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1.
The structure of glasses within the system Li2O–Al2O3–B2O3–P2O5 has been studied through 31P, 11B and 27Al Nuclear Magnetic Resonance, and the effect of Al2O3 substitution by B2O3 and P2O5 network formers on the structure and properties investigated for a constant Li2O content. Multinuclear NMR results reveal that substitution of Al2O3 for B2O3 and P2O5 network formers in a glass with composition 50Li2O·15B2O3·35P2O5 produces a change in boron environment from four-fold to three-fold coordination. Meanwhile aluminum can be present in four-, five- and six-fold coordinations a higher amount of Al(IV) groups is found for increasing alumina contents. The behavior of the glass transition temperature and electrical conductivity of the glasses has been interpreted as a function of the structural changes induced in the glass network when alumina is substituted for B2O3, P2O5 or both. Small additions of alumina produce a drastic increase in glass transition temperature, while it does not change for [Al2O3] greater than 3 mol.%. However, the electrical conductivity shows very different behavior depending on the type of substitution; it can remain constant when B2O3 content decreases or sharply decrease when P2O5 is substituted by Al2O3, which is attributed to a higher amount of BO3 and phase separation. 相似文献
2.
SiO2–B2O3 aerogels have been prepared by drying wet gels at a supercritical condition for ethanol in an autoclave. Aerogels have been nitrided for 6 h in flowing ammonia at the temperature of 1200 °C. It has been found that the amount of nitrogen incorporated in these aerogels always exceeds 20 wt%. This is a much higher value compared with the amount of nitrogen incorporated in a pure silica aerogel nitrided at the same conditions. The specific surface area of SiO2–B2O3 aerogels has been between 312 and 359 m2/g. After nitridation some shrinkage of aerogels has been observed and the surface area decreases about 20%. In FTIR spectra of SiO2–B2O3 aerogels a typical bands for SiO2 are observed. After nitridation a shift and broadening of 1100 cm?1 band to lower wavenumbers indicates that Si–N and B–N bonds are formed in nitrided aerogels. 相似文献
3.
《Journal of Non》1999,243(2-3):251-267
Glasses in a wide range of compositions in the ternary system xLi2SO4–yLi2O–zP2O5 where x ranges from 0 to 30 mol%, y ranges from 35 to 55 mol% and z ranges from 25 to 50 mol% have been prepared and their properties measured using infra-red, Raman, and 31P magic angle spinning nuclear magnetic resonance spectroscopic techniques. We conclude that a random close packing of phosphate and sulphate ions which also leads to formation of connected voids in the structure is consistent with our data. There is also evidence for formation of condensed sulphate–phosphate species in the liquid which may be retained in the glass structure. 相似文献
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5.
A transparent glass with the composition 60B2O3–30Li2O–10Nb2O5 (mol%) was prepared by the melt quenching technique. The glass was heat-treated with and without the application of an external electric field. The as-prepared sample was heat-treated (HT) at 450, 500 and 550 °C and thermoelectric treated (TET) at 500 °C. The following electric fields were used: 50 kV/m and 100 kV/m. Differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman, dc and ac conductivity, as a function of temperature, were used to investigate the glass and glass-ceramics properties. LiNbO3 crystals were detected, by XRD, in the 500 °C HT, 550 °C HT and 500 °C TET samples. The presence of an external electric field, during the heat-treatment process, improves the formation of LiNbO3 nanocrystals at lower temperatures. However, in the 550 °C HT and in the TET samples, Li2B4O7 was also detected. The value of the σdc decreases with the rise of the applied field, during the heat-treatment. This behavior can indicate an increase in the fraction of the LiNbO3 crystallites present in these glass samples. The dc and ac conduction processes show dependence on the number of the ions inserted in the glass as network modifiers.The Raman analysis suggests that the niobium ions are, probably, inserted in the glass matrix as network formers.These results reflect the decisive effect of temperature and electric field applied during the thermoelectric treatment in the structure and electric properties of glass-ceramics. 相似文献
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7.
