Sintering Aid Research Articles

Detection of calcium homogeneity distribution in magnesia-aluminum spinel using laser-induced breakdown spectroscopy

To further improve the yield of producing magnesium aluminum spinel and detect the distribution of sintering aid in raw materials, the Mg–Al spinel samples were prepared using MgO and Al2O3 as raw materials and CaO as sintering aids. Information on the distribution of the sintering aid Ca element in mixed samples was rapidly obtained by laser-induced breakdown spectroscopy (LIBS) mapping using a picosecond laser and a closed chamber filled with Ar gas. The optimal mixing time and environmental parameters of the raw materials were determined through optimization experiments, and the calibration models of Ca/Al and Ca/Mg were established with the intensities of Al and Mg characteristic lines as the internal standard. The correlation coefficient R2, Root Mean Square Error of Calibration (RMSEC) and Mean Relative Error (MRE) of different calibration curves were evaluated. The feasibility of LIBS technique to detect the uniform distribution of sintering aids in Mg–Al spinel is verified by comparing with the images scanned by X-ray energy dispersive spectroscopy (EDS). Finally, we performed LIBS scans in the depth direction and obtained the spatial distribution of the Ca element. This work opens up a new research route for realizing the application of LIBS analysis in magnesia-aluminum spinel.

A highly conductive Ce0.8Nd0.2O1.9 electrolyte with double sintering aids for intermediate-temperature solid oxide fuel cells

In this paper, the influence of Bi/Zn mass ratio on the phase composition, microstructure, sintering properties, and electrical properties of Bi/Zn co-added Nd0.2Ce0.8O1.9 (NDC) used for intermediate-temperature solid oxide fuel cells (SOFCs) was investigated. At 700 °C, the total conductivity of the NDC-based electrolyte (3Bi/1Zn-NDC) with the mass ratio 3:1 for Bi2O3 and ZnO was as high as 5.89 × 10−2 S cm−1, 4.60 and 4.51 times higher than the single addition of 4 wt% Bi2O3 and 4 wt% ZnO, respectively. In addition, the 3Bi/1Zn-NDC electrolyte exhibited a good physical and chemical compatibility with the electrode materials. The open circuit voltage (OCV) of the cell supported by the 3Bi/1Zn-NDC electrolyte was 0.67 V, and the output power density could reach 402.25 mW cm−2 at 700 °C. It showed stable power output and OCV in the long-term stability test within 50 h. Overall, the combination of 3 wt% Bi2O3 and 1 wt% ZnO was a very effective dual sintering aid for NDC electrolyte.

Vacuum sintering of Yb2O3 transparent ceramics: Effect of ZrO2 concentration on structural and optical properties

• Highly transparent ytterbium oxide (Yb 2 O 3 ) ceramics were successfully prepared by vacuum sintering method using ZrO 2 as a sintering aid. • ZrO 2 was found to be an effective sintering additive that can effectively inhibit Yb 2 O 3 grain growth and promote the removal of residual pores. • The effects of ZrO 2 doping concentration on the crystal structure, microstructure, optical transmittance, and band gap of Yb 2 O 3 transparent ceramics were studied for the first time. In this study, highly transparent Yb 2 O 3 ceramics were successfully fabricated via vacuum sintering at 1800 °C for 10 h with ZrO 2 as a sintering additive. The effect of zirconia doping concentration on crystal structure, microstructure, and optical properties of Yb 2 O 3 transparent ceramics was investigated. It was found that the introduction of zirconia could effectively prohibit grain growth while promoting the removal of residual pores. The mean grain size decreased from 39.04 µm to 4.27 µm as the Zr 4+ content increased from 0 to 5 at%. The 3 at% ZrO 2 -doped Yb 2 O 3 transparent ceramics have the best optical quality, with a transmittance of 75% at 1100 nm and about 81% in the mid-infrared region. This study indicates that Yb 2 O 3 transparent ceramics with good optical properties can be obtained by properly adjusting the addition amount of ZrO 2 . On this basis, the absorption spectra, emission spectra, and fluorescence lifetime of Yb 2 O 3 transparent ceramic were investigated. High transmittance and high activation cation density make Yb 2 O 3 transparent ceramics potential candidates for thin-disk laser elements.

