Paper Journal of the Ceramic Society of Japan 101 [10] 1101-1106 (1993) Phase Equilibria and Properties of Glasses in the Al2O3-Yb2O3-SiO2 System Yuichiro MURAKAMI and Hirokazu YAMAMOTO AdvancedTechnology Research Center, Mitsubishi Heavy Industries, Ltd., 1-8-1, Sachiura,Kanazawa-ku, Yokohama-shi 236 Al2O3-Yb2O3-SiO2系 の 相 平 衡 と ガ ラ ス の 性 質 村 上 勇一 郎 ・山本 博 一 三菱重工業 (株)基 盤技術研究所, 236横 浜市金沢区幸浦1-81 [Received May 10, 1993; Accepted July 13, 1993] The phase diagram and properties of glasses of the highest softening temperature in the rare-earth-con Al2O3-Yb2O3-SiO2 system were studied by X-ray diffrac taining aluminosilicate glasses. However, the glass tion, differential thermal analysis, scanning electron forming region and details of the properties of this microscopy and infrared absorption spectroscopy. The glass is still unknown. lowest solidus temperature in this system was 1500•Ž. Regarding the phase diagram of the 3-component The glass-forming region was determined by quench Al2O3-Ln2O3-SiO2 systems, phase diagram of the ing specimens after melting in an infrared image fur Al2O3-Y2O3-SiO2 system has been already repor nace. The glass transition temperature, the onset and ted.9)-11) Phase diagrams of the systems containing peak temperatures for crystallization were investigat ed as a function of composition and found to increase other rare-earth oxides have not been studied. with increase in SiO2 concentration. The activation Although phase diagrams of the rare-earth-containg energy for crystal growth in glasses tended to attain a systems are suggested to be similar to each other, maximum at the eutectic composition. It is suggested the liqudus and solidus temperatures of them are ex that Yb ion is mainly a network modifier in glasses. pected to be different depending on the kinds of rare The solidus temeperature of this system was compared earth elements. with those of the systems containing other rare-earth In this study, phase equilibria of the Al2O3-Yb2O3 oxides. - SiO2 system and the properties of glasses in this sys tem have been investigated, and the solidus tempera Key-words: Phase diagram, Al2O3-Yb2O3-SiO2 system, ture of this system has been compared with those of Glass, Glass forming region, Crystallization, Infrared spec tra, Solidus temperature, Rare-earth the other rare-earth-containing systems to clarify the difference of phase diagrams among them. 2. Experimental procedures 1. Introduction 2.1 Preparation of specimen and phase dia The Al2O3-Ln2O3-SiO2 systems (Ln=rare-earth gram element) produce the rare-earth-containing alumino The starting materials used were Al2O3 (purity: silicate glasses with high softening temperature, 99.9%, averaged particle size: 0.96ƒÊm) , Yb2O3 high elastic modulus and high alkaline urability,1)-7) (99.9%, 1.0ƒÊm) and SiO2 (99.99%, 0.94ƒÊm). and have attracted attention as a possible application These powders were mixed in ethanol to a given com to laser glass,1) glass fiber for fiber reinforcement,3) position. This mixture was dried and pressed into a radiotherapy,5) etc. compact of 10•~10•~40mm under a pressure of 70 Shelby and Kohli4) have studied the properties of MPa and then calcined at 1400•Ž for 1h. The cal these glasses and shown that the glass transition tem cined products were melted in an infrared image fur perature and the softening temperature tend to rise nace with a halogen lamp as the light source and as the radius of rare-earth ion decreases. As an ori quenched to prepare specimens. gin of this phenomenon, since the rare-earth ion is The liquidus and the solidus temperatures of each suggested to act as a network modifier in glasses, it specimen were determined by using a self-made is considered that the field strength of rare-earth ion differential thermal analyzer (DTA) during heating increases with decrease in ionic radius and that the at a rate of 5•Ž/min up to the maximum heating tem bond strength between rare-earth ion and surround perature of about 1700•Ž. In this analyzer, specimen ing oxygen may increase.4),7) In another glass system was embedded in a high purity alumina crucible with containing rare-earth element, Li et al.8) have report 10mm in diameter and 30mm in length and the tem ed that the rare-earth ion acts as a network modifier perature of specimen was measured directly by the in the BaO-Y2O3-SiO2 glasses. Pt 40%Re-Pt20%Re thermocouple. To estimate Because the ionic radius of Yb is smaller than the error of measuring temperature, the eutectic tem those of other rare-earth elements, the Al2O3-Yb2O3 perature of MgO-SiO2 and Al2O3-Y2O3-SiO2 sys