Abstract

Greenhouse gases are an increasingly present threat to our environment; to preserve the lifetime of our planet, reductions in emissions are necessary. This paper examines hydrogen turbines for reducing emissions, explores the current operational challenges and presents one potential solution in the form of ceramic matrix composites (CMCs) designed for this application. It explains the construction, material selection and manufacturing of CMCs, and selects several composites that are well suited for this application, explaining the nuances of each. This paper also explores other difficulties that may arise from implementation, like manufacturing costs, quality control, wear and tear, and repairability. Finally, it examines the current viability in hydrogen turbine applications and what the future of CMC technology might be able to offer to hydrogen turbines. 

1. Introduction

As greenhouse gases continue to detract from our environment, it is clear a solution to reduce this pollution is urgently needed. Of the pollutants found in the atmosphere, carbon dioxide (CO2) is the most prevalent and destructive. According to research by the Environmental Protection Agency, about 64% of the global net greenhouse gas emissions are CO2 produced from the burning of fossil fuels (United States Environmental Protection Agency, 2025). Of the global greenhouse gas emissions by sector, transportation makes up about 15% of the total (United States Environmental Protection Agency, 2025).

A clean alternative to traditional fossil fuels must be found to reduce these harmful emissions. One widely proposed solution is the development of hydrogen power, particularly hydrogen fuelled gas turbine engines, as hydrogen not only burns free CO2 emissions but also boasts impressive performance capabilities as a powerful fuel source (Stępień, 2021; Boretti, 2024; International Energy Agency, 2019).

However, there are still several challenges to consider surrounding the implementation of hydrogen as fuel. These challenges include hydrogen’s high flame speed and combustion characteristics, which can produce high local flame temperatures. High local flame temperatures increase the potential for nitrogen oxide (NOₓ) formation, flashback and combustion instability, as well as the production of water vapour, which accelerates degradation of engine materials (Stępień, 2021; Boretti, 2024; Marek, Smith & Kundu; 2005, Singh et al., 2025). Due to the intense environment that hydrogen combustion creates inside the engine – an environment traditional turbine materials are unable to withstand – highly resistant materials are needed for hydrogen to become a viable fuel alternative.

Among the materials researched for this role, ceramic matrix composites (CMCs) appear to show much potential as a solution. CMCs, particularly the silicon carbide/silicon carbide (SiC/SiC) composites, have proven to be able to withstand the intense heat and mechanical stress that typical materials, like metal alloys, cannot survive, becoming common in aerospace applications (Muktinutalapati, 2011; Varela, 2024). However, there are several operational challenges that need to be addressed when fabricating the correct CMC for the application. Steam and excessively high temperatures pose risks that need to be mitigated for their use. Also, the maintenance and wear and tear of CMCs, and their intricate manufacturing processes, currently limit widespread commercial adoption. This paper examines the implementation of CMCs in hydrogen-fuelled gas turbine engines by evaluating their advantages, current limitations, fabrication methods and the role of environmental barrier coatings in improving long-term performance.

2. Existing Technology in Conventional Gas Turbines

Before hydrogen-fuelled gas turbines became a viable option to consider for implementation, suitable high-temperature materials had to be developed to fit the conventional turbine model. Most conventional gas turbines rely primarily on nickel-based superalloys and thermal barrier coatings to protect components from the high heat (Muktinutalapati, 2011). While these materials proved successful in conventional engines, hydrogen combustion introduces new conditions that pushes them past their practical operating limits. As a result, engineers have turned increasingly toward materials like ceramic matrix composites and environmental barrier coatings as promising alternatives capable of surviving in the intense environment produced by hydrogen combustion (Varela, 2024; Fang, Gao & Song, 2023; Prasad & Bhaduri, 2017).

