Calcium Borosilicate Research Articles

Calcined colemanite as an additive for iron ore sintering process

During sintering process, iron ores, fluxes and coke are agglomerated into a desirable blast furnace feed. The degrading iron ore quality and environmental norms has forced sinter producers to look for additives which can improve the sintering process efficiency. For the current work, use of calcined colemanite as an additive was studied by adding it from 0% to 4% within the sinter raw blend through lab-scale pot trials. During the sintering process, calcined colemanite forms a Calcium Borosilicate (Ca11B2Si4O22) phase at temperature above 400 °C which latter gets dissociated within the liquid melt thus increasing the liquid slag formation. Increasing calcined colemanite up to 2% increases tumbler index from 56.27% to 61.67%, decreasing thereafter to 55.33% at 4% of calcined colemanite. The sinter yield (+5 mm) is also found to be maximum of 89.39% at 2% of calcined colemanite. An increase in calcined colemanite from 0% to 4% increases sintering time from 20 to 26 min, decreasing the overall sinter productivity from 2.35 to 1.99 t/m2/h. Before integrating calcined colemanite within the sintering process at plant scale, its cost and efficacy must be considered. An alternate approach can be combining it with an organic binder where the two can complement each other in providing the required sinter properties.

Weakening the silicate network through six-coordinated magnesium to achieve a high degree of crystallization of β-CaSiO3 in calcium borosilicate glass ceramics for 5G application

β-CaSiO3 with a low dielectric constant and low dielectric loss is one of the decisive components of commercial calcium borosilicate (CBS) low-temperature co-fired ceramic substrate. However, achieving a high degree of crystallization of β-CaSiO3 is difficult in CBS glass ceramics because of the competitive multiphase crystallization during sintering. We have shown that six-coordinated magnesium can be used to weaken the silicate network to achieve a high degree of crystallization of β-CaSiO3 in CBS glass ceramics. The appropriate MgO content to ensure a large amount of MgO6 production gradually destroys the [SiO4] tetrahedral network as the temperature increases, resulting in a β-CaSiO3 content of 76.2 vol%, when the MgO content is 2.71 mol%. The resulting material has the lowest dielectric constant (4.95@15 GHz) and dielectric loss (8 × 10−4@15 GHz), and the best three-point bend strength (77.43 MPa). Our work provides an effective method of changing the crystallization by modifying the glass network in silicate-based glass ceramics with a low dielectric constant.

Unveiling the effect of phase separation on crystallization of calcium borosilicate glass-ceramics

The CaO–B2O3–SiO2(CBS) glass-ceramics with low sintering temperature and good microwave dielectric properties have been applied on the famous commercial low temperature co-fired ceramics (LTCC) Tape for passivation substrate materials for 5G/6G technology. However, the phase separation and its relationship with the crystallization is rarely studied but extremely important for understanding and designing the high-performance CBS glass-ceramics. Herein, we find that the phase separation type of CBS glass-ceramics changes from metastable immiscibility to stable immiscibility with the increase of B2O3 content. In the metastable immiscible glass-ceramics, three phases are observed, including continuous borate-rich and silicate-rich phases as well as spherical silicate-rich phases. In the stable immiscible glass-ceramics, the silicate-rich phases transform into petal-liked shapes. β-CaSiO3 nuclei are formed in fractions with BO3/SiO4 equaling to 0.56. Notably the β-CaSiO3 nucleus do not grow after heat treatment at 850 °C, but grow at higher temperatures. Phase separation hinders the precipitation of β-CaSiO3 and promoted the formation of CaB2O4 and SiO2. In addition, interfacial defects caused by phase separation alter the crystal barrier and promote the formation of α-CaSiO3. However, α-CaSiO3 dissolves at 1000 °C and may provide Ca2+ cations together with the borate-rich phase for the regrowth of β-CaSiO3. Our work provides another perspective for understanding the effects of phase separation on crystallization in CBS glass-ceramics, contributing to improving the microwave dielectric performance by structural design.

