Synthesis of ZrSiO4 and Coesite in SiO2-ZrO2 System Under High Pressure

Synthesis of ZrSiO4 and Coesite in SiO2-ZrO2 SystemUnder High PressureXUE Yan-Feng,XU Da-Peng,ZHANG Guang-qiang,ZHOU Xian-feng,DING Zhan-hui,LIU Xiao-mei and SU Wen-hui1.College of Physics, Jilin University, Changchun 130012,P. China; 2,Center for the Condensed-MatterScience and Technology, Harbin Institute of Technology, Harbin 150001, P.R.China;3.International Center for Materials Physics ,Chinese Academy of Sciences ,Shenyang 110015,P.R.ChinaAbstract ZrSiO4 and coesite were obtained under high-pressure and high-temperature from the nano precursor of α-SiO2 and ZrO2.XRD and Raman measurements indicate that ZrSiO4 was formed at a temperature higher than 920℃ under a pressure of 3.6 GPa. As the pressure increased to 3.9 GPa, the ZrSiO4 formation temperature was reduced to 815℃. The formation temperature for coesite was 990℃under 3.9 GPa. The lower formation temperature for ZrSiO4, as compared to that for coesite, provided an experimental evidence that the coesite in the Earth’s surface usually occurs as inclusions in ZrSiO4.Keywords ZrSiO4;Coesite; High pressure synthesis; Mechanical ball milling1 IntroductionZrSiO4is widely used in ceramic, foundry, and refractory industries owing to its high thermal conductivity, chemical stability, and the ability to accommodate a number of dopant ions[1]. Coesite is one of the high-pressure polymorphs of SiO2, and natural coesite usually occurs as inclusions in zircon (ZrSiO4) from all types of gneiss[2].Based on the pressure and temperature of the experimental transformation of α-SiO2to coesite under high static pressure, a hypothesis[3]of plate subduction-exhumation has been presented to explain the formation of the coesite existing in the Earth’s crust in zones of buildup of the Earth’s plates. However, some experiment results indicate that there exists another possible formation mechanism for the coesite in the Earth’s crust[4].As is well known, the coesite is metastable and is easily transformed to α-SiO2 under ambient pressure. The fact that the coesite usually occurs as inclusions in ZrSiO4in the Earth’s crust implies that zircon(ZrSiO4)is the best vessel for coesite. Thus, the investigation of the formation of coesite accompanying ZrSiO4 under high pressure is very helpful for understanding the formation mechanism of the coesite in the Earth’s crust. We adopted a laboratory method combined with mechanical ball milling(MBM)and high static pressure suggested by Su et a1.[4]to prepare ZrSiO4and coesite, and compared their formation temperatures.2 ExperimentalThe raw materials used in the experiment were the mixture of α-SiO2and monoclinic ZrO2(m-ZrO2) with a molar ratio of 3：1.A P6 type mechanical ball mill was used for MBM. The rotating speed of the ball-milling vial was 350 r/min. The samples were first milled for 20h, then put into a boron nitride ampoule, which was encased in a graphite crucible, and pressed to the desired pressure of 3.6 and 3.9 GPa for 30 min at different temperatures. A belt-type two-anvil press was used for studying the crystallization of nano samples.A Rigaku D/max-rA 12 kW X-ray diffractometer with Cu Ka radiation was used to recordthe XRD pattern. A JY-HR 800 high-resolution Raman spectroscope was used(λex=632.8 nm). The wave number was corrected by the characteristic peak of single-crystal Si at 520 cm-1; the resolving power was 1 cm-1.3 Results and Discussion3.1 Phase Transformation of ZrO2 Treated by MBMFig.1 shows the XRD patterns of the mixture of α-SiO2 and m-ZrO2 after