12.21	4.5
0 wt % iron	6.43	3.5

Despite the sample produced with 15.0 wt% iron having porosity similar to that of the 5.0 wt% iron sample, its micro-hardness is lower, as seen in Table 2. This discrepancy is attributed to a reduction in the amount of hard components (TiC and alumina) and an increase in the amount of the softer metallic component (Fe). Furthermore, the increasing of iron content increases the proportion of the softer alumina phase relative to the harder TiC phase. These alterations in the relative volumes of phases due to iron addition are responsible for the decrease in micro-hardness with increasing iron content. ⁷¹

The combined addition of diluents (1.0 mol zirconia and 5.0 wt% iron metal) resulted in a notable increase in porosity, incomplete reaction, and lower hardness and fracture toughness. The measured micro-hardness and fracture toughness of these samples stand at 3.18 GPa and 4.61 MN/m3/2, respectively, underscoring a notable decrease in mechanical properties upon the addition of both diluents. This reduction is attributed to a marked rise in apparent porosity within the composite, coupled with incomplete reaction processes. ⁴⁴

On the other hand, composite ceramics serve as a primary method for enhancing the mechanical performance of ceramic materials. SiC is a widely utilized engineering ceramic, and it is believed that incorporating SiC into Al₂O₃ matrices will notably enhance the mechanical properties of monolithic Al₂O₃.^72,73 Niihara. ⁷⁴ documented that nanocomposite ceramics utilizing nano-silicon carbide particles as a secondary phase displayed superior mechanical properties. Incorporating 5 vol%-10 vol% submicron SiC particles into the Al₂O₃ matrix increased the bending strength of the composites from 350 MPa to over 1 GPa.

Xiaohong et al.. ⁷³ fabricated a composite material by combining mullite and corundum with silicon carbide (SiC), was using SiC, calcined bauxite, and kaolin through pressureless carbon-buried sintering (SiC-mullite-Al₂O₃). Aiming to develop cost-effective SiC-based composite ceramics for potential use as thermal storage materials in solar thermal power generation, capitalizing on their high density and exceptional thermal shock resistance. They showed that incorporating calcined bauxite significantly lowered the minimum sintering temperature to 1400 °C. The SiC-mullite-Al₂O₃ composite with 40 wt% calcined bauxite, sintered at 1500 °C, demonstrated optimal performance, exhibiting a density of 2.27 g·cm⁻³ and a bending strength of 77.05 MPa. Contrasting with the typical reduction in thermal shock resistance observed when SiC is combined with conventional clay. These SiC-mullite-Al₂O₃ composites, showing satisfactory performance, hold potential for use as thermal storage materials in solar thermal power generation systems. ⁷³

In a separate investigation by Jianfeng et al.. ⁷⁵ , Al₂O₃/SiC composite ceramics were fabricated using α-Al₂O₃ and SiC via a pressureless sintering technique. This study explored into the influence of SiC content on mechanical properties, phase compositions, and microstructure. Notably, at a SiC content of 20 wt% and a sintering temperature of 1640 °C, the sample achieved a hardness of 16.22 GPa and a thermal conductivity of 25.41 W/(m·K) at room temperature whereas the hardness of the monolithic Al₂O₃ is only 13.61 GPa, which is consistent with the results reported by many researchers.^58,76 The improvement of hardness is attributed to the incorporation of a hard secondary phase (SiC) and the refinement of the grains in the composites. ⁷⁵ As the SiC content increases, there is a decrease in the average grain size of Al₂O₃, suggesting that SiC hinders the growth of Al₂O₃ grains. This grain refinement contributes to the enhanced strength of the material, as it is one of the factors behind the strengthening mechanism. The bending strength of samples containing higher SiC content increased due to the more pronounced alteration in fracture mode and grain refinement induced by SiC. A higher hardness implies greater resistance to abrasion, suggesting the potential utilization of Al₂O₃/SiC composite as a solar heat absorber for third-generation solar thermal generation. Following the Griffith theory, the enhancement in bending strength of ceramic materials is attributed to two factors: the diminution of inherent flaws or micro-cracks within the ceramic, which heightens the energy barrier to crack propagation. ⁷⁷ Typically, the size of micro-cracks in ceramics correlates with the grain size of the material. In the context of the composite ceramics explored in this study, the incorporation of SiC results in the refinement of Al₂O₃ matrix grains and a reduction in micro-crack size, consequently bolstering the material's overall strength. ⁷⁵

