Low Densification Temperature Research Articles

Low-temperature synthesis of dense Si-based nitride ceramics for solar thermal storage: Role of cordierite as sintering additive

Direct nitridation method was used to prepare dense Si-based ceramics for solar thermal storage, and the effect of cordierite as sintering additive on the sintering behaviors of the ceramics was studied. The influence priority between densification and nitride content on the properties of thermal storage ceramics was discussed. Cordierite exhibited a good capability of promoting densification, and the densification temperature could reach 1500 °C. The liquid formed by cordierite helped to construct an interlocking structure of well-grown Si2N2O flakes. Results of hot stage microscopy and DTA indicated that the endothermic silicothermic reaction between Si and cordierite proceeded at 1440–1460 °C, and released SiO gas. The SiO gas inhibited the densification, but resulted in the low-temperature synthesis of nano-sized Si3N4 whiskers. Samples added with more cordierite showed the cost-effective merits as the smaller costs of raw materials, lower densification temperature, higher thermal conductivity (1.72 W m−1 K−1 deviation), and higher bending strength (34.3–68.1 MPa deviations), compared with the samples having the larger nitride content. Densification by adding cordierite as sintering additive showed the priority on the properties of thermal storage ceramics than increasing the nitride content.

Microwave Dielectric Properties of CaB2O4-CaSiO3 System for LTCC Applications

A novel composite ceramic with low densification temperature was fabricated using the conventional solid-state method. The XRD and Rietveld refinement results indicated that the two phases of CaB2O4 and CaSiO3 can coexist in all compositions. Furthermore, a phase transition of CaSiO3 ceramic from α-phase to β-phase was observed. A dense ceramic with excellent microwave dielectric properties (εr~6.4, Q × f~75,600 GHz, and a negative τf~26.9 ppm/°C) was obtained at x = 0.5 when sintered at 925 °C at the frequency of 14.2 GHz. A good chemical compatibility between the composite ceramic and Ag electrode was improved by elemental mapping results. A patch antenna was fabricated based on the simulated result. All results indicated that the 0.5 CaB2O4 + 0.5 CaSiO3 ceramic has large application potential in the LTCC field.

NaYW2O8: A novel glass-free microwave dielectric ceramic for LTCC application

Microwave dielectric ceramics are important materials for wireless communication devices because of their excellent dielectric properties. Tungstenate compounds with multiple scheelite structures can be used in low temperature co-fired ceramic (LTCC) devices because of their low densification temperature and high-quality factor. In this study, NaYW2O8 ceramics (NYW) were synthesized by a solid-state reaction method at a low densification temperature below the Ag melting point. The microstructure, morphology and microwave dielectric properties of NYW ceramics were investigated, and the effects of packing fraction and lattice energy on microwave dielectric properties were studied. The results showed that the microwave dielectric properties of NYW ceramics were influenced by the grain size and porosity, and deteriorated with the increase of porosity. In addition, the stacking fraction and lattice energy shared a similar trend with the quality factor. The NYW ceramics sintered at 925 °C exhibited excellent microwave dielectric properties with εr= 10.8, Q × f = 49,800 GHz (at 10.5 GHz), and τf= −26.5 ppm/°C. In particular, the NYW ceramics were found to have an excellent chemical compatibility with Ag. The above results indicate the NYW ceramics are candidate in LTCC applications.

Cutting performance improvement of Si3N4 ceramic cutting tools by adding boride

AbstractCutting performances of silicon nitride (Si3N4) ceramic cutting tools with and without boride additive (2.5 vol% ZrB2 or TiB2) prepared by hot‐pressing at 1500°C were investigated. Due to the α‐ to β‐Si3N4 phase transformation and low densification temperature, boride‐containing Si3N4 ceramics with high hardness and high toughness were obtained. The turning tests showed that the effective cutting lengths of the Si3N4–2.5 vol% TiB2 ceramic (∼2480 m) and Si3N4–2.5 vol% ZrB2 ceramic (∼2200 m) were higher than the monolithic Si3N4 ceramic (∼1780 m). As the toughness was improved while maintaining relative high hardness, the cutting performances of the boride‐containing Si3N4‐based inserts were improved by adding 2.5 vol% ZrB2 or TiB2. The improved cutting performance indicated that the boride‐containing Si3N4 ceramics are expected to be used in the field of ceramic cutting tools.