Hardening of (Ba0.5Na0.5)0.85Ba0.15TiO3 lead-free piezoelectric ceramics by adding (Bi0.5Na0.5)MnO3

The hardening of (Bi0.5Na0.5)0.85Ba0.15TiO3 (BNBT15) piezoelectric ceramics was investigated by adding raw materials with Bi0.5Na0.5MnO3 (BNM). BNBT15-BNM exhibited a single phase of BNBT15. BNM acts as a sintering aid for BNBT15 to produce domain pinning, and produces tetragonality based on BaTiO3 for increased stability. BNBT15-BNM hardens piezoelectric material with low Mn content, increasing the coercive field and mechanical quality factor. The mechanical quality factor of BNBT15-BNM (0.75 wt%) exceeded 1200. In high-power conditions, BNBT15-BNM (0.75 wt%) exhibited a vibration velocity twice that of hard-PZT. The quality factor gradually decreased with a high vibration velocity. The equivalent stiffness slightly decreased with strain, and the mechanical nonlinearity was much less than that of hard-PZT. BNBT15-BNM (0.75 wt%) has superior high-power properties, and is expected to be a candidate material for use in lead-free piezoelectric ceramics in high-power applications.

High-temperature ablation performance of Si3N4-Si2N2O-BN composites prepared using selective laser sintering

In this study, a Si3N4 radome with high-temperature ablation performance was successfully prepared using selective laser sintering (SLS). The results showed that cold isostatic pressing was beneficial for the densification of SLS-processed Si3N4-Si2N2O-BN ceramics and improved their high-temperature ablation resistance. The sintering aids formed a glass phase that covered the surface of the Si3N4 ceramics, effectively preventing further ablation. The mass ablation rate and linear ablation rate were 0.6 mg/s and 0.5 µm/s, respectively. This work combines the advantages of additive manufacturing with the adjustable performance of composites.

Low-temperature hot-press sintering of AlN ceramics with MgO–CaO–Al2O3–SiO2 glass additives for ceramic heater applications

Aluminum nitride (AlN) is used a ceramic heater material for the semiconductor industry. Because extremely high temperatures are required to achieve dense AlN components, sintering aids such as Y2O3 are typically added to reduce the sintering temperature and time. To further reduce the sintering temperature, in this study, a low-melting-temperature glass (MgO–CaO–Al2O3–SiO2; MCAS) was used as a sintering additive for AlN. With MCAS addition, fully dense AlN was obtained by hot-press sintering at 1500 °C for 3 h at 30 MPa. The mechanical properties, thermal conductivity, and volume resistance of the sintered AlN–MCAS sample were evaluated and compared with those of a reference sample (AlN prepared with 5 wt% Y2O3 sintering aid sintered at 1750 °C for 8 h at 10 MPa). The thermal conductivity of AlN prepared with 0.5 wt% MCAS was 91.2 W/m∙K, which was 84.8 W/m∙K lower than that of the reference sample at 25 °C; however, the difference in thermal conductivity between the samples was only 14.2 W/m∙K at the ceramic-heater operating temperature of 500 °C. The flexural strength of AlN–MCAS was 550 MPa, which was higher than that of the reference sample (425 MPa); this was attributed to the smaller grain size achieved by low-temperature sintering. The volume resistance of AlN–MCAS was lower than that of the reference sample in the range of 200–400 °C. However, the resistivity of the proposed AlN–MCAS sample was higher than that of the reference sample (500 °C) owing to grain-boundary scattering of phonons. In summary, the proposed sintering strategy produces AlN materials for heater applications with low production cost, while achieving the properties required by the semiconductor industry.