Additional investigation demonstrates that the incorporating aluminum nitride AIN into SiC can mitigate the reliability and toughness issues often associated with SiC ceramics. These issues stem from the reaction between SiC and AIN, which typically results in a comprehensive solid solution formation. The structural similarity and high-temperature properties shared by SiC and AIN can significantly improve their durability and mechanical performance. ⁷⁸

Besisa et al.. ⁷⁸ successfully fabricated high-density SiC/AIN composites with excellent thermal properties using a pressureless sintering technique. They utilized AlN, α-SiC, and β-SiC as raw materials, supplemented with Y₂O₃ and Al₂O₃ additives to enhance density levels. It was observed that sintering at 2080 °C for 2 h yielded a highly dense and enhanced SiC/AIN composite with the addition of 2.5 wt.% of Y₂O₃ and Al₂O₃. The densification process and AIN content were crucial in controlling the composite's characteristics. Furthermore, increasing the sintering temperature improved thermal expansion coefficient, diffusivity, and thermal conductivity values. The authors recommended these resulting composites for applications in solar energy utilization. ⁷⁸

Furthermore, Ortona et al.. ⁵⁰ prepared Tubular Si-infiltrated SiCf/SiC composites that consist of an inner cellular ceramic structure and an outer dense ceramic matrix composite (CMC) skin. These composites were produced via electrophoretic deposition of matrix phases followed by Si-infiltration, aimed at pre-feasibility testing for solar receiver applications. Intended for high-temperature receiver components in solar operations, such as gas turbines or combined cycles, these tubes can withstand temperatures up to 1300 °C and typical pressures exceeding 6 bar. The internal cellular structure enhances heat transfer from the irradiated outer surface to the working fluid within. ⁵⁰ Through experimental determination of heat transfer and permeability characteristics, effective properties were established and used in numerical models to forecast component performance under gas turbine service conditions. Additionally, they found that the heat transfer rate in a tube with a porous in-lay increased to approximately four times compare to the rate of an empty tube of the same size (Figure 1). ⁵⁰

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Figure 1.

Sample (left) “foam in-lay” and (right) “3D-printed in-lay” used for testing. ⁵⁰ .

Casalegno et al.. ⁶⁸ developed novel SiC ceramic materials for high-temperature open volumetric receivers. They prepared the highly porous SiC sintered in honeycomb shape by the extrusion and slip casting slurry and adhering to appropriate casting times, it is feasible to manufacture all-SiC solar receivers with commendable green strength and wall thickness, facilitating their assembly in the green state. This all-SiC honeycomb design improved oxidation resistance and a multi-part SiSiC 3D printed design for increased toughness, thermal conductivity, with high mechanical strength (54 ± 1.3 MPa) within the range of 2000 °C to 2400 °C. Also, gradient of porosity aimed at enhancing heat exchange efficiency, ranging from 83% to 92% from its inner to outer regions. A thermal treatment was developed to minimize reflected radiation on the final component. An innovative pressurless joining process involving in situ formation of a MoSi₂ particle-reinforced Si matrix composite effectively joins SiSiC-based cups and foams for thermal receivers (Figure 2). ⁶⁸

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Figure 2.

The solar receiver parts of the mock-up of: the SiSiC foam, the “L” shaped SiC substrate, the SiSiC pin. ⁶⁸

This joining method, coupled with mechanical fasteners, reinforces the receiver, enhancing its mechanical strength and durability in order to avoid interfacial cracking of the solar receiver, as seen in Figure 2.

In addition to the aforementioned materials, SiC and Si₃N₄ exhibit impressive properties conducive to solar applications, including robust thermal shock resistance, high strength, excellent wear resistance, and thermal conductivity. Nonetheless, achieving dense Si₃N₄ ceramic poses challenges with conventional sintering methods due to its strong covalent bonding. Moreover, pure Si₃N₄ exhibits poor oxidation resistance. ⁶⁴

The performance of Si₃N₄ can be significantly enhanced by employing a combination phase of MgAl₂O₄– Si₃N₄ composites, as fabricated by Wu et al.. ⁶⁴ via pressureless sintering and in-situ synthesis technique using α-Si₃N₄, α-Al₂O₃, and MgO as starting materials. The resulting sintered composites, processed at 1620 °C, demonstrated superior oxidation resistance, thermal shock resistance, and solar absorptance compared to Si₃N₄ ceramics prepared using similar methods. These composites are thus recommended as promising candidates for solar heat absorption. ⁶⁴

