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Available online at www.sciencedirect.com

ScienceDirect

Journal of the European Ceramic Society 34 (2014) 3513–3520

Preparation of zirconium carbide foam by direct foaming method

Fei Li a,b, Zhuang Kang a, Xiao Huang a,∗, Xin-Gang Wang a, Guo-Jun Zhang a,∗∗a State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Shanghai 200050, China

b University of Chinese Academy of Sciences, Beijing 100049, China

Received 23 January 2014; received in revised form 21 April 2014; accepted 16 May 2014Available online 11 June 2014

bstract

ltra light, highly porous, closed-cell structured ZrC foam can be produced in two steps. First, pre-ceramic foam is prepared by direct foamingf zirconia sol and phenolic resin. In the next step, the foamed green body is converted into ZrC foam after carbothermal reduction at 1600 ◦Cnder argon atmosphere. The obtained ZrC foam has porosity of 85% and possesses uniform cells with an average size of about 40 �m. The foam

◦

lso displays excellent thermal stability up to 2400 C. Its compressive strength and thermal conductivity at room temperature are 0.4 MPa and.94 W/(m K), respectively.

2014 Elsevier Ltd. All rights reserved.

eywords: Ultra high temperature ceramic foams; Zirconium carbide; Direct foaming; Carbothermal reduction

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. Introduction

Comparing to their organic partners, ceramic foams havexcellent thermal stability and outstanding resistance to organicolvents and chemical corrosion, which can lead to variousngineering applications, such as high temperature thermalnsulation, catalysis, molten metal or hot gas filtration and

ore.1–9 Several approaches have been developed to produceeramic foams and it appears that the microstructures/propertiesf ceramic foams are strongly dependent on the preparationrotocols.1,4,5 Partial sintering is the most straightforward pro-essing route for the preparation of porous ceramics.10,11 Buthis method usually results in porous ceramics with porosityower than 60 vol%.1 Ceramic foams with high porosity are usu-lly prepared by replica, sacrificial template and direct foamingethods, in which ceramic suspensions or preceramic polymers

re usually involved.1,4,5

Many oxide and silicon-based non-oxide ceramic foamsith porosity greater than 90 vol% have been prepared by

he forementioned three methods and have found numerous

∗ Corresponding author. Tel.: +86 2152414318; fax: +86 2152413122.∗∗ Corresponding author.

E-mail addresses: xiaohuang@mail.sic.ac.cn (X. Huang),jzhang@mail.sic.ac.cn (G.-J. Zhang).

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ttp://dx.doi.org/10.1016/j.jeurceramsoc.2014.05.029955-2219/© 2014 Elsevier Ltd. All rights reserved.

pplications.1,2,5 But mainly due to their relatively low meltingoints, few of these ceramic foams can be used at temperaturesbove 2000 ◦C.

Zirconium carbide (ZrC) is a typical member of the so-alled ultra high temperature ceramic (UHTC) family. Due to itsxtremely high melting point (>3400 ◦C), high hardness, excel-ent solid-phase stability and good thermomechanical properties,tc., ZrC has been considered as one of the most potentialandidates for high temperature applications often associ-ted with hypersonic aerospace vehicles and rocket propulsionystems.12–16 However, up to now, most researches on ZrC focusn the synthesis and sintering of the ceramic powder, the den-ification and the performance of the corresponding ceramicaterials. Unlike silicon carbide, whose foams have been well

tudied and become commercially available,17 the researchesn ZrC foams18 are very limited probably due to the harshynthesis conditions and the absence of appropriate preceramicrecursors.

It has been reported that ZrC ultrafine powders can berepared using various sol–gel precursors.12,13 More recently,ambo et al.18 reported the preparation of porous biomorphicrC/C composite by impregnating the pine wood in zirconia sol

nd pyrolyzing the sample in inert atmosphere. In this work, weeport the preparation of ZrC foams by employing a commer-ial foaming technique for phenolic resins. In the experiments,

3 n Ceramic Society 34 (2014) 3513–3520

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irconia sol is used as the zirconia precursor, while commer-ial foamable phenolic resin is used as the carbon source andoaming aid. By thermal-setting the wet foam and pyrolyzinghe foamed green body at 1600 ◦C, highly porous ZrC foam cane obtained.

