## 1 Introduction  
Porous ceramics have received significant attention in past decades [1] because of their extremely advantageous properties such as high thermal and chemical stability. These properties render the replacement of porous ceramics difficult with alternatives such as porous metals and polymers, thereby facilitating their utilization for different application fields. Among the various kinds of porous ceramic, reticulated porous ceramics are promising candidates for use in various application fields, especially where a high mass transfer and extremely low density are simultaneously required. Reticulated porous ceramics have a net-like pore structure with widely open cells, unlike foams formed by soap bubbles, which consist of fully closed cells. Reticulated porous ceramics are prepared by coating a reticulated polyurethane foam (as sacrificial polymer template) with a slurry consisting of ceramic particles, which will be the main and only constituent of the final product. Then, the ceramic slurry-coated reticulated polyurethane foam is heat-treated to burn off the reticulated polyurethane foam and finally sinter the coated ceramic particles. Typically, the porosity of reticulated porous ceramics is higher than 90%. Therefore, a highly inter-connected pore structure with high porosity amplifies one of the shortcomings (inherent brittleness) of ceramics. The mechanical instability of reticulated porous ceramics remains a challenging issue for their further application. Generally, the mechanical stability of typical porous ceramics depends on both their flexural and compressive strengths. However, it is interesting to observe that the mechanical stability of reticulated porous ceramics is mainly dependent on their compressive strength. For example, although the flexural strength of porous alumina was found to be significantly higher than that of a porous diatomite-kaolin composite [2], the compressive strength of reticulated porous alumina was similar to that of the reticulated porous diatomite-kaolin composite [3]. This discrepancy can be explained by their completely different pore characteristics, which are dependent on the preparation method of the porous ceramics. Therefore, the compressive strengths of various reticulated porous ceramics are different from those observed when they are prepared as other types of porous ceramics. Typical examples of compressive strengths of reticulated porous ceramics are: 1.60 MPa (prepared from alumina) [4], 1.59 \(\pm\) 0.13 Mpa [5] and 1.08 \(\pm\) 0.17 Mpa [6] (silicon carbide), 0.85 \(\pm\) 0.13 Mpa (zirconia) [7], 0.62 \(\pm\) 0.03 Mpa [8] and 0.73 Mpa [9] (mullite), 1.4 Mpa (aluminum nitride) [10], and 0.47 \(\pm\) 0.02 Mpa (cordierite) [11]. On the other hand, the compressive strengths of reticulated porous ceramics are strongly dependent on the pore density (expressed in pores per inch, PPI) and on whether the processing conditions are fully optimized or not. Interestingly, the above characteristics of reticulated porous ceramics provide an opportunity to use low-cost natural-based materials. If the processing conditions are adequately optimized, the compressive strength of reticulated porous ceramics prepared from low-cost natural-based materials such as clays can match that of ceramics prepared from conventional materials such as alumina and zirconia. Therefore, we recently, investigated diatomite as a feasible candidate for reticulated porous ceramics, among numerous low-cost natural-based materials. Unlike other materials of this group with plate-like shapes such as pyrophyllite [12], diatomite is uniquely advantageous for preparing porous ceramics. This is due to its porous and irregular shape, which does not require the addition of any kind of pore former or the application of a partial sintering technique. Interestingly, it is much more difficult to prepare a dense diatomite as compared to its counterpart. The strut walls of reticulated porous diatomite are also porous, unlike those of the reticulated porous ceramics, which are typically dense.