Furthermore, Zhang et al.. ⁷⁹ demonstrated that adding 1 wt.% of Sm₂O₃ to MgAl₂O₄-Si₃N₄ pressureless sintered composites enhances microstructure and stability at high temperatures. Sintering the composite at 1620 °C with 1 wt.% of Sm₂O₃ additive resulted in a bending strength of 339.4 MPa, 92.0% solar absorptance, and no damage after thermal shock. ⁷⁹

Reddy et al.. ⁸⁰ produced porous sialon ceramics via pressureless sintering at 1700 °C for 4 h in a nitrogen atmosphere, incorporating starch in the range of 0–5 wt.% to commercial grade Syalon 101 powder, composed of 90% silicon nitride (α-Si₃N₄), 1% aluminum nitride (AlN), 3% aluminum oxide (α-Al₂O₃), and 6% yttrium oxide (Y₂O₃). The study revealed that increasing levels of porosity led to decreased strength and hardness of sialons, while an upward trend in fracture toughness was observed in the host material as starch-induced porosity increased. The resulting porous sialon demonstrated a promising combination of dielectric and mechanical properties, rendering it suitable for applications such as heat exchangers, which can, in turn, be utilized for solar receivers. Nevertheless, further investigations are warranted to validate the material's suitability as a solar absorber, including assessments of thermal conductivity, solar absorbance, and oxidation resistance. ⁸⁰

In efforts to reduce the firing temperature and porosity of Si₃N₄ ceramics, rare-earth oxides (R₂O₃) such as La₂O₃, Gd₂O₃, and Y₂O₃ have been introduced to form a low-melting-point eutectic R–Si–O–N liquid with Si₃N₄ powder. Wu et al.. ⁶² utilized a pressureless sintering method to prepare O-Sialon/Si₃N₄ ceramic composites for solar absorbers using Si₃N₄ and low-purity Al₂O₃ with various rare-earth oxides (e.g., Yb₂O₃ and Gd₂O₃). Sintering at 1600 °C with the addition of 6 wt.% Gd₂O₃ yielded higher O-Sialon content, 23.29% porosity, 105.57 MPa bending strength, weight gain rate of 17.49 mg/cm² (at 1300 °C for 100 h), 75.16% solar absorption, 10.10% water absorption, and high oxidation resistance. These results indicate Gd₂O₃ as a more effective additive compared to Yb₂O₃, with bending strength showing a strong correlation with sintering temperature and rare earth oxide content. The highest bending strength was achieved at 1600 °C for the composite containing 6 wt. %.The addition of Gd₂O₃ was also observed to correlate with the composite's oxidation resistance, with composites exhibiting lower weight gain values demonstrating higher resistance to oxidation. ⁶²

Wu et al.. ⁶² conducted the synthesis of β-Sialon/Si₃N₄ composites through pressureless sintering at 1580 °C, utilizing α-Si₃N₄, calcined bauxite, and 1% aluminum nitride (AlN) as raw materials, along with Y₂O₃ and La₂O₃ as sintering additives. Their findings indicated that incorporating 3 wt.% of Y₂O₃ and 3 wt.% of La₂O₃ as additives yielded optimal mechanical properties, with a bending strength of 138.36 MPa. The resulting composite exhibited a thermal conductivity of 7.96 W/m.K and a solar absorptance of 91.10%. Moreover, the weight gain rate after oxidation, reported at 1100 °C for 100 h, was as low as 0.9331 mg/cm². This composite proves suitable for use as a heat-absorbing material in SPT systems. ⁴⁵

Sani et al.. ⁸¹ synthesized composite of ZrC, HfC, ZrB₂ and HfB₂ Ultra-High-Temperature-Ceramics (UHTCs) by hot pressing at 1930 ^oC. SiC-based material demonstrated a consistent microstructure composed of uniform grains less than 1 micrometer in size, with a porosity content of 5%. ⁸¹ They noted that enhancement in the performance of UHTCs compared to HfB₂for solar receiver applications, attributed to their notably lower emittance across the entire temperature range of 1100–1450 K investigated in this study. ⁶

