K2O B2O3 SiO2 Research Articles

Structure and Thermal Properties of High-Alkali Molybdenum-Containing Borosilicate Host Materials

To study immobilization properties of oxide borosilicate systems, we have assessed the effect of molybdenum on the structure, phase composition, and thermal properties of glass-ceramic materials prepared via rapid cooling of high-alkali melts in the Li2O–(Na2O–K2O)–B2O3–SiO2 system. The results demonstrate that the molybdenum-free materials consist of homogeneous borosilicate glass, which partially crystallizes during heat treatment (annealing). The only exception is a glass sample of the K2O–B2O3–SiO2 system, which has high thermal stability. The addition of molybdenum oxide to these materials in the high-temperature synthesis step initiates crystallization processes, which are most pronounced after heat treatment (annealing). In the materials containing one alkali metal cation in their composition, all of the added molybdenum oxide enters into the composition of the alkali metal molybdates embedded in a homogeneous amorphous highly polymerized borosilicate matrix. In the samples containing cations of two alkali metals in their composition, crystallization processes lead to the formation of a highly inhomogeneous crystalline material. The good homogeneity of the glass-ceramic materials prepared via rapid cooling of high-alkali molybdenum-containing melts of the Li2O–(Na2O–K2O)–B2O3–SiO2 system with one type of alkali metal cation in their composition allows them to be recommended for temporary immobilization of molybdenum oxide-rich radioactive waste.

Low‐temperature sintering of CaMgSi2O6-KBS composites with ultralow dielectric constant

In this paper, ultralow dielectric constant CaMgSi2O6-KBS composites (εr < 5) were fabricated via the solid-state route. The sintering temperature (ST) of CaMgSi2O6 ceramics was successfully reduced from more than 1200 °C–850 °C with assistance of the K2O–B2O3–SiO2 (KBS) glass. The impacts of KBS glass on phase compositions, microstructure, sintering activation energy and microwave dielectric properties of CaMgSi2O6 ceramics were systematically discussed. The X-ray diffraction results confirmed that the (1-x)CaMgSi2O6-xKBS composites possessed CaMgSi2O6 phase and SiO2 phase. The results of Rietveld refinement showed that the weight fraction of CaMgSi2O6 phase gradually decreased with increasing KBS glass and sintering temperature. The (1-x)CaMgSi2O6-xKBS (x = 0.5) composite sintered at 850 °C exhibits optimal microwave dielectric properties: εr = 4.58, Q × f = 13989 GHz (13.95 GHz), τf = -22.9 ppm/oC. It is a promising material for low-temperature co-fired ceramic (LTCC) applications which desire for ultralow dielectric constant materials.

Preparation of low-permittivity K2O–B2O3–SiO2–Al2O3 composites without the addition of glass

Abstract In the field of low temperature co-fired ceramic (LTCC), it remains a challenge to design the performance of LTCC with low permittivity less than 5. Here, the K2O– B2O3–SiO2–Al2O3 composites are prepared without the preparation of prior glass. Meanwhile, the factors of the CaO content on microstructure, phase structure and properties of the composites are considered systematically. The crystal structure measured by X-ray diffraction (XRD) shows that there are quartz and alumina as the crystal phases. The results reveals that the tailoring CaO content benefits sintering densification, low dielectric loss, great mechanical properties and low thermal expansion coefficient. As CaO content increases up to 2.8 wt%, the composites sintered at 850∘C have a dielectric constant of 4.94 and tanδ of 8 × 10−4 at 1 MHz, thermal expansion coefficient (CTE) of 8.5 ppm/∘C, and flexural strength of 150 MPa. As the mass fraction of CaO increases up to 3.2 wt%, the maximum flexural strength of 173MPa is achieved. The above study provides an effective approach for preparing the novel composites as a promising candidate for LTCC applications.

Enhanced thermal and mechanical properties of Li–Al–Si composites with K2O–B2O3–SiO2 glass for LTCC application

Abstract In this study, Li–Al–Si composites with K2O–B2O3–SiO2 (KBS) glass were synthesized by traditional solid-state method, and the phase composition, microstructure, sintering behavior as well as properties were systematically investigated. The specimen with 4 wt % Al2O3 sintered at 1020 °C exhibited a high thermal conductivity of 10.46 W/(mK) and a flexural strength of 180.23 MPa. The sintering temperature was reduced from 1020 °C to 900 °C using KBS glass frits as sintering additives. The sample with 2.0 wt % KBS, sintered at 900 °C for 2 h, possessed a relatively high thermal conductivity of 9.83 W/(mK), a high flexural strength of 215.09 MPa, and a low dielectric constant of 6.24, thus demonstrating its potential for LTCC application.

The Influence of Glass Composition on Iodine Solubility

AbstractTwo glass series in the ternary systems K2O-B2O3-SiO2 (KBS) and Na2O-B2O3-SiO2 (NBS) were studied in order to identify the main factors influencing the solubility of iodine. We established that iodine incorporation is strongly linked to the bulk chemistry, i.e. the SiO2/(B2O3+SiO2) molar ratio, and to the physical properties of the glasses, and we assessed three different solubility limits. Iodine in Si-rich glasses has a low solubility (≤1 mol% I) regardless of the alkali ion present. On the contrary, in B-rich glasses, the solubility is five times higher than in Si-rich glasses for Na-glasses, and more than six times higher for K-glasses. The strong dependence of iodine solubility on the bulk chemistry is related to the adaptability of the glass network. Furthermore, our data suggest that iodine is stable with different redox states in the glasses here analyzed.