2.1 Fuel Injection in Hydrogen Turbines

Fuel injection technology plays a crucial role in the overall performance of a combustion system. A fuel injection system has direct influence over combustion efficiency, emissions and engine stability. An effective and optimised system is the difference between an engine that misfires and one that performs exceptionally. Unlike conventional fuels, hydrogen possesses high flame speed, wide flammability range and extremely low ignition energy. While these properties make hydrogen a very capable high-performance fuel, they also create new challenges to address, such as flashback, combustion instability and increased production of nitrogen oxide (NOₓ) (Stępień, 2021; Boretti, 2024; Marek, Smith & Kundu, 2005, Singh et al., 2025). As such, ensuring the fuel injection system is designed to maintain stable engine operation and safe burning of hydrogen is a key concern in the development of hydrogen turbines. Application of historical methods, such as premixed combustion and diffusion combustion to hydrogen turbines, has proven to be incomplete. While diffusion combustion provided stable operation, it failed to regulate NOₓ emissions to a reasonable level (Marek, Smith & Kundu, 2005). Premixed combustion displayed significantly reduced NOₓ emissions but was unable to safely operate the more volatile hydrogen environment (Marek, Smith & Kundu, 2005). These limitations have motivated research towards new methods of fuel injection that can combine safe operation with regulated emissions, such as lean direct injection (LDI) and micromix combustion.

2.1.1 Lean Direct Injection (LDI)

Lean direct injection (LDI) is an advanced fuel injection system that injects hydrogen directly into the combustor through multiple small injectors while maintaining a lean fuel-air mixture (Marek, Smith & Kundu, 2005). Within the process of LDI, the hydrogen fuel is introduced to the compressed air immediately before combustion rather than being premixed upstream. This significantly reduces the risk of flashback while also allowing greater control over the combustion process. In addition, the use of multiple injectors promotes a more uniform distribution of fuel, resulting in a stable flame, lower NOₓ emissions and increased combustion efficiency (Marek, Smith & Kundu, 2005).

By operating with a lean fuel-air mixture, LDI lowers peak combustion temperatures, reducing the production of NOₓ while still maintaining high combustion efficiency. Together, these characteristics have made LDI a very attractive fuel injection technology for hydrogen-fuelled gas turbine engines. However, with all the improvements in emissions and stability, there are still downsides to this method. The complex design of the system makes it expensive to manufacture and difficult to implement at a large scale (Marek, Smith & Kundu, 2005). More research and optimisation of the system is necessary for it to become a feasibly adopted technology.

2.1.2 Micromix Combustion

Instead of forming a single large flame, micromix combustion technology relies on the use of many small-scale flames to create a more controlled and uniform combustion process. (Singh et al., 2025). Hydrogen fuel is divided into a multitude of miniature jets, each producing an individual flame that rapidly mixes with surrounding air (Singh et al., 2025). This process is an effort to reduce the scale and variability of mixing to a miniscule level, therefore significantly reducing NOₓ emissions with improved control and mitigating the likelihood of auto-ignition and flashback associated with premixing (Singh et al., 2025).

However, this technology still resides in the research and design stage and lacks full-scale engine testing. Furthermore, its complex construction requires hundreds of precisely manufactured injectors and materials, which makes it expensive and difficult to produce. Despite these challenges, micromix combustion is widely regarded as one of the most promising hydrogen combustion technologies in development (Singh et al., 2025). Its impressive stability and combustion control make it a great candidate for hydrogen-fuelled gas turbines, and due to its more uniform temperature distribution and reduced thermal stressors, micromix technology would seem to create an environment that is particularly compatible with advanced ceramic matrix composites designed for hydrogen turbine applications.

2.2 Operational Challenges

Hydrogen fuel sources have several operational challenges that must be addressed before practical and reliable turbine applications can become viable. When compared with traditional fossil fuels, hydrogen is far more volatile. Its low ignition energy, high flame speeds and wide flammability range, while great for a powerful reaction, creates some challenges regarding the operation of the engine, such as flashback and combustion instability (Stępień, 2021; Boretti, 2024; Marek, Smith & Kundu, 2005; Singh et al., 2025). Furthermore, the high operating temperatures of hydrogen combustion, coupled with its production of water vapour as a byproduct, make it difficult to find a material that is capable of surviving the combustion environment. Finding a material that can withstand such conditions is crucial to the success of hydrogen turbine technology.

