Naojiro Yoshida

Variation of the gel region with heat-treatment in the B2O3-Na2O-TiO2 system compared with the melt-quenched glass region

Variation of the gel region with heat-treatment and variation of the melt-quenched glass region with cooling rates were compared for the B2O3-Na2O-TiO2 system. Gels were prepared by the sol-gel method without catalyst using boron tributoxide (B(OBu)3) sodium methoxide (NaOCH3) and titanium tetraisopropoxide (Ti(OPr)4). The gel region was in the composition range B2O3 = 0 to 90, Na2O = 0 to 60, and TiO2 = 0 to 100 mol % at 50 ° C. The crystalline phases precipitated were boric acid (H3BO3), sodium metaborate hydrate (NaBO22H2O), and sodium hydroxide (NaOH), or sodium carbonate (Na2CO3). A 500 °C, heat treatment for 2 h reduced the gel regions to a composition range of B2O3 = 50 to 90, Na2O = 10 to 30 and TiO2 = 0 to 20 mol %, but treatment at 800 ° C produced melts which became glassy upon cooling. On the other hand, a twin-roller method produced a wide range of glass region which includes a high concentration of TiO2 up to 70 mol %. The as-prepared gel region was found to correspond fairly well to the twin-roller glass region and the thermally most stable gel region was close to the air-quenched glass region. It was speculated that the B2O3- or Na2O-rich composition had not gelled because of the high water solubility of these gels.

Behaviour of Andalusite Crystals in Molten Glass

紅石柱はケイ砂中の重鉱物としてガラス原料に混入するが, その形態は鉱床の型式によって異なる. この差異は紅柱石ガラスストーンの発生率に影響するが, びんガラス中には常に発生している. びんガラスに発生した多数のガラスストーンから紅柱石ストーンを収集するとともに単結晶の紅柱石とカレットによる反応試験を行った.その結果紅柱石の分解には二つの型が認められ, 繊維状のムライト結晶集合体のみを生成する場合と, その外側を針状のコランダム結晶を含むガラスの層が包む場合とがある. カレットとの反応試験から紅柱石の分解速度定数を定め, 活性化エネルギーを計算すると128kcal/molとなる. 槽窯内での紅柱石の挙動を反応試験とガラスストーン中の分解層の比較及び分解速度定数から考察すると大部分の紅柱石は槽窯内の1300°-1350℃の温度域を通過したことを示す.

Mineralogical Studies of Izumlyama Pottery Stone

Izumiyama pottery stone occurs in the vicinity of Arita-cho locating in north Kyushu area. The mass deposits composed of quartz and sericite containing an extremely small amount of pyrite and alum, and partly bring with orthclase, albite and kaolinite.The radial distribution of companion minerals form approximetely a concentric circles, the center of the mass being rich in feldspar near the surface, and in sericite near the center. These change reflects on the thermal properties of the stone.The chemical composition of sericite belongs, in this case, to the type in which the amount of the exchange of K2O by H2O is small. Hence the pottery stone has low refractivity.