Low temperature fired CaF2-based microwave dielectric ceramics with enhanced microwave properties

Low-temperature-fired microwave ceramics are key to realizing the integration and miniaturization of microwave devices. In this study, a facile wet chemical method was applied to synthesize homogenous nano-sized CaF2 powders for simultaneously achieving low-temperature sintering and superior microwave dielectric properties. Pure CaF2 ceramics sintered at 950 °C for 6 h with good microwave dielectric properties (εr = 6.22, Q×f = 36,655 GHz, and τf = −102 ppm/°C) was achieved. The microwave dielectric properties of the CaF2 ceramics were further improved by introducing LiF as a sintering aid. The sintering temperature of CaF2-based ceramics was effectively lowered from 950 °C to 750 °C with 10 wt% LiF doping, and excellent microwave dielectric properties (εr = 6.37, Q×f = 65,455 GHz, and τf = −71 ppm/°C) were obtained.

Improvement of density and electrochemical performance of garnet-type Li7La3Zr2O12 for solid-state lithium metal batteries enabled by W and Ta co-doping strategy

Solid-state lithium metal batteries (SSLMBs) have caught research interest for their desirable safety and energy density. However, low density, poor uniformity of the solid-state electrolytes (SSEs), and dendrite penetration through the SSEs are the major problems that hinder the progress in SSLMB's development. Herein, a co-doping strategy is proposed for garnet-type electrolyte by utilizing a well-designed lithium-rich additive Li2WO4 (LWO) doping into Li6·5La3Zr1·5Ta0·5O12 (LLZT). LWO addition yields a denser and more uniform material by acting as a sintering aid and providing an inner Li2O atmosphere. W substitutes the Zr element and forms Ta and W-doped LLZO, and second phase, which broadens the sintering temperature range of LLZT and avoids abnormal grain growth (AGG). With 2 wt% LWO, LLZT-2LWO has an ionic conductivity of 0.6 mS/cm and a relative density of 98.67%. Moreover, the critical current density (CCD) of LLZT-2LWO reaches 1.0 mA cm−2. LLZT-2LWO achieves long cycling stability for 300 h at 0.5 mA cm−2, showing an excellent dendrite-suppression capability. The full cell matched with LiNi0·6Co0·2Mn0·2O2 and sulfur cathode displays high discharge capacity and cycling stability. This modification strategy has high efficiency and is conducive to large-scale production, which opens a new opportunity for SSLMBs.

Study of lithium carbonate as sintering aid for tin oxide densification trough experimental designs: Main variables and microstructure changes

Tin oxide is one of the most extensively studied semiconductor materials due to its broad field of applications. On the one hand, its high conductivity and its corrosion resistance are the most remarkable properties. Therefore, one of the most developed uses in the recent decades has been as ceramic electrode for electrooxidation process. On the other hand, its poor sinterability hinders a broader use. As a result, the use of advanced techniques or sintering aids for obtaining low-porosity specimens is necessary. So far, many additives have been studied, CaCO3, Co3O4, Nb2O5 or MnO2, among others. In the present work, the sintering behaviour of SnO2-based powder, containing Li2CO3 as a sintering aid, which generates a liquid phase, has been analysed, since it is one of the additives that has been studied to a lesser extent. The effect of the amount of sintering aid just like the thermal treatment parameters (maximum temperature, heating rate and soaking time) on volumetric contraction's evolution has been studied through a factorial experiment designs 2n. The results show that an amount of lithium carbonate greater than 1mol.% is unfavourable to densification. With regards to the thermal cycle's parameters, it is advisable to have thermal treatments at high temperatures (1300°C) with moderate soaking times (1h), as maximum temperatures have the biggest influence on the densification followed by soaking time while the heating rate has a lesser influence. Under these conditions, a microstructure of closed and rounded pores is obtained, in which a residual phase is enclosed, but the small proportion of which prevents its characterisation.

Crystalline Structures, and Microwave Dielectric Properties of Low-Fired Li2ZnTi3O8 Ceramics Doped with TLBBC

low-fired Li2ZnTi3O8 ceramics were fabricated by a solid-state reaction method for developing LTCC applications. TLBBC mixed sintering aid was used to improve the sintering stability. X-ray diffraction analyses demonstrated that specimens corresponded well to the cubic crystal symmetry structure of Li2ZnTi3O8, accompanying with a little of impure phase Ca3Ti2O7 and LiBO2. The sintering temperatures of Li2ZnTi3O8 ceramics were lowered to 950 °C due to the formation of low melting point LiBO2. At x = 3, Li2ZnTi3O8 ceramics exhibited an microwave dielectric properties with εr = 21.0, tanδ = 5.76 × 10−4, Q × f = 14750 GHz, τf = −11.5 ppm/°C at 950 °C.

