Reactive silicon infiltration of carbon bonded preforms embedded in powder field modifiers heated by microwaves

Available online at www.sciencedirect.com

CERAMICS INTERNATIONAL

Ceramics International 41 (2015) 12439–12446 www.elsevier.com/locate/ceramint

Reactive silicon infiltration of carbon bonded preforms embedded in powder field modifiers heated by microwaves Giovanni Bianchia, Paolo Vavassorib, Brais Vilac, Giuseppe Anninod, Marco Nagliatie, Marcel Mallahc, Sandro Gianellaf, Massimiliano Vallee, Marco Orlandie, Alberto Ortonaa,n a

ICIMSI-SUPSI, Manno, Switzerland Petroceramics SPA, Stezzano, Italy c Fricke und Mallah Microwave Technology GmbH, Peine, Germany d Istituto per i Processi Chimico-Fisici, UOS Pisa, Consiglio Nazionale delle Ricerche, Pisa, Italy e Brembo SGL Carbon Ceramic Brakes, Stezzano, Italy f Erbicol SA, Viale Carlo Pereda 22, 6828 Balerna, Switzerland b

Received 5 May 2015; received in revised form 8 June 2015; accepted 19 June 2015 Available online 27 June 2015

Abstract Reactive silicon infiltration (RSI) is a process to produce silicon carbide parts by infiltrating microporous preforms bound by pyrolized carbon. Even if RSI is considered one of the fastest manufacturing techniques for the production of SiC parts, long time is required to heat and cool the electric furnaces used for their batch processing. In this paper, we show the benefits of applying microwave power to perform RSI. In this sense a new set up in which preforms are embedded into powder field modifiers is presented. The use of SiC/BN powders as microwave field modifiers revealed the twofold advantage of being an efficient way to heat up the components uniformly while being impermeable to molten silicon. Si–SiC bulk, composite and macroporous ceramics were successfully infiltrated in few minutes. Due to plasma formation, vacuum was not applied. Infiltrations were thus performed at ambient pressure. Finally the different microstructures produced by microwave heating at ambient pressure were compared with standard material produced by conventional heating under vacuum. & 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Keywords: Reactive silicon infiltration; Microwave heating; Si–SiC ceramics; Ceramic matrix composites; Ceramic foams

1. Introduction Silicon infiltrated silicon carbide ceramics (Si–SiC) were first obtained by Hillig et al. in the 70s [1]. Since then, many variants of these materials have been developed. Monolithic and particle or fibre reinforced ceramic composites have been produced [2] for the aerospace [3], automotive [4] energy [5,6] and antiballistic fields. Another promising application of these materials lays in the combustion technology [7]. It consists in the use of Si–SiC foam bodies produced by the replica of polyurethane foams with polymeric and SiC slurries followed n Correspondence to: Cantonale, Galleria 2 Manno 6928-CH, Switzerland. Tel.: þ 41 58 6666611. E-mail address: [email protected] (A. Ortona).

http://dx.doi.org/10.1016/j.ceramint.2015.06.087 0272-8842/& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

by pyrolysis and reactive silicon infiltration (RSI) [8]. These materials possess unique thermo-mechanical behaviour [9,10] such as high thermal shock resistance. Conventionally, RSI is performed with electric furnaces, heated by graphitic resistors. Even though RSI is considered one of the fastest manufacturing techniques of SiC based ceramics, long processing time is required to heat and cool the furnaces with components inside. Moreover, considering that RSI is usually implemented as a batch process, it is economically convenient to employ large furnaces which have even slower heating and cooling rates. Microwave (MW) heating has been successfully employed in SiC manufacturing by several processing routes. Danko et al. [11] compared material's properties of pre-ceramic polymers pyrolysed both by microwave and by conventional systems. SiC fibres

