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1.
The phase separation and crystallization behavior in the system (80 − X)SiO2 · X(Al2O3 + P2O5) · 5B2O3 · 15Na2O (mol%) glasses was investigated. Glasses with X = 20 and 30 phase separated into two phases, one of which is rich in Al2O3-P2O5-SiO2 and forms a continuous phase. Glasses containing a larger amount of Al2O3-P2O5 (X = 40 and 50) readily crystallize and precipitates tridymite type AlPO4 crystals. It is estimated that the phase separation occurs forming continuous Al2O3-P2O5-SiO2 phase at first, and then tridymite type AlPO4 crystals precipitate and grow in this phase. Highly transparent glass-ceramics comparable to glass can be successfully obtained by controlling heat treatment precisely. The crystal size and percent crystallinity of these transparent glass-ceramics are 20-30 nm and about 50%, respectively.  相似文献   

2.
I. Dyamant  E. Korin 《Journal of Non》2008,354(27):3135-3141
Glasses in the La2O3−CaO−B2O3 ternary system were studied. The glass forming range as determined by the appearance of the annealed cast was found to match previously published findings. Clear glasses were formed in the composition range of 5.7−19.1 mol% La2O3 with constant B2O3 content of 71.4 mol%, and in glasses of constant La2O3:CaO ratio of 1:4 with B2O3 content in the range of 71.4-55.0 mol%. The non-linear optical crystalline phase La2Ca2B10O19 was crystallized from the clear glasses after heat treatments, as determined by powder XRD. Two types of the LaBO3 crystalline phases were detected in the partially and the fully crystallized glass compositions outside the glass forming range. Data are reported for the glass transition temperature (Tg), dilatometric softening point (Td), linear coefficient of expansion (α), onset crystallization temperature (Tx), exothermal peak temperature (TP), density (ρ) and index of refraction (nD) in the clear glasses.  相似文献   

3.
Crystallization processes of Li2O-Ga2O3-SiO2-NiO system glasses have been studied by X-ray diffraction, differential calorimetry and optical absorption. Transparent glass-ceramic containing LiGa5O8:Ni2+ as the sole crystalline phase has been obtained from glass with the composition of 13Li2O-23Ga2O3-64SiO2-0.1NiO (in mol%) by the heat treatment in the temperature range from 923 to 953 K. It was revealed that the specific surface area of samples enhances crystallization of LiGaSi2O6 but obstructed that of LiGa5O8. LiGa5O8 grew to nano-sized crystallites dispersed in the glass matrices and did not affect the transparency seriously. In contrast, LiGaSi2O6 grew to crystallites with diameters more than 100 nm on the surface and made the glasses opaque. Optical absorption measurements revealed that doped Ni2+ occupied five-folded trigonal bipyramidal sites in the as-quenched glass matrices but six-folded octahedral sites of precipitated LiGa5O8 in the glass-ceramics. It was confirmed that transparent glass-ceramic containing Ni2+:LiGa5O8 was effectively obtained by the heat treatment at a temperature of 953 K for 10 h.  相似文献   

4.
Reduction in the temperature coefficient of the optical path length, dS/dT of Li2O-Al2O3-SiO2 glass-ceramics with near-zero thermal expansion coefficient was attempted using control of the temperature coefficient of electronic polarizability, ?, and the thermal expansion coefficient, α. The dS/dT value of 2.6 mol% B2O3-doped glass-ceramic was 12.5  × 10−6/°C, which was 0.9 ×  10−6/°C smaller than that of B2O3-free glass-ceramic. On the other hand, reduction in dS/dT through B2O3 doping was not confirmed in precursor glasses. Results showed that reduction in dS/dT of the glass-ceramic through B2O3 doping is caused by the reduction in ?. The reduction in ? from B2O3 doping was probably attributable to numerical reduction in non-bridging oxide ions with larger ? value by the concentration of boron ions in the residual glass phase. In addition, application of hydrostatic pressure during crystallization was effective to inhibit precipitation of β-spodumene solid solution, which thereby decreases dS/dT. The dS/dT value of B2O3-doped glass-ceramic crystallized under 196 MPa was 11.7 ×  10−6/°C. That value was slightly larger than that of silica glass. The α value of this glass-ceramic was smaller than that of silica glass.  相似文献   

