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1.
Glass in the MgO-Li2 O-A12 O3 -SiO2 system was observed to crystallize readily at temperatures from 700° to 900°C. The primary crystalline phase evolved was Li2 Si2 O5 , and the secondary phase evolved was Li2 SiO3 . The glass was amorphous after heating in air at 1050°C for 30 min. The addition of 0.5 wt% SiC powder resulted in the crystallization of Li2 SiO3 during heating in air at 1050°C for 30 min. It was suggested that the difference in crystallization behavior with Sic addition was due to dissolution of Sic into the oxide glass. 相似文献
2.
Antonio Pedro Novaes de Oliveira Tiziano Manfredini Luisa Barbieri Cristina Leonelli Gian Carlo Pellacani 《Journal of the American Ceramic Society》1998,81(3):777-780
Sintering and crystallization of a 23.12 mol% Li2 O, 11.10 mol% ZrO2 , 65.78 mol% SiO2 glass powder was investigated. By means of thermal shrinkage measurements, sintering was found to start at about 650°C and completed in a very short temperature interval (Δ T similar/congruent 100°C) in less than 30 min. Crystallization took place just after completion of sintering and was almost complete at about 900°C in 20 min. Secondary porosity prevailed over the primary porosity during the crystallization stage. The glass powder compacts first crystallized into lithium metasilicate (Li2 SiO3 ), which transformed into lithium disilicate (Li2 Si2 O5 ), zircon (ZrSiO4 ), and tridymite (SiO2 ) after the crystallization process was essentially complete. The microstructure was characterized by fine crystals uniformly distributed and arbitrarily oriented throughout the residual glass phase. 相似文献
3.
Lothar Wondraczek Joachim Deubener Scott T. Misture Regina Knitter 《Journal of the American Ceramic Society》2006,89(4):1342-1346
The formation of crystalline Li4 SiO4 and Li2 SiO3 from lithium orthosilicate glasses has been studied by means of in situ high-temperature X-ray diffraction. The first phase that crystallizes from the glass could not be identified, but was followed by the transformation to crystalline orthosilicate and metasilicate. Orthosilicate formation was tracked at temperatures between 600° and 650°C, whereas at higher temperatures, the formation of a small amount of crystalline metasilicate occurs. The kinetics of the initial phase of both crystallization processes are described by the Avrami–Erofeev equation, resulting in activation energies of 90 kJ/mol for the formation of the unidentified phase, and 68 kJ/mol for the formation of Li4 SiO4 . The rate constant for the crystallization of the unidentified phase is 0.014 s−1 at 510°C, equaling that of the orthosilicate formation at 630°C. After isothermal heat treatment for 100–800 s, depending on temperature, 80%–95% of the sample is crystallized and further crystallization is controlled by diffusion in both cases. 相似文献
4.
Strength and Microstructure in Lithium Disilicate Glass-Ceramics 总被引:1,自引:0,他引:1
MARCUS P. BOROM ANNA M. TURKALO ROBERT H. DOREMUS 《Journal of the American Ceramic Society》1975,58(9-10):385-391
The effect of heat treatment on the microstructure of Li2 O-Al2 O3 ·SiO2 glass-ceramics which contain crystals of either Li2 SiO3 , Li2 Si2 O5 , or both was investigated quantitatively. Strength determinations for abraded rods were correlated with heat treatment on the basis of both size and distribution of crystals and the type and amount of crystal phases present. The presence of Li2 Si2 O5 crystals enhanced the strength, whereas the presence of Li2 SiO3 crystals did not change the strength of the abraded parent glass. The interrelation between strength and microstructure is discussed. 相似文献
5.
Bo Zhang T Allan J. Easteal Neil R. Edmonds Debes Bhattacharyya 《Journal of the American Ceramic Society》2007,90(5):1592-1596
A sol–gel process is described for preparation of crystalline lithium disilicate (Li2 Si2 O5 ) from tetraethylorthosilicate and lithium ethoxide. The glass network structure and crystallinity resulting from heat treatment at temperatures from 150° to 900°C were investigated by nuclear magnetic resonance, X-ray diffraction, and differential scanning calorimetry/thermogravimetric analysis. Q3 structural units (SiO4 tetrahedra with three bridging oxygen atoms) formed in the amorphous gel at a low temperature (≤150°C) persist to elevated temperature (≤500°C) and directly transform to crystalline Li2 Si2 O5 at about 550°C. The heating schedule slightly affects the crystalline phase transformation. 相似文献
6.
