Evaluation of SiC-porcelain ceramics as the material for monolithic catalyst supports
Oleg SMORYGO
1
Alexander MARUKOVICH
a Vitali MIKUTSKI
1
Vladislav SADYKOV
0
0
Boreskov Institute of Catalysis
, 5, Lavrentiev Ave., 630090, Novosibirsk,
Russia
1
Powder Metallurgy Institute
, 41, Platonov Str., 220005, Minsk,
Belarus
Mechanical and thermal properties of SiC-porcelain ceramics were studied in the wide SiC content range of 0-95%. Microstructure evolution, shrinkage at sintering, porosity, mechanical strength, elastic modulus, coefficient of thermal expansion (CTE) and thermal conductivity were studied depending on SiC content. The optimal sintering temperature was 1200 , and the maximum mechanical strength corresponded to SiC content of 90%. Parametric evaluation of the ceramic thermal shock resistance revealed its great potential for thermal cycling applications. It was demonstrated that the open-cell foam catalyst supports can be manufactured from SiC-porcelain ceramics by the polyurethane foam replication process.
Introduction
Efficiency of catalytic process with strong heat flux
(e.g., hydrocarbon steam reforming) is strongly
dependent on the catalyst thermal conductivity.
Catalysts supported on the metal alloy monolithic
supports ensure effective heat transfer in reactors thus
providing a uniform temperature distribution (both
axial and radial), and this affects overall catalyst
performance [13]. Low robustness of metallic catalyst
supports due to corrosive degradation in the reaction
media (600900 , water vapor, decomposition
products of hydrocarbon, aggressive admixtures) limits
their practical application [1,4]. This problem does not
arise when the catalyst supports are made from various
oxide ceramics exhibiting excellent corrosive
resistance [57]. Conventional oxide ceramics,
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however, have low thermal conductivity which can be
the cause of strong temperature gradients within
catalytic reactor, and local hot zones can appear
resulting in the catalyst sintering and its fast
deactivation [8]. The use of the silicon carbide catalyst
supports in the hydrocarbon steam reforming and other
strongly endothermic or exothermic process [9] looks
promising taking into account their attractive
combination of high thermal conductivity and excellent
corrosive resistance. The data in Ref. [10] demonstrated
that the substitution of the alumina foam catalyst
supports by the silicon carbide ones results in the
increase of the cobalt based catalyst selectivity from
54% to 80% due to more uniform temperature
distribution in the reactor.
Extensive application of SiC catalyst supports is
restrained by the considerable manufacturing cost
resulting from high sintering temperature of above
2100 [11]. Ceramic materials with high SiC content
(up to 90%95%) and high mechanical strength
(450500 MPa) as well as SiC foam catalyst supports
can be synthesized via liquid phase sintering with
sintering aids like Al2O3Y2O3 [12,13]. This process is
often classified as low temperature sintering, but
actually the sintering occurs at rather high temperatures
of 17001800 . Besides, the process implies
protective sintering atmospheres in order to prevent SiC
oxidation, which also contributes to the product
manufacturing cost. That is why many efforts were
undertaken during the last decade to develop
compositions ensuring SiC based ceramics at much
lower sintering temperatures. It was found that ceramic
materials with high SiC content and reasonable
mechanical properties can be synthesized by sintering in
air with alkali or alkali-earth silicate sintering aids at
temperatures as low as 11001200 [1419]. Various
sintering aids containing alkali oxides were successfully
applied in these researches: porcelain and its polishing
residues, bentonite, and art glass. Potentially, if a
reasonable combination of mechanical and thermal
properties can be attained, this type of ceramics can
have a great commercial potential as the material for
monolithic catalyst supports: its low manufacturing cost
is predetermined by cheap initial materials and low
sintering temperature without special protective
atmosphere. However, no study performed complex
analysis of mechanical and thermal properties of this
type of ceramics before, and no study estimated this
type of ceramics as the material for monolithic catalyst
supports. Besides, the referred papers presented
experimental data on different and rather narrow SiC
content ranges, and hence the authors did not report on
the evolution of microstructure and properties in the
whole SiC content range.
In this paper, we studied sintering regimes,
microstructure evolution, and mechanical and thermal
properties of SiCporcelain ceramics in the wide SiC
content range of 095%. Complex analysis of
properties that influence the performance in thermal
cycling applications was performed, and SiCporcelain
ceramics potential as the catalyst support material was
analyzed via parametric evaluation. It was
demonstrated that open-cell ceramic foam catalyst
supports can be manuf (...truncated)