# Ceramic Matrix Composites for Aero Engine Applications--A Review
## 5 Non-Oxide CMCs
### Carbon Matrix CMCs  
Carbon as a solid varies in mechanical and thermal properties. Some carbons are highly porous, and others are impervious to liquids and gasses [9; 90]. These conditions result from structural effects of the geometry and amount of carbon phases with a crucial effect on the crystalline order. The literature review highlighted that there are three common carbon-based material categories: Carbon/Carbon, Carbon/Metal, and Carbon/Resin composites. Carbon-based composites are widely accepted in the aerospace industry. However, pure carbons and composites have oxidation problems and require additional oxidation-resistant reinforcements or coatings [91; 92; 93]. Carbon fused ceramics as a base material can be used to improve the composite's oxidation resistance and lifetime. These carbon-based ceramics include silicon carbide (SiC) due to its high oxidation, temperature, thermal shock stability, and high creep resistance [94; 95]. Moreover, the carbon base matrix is combined with carbon fibers (C/C) used as fillers/reinforcements. The carbon fibers must be aligned parallel to the external load of the carbon matrix and should be as long as possible. This allows the application of the maximum stress in the C/C CMC matrix [96; 97]. C/C composites have been applied in ballistic missile nose tips, nose caps, and leading edges of space shuttles [98]. Although there has been noticeable development in this type of ablative composite technology, there are still a number of applications where it cannot be used. These include the production of gas turbines, turbojet engines, internal combustion engines, nuclear reactors, etc. As all these systems operate under severely harsh service environments, significant advances in ablative systems could provide a huge success in the development of such structures [99]. * Carbon/Carbon matrix CMCs  
Historically, the main reason why composites based on ceramics and carbon fibers were fabricated was to avoid the failure of the ceramic parts at increased loads. The production of carbon matrix CMCs requires physical and chemical compatibility between the carbon and ceramic particles. Carbon/carbon CMCs are used both as a filler and a base matrix, where the latter is the connecting source for the fillers, allowing for the composite to have different structures and textures [100]. Some examples where carbon is used as a filler or reinforcement are carbon fibers, which allow for a variety of different property composites by selecting the needed precursors and shapes (strand, yarn, or chopped). In addition, for the fabrication of carbon-ceramic CMCs, the composite must have a service temperature that reaches up to 1600-1800 \({}^{\circ}\)C, as this is the temperature where most ceramics crystallize. Carbon/Carbon composites, also known as carbon fiber reinforced carbon (CFRC) or reinforced carbon/carbon (RCC), are CMC material matrices including carbon fiber reinforcements in a matrix of graphite [101; 102]. Over the past three decades, carbon fibers have been one of the most recognizable reinforcements for advanced composites used in aerospace applications [103]. They are a few microns thick, lightweight, very strong, and stiff black synthetic fibers, consisting of long aromatic molecular chains comprising  
Figure 5: Non-oxide CMC material categories. mainly carbon. Their main advantage is the increased toughness. Research has shown that carbon fibers can improve mechanical and thermal properties by up to ten times without increasing the final weight of the composite. Carbon composites have been tested under high temperature and pressure conditions, which allows them to be used in different types of ceramic, polymer, and metal matrices [104]. Nevertheless, carbon fiber-reinforced carbon CMCs exhibit high fracture toughness and pseudo-plasticity [10; 76]. They are heat-resistant but suffer from drastic material consumption in oxidizing atmospheres due to the oxidation of carbon and the creation of carbon oxide (CO) and carbon dioxide (CO\({}_{2}\)) [47].