The crystallization mechanism in a modified Li2 O-Al2 O3 -SiO2 glass containing P2 O5 nucleating agent was investigated by transmission electron microscopy, X-ray diffraction, and differential thermal analysis. During an initial 1000°C treatment P2 05 and Li2 O react to precipitate Li3 PO4 crystallites. At lower temperatures cristobalite, lithium metasilicate, and lithium disilicate crystallize by epitaxial growth on those Li3 PO4 crystallites. Crystallographic orientation relations for epitaxy were determined by electron diffraction, and lattice misfits were found to be in the range –5.3 to +3.8%. These results provide the first direct proof that glass-ceramics can crystallize by epitaxial growth on heterogeneous nuclei formed from intentionally added nucleating agents. 相似文献
7.
Christophe Téqui Paul Grinspan Pascal Richet 《Journal of the American Ceramic Society》1992,75(9):2601-2604
The heat capacities of liquid Li2 SiO3 and Li2 Si3 O7 have been determined through drop calorimetry measurements to complement available data on lithium, sodium, and potassium silicate melts. The composition and temperature dependences of the heat capacity depends specifically on the nature of the alkali element, indicating that the temperature-induced structural changes that take place in the melts are specific. The properties of crystalline Li2 SiO3 have also been determined above 298 K. The enthalpy of fusion at 1474 K is 71.3 ± 0.6 kJ/mol, in agreement with previous measurements. In contrast to other silicate compounds, and especially the isostructural crystal Na2 SiO3 , Li2 SiO3 shows almost no premelting effects. 相似文献
8.
A. R. WEST 《Journal of the American Ceramic Society》1978,61(3-4):152-155
Phase relations in the system Li2 O-CaO-SiO2 were studied by the quenching method. Four stable ternary compounds were found (Li2 Ca3 Si6 Ol6 , Li2 Ca4 Si4 O13 , Li2 Ca2 Si2 O7 , and Li2 CaSiO4 ) as well as phase Y , which is probably a metastable orthosilicate fairly close to Ca2 SiO4 in composition. X-ray powder data are given for the new phases. Eleven subsolidus compatibility triangles and thirteen liquidus invariant points were located. Melting relations were determined for that part of the system bounded by Li2 SiO3 , Li2 CaSiO4 , Ca2 SiO4 , and SiO2 . The join Li2 SiO3 -CaSiO3 is binary. 相似文献
9.
Angelo Montenero Franco Ugozzoli Dino Schiroli Guglielmina Gnappi D. Camillo Giori L. David Pye 《Journal of the American Ceramic Society》1989,72(6):1066-1069
Glasses of composition Na2 O·2SiO2 containing iron oxide are obtained by the gel technique. The results show that the iron atoms accelerate the formation of the glass, whereas when they are present in low percentage (∼2%), the temperature necessary to obtain the glass phase is higher. During heat treatment at 250°C, two silicates are formed: Na2 SiO3 and Na4 SiO4 . When the iron content is low, they change at 650°C into Na2 Si2 O5 , but when the iron content is higher (∼6%), this silicate does not form and the system becomes vitreous. 相似文献
10.
An intimate Ba-Al-Al2 O3 -SiO2 powder mixture, produced by high-energy milling, was pressed to 3 mm thick cylinders (10 mm diameter) and hexagonal plates (6 mm edge-to-edge width). Heat treatments conducted from 300° to 1650°C in pure oxygen or air were used to transform these solid-metal/oxide precursors into BaAl2 Si2 O8 . Barium oxidation was completed, and a binary silicate compound, Ba2 SiO4 , had formed within 24 h at 300°C. After 72 h at 650°C, aluminum oxidation was completed, and an appreciable amount of BaAl2 O4 had formed. Diffraction peaks consistent with hexagonal BaAl2 Si2 O8 , BaAl2 O4 , β-BaSiO3 , and possibly β-BaSi2 O5 were detected after 24 h at 900°C. Diffraction peaks for BaAl2 O4 and BaAl2 Si2 O8 were observed after 35 h at 1200°C, although SEM analyses also revealed fine silicate particles. Further reaction of this silicate with BaAl2 O4 at 1350° to 1650°C yielded a mixture of hexagonal and monoclinic BaAl2 Si2 O8 . The observed reaction path was compared to prior work with other inorganic precursors to BaAl2 Si2 O8 . 相似文献
11.
