CaO B2O3 SiO2 Research Articles

Influence of FeSiAl Content on the Morphological Evolution and Electromagnetic Properties of FeSiAl/CaO–B2O3–SiO2 Microwave-Absorbing Coatings

CaO–B2O3–SiO2 (CBS) is a promising lightweight, low-dielectric matrix material for high-temperature microwave-absorbing coatings. However, the comprehensive study of absorbent morphology evolution within such coatings and its influence on electromagnetic (EM) performance has not been conducted. In this work, a series of FeSiAl (FSA)/CBS composite coatings with various FSA contents were fabricated using atmospheric plasma spraying. The morphological evolution of the FSA phase and the resulting EM properties of the coatings were systematically analyzed. Experimental findings show that during the spraying process, when the size of FSA clusters in the composite powder exceeds the thickness of CBS splats, FSA clusters form a rigid contact with the underlying solidified coating, leading to the development of a lamellar structure. This lamellar FSA phase creates local conductive networks, which significantly increase the complex permittivity of the coating. These results provide valuable guidance for controlling absorbent morphology and optimizing the EM properties of CBS-based coatings.

Polymer-derived coatings with La2Zr2O7 and glass fillers: Preparation and characterisation

This study investigated the impact of La2Zr2O7 (LZ) and different types of glass on the performance of polymer-derived ceramic (PDC) coatings on AISI 441 stainless steel substrates. Four double-layer PDC-based glass-ceramic coatings containing LZ and different glass fillers were prepared by dip coating. The LZ powder was synthesised by solid-state reaction (SSR): powder morphology, crystal structure, and thermal stability were analysed. X-ray diffraction (XRD) detected a LZ pyrochlore phase after annealing at 1300 and 1400 °C with a trace of t-ZrO2. Four different glass compositions, namely BaO-Al2O3-SiO2 (BAS), BaO-Al2O3-La2O3-B2O3-SiO2 (BALBS), CaO-B2O3-SiO2 (CBS), and BaO-ZnO-MgO-B2O3-SiO2 (BZMBS), were also synthesised as fillers for PDC coatings. The glass transition and crystallisation temperatures of the glasses were determined using differential scanning calorimetry (DSC). The coating systems, consisting of a Durazane 2250 bond coat and a top coat (Durazane 1800 + LZ filler + different glass sealants), were prepared. After pyrolysis of the coatings at 900 °C, some of the glasses partially crystallised. Scanning electron microscopy (SEM) revealed that the layers containing BAS, BALBS and CBS glass were dense, with good adhesion to the substrate, and with occasional presence of larger pores and cracks. Delamination of the upper layer was observed in the coating with the BZMBS glass filler.

Crystallization and microwave dielectric properties of CaO-B2O3-SiO2 glass-ceramic/Al2O3 for LTCC applications

High-frequency electronic devices with low dielectric loss and electronic components with high integration densities require high-performance electronic packaging materials. In this study, materials primarily composed of CaO-B2O3-SiO2 (CBS) with an elevated boron content were fabricated through solid-phase sintering using Al2O3 as the ceramic phase. The phase compositions, densification process, microstructures, thermal conductivity, thermal expansion, and dielectric properties of the LTCC were investigated. Remarkably, the CBS-1 LTCC composite sintered at 850 °C for 4 h, exhibited a dense and nonporous microstructure. It demonstrated exceptional thermoelectric properties, including a thermal shrinkage of 5.61 %, coefficients of thermal expansion of 4.86 ppm/°C, thermal conductivity of 2.36 W/m·K, dielectric constant (εr) of 4.88, and tan δ of 1.05× 10−3 at 15 GHz. These characteristics are conducive to minimizing the signal propagation time delay and filtering noisy signals. Consequently, the CBS-1 LTCC composite emerged as a promising substrate for LTCC applications.