. Experimental

.1. Materials

Zirconium oxychloride octahydrate (ZrOCl2·8H2O, 99%)as purchased from Shanghai Diyang Chemical Co., Shanghai,hina, used as received. Hydrogen peroxide 30% (AR grade)nd ethanol (AR grade) were purchased from Sinopharm Chem-cal Reagent Co., Shanghai, China, and used without furtherurification. Deionized water (DI water) was prepared in-housey using a Thermo Scientific Barnstead Easypure II system. Phe-olic resin, pentane (blowing agent), Tween 20 (emulsifier) anditric acid (curing agent) were obtained from Zhejiang Xinzunnergy Conservation Building Materials Co., Ltd, China.

.2. Preparation of zirconia sol

Zirconia sol was prepared according to the reportediterature.19 Zirconium oxychloride (ZOC) was dissolved inwater/ethanol solution. Then hydrogen peroxide was slowly

dded into the ZOC solution. The overall molar ratio of watero ZOC was controlled at 10, while that of hydrogen peroxideo ZOC was 5. After hydrogen peroxide addition, the mixtureas stirred at room temperature for 24 h before it was further

oncentrated to yield zirconia sol by rotary evaporation. Thebtained sol has a solid content of 60%.

.3. Foaming process

A commercial foaming process for phenolic resin was appliedere. Typically, phenolic resin, emulsifier (Tween 20), blow-ng agent (pentane), zirconia sol and curing agent (citric acid)ere vigorously stirred to form a viscous foamable mixture.he mixture was stirred for 6 min, and then it was poured into a00 mm × 100 mm × 20 mm rectangular Teflon mold and keptn an oven at 75 ◦C for 4 h to let the foaming process completend the foamed body ripen. The amount of phenolic resin usedn the mixture was based on the carbon to zirconium molar ratio,hich was controlled at 10. The amount of emulsifier, blowing

gent and curing agent applied were 5%, 7% and 19% of theeight of phenolic resin, respectively. The flow chart of the ZrC

oam preparation is illustrated in Scheme 1.

.4. Heat treatment

The foamed green body was pyrolyzed at 1400 ◦C for 2 h◦

r 1600 C for 1 h under flowing argon atmosphere in a tube

urnace with a heating rate of 3 ◦C/min.In order to investigate its high temperature stability, the

btained ZrC foam was cut into small blocks and each block was

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Scheme 1. Flow chart of ZrC foam preparation.

ged under argon atmosphere at 1800, 2000, 2200 ◦C for 1 h or400 ◦C for 10 min (graphite furnace, 10 ◦C/min), respectively.

.5. Characterization

The morphology of the foam was observed using a JEOLSM-6700F scanning electron microscope. The average foamell sizes were determined by image analyses on SEM imagessing Image-Pro Plus 5.0. More than 100 cells were measuredo give out average cell diameter for each sample. Transmis-ion electron micrographs (TEM) were recorded on a JEOLEM-2100F transmission electron microscope at 200 kV. Pho-ographs were taken by a HTC One S camera. X-ray diffractionXRD) patterns were collected by using a Rigaku D/Max-2200C X-ray diffractometer with Cu target (40 kV, 40 mA). Theore structure of the foams was characterized by mercury intru-ion porosimetry (MIP, AutoPore 9500). Compressive strengthas measured by an Instron 5592 universal testing machine withcrosshead speed of 0.5 mm/min on samples with dimensionsf 10 mm × 10 mm × 10 mm. Thermogravimetric analysis was

erformed on a Netzsch STA 449F3 in oxygen at a heating ratef 10 ◦C/min to calculate the weight percentage of ZrC in theyrolyzed foam.

F. Li et al. / Journal of the European Ceramic Society 34 (2014) 3513–3520 3515

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atsZSndf0.17 g/cm3. The pre-ceramic and ceramic foams having similardensity is probably because the weight loss during pyrolysis iscompensated by the volume shrinkage.

Fig. 1. A photograph of a cut foamed green body.

The thermal conductivity, λ, of the foam was determinedy laser flash diffusivity technique. The thermal diffusivity, α,as measured on a Netzsch LFA 427 in the temperature range5 ◦C to 300 ◦C in air (sample: Φ 10 mm by 1.5 mm thickness).he specific heat capacity, Cp, was measured on a Netzsch STA49F3 at temperature range 25–300 ◦C in flowing air with aeating rate of 10 ◦C/min. The bulk density, ρ, Cp and α werehen used to calculate the thermal conductivity based on Eq. (1):

= a × r × Cp (1)

. Results and discussion

.1. Preparation of the ZrC foams

Fig. 1 shows a photograph of the foamed green body whichas cut into a block of 10 cm × 5 cm × 2 cm. The red outlook is

oming from the phenolic resin. In the picture, the foam showsne pore structure by naked eyes. Both the surface and the crossection of the foam seem homogeneous and no obvious voidsre observed. It has a bulk density of 0.17 g/cm3 and a porosityf 85% (based on MIP, vide infra). Apparently, the mixture ofur zirconia sol and phenolic resin at C/Zr of 10 has excellentoamability.

