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Abstract: Japanese traditional red overglaze enamel decorations on porcelain known as akae are produced using lead‐containing frits, leading to a problem of lead release. Although many lead‐free frits have been developed, a well‐colored akae has not yet been realized, mainly because of no information on the reaction between lead‐free frits and hematite during the heating process in akae production. To reveal the effect of such interaction between the frits and hematite in akae on the color tone, various akae test pieces were prepared and investigated. On using low‐melting‐point lead‐free alkali borosilicate glass system, which contain zinc oxide, the formation of zinc ferrite proceeds simultaneously with the dissolution and particle growth of hematite in the frit melt. The particle growth rate due to dissolution and precipitation in the frit melt is faster than that due to sintering of particles caused by heat treatment of hematite powder in dry process. The dissolving capacity and promoting effect of particle growth depended on frit compositions. We also showed that the composition of akae glass layer varies because of ions diffusing from the glaze layer. Compositional changes in the akae glass could strongly affect the reactivity between the frits and hematite, resulting in variation in the color tone, the crystal phases formed, and their segregated states. [ABSTRACT FROM AUTHOR]

The formation of a plumbate network in binary lead silicate glasses was examined based on the leaching behavior of Pb2+ in lead silicate glasses over a wide composition region. The effective diffusion coefficient of Pb2+ at 40°C was on the order of 10−17 m2/s for PbO<35 mol% glasses, and increased three orders of magnitude for 35–50 mol% PbO contents. Such a steep composition dependence is considered to be because of changes in the medium or longer range structure. That is, it is proposed that the plumbate network forms a percolative 3D network in the composition region to form diffusion paths for the lead ions. In addition, the present results indicate that the lead ion exists as a network former over the entire glass forming composition range of the binary silicate glasses. [ABSTRACT FROM AUTHOR]

Structure ofxPbO–(100− x)SiO2 (x=25–89) glasses has been investigated by means of the X-ray and neutron diffraction and29Si MAS NMR measurements. In the radial distribution functions of all the glasses, the Pb–O correlation was observed at 0.23 nm, indicating that the PbO3 trigonal pyramids units do exist in the whole glass forming composition range. Furthermore the existence of the first Pb–Pb correlation at∼0.385 nm in the whole composition range suggests that the basic structural unit is considered to be a Pb2O4 unit, which consists of the edge-shared PbO3 trigonal pyramids. These results strongly imply that the Pb2O4 units participate in the glass network constructed by SiO4 tetrahedra even at low PbO content. Differing from other lead-containing glass systems, these structural characteristics of Pb ions in the PbO–SiO2 glass system are responsible for the extremely wide glass-forming region. [ABSTRACT FROM AUTHOR]

Investigates the structure of PbO-B[sub 2]O[sub 3] glasses using X-ray diffraction and B MAS nuclear magnetic resonance techniques. Structural models of lead borate glass; Impact of PbO content on lead atom coordination; Formation of glass networks in higher-PbO glasses; Distribution of lead ions in the borate network; Limitation in the glass-forming region of binary glasses.