Impacts of substitution of Fe2O3 for SiO2 on structure and properties of borosilicate glasses containing MoO3

Borosilicate glass is an effective matrix for vitrification of high-level nuclear waste. However, the solubility of molybdenum is lower. In this paper, the impacts of Fe2O3 replacing SiO2 on the phase, glass structure, and chemical durability of a simplified calcium borosilicate glass containing molybdenum were investigated. According to XRD, Raman, and FTIR spectra, replacing SiO2 with Fe2O3 makes the glass structure polymerize first and then depolymerize. Furthermore, when Fe2O3 replaces SiO2 up to 5 mol%, the samples show a fully amorphous character, and the glasses show a more disordered structure. The solubility of Mo in the simplified calcium borosilicate glass can be enhanced by extending the depolymerization regions and introducing Fe3+ to compensate for the charge of [MoO4]2−. Moreover, the substitution of Fe2O3 can improve the chemical durability of glass waste form. As a result, the borosilicate glass containing 6 mol% Fe2O3 is a potential matrix to immobilize Mo-containing HLW.

Alkali field strength effects on optical, dielectric, and conducting properties of calcium borosilicate glasses

This paper reports the alkali field strength effect on structural, optical, dielectric, and conducting properties of calcium borosilicate glasses. Glass compositions 60SiO2–5B2O3–15CaO-20R2O (where R = Li, Na, K) are synthesized by melt-quench technique. The density shows an increasing trend with the increasing atomic weight of substituted alkali metal oxides. On the other hand, the hardness and elastic modulus are found to decrease from Li2O to K2O. The tendency of oxide ions to donate electrons is found to increase with decreasing field strength of alkali ions in the glass. The optical band gap of glasses is found in the insulating range, i.e. 4.27 eV–4.38 eV. The diffusion coefficient and conductivity of Li2O-containing glass is the highest followed by Na2O and K2O. Present synthesized glasses are found to be suitable for use as a substrate in thin film solar cells.

Alumina joints brazed by screen-printed B4C–SiO2 in air

In this study, B4C–SiO2 was employed as the joining material via a screen-printing method to join alumina (Al2O3) ceramics at 1000 °C in ambient air. Effects of mass ratios of B4C and SiO2 ranging from 1:0.5 to 1:2.5 on the composition, microstructure, and mechanical properties of the joints were investigated. When the content of SiO2 was equal or greater than that of B4C, the interlayer of the brazed joints was defect-free and consisted of Al4B2O9 whiskers and calcium borosilicate glass based on microscopically electronic analyses. With the content of SiO2 increased, the shear strength of the joints increased first and then decreased. The average shear strength of the joint reached the maximum value of 110 ± 19 MPa when the mass ratio of B4C to SiO2 was 1:2. The current study demonstrated that the screen-printed B4C–SiO2 system could be a very beneficial approach to obtain high strength Al2O3 joints with defect-free interlayer at relatively low joining temperatures in air.

Chemical characterization of variably degraded fibre glass reinforced plastic from the marine environment

Glass reinforced plastic (GRP) constitutes the commonest component of small sea going craft of all descriptions. This study provides a baseline molecular and elemental account of GRP's recovered from the marine environment. Fourteen samples of GRP sourced from scrapyards and one sample sourced from a GRP boat manufacturer were examined. Samples were analysed by x-ray fluorescence and mid infrared (MIR). The latter technique confirmed that all samples contained the same polyester resin, poly diallyl phthalate (PDP). The two techniques in combination indicate the presence of aluminium calcium borosilicate E-glass fibres (E denotes electrical) of variable origins. MIR results are consistent with hydrolysis of polyester, weakening of the glass fibre resin interface facilitating exposure of e-type fibres to water which accelerates fibre breakage. The implication being that aging of GRP in the marine environment represent sources for micro (<5 mm) and macro plastic release, plus fragmented asbestiform-like silicate fibres.