12440

G. Bianchi et al. / Ceramics International 41 (2015) 12439–12446

preforms were efficiently infiltrated with SiC by MW chemical vapour deposition (CVD) [12] thanks to the inverse temperature profile of the preform. RSI was successfully accomplished by Karandikar et al. [13]. They showed that the composites' properties made by microwave assisted process (MASS) and by conventional methods were comparable, with the advantage of a sensible process time reduction when using MW heating. Because of the low dielectric loss factor most ceramics possess, MW energy can penetrate them effectively, theoretically leading to uniform heating. Ceramics' low dielectric factor, on the other hand, does not allow the absorption of large amounts of energy. In order to improve energy absorption, materials are thus placed into a cavity where many reflections occur. The drawback of this setup is the appearance of the so called “hot spots”, due to the non-uniform distribution of the thermal energy into the ceramic material, which results in high thermal gradients. On the other hand in RSI, thermal gradients in the part must be carefully avoided. Temperature differences across the preform will lead to an uneven infiltration. In the case of sintering, Patterson et al. [14], to overcome such a problem, embedded the parts to be heated in a powder bed in order to modify the field around the ceramic part and further heat the samples by conduction. In order to exploit MW in industrial processing, where the size of the processed parts can be large with respect to the electromagnetic wavelength, some issues must be solved. The most relevant ones are probably the intensity and the average distribution of the MW electric field |E| in the part's volume, for a given MW source power. These quantities in fact determine the efficiency and the homogeneity of its heating. Several computational and experimental techniques have been developed to determine the distribution and magnitude of the field |E| [15]. These techniques require a detailed knowledge of the dielectric properties of the part at the temperatures of the processes, since very often the presence of the part into the cavity introduces a re-arrangement of the MW fields. Moreover, the knowledge of the component dielectric properties is necessary also to predict and control the MW heating rate. This is one of the reasons why components embedding into powders shows several advantages. The variability of the dielectric properties as a function of the composition and temperature of the α-SiC powders used as powder beds (grain size D50 of 9.371 μm) is given in Fig. 1. Here, the real (ε0 ) and imaginary (ε″) part of the dielectric permittivity ε are shown for a frequency of 2.45 GHz and temperatures ranging from room temperature to 1100 1C. They were measured on powders as produced (standard in Fig. 1) and after a thermal treatment in flowing Nitrogen (pre-ox in Fig. 1). Different ε0 and ε″ values mean different heating rates of the powder. The employed measurement technique, similar in its basic approach to that of Hutcheon and coworkers [16], will be detailed in a future work. 2. Experimental 2.1. MW equipment description The MW furnace (Fig. 2) consists of a stainless steel vessel with a working zone of 250 mm in diameter and 150 mm in height. The double walls vessel (designed for vacuum levels up to 10  7 mbar)

10,5

Std Pre-ox.

10,0 9,5 9,0

ε'

8,5 8,0 7,5 7,0 6,5 0

200

400

600

800

1000

800

1000

1200

T Std Pre-ox.

0,8 0,7 0,6

ε''

0,5 0,4 0,3 0,2 0,1 0,0 0

200

400

600

1200

T

Fig. 1. Real (top) and imaginary (bottom) part of the dielectric permittivity of SiC powder samples (powder was not pressed).

is water-cooled. The steel chamber is connected to four circular waveguides carrying a TM01 mode at 2.45 GHz. Each waveguide is supplied by an independent microwave generator delivering a power of 2 kV. As shown in Fig. 2, the system accounts on several sensors which are sending signals to the control rack. The latter, connected to a PC via USB cable, controls the power to be delivered by each generator according to the PC instructions. Labview (National Instrument, Austin, TX, USA) monitoring and control software is installed on the PC. The software displays process parameters such as: temperature, emitted and reflected microwave power on each generator and alarms. Important preprocessing operations like impedance matching are accomplished using the semiautomatic 3-stub tuners, which are remotely adjusted from touch panels on the control rack. To improve in-plane temperature uniformity, a vertical rotation system is also installed. Angular velocities from 1 to 30 RPM can be selected. Samples' temperature is measured from the top of the furnace (Fig. 2) with an optical pyrometer (PYROSPOT DSR 10N, DIAS Infrared, Dresden, Germany) equipped with a digital camera. This pyrometer utilizes a 2-colour system which has the advantage of measuring the temperature independently from the material's emissivity. The pyrometer accuracy was anyway verified by measuring the liquid to solid temperature transition of silicon at 1423 1C (Fig. 4).