Recycling of extracted titanium slag and gold tailings for preparation of self-glazed ceramic foams

Self-glazed ceramic foams were successfully synthesized via powder sintering method, using extracted titanium slag (ETS) and gold tailings (GT) as raw materials without adding any sintering aids and foaming agents. Influence of ETS addition and sintering temperature on crystal phase evolution, physical–mechanical properties, and micro-morphology of ceramic foams was systematically studied. Results indicated that products sintered at 1180 °C with 30 wt% ETS and 70 wt% GT showed the best performance, i.e., bulk density of 1.66 g cm−3, flexural strength of 20.4 MPa, water absorption of 0.14%, open porosity of 0.23%, and glaze Vickers hardness of 6.5 GPa. Moreover, it was observed that there existed strong correlation between bulk density and bending strength. Self-glazed ceramic foams developed in this study are expected to be used as building envelope materials and provide new ideas for effective reuse of other similar solid wastes.

Low loss and good chemical compatibility with silver electrodes of Cu2+-substituted Ba3Ti4Nb4O21 ceramics realizing low temperature co-fired ceramics technology: Crystal structure, vibration modes and chemical bonds studies

New low loss and low-sintering temperature co-fired Ba3-xCuxTi4Nb4O21 (BCTN, 0 ≤ x ≤ 0.12) ceramics with 0.60 wt% Li2O-B2O3-SiO2-CaO-Al2O3 (LBSCA) glass were prepared by solid-state reaction methodology. This work showed that CuO and LBSCA were effective sintering aid, which improved the densification and decreased sintering temperature. Thus, the excellent microwave dielectric properties of BCTN ceramics (x = 0.08) were obtained after sintering at 925 ℃ with εr ~ 44.18, Q×f ~ 17,860 GHz (@ 5.6 GHz) and τf ~ 94.76 ppm/℃. Q×f value was increased nearly 3-fold compared to pure BTN ceramics (~ 6090 GHz). Based on the P-V-L bond theory, the Ti-O and Nb-O bonds together contributed greatly to εr. The Nb-O bonds was the main factor affecting the internal loss on Q×f. The τf closely related to the oxygen octahedron [Ti1/Nb1O6]. The BCTN ceramics would not react with Ag electrodes, and had great potential to be used in LTCC microwave devices.

Effect of Sintering Aids on Performance of Manganese Tailings Permeable Bricks

As a kind of sponge city water-permeable material, permeable brick has good water permeability, chemical stability, corrosion resistance and weather resistance. Therefore, the development of permeable brick also broadens the engineering application market for its application. The discharge of a large amount of manganese slag will cause serious environmental pollution, and the problem of manganese tailings accumulation is serious. There is no ideal treatment method at present. In this paper, manganese tailings slag is used as the main raw material to prepare sponge city permeable bricks, thereby turning waste into treasure. Through research, the permeable brick with MgO used as sintering aid has very low compressive strength and good water permeability. CaO used as a sintering aid has high compressive strength and low water permeability. The porosity and water permeability of permeable bricks increase with the increase of CaCO3, but the compressive strength is opposite. In comparison, the permeable bricks prepared with three different sintering aids, 3% CaCO3 and 2% MgO as sintering aids have good water permeability and superior compressive strength. The permeability coefficient of the permeable brick prepared with 3%CaCO3 and 2%MgO as sintering aids is 2.0×10-2cm/s, and the compressive strength is 1.3MPa.

