Isovota developed silica fiber/alumina CERAPREG, enabling ceramic matrix composite components to be used for a long time at 900°C. The processing method is similar to epoxy prepreg, and the dielectric properties are similar to quartz.

The oxide CMC components manufactured using Isovota CERAPREG include aircraft engine exhaust mixers, ceramic honeycomb core plates and complex tubular structures. The composite battery tray consists of organic sheets, CERAPREG and molding compounds.

It is reported that Isovota (Vienna-Nieddorf, Austria) is one of the largest producers of aircraft cabin interior laminates in the world and also the largest supplier of interior prepreg materials globally. The company has 1,500 employees in 16 locations across three continents and possesses expertise in impregnation, lamination, compression molding, mechanical processing, polymer chemistry, and process technology.

With decades of experience in high-performance epoxy resins and phenolic resins, Isovota is able to meet the strict fire, smoke, and toxicity (FST - fire, smoke and toxicity) requirements for aircraft cabins/driver cabins/cargo applications. Isovota sees the growing demand for materials that can work at higher temperatures. 'Most traditional aerospace thermosetting resins fail below 300°C,' explained Peter Wagner, the vice president of technology at Isovota. 'With the growth of electric vehicles (EVs) and new mobile and space applications, we may see a demand for materials that can withstand up to 900°C, but without the high cost of traditional ceramic matrix composites (CMC-ceramic matrix composites), which are more difficult and time-consuming to manufacture.'

The CMC components are made of CERAPREG.

Isovota developed CERAPREG as an alternative, which is a combination of silica fibers and a silica-alumina (alumina) matrix. This enables CMC components to be lighter in weight compared to metals, but is cheaper than Nextel (3M, Minneapolis, Minnesota, USA) or more expensive silicon carbide (SiC) fibers. Wagner said: 'The mechanical properties and temperature resistance of parts made from CERAPREG are not as high as those of SiC/SiC or carbon/carbon CMC, but this material provides good performance in structures that need to operate continuously in harsh high-temperature environments, such as exhaust components for unmanned aircraft and electric vehicle batteries or battery compartments.'

Silicon dioxide, silicon carbide and quartzfibers

Silica fibers are mainly composed of silicon dioxide (SiO2), while silicon carbide fibers are compounds of silicon (Si) and carbon (C). Wagner said that the latter requires a lengthy manufacturing process and is more expensive than silica fibers. Silica fibers are easier to produce and are usually manufactured using a process similar to that of glass fibers, such as melt spinning.

The CMC parts made of 620 g/m2 CERAPREG include an antenna cover composed of four layers and a honeycomb structure, as well as a charging stand made of two layers.

The silica fibers used by Isovolta in CERAPREG are not quartz either, but due to the purity of the fibers being over 95% silica, they share similarities. Wagner pointed out: 'When tested at a frequency of 76.5 gigahertz, the dielectric properties of the fibers we used were actually below 3.0.' 。'Our tests using the Radom epoxy resin system combined with silica fibers have shown similar results. We are currently verifying the use of these two combinations in antenna covers.'

He added that although silica fibers can withstand a one-time exposure of up to 1600°C, they start to degrade above 950°C. CERAPREG was developed for long-term exposure at temperatures up to 900°C.

Ox-Ox System

Although SiC/SiC materials operate at higher temperatures (such as 1200-1600°C), the alumina matrix's alumina (alumina, Al2O3) fibers (referred to as Ox-Ox) typically operate at temperatures up to 1200°C, but do not face the oxidation degradation risks that SiC/SiC and carbon fiber/carbon matrix (C/C) materials may encounter.

CERAPREG is also an Ox-Ox system that produces oxide CMC (OCMC), but uses silica fibers and silica-alumina matrix. 'The CERAPREG we designed offers a variety of performances,' Wagner said. 'This includes long-term performance at 900°C, more cost-effective, easier handling and part manufacturing, as well as radar transparency. However, if long-term use at higher temperatures is required, then I would consider traditional alumina/alumina CMC. There are new companies producing alumina fibers, so availability and prices should decrease. We have also tested and produced alumina Ox-Ox CMC.'

Various shaped parts made with CERAPREG

Various shaped parts made with CERAPREG

Wagner described the parts shown on the right, including the mixer structure used in the aerospace exhaust system, the curved sandwich structure made of eco-ceramic honeycomb from Euro Composites (Essentia, Luxembourg), and various CMC tubes. 'These are test parts, but all demonstrate the ability of CERAPREG to handle complex shapes and its excellent mechanical properties.'