G. Bianchi et al. / Ceramics International 41 (2015) 12439–12446

12441

Table 1 Powder beds materials properties and composition. Material

Composition [wt%] Grain size D50 [lm] Crystal structure

SiC (99.0%) 75 BN (99.9%) 25

6.5 7.4

β-SiC (3C) α-BN (hexagonal)

Pyrolysis of the parts (Tmax ¼ 900 1C) in flowing nitrogen was finally performed. 2.2.4. C–SiC foams Two α-SiC powders, a plastic binder and an organic solvent were mixed by ball milling to make a stable slurry with a viscosity of about 800 mPa s. Polyurethane foams (10 pores per inch: PPI) were dipped into the slurry and hanged in order to drain the excess liquid. The bodies were dried overnight. They were then pyrolysed at 1000 1C, following a heat ramp of 50 1C/h, under a nitrogen flow. After pyrolysis, the samples consisted in a network of hollow struts with a residual microporosity of  30%. Fig. 2. Scheme of the microwave furnace.

2.2. Materials Preforms were prepared by the different manufacturers. A concise description of them is given in the following paragraphs. Since they are considered in this work as starting materials details on their manufacturing are omitted, we encourage the interested reader to go through the wide literature reporting on how to prepare them [17–19]. 2.2.1. Powder beds Powder was composed by silicon carbide and boron nitride (details in Table 1) thoroughly blended by dry mixing (EL-1, Gustav Eirich, Hardheim, Germany) for 2 h. 2.2.2. C–SiC tiles Silicon carbide performs were prepared by mixing two different powders of “black silicon carbide” (99.50% SiCþ oxides) of 280 and 1000 F.E.P.A grain size (FEPA Standard 42/1984) and 10 wt% phenolic resin powder (Bakelite, Germany). The mix was loaded into a mould and compacted by uniaxial pressing at 10 MPa. The mould was heated at 150 1C for resin cross linking. The tiles (100  100  10 mm3) were pyrolized in flowing nitrogen at a maximum temperature of 700 1C. After pyrolysis, the porosity of the preforms was about 30%. 2.2.3. C–C composites The carbon–carbon used as preforms were made by highly porous fibrous bodies obtained by the pyrolysis of chopped carbon fibres reinforced plastic composites which were made by dry mixing carbon fibres and phenolic resin in powder form followed by uniaxial compression moulding at 150 1C.

2.2.5. Silicon Coarse powder of 99.6% pure metallic silicon (HQ1, Sicerma, Erkelenz, Germany), grit size of 0.2–2.0 mm, was used for RSI. 2.3. Processing The infiltration process was carried out with the MW equipment described in Section 2.1 using an original set-up represented in Fig. 3. It consisted in thin (1–2 mm) alumina cylindrical crucible (mostly transparent to MW) hosting the preform, the silicon grains and the powder bed. Rigid porous carbon felts were used to support the preform and to guide the molten silicon upon its melting. SiC/BN powders were uniformly distributed around the preform and the silicon to fill the empty space into the crucible. A boron nitride tube was placed as shown in Fig. 3, enabling temperature measurement directly on the preform surface, otherwise covered with the SiC powder. The crucible was closed with a refractory lid of thin alumina with a central hole for the boron nitride tube. The set-up was placed inside the working zone of the furnace and vacuum applied till reaching 0.1 mbar of residual pressure. The vessel was then re-filled with argon gas at 200 mbar above ambient pressure. Rotation speed was set at 10 RPM. Before every thermal treatment, impedance matching was performed using one microwave generator at a time (running at 30% of full power) in order to minimize the reflected energy. This was accomplished by adjusting the position of the slides and the stubs. Setup, with minimized power reflections, was pre-heated for 60 s at 50% full power to reduce the risk of plasma formation. Higher power was then continuously applied (again, depending on the setup) by controlling the four generators independently. If plasma was occurring, the power was interrupted for 2 s to cut down plasma sustaining energy and then progressively restored. As

12442

G. Bianchi et al. / Ceramics International 41 (2015) 12439–12446

powder. Temperature was measured directly on the silicon grains and the heating ramp presented a similar behaviour to that of the complete setup. Main differences consisted in a higher initial heat rate of 8 1C/s and a lower first dwell temperature of the curve, which could be due the different mass of the setup. Even without the contribution of the exothermic chemical reaction, the curve presents a steep increase around the silicon melting point. We suspect that this due to the silicon solid to liquid phase change with a consequent better coupling with the MW power. Dashed line corresponds to a modified set-up containing only a carbon–carbon preform. An almost linear monotonic temperature rise was observed. The set up was then brought to room temperature by natural cooling. A much faster cooling could be achieved by removing the set up from the furnace and let it cool outside. The infiltrated preform was finally removed from the powder and detached from the supports. SiC/BN powder was reused after sieving.