《Journal of Non》1986,81(3):337-350
Glass-forming tendencies of melts in the systems (alkali oxide or alkaline earth oxide)-Nb2O5Ga2O3 were examined by an ordinary crucible-melting technique. The glass-forming tendency increased with increasing radius of alkali or alkaline earth ion in the respective groups. Clear glasses were obtained on a practically useful scale in the systems (K2O or Cs2O)Nb2O5Ga2O3 and (SrO or BaO)Nb2O5Ga2O3. The infrared absorption spectra indicated that the Ga3+ ions in the glasses are tetrahedrally coordinated with oxygen ions. The glasses showed high optical transmissions from the ultraviolet region of 0.3 μm in wavelength to the infrared region of 7 μm, except for a region near 3 μm. The absorption near 3 μm, which is attributed to OH vibration, could be eliminated by replacing part of the carbonate in the raw materials with a fluoride and melting the mixture of raw materials in a dry N2 gas atmosphere. The glass-forming tendencies of the melts and the optical transmissions of the glasses were discussed in terms of the glass structure. 相似文献
8.
Z. Amirahmadi V.K. Marghussian A. Beitollahi S.M. Mirkazemi H. Sarpoolaky 《Journal of Non》2011,357(16-17):3195-3199
A glass with the composition of 35Na2O–24Fe2O3–20B2O3–20SiO2–1ZnO (mol%) was melted, quenched, using a twin roller technique, and subsequently heat treated in the range 485–750 °C for 1–2 h. This led to the crystallization of magnetite as the sole or the major crystalline phase.Heat treatment at lower temperatures resulted in the crystallization of magnetite crystals 7–20 nm in diameter, whereas heat treatment at higher temperatures produced higher quantities of magnetite and much larger crystals. The room temperature magnetization and coercive force values were in the range of 6–57 emu g? 1 and 0–120 Oe, respectively for the heat treated glasses. 相似文献
9.
E. F. Dolzhenkova M. B. Kosmyna B. P. Nazarenko V. N. Baumer 《Crystallography Reports》2003,48(4):682-685
The anisotropy of microhardness of β-barium borate single crystals β-BaB2O4 (BBO) is studied by the sclerometry method on the (0001) basal plane, the $(10\bar 10)$ plane of the hexagonal prism, and the $(11\bar 20)$ plane of the trigonal prism. It is shown that the anisotropy observed in the crystal is determined by the directions of covalent B-O bonds. It is established that the anisotropy of microhardness correlates with the system of cleavage planes. 相似文献
10.
《Journal of Non》1986,79(3):285-294
The structure of Na2OGeO2 melts in the temperature range from 1100 to 1150°C has been investigated with the high temperature X-ray diffraction technique. Comparing the radial distribution functions obtained for the melts with those for the corresponding glasses, the first peak due to the GeO interatomic distance is invariant upon melting, although it becomes broader due to thermal vibration. The second peak for the GeGe interatomic distance for melts shifts toward the large distance, which is explained by broadening of the GeOGe bond angle, not by the thermal expansion of the GeOGe bond. The composition dependences of GeO distances and coordination numbers of the Ge4+ ion of the melts are found to be almost the same as the corresponding glasses, indicating that even in melts at such high temperatures 6-fold coordinated Ge4+ ions are present and their content changes with the Na2O content as in the case of the corresponding glasses. 相似文献
11.