Titanium in the Structure of Alkali Borosilicate Glasses

Vibrational spectroscopy is used to show that the effect of adding titanium to K2O–B2O3–SiO2 glasses differing by the ratio of the boron and alkali metal contents is different. This result reflects the change in the structural role of titanium in the glass and is important for evaluating the influence of titanium additions on the properties of alkali borosilicate glass in the process of improving the glassy matrix materials used for the immobilization of radwastes.

Sintering behavior and microwave dielectric properties of TiO2 added Ba4(Sm0.5Nd0.5)28/3Ti18O54 ceramics with K2O–B2O3–SiO2 glass

K2O–B2O3–SiO2 (KBS) synthesized via a solid-state reaction process was chosen as a novel sintering aid for Ba6–3x(Sm1-y, Ndy)8+2xTi18O54 + 2TiO2 (x = 2/3 and y = 0.5; BSNTT) ceramics. Effects of KBS doping on sintering behavior, microstructure and microwave dielectric properties of BSNTT ceramic were investigated. The appropriate KBS addition significantly lowered the sintering temperature of BSNTT ceramic with slightly damaging its microwave dielectric properties. The X-ray diffraction results showed that all the well sintered samples exhibited the main phase Ba(Sm,Nd)2Ti4O12 and a certain amount of Ba2Ti9O20 and TiO2 secondary phases. Besides, the other secondary phase Sm2Ti2O7 formed when 9 wt% KBS added. Then the scanning electron microscopy micrographs of the optimally well-sintered (1075 °C for 3 h) ceramics showed a dense microstructure. With the increasing content of KBS addition, both the dielectric constant (er) and quality factor (Q × f) value decreased. At last, the good microwave dielectric properties of er = 68.8, Q × f = 6766 GHz, τf = 28.76 ppm/°C were obtained for BSNTT + 5 wt% KBS ceramic sintered in air at 1075 °C for 3 h.

Low temperature sintering and characteristics of K2O–B2O3–SiO2–Al2O3 glass/ceramic composites for LTCC applications

The K2O–B2O3–SiO2, K2O–B2O3–SiO2–2 %Al2O3, K2O–B2O3–SiO2–4 %Al2O3 glasses with different Al2O3 content were prepared. Different proportions (50, 55, 60, 65, 70 %) of the three glasses were respectively mixed with alumina ceramic-filler, then the mechanical and dielectric properties were investigated. The results showed K2O–B2O3–SiO2–2 %Al2O3 glass/alumina filler (glass:alumina = 60:40) had the excellent comprehensive properties, so further study was continued with part of alumina ceramic-filler replaced by the silica ceramic-filler on this composite. Then the X-ray diffraction analysis revealed that the alumina and silica fillers existed as the crystal phase, and the densification was seriously damaged when the silica content reached to three quarters of the fillers. With the increase of the silica-filler, the composites’ density and dielectric constant exhibited uniform decrease, but thermal expansion coefficient (TEC) uniformly increased. When the glass:alumina:silica was equal to 60:30:10, a best composite property was presented as a bulk density of 2.582 (g cm−1), a dielectric constant of 6.1 and a dielectric loss of 2 × 10−3 at 1 MHz, a flexural strength of 168 MPa, and a TEC of 8.62 × 10−6 °C−1.

Rheological properties of borosilicate glasses and melts

The effect of concentration and structural factors on the character of the temperature dependence of the viscosity of glasses in the systems K2O–B2O3–SiO2 and Na2O–B2O3–SiO2 in the range 109 – 104 Pa ⋅ sec is determined. It is shown that the effect of boron and potassium oxides on the temperature dependence of the viscosity near the transition from the liquid into the plastic state is complex.

Behavior of water in sodium and potassium borosilicate glasses

IR spectroscopy was used to study the behavior of water in model glasses of the systems Na2O–B2O3–SiO2 and K2O–B2O3–SiO2. It was determined that hydroxyl groups and water in molecular form are present in such alkali borosilicate glasses obtained by quenching water-bearing melt. The water distribution between its forms and silicate and borate components of the glass structure depends on their chemical composition. Proton-cation exchange with the participation of non-bridge oxygen atoms and coordinated alkali-metal ions is involved in the process leading to the formation of hydroxyl groups.

THE DEVELOPMENT OF AN ENAMEL ON A EUTECTIC BASIS1

The object of the investigation was to develop eutectic solvent for an enamel by the combination of several eutectics, then to add silica to increase the refractoriness of the enamel up to the limit of its capability to dissolve silica without endangering its bond to the metal body. This naturally involved a study of the entectic compositions of the RO–B2O3–SiO2 systems. Since the Na2O–B2O3-SiO2, K2O–B2O3–SiO2, and PbO–B2O3-SiO2 detormation eutectics are known a knowledge of the CaO-B2O3-SiO2 system was necessary. A study of the high B2O3 area of this system was made at approximately 4% intervals. A member high in CaO and SiO2, and which on repeated fusions showed practically 100% glass, was selected as a practical member to blend with the Na2O-B2O3–SiO3 and the PbO-B2O3–SiO2 eutedic to form a eutectic solvent for an enamel. Combinations of these eutectics and the CaO-B2O3-SiO2 mixture were made and applied to cast iron by the dry process. Additions of SiO2 were also made to these enamels up to 1.5 molecular equivalents. The physical properties of these enamels such as brilliancy, smoothness of surface, texture, bonding power, solubility in water, and resistance to acid attack were also determined.