BN Tube Crucible lid SiC/BN Powder

Preform Carbon Felt

Carbon Felt

Silicon Molten Silicon flow Crucible Fig. 3. Infiltration set-up representation.

2.4. Characterization

1800 1700 1600 Temperature [°C]

1500 1400 1300 1200 1100

Silicon (only)

1000

Cf-C (only)

900

Cf-C (80% Si pick-up)

800

Si melting temperature

700

0

200

400

600

800

1000

1200

1400

Time [s]

Fig. 4. Heating ramp of single constituent materials and of the complete and set-up. 1800 1C was the reading limit of the pyrometer.

an example, Fig. 4 shows the temperature profile of the set up with a carbon–carbon preform. Aside RSI, to discriminate the effects of pure MW heating from the contribution of the exothermic reaction between carbon and silicon in Eq. (1), silicon and carbon–carbon were heated separately.   Siliquid þ Csolid ¼ SiCsolid ΔH ¼  73 kJ mol  1 ð1Þ The solid line in Fig. 4 shows a heating ramp for a typical infiltration process. Silicon melting temperature was reached in less than 400 s, achieving heating rates up to 6 1C/s. Heat rate gradually decreased while approaching 1450 1C. A subsequent remarkable rise in temperature was then measured up to the pyrometer full scale limit even if, from 480 s on, power was reduced to 30% of the full power. Dot dashed line in Fig. 4 shows the temperature evolution of the reference setup containing only silicon embedded into the

Microscopic analysis was performed with a scanning electron microscope (SEM) equipped with a device for energy-dispersive X-ray spectroscopy (EDS) (JSM6010plus/LA, JEOL, Tokyo, JP). Analysis was performed in backscattered electrons mode with a voltage of 20 kV and a beam current of 40 mA. Si–SiC tiles were machined with diamond tools (30×3×4) mm3 and tested using a bending tester (NETZSCH,Selb, D) according to a standard procedure (ISO 10545-4:2004). Ceramic foams were diamond milled on two opposite faces in order to have two parallel planes on which load was applied. Compression tests were carried out using a universal testing machine (Z050, Zwick/Roell, D). A 50 kN load cell (Zwick/ Roell, D) was used to measure the load while the strain was calculated from the cross head position. A deformation speed of 0.1 mm min  1 and a preload of 10 N were selected as loading conditions. Strain values were those measured by the displacement of the cross head which represents the length change of not only the specimen but also the spacers/rams. Strain values should be considered as qualitative because of the very low deformations occurring into a ceramic foam before cracking. Strain however was not used into the discussion which refers only to foams' strength. 3. Results and discussion This work attempts to demonstrate the feasibility of RSI on different carbon bonded preforms embedded in powder field modifiers heated by microwaves. Several samples with significant dimensions were successfully processed (Fig. 5). The goal was to achieve the theoretical full density: meaning that molten silicon was able to completely fill the porous preforms described in the previous paragraphs. As previously stated, during RSI chemical reactions and capillary action are concurrently taking place [20–22]. It was even demonstrated that, without chemical reaction, infiltration would not occur [23]. On the other hand the formation of SiC

G. Bianchi et al. / Ceramics International 41 (2015) 12439–12446

12443

Fig. 5. Samples produced by MW RSI. A Si SiC ceramic antiballistic plate (Petroceramics), parts of a Si SiC composite for brake disks (BSCCB) and a Si SiC foam (Erbicol).