Characterization of Na2M2TeO6 (M = Ni, Zn) for Oxide-Based All-Solid-State Sodium-Ion Batteries

All-solid-state sodium (Na) ion batteries (SiBs) are promising high-safety and low cost alternatives to current lithium (Li) ion batteries (LiBs), particularly suitable for the application to large-scale electrical energy storage systems. Development of inorganic solid Na-ion conducting materials used for solid electrolyte is most critical issue to realize all-solid-state SiBs. The solid electrolyte materials should have not only high Na-ion conductivity at room temperature but also chemical and electrochemical stabilities against both cathode and anode active materials. Oxide based solid electrolytes have lower conductivity and poorer deformability than sulfide based one, but they have other advantages such as their chemical stability in air and easiness for handling.Na2M2TeO6 (M = Zn, Mg, Ni, Co, etc.) with a P2-type honeycomb layered structure has been reported as a fast Na-ion conducting oxide [1]. Particularly, Na2Zn2TeO6 (NZTO) is an attractive candidate for a solid electrolyte material because of the high ionic conductivity well above 10-4 S cm-1 at room temperature, wide electrochemical potential window and lower densification temperature than other oxide-based Na-ion conductors such as NASICON and Na-β alumina [2–4]. On the other hand, Na2Ni2TeO6 (NNTO) has been investigated as a cathode active material for SiB operating at 3–4 V vs Na/Na+ [5,6]. Because of the similarity in their crystal structure and constituent elements, NNTO cathode and NZTO as solid electrolyte may be co-sintered without forming undesired secondary phases to fabricate all-solid-state SiBs.In this work, we investigated firstly the reactivity between NNTO and NZTO powders at annealing temperature between 500 ºC and 800 ºC in air. From XRD measurements, it was found that the reaction between NNTO and NZTO is negligible at annealing temperature below 700 ºC while when annealed at 800 ºC, they forms a solid-solution phase without forming any secondary phases. Based on this result, we fabricated NNTO-NZTO laminate via co-sintering NNTO and NZTO pellets at 700 ºC in air. Thicknesses of NNTO and NZTO layers in the laminate were set to 1 mm.From impedance measurements, apparent ionic conductivity of the NNTO-NZTO laminate was estimated to be approximately 0.1 mS cm-1 at 27 ºC, which is close to the prediction with taking into account only the conductivity of individually sintered NNTO (= 0.04 mS cm-1) and NZTO (= 0.36 mS cm-1) at 700 ºC. This indicates that the interfacial resistance between NNTO and NZTO layers is not so large. In addition, using the NNTO-NZTO laminate with NNTO layer thickness of 80 µm, electrochemical Na extraction reaction from NNTO layer through NZTO solid electrolyte was demonstrated via galvanostatic testing at room temperature. Obtained results are very fundamental but can be applied to fabricate all-solid-state SiBs with NNTO cathode and NZTO solid electrolyte via simple co-sintering process in future.

Hybrid microwave sintering of alumina and 3 mol% Y2O3-stabilized zirconia in a multimode cavity – Influence of the sintering cell