A new biocompatible phosphate free mesoporous calcium borosilicate glass-ceramics for medical application

Boron plays an important role in life processes such as bone growth and maintenance. Structural and bioactivity properties of phosphate free novel composition of calcium borosilicate mesoporous glass–ceramic is reported. X-ray diffraction studies indicate the amorphous nature of sample and Fourier transmission infrared spectroscopy reveal the possible bending and stretching vibration modes of silicate and borate groups. N2 adsorption–desorption studies reveal the mesoporous structure with average pore diameter of 28 nm and surface area of 101 m2 g−1. The sample exhibits good bone-like hydroxyapatite layer formation after soaking in stimulated body fluids. Biocompatibility test of sample carried out by using myoblasts cell derived from muscle of mouse indicates an excellent biocompatibility.

Characterization of immiscibility in calcium borosilicates used for the immobilization of Mo6+ under Au‐irradiation

AbstractThe aim of this paper was to assess factors affecting primary and secondary phase separation in simplified calcium borosilicate glasses studied for nuclear waste applications. Several glasses with varying [MoO3] and [B2O3] were synthesized and exposed to Au‐irradiation to examine compositional effects on glass structure and domain size of separated phases induced by accumulated radiation damage resulting from α‐decay over a ~1000 year timeframe. The produced glasses fell within the immiscibility dome of CaO−SiO2−B2O3 and showed a unique microstructure of embedded immiscibility with three identifiable amorphous phases according to electron microscopy, Raman spectroscopy, and diffraction. These glasses were then bombarded with 7 MeV Au3+ ions to a dose of 3 × 1014 ions/cm2 creating an estimated ~1 dpa of damage. Several changes to the morphology, spatial distribution, and size of secondary phases were observed, indicative of significant structural reorganization and changes to the chemical composition of each phase. A general mechanism of coalescence to form larger particles was observed for [MoO3] &lt; 2.5 mol%, whereas segregation to form smaller more evenly distributed particles was seen for [B2O3] ≤ 15 mol% and [MoO3] ≥ 2.5 mol%. These microscopic changes were concurrent to surface‐bulk diffusion of Ca and/or Mo ions, where the direction of diffusion was dependent on [B2O3] with a barrier identified at ~20 mol%, as well as cross‐phase diffusion of said ions. These modifications occurred in part through the formation of distorted ring structures within the borosilicate network, which enabled the increased dissolution of isolated (MoO4)2− units. Au‐irradiation was therefore able to increase the solubility of molybdenum and alter the structure and composition of secondary phases with the extent of modification varying with [MoO3] and [B2O3]/[SiO2], though glasses notably remained heterogeneous. The collective results suggest that radiation and composition can both be used as design tools to modulate the domain size and distribution of separated phases in heterogeneous glasses.

The effect of particle size on radiation shielding properties for bismuth borosilicate glass

The aim of this work is to study the radiation shielding properties of size dependent bismuth in sodium calcium borosilicate glasses. The Bi2O3 in these glasses have the particle size in micrometer (M-BNCBS) have been compared the radiation shielding properties with the glasses that replaced the Bi2O3 with Bi nano-powder (N-BNCBS). The results show that the density of M-BNCBS and N-BNCBS is higher at higher concentration of Bi and the particle size of Bi does not affect to the density of glasses. The molar volumes increase with Bi content and show the higher in N-BNCBS with relative different increase with Bi content due to the NBOs more created. The N-BNCBS have the values of mass attenuation coefficients, effective atomic numbers and electron densities higher than M-BNCBS due to the larger electron cloud density in N-BNCBS. The half value layer of N-BNCBS found to be less than M-BNCBS. These results show that the particle size will affect the radiation shielding properties. Moreover, the radiation shielding properties of these glasses found to be better than Commercial window glass and some standard shielding concrete when compared.