on the capillary walls slows down or even blocks silicon infiltration [22–25]. Further work needs to be performed on calibrated preforms with a narrow and repeatable pore size range in order to correlate the final material's microstructure with relevant control parameters in MW heating. 3.1. Si–SiC tiles (ex C–SiC tiles) C–SiC tiles contain large amounts of silicon carbide powders bound by small quantities of vitreous carbon. Capillary flow was dependant on the carbon distribution inside the preform. This might have locally blocked infiltration because of pore clogging and also because some gas (vacuum was not applied) was entrapped inside the porosity. This is evidenced in Fig. 6A showing one preform infiltrated by MW heating at ambient pressure and one by conventional technique in vacuum (Fig. 6B). MW infiltrated samples presented a certain degree of porosity, which is absent in the standard product. The small size pores (few microns) were not uniformly distributed, but rather concentrated in some areas; larger pores were randomly located. Never the less large regions of fully-infiltrated material could be observed. The lack of infiltration of smaller pores could be ascribed to the infiltration issues above mentioned. Lastly, a non-uniform temperature distribution in these large preforms (Fig. 5) might also have affected infiltration [20]. To assess the impact of porosity on the mechanical characteristics of the material, three-point bending was performed on samples cut both from well infiltrated areas and porous regions. Results are reported in Table 2. Flexural strength and flexural modulus of the fully infiltrated parts were very close to the standard material (Table 2), whereas porous parts presented lower (50%) flexural strength, but no significant change in stiffness. 3.2. C–Si–SiC composites (ex C–C preforms) Preforms after pyrolysis were made by different phases of carbon. This might be kept in mind since in this case all the preform constituents reacted with silicon. The two carbon phases in the preform are: the quasi-graphite of the fibres and the amorphous (or vitreous) carbon deriving from the pyrolysis of the phenolic

Fig. 6. SEM images of the section of a Si–SiC sample infiltrated by MW (A) compared with a sample infiltrated by conventional heating method (B). The dashed line in (A) limits a portion of dense and uniform material.

resin. Fibres do react quite violently with molten silicon due to the large amounts of defects in their lattice structure which favours the combination of the free carbon atoms with silicon. This is why fibres are often protected from molten silicon via and interphase coating. Vitreous carbon is less reactive and tends to form a bulk β-SiC layer which acts as a diffusion barrier for the incoming silicon. Infiltration performance is usually quantified by component final density and silicon uptake (Table 3). The C–C preforms

12444

G. Bianchi et al. / Ceramics International 41 (2015) 12439–12446

Table 2 Flexural strength and modulus of fully infiltrated and porous portions of the material compared to the characteristics of the standard Si–SiC materials. Standard product

Flexural strength [MPa] Flexural modulus [GPa]

Table 3 Density and silicon uptake of the MW in respect of their initial weight of standard and MW heated samples.

MW heating Fully infiltrated

Porous portions

4157 40

384718

1467 37

2347 49

223752

2297 50

Density (g/cm3) Silicon uptake (% of the initial weight)

Standard product

Samples infiltrated by MW

2.0–2.5 70–110

2.05–2.20 55–75

infiltrated by microwave showed porosity values higher than the standard Si–SiC composites due to the presence of unfilled intrabundle, long and narrow macropores (Fig. 7A). These pores are not present into the fully infiltrated samples produced with the conventional process (Fig. 7B). Large pores were not filled because vacuum was not applied during MW processing (to avoid plasma formation) while it is done in the conventional route. 3.3. Si–SiC foams (ex C–SiC foams). Ceramic foams processing was in this case easy to perform because the powder bed could penetrate the foam structure, allowing a uniform heating. On the other hand, the selected dwelling time was too short and molten silicon did not reach the periphery of the foam (white features in Fig. 5). This is also confirmed in Fig. 8A, where well infiltrated regions still contain free carbon, revealing once more that the process time was not sufficient for a complete reaction. Porous foams struts sometimes may contain larger pores which were generated by air bubbles entrapped into the slurry during replica. Fig. 8 also shows that samples macroporosities, i.e. circular cavities (originally gas bubbles), were filled in the conventional process (Fig. 8B) while they remain empty in the MW process. Again, this is because vacuum was applied in the conventional process whereas not during MW heating. MW processed foams revealed a compressive strength roughly half of the conventionally processed ones (Fig. 9). Again, this was because not all the foam's struts were fully infiltrated [26]. 4. Conclusions Microwave reactive silicon infiltration of porous preforms embedded in powder field modifiers proved to be an effective method with respect to process time and energy consumption. The use of SiC/BN powder beds is an efficient way to convert MW power into heat while keeping temperature fairly uniform and without dispersing molten silicon upon its melting. Si–SiC bulk, composite and porous ceramics were successfully infiltrated in minutes. These encouraging results are a spur to further study how to optimize product microstructure. It is believed that this improvement could be accomplished once an appropriate setup will be devised. Indeed, the setup is strictly dependant on the part mass and shape which are in turn