Byeong Kon Kim Yong Soo Cho Jung Won Lee Jong Won Lee Jun Kwang Song 《Journal of the American Ceramic Society》2008,91(2):687-689
The compatibility and crystallization of dielectric thick films, consisting of a bismuth borosilicate glass and crystalline cordierite, on a LiZn ferrite substrate were investigated by focusing on phase development and microstructural changes. Significant diffusion of Li and Fe from the substrate to the dielectric was confirmed as unexpected crystalline phases such as Li2 Al2 Si3 O10 and Fe2 O3 were found in the thick films fired at 850°C. The crystallization was believed to be initiated from the film interface and developed further toward the film surface as evidenced from cross-sectional microstructures of the films with additional firings. The degree of crystallization and the relative contents of the observed phases were dependent on the ratio between the glass and cordierite and the number of refirings. 相似文献
12.
Michael K. Cinibulk Gareth Thomas Sylvia M. Johnson 《Journal of the American Ceramic Society》1990,73(6):1606-1612
Densifying silicon nitride with a YSiAlON glass additive produced 99% dense materials by pressureless sintering. Subsequent heat-treating led to nearly complete crystallization of the amorphous intergranular phase. Transmission electron microscopy revealed that for heat treatments at 1350°C, only β-Y2 Si2 O7 was crystallized at the grain boundaries. At a higher temperature of 1450°C, primarily YSiO2 N and Y4 Si2 O7 N2 in addition to small amounts of Y2 SiO5 were present. Al existed only in high concentrations in residual amorphous phases, and in solid solution with Si3 N4 and some crystalline grain-boundary phases. In four-point flexure tests materials retained up to 73% of their strengths, with strengths of up to 426 MPa, at 1300°C. High-strength retention was due to nearly complete crystallization of the intergranular phase, as well as to the high refractoriness of residual amorphous phases. 相似文献
13.
Equilibrium relationships in the system Al2 O3 -Ce2 Si2 O7 in inert atmosphere have been investigated in the temperature range 900° to 1925°C. A simple eutectic reaction was found at 1375°C and 51 mol% Ce2 Si2 O7 . A high-low polymorphic transformation in Ce2 Si2 O7 was observed at 1274°C. New XRD patterns are suggested for both polymorphs of cerium pyrosilicate. The melting point of Ce2 Si2 O7 was found to be 1788°C. A value for ΔH°m,Ce2Si2O7 of 36.81 kJ/mol was calculated from the initial slope of the experimentally determined liquidus in equilibrium with the pyrosilicate phase. 相似文献
14.
Niobium pentoxide (T form, orthorhombic system) was utilized to promote devitrification in Li2 O · Al2 O3 · 6SiO2 glasses. Two or more mole percentage of this nucleating dopant enhanced crystallization in these glasses. Glasses containing 4.0 and 8.0 mol% T-Nb2 O5 exhibited a high tendency to form dispersed TT-Nb2 O5 (monoclinic system) precipitates during the glass quenching process. The crystallization process in glasses containing 2.0 or 4.0 mol% T-Nb2 O5 occurred as microphase separation, followed by the formation of dispersed TT-Nb2 O5 crystalline precipitates (760°C), followed by β-quartz solid-solution ( ss ) formation (850° to 900°C) heterogeneously nucleated from the precipitates. β-quartz( ss ) transformed to β-spodumene( ss ), along with a polymorphic transition from the TT-Nb2 O5 to M-Nb2 O5 (tetragonal system) crystalline phase. 相似文献
15.
IRVIN C. HUSEBY† HANS L. LUKAS GÜNTER PETZOW 《Journal of the American Ceramic Society》1975,58(9-10):377-380
The 1780°C isothermal section of the reciprocal quasiternary system Si3 N4 -SiO2 -BeO-Be3 N2 was investigated by the X-ray analysis of hot-pressed samples. The equilibrium relations shown involve previously known compounds and 8 newly found compounds: Be6 Si3 N8 , Be11 Si5 N14 , Be5 Si2 N6 , Be9 Si3 N10 , Be8 SiO4 N4 , Be6 O3 N2 , Be8 O5 N2 , and Be9 O6 N2 . Large solid solubility occurs in β-Si3 N4 , BeSiN2 , Be9 Si3 N10 , Be4 SiN4 , and β-Be3 N2 . Solid solubility in β-Si3 N4 extends toward Be2 SiO4 and decreases with increasing temperature from 19 mol% at 1770°C to 11.5 mol% Be2 SiO4 at 1880°C. A 4-phase isotherm, liquid +β-Si3 N4 ( ss )Si2 ON2 + BeO, exists at 1770°C. 相似文献
16.