Characteristics and dielectric properties of ZrO2-doped calcium borosilicate glass-ceramics

The influence of zirconium dioxide (ZrO2) content on crystallization, densification, and dielectric performance of calcium borosilicate (CBS) glass-ceramics was systematically investigated by differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and electrical measurements. The results revealed that ZrO2 doping reduced the crystallization temperature of CBS glass-ceramics and introduced crystalline phase of another impurity; however, excessive ZrO2 led to an increase in the crystallization temperature. Furthermore, the increase of ZrO2 content promoted the precipitation of wollastonite crystal phase. However, excessive ZrO2 damaged the close arrangement of wollastonite crystal grains in the microstructure and weakened the dielectric properties of the CBS glass-ceramics. Under optimal sintering conditions, the CBS glass-ceramics with molar ratio of n(Ca):n(Si):n(B) = 1:1:0.6 and ZrO2 content of 1 wt.% resulted in dielectric constants of 3.6 and 3.7 and a dielectric loss of 2.9 × 10−3 and 6.1 × 10−3 at 1 and 10 MHz, respectively.

Growth Mechanism and Structure Evolution during Nucleation of Calcium Borosilicate Crystal in CaO–SiO&lt;sub&gt;2&lt;/sub&gt;–B&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Based Fluorine-free Mold Flux

Growth Mechanism and Structure Evolution during Nucleation of Calcium Borosilicate Crystal in CaO–SiO&lt;sub&gt;2&lt;/sub&gt;–B&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Based Fluorine-free Mold Flux

Swift heavy ion-irradiated multi-phase calcium borosilicates: implications to molybdenum incorporation, microstructure, and network topology

A series of calcium borosilicate glasses with varying [B2O3], [MoO3], and [CaO] were prepared and subjected to 92 MeV Xe ions used to simulate the damage from long-term α-decay in nuclear waste glasses. Modifications to the solubility of molybdenum, the microstructure of separated phases, and the Si–O–B network topology were investigated following five irradiation experiments that achieved doses between 5 × 1012 and 1.8 × 1014 Xe ions/cm2 in order to test the hypotheses of whether irradiation would induce, propagate, or anneal phase separation. Using electron microscopy, EDS analysis, Raman spectroscopy, and XRD, irradiation was observed to increase the integration of MoO42− by increasing the structural disorder within and between heterogeneous amorphous phases. This occurred through Si/B-O-Si/B bond breakage and reformation of boroxyl and 3/4-membered SiO4 rings. De-mixing of the Si–O–B network concurrently enabled cross directional Ca and Mo diffusion along defect created pathways, which were prevalent along the interface between phases. The initiation and extent of these changes was dependent primarily on the [SiO2]/[B2O3] ratio, with [MoO3] having a secondary effect on influencing the defect population with increasing dose. Microstructurally, these changes to bonding caused a reduction in heterogeneities between amorphous phases by reducing the size and increasing the spatial distribution of immiscible droplets. This general increase in structural disorder prevented crystallization in most cases, but where precipitation was initiated by radiation, it was re-amorphized with increasing dose. These outcomes suggest that internal radiation can alter phase separation tie lines, and can therefore be used as a tool to design certain structural environments for long-term encapsulation of radioisotopes.

Effect of TiO2 doping on crystallization, microstructure and dielectric properties of CBS glass-ceramics

In this study, calcium borosilicate (CaO-B2O3-SiO2, CBS) glass-ceramics were fabricated using chemically pure CaO, SiO2, and B2O3 as raw materials. Differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and electrical measurements were conducted to explore the effect of titanium dioxide (TiO2) doping on crystallization, microstructure, and dielectric properties of CBS glass-ceramics. Furthermore, the influence of sintering temperature and sintering schemes on crystalline phases of CBS glass-ceramics was systematically investigated. Results showed that the increase of TiO2 content led to the reduction in sintering temperature of CBS glass-ceramics and promoted the precipitation of wollastonite crystal phase. For instance, with the increase of content of TiO2 from 0 to 3 wt%, transition temperature and crystallization temperature were reduced by 12.9 and 27.6 °C, respectively. However, excessive TiO2 affected the precipitation of wollastonite crystal phase, destroyed crystal structure, and damaged close arrangement of crystal grains. Moreover, higher TiO2 content was found to weaken dielectric properties of CBS glass-ceramics. In this study, the best molar ratio of ingredients, meeting that of ideal target material, is n(Ca): n(Si): n(B) = 1:1:0.6, with doping mass fraction of 2 wt% of TiO2. After optimal sintering procedure, dielectric constant of the best sample was found to be 1.4 (1 MHz), 1.3 (10 MHz), and dielectric loss was 3.9 × 10−3 (1 MHz) and 3.8 × 10−3 (10 MHz).