In microwave (MW) sintering, samples directly heat by absorption of the electromagnetic field, leading to a fast volumetric heating. Thus, the materials are heated thanks to their own dielectric properties. In multimode cavities, samples are always heated with a sintering cell in order to get an insulation of the samples and a heating homogeneity. However, to date, very limited research has been carried out to study the effects of materials used in the sintering cell. In this paper the microstructure and densification of Al2O3 and 3Y-TZP were investigated and compared between three different sintering cells. The used sintering cell contains three main elements: thermal insulators, a SiC susceptor and a protective mullite tube. Higher final densities (98.3 ± 0.6% and 98.6 ± 0.6% of T.D. for Al2O3 and 3Y-TZP respectively), lower densification temperatures and better microstructure homogeneity were obtained by using the sintering cell containing both mullite tube and SiC susceptor. But, sintering using the sintering cell without the SiC susceptor was also possible, especially for the lowest lossy material,i.e., Al2O3. This can be explained by a possible susceptor effect of the mullite tube. However, the microstructural observations showed a difference of homogeneity in the microstructure for Al2O3 and 3Y-TZP with some sintering cells. It can be linked to the difference of dielectric properties of the two materials. The influence of the sintering cell is less critical for 3Y-TZP, which couples better with MW than Al2O3. It was also observed that densification curves were switched to higher temperatures during sintering with the presence of SiC susceptor and without mullite tube. These results were justified by an error in the temperature measurement of the IR-pyrometer.

Processing and characterisation of BaZr0.8Y0.2O3−δ proton conductor densified at 1200 °C

BaZr0.8Y0.2O3−δ densifies at 1200 °C on employing a combination of Ba excess, ZnO sintering additive and nanopowders prepared by a sol–gel route. The low densification temperature decreases grain-boundary resistance despite the lower grain size.

Experiment and calculation: The Li(Zn, Mn)PO4 solid solution ceramics with low dielectric constant, high quality factor, and low densification temperature

Abstract The microstructure, sintering and microwave dielectric properties of (1−x)LiZnPO4+xLiMnPO4 (x = 0.0–1.0) composite ceramics were discussed specifically through density functional theory calculation and solid-state reaction experiment. The (1−x)LiZnPO4+xLiMnPO4 (x = 0.0–1.0) composite ceramics were characterised using network analyser, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and differential–thermal and thermo-mechanical analyser. The solid solution of Mn2+-ion-doped LiZnPO4 ceramic and Zn2+-ion-doped LiMnPO4 ceramic formed when the LiMnPO4 ceramic was added into the LiZnPO4 ceramic. The modification of the bond length, bond population and electron density could be observed in the ZnO4 tetrahedron and MnO8 octahedron. Moreover, the densification window of the LiZnPO4 ceramic decreased slightly. Experimental results were specifically explicated by the calculation result. Peak dielectric properties were obtained when x = 0.3 sintered at 800 °C, er = 5.83, Q × f = 71,007 GHz, τf = −82.84 ppm/°C and relative density = 97.33%. The addition of the LiMnPO4 ceramic is an effective method for improving the sintering and microwave dielectric properties of the LiZnPO4 ceramic.

Enhanced copper micro/nano-particle mixed paste sintered at low temperature for 3D interconnects

An enhanced copper paste, formulated by copper micro- and nano-particles mixture, is reported to prevent paste cracking and obtain an improved packing density. The particle mixture of two different sizes enables reduction in porosity of the micro-paste and resolves the cracking issue in the nano-paste. In-situ temperature and resistance measurements indicate that the mixed paste has a lower densification temperature. Electrical study also shows a ∼12× lower sheet resistance of 0.27 Ω/sq. In addition, scanning electron microscope image analysis confirms a ∼50% lower porosity, which is consistent with the thermal and electrical results. The 3:1 (micro:nano, wt. %) mixed paste is found to have the strongest synergistic effect. This phenomenon is discussed further. Consequently, the mixed paste is a promising material for potential low temperature 3D interconnects fabrication.