Glass frit and method of forming electrical insulating coatings on steel substrates of film heaters

Electric film heaters (EFHs) applied on flat steel substrates show promising potential in the production of heating devices. The basis for manufacturing EHFs is heat-resistant steel, the surface of which is coated with a heat-resistant electrical insulation coating. These coatings are glass crystalline and are applied mainly by screen printing. Compared to screen printing, the electrophoretic method of coating is more productive. In this work, glass in the MgO–CaO–B2O3–SiO2 oxide system was chosen for obtaining glass crystalline coatings. The paper provides a description of the material composition and the method used to prepare a suspension for еру electrophoretic deposition of coating. The main technological parameters for forming electrophoretic coatings with a specific thickness are determined based on experimental results. Utilizing calculated data on the properties of the selected glass, the study substantiates the most rational temperature and time regime for coating firing. These conditions promote crystallization and result in the production of heat-resistant coatings with sufficient electrical insulating properties for steel substrates of EFHs.

Characteristics of a CaO–B2O3–SiO2–Al2O3–ZnO-based sandwich substrate and its dielectric properties in the 5G millimeter-wave band

In this study, a 34.5CaO–23B2O3–33.5SiO2–6Al2O3–3ZnO (CBSAZ) glass-ceramic substrate was prepared using a sol–gel method. A porous CaO–B2O3–SiO2–Al2O3–ZnO layer (CBSAZ0.5C) with a porosity of 72.6 % and thickness of 365 μm was inserted between two ∼120 μm thick dense CBSAZ layers to form a tri-layer substrate (CBSAZ/CBSAZ0.5C/CBSAZ). The dielectric constants (εr) and dielectric losses (tanδ) of the dense CBSAZ substrate at 20 and 60 GHz were 6.90 and 0.029, respectively, and 6.96 and 0.017, respectively. These values were almost independent of frequency. In contrast, the εr and tanδ values of the CBSAZ/CBSAZ0.5C/CBSAZ sandwich substrate at 20 and 60 GHz were 3.59 and 0.022, respectively, and 3.11 and 0.020, respectively. Thus, the εr value of the CBSAZ/CBSAZ0.5C/CBSAZ sandwich substrate was significantly lower than that of the CBSAZ substrate, whereas the tanδ and κ values of the CBSAZ/CBSAZ0.5C/CBSAZ and CBSAZ substrates were similar.

Sintering behaviors, microstructure and properties of CaO–B2O3–SiO2 glass-ceramics for LTCC applications

The aim of this work was to investigate the impacts of MgO on the crystalline behaviors, microstructure, and properties of CaO–B2O3–SiO2 (CBS) glass-ceramics. In the study, the CBS samples with various MgO contents were developed via the melting and quenching route. Subsequently, a CBS casting tape and a multi-layered LTCC microcircuit module were created by using the tape casting method. Results indicated that MgO could break the glass network and promote the formation of liquid phase during the sintering process. A suitable amount of MgO additive promoted densification during firing process and improved the properties of the CBS materials. The CBS sample with 1.5 wt% MgO fired at 875 °C exhibited outstanding properties, including a dielectric constant (εr) of 6.5 (at 10 GHz), a dielectric loss (tan δ) of 8 × 10−4, a flexural strength of 167 MPa, a coefficient of thermal expansion (CTE) of 6.8 ppm/°C, and a thermal conductivity (λ) of 2.2 W/mK. In addition, this LTCC material demonstrated good co-firing compatibility with silver electrodes and superior temperature stability, showing its great potential for microelectronic applications.