being treated for 20h by mechanical ball milling. All diffraction peaks of ZrO2, and SiO2 were broadened and the amorphous peak background was observed in a diffraction angle(2θ) range of about 20°to40°, indicating that a part of the sample has started amorphization. The diffraction peaks of α-SiO2 were still observed. Therefore, it in dicates that α-SiO2 was stable during the MBM process. On the other hand, a new peak at 30.2°was observed. The analysis shows that the (101) diffraction peak of tetragonal ZrO2(t-ZrO2) indicates that part of m-ZrO2was transformed into t-ZrO2. The transformation of m-ZrO2 to t-ZrO2 should be related to the reduction of the grain size of ZrO2[5]. Therefore, the effects of MBM were grain refinement and amorphization of the sample.Fig.1 XRD patterns of the samplesa. Initial a-quartz；b. initial m-ZrO2；c. sample milled for 20 h.3.2 Synthesis of ZrSiO4 Under High-pressure and at High-temperatureZircon has a tetragonal structure with the space group I41/amd (a=0.6607 nm and c=0.5981 nm)[6]. The ideal structure consists of chains of edge-sharing, altemating SiO4 tetrahedra, and ZrO8 triangular dodecahedra extending parallel to the crystallographic c axis. The formation temperatures reported for ZrSiO4 synthesized by solid state reaction under ambient condition were above 1 400 ℃[7]. Sol-gel techniques are mostly used to achieve high purity and very reactive powders, which can depress the formation temperature effectually[8].The XRD patterns of samples synthesized under 3.6 GPa are illustrated in Fig.2. It can be seen that the XRD pattern of the sample prepared at 630℃ is the same as that of the ball milling mixture(Fig.1 curve c). NO ZrSiO4 product was formed. As the temperature increased to 920℃, the diffraction peaks of ZrSiO4 appeared. The formation temperature for ZrSiO4 under pressure 3.6 GPa was considerably lower than that reported for solid state reactions[7] under ambient conditions. When the temperature was increased to 1060℃, all the diffraction peaks of m-ZrO2 disappeared, but the diffraction peaks of t-ZrO2still remained. The grain size of ZrO2 did not diminish, andgrew slowly under high pressure and at high temperature, which can be seen from the XRD results. This suggests that there should be another mechanism governing the formation of Si-O-Zr chemical bonds[9-11]. α-SiO2was stable under 3.6 GPa because superfluous α-SiO2was not transformed into coesite even at a temperature as high as 1200℃.Fig. 2 XRD patterns of the samples synthesized under 3．6 GPa at different temperaturesa. 630℃；b. 920℃；e. 1060℃；d. 1200℃．Itoh[12] suggested that the formation of ZrSiO4 has two processes under ambient conditions：α-SiO2+t-ZrO2→ZrSiO4 (1)or c-SiO2+t- ZrO2→ZrSiO4 (2)Reaction(1) has priority over reaction(2).In this experiment, no other phase of SiO2 appeared and no m-ZrO2 remained under 3.6 GPa suggesting that reaction(1) has priority over reaction(2) even under high pressure. Fig.3 shows the XRD patterns of the samples obtained under 3.9 GPa at different temperatures. When the temperature was 990℃, the product still containedt-ZrO2[13], but the diffraction peaks of coesite appeared. When the temperature was increasedto1200℃, the diffraction peaks were only contributed from ZrSiO4 and coesite, showing that the reaction is complete.Fig. 3 XRD patterns of the samples synthesized under 3.9 GPa at different temperaturesa. 815℃；b. 990℃；c. 1200℃．