Microstructure and properties of functional magnesium titanate ceramic joint brazed by bismuth-borate glass

Bismuth-borate glass braze (Bi25) with low melting point was utilized to braze magnesium titanate ceramic (MTC) in this work. The interfacial reaction between MTC and bismuth-borate glass braze made a well brazing possible. First, the Zn atoms from the glass seam substituted Mg atoms from MTC forming the phase (Zn,Mg)₂TiO₄ of lamellar morphology, which reacted with [BiO₆] (or [BiO₃]) from glass seam and then generated Bi₄Ti₃O₁₂ of granular and sheet-like morphologies. The Mg²⁺ deriving from the reactions above reacted with [SiO₄] unit from glass seam and generated Mg(SiO₃) of granular and stripe-like morphologies. The shear strength increased first and then decreased with the increase of brazing temperature constantly. It reached a maximum value of 72 MPa at 725 °C. The dielectric loss tangent of joints always tended to zero at high frequency, and the dielectric constant of joints brazed at 750 °C was closest to that of base MTC itself.     

Microstructures and mechanical properties of brazed Al2O3/Cu joints with bismuth glass

Alumina ceramics and copper were vacuum brazed using a bismuth-borate-zinc glass at temperatures between 660 and 720 °C for 20 min. The interfacial phases were characterized and the influence of brazing temperatures on microstructure of the joints were investigated. Shear tests of brazed joints under different conditions were also performed, and the joint fracture was observed and analyzed to determine the influence of brazing temperatures on the joint mechanical properties. Al₂O₃ ceramic/Al₂O₃ + glass phase/ZnAl₂O₄ + glass phase/(Ni, Cu)O/Ni(s.s) + BiNi/copper was identified as the main structure of the Al₂O₃ joints brazed with the glass. As the brazing temperature increased, the (Ni, Cu)O oxide layer in the joint was observed to thicken and extend to both sides gradually. The amount of BiNi formed in the Ni coating layer increased, and the scattered ZnAl₂O₄ particles gradually grew. When the brazing temperature reached 700 °C, ZnAl₂O₄ particles agglomerated on the alumina ceramic side, and glass permeated into the alumina base material. The shear strength of the joint first increased and then decreased with the increase of brazing temperature. The shear strength reached the maximum value of 21.1 MPa when brazed at 680 °C.     

Formulation and characterization of black ceramic ink for a digital ink-jet printing

Formulation of black ceramic ink and its ink-jet printability on a glass substrate were investigated. The thermal and chemical stabilities of CoFe_2-xCr_xO₄ and Ni_0.925Mn_0.075Fe_1.875-xCr_xMn_0.125O₄ black inorganic pigments were analyzed with various amounts of Cr substitutions. The ceramic ink was prepared using the pigment composition that demonstrated color stability during the high temperature glazing process with a minimal Cr substitutional amount. After the dispersion stability and rheological property were optimized, the ceramic ink was suitably jetted from a print head as a single sphere-shaped droplet without satellite droplets. To improve the printability of the ceramic ink, the glass substrate was treated with a perfluorooctyl trichlorosilane (PFTS) solution. As a result, the PFTS surface treatment increased the contact angle of the ceramic ink droplets on the glass substrate and effectively minimized the ink spreading phenomena.     

Sintering of sodium conducting glass ceramics in the Na2O-Y2O3-SiO2-system

A solid electrolyte is a core component for the development of low temperature sodium batteries with metallic Na-anode. The Na₅YSi₄O₁₂ (N5) composition in the Na₂O-Y₂O₃-SiO₂ system shows a high ionic conductivity comparable to NASICON or β-Al₂O₃. Up to date glass ceramic solid electrolytes of this type have been mainly prepared by crystallization of monolithic, molten glass components. We show that this material can be processed via the glass-ceramic powder route starting with a glass powder. A glass with a composition according to the stoichiometry of the Na₅YSi₄O₁₂-phase and tailored by addition of P₂O₅ allows the separation of sintering and crystallization of the glass powder resulting in dense microstructure. Thermophysical properties and phase content have been correlated with ionic conductivity. The densification and crystallization are completed at temperatures below 1100 °C. Grain conductivities up to 0,18 mS cm^?1 at room temperature in sintered glass ceramic microstructures are demonstrated.     