2.2.1 Temperature

Inside a hydrogen combustor, a flame of approximately 2,100℃ is released. With the aid of intense air-cooling techniques, the surface temperatures inside the turbines range from 1500℃ to 1700℃ (Muktinutalapati, 2011). However, the decreased temperature still causes extreme thermal stresses on materials in contact with the combusting hydrogen, which ultimately leads to rapid material degradation.

While metals are still incapable of withstanding such elevated temperatures, researchers have identified materials that show great promise: ceramic matrix composites (Muktinutalapati, 2011; Varela, 2024). CMCs are lightweight and capable of maintaining form in temperatures beyond the practical limits of nickel-based superalloys (Muktinutalapati, 2011; Varela, 2024). Their reinforced structure allows them to retain structural integrity at high temperatures and to degrade at a much more reasonable rate than any other material tested thus far. The ability of CMCs to operate at higher temperatures also reduces the amount of cooling air required. This allows a greater portion of the compressed air to participate in combustion, improving overall turbine efficiency.

2.2.2 Steam

As a result of the chemical properties of hydrogen and the air it interacts with, water vapour is formed as a byproduct of the combustion process. Steam causes major issues within the engine materials as the water vapour accelerates the oxidation and corrosion of materials, as well as the degradation of lubricants (Fang, Gao & Song, 2023). It also increases the effect of thermal shock: the cracking of a solid material when exposed to drastic and rapid change in temperature. Another issue is that water vapour is quite harmful to many non-oxide CMCs, causing continuous oxidation and recession (Varela, 2024; Fang, Gao & Song, 2023). This destructive interaction has spurred the development of environmental barrier coatings, a protective layer between the CMC and water vapour to shield from negative interactions. These coatings significantly improve the lifespan of CMC components, making them essential technology for hydrogen-fuelled gas turbines (Fang, Gao & Song, 2023).

3. Ceramic Matrix Composites

A ceramic matrix composite is an engineered material designed to tackle the problems posed by traditional monolithic ceramics. The challenges include thermal fatigue and shock, creep cracks, low fracture toughness and lack of tensile strength (Prasad & Bhaduri, 2017). Thermal fatigue occurs when a material is subjected to repeated hot and cold cycles, leading to cracks. Creep cracks form from discontinuities in the polycrystalline structure of the ceramics and grow with heat and stress. Both thermal fatigue and creep cracks result in reduced performance stemming from cracks (Prasad & Bhaduri, 2017).

3.1 Structure

To improve both the thermal and mechanical characteristics of ceramics, additions have been made to create a composite. These additions range from the inclusion of reinforcing fibres to an engineered fibre-matrix interface and a ceramic matrix (Shrivastava et al., 2024; Prasad, Kumar & Subramanyam, 2017).

Ceramic reinforcements are the primary way the ceramic’s tensile strength is improved. Reinforcements come in two primary forms: continuous fibres and discontinuous fibres (Shrivastava et al., 2024; Prasad, Kumar & Subramanyam, 2017). 

Continuous fibres are long segments of fibres included in the matrix. They offer superior strength when compared with discontinuous and particle reinforcements. However, they exhibit anisotropic properties. They come in two forms: monofilament reinforcements and multifilement reinforcements (Prasad, Kumar & Subramanyam, 2017). 

Monofilament reinforcements are often constructed with boron, borsic (boron coated with silicon carbide) and silicon carbide monofilaments with diameters of 100-150μm, and are usually made with chemical vapour decomposition (CVD) (Prasad, Kumar & Subramanyam, 2017). Multifilament reinforcements, or tows, such as Nicalon (SiC), Sumitomo (alumina) and carbon fibres are fabricated through pyrolysis of organometallic compounds in the form of tows (bundles of thousands of 3-10μm diameter fibres) or weaves of the fibres (Prasad, Kumar & Subramanyam, 2017). 

Discontinuous fibres, or whiskers, are shorter lengths of fibres interspaced in the matrix. SiC whiskers show the greatest potential for improving the properties of ceramics, showing better elastic modulus and tensile strength (Prasad, Kumar & Subramanyam, 2017). While they lack the same strength and stiffness provided by continuous fibre reinforcement, their isometric properties and ease of manufacturing make them appealing for certain applications (Prasad, Kumar & Subramanyam, 2017). 