Naruporn Kanchanarat Cheryl A. Miller Paul V. Hatton Peter F. James Ian M. Reaney 《Journal of the American Ceramic Society》2005,88(11):3198-3204
Previous work by Miller et al . (2000–2004) has demonstrated that canasite-based glass ceramics have potential for use as biocompatible glass ceramics in hard-tissue augmentation. Several compositional modifications with respect to the stoichiometric formula (K2 Na4 Ca5 Si12 O30 F4 ) were studied and biocompatibility in simulated body fluid was reported. However, the mechanism(s) of crystallization were not investigated in detail. The purpose of this study was to examine the early stages of nucleation and growth in four glass compositions using X-ray diffraction and transmission electron microscopy. In stoichiometric compositions (CAN1), laths of predominantly frankamenite homogeneously nucleate throughout the glass at ∼700°C without the presence of a nucleating phase. However, in Na2 O-deficient compositions (CAN2), CaF2 particles (650°C) act as nucleating sites for canasite laths (700°C). In CaO-rich compositions (CAN3), CaF2 particles (650°C) once again act as nucleating sites but for xonotlite (700°C) rather than canasite laths. Instead, frankamenite and canasite crystallize to become the dominant phases at >700°C. In P2 O5 -modified compositions (CAN4), CaF2 and fluorapatite, present on cooling, act as nucleating agents for canasite (750°C). 相似文献
17.
γ-Y2 Si2 O7 is a promising candidate material both for high-temperature structural applications and as an environmental/thermal barrier coating material due to its unique properties such as high melting point, machinability, thermal stability, low linear thermal expansion coefficient (3.9 × 10−6 /K, 200°–1300°C), and low thermal conductivity (<3.0 W/m·K above 300°C). The hot corrosion behavior of γ-Y2 Si2 O7 in thin-film molten Na2 SO4 at 850°–1000°C for 20 h in flowing air was investigated using a thermogravimetric analyzer (TGA) and a mass spectrometer (MS). γ-Y2 Si2 O7 exhibited good resistance against Na2 SO4 molten salt. The kinetic curves were well fitted by a paralinear equation: the linear part was caused by the evaporation of Na2 SO4 and the parabolic part came from gas products evolved from the hotcorrosion reaction. A thin silica film formed under the corrosion scale was the key factor for retarding the hot corrosion. The apparent activation energy for the corrosion of γ-Y2 Si2 O7 in Na2 SO4 molten salt with flowing air was evaluated to be 255 kJ/mol. 相似文献
18.
Masahiro Tatsumisago Hiroshi Narita Tsutomu Minami Masami Tanaka 《Journal of the American Ceramic Society》1983,66(11):c210-c211
Twin-roller quenching was attempted for 15 pseudobinary systems combining two chosen from the lithium ortho-oxosalts, i.e. Li3 BO3 , Li4 SiO4 , Li4 GeO4 , Li3 PO4 , Li2 SO4 , and Li2 WO4 . Glassy flakes were obtained in almost all systems. Glass formation was easier in systems containing large amounts of Li3 BO3 or Li2 WO4 compared to those containing Li4 GeO4 or Li3 PO4 . Glass transition, crystallization, and liquidus temperatures were determined. Infrared spectra revealed that the glasses consisted of Li+ ions and discrete ortho-oxoanions only . 相似文献
19.
The enthalpies of solution in molten 2PbO·B2 O3 at 690°±2°C of cordierite, Mg2 Al4 Si5 O18 , and of a glass of cordierite composition were determined. From these data, the enthalpy of formation of cordierite from the component oxides is -16.1±1.7 kcal/mol and its heat of fusion +54.0±2.0 kcal/mol. 相似文献
20.
The glassforming region in the system was roughly outlined and liquidus data were obtained for the three joins LiPO3 -BPO4 , Li4 P2 O7 -BPO4 , and Li3 PO4 -Li2 B4 O7 . Compatibility relations for the ternary subsystems Li4 P2 O7 -BPO4 -P2 O5 and Li2 O-Li3 PO4 -Li2 B8 O13 were established. Two ternary compounds with the probable compositions 22Li2 O - 11B2 O3 - 13P2 O5 and 2Li2 O 3B2 O3 P2 O5 were detected. 相似文献