An original precipitation route toward the preparation and the sintering of highly reactive uranium cerium dioxide powders

The preparation of dense U1−xCexO2 mixed dioxides pellets was achieved from the initial precipitation of highly reactive precursors. In a first step, a wet chemistry route, based on the mixture of U4+ and Ce4+ in acidic solution with large excess of NH4OH, was set up to reach the precipitation of the cations. The solid phase was then dried under vacuum to avoid aggregation phenomena. Further characterization of the powders by XRD, EDS and TEM revealed the formation of hydrated U1−xCexO2⋅nH2O that probably resulted from the aging of hydroxide compounds. Also, microscopy investigations evidenced the nanosized character of the powder which was associated to high values of specific surface area, typically in the 100–150m2g−1 range.The behavior of U1−xCexO2⋅nH2O versus temperature was investigated in a second part. If the increase of the heat temperature allowed one to observe an improvement of the crystallization state linked with the growth of crystallites, it was also accompanied by a strong decrease of the powders reactivity. On this basis, sintering tests were conducted in reducing atmosphere on the compounds as prepared. Dilatometry experiments indicated a low densification temperature compared to other ways of preparation reported in the literature. Also, the pellets prepared after firing at different temperatures (1350–1550°C) showed that a wide range of microstructures was achievable. Particularly, bulk materials with densities of 90–95% of the calculated value could be prepared with average grain size ranging from around 100nm to more than 5μm. This simple process of elaboration of dense materials from highly reactive hydrated oxide precursor thus appears as a very interesting way to prepare actinide oxides materials.

Improvement of electrical conductivity of silicon nitride/carbon nano-fibers composite using magnesium silicon nitride and ytterbium oxide as sintering additives

In order to find out the influence of sintering additives on the electrical conductivity of Si3N4-based ceramics composites with dispersed carbon nano-fibers (CNFs) two different mixtures of sintering additives were tested – Al2O3/Yb2O3 and MgSiN2/Yb2O3, respectively. Optimization of hot-pressing conditions was performed for each mixture. The results show that the electrical conductivity can be effectively increased up to 1315 S/m by replacement of traditional sintering aid – alumina, with magnesium silicon nitride, while the mechanical properties remained on the same level. Other advantages of using MgSiN2 instead of alumina are the preservation of higher amounts of CNFs in the ceramic composite and lower densification temperature (1500 °C) compared to samples sintered with alumina-based sintering aids (1550 °C).

Effects of local Joule heating during the field assisted sintering of ionic ceramics

Abstract Recent investigations regarding the role of applied fields on the grain growth and densification behavior of ionic ceramics are providing strong insights into the efficacy of Field Assisted Sintering Technique (FAST), aka Spark Plasma Sintering (SPS). Explanations of the observed behaviors, such as grain growth suppression and densification enhancement, are based upon the conjectured presence of a Joule heating driven temperature differential between grain interfaces and grain cores. These differentials were thought to be responsible for providing increased densification rates and lower densification temperatures through grain growth suppression and/or increased local kinetics at the forming necks. In this paper, we analyze the energetic, thermal, and practical details of this process in the context of the commonly accepted stages of sintering.

Studies on ionic conductivity of stabilized zirconia ceramics (8YSZ) densified through conventional and non-conventional sintering methodologies

Densification studies of 8 mol% yttria stabilized zirconia ceramics were carried out by employing the sintering techniques of conventional ramp and hold (CRH), spark plasma sintering (SPS), microwave sintering (MWS) and two-stage sintering (TSS). Sintering parameters were optimized for the above techniques to achieve a sintered density of >99% TD. Microstructure evaluation and grain size analysis indicated substantial variation in grain sizes, ranging from 4.67 μm to 1.16 μm, based on the sintering methodologies employed. Further, sample was also sintered by SPS technique at 1425 °C and grains were intentionally grown to 8.8 μm in order to elucidate the effect of grain size on the ionic conductivity. Impedance spectroscopy was used to determine the grain and grain boundary conductivities of the above specimens in the temperature range of RT to 800 °C. Highest conductivity of 0.134 S/cm was exhibited by SPS sample having an average grain size of 1.16 μm and a decrease in conductivity to 0.104 S/cm was observed for SPS sample with a grain size of 8.8 μm. Ionic conductivity of all other samples sintered vide the techniques of TSS, CRH and MWS samples was found to be ∼0.09 S/cm. Highest conductivity irrespective of the grain size of SPS sintered samples, can be attributed to the low densification temperature of 1325 °C as compared to other sintering techniques which necessitated high temperatures of ∼1500 °C. The exposure to high temperatures while sintering with TSS, CRH and MWS resulted into yttria segregation leading to the depletion of yttria content in fully stabilized zirconia stoichiometry as evidenced by Energy Dispersive Spectroscopy (EDS) studies.