5.
The crystallization behavior of glass with the composition: 55.6 mol% SiO2, 22.8 mol% Al2O3, 17.7 mol% ZnO and 3.84 mol% of TiO2 as nucleating agent and with different particle sizes has been studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and tranmission electron microscopy (TEM). In glass powders two crystalline phases: zinc-aluminosilicate s.s. with high-quartz structure, Znx/2AlxSi3−xO6, (x varies dependent on heat-treatment temperature) and gahnite are formed. The ratio of these phases depends on particle sizes. In bulk glass, however, gahnite is the sole crystalline phase. The composition of initially formed zinc-aluminosilicate s.s. was determined by Rietveld refinement of XRD patterns to be Zn0.69Al1.38Si1.62O6. With temperature increase, the amount of zinc-aluminosilicate s.s decreased with simultaneous reduce of zinc and aluminum incorporated in the structure. Eventually at 1423 K almost pure high-quartz structure was formed. The activation energies of zinc-aluminosilicate s.s. and gahnite crystallization were determined by non-isothermal method to be 510 ± 18 and 344 ± 17 kJ mol−1, respectively. The latter value matches well with those cited in literature for crystal growth of gahnite in similar glasses. That is attributed to the fact that the high-quartz structure acts as a precursor for gahnite crystallization.  相似文献   

6.
Calcium phosphate based bioactive quaternary glass systems P2O5-CaO-Na2O-K2O were prepared by melt growth technique. Glasses were prepared in five different compositions by fixing P2O5 at 47 mol% and CaO at 30.5 mol% and by varying the K2O and Na2O concentrations. The structural properties of the glasses are analyzed using X-ray diffraction (XRD) studies and scanning electron microscopy (SEM) studies; and the composition of the glasses are studied using energy dispersive X-ray spectrum (EDS). The microhardness of the glass systems are studied by Vickers hardness measurements and the bioactivity of the glasses are studied using in vitro study. The thermal properties have been examined by means of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The ultrasonic velocity measurements show that the addition of K2O contents produces non-bridging oxygen ion and hence weaken of the glass structure. The weakening of the glass structure reduces the ultrasonic velocity and hence an increase in attenuation.  相似文献   

7.
Glasses of the system: (70−x) TeO2 + 15B2O3 + 15P2O5 + xLi2O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by melt quench technique. Dependencies of their glass transition temperatures (Tg) and infrared (IR) absorption spectra on composition were investigated. It is found that the gradual replacement of oxides, TeO2 by Li2O, decreases the glass transition temperature and increases the fragility of the glasses. Also, IR spectra revealed broad weak and strong absorption bands in the investigated range of wave numbers from 4000 to 400 cm−1. These bands were assigned to their corresponding bond modes of vibration with relation to the glass structure.  相似文献   

8.
Room temperature electron spin resonance (ESR) spectra and temperature dependent magnetic susceptibility measurements have been performed to investigate the effect of iron ions in 41CaO · (52 − x)SiO2 · 4P2O5 · xFe2O3 · 3Na2O (2 ? x ? 10 mol%) glasses. The ESR spectra of the glass exhibited the absorptions centered at g ≈ 2.1 and g ≈ 4.3. The variation of the intensity and linewidth of these absorption lines with composition has been interpreted in terms of variation in the concentration of the Fe2+ and Fe3+ in the glass and the interaction between the iron ions. The magnetic susceptibility data were used to obtain information on the relative concentration and interaction between the iron ions in the glass.  相似文献   