The “fingerprint” effect of Raman spectroscopy has been widely used to study the phase structures of materials, especially those synthesized under high-pressure and high-temperature[l4,15]. The room-temperature micro-Raman spectra of samples are illustrated in Fig.4. Generally, ZrSiO4 has 12 Raman vibrational modes: 2A lg+4B1g+B2g+5E g[16]. Here, we observed four Raman modes.A strong υ3 peak near 1007 cm-1 is assigned to anti-symmetric stretching of the SiO4 group and has B1g symmetry. The other three peaks at about 974,439, and 355 cm-1 are attributed to the Si-O stretching band(υl: symmetric stretching) with A1g symmetry, the bending mode υ2 with A1g symmetry, and the υ4 mode with E g symmetry, respectively. The observation of the four Raman peaks for all the samples prepared suggests the formation of ZrSiO4 under high pressure and at high temperature.Fig．4 Raman spectra of the samples synthesizedunder high-pressure and high-temperaturea. 3.6 GPa, 1060℃;b. 3.6 GPa, 1200℃;c. 3.9GPa, 990℃;d. 3.9GPa, 1200℃.3.3 Transformation of α-SiO2 to CoesiteIn this experiment, the transformation of α-SiO2 to coesite occurred only under 3.9 GPa (Fig.3 curves b and c). In the Raman spectra shown in Fig.4, the peak at 47l cm-1 observed for samples a and b is assigned to the A1vibration mode of α-SiO2, a characteristic Raman peak of α-SiO2. As the pressure increased to 3.9 GPa, the peak at 471 cm-1 was not observed, while the characteristic Raman peaks of coesite near 524cm-1(sample c) and 526 cm-1(sample d)appeared. This implies that α-SiO2 was transformed into coesite, which is consistent with the analysis of the XRD results.It should be noted that the transformation temperature and me pressure for α-SiO2 to coesite are respectively higher than the previous reported values for pure α-SiO2[4]. The reasons we suggest are: (1) the starting materials used in this study were a mixture of α-SiO2 and ZrO2. ZrO2 may affect the process of amorphization of α-SiO2 during MBM and there was no intermediate metastable phase[4] of α-SiO2 induced by lower-energy MBM. The intermediate metastable phase of α-SiO2 during the process of MBM has been considered to be the prerequisite condition for producing coesite by a lower condition of high-static-pressure-induced crystallization of amorphous α-SiO2. (2)ZrSiO4 is easily formed under relatively low pressure and temperature, which restrains the transformation of α-SiO2 to coesite.References[1]sigh R.N., J.Am.Ceram.Soc.,1990,73(8),2399[2]Zhang A.D., Liu L., Sun Y., et al., Chin. Sci. Bull., 2004,49(22),2335[3]Bohlen S.R., Boettcher A.L., J. Geo. Res., 1982,87,7073[4]Su W.H., Liu S.E., Xu D.P., et a1.,Physical Review B, 2006,73,144110[5]Garvie R.C., Goss M.F., J. Mater. Sci., 1986,21,1253[6]Hazen R.M., Finger L.W., J. Geo. Res., 1979,84,6723[7]Tartaj P., Sevna C.J., Moya J.S., et al., Mater Sci., 1996,31,6089[8]Chakrabarti S., Sada J., Biswa A., J. Mater. Sci. Left., 1992,11(16),1124[9]Sirarat K., Piyasan P., Warapom T., et al., Mater. Proc. Teehno1.,2003,136,186[10]Chen S.G., Yin Y,S., Wang D.P., et al., Chin. Ceram. Soc., 2004,32(6),666[11]Xie C., Xu Z.L., Yang Q.J., et a1., Chem. Res. Chinese Universities,2005,21(I),48[12]Itoh T., J Crystal Growth, 1992,125(2),223[13]Zhang F., Hua W. M., Chem. J. Chinese Universities,1999,20(6),909[14]Richet P.,Nature, 1988, 331, 56[15]Li L.P., Li G.S., Che Y.L., et a1.,Chem.Mater.,2000,12,2567[16]Dawson P., Hargreave M.M., Wilkinson G.D.,J.Phys.C,1971,4(2),240 .ZrSiO4在高压力下SiO2氧化锆系统中的柯石英的合成XUE Yan-Feng,XU Da-Peng,ZHANG Guang-qiang,ZHOU Xian-feng,DING Zhan-hui,LIU Xiao-mei and SU Wen-hui1.大学的物理, 吉林大学, 长春,130012,体育中国；2.凝聚物质研究中心科学与技术, 哈尔滨研究所的技术,哈尔滨,150001号；3.国际中心材料物理, 中国科学院, 沈阳,110015,P.R.China摘要ZrSiO4和柯石英取自高压和高温下的α-SiO2纳米前体和ZrO2。