The effect of CaO/SiO2 and B2O3 on the sintering contraction behaviors of CaO-B2O3-SiO2 glass-ceramics

We investigate the effect of CaO/SiO2 (molar ratio) and B2O3 content on the structure and sintering contraction behaviors of Calcium borosilicate (CaO–B2O3–SiO2, CBS) glass-ceramic through the dilatometer and the Fourier transform infrared (FTIR) spectroscopy. The results show that the sintering-shrinkage of CBS glass-ceramics is promoted dramatically with the increase of CaO/SiO2 to 1.14, and then keeps nearly constant as the CaO/SiO2 further increases. This phenomenon is correlated with the degree of polymerization (DOP) of the Si–O network structure modulated by the CaO/SiO2, additionally, two sintering shrinkage peaks, corresponding to two-step depolymerization, are detected in the sintering-shrinkage curves of the CBS glass-ceramic as the B2O3 content is elevated to 13.6 mol%. Meanwhile, the shrinking rate of CBS glass-ceramics is increased from 8 × 10[Formula: see text] to 37 × 10[Formula: see text] min[Formula: see text] and the softening point is decreased from 736[Formula: see text]C to 691[Formula: see text]C with the increase of B2O3 content from 6.8 to 20.8 mol⋅%. This is due to the introduction of BO3 trihedral into Si–O–Si three-dimensional structure, which greatly reduces the uniformity and symmetry of the networks, inducing the decrease of the strength for the whole Si–O–Si network structures. The results obtained in this paper reveal the relationship between the glass structure and sintering behavior of the CBS glass-ceramic, which gives an avenue to improve its physical properties.

Tunable colors and applications of Dy3+/Eu3+ co‐doped CaO‐B2O3‐SiO2 glasses

AbstractA series of Dy3+/Eu3+ single‐ and co‐doped calcium borosilicate luminescent glasses were prepared by the conventional high temperature melt‐quenching method. A compact glass structure is obtained by the addition of Dy3+/Eu3+ ions, which is verified by the physical properties of synthetic glasses. As network modifiers, Dy3+/Eu3+ fill in the interspaces of glass network and contribute to the conversion of [BO3] to [BO4]. Dy3+/Eu3+ co‐doped calcium borosilicate glasses can emit white light, which consists of blue, yellow, and red light under 387 nm excitation. The emission spectra and decay curves of the white‐emitting glasses have proved the existence of energy transfer. The average lifetime of Dy3+ decreases from 0.251 to 0.165 ms with the increasing Eu3+ concentration. Changing rare earth ions concentration, CIE color coordinates of Dy3+/Eu3+ co‐doped glass shifts from cyan to white with increasing excitation wavelength. A white‐light emission is obtained when the concentration of Dy3+ and Eu3+ equals to 4% and 2%, respectively. Moreover, the Dy3+/Eu3+ co‐doped calcium borosilicate glass shows high‐thermal stability and it may be applicable for high‐quality white LEDs based on high power near ultraviolet (n‐UV) LED chip in the future.