9.
Bing Zhang  Li Song  Fengzhen Hou 《Journal of Non》2008,354(18):1948-1954
Glasses in the ternary system ZnO-Sb2O3-P2O5 were investigated as potential alternatives to lead based glasses for low temperature applications. The glass-forming region of ZnO-Sb2O3-P2O5 system has been determined. Structure and properties of the glasses with the composition (60 − x)ZnO-xSb2O3-40P2O5 were characterized by infrared spectra (IR), differential thermal analysis (DTA) and X-ray diffraction (XRD). The results of IR indicated the role of Sb3+ as participant in glass network structure, which was supported by the monotonic and remarkable increase of density (ρ) and molar volume (VM) with increasing Sb2O3 content. Glass transition temperature (Tg) and thermal stability decreased, and coefficient of thermal expansion (α) increased with the substitution of Sb2O3 for ZnO in the range of 0-50 mol%. XRD pattern of the heat treated glass containing 30 mol% Sb2O3 indicated that the structure of antimony-phosphate becomes dominant. The improved water durability of these glasses is consistent with the replacement of easily hydrated phosphate chains by corrosion resistant P-O-Sb bonds. The glasses containing ?30 mol% Sb2O3 possess lower Tg (<400 °C) and better water durability, which could be alternatives to lead based glasses for practical applications with further composition improvement.  相似文献   

10.
Specimens of the glassy system: (70 − x)TeO2 + 15B2O3 + 15P2O5 + xLi2O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by the melt-quenching. An ultrasonic pulse-echo technique was employed, at 5 MHz, for measuring: the ultrasonic attenuation, longitudinal and shear wave velocities, elastic moduli, Poisson ratio, Debye temperature and hardness of the present glasses. It is found that the gradual replacement of TeO2 by Li2O in the glass matrix up to 30 mol% leads to decrease the average crosslink density and rigidity of prepared samples which affects the properties, i.e., the hardness, ultrasonic wave velocities and elastic moduli are decreased, while the Poisson ratio and the ultrasonic attenuation are increased. Also, optical absorption spectra were recorded in the range, 200-800 nm for these glasses. The obtained results showed that a gradual shift in the fundamental absorption edge toward longer wavelengths occurred. Values of both of the optical energy gap, Eopt, and width tails, ΔE, are determined. It is observed that Eopt is decreased and ΔE increased with the increase of Li2O in the glass matrix up to 30 mol%. The compositional dependences of the above properties are discussed and correlated to the structure of tested glasses.  相似文献   

11.
The influence of Cr2O3 on glass forming characteristics and physical properties of PbO-Fe2O3-P2O5 glasses has been investigated by Raman and Mössbauer spectroscopies, X-ray diffraction analysis (XRD), Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM) and impedance spectroscopy. Glasses of the general composition xCr2O3-(28.3-x)PbO-28.7Fe2O3-43.0P2O5, 0 ≤ × ≤ 10, (mol%) were prepared by conventional melt-quenching technique. The compositions containing up to 4 mol% Cr2O3 formed fully amorphous samples and their Raman spectra show systematic increase in the fraction of orthophosphate Q0 units with increasing Cr2O3 content and O/P ratio.On the other hand, compositions containing 8 and 10 mol% Cr2O3 partially crystallized during cooling and annealing to Fe7(PO4)6, Fe2Pb3(PO4)4 and Cr2Pb3(PO4)4. A high tendency for crystallization of these melts is related to the high O/P (> 4) and Fe2+/Fetot (≈ 0.60) ratios.Electrical conductivity of xCr2O3-(28.3-x)PbO-28.7Fe2O3-43.0P2O5, 0 ≤ × ≤ 10, (mol%) compositions is independent of Cr2O3 and controlled entirely by the polaron transfer between Fe2+ and Fe3+ ions.  相似文献   