The interface between the matrix and the reinforcing fibre is critical to the efficacy of the reinforcement (Shrivastava et al., 2024; Prasad, Kumar & Subramanyam, 2017). Without a proper interface coating on the reinforcement, the fibres will have limited success bridging cracks via fibre pullout. Important to note is that the interface is deliberately weaker than the reinforcing fibres to facilitate better crack propagations though pullout (Prasad, Kumar & Subramanyam, 2017). There are two main methods interfaces used to bond to the matrix: mechanical and chemical. 

Mechanical bonding is a generally weaker bonding occurring from a difference in the coefficient of thermal expansion (CTE) or in elastic modulus between the matrix and the reinforcement. It is efficient in load transfer parallel to the interface and can give substantial benefits to brittle ceramics through pullout/bridging (Prasad, Kumar & Subramanyam, 2017). 

Chemical bonding is, by comparison, much stronger, providing a much better interface between the reinforcement and the matrix. That being said, if the interface compound is brittle, problems can naturally arise, as the success of reinforcing fibres depends on a careful balance that allows the fibres to pull out, but not with such ease that leaves them unable to effectively bridge cracks (Prasad, Kumar & Subramanyam, 2017).

3.2 Ceramic Matrix Material

The material used in the matrix has a significant role in determining the attributes the matrix has, with there being two main categories of CMCs: oxide CMCs and non-oxide CMCs.

3.2.1 Oxide CMCs

Oxide CMCs are characterised by their composition of inorganic oxide compounds, with metallic and metalloid composition and low fracture toughness (Karadimas & Salonitis, 2023). Notably, their maximum operational temperature of 1200 ℃ causes extensive creep cracking at higher temperatures. With the inclusion of multistrand fibres, crack propagation slightly improves, thus improving crack, thermal shock and elongation resistance. The two main oxide CMCs are alumina (AL2O3) and aluminosilicate (3AL2O3, 2SiO2). Although they have good mechanical attributes, their thermal limitations render them ill-suited for hydrogen turbine applications, where operational temperatures reach over 1500 ℃ (Deb et al., 2025).

3.2.2 Non-Oxide CMCs

In contrast, non-oxide CMCs are characterised by their covalent bonds, allowing better crack propagation, and include both conductive and non-conductive carbides. The addition of the fibre-matrix interface allows for much higher toughness compared to oxide-CMCs, with fibre failure being the cause of oxide failure. Non-oxide CMCs also exhibit higher thermal resistance; although at higher temperatures their oxidation resistance is much lower (Karadimas & Salonitis, 2023). Therefore, specialised coatings are required to make non-oxide CMCs viable for hazardous environments. These higher operational temperatures may make them applicable for use in hydrogen turbines.

3.3 Manufacturing Methods

The method used to manufacture a CMC has many effects on its final strength. Due to the high manufacturing temperatures, traditional sintering causes deterioration of both the ceramic and the reinforcements. Advanced methods allow for lower porosity, thus increasing the toughness of the CMC (Prasad, Kumar & Subramanyam, 2017; Karadimas & Salonitis, 2023).

3.3.1 Polymer Infiltration and Pyrolysis

Polymer infiltration and pyrolysis (PIP) is characterised by a low-viscosity polymer that is introduced to a fibre-reinforcing structure, then heated without oxygen to turn the polymer into a ceramic (Shrivastava et al., 2024; Karadimas & Salonitis, 2023). This process is repeated many times until the suitable dimensions have been achieved, as the ceramic shrinks around the preform while it cools. Advantages include a lower fabrication temperature, reducing damage to the structure (Santhosh et al., 2021), greater control of the microstructure of the ceramic, the ability to fabricate a wide variety of matrices, reinforcement shapes and sizes, and the lack of free silicon present in the final composite. Drawbacks include the presence of micropores and a high manufacturing cost and time compared to other methods (Shrivastava et al., 2024).