Foaming process is quite complicated. Many technical factorselated to the foamability and foam stability as well as environ-ental and cost effective issues need to be taken into account

uring processing. To simplify the situation, a mature and widelysed commercial phenolic resin foaming process is applied. Theey in our protocol is to prepare a zirconia sol which has goodompatibility with foamable phenolic resin. In our experiments,he foamability worsens as the Zr content increases because thenorganic zirconia sol affects the foamability of the organic phe-olic resin. The research work to make zirconium-containingrecursor of better compatibility with foamable polymers is stillnder progress.

The foamed green bodies were pyrolyzed at 1400 ◦C forh or 1600 ◦C for 1 h respectively. The XRD patterns of theyrolyzed foams are shown in Fig. 2. It appears that after pyrol-sis at 1400 ◦C for 2 h, the existence of m-ZrO2 and t-ZrO2 is

till obvious. Since the carbon from phenolic resin is excessive,t indicates that the carbothermal reduction has not completednd higher reaction temperature is needed. After pyrolysis at600 ◦C for 1 h, the carbothermal reduction has completed as

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ig. 2. XRD patterns of the foamed green bodies after being pyrolyzed at 1400or 2 h and 1600 ◦C for 1 h in Ar.

nly ZrC phase can be indexed in the XRD pattern. Based uponeight loss of the obtained ZrC foam in oxygen atmosphere and

ssuming ZrO2 as the only product,20 the ZrC content in the as-yrolyzed foam is calculated to be 53 wt%, and the other 47 wt%s amorphous carbon.

The pictures of ZrC foams obtained after pyrolysis at 1400nd 1600 ◦C are shown in Fig. 3. After pyrolysis, the foams main-ain their original shapes with ∼65% volume shrinkage and notructural damages are observed. The pictures of 1600-pyrolyzedrC foams after high temperature aging are also shown in Fig. 3.imilarly, no geometric changes and structural damages areoticed in the ZrC foam after aging, indicating its excellentimensional stability at high temperatures. The densities of theoams, which are calculated by mass over volume, are all around

ig. 3. Photographs of the as-pyrolyzed foams at 1400 and 1600 ◦C in Ar, andhe 1600-pyrolyzed foams after high temperature aging in Ar.

3516 F. Li et al. / Journal of the European Ceramic Society 34 (2014) 3513–3520

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ig. 4. SEMs of the (a) pre-ceramic foam, (b) ZrC foam after 1600 ◦C pyrolysish in Ar and (f) 2400 ◦C for 10 min in Ar. The scale bars are 30 �m.

.2. Microstructure analyses

MIP is a very powerful analytical tool for porous materialsith pore size between 0.0035 and 500 �m.21 MIP results of

he pre-ceramic and ceramic foams are summarized in Table 1.

able 1ummary of MIP data.

ample Bulk density at0.53 psia (g/mL)

Porosity(%)

Median poresize (�m)

oamed green body 0.17 86 3.4yrolyzed at 1600 ◦C 0.16 85 8.0hermal agingAged at 1800 ◦C 0.17 84 11.3Aged at 2000 ◦C 0.19 84 11.6Aged at 2200 ◦C 0.19 83 11.8Aged at 2400 ◦C 0.16 90 14.7

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r and ZrC foams after further aging at (c) 1800 ◦C, (d) 2000 ◦C, (e) 2200 ◦C for

he results show that the bulk densities and porosities of allhe foams are close. And the bulk density data from MIP areonsistent with the densities calculated by mass over volume.