12.
N. Baizura 《Journal of Non》2011,357(15):2810-2815
Tellurite 75TeO2-(10 − x)Nb2O5-15ZnO-(x)Er2O3; (x = 0.0-2.5 mol%) glass system with concurrent reduction of Nb2O5 and Er2O3 addition have been prepared by melt-quenching method. Elastic properties together with structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo-overlap technique at 5 MHz and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Shear velocity, shear modulus, Young's modulus and Debye temperature were observed to initially decrease at x = 0.5 mol% but remained constant between x = 1.0 mol% to x = 2.0 mol%, before increasing back with Er2O3 addition at x = 2.5 mol%. The initial drop in shear velocity and related elastic moduli observed at x = 0.5 mol% were suggested to be due to weakening of glass network rigidity as a result of increase in non-bridging oxygen (NBO) ions as a consequence of Nb2O5 reduction. The near constant values of shear velocity, elastic moduli, Debye temperature, hardness and Poisson's ratio between x = 0.5 mol% to x = 2.0 mol% were suggested to be due to competition between bridging oxygen (BO) and NBO ions in the glass network as Er2O3 gradually compensated for Nb2O5. Further addition of Er2O3 (x > 2.0 mol%) seems to further reduce NBO leading to improved rigidity of the glass network causing a large increase of ultrasonic velocity (vL and vS) and related elastic moduli at x = 2.5 mol%. FTIR analysis on NbO6 octahedral, TeO4 trigonal bipyramid (tbp) and TeO3 trigonal pyramid (tp) absorption peaks confirmed the initial formation of NBO ions at x = 0.5 mol% followed by NBO/BO competition at x = 0.5-2.0 mol%. Appearance of ZnO4 tetrahedra and increase in intensity of TeO4 tbp absorption peaks at x = 2.0 mol% and x = 2.5 mol% indicate increase in formation of BO.  相似文献   

13.
Eun-Sub Lim 《Journal of Non》2006,352(8):821-826
A BaO-B2O3-SiO2 glass system was chosen as a candidate composition for the application to Pb-free low temperature sinterable glass. The effect of BaO content on the crystallization, sintering behavior, and properties of the glasses was examined. Both the glass transition temperature and crystallization temperature decreased as the BaO content increased. Crystallization easily occurred during sintering with a BaO content of more than 50 mol%, which effectively inhibited the over-firing phenomenon. The dielectric characteristics and thermal expansion coefficient of the glasses were examined and the results were explained on the basis of the crystallization and densification of the specimens.  相似文献   

14.
The effect of the variation in phosphate (P2O5) content on the properties of two series of bioactive glasses in the quaternary system SiO2-Na2O-CaO-P2O5 was studied. The first series (I) was a simple substitution of P2O5 for SiO2 keeping the Na2O:CaO ratio fixed (1:0.87). The second series (II) was designed to ensure charge neutrality in the orthophosphate (), therefore as P2O5 was added the Na2O and CaO content was varied to provide sufficient Na+ and Ca2+ cations to charge balance the orthophosphate present. Network connectivity’s of the glasses were calculated, and densities and thermal expansion coefficients predicted using the Appen and Doweidar models, respectively. Theoretical densities were measured using the Archimedes principle. Characteristic temperatures, namely the glass transition temperature, Tg, and crystallization temperatures, Tx, were obtained using differential analysis (DTA). Two crystallization exotherms were observed for both glass series (Txi and Txii). Both Tg and Tx decreased with P2O5 addition for both series. The working range of the glasses, Tx-Tg was shown to increase to a maximum at around 4 mol% P2O5 then decrease at higher P2O5 contents for both series. Thermal expansion coefficients were measured using dilatometry increasing with P2O5 addition and showed good agreement with the Appen values. Dilatometric softening points, Ts, were also measured, which increased with P2O5 addition. X-ray diffraction (XRD) was performed on the glasses to confirm their amorphous nature. The glass containing 9.25 mol% P2O5 from series I exhibited well-defined peaks on the XRD trace, indicating the presence of a crystalline phase.  相似文献   