Sintering Aid‐Assisted Growth of 0.95(K0.5Na0.5)NbO3–0.05(Bi0.5Na0.5)(Zr0.85Sn0.15)O3 Single Crystals by the Solid‐State Crystal Growth Method and Their Characterization

In this work, 0.95(K0.5Na0.5)NbO3–0.05(Bi0.5Na0.5)(Zr0.85Sn0.15)O3 (KNN–BNZS) lead‐free piezoelectric single crystals are grown by the solid‐state crystal growth (SSCG) method and their phase transitions and properties characterized. Addition of an appropriate amount of Li2CO3 and Bi2O3 sintering aids considerably promotes single‐crystal growth. Chemical composition of the single crystal is similar to the nominal composition with a slight deficiency in Na and K as evaluated by electron probe microanalysis (EPMA). X‐Ray diffraction (XRD), electrical property measurements, and temperature‐controlled Raman scattering reveal that the phase transition near room temperature is from a rhombohedral to an orthorhombic or tetragonal phase. Wide temperature range Raman scattering and dielectric properties consistently indicate transitions associated with the phase transformations or boundaries of a phase coexistence region and further details. Nontrivial frequency dependence of dielectric properties is successfully parameterized by capacitance relaxations described by Debye and Cole–Cole responses with special constant phase elements with fixed exponents of 0.5 (Warburg elements). High‐frequency dielectric constants and additional dielectric relaxations and dc relaxations are deconvoluted. The modeling parameters indicate the phase transition temperatures (or boundaries of the phase coexistence region) unambiguously. Polarization–electric field and bipolar strain–electric field hysteresis loops show that the single crystal is a classic lossy ferroelectric material.

An Innovative Solid-State Approach to Zinc Orthostannate: Remarkable Sintering Temperature Reduction via Lithium Doping and Mechanochemical Activation of Low-Melting Precursors

Zinc orthostannate, often called zinc tin oxide (ZTO), possesses unique physical characteristics and is a promising wide band gap (3.6 eV) n-type semiconductor material for a broad range of applications. The standard solid-state fabrication of ZTO requires prolonged heat treatment of zinc oxide and stannic oxide powders at around 1000 °C. The biggest drawback of this process is the evaporation of zinc oxide during the synthesis. We report an innovative and efficient mechanochemically supported solid-state approach to Li-doped ZTO synthesis with the implementation of a low-melting lithium hydroxide sintering aid, which offers a significant lowering of the sintering temperature down to 850 °C and time to 90 min, maintaining the high quality of the resulting Li-doped ZTO materials. The effect of sintering temperatures in the range 850–900 °C on photoluminescence characteristics of the ZTO materials was studied, and the PL spectra well corroborate with the XPS data and the presence of O as well as Zn or Sn vacancies. The band gap value of the resulting ZTO materials oscillated around 3.6 eV. Moreover, a comprehensive spectroscopic and microscopic examination of the optimized Li-doped ZTO materials provided more profound insight into its vacancy-mediated formation via liquid-phase sintering and its gradual advancement in the low-temperature regime of 850–900 °C. Additionally, the surface analysis of the selected highest quality materials enabled the determination of the Zn diffusion from the Li-doped ZTO lattice to its surface, expanding the knowledge of the diffusion–evaporation process.

Effect of Bi2O3–B2O3 as a sintering aid in microstructure and dielectric properties of Fe2Mo3O12 electroceramic

Molybdates from A2Mo3O12 family have been widely investigated due to its low sintering temperature, low thermal expansion coefficient, and low dielectric loss. Fe2Mo3O12 (FMO) is an oxide from this family and widely used in the catalytic field. The aim of this work is to evaluate the influence of the Bi2O3–B2O3 as a sintering aid in the microstructure and dielectric properties of FMO. The diffraction results showed that the FMO with the monoclinic structure phase was obtained after the calcination process (650 °C). Mössbauer spectroscopy showed the formation of Fe2O3 after the sintering process at 800 °C. The scanning electron-microscopic image demonstrates an increase of the grain as a function of sintering aid concentration. The samples were analyzed using the impedance spectroscopy at radiofrequency with temperature variation. The Nyquist diagram obtained in this temperature range was fitted from an equivalent circuit with three R-CPE associations, corresponding to the morphology of the electroceramics. For dielectric properties in the microwave, all the samples showed values of εr lower than 10. Values of Q x f above 14,132.35 GHz were achieved. The thermal stability was evaluated by the temperature coefficient of resonant frequency (τf). The lowest τf values of − 6.55 ppm/°C and − 4.35 ppm/°C (near-zero) were measured to FMO and FMO mixed with 7.5 wt % Bi2O3–B2O3, respectively. Based on these results, FMO can be used to low-permittivity ceramic for low-temperature co-fired ceramics (LTCC) applications, antenna substrate, and millimeter-wave range.

