ceramic foam synthesis and its modification for use at high temperature

8/12/2019 Ceramic Foam Synthesis and Its Modification for Use at High Temperature

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INTRODUCTION

Ceramic foam is currently a very excitingarea of research due to its wide applicability. Manyof the authors have conducted extensive reviewson the subject. Buciuman1mentioned that ceramicfoams have been in development for around threedecades, and are now used commercially as filtersfor molten metal and hot gases. In recent years,

ORIENTAL JOURNAL OF CHEMISTRY

www.orientjchem.org

ISSN: 0970-020 XCODEN: OJCHEG

2011, Vol. 27, No. (4):Pg. 1293-1301

Est. 1984

An International Open Free Access, Peer Reviewed Research Journal

Ceramic Foam Synthesis andIts Modification for Use at High Temperature

KAREN PEA, VANESSA S. GARCIA-CUELLO,LILIANA GIRALDO and JUAN CARLOS MORENO-PIRAJAN*

Department of Chemistry, Faculty of Sciences, Universidad Nacional de Colombia, CiudadUniversitaria, Carrera 30 No. 45 03, edificio 451, Bogot-Colombia.

Research Group on Porous Solid and Calorimetry, Department of Chemistry, Faculty of Sciences,Universidad de Los Andes, Carrera 1 No. 18 A 10, Bogot, Colombia

*Corresponding author: Tel.: +57 1 3394949 2786. E-mail address: [email protected]

(Received: September 20, 2011; Accepted: November 19, 2011)

ABSTRACT

Many properties of open-cell ceramic foam prepared by means of the sponge replicationmethod can be controlled by adjusting the viscosity of the ceramic slip with respect to the porecount of the polymer sponge template. Ceramic foam obtained by this method was subsequentlycoated with various materials, such as urea-formaldehyde and carboxymethylcellulose (CMC),and its structural properties were analysed and interpreted in order to establish its potentialapplicability as a thermal insulator. Ceramic foams were prepared with different densities byvarying the density of the ceramic slurries used (1.1845, 1.2798, 1.3567, 1.54332, 1,6543 and1,7234 g/cm3). The physical properties of the ceramic foam produced, such as density, werecharacterised according to ASTM C 271-94, whereas porosity was characterised using theArchimedes method. The foams were analysed with XRD, SEM and FTIR, among other techniques.

Key words: Foam, Ceramic, Isolated temperature, Mullite.

however, other applications have also beenexplored. For instance, the potential for ceramicfoams as catalyst carriers, burner heads, or fuel-cell electrodes has gained increasing interest.Ceramic foams can be highly suitable catalyticcarriers where a low pressure drop is mandatory. Incomparison to honeycomb monoliths, they offer theadditional advantages of radial mixing within thebody and enhanced mass and heat transfer due to


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1294 PENA et al., Orient. J. Chem., Vol. 27(4),1293-1301 (2011)

the turbulence of the flow. Foam carriers exhibit ahigh contact surface between the gas phase andthe solid, and can be manufactured in different

geometries, allowing for adjustment of axial or radialflow patterns in the reactor. Pioneering workreported in the field of catalysis with foam carriersconcerned the partial oxidation of hydrocarbons1-4,catalytic combustion5,6, and the removal of soot fromdiesel exhaust1,7,8. There are several routes formanufacturing ceramic foams. Among these, thepolymer sponge replication method ofSchwarzwalder and Somers9 is most suitable forthe fabrication of oxidic, reticulated foams with easilyaccessible, open cells10,11. This method consists ofcoating an elastic polymer sponge with open cells

with a slip containing the precursors of the ceramicmaterial together with other additives. Coating isachieved by immersing the polymer sponge into theslip, expelling the excess (e.g. by compression), anddrying. Subsequently, the green body is exposed toa temperature treatment. In a first stage, the organicskeleton is burned off in air. At temperatures above1400C, the particles forming the ceramic replicaare sintered.