SEMs of the pre-ceramic and ceramic foams after 1600 ◦Cyrolysis are shown in Fig. 4a and b. Fig. 4a clearly shows thelosed cells structure of the foam with the existence of severalroken cells possibly from mechanical cutting, which resembleshe foamed phenolic resin (without zirconia sol). The commer-ial foaming process applied here is known to produce foamith closed cell structure.22,23 The cells in Fig. 4a look slightly

longated to one direction. Actually, it elongated to the riseirection, which is commonly observed in open-mold foamingrocess.24

After high temperature pyrolysis, the ceramic foam (Fig. 4b)

aintains the similar morphology as the pre-ceramic foam,

xcept that the cell elongation became less obvious prob-bly because the cells relaxed during heat treatment. The

F. Li et al. / Journal of the European Ceramic Society 34 (2014) 3513–3520 3517

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ig. 5. SEMs of the struts in (a) pre-ceramic foam and ZrC foams aged at (b) 2re 2 �m.

recursor-to-ceramic conversion in our cases at least involveshe decomposition of the phenolic resin and zirconia sol andarbothermal reduction of zirconia with carbon. Thus it is rea-onable to observe the reduction in cell size, which decreasesrom about 60 �m in the pre-ceramic foam to about 40 �m inhe foam after pyrolysis at 1600 ◦C for 1 h. Fig. 4c–f shows thathere are no obvious morphological changes after the pyrolyzed

oams were further aged at 1800–2400 ◦C, which is also an indi-ation of the good high temperature stability of the ZrC foam.ig. 5 shows some typical struts of the pre-ceramic foam and

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Fig. 6. TEM images of one typical (a) strut and (b) ce

, (c) 2200 ◦C for 1 h in Ar and (d) at 2400 ◦C for 10 min in Ar. The scale bars

igh temperature aged ZrC foams. The thickness of the struts isll about 3–4 �m. Again, high temperature aging did not causebvious changes to the struts structure.

TEM images of one typical strut and cell wall of ZrC foamfter pyrolysis at 1600 ◦C are shown in Fig. 6. In TEM images,he dark phases are ZrC, and light phases are amorphous carbon.t is obvious that the phase distributions in the strut and cell

all are different. In the cell wall, it appears that carbon is the

ontinuous phase with ZrC particles embedding in the carbonatrix, while in the struts ZrC forms the dominant phase. This

ll wall of ZrC foam after pyrolysis at 1600 ◦C.

3 n Ceramic Society 34 (2014) 3513–3520

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ight be due to the drainage and mass migrated to the struturing foaming process.4

SEM results show that there are no obvious changes in theell size after high temperature pyrolysis and thermal aging.owever, very interestingly, the average pore sizes of the foams

nd pore size distribution from MIP (Table 1 and Fig. 7) showome significant changes. The average pore size increases from.4 �m in pre-ceramic foam to 8.0 �m in ZrC foam after pyroly-is. When the ZrC foams were further aged at high temperatures,heir average pore sizes based on MIP seem to increase furthers aging temperature.

In principle, MIP gives out the size of the largest entranceoward a pore, not the actual inner size of a pore.21,25 Accordingo Washburn equation (a modified Young–Laplace equation, Eq.2)),21 in MIP experiment, the pore size is calculated based onhe pressure applied to force mercury intruding the pores. Thearger the pressure is, the smaller the pore size is.

P = 2 × γ × cos θ/rpore (2)

here �P is the pressure across the interface, γ is the surfaceension of mercury, θ is the contact angle between the solid and

ercury, and rpore is the calculated radius.In our cases, the closed cell walls can be broken when the

pplied pressure reaches a certain value. And then mercuryntrudes into the cells to give out information of the pore struc-ure. Because extra pressure is needed to break the cell walls, thealculated pore sizes are much smaller than cell sizes observedrom SEMs.21 The increase of pore sizes after high temperatureyrolysis and aging indicates that less pressure is required toorce mercury to intrude into the cells, which implies that theell wall strength decreases after pyrolysis and further decreasespon aging.

.3. Compressive strength of the ZrC foams

A preliminary study on the mechanical properties of the ZrCoam obtained from 1600 ◦C pyrolysis was carried out. Fig. 8ahows a typical compressive strain-stress curve of the ZrC foam,hich has a compressive strength of 0.4 MPa. Generally, the

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ig. 8. (a) Typical compressive stress-strain response of ZrC foam from 1600 ◦C py600 ◦C pyrolysis, and ZrC foams being aged at 1800, 2000, 2400 ◦C respectively (d

Fig. 7. Pore size distribution of the pre-ceramic and ZrC foams by MIP.

ependence of the strain-stress of ceramic foams can be dividednto two different stages: linear elastic and a plateau region.26,27

pon compression, the foam undergoes a progressive collapsef the cells, with the lower part of the foam remains completelyndamaged.28 In the plateau region, the stress is assumed toe independent of the strain as part of the structure collapses,hile other parts of the structure remain elastic.28 Beyond thelateau, densification takes place and the stress rises sharplys complete densification begins. These characteristics are alsoypical of other ceramic foams, and have already been discussedy Ashby and Gibson8,9 and other researchers.26–29In Fig. 8b,he compressive strength decreases with pyrolysis and agingemperatures initially, and then shows a slightly increase afterging at 2400 ◦C. The compressive response of a closed ceramicoam is largely depended on the strength of the cell walls and thetruts.28,30 The decrease of the compressive strength of the ZrCoams in Fig. 8b is probably due to the decrease of the strengthf the cell walls, which is consistent with the MIP observations.