The research conducted by Sani et al.. ⁸² examined the high-temperature emittance, spectral reflectance at room temperature, and structural as well as compositional features of samples made from ZrB₂, HfB₂, and HfC with the aim of assessing their suitability for solar receiver applications. Dense and porous/rough samples of each material were studied, and their spectral attributes were analyzed and contrasted with those of reference solar absorber materials, Al₂O₃ and SiC. The emittance values obtained for the two boride materials were similar. Similarly, at comparable density and finishing levels, the carbide material exhibited a slightly elevated emittance and displayed a more significant reliance on temperature variations. Nevertheless, it's noteworthy that across all samples investigated, including the porous or roughened ones, the recorded emittance remained notably lower than that of the reference SiC. This favorable comparison highlights the potential of Ultra-High Temperature Ceramics (UHTCs) over conventional materials utilized in solar absorbers. Thus, the desirable attributes of good spectral selectivity, low thermal emittance, and robust high-temperature stability render UHTC ceramics promising candidates for innovative high-temperature solar receivers. ⁸³

Another investigation focuses on the synthesis and characterization of ultra-high temperature ceramics (UHTCs) by Sani et al.. ⁸³ The study particularly explored into the production and detailed analysis of highly dense, pure zirconium and tantalum diborides, with a specific emphasis on their potential use in thermal solar energy applications. Comparing the two processing methods for preparing bulk ZrB₂ and TaB₂ dense ceramics using the self-propagating high temperature synthesis/Spark Plasma Sintering (SHS/SPS) and active spark plasma sintering (RSPS). They observed that the optical properties of the final products are nearly identical. However, slight variations in reflectance values are noted when analyzing ZrB₂ specimens. These differences are attributed mainly to variations in pore size between the two types of ZrB₂ samples, impacting their roughness (Rt) values. Nonetheless, both borides exhibit step-like reflectance spectra, resulting in high solar absorbance and low thermal emittance at elevated temperatures. The spectral disparities between ZrB₂ and TaB₂ are confined to the wavelength range of 550 to 2600 nm, leading to a slightly higher absorbance-to-emittance ratio (a/ε) for TaB₂ compared to ZrB₂. Regarding the direct use of monophasic UHTCs at high temperatures in oxidative environments, it's noted that both tantalum and zirconium diborides begin to oxidize above approximately 600 °C, leading to rapid material degradation unless suitable additives are introduced. Therefore, for applications such as solar absorbers, where high temperatures are involved, additives like silicon-containing compounds (SiC, MoSi₂, etc.) must be incorporated to enhance oxidation resistance and enable utilization under more severe thermal conditions. ⁸⁴

Musa et al.. ⁸⁴ synthesized four sets of products HfB₂, HfC, HfB₂-SiC, and HfB₂-HfC-SiC products comprising monophasic, binary, and ternary Hf-based Ultra-High-Temperature Ceramics (UHTCs) using the SHS-SPS and R-SPS techniques. All sintered specimens exhibit relative densities exceeding 95%, with composite systems nearing theoretical density values, attributed to the advantageous role of SiC as a sintering aid, which also enhances the oxidation resistance of the resultant Ultra-High-Temperature Ceramics (UHTCs). The optical properties are significantly influenced by the material composition, with SiC addition typically leading to increased solar absorbance and reduced spectral selectivity compared to pure UHTC boride and carbide phases. So, the presence of spectrally selective, thermally stable, and highly efficient sunlight absorbers is a critical factor in advancing solar energy technologies capable of operating under high temperatures. ⁸⁵

Ultra-high temperature ceramic matrix composites (UHTCMCs) represent a novel category of composites blending boride phases with carbon fibers to yield innovative structural and functional attributes, initially tailored for aerospace purposes. This study pioneers the investigation into the optical behavior of UHTCMCs, contemplating their potential role as solar absorbers in Concentrating Solar Power (CSP) systems operating at elevated temperatures. ⁵⁷

