Patent ID: 7288131

Claim:
A porous honeycomb structure comprising: a plurality of partition walls containing cordierite as a main component and comprising a porous ceramic having a porosity of 55 to 75% and an average pore diameter of 15 to 35 μm, characterized in that pores of the partition walls have a pore distribution represented by the following condition formula (1): Lr> 0.3 ×P/ 100+0.91 (1), “in the above condition formula (1), Lr means an average developed length ratio obtained by the following equation (2), and P means a porosity obtained from a total pore volume measured by a mercury press-in type porosimeter, assuming that a true specific gravity of cordierite is 2.52 g/cc:” Lr=Lo/ 4 (2), “in the above equation (2), Lo means an average developed length (an average value of lengths including the surfaces of the pores opened in the partition wall surfaces) obtained when using a surface roughness measuring instrument and checking optional ten places on the partition wall surfaces every 4 mm (straight line length ignoring presence of the pores opened in the partition wall surfaces) along the partition wall surfaces with a stylus, and Lr means the average developed length ratio,” and wherein the pores of the partition walls have a tomographic pore distribution represented by the following condition formula (3) in a partition wall thickness direction: X <−33 ×P/ 100+28 (3), “in the above condition formula (3), X denotes an average value of a primary component amplitude spectrum (F) and a secondary component amplitude spectrum (S) obtained from the following equations (4) and (5), and P means a porosity obtained from the total pore volume measured by the mercury press-in type porosimeter, assuming that the true specific gravity of cordierite is 2.52 g/cc:” F= √{square root over (X SRe (1) 2 +X SIm (1) 2 )}{square root over (X SRe (1) 2 +X SIm (1) 2 )} (4) “in the above equation (4), F denotes the primary component amplitude spectrum assuming k=1 in the following conversion equation (6), and X SRe (1) and X SIm (1) denote a real part and an imaginary part, respectively, assuming k=1 in the conversion equation (6):” S= √{square root over (X SRe (2) 2 +X SIm (2) 2 )}{square root over (X SRe (2) 2 +X SIm (2) 2 )} (5) “in the equation (5), S denotes the secondary component amplitude spectrum assuming k=2 in the following conversion equation (6), and X SRe (2) and X SIm (2) denote a real part and an imaginary part, respectively, assuming k=2 in the conversion equation (6),” X s ⁡ ( k ) = ∑ n = 0 255 ⁢ x ⁡ ( n ) ⁢ ( cos ⁢ ⁢ 2 ⁢ π ⁢ ⁢ k 256 · n - jsin ⁢ 2 ⁢ π ⁢ ⁢ k 256 · n ) ( 6 ) “in the conversion equation (6), X S (k) denotes a discrete Fourier transform, k denotes a degree, n denotes an integer of 0 to 255 indicating a divided position, when a partition wall section is divided into 256 in order in a thickness direction from a partition wall outermost surface portion (n=0), and X(n) denotes an area ratio occupied by a pore portion in a partition wall section region to the divided position of n to n+1.”