There are several developments that havebeen published in the area of the synthesis of

ceramic foam and the various uses they may have.Have published a number of routes for ceramicfoams according to the final application is requiredto give. In this work, we have based on alreadypublished work1, we want to enhance the processof ceramic foam synthesis and the study of density,but mainly we wish to explore the use of simpletreatments with molecules for establishing whetherorganic chemical compounds can improve theirthermal isolation properties.

EXPERIMENTAL

Foams synthesisIn our research, the procedure used for

the synthesis of ceramic foam is based on thepublication of Buciuman1. The ceramic foam carrierswere made by means of the polymer foam replicationmethod9. Polymer sponges were used (polyester,Koepp AG), with a pore size of the range of 50 ppi,

and cut into pieces of 30-60 mm diameter. Most ofthe work reported here was carried out with alumina-mullite foams. For the preparation of the respective

slip, the ceramic precursors (boehmite, kaolin andsilica in a weight ratio of 4.5:3.5:2) were suspendedin water containing poly(vinylpyrrolidone) (Luviskol,BASF) as an organic binder and Dolapix PC 67(Zschimmer & Schwarz) as a deflocculant. Themixtures were milled with alumina balls for 45 min.The slip was used to coat polymer sponges ofdifferent pore counts with 50 ppi. The variouscombinations used for the production of the otherfoam ceramics are summarised in Table 1. The solidcontent (based on the mixtures) was varied toproduce ceramic slurries with densities of 1.1845,

1.2798, 1.3567, 1.54332, 1.6543 and 1.7234 g/cm3,in a distilled water medium12. Coating was performedby immersing the sponge pieces in the slurry,squeezing them, and passing them through rollerspreset at 80% impression to expel the excess slip.The bodies were dried for 24 h at room temperatureand heated at 1C/min to 700C, and then a furtherat 10C/min to the final temperature (1800C), whichwas held for 500 min to achieve sintering of theceramic.

Characterization of foams synthesized

The properties of the ceramic foamproduced were characterised according to ASTMC 271-94 and the porosity was characterised usingthe Archimedes method. The morphological studywas performed using a scanning electronmicroscope (JEOL). Different analysis techniqueswere used to characterise the synthesised ceramicsamples: with CuK radiation. Powder diffractiondata were collected in the 2ranges 480 in stepsof 0.02 2, with 1s per step. The operating voltageand current were 40 kV and 45 mA. Photographs ofsamples were taken with a digital camera (Casio,

Japan). Scanning Electron Microscopy micrographswere obtained with a Hitachi S-2400 instrument.Nitrogen adsorption isotherms were measured atliquid N

2 temperature (-196 C) and N

2 pressures

ranging from 10-6 to 1.0 p/po

with a Autosorb 3B(Quantachrome, Boynton beach, USA)13,14. Thechemistry of the ceramic foam synthesised wascharacterised by IR spectroscopy(Nicolet, US.).


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1295PENA et al., Orient. J. Chem., Vol. 27(4),1293-1301 (2011)

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Fig. 1: (a) Porosity and (b) bulk density of ceramic foam as a function of increasing slurry density

Fig. 2: Infrared spectra of different synthesised ceramic foams


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Fig. 3: DRX of ceramic foam synthesised

Fig. 4: Images of ceramic foams: a) Ceramic synthesised by normalprocedure, b) Ceramic foam under high thermal treatment

(a) (b)

species in the interlayer space of the aluminosilicatematerial as a result of the impregnation action.

This result is confirmed by the reductionin basal spacing, after impregnation, resulting in amore stable species and a larger cell volume.

Figure 4 show a photograph of the ceramicfoam produced in this research. Figure 4a showthe foam synthesized according to the procedureproposed initially, and Figure 4b shows the sampletreated at a high temperature to analyse its stabilitywith respect to this variable. It can be seen that itslattice is virtually the same, which is observable

without thermal treatment, so the foam can be usedas an isolated thermic layer, for example.

