## 1 Introduction  
Porous ceramics have been extensively studied [1], because they possess various advantageous properties. Exceptionally high thermal and chemical stability of porous ceramics has secured their position in the market, made their position secure, overwhelming their competitors such as porous polymers and porous metals. Among the various types of porous ceramics, reticulated porous ceramics have well-defined open pore structures, whose porosity is generally above 90%. Therefore, reticulated porous ceramics [2] are prepared using various types of ceramics that are laid in an extreme edge of the advantages of porous ceramics. However, the inherent low mechanical stability of reticulated porous ceramics which is a disadvantageous legacy of ceramics severely inhibits their application in various fields. The maximum obtainable compressive strengths of reticulated porous ceramics, which it strongly depend on the PPI (pores per inch), are generally low, such as reticulated porous alumina (1.60 MPa) [3], reticulated porous aluminum nitride (1.4 MPa) [4], reticulated silicon nitride (2.67 MPa) [5], reticulated porous silicon carbide ((1.59 \(\pm\) 0.13 MPa) [6] and (1.08 \(\pm\) 0.17 MPa) [7]) reticulated porous zirconia (0.85 \(\pm\) 0.13 MPa) [8],reticulated porous cordierite (\(0.47\pm 0.02\) MPa) [9], reticulated porous yttrium disilicate (1.28 MPa) [10], and reticulated porous mullite (\(0.62\pm 0.03\) MPa) [11]. Therefore, there are two possible ways to enlarge the application fields of reticulated porous ceramics: by minimizing the weak point, and maximizing the strong point. To minimize the weak point, several approaches have been investigated to improve the compressive strengths of reticulated porous ceramics. For example, dip-coating [12], whisker-reinforcement coating [5], slurry rheology modification [13], multiple slurry coatings [14], centrifuge coating [15], and vacuum infiltration coating [16], have been introduced to enhance the compressive strengths of reticulated porous ceramics. The authors also previously reported that the compressive strength of the reticulated porous alumina can be improved by increasing the sintering temperature and/or number of alumina coating layers [17]. However, in this study, the authors attempted to maximize the strong point of reticulated porous ceramics, such as low cost, low density, and high permeability. Generally, if the PPI of reticulated porous ceramic approaches the value of 10, the preparation is easy. However, it is difficult to handle and use them practically owing to the high fragility, inevitably induced by the combination of high porosity, large pore size, insufficient number of strut walls, and inherent brittleness of ceramics. In contrast, if the PPI of reticulated porous ceramic approaches the value of 60, the preparation is difficult because completely coating the internal pores with ceramic slurry is difficult. It is also very difficult to remove the excess ceramic slurry and enable the formation of a thin ceramic coating over the struts of the sacrificial polymer template [1]. Consequentially several blocked inter-connected pores are formed, generated by the remnants of ceramic slurry, which should have been removed but remained after the squeezing process, this can severely degrade the two main advantages of reticulated porous ceramics: low density and high permeability. Hence, the authors introduced diatomite as a feasible candidate for reticulated porous ceramic innovatively because diatomite is an inherently porous and irregular natural low-cost material. Detailed descriptions and basic properties of diatomite have been comprehensively explained in previous reports [18; 19; 20; 21; 22; 23; 24; 25; 26; 27]. Recently, the authors reported several types of porous diatomite such as (1) uniaxially-pressed diatomite-based support layers for microfiltration [18; 19; 20; 21; 22; 23; 24; 25; 26; 27], (2) extruded diatomite-based support layers for microfiltration [28; 29], and (3) particle-stabilized diatomite foam with a bimodal pore structure [30].