Interfacial evolution mechanism of MgAl2O4/MgAl2O4 joints bonded with lanthanum glass

The La₂O₃-SiO₂-B₂O₃ (LSB) glass filler with high softening temperature was first used to join MgAl₂O₄ ceramic. An interfacial layer composed of Al₂O₃ was formed due to the solubility difference of MgO and Al₂O₃ in the LSB glass filler. As a result, the addition of Al₂O₃ into the LSB glass filler caused the increase of interfacial layer thickness. On the contrary, the addition of MgO into the LSB glass filler led to the decrease of interfacial layer thickness. When the adding content of MgO was 6 wt%, the interfacial layer disappeared and completely amorphous brazing seam was obtained. The in-line transmittance of joints decreased with the increase of the thickness of interfacial layer. The optimal in-line transmittance of joint bonded with La₂O₃-SiO₂-B₂O₃-MgO (LSB6M) glass filler reached 82.9% at 1000 nm. Meanwhile, the average flexural strength of joints was about 196.2 MPa, which was equal to the strength of MgAl₂O₄ substrate.     

Microstructure,mechanical and optical properties of MgAl2O4/MgAl2O4 joints bonded using CaO-Al2O3-SiO2 glass filler

Transparent MgAl₂O₄ ceramics were bonded by using CaO-Al₂O₃-SiO₂ (CAS) glass filler. The CAS glass filler exhibited the same thermal expansion behavior as MgAl₂O₄ ceramic and excellent wetting ability on the surface of MgAl₂O₄ ceramic. When the cooling rate of 15 °C/min was used, no interfacial reaction was observed and the amorphous brazing seam could be obtained. However, low joining temperature (1250 °C) led to the formation of pores and high joining temperature (1400 °C) resulted in the formation of cracks. Furthermore, the slow cooling rate of 5–10 °C/min induced the crystallization of CaAl₂Si₂O₈ and Mg₂Al₄Si₅O₁₈ due to the dissolution of MgAl₂O₄ substrate. The optimal flexural strength of 181–189 MPa was obtained when the joining temperature and cooling rate were 1300–1350 °C and 15 °C/min respectively. Moreover, the in-line transmittance of the joint at 1000 nm was 82.1%, which was slightly lower than that of MgAl₂O₄ ceramic (85.6%).     

Effect of B-site substitution on the luminescence,thermal stability and temperature sensitivity of Ba2NaNb5O15:Eu3+/Er3+ glass ceramics

Transparent glass ceramic with Ba₂NaNb₅O₁₅ as the main crystal phase was prepared, and the appropriate heat treatment condition was selected as 710 °C/150 min through various characterizations. The luminous intensity and thermal stability were enhanced significantly when the glass ceramic was used as the luminous matrix. After introducing Ti⁴⁺ ions as charge compensators, the luminescence performance and thermal stability were further improved, and the reasons for this were analyzed. At 458 K, the luminous intensity of 0.5%Eu³⁺ doped glass ceramic containing 0.5%Ti⁴⁺ can maintain about 65% of room temperature with a chromaticity shift of 5.16 × 10⁻². The relative and absolute sensitivities of 0.7%Er³⁺ doped glass ceramic were 4.04 × 10⁻³ K⁻¹ and 1.31% K⁻¹. Introducing Ti⁴⁺ ions would weaken the population redistribution ability of ²H_11/2 and ⁴S_3/2 levels and reduce the temperature sensitivity. However, the sample containing Ti⁴⁺ shows good thermal stability, its green emission at 458 K has a small chromaticity shift of 6.45 × 10⁻³. The research shows that the glass ceramic can be used as a good luminescent host material, and Eu³⁺/Er³⁺ doped glass ceramic can be used in the fields of LEDs or temperature sensing.     

Joining ZTA ceramic by using Dy2O3-Al2O3-SiO2 glass ceramic filler

In this paper, a novel Dy₂O₃-Al₂O₃-SiO₂ (DAS) glass ceramic was designed and prepared for joining zirconia toughened alumina (ZTA) ceramic. The crystallization, thermal expansion behavior and wetting behavior of the DAS glass filler were studied. The effect of cooling rate and joining temperature on the microstructure and flexural strength of joints was investigated. The results show that slow cooling rate (15 °C/min) leads to crystallization of brazing seam, which causes the formation of pores in the joints due to the large density difference between the glass and the crystalline phases. The dissolution of ZrO₂ from ZTA substrate into the filler during joining process improves the mismatch of the coefficient of thermal expansion (CTE) between the brazing seam and substrate. The maximum flexural strength of 535 MPa is obtained when the joining temperature and cooling rate are 1475 °C and 50 °C/min, respectively.     