Other research investigated ZrB₂ ceramic samples reinforced with carbon fibers, with a focus on their microstructural and optical properties for potential application as solar absorbing materials in high-temperature thermodynamic solar plants. These composites exhibited substantial fractions of ZrB₂ (∼40 vol%) and carbon fibers (up to 60 vol%). The chosen approach involves the method of slurry impregnation and sintering, enabling the production of both dense and porous samples. ⁵³ Through this method, composites with significant fractions of ZrB₂ phase and a high proportion of carbon fibers were successfully achieved. The incorporation of carbon fibers led to a notable alteration in the optical properties of the samples compared to pure boride. Specifically, they observed a consistent increase in solar absorptance, demonstrating the considerable potential of these carbon-fiber-reinforced borides for solar absorber applications. In summary, the enhanced optical properties, coupled with high mechanical strength even under elevated temperatures, damage tolerance, thermal shock resistance, and lightweight nature, make fiber-reinforced ultra-high temperature ceramic composites highly promising as a novel concept for ultra-high-temperature solar absorber materials. ⁵³

Application of ceramics and ceramic matrix composites as solar thermal receiver

Solar thermal receivers play a central role in concentrating solar power (CSP) systems, where they absorb concentrated sunlight and convert it into heat for powering steam turbines or other heat engines. Ceramics and CMCs find numerous applications within solar thermal receivers, including:

Traditional ceramics, including materials like alumina (Al₂O₃), aluminasilicate, and zirconia (ZrO₂), have long been utilized in solar thermal receivers due to their excellent thermal stability, corrosion resistance, and high melting points. These ceramics provide the structural integrity necessary to withstand the harsh operating conditions of CSP systems. ⁴⁶

Conclusion

Ceramics and Ceramic matrix composites represent a promising solution for advancing solar thermal technology and enabling the widespread adoption of solar energy. The choice of ceramics and CMCs in solar thermal receivers underscores their exceptional thermal properties, mechanical strength, and corrosion resistance to harsh environmental conditions. Among these materials, alumina, silicon carbide, zirconia, mullite, silicon carbide/ silicon carbide composites, and ultra-high temperature ceramic have emerged as prominent candidates, each offering distinct advantages suited to the rigors of CSP systems. As research and development efforts continue to progress, the integration of CMCs into solar thermal receivers holds the promise of unlocking new possibilities for sustainable energy generation and accelerating the transition towards a greener future. Advanced ceramic composites, novel coating technologies, and innovative manufacturing techniques are being explored to further optimize the efficiency and reliability of CSP systems. Alumina, with its high-temperature stability and chemical inertness, serves as a reliable matrix material, while silicon carbide boasts superior thermal conductivity and mechanical strength, making it ideal for absorbing and transferring solar energy efficiently. Zirconia contributes excellent thermal insulation properties, crucial for minimizing heat loss within the receiver, while mullite provides resilience against thermal shock and rapid temperature fluctuations. Moreover, the advent of alumina/ silicon carbide and silicon carbide/silicon carbide (SiC/SiC) composites introduces lightweight alternatives without compromising thermal performance, addressing the need for weight reduction in solar thermal receivers. Additionally, Fiber-reinforced UHTCMCs enhanced optical properties, coupled with high mechanical strength at elevated temperatures, thermal shock resistance, and lightweight nature, extends the spectrum of materials available for consideration, opening avenues for further innovation in receiver design and performance optimization.

The synergy between materials science, engineering ingenuity, and renewable energy initiatives is evident in the continual refinement of ceramic-based solutions for solar thermal applications. Ongoing research efforts in the field of ceramics for solar thermal receivers continue to focus on enhancing material properties, reducing manufacturing costs, and improving overall system performance. Looking ahead, as solar thermal technology continues to evolve, so too will the role of ceramics and CMCs in shaping its trajectory. Through interdisciplinary collaboration and a commitment to sustainability, we can harness the full potential of these advanced materials to propel us towards a future powered by clean, renewable energy sources, ultimately paving the way for a more sustainable and resilient energy landscape.

Future perspectives of ceramics and ceramic matrix composites as solar thermal receivers

Solar thermal energy has emerged as a promising renewable energy source, offering significant potential for sustainable electricity generation. Among the key components of solar thermal power plants, the solar receiver plays a crucial role in capturing and converting sunlight into thermal energy. In recent years, there has been growing interest in utilizing ceramics and ceramic matrix composites (CMCs) as materials for solar thermal receivers due to their exceptional thermal properties, mechanical strength, and resistance to high temperatures. The perspectives on the use of ceramics and CMCs in solar thermal receivers, highlighting their advantages, challenges, consideration and Opportunities for improving ceramic-based solar receivers.