A novel high-temperature FeSiAl/CaO–B2O3–SiO2 microwave absorption coating prepared via atmospheric plasma spraying

In this paper, CaO–B2O3–SiO2 (CBS) is utilized as matrix material of microwave coating for the first time to achieve high-performance microwave absorption under high-temperature. A series of FeSiAl (FSA)/CBS composite coatings were prepared via atmospheric plasma spraying. The impact of spraying power on the microstructure, electromagnetic properties, and high-temperature stability of as-sprayed coatings were studied. The experimental results reveal that CBS could effectively suppress the formation of the lamellar structure of FSA as the low initial melting temperature, also form unexpected Fe2SiO4 structure with FSA during the spraying process. The increase in complex permittivity of the coating is primarily attributed to enhanced coating density and the development of Fe-rich regions within the CBS matrix. Furthermore, the dense coating prevents the oxidation of FSA and exhibits high-temperature stability. Our coating of 1 mm thickness has a reflection loss below −5 dB with frequency range of 7–14.8 GHz at 500 °C.

Preparation of Sol-Gel-Derived CaO-B2O3-SiO2 Glass/Al2O3 Composites with High Flexural Strength and Low Dielectric Constant for LTCC Application.

Low-temperature co-fired ceramic (LTCC) substrate materials are widely applied in electronic components due to their excellent microwave dielectric properties. However, the absence of LTCC materials with a lower dielectric constant and higher mechanical strength restricts the creation of integrated and minified electronic devices. In this work, sol-gel-derived CaO-B2O3-SiO2 (CBS) glass/Al2O3 composites with high flexural strength and low dielectric constant were successfully prepared using the LTCC technique. Among the composites sintered at different temperatures, the composites sintered at 870 °C for 2 hours possess a dielectric constant of 6.3 (10 GHz), a dielectric loss of 0.2%, a flexural strength of 245 MPa, and a CTE of 5.3 × 10-6 K-1, demonstrating its great potential for applications in the electronic package field. By analyzing the CBS glass' physical characteristics, it was found that the sol-gel-derived glass has an extremely low dielectric constant of 3.6 and does not crystallize or react with Al2O3 at the sintering temperature, which is conducive to improving the flexural strength and reducing the dielectric constant of CBS glass/Al2O3 composites.

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.

Effects of CaO additive on sintering behaviour and properties of CaO–B2O3–SiO2 glass-ceramics for LTCC applications

The effects of CaO additive on the phase composition, sintering behaviour, microstructure, and properties of CaO–B2O3–SiO2 (CBS) glass-ceramics were investigated. The results revealed that a small amount of added CaO (0.5 wt%, 1 wt%) facilitated the transformation of α-CaSiO3 to β-CaSiO3 and improved the crystallinity. When the amount was greater than 1 wt%, it weakened this transformation and also decreased the crystallinity. The pure CBS sample needed a sintering temperature of 850 °C for maximum densification, whereas the CaO-added samples achieved densification at a sintering temperature of 750–770 °C. The addition of an appropriate amount of CaO significantly enhanced the densification, dielectric properties, and flexural strength of CBS glass-ceramics. However, the addition of CaO had minimal impact on the coefficient of thermal expansion (CTE), which varied from 7.69 to 8.51 ppm/°C. The sample doped with 1 wt% CaO was sintered at 770 °C for 15 min, and it exhibited fairly ideal performance with a bulk density of 2.64 g/cm3, εr of 6.43, tanδ of 0.9 × 10−3 (15 GHz), and a CTE value of 7.69 ppm/°C.

Relationship between the structural and dielectric properties of sol-gel derived CaO–MgO–B2O3–SiO2 glass-ceramics for 5G applications in the millimeter-wave bands