◦

fter 2400 C aging, the strength of the struts could be enhancedy the neck formation between ZrC particles,31 which leads tohe exceptional increase of the compressive strength.

rolysis; (b) Compressive strength of the pre-ceramic foam, the ZrC foam fromata are average of 5 individual measurements).

F. Li et al. / Journal of the European Cera

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ig. 9. Temperature dependence of thermal conductivity of the ZrC foamsbtained from pyrolysis at 1600 ◦C for 1 h.

.4. Thermal conductivity of the ZrC foam

The thermal conductivity of the ZrC foam is determinedy laser flash technique, which is 0.96 W/(m K) at 50 ◦C and.36 W/(m K) at 300 ◦C (limited by our current apparatus). Ashown in Fig. 9, the thermal conductivity increases as tempera-ure, more rapidly in the range 50–200 ◦C, and more slowly inhe range 200–300 ◦C. The heat conduction in a cellular solid is auite complicated.30 To simplify, the overall thermal transfer inhe ZrC foam can be the sum of the heat conduction through theell walls or struts and radiative heat transfer.30,32 Although theeat conduction through the solid decreases with increasing tem-erature for ceramic materials, radiative heat transfer throughhe cells increases as the cube of the temperature,27,30 which ishe major reason for the increase of thermal conductivity versusemperature.

. Conclusions

Low density, highly macroporous, closed cell structured ZrCoam can be prepared by a commercial foaming technique forolymeric foams and a following high temperature ceramiza-ion. Pre-ceramic foam is first prepared by co-blowing of airconia sol and phenolic resin. The foamed green body is con-erted to ceramic foam after 1600 ◦C pyrolysis under argonhereafter. The ZrC foam obtained has a large porosity of 85%nd cells with an average size of about 40 �m.

Thermal aging experiments illustrate that the obtained ZrCoam has excellent thermal stability up to 2400 ◦C, which isery promising for potential ultra high temperature applications.here are no obvious macro- and micro-structure changes after

hermal aging by direct and SEM observations. MIP resultseveal that the thermal aging may weaken the strength of theell walls, thus lead to the decrease of the compressive strengthf the ZrC foam.

Our work demonstrates that zirconium-based sol-gel pre-ursor can be an efficient precursor for making ZrC foams. Welso believe that this easy, low-cost foaming method could be a

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mic Society 34 (2014) 3513–3520 3519

eneral approach to prepare other UHTC foams and SiC foams well.

cknowledgements

Financial support from the Chinese Academy of Sciencesnder the Program for Recruiting Outstanding Overseas ChineseHundred Talents Program), Science and Technology Com-ission of Shanghai Municipality (# 11ZR1442200) and theational Natural Science Foundation of China (Nos. 11205229,1002168) are gratefully acknowledged.

eferences

1. Ohji T, Fukushima M. Macro-porous ceramics: processing and properties.Int Mater Rev 2012;57:115–31.

2. Colombo P. Engineering porosity in polymer-derived ceramics. J Eur CeramSoc 2008;28:1389–95.

3. Colombo P. In praise of pores. Science 2008;322:381–3.4. Studart AR, Gonzenbach UT, Tervoort E, Gauckler LJ. Processing

routes to macroporous ceramics: a review. J Am Ceram Soc 2006;89:1771–89.

5. Colombo P. Conventional and novel processing methods for cellular ceram-ics. Philos Trans R Soc A 2006;364:109–24.

6. Colombo P, Bernardo E. Macro- and micro-cellular porous ceramics frompreceramic polymers. Compos Sci Technol 2003;63:2353–9.

7. Fujiu T, Messing GL, Huebner W. Processing and properties of cellular silicasynthesized by foaming sol-gels. J Am Ceram Soc 1990;73:85–90.

