Yunlong Yue

Dielectric properties of quaternary calcium aluminoborosilicate system glasses

Abstract Series of alkaline earth aluminoborosilicate glasses were prepared by conventional melt quenching technique. Several studies including infrared spectra, density and dielectric properties of these glasses have been carried out. Infrared spectra indicated that with increasing boron oxide, more borate units were connected with silicate and aluminum units, that with decreasing calcium oxide, less dangling bonds along with non-bridging oxygen ions and more strong bonds like B–O–Si and B–O–Al formed, and that the glass structure was tightened. Capacitance decreased with increasing frequency, and relative dielectric constant ϵ′ and dielectric loss tan δ at 1 MHz decreased with increasing boron oxide content at the expense of calcium oxide. The decrease in capacitance with frequency was attributed at low frequency, to polarisability arising from electronic, ionic and orientational components, while at higher frequencies, the orientational polarisability is nearly absent. The total polarisability of glass decreased due to the lower polarisability of B3+ cations and oxygen anions in boron oxide in comparison with calcium oxide.

Effects of cation field strength on structure and properties of boroaluminosilicate glasses

Abstract Among the most important adjustable compositional variables in controlling glass and glass melt properties were the relative proportions of network modifiers with varying cation field strength (ratio of charge/radius). In alkaline earth boroaluminosilicate glasses RO–B2O3–Al2O3–SiO2 (R = Mg, Ca, Sr, Ba), the changes of structure and properties caused by variations in the ratio RO/BaO were investigated. The structural role of RO was investigated by Fourier transform infrared spectroscopy and nuclear magnetic resonance. Chemical durability was evaluated by weight losses of glass samples after immersion in HCl and NaOH solutions. High resolution scanning electron microscopy was used to examine the surface micrographs of corroded glass samples. The dielectric constant and tangent loss were measured at 1 MHz. The results indicated that the fraction of four-coordinated boron atoms (N4), chemical durability and dielectric properties increased in the order Mg>Ca>Sr>Ba.

Thermal, chemical and structural characteristics of Sm2O3 doped non-alkaline aluminoborosilicate glasses

Abstract Glasses in SiO2–Al2O3–B2O3–RO system doped with Sm2O3 content (0–4·5 wt-%) were prepared by the conventional melt quenching technique. The relationship among composition, structure and thermal durability of the glasses was investigated using differential thermal analysis (DTA), high filed 11B and 27Al magic angle spinning nuclear magnetic resonance. Chemical durability of Sm2O3 doped glasses was evaluated by weight losses of glass samples after immersion in HCl solution, scanning electron microscope (SEM) was used as an aid to examine the surface structure of corroded glass samples. The DTA showed that with the increase in Sm2O3 content, thermal durability of glasses was improved, and the tendency of crystallisation was inhibited. Nuclear magnetic resonance results showed that increasing Sm2O3 content dramatically increased the content of four-coordinated boron (BO4) and four-coordinated aluminium (AlO4). In addition, the results of acid resistance showed that the weight losses decreased with increasing Sm2O3 content, which was in accordance with SEM.

EFFECT OF TiO2 ON STRUCTURE AND DIELECTRIC PROPERTIES OF RO-Al2O3-B2O3-SiO2 (R = Ca, Mg) GLASSES

RO-Al2O3-B2O3-SiO2 (R = Ca, Mg) glasses containing different concentrations of TiO2 (ranging from 0 to 9 mol.%) were prepared by conventional melting method. When TiO2 was present in lower concentrations (≤ 6 mol.%), Fourier-transform infrared spectroscopy (FTIR) indicated that titanium ions took part in network forming positions. However, for further increase in the concentration of TiO2 (> 6 mol.%), FTIR data indicated the formation of TiO4 tetrahedrons and TiO6 octahedrons. The glass transition temperatures (Tg) were determined using a differential scanning calorimetry (DSC). The Tg variation with the concentration of TiO2 showed an increasing trend up to 6 mol.% of TiO2 and beyond this concentration, Tg was found to decrease. The dielectric constant er and loss tan δ continued to decrease with the concentration of TiO2 up to 6 mol.% and beyond that er and tan δ were found to increase. This behavior was mainly explained in terms of the rigidity of glass network.