Xiao Hu Guillaume Guery Joshua Boerstler J. David Musgraves Don Vanderveer Peter Wachtel Kathleen Richardson 《Journal of Non》2012,358(5):952-958
Glass ceramic materials with composition 75TeO2–xBi2O3–(25-x)ZnO (x = 13, 12, 11) possessing transparency in the near- and mid-infrared (MIR) regions were studied in this paper. It was found that as the Bi2O3 content increased in the glass composition, the observed crystallization tendency is enhanced, and high crystal concentrations were obtained for the glasses with high Bi2O3 content while maintaining transparency in the MIR region. Crystal size in the glass ceramic was reduced by adjusting the heat treatment conditions; the smallest average size obtained in this study is 700 nm. Bi0.864Te0.136O1.568 was identified using X-ray Diffraction (XRD) and found to be the only crystal phase developed in the glass ceramics when the treatment temperature was fixed at 335 °C. The morphology of the crystals was studied using Scanning Electron Microscopy (SEM), and crystals were found to be polyhedral structures with uniform sizes and a narrow size distribution for a fixed heat treatment regime. Infrared absorption spectra of the resulting glass ceramics were studied. The glass ceramic retained transparency in the infrared region when the crystals inside were smaller than 1 μm, with an absorption coefficient less than 0.5/cm in the infrared region from 1.25 to 2.5 μm. The mechanical properties were also improved after crystallization; the Vickers Hardness value of the glass ceramic increased by 10% relative to the base glass. 相似文献
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13.
Ki-Dong Kim 《Journal of Non》2008,354(15-16):1715-1720
The influence of K2O/(MgO + K2O) on some melt properties, including crystallization during cooling of melts and glass-forming ability, was investigated in the Li2O–Al2O3–SiO2 system with low Al2O3 content. The dependence of viscosity on K2O/(MgO + K2O) above 1000 °C showed a monotonic decrease due to the reduction of [MgO4] concentration and the conductivity also decreased due to the larger ion radius of K. The temperature dependence of conductivity for all melts showed an abrupt change at one temperature due to crystallization in which temperature of crystallization decreases with increase of K2O. The crystallization behavior near liquidus temperature was studied quantitatively by calculating the crystal volume fraction from apparent viscosity value. The glass-forming ability of the melts was discussed by using data related with viscosity and crystallization. Finally, it was suggested that the melts with K2O/(MgO + K2O) ? 0.75 have a good glass-forming ability. 相似文献
14.
M. John Plater Mark R. St J. Foreman R. Alan Howie 《Journal of chemical crystallography》2000,30(7):445-447
The title compound exists as a 1D coordination polymer consisting of succinate anions, manganese cations and 2,2-bipyridyl molecules. Twelve water molecules are present in the unit cell and are part of a hydrogen bonding system. Some of these waters are binding to manganese cations while others are only participating in hydrogen bonding. The structure has a monoclinic space group P21/c with a = 8.2750(3) Å, b = 11.5104(3) Å and c = 16.9113(6) Å, = 95.2727(16); V = 1603.96(9) Å3 and Z = 4. 相似文献
15.
B11 NMR spectra have been used to study the structure of glasses in the system K2OB2O3P2O5. The results indicate that the glasses do not contain an appreciable number of boron atoms in BO3 units with one or two non-bridging oxygens. The fraction N4 of boron atoms in BO4 units is measured and analyzed according to a structural model containing the following elements. (1) If the binary borophosphate system forms glasses, they consist of a borophosphate (BPO4) network and a borate network for K<1, or a borophosphate (BPO4) network and a phosphate network for K>1, where K = mol.% P2O5/mol.% B2O3. (2) The conversion rates of BO4 units (i.e. the rate of production or destruction by added oxygens) in the borate network and the borophosphate (BPO4) network are given as (+2) and (?0.38), respectively. (3) K+1 ions are proportionally shared between the two networks; (i.e. between the borate and borophosphate (BPO4) networks for K<1, and between the phosphate and borophosphate (BPO4) networks for K>1). 相似文献
16.
The effect of the substitution of ZnO for TiO2 on the chemical durability of Bi2O3–SiO2–ZnO–B2O3 glass coatings in hot acidic medium (0.1 N H2SO4 at 80 °C) for different times was studied. The thick films produced by a screen-printing method and heat treated at 700 °C/5 min were analyzed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The glass from the Bi2O3–SiO2–ZnO–B2O3 system developed Zn2SiO4 and a glassy phase that were readily attacked by hot 0.1 N sulfuric acid, whereas the heat treated coating from the Bi2O3–SiO2–TiO2–ZnO–B2O3 system presented a finer microstructure with thin interconnected Bi4Ti3O12 crystals and a glassy phase more resistant to hot 0.1 N sulfuric acid attack etching. 相似文献
17.