In this study, CaO–MgO–B2O3–SiO2 glass-ceramics were fabricated using a sol–gel method, and their dielectric properties in the millimeter-wave (mm-wave) bands were evaluated. The glass transition temperature of the as-prepared CaO–MgO–B2O3–SiO2 glass-ceramics decreased slightly with increasing MgO/CaO ratio because the field strength of Mg2+ ions was higher than that of Ca2+ ions. After sintering at 900–950 °C, only orthorhombic CaB2O4 or monoclinic Mg2B2O5 crystallites were observed in the X-ray diffraction (XRD) patterns of the glass-ceramics, depending on the MgO/CaO ratio. The Fourier-transform infrared and Raman spectra of the glass-ceramics confirmed the XRD results. The quantity and grain size of crystallites and the content and size of pores of the glass-ceramics decreased with increasing MgO/CaO ratio. The CaO–MgO–B2O3–SiO2 glass-ceramics exhibited excellent mm-wave dielectric properties. For example, the 7.3CaO‒7.2MgO‒22.2B2O3‒63.3SiO2 glass-ceramic exhibited a dielectric constant of 4.21 and a dielectric loss of 0.0025 at 60 GHz, a breakdown strength of 14.9 kV/mm, an electric resistivity of 7.64 × 1013 Ω cm, a coefficient of thermal expansion of 4.0 ppm/°C, and a thermal conductivity of 1.29 W/mK. The low-dielectric-constant and low-loss characteristics of the MgO–CaO–B2O3–SiO2 glass-ceramics prepared in this study enables to provide very low propagation delay of signals and to offer low signal attenuation in 5 G applications.

Microwave dielectric characterization and densification mechanism analysis of CaO‐B2O3‐SiO2 glass–ceramic/Al2O3 composites for LTCC applications

AbstractIn this study, nine component points were designed based on a CaO‐B2O3‐SiO2 (CBS) glass system with a high boron content, and CBS glass/Al2O3 composites were developed for low‐temperature co‐fired ceramic (LTCC) applications. Furthermore, the densification process, phase compositions, microstructures, and properties were investigated. The results indicated that the softening of glass and interfacial reaction between the glass and Al2O3 were the two most important factors affecting LTCC's densification process. The real‐time shrinkage rate of LTCC during sintering was simulated using the thermal shrinkage curve and combined with DTA and X‐ray diffraction. It was proven that the formation of the CaAl2(BO3)O phase contributed to the reduction in glass viscosity and promoted the formation of a dense structure. The LTCC composite with 30 vol% glass sintered at 850°C exhibited a coefficient of thermal expansion of 4.55–6.35 ppm/◦C, εr of 3.5–5.0, and a minimum tan δ of 0.0018 at 15 GHz. Therefore, these properties make the CBS–LTCC more suitable for high‐frequency applications.

Enhanced thermal conductivity and mechanical performance of CaO–B2O3–SiO2 glass ceramic with AlN addition for LTCC applications

As electronic devices with high integration and reliability are developed, the need for electronic packaging materials with good thermal conductivity, dielectric properties, and mechanical properties has increased. In this study, a CaO–B2O3–SiO2 (CBS) glass ceramic with added aluminium nitride (AlN) was prepared via tape casting and solid phase sintering. The sintering behavior, phase compositions, microstructure, thermal conductivity, mechanical properties, and dielectric properties of the material were investigated. The addition of AlN greatly enhanced the thermal conductivity and improved the mechanical properties of the composite. The CBS/AlN composite with 40 wt% AlN sintered at 860 °C for 20 min exhibited excellent performance with a thermal conductivity of 6.23 W/(m⋅K), a coefficient of thermal expansion (CTE) of 6.11 ppm/°C, a flexural strength of 212.6 MPa, a dielectric permittivity of 7.2–7.36 with a relatively low dissipation factor of 0.0003–0.002 (1 kHz–10 MHz), and a weak temperature dependence of the dielectric permittivity. Moreover, the excellent chemical compatibility with silver made such CBS/AlN composites a promising material for electronic substrate applications.