Joining transparent spinel ceramics using refractive index–matched glass

Ceramic joining by glass is a promising method of the preparation of large transparent ceramics from small blocks. The chemical composition of glass was optimised to match the coefficient of thermal expansion and refractive index of transparent magnesium aluminate (MgAl₂O₄) ceramics. A two-step joining method was developed to join MgAl₂O₄ ceramics with a reduced number of bubbles in the joint, and the thermal properties of the optimised glass were evaluated to determine the joining temperature. Two transparent MgAl₂O₄ blocks were joined by a glass layer that was approximately 20 µm thick. The joint area could not be distinguished with a naked eye. The transmittance of the joined body vertical to or parallel through the glass layer was approximately the same as that of the ceramics. The average three-point bending strength of the joint reached 202 ± 33 MPa, which was 64% that of the ceramic body.     

Modification of glass network and crystallization of CaO–Al2O3–MgO–SiO2 based glass ceramics with addition of iron oxide

Modification of glass network and crystallization process of a CaO–Al₂O₃–MgO–SiO₂ (CAMS) based glass ceramic to form diopside through addition of iron oxide were investigated using differential thermal analysis (DTA), Raman spectrum, X-ray diffraction, SEM and EBSD techniques. The experimental results showed that addition of Fe₂O₃ led to remarkable reductions in both the glass transition temperature (Tg) and crystallization temperature (Tp) of the CAMS glass ceramic. At addition level below 5 wt%, the Tg and Tp temperatures were 651°C and 903°C, respectively, and the crystallization only occurred on the surface of the glass ceramic samples. Increasing the addition level to 10 wt% and 15 wt%, not only led to reduction in the Tg and Tp temperatures to 643-641°C and 892-876°C, respectively, but also promoted the formation of crystalline diopside throughout the CAMS samples. Based on the results of Raman spectrums, it was confirmed that Fe₂O₃ addition reduced the strength of glass connection as a result of chemical reactions between the isolated Si–O tetrahedron and Fe³⁺ ion, forming Fe³⁺O₄–SiO₄, which can be regarded as Q₂ unit. And this is the first experimental evidence that proving the approach of Fe³⁺ mending glass network. Microstructural examination also identified the formation of large numbers of spherical Fe-enriched regions within the CAMS glass matrix as a result of the amorphous phase separation due to the Fe₂O₃ addition. The interfaces between the Fe-enriched regions and the glass matrix acted as preferred nucleation sites for the diopside, facilitating the crystallization. Crystallographic analysis using EBSD technique determined the <001> as the most favorite growth direction for the diopside crystals in the CAMS based glass ceramic.     

Bioactive fluorapatite-containing glass ceramics

Fluorapatite-containing glass ceramics were synthesized on the basis of the glass-forming system SiO₂–Al₂O₃–P₂O₅–CaO–CaF₂. The introduction of phosphorus and fluorine containing materials, as well as the specific regime of heat treatment of the glasses gave glass ceramic materials with crystalline phases of the apatite group—fluorapatite (Ca₁₀(PO₄)₆F₂), apatite (Ca₃(PO₄)₂), vitlokite (Ca₉P₆O₂₄), etc. The X-ray phase analysis showed that the main phase in all the glass ceramic samples was fluorapatite. The phase composition, structure and some of the basic properties of the glass ceramic samples were determined.     

Effect of TiO2 on the crystallization,thermal expansion and wetting behavior of Nd2O3-Al2O3-SiO2 glass ceramic filler

The crystallization behavior, microstructure, crystalline phases, microhardness, coefficient of thermal expansion (CTE), and wetting behavior of Nd₂O₃-Al₂O₃-SiO₂ (NAS) glass ceramics with different TiO₂ content were investigated. The results show that the content of crystals increases and the size of crystals decreases with the increase of TiO₂ content. Moreover, the formation of Nd₂SiO₅ leads to the increase and the precipitation of Al₆Si₂O₁₃ results in the decrease in the CTE value of NAS glass ceramics. As a result, the CTE of NAS glass ceramics can be controlled in the range of 4.2–9.2 × 10⁻⁶/℃. These values are suitable for matching bonding to most ceramics with different CTE. Indeed, contact angle measurement demonstrates that the NAS glasses with 3 %, 6 % and 9 % TiO₂ possess excellent wettability on the Al₂O₃, ZrO₂ and zirconia toughened alumina (ZTA) ceramic, respectively.     

