Structure and properties of glassy substances in the oxide system Li2O–B2O3–SiO2

The effect of Na2O, K2O, Li2O, F and B2O3 contents on the crystallization and relative opacity of low temperature melting TiO2-opacified porcelain enamels was investigated by means of DTA, XRD, SEM observations and a Hunter color difference meter. An increase in Na2O, K2O and Li2O content in frit raised the temperature of crystallization peak of DTA, while the increase in B2O3 and F content lowered the temperature of the peak. The opacity of the enamel fired at 690°C showed a maximum value with the change in the Na2O, K2O, Li2O, F and B2O3 contents. The developed TiO2-opacified porcelain enamel frit was capable of firing at temperatures lower than 690°C, which is 110°C lower than commercial frits.

Fabrication of a high lithium ion conducting lithium borosilicate glass

Free volume properties of a series of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) membranes, which were produced by various nonisothermal crystallization processes (rapid‐, step‐, and slow‐cooling processes), were investigated using positron annihilation lifetime (PAL) spectroscopy over a temperature range of 25–90 °C. From the annihilation lifetime parameters, the temperature dependence of free volume size, amount, size distribution, and fractional free volume and thermal expansion properties of free volume were discussed. A model which assumed that amorphous phase was subdivided into mobile and rigid amorphous fractions (MAF and RAF) in the semicrystalline polymer was considered to interpret the temperature dependence of those free volume properties. Morphological observation of the semicrystalline polymer by small‐angle X‐ray scattering (SAXS) indicated that the rapid‐cooled (cold‐crystallized) membranes showed a much thinner thickness of the repeating lamellar/amorphous layers and most likely higher amount of RAF, which restrained the chain motion, than the step‐ and slow‐cooled (melt‐crystallized) membranes. The difference of free volume properties among various PHBV membranes was created according to the crystalline structure of the polymer from different thermal history. The polymer crystallized with slower cooling rate induced higher crystallinity and resulted in less free volume amount and lower fractional free volume. In addition, the thermal expansion coefficients of free volume size were affected by the crystallization rate of PHBV polymer. Larger distribution of the free volume size of melt‐crystallized membranes was observed as a result of the bimodal distribution of the lamellar periodicity and less amount of RAF than that of the cold‐crystallized membranes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 855–865, 2009

A method of controlling the thermal expansion of lightweight metals through the insightful incorporation of unidirectional carbon fiber reinforced polymer (CFRP) is demonstrated. The local and directional coefficients of linear thermal expansion (CLTE) of a carbon fiber composite reinforced aluminum (CFRP/Al) specimen can be controlled by tailoring the CFRP volume fraction and CFRP layup orientation, with a 36% reduction in CLTE achieved as compared to the baseline 7075 aluminum at a CFRP volume fraction of 0.26. When a unidirectional CFRP reinforcement is considered, the CLTE as predicted by the modulus modified rule of mixtures is within 1.3% of experimentally obtained values for CFRP volume fractions of 0.10, 0.16, and 0.26. Thermal digital image correlation (T‐DIC) was performed to obtain local and directional CLTE values for the anisotropic CFRP/Al specimens which indicated CLTE is heterogeneous across the specimen length and width, which is otherwise undetected using standard quartz rod dilatometry to measure the CLTE of the macroscopic sample. Evidence for a minimum critical CFRP reinforcement length is also considered based upon the local thermal strain data collected by T‐DIC. Using the mixed material approach presented here, it is possible to minimize or eliminate the thermal expansion mismatch effects that occur in mixed material structures, such as an automotive body structure (i.e., body in white).

To clarify the relationship between crosslinking density and physical properties of phenol–formaldehyde novolac cured epxy resin and factors governing their physical properties, we studied various properties of cured resins having different crosslinking densities. The resins were prepared with various curing accelerators and raw epoxy resins having different molecular weights. We found that as the crosslinking density of a cured resin increases, glass transition temperature (Tg) rises and the relaxation time becomes longer. Furthermore, in the rubbery region, the coefficient of linear thermal expansion drops and the elastic modulus become larger, while, in the glassy region, the coefficient of linear thermal expansion, specific volume, water absorption, diffusion coefficient, and permeability all increase but the elastic modulus becomes smaller. The WLF analysis on the relaxation behaviors of typical cured resin showed that cured resin with a higher crosslinking density decreases in the fractional free volume. This behavior is completely opposite from the relationship predicted from the temperature dependency of specific volume. While the coefficient of thermal expansion of free volume decreases as the crosslinking density increases for the cured resin, it coincides well with the tendency predicted from the difference in coefficient of cubic thermal expansion in the rubbery and glassy regions of each cured resin. That the free volume obtained from WLF analysis shows a relationship opposite to the predicted free volume as based on the temperature dependency of specific volume is explained as follows: Namely, the free volume obtained from the WLF analysis is a hole free volumeVhwhich contributes to fluidity andVhdecreases with the crosslinking density. On the other hand, the free volume predicted from the specific volume is a sum of the interstitial free volumeViandVh.Viincreases with the crosslinking density and thisViincrease exceeds the decrease ofVh. Therefore, the free volume predicted from the specific volume increases with the crosslinking density. Consequently, the influence of free volume on the relationship between the crosslinking density and physical properties of cured resin can be interpreted as follows. As the crosslinking density increases on cured resins,Tgrises, the relaxation time is lengthened, and the coefficient of linear thermal expansion becomes smaller in the rubbery region because, as the crosslinking density increases,Vhdecreases. Since crosslinking density increases on cured resins, the coefficient of linear thermal expansion, water absorption, diffusion coefficient, and permeability become larger, and the elastic modulus becomes smaller in the glassy region because, as the crosslinking density increases,Viincreases and, accordingly, molecular chain packing becomes looser; i.e., the specific volume increases. © 1993 John Wiley & Sons, Inc.

