Strong ceramic foams from polyurethane templates

Abstract

The most conventional manufacturing route for ceramic foams with open cells consists of coating reticulated polyurethane foams. The resulting material has well defined cell size, but suffers from low mechanical strength owing to the presence of hollow struts. As a result, the performance and utilisation of ceramic foams manufactured by this method are limited in certain applications. One solution to overcoming this inherent disadvantage is to use a stronger ceramic coating material and to ameliorate the wetting of the polyurethane template. Such a material is reaction bonded Al 2 O 3 (RBAO), which has high mechanical strength as a result of its fine grain structure, with less or even without glassy phases at the grain boundaries. The present work demonstrates the feasibility of producing strong ceramic foams by using a reaction bonded modified replica technique starting from polyurethane templates varying in both composition and cell size distribution.

Increased Mechanical Stability and Thermal Conductivity of Alumina Reticulated Porous Ceramics (RPC) by Nanoparticle Infiltration Processing

“…[3,18] The thermal conductivity was determined with the Transient Plane Source method (TPS 2500 S, Hot Disk AB, Gothenburg, Sweden) with a 10 mm sensor (8563, Hot Disk AB) between two specimens (face grinded with a 2 mm diamond grinding disc, approx. 44 Â 44 Â 16.5 mm).…”

“…Linear regression results in ln(C à ) ¼À0.4(4), slope n ¼ 2.5 (1), and R 2 ¼ 0.98 without constraints, using s b ¼ 400 MPa for dense alumina. [3,18] The calculated intercept exhibits a high uncertainty, but more significant is n. According to Equations 1 and 2, exponent n determines the dependency of the relative strength on the relative density, with an increasing n corresponding to a higher dependency. In ref., [22,26] n ¼ 1.5 was deduced, which is significantly lower than n obtained from fitting the reference samples within this work.…”

“…[16] Unfortunately, it is not possible to compare the strength directly, due to different measuring geometry, sample geometry (size, relative density, cell size), or other missing measurement parameters. [7,16,18] The Weibull moduli m range from 1.9 to 5.7 and exhibit no obvious correlation to varied parameters (T max1 , T max2 , colloid, infiltration technique; Table 2). The scattering range suggests an influence of the sample preparation, but differences in preparation were not identified, and the Weibull moduli as calculated are in the range as reported for comparable cellular materials.…”

Processing Routes to Macroporous Ceramics: A Review

“…68 Figure 4 shows that the strut flaws reduce the compressive strength of replica-derived porous ceramics to levels usually lower than the strength theoretically predicted for open cell structures. 76 Many attempts have been made to avoid this shortcoming by, for instance, improving the wetting of the suspension on the sponge with the help of additives, 21,25 performing a second impregnation step to fill the cracks in the ceramic struts, [17][18][19]22 and introducing fibers 77,28 or reactive compounds 25 to enhance the material's Impregnation with preceramic polymers SiOC-C composites 63 Liquid precipitation of precursors Macroporous zeolites, 64 Calcium phosphate-based composites integrity. In contrast to ceramic suspension-derived reticulated structures, cellular materials obtained from preceramic polymers have crack-free struts due most likely to the improved wetting on the sponge and the partial melting of the cross-linked polymer during pyrolysis.…”

Novel preparation of graded porous structures for medical engineering

“…This effect could be due to the ethanol improving the attachment of the sprayed ceramic particles by moistening the polymeric surface, in addition to the fact that the ceramic suspension also contains ethanol. The strength of ceramic reticulated foams can be increased by improving the wetting of the PU foam template (Luyten et al 2005). Polymeric foams have been pretreated with ethanol to improve the wettability of the foam (Mikos et al 1994;Boccaccini et al 2003).…”