The Influence of CaF2 Doping on the Sintering Behavior and Microwave Dielectric Properties of CaO-B2O3-SiO2 Glass-Ceramics for LTCC Applications

With the rapid development of microelectronic information technology, microelectronic packaging has higher requirements in terms of integration density, signal transmission speed, and passive component integration. Low temperature co-fired ceramics (LTCC) exhibit excellent dielectric properties and low temperature sintering properties, which meets the above-mentioned requirements. This work investigates the effects of CaF2 doping (0–16 mol%) on the glass structure, sintering behavior, crystallization, microstructure, and microwave dielectric properties of the CaO-B2O3-SiO2 (CBS) glass-ceramic system. Glass-ceramics were prepared using the conventional melting and quenching method. The physical and chemical properties of the glass-ceramics were analyzed using various techniques including TMA, SDT, FTIR, XRD, SEM, and a network analyzer. The results indicate that CaF2 doping can effectively reduce the sintering temperature and softening temperature of CBS ceramics. It also substantially improves the densification, dielectric, and mechanical properties. The appropriate amount of CaF2-doped CBS glass-ceramics can be sintered below 800 °C with a low dielectric constant and loss at high frequency (εr < 6, tanδ < 0.02 @ 10~13 GHz). Specifically, 8 mol% CaF2 doped CBS glass-ceramics sintered at 790 °C exhibit excellent microwave dielectric and thermal properties, with εr ~ 5.92 @ 11.4 GHz, tanδ ~ 1.59 × 10−3, CTE ~ 7.76 × 10−6/°C, λ ~ 2.17 W/(m·k), which are attractive for LTCC applications.

Stabilizing the anti-ferroelectric phase in NaO–Nb2O5–CaO–B2O3–SiO2–ZrO2 glass-ceramics using the modification of K+ ion

NaNbO3 anti-ferroelectric (AFE) material exhibits a unique and irreversible phase transition, which makes it change into ferroelectric phase and prevents its implementation in high energy storage material. In this work, we use an approach to stabilize the anti-ferroelectric phase at room temperature by the modification of K+ in NaO–Nb2O5–CaO–B2O3–SiO2–ZrO2-xK + glass-ceramics. The correlation between K+ content and anti-ferroelectric stability is studied through the X-ray diffraction, microstructure, and dielectric properties. It is found that ferroelectric phase gradually transforms to anti-ferroelectric phase first and then anti-ferroelectric phase disappears with K+ doping in glass-ceramic due to two mechanisms that the un-crystallized modifier K+ into glass network reduce the connectivity of the glass network, the activation energy needed for crystallization and the tolerance factor (t), besides overmuch K+ into NaNbO3 crystalline phase leads to the increase of tolerance factor and the production of impurity phase. The phase transition has been confirmed through the double polarization loops, AFE phase and permittivity peak. The results show that the K+ doped into NaO–Nb2O5–CaO–B2O3–SiO2–ZrO2-xK + glass system can effectively stabilize AFE phase, when x＞4%, the stability of NaNbO3 anti-ferroelectric phase will decrease and impurity phases will precipitate in glass-ceramic.

Effect of Ta2O5 addition on the structure, crystallization mechanism, and properties of CaO–B2O3–SiO2 glasses for LTCC applications

CaO–B2O3–SiO2–Ta2O5 (CBST) glass-ceramics, with different Ta2O5 content, (up to 6 mol%), have been prepared by using glass melt quenching followed by heat treatment between 800 and 880 °C. The Fourier Transform Infrared (FTIR) results showed that the stronger the attraction of Ta5+ to the oxygens in the BO33− and SiO32− structures, the more easily the B–O and Si–O bonds will be destroyed. The underlying reason is most probably the high field strength of Ta5+, which results in a weakening of the vibration intensities of the [BO3] and [SiO4] units. Moreover, the Differential Scanning Calorimetry (DSC) results showed that the softening point (Tg), crystallization starting temperature (Tc1), and exothermic crystallization peak temperature (Tp1), of the CaSiO3 phase, shifted to higher values with the addition of Ta2O5. Also, the crystallization activation energy (Ea) and the glass stability factor (ΔT) of the CaSiO3 phase increased, which indicated that the CaSiO3 phase of the glass became inhibited by the addition of Ta2O5. It was, thus, obvious that there was a need of glass characterization. The results of the crystallization kinetics showed that the critical cooling rate decreased with the addition of Ta2O5, which indicated that the viscosity of the system had increased. The CBST glass-ceramics, containing 1 mol% Ta2O5, that were sintered at 875 °C for 15 min showed excellent dielectric properties: εr = 6.22 and tanδ = 1.19 × 10−3 (1 MHz). To sum up, CaO–B2O3–SiO2–Ta2O5 glass-ceramics are potential low temperature co-fired ceramic substrate materials.