ZnO as sintering aid and reactant for reactive flash sintering at room temperature

In this paper, ZnO was used as a sintering aid as well as reactant in the reactive flash sintering (RFS) of zinc-containing ceramic materials at room temperature (25 °C). The RFS of ZnO-based ceramics, both ZnAl2O4 and Zn2TiO4, were achieved with the application of a high electric field. Contrary to previous reports, the RFS of ZnAl2O4 was divided into two stages according to temperature changes, and the effect of the reaction exotherm on the RFS was presented for the first time in this paper. In addition, the RFS produced a larger grain size of ZnAl2O4 than conventional sintering did.

Fretting damage behaviors of silicon nitride balls with different sintering aids and processes under grease lubrication

Taking silicon nitride (Si3N4) balls prepared using different sintering processes and sintering additives as objects, their tribological properties against bearing steel were investigated under grease lubrication conditions with heavy loads and high-frequency fretting, followed by analyzing the wear and fatigue damage behaviors. The results show that the Si3N4 balls prepared by adding 5AlEr and using the GPS1850 presented enhanced wear resistance and a low, stable friction coefficient ((6.10 ± 1.06)× 10−4 mm2). An appropriate increase in the temperature during GPS and selection of a sintering additive with a small cation radius were conducive to improving the wear resistance of Si3N4 balls. In addition, a strong adhesive friction film was formed through chemical reactions on the wear surface, which further protected the Si3N4 balls.

High-strength and wave-transmitting Si3N4–Si2N2O-BN composites prepared using selective laser sintering

In this study, high-strength and wave-transmission silicon nitride (Si3N4) composites were successfully developed via selective laser sintering (SLS) with cold isostatic pressing (CIP) after debinding and before final sintering, and the optimal moulding process parameters for the SLS Si3N4 ceramics were determined. The effects of the sintering aids and secondary CIP on the bulk density, porosity, flexural strength, fracture toughness, and wave-transmitting properties of the Si3N4 composites were studied. The results showed that the increased CIP pressure was beneficial to the densification of SLS Si3N4 ceramics and improved their mechanical properties. However, the wave-transmitting performance decreased as the CIP pressure increased. The Si3N4 ceramics prepared by the moulding of sample S11 were more in line with the performance requirements of the radomes. To obtain good comprehensive performance, an additional 3% of interparticle Y2O3 was added to the pre-printed mixed powder of granulated Si3N4 particles and resin and the secondary CIP pressure was adjusted to 280 MPa. After sintering, the bending strength, fracture toughness, and dielectric constant of the Si3N4 ceramics were 651 MPa, 6.0 MPa m1/2, and 3.48 respectively. This study provides an important method for preparing of Si3N4 composite radomes using SLS process.

Optimization of the Mo-Cr binary system for Nanophase Separation Sintering

Like many refractory metals, molybdenum-based alloys present a host of desirable properties for high temperature applications, but have challenging processing constraints. Nanophase separation sintering (NPSS) is a novel sintering process that has been shown to promote rapid pressureless sintering in other BCC metals such as W and Cr. These unique traits are achieved through the development of a transient secondary solid phase neck that first forms and then resolutionizes during the sintering cycle. Both of these processes promote extra mass transport and therefore accelerate sintering to from a dense material. In the present work we use the design criteria for NPSS to identify Cr as a preferred NPSS sintering aid candidate for Mo, a base metal not previously sintered by NPSS. Constant heating rate sintering experiments and ex-situ SEM and EDS on Mo-Cr alloys confirm that the critical mechanisms associated with NPSS occur in this system. Further experiments explore the effect of lower temperature isothermal holds and sintering aid content on the densification of the material. Cr is a particularly desirable sintering aid because it is fully soluble, leaving no permanent second phase or promoting rapid grain growth, which might compromise the high temperature properties of a Mo-based alloy.