The big advantage is that very openstructures without openings could be realized withsufficient strength (up to 3MPa in 3p-bending).Moreover, the sponge-replica technique allows forvarying the cell size by changing the spongetemplate. Figure 5 shows a series of scanningelectron microphotographic plates. Figure 5acorresponds to the ceramic foam from the normalprocedure. This is characterised by large, well-defined pores. Figure 5b corresponds to the CMC-coated ceramic foam, the phenomenon observed


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Fig.5: Scanning electron microscope of ceramic foams. a) Ceramic foam by normal procedureb) Ceramic foam with coated CMC. c) Ceramic foam with coated urea-formaldehyde resin

(c)

(b)(a)

here is very interesting as the porosity is completelyclosed. This is important because in the resistanceand temperature isolation tests this ceramic realizedthe best results. Finally, the ceramic foam treatedwith urea-formaldehyde (see Figure 5c) also shows

blocked pores, although with minor resistance totemperature. On the other hand, the nitrogenadsorption isotherms did not develop on the surfacearea (not shown) whose highest value wasachieved on the initial ceramic foam with a value of7 m2/g, whilst the CMC-coated ceramic foampresented an area of up to 2 m2/g, which we believecontributed to the high performance of thesynthesized foams regarding their insulation againsttemperature.

When testing the ability of insulation fortemperature results showed that ceramic foamcoated with CMC and phenol-formaldehyde resin,shower of major capacity, registering temperaturesup to 1200 C so that the temperature in the

external environment was greater than 40 C. Thesetests are not described in this work and that will bethe subject of another publication which is fullyexplained as the experiments conducted and resultsachieved

CONCLUSIONS

Ceramic foams were successfullyfabricated using the polymeric foam replicationmethod. It was observed that the properties of


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ceramic foam are greatly influenced by the densityof the ceramic slurry. An increase in the density ofthe ceramic slurry enhances the strength of the foam

as well as its density, thus making the foam denser.Coating with CMC and urea-formaldehyde resinshowed an improvement in the properties of ceramicfoam, turning it into a material with excellentinsulation properties. This result is explained by thefact that these materials cause a closure of the pores,shown by the measurements of nitrogen adsorptionisotherms. Temperatures of up to 1200C were

registered without that the structure of foamssignificantly affect

ACKNOWLEDGMENTS

The authors wish to thank the MasterAgreement established between the University ofAndes and the University National of Colombia, andthe Memorandum of Understanding entered intoby the Departments of Chemistry of bothuniversities.

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3. Twigg M.V., Richardson J.T., Preparation andproperties of ceramic foam catalyst supports.In: Studies in Surface Science and Catalysis:Preparation of Catalysts VI, G.Poncelet, J.Martens, B. Delmon, P.A. Jacobs, P. Grange,(eds.) Elsevier: Amsterdam, 91: 345 (1995).

4. Cerri I, Saracco G, Specchia V., Catal. Today,60: 21 (2000).

5. Antsiferov V.N., Kalashnikova M.Y., MakarovA.M. Filimonova I.V., Russ. J. Appl. Chem.70(1): 105 (1997).

6. Saracco G, Badini G, Specchia V., Chem.Eng. Sci.54:3035 (1999).

7. Van Setten B.A., Bremmer J, Selles S.J.,Makkee M, Moulijn J.A., Catal. Today53: 613

(1999).8. Ciambelli P, Palma V, Russo P, Vaccaro S.,

Combust. Sci. Technol.153: 325 (2000).9. Schwarzwalder K, Somers A.V., Method of

making porous ceramic articles. U.S. Patent3 090 094, 1963.

10. Saggio-Woyanski, C.E. Scott Minnear W.P.,Am. Ceram. Soc. Bull.71: 1674 (1992).

11. L.M. Shepard, Porous ceramics: Processingand applications. In: Ceramic Transactions:Porous Materials, K. Ishizaki, L. Sheppard,S. Okada, T. Hamasaki, B. Huybrechts, (eds.)American Ceramic Society: Westerville, OH,31: p. 3 (1993).

12. Muhamad M.A.A., Hongb L.C., Ahmad Z.A.Aki H.M., Journal of materials processingtechnology,207: 235 (2008).

13. Garcia-Cuello V.S., Giraldo L, Moreno-PirajnJ.C., J. Chem. Eng. Data.,56: 1167 (2011).

REFERENCES

ceramic foam synthesis and its modification for use at high temperature

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