3.3.2 Reactive Melt Infiltration

Reactive melt infiltration (RMI) involves having a molten metal or metalloid that permeates a porous premold (Karadimas & Salonitis, 2023; de Jongh & Eggenhuisen, 2013). There are two main types of RMI: direct melt oxidation (DMO) and liquid melt infiltration (LMI). Both function where the metal forms into a ceramic through a reaction, usually with either a coating on the reinforcements or with an atmosphere of choice. DMO is commonly used to make alumina matrices, where molten aluminum infiltrates the porous preform from one side while oxygen is present at the other end, creating a moving oxidation front of ceramic (Shrivastava et al., 2024). Though RMI is quicker and less expensive than other methods, not all the melt will react, leaving pockets of non-ceramic. The residual free silicon or aluminum, combined with higher temperatures of LMI that can damage reinforcements, weaken the strength of the composite.

3.3.3 Chemical Vapour Infiltration

Chemical vapour infiltration (CVI) takes place inside a hot or cold wall reactor, in which a preform is placed and heated to intermediate temperatures (900-1100℃) (Shrivastava et al., 2024; Karadimas & Salonitis, 2023) and a gaseous precursor deposits onto the preform over time, slowly building up layers and filling the pores in the form. This method, while both time consuming and costly, yields superb strength and temperature resistance, despite its higher porosity compared to other methods. These attributes make it ideal for hydrogen turbine applications, where temperature resistance is crucial.

3.4 Noteworthy CMCs for Potential Use

Among the literature, several composites showed promise for use in hydrogen turbines. These composites, all non-oxide composites, are highlighted because they exhibited high performance under similar conditions to hydrogen turbine operation.

3.4.1 Yttria-Stabilised Zirconia Fibre-Reinforced Silicoboron Carbonitride

One promising material system for hydrogen-fuelled gas turbines is the Yttria-stabilised Zirconia fibre-reinforced silicoboron carbonitride (YSZ/Si(B)CN) ceramic matrix composite. This composite combines the excellent thermal stability and low thermal conductivity of YSZ with the oxidation resistance and mechanical durability of polymer-derived Si(B)CN ceramics (Varela, 2024; Wang et al., 2025; Deb et al., 2025). In order to withstand the combustion environment of a hydrogen turbine, a material must be able to maintain structural integrity at extreme temperatures, while also resisting the effects of oxidation and degradation. In this material compound, the YSZ fibres provide for excellent thermal insulation, protecting underlying structures from the intense thermal stresses the engine produces (Wang et al., 2025; Deb et al., 2025). Simultaneously, the underlying Si(B)CN matrix contributes to high-temperature operation ability, creep resistance and oxidation protection (Wang et al., 2025; Deb et al., 2025). These characteristics make YSZ/Si(B)CN composites a promising candidate for use in hydrogen turbines, particularly in regions exposed to the most extreme temperatures and corrosive steam environments.

Despite its advantages, however, the implementation of YSZ/Si(B)CN composites in hydrogen turbines still presents several challenges. The fabrication of Si(B)CN-based ceramics is a complex and tedious task, involving many repeated steps of extremely precise manufacturing, making widespread production expensive and difficult (Wang et al., 2025). Furthermore, while the YSZ fibres provide exceptional insulation, its low toughness as compared to traditional turbine alloys create concerns about its reliability under mechanical loading (Wang et al., 2025). Further research is required to optimise the material to survive long-term stress and extensive use, and implementation in non-specialised areas may not be possible due to its high-cost production.

3.4.2 Silicon Carbide Matrices with Boron Nitride Interfaces

Silicon carbide matrices are the current benchmark CMC for aerospace applications, with extensive research taking place to improve them further (Kiser et al., 2017). Exhibiting high strength, low density, high thermal stability and low thermal creep (Zhu et al., 1999), they are well suited for hot sections of turbines. Additionally, their physical properties allow for reduced design complexity. While demonstrating superb performance under elevated temperatures in normal atmosphere, with the addition of steam, the matrix’s mechanical properties and creep resistance significantly degrade (Ruggles-Wrenn et al., 2018). 