Structure–property relationships and densification-crystallization behaviours of simplified lithium disilicate glass compositions

Li2O–B2O3–SiO2 (LBS) synthesized via a solid-state reaction process was chosen as a novel sintering aid for BaO–0.15ZnO–4TiO2 (BZT) ceramics and compared with LBS glass. The influence of LBS on the sintering behaviors, phase evolution, microstructure and microwave dielectric properties of the resulting BZT ceramics have been investigated in detail. The addition of LBS significantly lowers the sintering temperature of the BZT ceramics from 1150 to 900 °C without damaging its microwave dielectric properties. Small amount of LBS promote the densification of BZT ceramic and improve the dielectric properties. However, excessive LBS additions lead to growth of abnormal grain, deteriorating the dielectric properties of the BZT ceramic. The BZT ceramics doped with 8 wt% LBS addition could be well sintered at 900 °C for 0.5 h and show excellent microwave dielectric properties of: er = 27.72, Q × f = 20,381 GHz, τf = 5.18 ppm/ °C.

The mechanical properties of glasses in the Li2O–B2O3–P2O5 system are investigated as a function of the boron oxide content in the range from 5 to 30 mol % at a constant lithium oxide content of 45 mol %. It is demonstrated that, as the B2O3 content increases, the density of glasses passes through a maximum at 20 mol % B2O3 and the molar volume decreases gradually. The elastic modulus and the hardness of glasses monotonically increase with an increase in the B2O3 content. An increase in the B2O3 content leads to a decrease in the structural strength (measured using the method of three-point bending of fibers) and the fracture toughness (determined by the microindentation technique). The assumption is made that the decrease in the strength characteristics is caused by the phase separation developed in the structure of lithium phosphate glass with an increase in the B2O3 content.

Effect of B2O3–Li2O on microwave dielectric properties of (Ca0.275Sm0.4Li0.25)TiO3 ceramics

The coefficient of thermal linear expansion (CTE) of a superplastically elongated 3Y-TZP (3 mol.% yttria stabilized tetragonal zirconia polycrystal) was investigated. The experiments were conducted by using a push-rod dilatometer at a wide temperature range from 300K to 1473K. The experimental results indicated that CTE increased from 11.0×(10)^<-6>K^<-1> to 12.0×(10)^<-6>K^<-1> with increasing temperatures from 773K to 1200K and then showed temperature independence. Also, deformation-induced change in microstructures such as volume of cavitations fraction, the average grain size and grain aspect ration has little effect on CTE within to present experimental range.

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Borate glasses containing Li2O and fixed concentration of heavy metal oxide Bi2O3 are prepared by melt quenching technique. Density of the glasses has been found to increase slightly with Li2O content whereas molar volume and glass transition temperature decreases. IR spectroscopy was used for structural studies of these glasses in the range from 400 to 4000 cm−1. IR analysis showed that Bi3+ cations are incorporated in the glass structure as (BiO6) octahedral units and boron ions are incorporated as (BO3) and (BO4) units. As the Li2O content increases in the glass, some of the BO3 trigonal units get converted into BO4 tetrahedral units and non-bridging oxygens have been formed. The optical transmittance spectra have been recorded at room temperature. The cut-off wavelength shows a red shift, the optical band gap decreases and polarizability increases with Li2O content. The compositional dependence of different physical properties such as density, molar volume optical band gap and optical basicity has been studied and correlated with the glass structure.

Specific features of the IR spectra of silicate glasses

The object of the paper is an investigation of the glasses of the (As2S3)x(AsSe0.5Te0.5I)100-x. type for 65≤;x≤;95, using methods of thermomechanical analysis. Values of the thermal coefficients of linear expansion in solid and visco-plastic phase were determined. it was shown that introducing arsenic-sulfide in glass-matrix AsChI, i.e. (AsSe0.5Te0.5I), leads to an increasing stability of these glasses. The characteristic temperatures of softening Tg and the temperature of the beginning of deformation tw increase by increasing content of As2S3. The analytical forms of dependence of four significant physical values αg, αl, Tg, Tw, as a function of As2S3 content in the structure of glasses were fitted.

Thermomechanical study of non-crystalline chalcogenides in the As-S-Cd systemThe work analyzes the thermomechanical behavior of glasses of the pseudobinary system (As2S3)100-x(CdS)x, consisting of variable ratios of the classical amorphous semiconducting compound As2S3and CdS molecule, which is used in manufacturing of photoresistors sensitive to visible and near infrared light. The study encompassed the determination of the thermal coefficients of linear expansion in solid and visco-plastic phases, softening temperature, and the temperature of the beginning of deformation. The results show that the values of these parameters increase with increase in the share of CdS in the initial matrix, as well as the reduction of instructural strength of the correlation matrix of glass. The analytical forms of dependence of significant physical values αg,Tg,Tw, as a function of CdS content in the structure of glasses were fitted to the measured data. Based on the obtained coefficients of linear expansion, the Poissons coefficient was also calculated.