Fig. 7. (A) SEM image of the section of a carbon–carbon sample infiltrated by microwave heating showing oblong pores. (B) SEM image of the section of a carbon ceramic sample infiltrated by conventional heating method.

themselves sensitive to MW coupling. Once these issues will be solved, MW reactive silicon infiltration will be successfully applied on an industrial scale. As a final remark, it has to be noted that standard processes of these very components are commonly performed under 10  2 mbar residual pressure. This is apparently the only way to fill large pores. Indeed vacuum removes oxygen which is the cause low wettability of molten silicon on the porous preform inner surface. With the required levels of vacuum, MW immediately ignited plasma. Possible future work could aim at suppressing plasma, with a different

G. Bianchi et al. / Ceramics International 41 (2015) 12439–12446

12445

MW system design or, as already done in PVD, taking advantage of it. Acknowledgements 10 μm

The research leading to these results has received funding from the European Union Seventh Framework Program (FP7/ 2007–2013) under grant agreement No. 280464, Project “High-frequency ELectro-Magnetic technologies for advanced processing of ceramic matrix composites and graphite expansion” (HELM). References

10 μm

Fig. 8. SEM images of the ceramic foams. The MW processed samples (A) showed macro-porosity with regions of un-reacted carbon (darker regions in the zoomed window). The samples processed with conventional heating in vacuum (B) showed fully dense microstructures and any un-reacted carbon.

3.5 Sample MW 1 Sample MW 2

Compression Stress [MPa]

3

Sample Erbicol 2 Sample Erbicol 3

2.5 2 1.5 1 0.5 0

0

0.1

0.2 0.3 Strain [%]

0.4

0.5

Fig. 9. Stress strain curves of the ceramic foams loaded under compression. Black lines correspond to the standard product while the red ones to MW RSI. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

[1] W.B. Hillig, R.L. Mehan, C.R. Morelock, V.J. Decarlo, W. Laskow, Silicon–silicon carbide composites, Am. Ceram. Soc. Bull. 54 (12) (1975) 1054–1056. [2] G. Corman, K. Luthra, Silicon melt infiltrated ceramic composites (HiPerComp™), in: N.P. Bansal (Ed.), Handbook of Ceramic Composites, Springer, Berlin, 2005, pp. 99–115. [3] P. Spriet, CMC applications to gas turbines, in: N.P. Bansal, J. Lamon (Eds.), Ceramic Matrix Composites, John Wiley & Sons, Inc., Hoboken, NJ, USA, 2014, pp. 591–608. [4] W. Krenkel, B. Heidenreich, R. Renz, C/C–SiC composites for advanced friction systems, Adv. Eng. Mater. 4 (7) (2002) 427–436. [5] A. Ortona, D. Trimis, V. Uhlig, R. Eder, S. Gianella, P. Fino, G. D'Amico, E. Boulet, C. Chazelas, T. Gramer, E. Cresci, J.G. Wunning, H. Altena, F. Beneke, M. Debier, SiSiC heat exchangers for recuperative gas burners with highly structured surface elements, Int. J. Appl. Ceram. Technol. 11 (5) (2014) 927–937. [6] C. Sauder, Ceramic matrix composites: nuclear applications, in: N. P. Bansal, J. Lamon (Eds.), Ceramic Matrix Composites, John Wiley & Sons, Inc., Hoboken, NJ, USA, 2014, pp. 609–646. [7] D. Trimis, F. Durst, Combustion in a porous medium-advances and applications, Combust. Sci. Technol. 121 (1-6) (1996) 153–168. [8] G. Adler, M. Graeber, M. Standke, H. Jaunich, H. Stoever, R. Stoetzel, Open-cell expanded ceramic with a high level of strength, and process for the production thereof EP0907621, 1996. [9] A. Ortona, S. Pusterla, P. Fino, F.R.A. Mach, A. Delgado, S. Biamino, Aging of reticulated Si–SiC foams in porous burners, Adv. Appl. Ceram. 109 (4) (2010) 246–251. [10] F.R.A. Mach, F.V. Issendorff, A. Delgado, A. Ortona, Experimental investigation of the oxidation behaviour of sisic foams, in: R. Narayan, P. Colombo (Eds.), Advances in Bioceramics and Porous Ceramics: Ceramic Engineering and Science Proceedings, Volume 29, Issue 7, John Wiley & Sons, Inc., 2009, pp. 299–311. [11] G.A. Danko, R. Silberglitt, P. Colombo, E. Pippel, J. Woltersdorf, Comparison of microwave hybrid and conventional heating of preceramic polymers to form silicon carbide and silicon oxycarbide ceramics, J. Am. Ceram. Soc. 83 (7) (2000) 1617–1625. [12] B. Cioni, A. Lazzeri, Modeling and development of a microwave heated pilot plant for the production of SiC-based ceramic matrix composites, Int. J. Chem. React. Eng. 6 (1) (2008). [13] P. Karandikar, M. Aghajanian, D. Agrawal, J. Cheng., Microwave assisted (MASS) processing of metal–ceramic and reaction-bonded composites, in: R. Tandon, A. Wereszczak, E. Lara-Curzio (Eds.), Ceramic Engineering and Science Proceedings, American Ceramic Society, John Wiley & Sons, Inc., Hoboken, NJ, USA, 2007. [14] M. Patterson, P. Apte, R. Kimber, R. Roy, Batch process for microwave sintering of Si3N4, MRS Proc. 269 (1992) 291–300. [15] B. Vila, The importance of virtual experimentation in the design of industrial microwave heating systems, in: Proceedings of the 7th International Scientific Colloquium Modelling for Electromagnetic Processing, Hannover, Germany, 2014.