Preparation of Ba0.55Sr0.4Ca0.05TiO3 Powders by Chemical Co-Precipitation for Low Temperature Sintering Ferroelectric Ceramics

Ba0.55Sr0.4Ca0.05TiO3 (BSCT) powders were prepared both by chemical co-precipitation and solid-state reaction. The characterization by SEM reveals that BSCT powder(coded as BSCTc) prepared via chemical co-precipitation is with analogous sphericity mophlogy. Specific surface area analysis shows that BSCTc powder has much larger specific surface area of 15.32 m2.g−1 and smaller particle size of 0.085 μm. Different effects of the two BSCT powders on sintering behavior and microstructure of the ceramic were compared. The results show that the BSCTc powder possess higher sintering activity and can lead to lower densification temperature. When sintering aids (0.032 mol H3BO3-0.01 mol Li2CO3) was added, the sintering temperature of the BSCTc samples is 870°C and the fired density is 5.16 g.cm−3.

Enhanced piezoelectric properties of lead zirconate titanate sol-gel derived ceramics using single crystal PbZr0.52Ti0.48O3 cubes

Piezoceramic materials have attracted much attention for sensing, actuation, structural health monitoring, and energy harvesting applications in the past two decades due to their excellent coupling between energy in the mechanical and electrical domains. Among all piezoceramic materials, lead zirconate titanate (PZT) has been the most broadly studied and implemented, in industrial applications due to its high piezoelectric coupling coefficients. Piezoceramic materials are most often employed as thin films or monolithic wafers. While there are numerous methods for the synthesis of PZT films, the sol-gel processing technique is the most widely used due to its low densification temperature, the ease at which the film can be applied without costly physical deposition equipment and the capability to fabricate both thin and thick films. However, the piezoelectric properties of PZT sol-gel derived films are substantially lower than those of bulk materials, which limit the application of sol-gel films. In comparison, single crystal PZT materials have higher piezoelectric coupling coefficients than polycrystalline materials due to their uniform dipole alignment. This paper will introduce a novel technique to enhance the piezoelectric properties of PZT sol-gel derived ceramics through the use of single crystal PbZr0.52Ti0.48O3 microcubes as an inclusion in the PZT sol-gel. The PZT single crystal cubes are synthesized through a hydrothermal based method and their geometry and crystal structure is characterized through scanning electron microscopy (SEM) and x-ray diffraction (XRD). A mixture of PZT cubes and sol-gel will then be sintered to crystallize the sol-gel and obtain full density of the ceramic. XRD and SEM analysis of the cross section of the final ceramics will be performed and compared to show the crystal structure and microstructure of the samples. The P-E properties of the samples will be tested using a Sawyer–Tower circuit. Finally, a laser interferometer will be used to directly measure the piezoelectric strain-coupling coefficient of the PZT sol-gel ceramics with and without PZT cube inclusions. The results will show that with the integration of PZT crystal inclusions the d33 coupling coefficient will increase more than 200% compared to that of pure PbZr0.52Ti0.48O3 sol-gel.

Fabrication of scandium stabilized zirconia thin film by electrostatic spray deposition technique for solid oxide fuel cell electrolyte

A cost-effective and promising simple deposition method, electrostatic spray deposition (ESD), was used to fabricate dense scandium stabilized zirconia (ScSZ) thin films. The effect of solvent mixtures on their surface morphology was investigated. The films deposited using a mixed ethanol-butyl carbitol solvent with high boiling point showed higher smoothness compared with those deposited using ethanol and a mixture of ethanol and ethylene glycol, respectively. Single-phase ScSZ dense films were formed within 2 h at a low deposition temperature of 450 °C. Analysis of as heat-treated films using scanning electron microscope and atomic force microscope also indicated the formation of the uniform, smooth and dense thin films even at a low densification temperature. Furthermore, the ScSZ film deposited under the optimal condition showed the maximum in electrical conductivity of approximately 0.33 S cm − 1 at a low operating temperature of 800 °C.