Kai Zheng Shengbing Yang Jiaojiao Wang Christian Rűssel Changsheng Liu Wen Liang 《Journal of Non》2012,358(2):387-391
A novel Na2O–K2O–CaO–MgO–SrO–B2O3–P2O5 borophosphate glass fiber is prepared. The thermal properties including differential thermal analysis (DTA) and viscosity measurement of the glass were presented. The tensile strength of the glass fiber is measured. The reaction of the glass fibers in the SBF solution is characterized by XRD, FTIR and SEM. XRD and FTIR indicate that the carbonate hydroxyapatite has formed rapidly on the glass. Cell attachment, spreading and proliferation on the glass are determined by MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide] assay method using Human osteosarcoma MG-63 cells. The bioactivity and biocompatibility of the glass fiber make it a good potential prospect in the field of tissue engineering. 相似文献
18.
U. Hoppe N.P. Wyckoff M.L. Schmitt R.K. Brow A. Schöps A.C. Hannon 《Journal of Non》2012,358(2):328-336
The atomic structures of two V2O5–P2O5 glasses and vitreous (v-) V2O5 were investigated by X-ray and neutron diffraction. The V=O double bond is a common characteristic of the VOn units that constitute the structures of the glasses. VO5 square pyramids with elongated bonds of ~ 0.190 nm to the pyramidal base are found for the 50V2O5–50P2O5 glass. These weaker V–O bonds are balanced in V–O–P bridges by overbonded P–O bonds. The V(IV) sites, which account for 19.7% and 35.2% of the total V sites in the 73V2O5–27P2O5 and 50V2O5–50P2O5 glasses, respectively, form similar pyramids in agreement with the structure of crystalline (VO)2P2O7. The short-range structure of v-V2O5 and the 73V2O5-27P2O5 glass is formed of mixtures of VO5 and VO4 pyramids. A significant amount of V···O distances > 0.22 nm found for all glasses belong either to linkages V=O···V or to three-coordinated O sites. 相似文献
19.
Large single crystals of β-Mn2V2O7 are successfully grown at a slow cooling rate using flux method in a closed crucible. The grown crystals exhibit a characteristic morphology with natural (1 1 0) and (3 5 0) facets. X-ray diffraction and chemical analyses show that the grown crystals have high quality. 相似文献
20.
Ch. Srinivasa Rao V. Ravikumar T. Srikumar Y. Gandhi N. Veeraiah 《Journal of Non》2011,357(16-17):3094-3102
A series of Li2O–Al2O3–ZrO2–SiO2 glasses doped with different concentrations of WO3 (0 to 5.0 mol.%) have been synthesized. Differential thermal analysis of the samples indicated increasing glass forming ability with the increasing concentration of WO3 in the glass matrix. A variety of spectroscopic (optical absorption, IR, Raman and ESR) and dielectric properties (over a range of frequency and temperature) of these glasses have been investigated. The optical absorption and ESR spectral studies have pointed out that a part of tungsten ions do exist in W5+ state in addition to W6+ state especially in the samples containing low concentration of WO3. The IR and Raman spectral studies have suggested that there is a decreasing degree of disorder in the glass network with increase in the concentration of WO3. The values of dielectric parameters viz., dielectric constant, loss and ac conductivity at any frequency and temperature are observed to decrease as the concentration of WO3 is increased. Such changes have been attributed to decrease of redox ratio or decreasing proportions of W5+ ions that act as modifiers in the glass network. The quantitative analysis of the results of ac conductivity and dielectric properties have indicated an increase in the insulating character of the glasses with the concentration of WO3; this is attributed to the presence of tungsten ions largely in W6+ ions that participate in the glass network forming with WO4 structural units. 相似文献