15.
Glasses in the ternary system PbO-MoO3-P2O5 were prepared in three compositional series (100 − x)[0.5PbO-0.5P2O5]-xMoO3 (A), 50PbO-yMoO3-(50 − y)P2O5 (B) and (50 − z)PbO-xMoO3-50P2O5 (C) and their structure was studied by Raman and 31P NMR spectroscopies. In the compositional series (100 − x)[0.5PbO-0.5P2O5]-xMoO3 homogeneous glasses were prepared in the concentration region of 0-70 mol% MoO3. Their glass transition temperature increases with increasing MoO3 content having a maximum at x = 50 mol% MoO3. 31P MAS NMR spectra reveal that in the glass series (A) the incorporation of MoO3 results in the shortening of phosphate chains and gradual transformation Q2 units into Q2 and Q0 units, prevailing in glasses with a high MoO3 content. Octahedral structural units MoO6 dominate in most glass compositions and they are present also in the structure of Pb(MoO2)2(PO4)2 compound corresponding to the glass composition 50Pb(PO3)2-50MoO3. The analysis of Raman spectra of glasses of the (B) series with a high MoO3 content showed the transformation of octahedral MoO6 units into tetrahedral MoO4 units.  相似文献   

16.
Glasses in the ternary ZnO-P2O5-TeO2 system were prepared and studied in two compositional series (100 − x)[0.5ZnO-0.5P2O5]-xTeO2 (X-series) and 50ZnO-(50 − y)P2O5-yTeO2 (Y-series) within the concentration range of x = 0-60 and y = 0-40 mol% TeO2. Their structure was studied by Raman and 31P MAS NMR spectroscopies. The incorporation of TeOx units into the structural network is associated with the depolymerisation of phosphate chain structure as revealed by both methods. At a high TeO2 content isolated PO4 tetrahedra are formed in the structure of glass series Y, while diphosphate O3P-O-PO3 groups are present in the structure of the glass series X. In the structure of glass series Y tellurium atoms form predominantly TeO3 trigonal pyramids, whereas in the X glass series TeO4 trigonal bipyramids prevail in the glass structure. The addition of TeO2 to the parent zinc metaphosphate glass results in a decrease of glass transition temperature in both compositional series associated with the replacement of stronger P―O bonds by weaker Te―O bonds.  相似文献   

17.
The effect of the variation in phosphate (P2O5) content on the structure of two series of bioactive glasses in the quaternary system SiO2-Na2O-CaO-P2O5 was studied. The first series (I) was a simple substitution of P2O5 for SiO2 keeping the Na2O:CaO ratio fixed (1.00:0.87). The second series was designed to ensure charge neutrality in the orthophosphate , therefore as P2O5 was added the Na2O and CaO content was varied to provide sufficient Na+ and Ca2+ cations to charge balance the orthophosphate present. The glass network connectivity (NC) was calculated for each glass and a modification for the presence of a separate P2O5 phase was included (NC′). 31P and 29Si magic-angle-spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was performed on glass series I and II to determine the structural units present and their relation to glass properties. 31P MAS-NMR spectra of series I resulted in a broad resonance around 9 ppm corresponding to orthophosphate in an amorphous environment. The 9.25 mol% P2O5 glass shown to be partially crystalline by X-ray diffraction was heat treated, and the 31P MAS-NMR spectrum showed a sharp peak around 3 ppm corresponding to calcium orthophosphate or sodium pyrophosphate and overlapping broader peaks at 8.5, 10.5 and 14 ppm possibly corresponding to two mixed calcium-sodium orthophosphate phases and amorphous sodium orthophosphate respectively. 31P MAS-NMR spectra of series II resulted in a broad resonance around 10.5 ppm corresponding to orthophosphate in an amorphous environment. 29Si MAS-NMR spectra of glasses from series I showed a shift in the resonance peak from around −78 to −86 ppm indicating an increase in Q3 species in the glass and a reduction in Q2 with phosphate addition confirming the presence of orthophosphate. The heat treated sample showed a sharp 29Si-NMR resonance at −88 ppm, indicating a crystalline Q2 six-membered combeite (Na2O · 2CaO · 3SiO2) silicate-type phase, which was confirmed by powder X-ray diffraction. 29Si MAS-NMR spectra of glasses from series II showed no shift in the resonance at around −78 ppm across the series, confirming an orthophosphate environment.  相似文献   