12446

G. Bianchi et al. / Ceramics International 41 (2015) 12439–12446

[16] R. Hutcheon, M. De Jong, F. Adams, A system for rapid measurements of RF and microwave properties up to 1400 1C, J. Microw. Power Electromagn. Energy 27 (2) (1992) 87–92. [17] W. Krenkel, Ceramic Matrix Composites: Fiber Reinforced Ceramics and Their Applications, John Wiley & Sons, Hoboken, NJ, USA, 2008. [18] N.P. Bansal, J. Lamon, Ceramic Matrix Composites: Materials, Modeling and Technology, John Wiley & Sons, Hoboken, NJ, USA, 2014. [19] M. Scheffler, P. Colombo, Cellular Ceramics Structure, Manufacturing, Properties and Applications, Wiley-VCH, Weinheim, 2005, p. 645. [20] E.O. Einset, Capillary infiltration rates into porous media with applications to silcomp processing, J. Am. Ceram. Soc. 79 (2) (1996) 333–338. [21] O. Dezellus, N. Eustathopoulos, Fundamental issues of reactive wetting by liquid metals, J. Mater. Sci. 45 (16) (2010) 4256–4264. [22] R. Israel, R. Voytovych, P. Protsenko, B. Drevet, D. Camel, N. Eustathopoulos, Capillary interactions between molten silicon and porous graphite, J. Mater. Sci. 45 (8) (2010) 2210–2217.

[23] V. Bougiouri, R. Voytovych, N. Rojo-Calderon, J. Narciso, N. Eustathopoulos, The role of the chemical reaction in the infiltration of porous carbon by NiSi alloys, Scr. Mater. 54 (11) (2006) 1875–1878. [24] D. Sergi, L. Grossi, T. Leidi, A. Ortona, Surface growth effects on reactive capillary-driven flow: Lattice Boltzmann investigation, Eng. Appl. Comput. Fluid Mech. 8 (4) (2014) 549–561. [25] D. Sergi, L. Grossi, T. Leidi, A. Ortona, Lattice Boltzmann simulations on the role of channel structure for reactive capillary infiltration, Eng. Appl. Comput. Fluid Mech. (2015) 1–23. [26] E. Rezaei, G. Bianchi, S. Gianella, A. Ortona, On the nonlinear mechanical behavior of macroporous cellular ceramics under bending, J. Eur. Ceram. Soc. 34 (10) (2014) 2133–2141.