8. Ashby MF, Sammis CG. The damage mechanics of brittle solids in com-pression. Pure Appl Geophys 1990;133:489–521.

9. Ashby MF, Medalist RFM. The mechanical properties of cellular solids.Metall Trans A 1983;14:1755–69.

0. Zhang G-J, Yang J-F, Ohji T. Fabrication of porous ceramics with unidirec-tionally aligned continuous pores. J Am Ceram Soc 2001;84:1395–7.

1. Yang J-F, Zhang G-J, Ohji T. Porosity and microstructure control of porousceramics by partial hot pressing. J Mater Res 2001;16:1916–8.

2. Katoh Y, Vasudevamurthy G, Nozawa T, Snead LL. Properties of zirconiumcarbide for nuclear fuel applications. J Nucl Mater 2013;441:718–42.

3. Sacks MD, Wang CA, Yang ZH, Jain A. Carbothermal reduction synthesisof nanocrystalline zirconium carbide and hafnium carbide powders usingsolution-derived precursors. J Mater Sci 2004;39:6057–66.

4. Wang X-G, Liu J-X, Kan Y-M, Zhang G-J. Effect of solid solution formationon densification of hot-pressed ZrC ceramics with MC (M = V, Nb, and Ta)additions. J Eur Ceram Soc 2012;32:1795–802.

5. Wang X-G, Zhang G-J, Xue J-X, Tang Y, Huang X, Xu C-M, et al. Reactivehot pressing of ZrC–SiC ceramics at low temperature. J Am Ceram Soc2013;96:32–6.

6. Wang X-G, Guo W-M, Kan Y-M, Zhang G-J, Wang P-L. Densificationbehavior and properties of hot-pressed ZrC ceramics with Zr and graphiteadditives. J Eur Ceram Soc 2011;31:1103–11.

7. Eom J-H, Kim Y-W, Raju S. Processing and properties of macrop-orous silicon carbide ceramics: a review. J Asian Ceram Soc 2013;1:220–42.

8. Rambo CR, Cao J, Rusina O, Sieber H. Manufacturing of biomorphic(Si, Ti, Zr)-carbide ceramics by sol–gel processing. Carbon 2005;43:1174–83.

9. Zhou C-H, He C, Hu X-F, Luo H-J. Preparation and characterization ofstable zirconia sol. Glass Enamel 2001;29:41–4.

0. Garcia-Marquez A, Portehault D, Giordano C. Chromium nitride andcarbide nanofibers: from composites to mesostructures. J Mater Chem2011;21:2136–43.

1. Giesche H. Mercury porosimetry: a general (practical) overview. Part PartSyst Char 2006;23:9–19.

2. Lunt J, MacPherson EJ, Meunier PJ. Closed cell phenolic foam. US Patent4,545,119; 1986.

3 n Cer

2

2

2

2

2

2

2

3

3architectures. J Eur Ceram Soc 2013;33:1599–607.

520 F. Li et al. / Journal of the Europea

3. Cornick M. Foam. In: Pilato L, editor. Phenolic resins: a century of progress.New York: Springer; 2010. p. 189–208.

4. Gibson LJ, Ashby MF. Cellular solids: structure and properties. 2nd ed.Cambridge, UK: Cambridge University Press; 1997.

5. León, León CA. New perspectives in mercury porosimetry. Adv ColloidInterfac 1998;76-77:341–72.

6. Tondi G, Zhao W, Pizzi A, Du G, Fierro V, Celzard A. Tannin-based rigidfoams: a survey of chemical and physical properties. Bioresour Technol

2009;100:5162–9.

7. Bourret J, Michot A, Tessier-Doyen N, Naït-Ali B, Pennec F, Alzina A, et al.Thermal conductivity of very porous kaolin-based ceramics. J Am CeramSoc 2014;97:938–44.

3

amic Society 34 (2014) 3513–3520

8. Brezny R, Green DJ. Mechanical behavior of cellular ceramics. In: Matersci tech-lond. Weinheim: Wiley-VCH; 2006. p. 467–516.

9. Colombo P, Modesti M. Silicon oxycarbide ceramic foams from a prece-ramic polymer. J Am Ceram Soc 1999;82:573–8.

0. Scheffler M, Colombo P. Cellular ceramics: structure, manufacturing, prop-erties and applications. Weinheim, Germany: Wiley-VCH; 2005.

1. Landi E, Sciti D, Melandri C, Medri V. Ice templating of ZrB2 porous

2. Smith DS, Alzina A, Bourret J, Nait-Ali B, Pennec F, Tessier-Doyen N,et al. Thermal conductivity of porous materials. J Mater Res 2013;28:2260–72.