SiO2 system is expected to produce glasses with the tems10),11) was analyzed by this analyzer and it was 1101 1102 Phase Equilibria and Properties of Glasses in the Al2O3-Yb2O3-SiO2 System found that the accuracy of temperature was •}2•Ž. In order to determine the phase diagram at 1550•Ž, specimen was heat-treated at 1550•Ž for 0.5h in a high purity alumina crucible and then quen ched to prepare specimen for X-ray analysis. The specimen, which had small quantity of liquid phase and no softening due to melting at 1550•Ž, was fur ther heat-treated at the same temperature for a maxi mum of 10h until the phase equilibrium is confirmed to be attained by the X-ray analysis. These specimen were cut and polished and then analyzed y the X ray diffraction to determine the crystal structure and to identify the phases. The phases at other tempera Fig. 1. Liquidus temperature of the 2-component system as a ture were analyzed by the same method using speci function of Al2O3 content; men quenched from each temperature. The micros (a) (Yb2O3)37.9(SiO2)62.1-(Al2O3)70.2(SiQ2)29.8 tructures of specimens were analyzed y scanning ,(b) (Yb2O3)33.3(SiO2)66.7-(Al2O3)60(SiO2)40, (c) (Yb2O3)26.2(SiO2)73.8-(Al2O3)57.9(SiO2)42.1, electron microscopy (SEM) and the X-ray microanal (d) (Yb2O3)22.1(SiO2)77.9-(Al2O3)52.3(SiO2)47.7, ysis (EPMA). (e) (Yb2O3)19.9(SiO2)80.1-(Al2O3)49(SiO2)51. To compare the solidus temperatures of the (f) (Yb2O3)18.6(SiO2)81.4-(Al2O3)46.9(SiO2)53.1. present system to those of the other rare-earth con (g) (Yb2O3)15.7(SiO2)84.3-(Al2O3)41.9(SiO2)58.1, taining systems, the solidus temperature of speci (h) (Yb2O3)13.2(SiO2)86.8-(Al2O3)37.1(SiO2)62.9, (i) (Yb2O3)12.3(SiO2)87.7-(Al2O3)35.2(SiO2)64.8, mens with (Al2O3)20(Ln2O3)20(Si2O3)60 composition (j) (Yb2O3)9.2(SiO2)90.8-(Al2O3)28.2(SiO2)71.8. were also determined y DTA, where Ln represents Dy, Er, G, La, Nd, Sm, Y and Yb. Purity and averaged particle size of the rare-earth oxides are Al2O3 (A) , Yb2O3 (Y) and liquid phase (L). 99.9% and 1ƒÊm, respectively. The solidus tempera Figure 1 represents the composition dependence tures of the specimens below 1400•Ž were deter of liquidus temperature in the ten types of 2-compo mined y a Rigaku TAS200 system differential ther nent systems (Yb2O3)100-p(SiO2)p-(Al2O3)100 -q mal analyzer (accuracy of temperature: •}1•Ž). (SiO2)q determined by DTA. These results can clari 2.2 Preparation of glasses and properties fy the region of the existence of liquid phase at high The calcined products described above were melt temperature. The composition dependence of liqui ed in an infrared image furnace and quenched to pre dus temperature in each system attained a minimum. pare glasses and then the glass-forming region was An arrow in Fig. 1 depicts a composition with the determined. The glass transition temperature (Tg) lowest liquidus temperature in this system, i.e. the and the onset and peak temperatures of crystalliza ternary eutectic composition (Al2O3)23 .6(Yb2O3)10.3 tion (Tc and T0, respectively) were determined by (SiO2)66.1), where its eutectic temperature is DTA (Rigaku TAS200 system) at a heating rate of 1500•Ž. 5•Ž/min as a function of composition. The heating Phase boundary of the liquid phase at 1550•Ž was rate of DTA was varied in a range from 3 to 10•Ž/ determined by plotting the compositions where the li min and the activation energy for crystal growth in quidus temperature becomes 1550•Ž in the liquidus glasses was determined by analyzing the heating temperature vs. composition curves shown in Figs. rate dependence of T0. The Fourier transform in 1, 4, 5 and 6, and the phase diagram was determined frared absorption spectra of glasses were also meas by analyzing the crystal structure of specimens quen uredure d to clarify the role of rare-earth ion in glasses y ched from 1550•Ž by X-ray diffraction. The phase di a JEOL FT-IR spectrophpotometer. agram of the Al2O3-Yb2O3-SiO2 system at 1550•Ž o btained in this work is shown in Fig. 2. Liquid phase 3. Results and discussion does not appear in a region of higher Yb2O3 composi 3.1 Phase equilibria in Al2O3-Yb2O3-SiO2 sys tion than that of the straight line between D and G in tem Fig. 2. The AY phase (Al2Yb4O9) was confirmed to The phase diagrams established in this study were exist at 1550•Ž by the X-ray analysis, which is in of the 3-component Al2O3-Yb2O3-SiO2 system at agreement with the phase diagram of the 2-compo 1550•Ž and of the three types of 2-component sys nent Al2O3-Yb2O3 system by Mizuno and Nogu tems Yb2Si2O7-Al6Si2O13, Al1 .25Yb0.75O3-SiO2 and chi,12) Al1 .44Yb0.56O3-Si02.