First, we succeeded in synthesizing and sintering cordierite ceramics via the solid state reaction route without the melting process by using single phase oxide powders. They are highly pure and fine amorphous silica, α -alumina and magnesia powders.Usually, cordierite ceramics was synthesized by a sol-gel route. Alternatively, it was prepared by a solid state reaction route using impure minerals such as talc, or the other which required melt-quenching and crystallization processes, though using single phase raw material powders. This is probably because single phase raw material powders especially alumina are deficient in reactivity. We have succeeded in synthesizing cordierite ceramics via the solid state reaction route without meltquenching and crystallization processes, by adopting a reactive α -alumina as one of raw material powders. As a result, cordierite formation of the starting raw material mixture went to completion at 1270°C. The mixture was sintered at 1430°C for 2 h. Its bulk density reached 98% theoretical, its flexural strength reached 243 MPa, which agreed with the best value already reported, its fracture toughness was 3.5 MPa·m 1/2 far larger than the reported value of 2.3 MPa·m 1/2 , its thermal expansion coefficient (from RT. to 800°C) is 1.8 × 10 -6 /K, which might be probably the ultimately smallest value experimentally expected and its dielectric constant was sufficiently small as 4.8 to 5.2 between extremely a wide frequency range, namely, from 1 MHz to 1 GHz with low loss tangent of < 6 × 10 -3 . These properties were found more excellent or at least comparable compared with the best properties reported already and suitable for substrate materials on micro-electronic applications.

Low‐temperature sintering of high‐strength β‐eucryptite ceramics with low positive coefficient of thermal expansion (CTE) was attained using Li2O–GeO2 sintering additive. High‐purity β‐eucryptite could be synthesized using high‐purity and fine amorphous silica, α‐alumina, and lithium carbonate powder mixture at 950°C via the solid‐state reaction route. Accordingly, the mixture was calcined at 900°C, pulverized, compacted, and sintered at 1020°C for 2 h with the sintering additive. The sintering temperature could be lowered by about 300°C, compared with the sintering temperature previously reported. The relative density of the sintered sample reached 99% of true density. Its flexural strength and indentation fracture toughness were 214 MPa and 2.5 MPa·m1/2, respectively. Its CTE (from room temperature to 800°C) was 1.2 × 10–6/K. Its dielectric constant was 5.5 with a loss tangent of 7.5 × 10–3. However, prolonged sintering time resulted in large negative CTE and mechanical weakness in the sintered samples. Microcracks were introduced with prolonged sintering time, which caused their large negative CTE with mechanical weakness.

Low temperature sintering of ¢-spodumene ceramics with low coefficient of thermal expansion (CTE) was attained using Li 2 O Bi 2 O 3 sintering additive. High purity ¢-spodumene could be synthesized at 1150°C using high purity and fine amorphous silica, £-alumina and lithium carbonate powder mixture via the solid state reaction route. The mixture was calcined at 800°C, pulverized, compacted, and sintered with or without the sintering additive at 8001350°C for 2 h. The relative density reached 95% for the sample sintered with 3 mass % of Li 2 OBi 2 O 3 additive at 1050°C for 2 h. As a result, sintering temperature could be lowered about 200°C by adding the sintering additive, compared with the sintering temperature previously reported. The flexural strength of the sample sintered with 3% of Li 2 OBi 2 O 3 additive at 1050°C for 2 h was 118 MPa. Its CTE (from R.T. to 800°C) was 0.2 © 10 ¹6 /K. Its dielectric constant was 8.2 with loss tangent of 1.4%.

The simplified one‐step hydrothermal synthesis, in which SiO2 is directly reacted with aqueous NaOH in the presence or absence of tetrapropylammonium bromide (TPABr) and tetrabutylammonium bromide (TBABr) as the template compound, was investigated. The reaction in the absence of the template compounds leads to the production of pure magadiite, whereas pure Si‐ZSM‐5 is produced by the reaction in the presence of TPABr. On the other hand, crystalline magadiite/Si‐ZSM‐11 composites are synthesized by the reaction in the presence of TBABr. Furthermore, for the composites, the particle sizes of the magadiite and Si‐ZSM‐11 may be influenced by the TBABr concentrations. It was also found that the compositions of magadiite and Si‐ZSM‐11 in the composites can be controlled by regulating the NaOH concentrations.