Crystal Structures and Mechanism of Thermal Expansion of High Cordierite and Its Solid Solutions

Abstract

The crystal structure of high cordierite and that of high cordierite solid solutions containing either Mn or Ga or Ge were refined. The structural changes caused by substitutions and the characteristic features of deformations of each T1O4, T2O4 tetrahedron and MO6 octahedron were clarified. Thorough crystal chemical considerations led to a conclusion that the structure of Mn‐bearing solid solution at room temperature may be regarded as a model structure of high cordierite at an elevated temperature. On the basis of the thermal expansion mechanism derived from this consideration, the thermal expansion behavior of the solid solutions is presented.

Low temperature sintering of .ALPHA.-cordierite ceramics with low thermal expansion using Li2O-Bi2O3 as a sintering additive

“…In addition, lattice constants change in the sintered sample was found by adding the sintering additive. The values of lattice constants for the sample without the sintering additive were evaluated as a 0 = 0.9770 nm and c 0 = 0.9350 nm respectively, in exact agreement with the values reported by Ikawa et al 11) On the other hand, the obtained values of the sample with the sintering additive were a 0 = 0.9749 nm and c 0 = 0.9316 nm, which were considerably decreased compared with those of the samples without sintering additive. It suggests that Mg 2+ ions in the sintered sample might be substituted partially by Li + ions contained in the sintering additive.…”

“…1. Its density reaches a maximum of 2.53 g/cm 3 at 1050°C, which is 97% of its true density = 2.61 g/cm 3 . By adding the sintering additive, sufficiently densified ¡-cordierite ceramics was obtained at a considerably low temperature of 1050°C, at which the ceramics could be co-fired with electrode metals such as copper, gold, or 85 silver-15 palladium alloy.…”

“…A densification almost goes to completion at 1350°C, corresponding to the second shrinkage of the dilatometric curve. The density reaches finally a maximum of 2.53 g/cm 3 (relative density = 98%) at 1430°C. The true density of the sample was determined as 2.59 g/cm 3 by the conventional pycnometer method.…”

“…The density reaches finally a maximum of 2.53 g/cm 3 (relative density = 98%) at 1430°C. The true density of the sample was determined as 2.59 g/cm 3 by the conventional pycnometer method. On the other hand, for the sintered sample with the sintering additive, a densification is found to occur abruptly in the temperature range between 1000 and 1100°C, corresponding to the abrupt shrinkage from 1000°C observed in the dilatometric curve.…”

“…1) Cordierite ceramics is one of the candidates as a substrate material for microcircuit applications in electronic fields due to its low thermal expansion coefficient 2), 3) and low dielectric constant. 4), 5) We have succeeded in synthesizing cordierite ceramics by the conventional solid state reaction without melt-quenching and crystallization processes using highly pure, fine and reactive oxide powders, and sintering using fine pulverized powder without sintering additive.…”