Tuning Al 2O 3 crystallinity under supercritical fluid conditions: Effect on sintering

Supercritical fluids have been used to prepare alumina powders. This versatile technique allows the tuning of the crystallinity of the obtained powders by a simple modification of the fluid's nature. Amorphous or boehmite alumina could be successfully synthesised using either CO 2/Ethanol or H 2O/Ethanol, respectively. The two powders present very different sintering paths, which have been correlated to the grain morphology and crystalline state of the powders. We have established that the alumina elaborated in CO 2/ethanol exhibited a significant decrease of the γ-Al 2O 3 → α-Al 2O 3 transition temperature resulting in a lower densification temperature.

Complex permittivity and permeability of Co-substituted NiCuZn ferrite at rf and microwave frequencies

NiCuZn ferrite has recently attracted a lot of attention for its application in high frequency (up to a few GHz) multilayer chip inductors (MLCIs) and for other microwave devices owing to their favorable electromagnetic properties and low densification temperature. In order to study the effect of substitution of cations by cobalt in small concentration on the dielectric and magnetic properties at low and high frequencies, bulk polycrystalline ferrite samples of starting composition (Ni0.2Cu0.2Zn0.6)1 − x Co x Fe2O4, having x = 0, 0.01, 0.03 and 0.05, were prepared by citrate precursor method. Pure spinel (cubic) ferrite formation was confirmed by powder X-ray diffraction technique. Complex permittivity and permeability were measured at microwave frequencies (X-band) using the cavity perturbation method, which is a non-contact method. The values of real part of permittivity (e ′) vary in the range 7–9.6 and of the imaginary part (e ″) vary from 0.020–0.120, whereas real part of the permeability (μ′) lies in the range 2.6–14.0 and the imaginary part of permeability (μ″) varies from 0.5–6.0. It is observed that there is an increase in μ′ and decrease in the magnetic loss (tan δ μ) on increasing the cobalt concentration from x = 0 to x = 0.05. The variation of these parameters, both with frequency in X-band and with the cobalt concentration, is discussed in this paper.

Mechanical Properties of SiC Short-Fibre-Reinforced SiC Composites Fabricated by Tape Casting and Hot-Pressing

In order to examine the effects of sintering additives on microstructure and mechanical properties of SiC short-fibre-reinforced SiC composites, a ZrO2-Y2O3-Al2O3additive system was applied in this study. The aim of this study was to investigate the influence of the sintering additives on the mechanical properties of SiC/SiC composites using Tyranno SA short fibres. A ZrO2-Y2O3-Al2O3mixture was chosen for fabrication of the short-fibre-reinforced SiC composites as sintering additives because of their relatively low densification temperature and non-reactivity with SiC. Compare with the previous results, the influence of sintering additives on the mechanical and thermal properties of the SiC/SiC composites was discussed.

Sintering and Ionic Conductivity of CuO-Doped Tetragonal ZrO2 Prepared by Novel Colloidal Processing.

Suspensions of Cu2+ adsorbed tetragonal ZrO2 (3Y-TZ: 3mol%Y2O3-doped tetragonal zirconia) powder were prepared and their green bodies consolidated without powdering process by a pressure filtration method. Green bodies with a narrow pore size distribution were obtained after cold isostatic pressing of the pressure filtrated bodies. Small amounts of CuO addition resulted in lower densification temperature by the aid of a liquid phase. Bulk and grain-boundary conductivities were measured by a complex impedance method. Bulk conductivity was nearly independent of CuO addition but grain-boundary conductivity decreased with CuO addition.