Low-Temperature Synthesis of Nano-Crystalline MgTi2O5 Powders by Aqueous Sol-Gel Process

The pseudobrookite-structure MgTi2O5 was successfully synthesized by the aqueous sol-gel method using titanium dioxide and magnesium nitrate as starting materials instead of expensive organic solvent and metal alkoxides. The as-prepared nanopowders were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA) and transmission electron microscope (TEM), respectively. The results showed that the calcinations process of gel consisted of a series of oxidation and combustion reactions, accompanied by significantly exothermal effects. Highly reactive nanosized magnesium titanate powders were successfully obtained at 650 °C with less than ~100 nm.

INFLUENCE OF La2O3 ADDITIONS ON CHEMICAL DURABILITY AND DIELECTRIC PROPERTIES OF BOROALUMINOSILICATE GLASSES

Boroaluminosilicate glasses containing La2O3 were prepared by the normal quenching method. The glass transition temperatures (Tg) were measured by differential scanning calorimetry (DSC). The structural role of RO was investigated by nuclear magnetic resonance (NMR). Chemical durability was evaluated by weight losses of glass samples after immersion in HC1 solution. High resolution scanning electron microscopy (HR-SEM) was used to examine the surface micrographs of corroded glass samples. The dielectric constant and tangent loss were measured in the frequency range 10–106 Hz. The results revealed that chemical durability and dielectric properties increased with increasing La2O3 content.

Study on the Synthesis of Nano-Crystalline Mg2SiO4 Powders by Aqueous Sol-Gel Process

The forsterite-structure Mg2SiO4 was successfully synthesized by the aqueous sol-gel method using Si sols dioxide and magnesium nitrate as starting materials instead of expensive organic solvent and metal alkoxides. The as-prepared nanopowders were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscope (SEM), respectively. The results showed that the calcination process of gel consisted of a series of oxidation and combustion reactions, accompanied by significantly exothermal effects. Highly reactive nanosized Mg2SiO4 powders were successfully obtained at 850 °C with particle size of 60~80 nm.

Effect of P2O5 on Microstructure and Properties of Calcium Aluminoborosilicate Glasses

In alkaline earth aluminoborosilicate glasses containing P2O5, the changes of structure and properties caused by variations in the ratio P2O5/B2O3 were investigated. The structure was investigated by Fourier transform infrared spectroscopy and nuclear magnetic resonance. The dielectric constant and tangent loss were measured at 1 MHz. Chemical durability was evaluated by weight losses of glass samples after immersion in water. The results indicated that the fraction of four-coordinated boron atoms (N4), chemical durability and dielectric properties increased with increasing P2O5/B2O3 replacements.

EFFECT OF MgO ON STRUCTURE AND DIELECTRIC PROPERTIES OF CaO–Al2O3–B2O3–SiO2 GLASSES

The effect of MgO on structure and dielectric properties of aluminoborosilicate glasses was investigated. FTIR data indicated that glass network was mainly built by tetrahedral [SiO4], [BO4], [AlO4] and trigonal [BO3]. A small amount of AlO5 or AlO6 units also existed. The glass system was characterized with lower dielectric constant (4.17 ~ 4.6) and dielectric loss (12.3 × 10-4 ~ 14.77 × 10-4) at 1 MHz. With the increase of MgO content, the quantity of AlO5 or AlO6 units decreased. The variation of density showed a decreasing tendency. The dielectric constant and loss were all found to decrease.

Properties of Aluminosilicate Glasses Prepared by Red Mud with Various [Al 2 O 3 ]/[CaO] Mass Ratios

By introducing other oxide materials (SiO2, Al2O3, CaO) into the red mud, all materials were melted into aluminosilicate glasses. On the basis of 17.2Fe2O3-5.7CaO-18.2Al2O3-50SiO2-5.9Na2O-3TiO2 system glasses, [Al2O3]/[CaO] mass ratio changed further. For each sample, the assignment of IR absorption bands for aluminosilicate glasses was investigated by Fourier transform infrared spectroscopy and the glasstransition temperature and high temperature molten state were studied by differential scanning calorimetry. According to X-Ray diffraction and differential scanning calorimetry, the behavior of crystallization was analyzed. The results show that the glass structures of three-dimensional network are depolymerized and the amount of non-bridging oxygens increases gradually with network modifier CaO replacing network intermediate Al2O3 when [Al2O3]/[CaO] ratio of aluminosilicate glass decreases from 4.05 to 0.66, resulting in decreasing density, melting temperature, crystallization peak temperature and glass-transition temperature. As [Al2O3]/[CaO] mass ratio decreases, the concentration of crystallized phase maghemite (γ-Fe2O3) will increase which provides the possibility for production of black glass-ceramic further.