Enhanced luminescence in Tb3+-doped germanate glass ceramic scintillators containing CaF2 nanocrystals

Tb³⁺-doped germanate glass ceramics containing CaF₂ nanocrystals were prepared by melt quenching method with subsequent heat treatment. Their microstructures were investigated by XRD and TEM techniques. Their optical properties were studied by the transmittance, the photoluminescence, and the X-ray excited luminescence (XEL). The luminescence intensity in the glass ceramics under 377 nm light and X-ray excitations is significantly enhanced. The maximum integrated XEL intensity of the glass ceramics is about 50% of that of the commercial Bi₄Ge₃O₁₂ (BGO) scintillating crystal. The results indicate that Tb³⁺-doped germanate glass ceramic could be a promising scintillating material used in X-ray detection for slow event.     

Development of CaO-rich blast furnace slag containing fluorine mica-based glass ceramic coatings

In the present study, Blast Furnace Slag (BFS) waste was evaluated as a sustainable, cost-effective CaO, SiO₂, Al₂O₃ and MgO substitute for inorganic oxides for the production of frit, a raw material for glass ceramic production. Two different frits were prepared to compare a commercially available frit (F-STD) with frit produced using BFS waste (F-BFS). The samples were characterized by XRF, XRD, heating microscopy, dilatometry and TG-DTA to determine the chemical composition, phase formation and thermal properties. The frits were applied on steel using the electrostatic spray method and subsequently thermally treated at 830 °C for 4.5 min. The reference (GC-STD) and partially BFS-substituted glass ceramic (GC-BFS) coatings were examined by XRD, SEM-EDS and ICP-MS experiments. The main crystal phase for both samples was Ni-substituted fluorine mica (KLiNi₂Si₄O₁₀F₂). GC-BFS was slightly more amorphous (70%) than GC-STD (69.1%), which was correlated with the thermal properties of the BFS waste. Likewise, ICP-MS analysis after a boiling citric acid test (ISO 28706-1: 2008) revealed that the GC-BFS had relatively higher chemical resistance. The total release from the reference sample (GC-STD) was 23.556 mg/L, whereas the total release from the sustainably produced sample (GC-BFS) was 21.451 mg/L, which was consistent with the XRD results.     

Preparation of glass–ceramic glazes for fast firing applications by CaF2 substitution with B2O3 in the CaO–CaF2–Al2O3–SiO2 system

The present work aims to obtain glass–ceramic glazes for floor tile applications. In this regard, CaF₂ was gradually replaced by B₂O₃ in the glass compositions belonging to the CaO–CaF₂–Al₂O₃–SiO₂ system. This substitution led to a noticeable decrease of crystallization peak temperatures and to an alteration of the crystallization trend. In the B₂O₃ bearing glazes, anorthite and gehlenite were identified as the major and minor crystalline phases, respectively. During concurrent crystallization and sintering based on the fast firing program, glass–ceramic glazes containing 9 weight parts of fluorine and 12 weight parts of boron oxide showed the most desirable sinterability. The optimized glass–ceramic glazes offered acceptable micro-hardness, whiteness and thermal expansion behavior after fast firing heat treatment.     

Phase-separation engineering in fluorozirconate glass for designing and fabricating of transparent perfluorinate glass ceramic

Perfluorinate glass ceramics with ultra-low phonon energy are very important optical and photonic materials. Unfortunately, there is no suitable method to obtain transparent perfluorinate glass ceramics due to poor thermal stability of fluoride glass. As a result, wide applications of glass ceramics in advanced infrared systems are restricted. Here, an effective method based on phase-separation engineering is used to develop transparent perfluorinate glass ceramics. In this article, a novel transparent Er³⁺-doped ZnZrF₆-Ba₆Zn₇F₂₆ perfluorinate glass ceramic was designed and fabricated by phase-separation engineering. The sample exhibits low phonon energy (564 cm⁻¹), ultra-wide transmission range (0.33–8.2 μm, T ≥ 50 %), and strong infrared emission, which is better than that of ZBLAN glass, oxide-, and oxyfluoride-glass ceramics. These good properties of the perfluorinate glass ceramic demonstrate that phase-separation engineering not only offers an effective approach to obtain perfluorinate glass ceramics but also provides wide-ranging opportunities for advanced infrared optical and photonic materials.     

Erbium-doped LAS glass ceramics prepared by spark plasma sintering (SPS)

Dense nanocrystalline glass ceramics of the Li₂O–Al₂O₃–SiO₂ (LAS) system were obtained by spark plasma sintering (SPS) of powders prepared by sol–gel method. The low thermal expansion LAS glass ceramic was chosen as host matrix for erbium ions. ZrO₂ was added both as a nucleating agent and as a possible good environment for the rare earth. The developed crystalline phases were analysed by X-ray diffraction (XRD) and the amorphous phase was quantified. Scanning and transmission electron microscopy (SEM, TEM) was used to investigate the microstructure. A different behaviour during the crystallisation process was observed between the sample prepared through the sintering of powders and the glass produced by the melting technique. A photoluminescence characterisation was also performed.     