18.
The vitrification and crystallization behavior of melts produced at 1400 °C in the ternary system of K2O-B2O3-TiO2 is investigated. It is shown that there are two fields of compositions (indicated in mol%) which allow obtaining the glass-ceramic materials with continuous glassy matrix after the cooling of molten compositions. In the first field [TiO2] = 25-57, [K2O] = 30-50 and [B2O3] = 0-25, the glass-ceramics consisted of the potassium-titanium-borate glassy phase and different crystalline potassium titanates (K4Ti3O8, K2Ti2O5, K2Ti4O9, K2Ti6O13). The ratio of TiO2:K2O in the obtained titanates increases with [TiO2] and [B2O3]. In the second field, [TiO2] = 7-37, [K2O] = 0-25 and [B2O3] = 52-93, the obtained glass-ceramics consisted of a similar vitreous phase, as mentioned above, and TiO2 crystals. During the cooling of the melts, short whiskers-like crystals of anatase formed in the compositions with relatively low [TiO2] and relatively high [K2O], whereas long fiber-shaped crystals of rutile appeared with the compositions characterized with relatively high [TiO2] and relatively low [K2O]. The possible application of the obtained glass-ceramic materials as a source of fibrous TiO2, for composite reinforcement, and as solid lubricants is discussed.  相似文献   

19.
Tungstate fluorophosphate glass compositions with high WO3 concentration were prepared in the ternary system (80−0.8x)NaPO3-(20−0.2x)BaF2-xWO3 with x = 40,50 and 60 mol%. Transparency decreases as WO3 concentration increases but can be improved by addition of oxidizing systems such as CeO2 or Sb2O3/NaNO3. Characterizations by thermal analysis (DSC) point out that an increase in the amount of WO3 results in a higher glass transition temperature. In addition, such compositions are very stable against devitrification since samples containing 40% and 50% of WO3 donot even exhibit the expected crystallization event. In these samples, the stability against crystallization decreases with the WO3 content and vitreous sample containing 60% of WO3 exhibits an endothermic event around 620 °C due to crystallization of monoclinic WO3 phase. In these glasses, it was shown that the nucleation stage can be induced by thermal-treatment when external nucleating agents such as Ti or Sb are used. Finally, gold-doped samples exhibit a higher crystallization tendency and monoclinic WO3 phase can be grown in such glasses.  相似文献   

20.
I. Dyamant  E. Korin 《Journal of Non》2011,357(7):1690-1695
The non-isothermal crystallization kinetics of La2CaB10O19 (LCB) from a La2O3-CaO-B2O3 glass was studied. Differential thermal analysis methods were performed on three glass powders to obtain the kinetic parameters of LCB crystallization mechanism. The activation energies for overall crystallization (E), obtained by the methods of Kissinger and Ozawa, were in the range of 479-569 kJ/mol. Multiple (five) analysis methods were used to estimate the Avrami exponent (n), which could consequently be reduced into the single value of n = 3.1 ± 0.3. The growth morphology index (m) of LCB was corroborated by microscopy (optical and electron) images, which revealed a three dimensional growth. Energy dispersive spectroscopy confirmed that LCB is the crystallizing phase from the glass by an interface controlled mechanism. The parameters of the Johnson-Mehl-Avrami kinetic model for the analysis of LCB crystallization from glass were found to be n = m = 3.  相似文献   

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