The reasons and methods of Ox-Ox prepreg

Why sell the pre-impregnated materials? Wagner said: 'Because it enables the company to manufacture parts more quickly.' 。'You can purchase oxide fibers and fabrics, but you still need some kind of matrix to manufacture CMC, and not many companies know how to do this. Pre-pregs make the manufacturing of parts easier, but only a few companies are likely to sell this material. These companies usually also want to manufacture CMC parts, while Isovota is purely a material seller. We tell customers how to process the pre-pregs and provide training on how to use this material and manufacture simple parts, but they don't have to share any details about what they will produce or how they will produce it. '

This battery tray consists of an organic sheet base layer, a Cerapreg CMC intermediate layer and a die-casting compound top layer. These layers are preheated in a convection oven at 220°C, transferred to the mold using a needle holder, and then molded in a heated press. Cerapreg is exposed to approximately 45 minutes at about 220°C, providing heat resistance and flame retardancy as described below.

He continued, 'The prepreg we designed is non-toxic and easy to handle. Apart from the oven, no special equipment is required.'。(Parts can also be manufactured using the press machine as shown in the figure on the right.) 'Furthermore, employees who are familiar with the polymer composite prepreg should be able to use it without special training, but we will definitely provide as much training as needed - whether in our factory or at the customer's location.

Wagner said: 'Another issue is that if this prepreg is solvent-based, it may shorten its shelf life.' 。'Our prepreg is water-based - we do have a polymer adhesive, but it constitutes less than 5% of the material. This provides a longer shelf life - currently it's 6 months, but it may be extended - and no additional extraction equipment or measures are required to handle volatile organic compounds.'

The material was originally a water-based ceramic slurry. Wagner said: 'Then, we combined it with silica fiber fabric and used short heat treatment cycles to manufacture the prepreg.' 。'Typically, you have a horizontal or vertical prepreg production line, but using ceramics is preferred because it is a water-based slurry. We actually don't want to dry it. Instead, we want to keep it as moist as possible to ensure that it doesn't dry out during transportation to the customers, while maintaining its moldability and formability. To achieve this, we modified the production line to ensure the necessary moisture content and mechanical properties are maintained. Then we packaged it in a form that is convenient for customers to process.' He pointed out that CERAPREG should be stored at a temperature of 5-20°C, but it must not be frozen.

Performance, components, future development

Currently, CERAPREG has two standard products. One has a fabric weight of 600 grams per square meter (gsm) and a thickness of 0.7-0.8 millimeters. The other has a fabric quality of 300gsm and a thickness of less than 0.6 millimeters. Their resin density, thermal and dielectric properties are as follows. Wagner said: 'For these two materials, our tensile strength is at least 40 megapascals, but when tested in the fiber direction, we used the 300gsm material and achieved more than 60 megapascals, and one component manufacturer even reached 75 megapascals.'

Selected mechanical properties shared by the 600 and 300 g/m2 CERAPREG products

Although the maximum continuous operating temperature is 900°C, Wagner stated that Isovota has reduced the test temperature for CERAPREG components to 2000°C. 'We are continuing to collaborate with the Fraunhofer Institute and other research institutions in Austria to comprehensively characterize the mechanical properties of the material at 700-1000°C,' he explained. 'We are sharing these data with our customers.'

Wagner said that the maximum temperature that CERAPREG components can withstand depends on the combination of time and load. 'If your load is small and you just want a thermal insulation layer? Then you can increase the temperature. For more structural components, the maximum temperature also depends on the type of load they must withstand, such as cyclic, vibration or shock loads. You can model these, but you also have to build and test CMC components.'

Isovota not only tests materials, but also tests CERAPREG components, for example, as thermal insulation layers for automotive and electric vehicle applications. Wagner pointed out: 'We are also researching eVTOLs because in both cases, they not only need thermal resistance, but also need to be lightweight and strong.' 。'We are conducting tests to simulate the thermal runaway of metal powder in the battery when it is subjected to high-temperature ejection. In this scenario, even if you have excellent heat insulation and flame resistance, these projectiles will impact the material and create holes, thereby compromising the insulation performance.'

A flame test was conducted on the carbon fiber composite layering board that was adhered to the CERAPREG laminate, and no damage was observed after 5 minutes.

Isovota also completed the flame tests for the hybrid components. For instance, they bonded a 1-millimeter-thick carbon fiber reinforced polymer (CFRP) laminate to a 2-millimeter-thick CERAPREG laminate. Wagner said: 'We conducted the test at 1200°C. After 5 minutes, the back side only reached 600°C, but there was no obvious damage.' 。'CERAPREG enhances the thermal properties of CFRP, but if you want to improve the mechanical properties of CERAPREG, it is very easy to bond it to epoxy or cyanate ester CFRP.' Isovolta also tested aerogel and mica laminates of 1 mm and 3 mm thick CERAPREG sheets.

Wagner said, 'Isovota sees many possibilities for CERAPREG and many ways to utilize its CMC properties.' 'We are also continuing to explore new manufacturing options, including thermal in and out pressing.'

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Original text: 'A different Ox-Ox prepreg for faster, more affordable CMC options'2025.7.9

Yang Chaofan2925.7.14