Effect of RuO2 crystallinity and particle size on electrical property of LTCC resistors

The crystallization and sintering process of RuO[Formula: see text]xH2O nanoparticles have been investigated in this paper. The effect of RuO2 crystallinity and particle size on the sheet resistance of RuO2-based resistor paste after being co-fired with CaO–B2O3–SiO2 green tapes has been reported. The results show that the nanoparticles are not fully crystallized below 600[Formula: see text]C, and the effect of high-density defects, such as grain boundaries and dislocations on the residual resistance ([Formula: see text] of RuO2 particles, is significant. So, the sheet resistance decreases with the increase of crystallinity and the weakening of electron wave scattering. Above 600[Formula: see text]C, the effect of crystal imperfections on [Formula: see text] is greatly weakened. However, the number of conductive chains formed in co-fired resistor decreases with the increase of particle size, thus the sheet resistance gradually raises. When the dwelling time is increased to 3 h, the RuO2 is mostly crystallized and the effect of crystal imperfections on [Formula: see text] is negligible, and the sheet resistance mainly depends on particle size of RuO2. Using RuO2 particles with low crystallinity, small size and narrow particle-size distribution as conductive phase is expected to solve the problem of poor sheet resistance uniformity in high resistance paste for LTCC application.

Scintillation and Thermally Stimulated Luminescence Properties of Sn-doped CaO–B2O3–SiO2 Glasses

Scintillation and Thermally Stimulated Luminescence Properties of Sn-doped CaO–B2O3–SiO2 Glasses

Tailoring sintering kinetics and dielectric properties of Li2SiO3 ceramics by CaO–B2O3–SiO2 glass dopant for LTCC substrate applications

Tailoring sintering kinetics and dielectric properties of Li2SiO3 ceramics by CaO–B2O3–SiO2 glass dopant for LTCC substrate applications

Physical and structural characteristics of sol–gel derived CaO–B2O3–SiO2 glass-ceramics and their dielectric properties in the 5G millimeter-wave bands

In this study, sol–gel derived CaO–B2O3–SiO2 glass-ceramics with a set B2O3 content of 22.2 mol% and CaO/SiO2 ratios ranging between 0.15 and 0.27 were used for low-temperature cofired ceramic applications in the 5G millimeter-wave bands. X-ray diffraction analysis, scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy data indicated that, unlike the typical CaO–B2O3–SiO2 glass-ceramics prepared via melting resulted in the presence of calcium silicates, the CaO–B2O3–SiO2 glass-ceramics in this study comprised only an amorphous phase containing different amounts of CaB2O4 crystallites depending on the CaO/SiO2 ratio. Among the formulations evaluated, the 14.5CaO‒22.2B2O3‒63.3SiO2 glass-ceramic sintered at 950 °C exhibited a dielectric constant of 4.33 and a dielectric loss of 0.0012 at 60 GHz, which conferred its low signal propagation delay and low signal attenuation in applications. In addition, the electrical resistivity, breakdown strength, thermal conductivity, and coefficient of thermal expansion of the 14.5CaO‒22.2B2O3‒63.3SiO2 glass-ceramic were 1.72 × 1012 Ω cm, 15.49 kV/mm, 1.70 W/mK, and 4.1 ppm/°C, respectively. The 14.5CaO‒22.2B2O3‒63.3SiO2 glass-ceramic exhibited excellent insulating properties, facilitating its use as substrate material; moreover, its thermal properties matched those of Si and GaAs.