The loss of performance comes as steam oxidises the matrix, interphase and the reinforcements. Research for improving SiC/SiC composites is ongoing, with advanced multistep manufacturing processes promising even higher thermal capabilities, and innovations in coatings designed to decrease the threats posed by steam and salts (Kiser et al., 2017; Zhu, 2018). These are especially relevant as steam is a byproduct of hydrogen combustion, posing risks that need to be addressed. These innovations will make future applications in hydrogen turbines more feasible, thus mitigating the danger steam poses to SiC matrices.

3.4.3 Silicon Carbide and Boron Carbide Matrix

One of the primary issues presented by SiC/SiC composites is their inferior performance in environments with steam. An innovative approach to this solution beyond environmental coatings is the use of multilayered CMCs, composed of alternating layers of SiC and boron carbide (BC) (Ruggles-Wrenn et al., 2018; Li, Reynaud & Fantozzi, 2020; Ruggles-Wrenn & Pope, 2015). In addition, the use of a multilayered interface coating consisting of pyrolytic carbon and boron carbide inhibits fibre oxidation and facilitates a weak fibre-matrix interface. Boron carbide was chosen because its oxidation products form a glassy phase at higher temperatures, insulating the SiC matrix as cracks form (Ruggles-Wrenn et al., 2018; Ruggles-Wrenn & Pope, 2015). This glass prevents oxidation and provides additional toughness to the material, as it slows further crack growth and seals existing cracks from potentially damaging steam. 

Under mechanical testing, the multilayered SiC/BC composite exhibited superior performance to both MI-SiC and CVI-SiC in the majority of tested benchmarks, both in steam and in air. It had a higher ultimate tensile strength and significantly longer lifetimes at high temperature and high load testing, outperforming both materials by an order of magnitude in fatigue life cycles at loads higher than their proportional limit strength (PLS) (Ruggles-Wrenn et al., 2018). Although its PLS is lower than both MI-SiC and CVI-SiC, the success can be attributed to the extensive cracking allowing it to outperform the others. In high stress applications, it begins cracking earlier, gradually approaching failure, compared to a more rapid failure of other SiC composites. The gradual failure is aided by glass formation, where glass fills the cracks, sealing and reinforcing the matrix at elevated temperatures, but can reduce mechanical properties at room temperature (Ruggles-Wrenn et al., 2018). Even with these drawbacks in consideration, the superb resistance to steam makes it a viable candidate in hydrogen turbine applications (Ruggles-Wrenn et al., 2018; Ruggles-Wrenn & Pope, 2015).

4. Potential Issues with Implementation

Several CMCs show much promise for use in hydrogen turbines though modifications to the architecture of the turbine may be necessary for implementation. There are still several practical issues needing to be addressed before their widespread implementation in the industry. These include cost effectiveness in manufacturing, quality control and longevity.

4.1 Manufacturing

Manufacturing CMCs with characteristics desirable in hydrogen turbine applications tends to be quite expensive. This cost comes from the need to rely on more advanced and time-consuming methods, although there exists a wide array of manufacturing methods for CMCs. Cheaper methods, like sintering or RMI, tend to exhibit lesser performance, damaging reinforcing fibres with higher fabrication temperatures (Shrivastava et al., 2024). Additionally, inexpensive manufacturing methods produce high porosity and suboptimal microstructure or impurities in the composite from free silicon or aluminum in the case of RMI (Shrivastava et al., 2024). Conversely, higher performing methods like PIP and CVI tend to take longer to manufacture components, requiring multiple infiltration cycles, leading to increased cost in applications (Shrivastava et al., 2024; Santhosh et al., 2021).