Densification,flexural strength and dielectric properties of CaO-MgO-ZnO-SiO2/Al2O3 glass ceramics for LTCC applications

Novel glass ceramics for LTCC applications with high flexural strength can be achieved by CaO-MgO-ZnO-SiO₂(CMSZ) glass cofiring with Al₂O₃. The sintering shrinkage behavior, crystalline phases, mechanical and dielectric properties, and thermal expansion of the CMZS/Al₂O₃ glass ceramic were determined. The X-ray diffraction results revealed that multiphases (CaMgSi₂O₆, Al₂Ca(SiO₄)₂ and ZnAl₂O₄) formed in the sintering process of the CMZS/Al₂O₃ glass ceramic. The flexural strength of CMZS/Al₂O₃ glass ceramics first increases and then decreases with increasing Al₂O₃ content. The CMZS/Al₂O₃ glass ceramic with 50 wt % Al₂O₃ sintered at 890 °C for 2 h achieved the best performance, with a maximum flexural strength of 256 MPa, dielectric constant (ε_r) of 7.89, dielectric loss (tan δ) of 3.41 × 10⁻³ (12 GHz), temperature coefficient of resonance frequency (τ_f) of −29 ppm/°C, and the CTE value of 7.93 × 10⁻⁶/°C.     

Wetting behavior and bonding characteristics of bismuth-based glass brazes used to join Li-Ti ferrite systems

A series of bismuth-based glass brazes were used to join Li-Ti ferrite. The wetting behavior and bonding characteristics of glass brazes utilized to join Li-Ti ferrite were systematically investigated. The glass brazes feature a good CTEs match, and a favorable wetting ability over Li-Ti ferrite mating surfaces. Upon brazing, the Bi-rich phases (Bi₄₆Fe₂O₇₂, Bi₁₂SiO₂ and Bi₂₄B₂O₃₉) and Zn-rich phase (ZnO) were observed in the Li-Ti ferrite/Bi40 and Li-Ti ferrite/Bi35 joints. The Zn₂SiO₄, ZnFe₂O₄ and Bi₅Ti₃FeO₁₅ whiskers were detected in the Li-Ti ferrite/Bi25, Li-Ti ferrite/Bi20 and Li-Ti ferrite/Bi25-BC joints, respectively. No crystalline phase was detected in the Li-Ti ferrite/Bi30-BF joint. Multiple factors impact the joint strength, such as the three-point bending strength of glass brazes, the CTE match of the glass braze and the Li-Ti ferrite, as well as the crystal phases within the seam. The joint strength has the maximum value of 86 MPa for a Li-Ti ferrite/Bi25-Ba couples. The main impact is attributed to the strengthening effect of Bi₅Ti₃FeO₁₅ whiskers. The dielectric properties of Li-Ti ferrite/glass braze joints show a stronger frequency dependence than that of Li-Ti ferrite at low frequency. This is attributed to the formation of new interfaces. The glass matrix or a crystal phase with a higher dielectric constant could counteract the decrease in the dielectric constant of heat-treated Li-Ti ferrite. Therefore, the dielectric constant of joint, especially that of Li-Ti ferrite/Bi25-BC joint, would be near that of the original Li-Ti ferrite at a high frequency. Meanwhile, no increase in the dielectric loss tangent of a joint takes place.     

Joining MgAl2O4 ceramics using ZnO–Al2O3–SiO2 glass ceramic with precipitated ZnAl2O4

In this work, crystallization, thermal expansion and wetting behavior of ZnO–Al₂O₃–SiO₂ (ZAS) glass were first investigated. The results showed that ZnAl₂O₄ was precipitated from ZAS glass after crystallization treatment. Crystallization increased the coefficient of thermal expansion (CTE) of ZAS glass ceramic due to the high CTE of ZnAl₂O₄. In addition, ZAS glass exhibited good wettability on the surface of MgAl₂O₄ substrate. On this basis, ZAS glass was used to join MgAl₂O₄ ceramic, and the microstructure and mechanical properties of joints obtained with different cooling methods were investigated. The flexural strength of joints was related to the content of ZnAl₂O₄ crystals in the brazing seams. Additional nucleation and crystallization treatment during cooling process improved the crystallinity of brazing seam, resulting in better matching of the CTE of brazing seam with that of MgAl₂O₄ ceramic. The maximum flexural strength of joints reached 201 MPa, which was equivalent to the strength of MgAl₂O₄ ceramic.