Antibacterial and structural properties of mesoporous Ag doped calcium borosilicate glass-ceramics synthesized via a sol-gel route

Structural, electrical, bioactivity and antibacterial properties of mesoporous Ag doped calcium borosilicate glass-ceramics are reported. A simple sol-gel route was used to synthesize the mesoporous glass-ceramics. N2 adsorption–desorption studies reveal the mesoporous structure of the samples. The embedment of nano-sized Ag metallic particles in glass matrix was confirmed for Ag doped sample calcined at 600 °C by X-ray diffraction, UV–visible, and transmission electron microscopic analyses. Ac conductivity is used to study the electrical relaxation processes. Ag nanoparticle-embedded sample reveal nearly constant loss behaviour, whereas silver ions alone embedded sample show universal dielectric relaxation behaviour. Ag doped samples exhibit good antibacterial properties without compromising the bone-like apatite layer formation. The antibacterial effect against Gram negative bacteria is higher for Ag doped sample calcined at 600 °C which exhibits a dominant nearly constant dielectric loss feature.

Bioactivity and Antibacterial Studies on Silver Nanoparticles Embedded Calcium Borosilicate Ceramics

We report the structural, bioactivity and antibacterial effect of silver nanoparticle embedded calcium borosilicate ceramics obtained by a simple sol-gel route and post annealing approach. The structural properties were studied by means of powder X-ray diffraction (XRD), UV-visible, Fourier transform infrared (FTIR) and transmission electron microscopy (TEM). The glass-ceramic nature of the sample was confirmed by XRD and FTIR. TEM and UV spectrum reveal the Ag nanoparticle embedment on amorphous matrix. The hydroxyapatite layer formation is investigated by in-vitro approach using Dulbecco’s Modified Eagle’s Medium. The antibacterial effects were tested with different bacteria using an agar well diffusion method. Samples show good antibacterial effect without compromising the formation of hydroxyapatite.

Femtosecond Laser Ablation-ICP-Mass Spectrometry and CHNS Elemental Analyzer Reveal Trace Element Characteristics of Danburite from Mexico, Tanzania, and Vietnam

Danburite is a calcium borosilicate that forms within the transition zones of metacarbonates and pegmatites as a late magmatic accessory mineral. We present here trace element contents obtained by femtosecond laser ablation-inductively coupled plasma (ICP)-mass spectrometry for danburite from Mexico, Tanzania, and Vietnam. The Tanzanian and Vietnamese samples show high concentrations of rare earth elements (∑REEs 1900 µg∙g−1 and 1100 µg∙g−1, respectively), whereas Mexican samples are depleted in REEs (&lt;1.1 µg∙g−1). Other traces include Al, Sr, and Be, with Al and Sr dominating in Mexican samples (325 and 1611 µg∙g−1, respectively). Volatile elements, analyzed using a CHNS elemental analyzer, reach &lt;3000 µg∙g−1. Sr and Al are incorporated following Ca2+ = Sr2+ and 2 B3+ + 3 O2− = Al3+ + 3 OH− + □ (vacancy). REEs replace Ca2+ with a coupled substitution of B3+ by Be2+. Cerium is assumed to be present as Ce4+ in Tanzanian samples based on the observed Be/REE molar ratio of 1.5:1 following 2 Ca2+ + 3 B3+ = Ce4+ + REE3+ + 3 Be2+. In Vietnamese samples, Ce is present as Ce3+ seen in a Be/REE molar ratio of 1:1, indicating a substitution of Ca2+ + B3+ = REE3+ + Be2+. Our results imply that the trace elements of danburite reflect different involvement of metacarbonates and pegmatites among the different locations.

Rigid-resilient transition in calcium borosilicate sealing glass–ceramics: Effect of preferred orientation

At present, the insufficient thermo-mechanical stability of sealing glass presents a challenge for solid oxide fuel cells (SOFCs). In this work, we report for the first time that a rigid-resilient transition occurs in a calcium borosilicate sealing glass upon heating at 700 °C for different durations. The elastic modulus increases from 28.1–40.0 GPa for 24 h to 92.3–105.1 GPa for 100 h, while the corresponding hardness increases from 2.5–3.1 GPa to 8.1–9.2 GPa. In addition, a possible mechanism for the rigid-resilient transition has been proposed. The reported results provide a new approach to solve the sealing problem of SOFCs.