Furthermore, quality control is often difficult to conduct on CMCs. A significant portion of the material’s strength is determined by the presence, size and density of pores on the internal section of the composite (Oliveira et al., 2025). Non-destructive testing is focused on identifying these defects inside, with methods including thermal imaging, X-ray radiography and computerised tomography (Oliveira et al., 2025; Mei, 2009). Both radiography and thermal imaging show the presence of defects in two dimensions, but struggle to show the precise measurements of the defect. Computerised tomography works similarly to radiography; however, it acquires X-ray images at various angles to give a complete picture of defects present, allowing accurate assessment (Mei, 2009). Tomography fills a supporting role in assessment rather than the primary approach, with the numerous X-rays requiring more resources. These methods do allow for sufficient quality control, ensuring that CMC components in hydrogen turbines are up to standard, although not without an additional cost.

4.2 Wear and Tear, and Repairability

Ceramic matrix composites have been enhanced so that when a load surpasses the proportional limit strength, the composite cracks progressively rather than failing outright. However, these cracks lead to an eventual reduction in strength and can form both internally and externally. These defects make assessment of a ceramic in use difficult, as previous methods for analysing defects may lack the resolution required to see small cracks that are precursors to larger cracks and eventual failure. These cracks are also exacerbated by thermal fatigue or the presence of steam or other oxidising environmental effects (Ruggles-Wrenn et al., 2018; Tejero-Martin et al., 2021; Li, Reynaud & Fantozzi, 2020), which damage the reinforcements or the interface layer. It is also important to note that unlike traditional nickel-based superalloys, CMCs lack the ability to be welded or otherwise repaired to the same extent as the former, with reapplication of coatings and surface patching being the extent of such repairs. The flaws present in CMCs, as well as oxidation, are permanent changes to the microstructure of the composite and can be mitigated or delayed through self-healing matrices, but not repaired (Paladugu et al., 2022). The result is a change in maintenance philosophy necessary for long term applications of CMCs in hydrogen turbines, requiring careful monitoring and assessment to ensure structural integrity, and planning to ensure ease of replacement.

5. Discussion

Despite both the high manufacturing costs and the maintenance challenges CMCs pose, they exhibit considerable promise in hydrogen applications. SiC/SiC matrices, with environmental barrier coatings or a multilayer composite designed to minimise oxidation, address the issue of steam and exhibit sufficient strength to be used in hydrogen turbine applications. Improvements to the manufacturing process, like multistep processes mixing various fabrication techniques, also show promise to further improve thermal capabilities, potentially surpassing 1500℃ and increasing the scope of CMC applications (Kiser et al., 2017). Additional improvements to reinforcing fibres and the interface, aimed at reducing oxidation and improving crack bridging and stress distribution, could see improvements in the strength of CMCs and make a wide range of applications available. CMCs are a young area of material science, with research beginning in full swing in the 1990s and remain a promising field for ultra-high temperature materials. Furthermore, with the exploration of multilayer matrices, like SiC layered with BN, improved resistance to harmful environmental conditions will continue to improve (Tejero-Martin et al., 2021).

With such rapid growth in capabilities, CMCs will undoubtedly see many more applications in the future, especially in aerospace industries, where increasingly lightweight composites continue to appeal. That being said, even considering the composites specifically mentioned in this paper, CMCs are unlikely to be able to solve the issues presented by hydrogen turbines with their current limitations. With improvements in their current capabilities, it is likely that CMCs will play a significant role in the future of hydrogen turbines, but they currently lack the longevity and cost effectiveness needed to be an appropriate solution to the problems inherent to hydrogen combustion. When manufacturers improve their processes to allow for quicker and more efficient production of high-performance CMCs, and when more advanced technologies emerge to assess the stability of the composite, applications may become viable. While CMCs are already in place in many aerospace applications, the harsher requirements of hydrogen turbines need more time to be met by CMCs (Kiser et al., 2017; Tejero-Martin et al., 2021).

6. Conclusion

Hydrogen turbines are an important player in sustainable power generation, with no significant greenhouse gas emissions. The challenges faced by them, including high operational temperatures and steam production, need to be addressed before implementation can begin. CMCs are an appealing solution, with high temperature resistance, a lightweight nature and high strength. Composed of a ceramic matrix, a reinforcing fibre structure and an interface between the two, CMCs may be able to solve the issues inherent in hydrogen turbines in the future, but current iterations lack either the resistance to steam or the longevity under high temperatures to make application successful.

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