Suitable Sintering Aids Research Articles

Densification, microstructure, and wear properties of TiB2-TiC-GNP and TiB2-TiC-BN composites

In this study, TiB2–TiC, TiB2–TiC-GNP, and TiB2-TiC-BN composites were produced via spark plasma sintering (SPS). The densification and sintering behavior, phase and Raman spectroscopy analyses, microstructural properties, Vickers microhardness, and wear behavior of the binary and ternary composites were investigated. The addition of various amounts of TiC to TiB2 resulted in nearly complete densification. The TiB2–TiC-GNP specimens exhibited a relative density of more than 99 %; in contrast, the addition of BN did not contribute to the densification. The Vickers hardness of the GNP-added composites was ∼25 GPa, whereas hBN addition to the matrix decreased the hardness to ∼22 GPa (∼9 % decrease). According to the wear test, the addition of GNPs did not result in a significant change in the TiB2–TiC matrix; however, the addition of hBN increased the specific wear rate of the matrix by ∼100 %. The GNPs did not have a negative effect on the densification, microstructural, or mechanical properties, such as the Vickers hardness and wear resistance. Hence, they were determined to be a more suitable sintering aid for matrix composition than hBN.

Development of a Solid-State Ta-Doped Lithium Lanthanum Zirconium Oxide Electrolyte for All-Solid-State Lithium Batteries (ASSLBs)

Large, high-power batteries are necessary for electric vehicles. The safety of batteries is also crucial, as damaged batteries should not be combustible. Moreover, in some cases batteries need to operate a modestly high temperatures in the range of 100 - 150 0C. All-solid-state lithium batteries (ASSLBs) can handle these requirements with ceramic electrolytes, lithium intercalation cathodes, and lithium metal anodes. Although ASSLBs using variations on this material set have been demonstrated, they tend to have low power, in part because of low ionic conductivity, as well as low rates of interfacial reaction between electrodes and electrolytes. Various strategies are being investigated to address the challenge of low power including operating at elevated temperatures, using doped electrolytes, increasing the contact area between the electrodes and the electrolyte, and through engineering of the interfaces between electrodes and electrolytes.Using tape casting followed by sintering, we are producing thin (~20µm) and dense Ta-doped Lithium Lanthanum Zirconium Oxide (LLZTO) films, and also LLZTO pellets. The challenge of Li-loss during sintering has been addressed by using suitable sintering aids and sacrificial Li source. We have characterized LLZTO films and pellets using techniques such as XRD, SEM, and SEM EXA. The electrochemical properties of the LLZTO electrolyte including ionic conductivity have been measured. This is the first step in the creation of a full cell with engineered electrodes and interfaces. An analytical model has been developed to examine the effect of thickness of anode, cathode, and current collector on energy density.

Effects of Li–B–Si–Ca–Mn glass addition on the densification, microstructure, and dielectric properties of (Ca,Sr)(Zr,Ti)O3 ceramics

Finding a suitable sintering aid to lower the sintering temperature of the dielectric material is important for making multilayer ceramic capacitors (MLCCs) with copper electrodes. In this study, Li–B–Si–Ca–Mn (LBSCM) glasses were prepared by melt quenching with the addition of an anti-reduction agent as a sintering aid for (Ca0.7Sr0.3)(Zr0.97Ti0.03)O3 dielectric ceramics (CSZT). Based on the defect chemistry and interaction between CSZT and LBSCM glass, the effects of the Li–B–Si glass addition on the sintering, microstructure, and dielectric properties of CSZT were investigated. It was found that the addition of 5 wt% LBSCM glass resulted in a dense microstructure after sintering at a temperature range of 975 °C–1100 °C in 99%N2–1%H2. The capacitance at 1 MHz between 140 and 150 pF, loss of about 0.19%, the breakdown voltage of about 1050 V, insulation resistance around 1011 Ω were obtained for the MLCCs with the size of 0805 using the CSZT added with 5 wt% LBSCM glass as the raw material and copper as the inner electrode sintered at 1000 °C for 1 h and 3 h under a reduction atmosphere of 1% H2/99% N2 mixture gas. This suggests that the CSZT added with 5 wt% LBSCM can be a good candidate as a dielectric material for MLCCs with copper electrodes.

Raman spectroscopic, infrared spectra and microwave dielectric properties in the (ZrTi)1−x(Al1/2Nb1/2)2xO4 ceramics

A series of (ZrTi)1−x(Al1/2Nb1/2)2xO4 (0.12 ≤ x ≤ 0.30) ceramics with suitable sintering aids of 0.5 wt% CuO were successfully synthesized by the conventional solid-state processing. The XRD analysis suggested that the main crystalline phase of the well-densified ceramics belonged to α-PbO2-type structure. The SEM demonstrated that the appropriate sintering aids and the proper sintering temperature led to a densification of the ceramics by observing the microstructure. Raman spectroscopic and Far Infrared reflectivity spectra were applied to explore the relation between microwave dielectric properties and microstructure by learning the phonon vibrational modes. An excellent microwave dielectric properties (er ~ 36.5, Qf ~ 36200 GHz, τf ~ 0 ppm/°C) was achieved in (ZrTi)1−x(Al1/2Nb1/2)2xO4 ceramics sintered at 1350 °C for 4 h when x = 0.18. The results revealed this ceramic system is a very promising candidate for microwave dielectric applications requiring extremely near zero τf.

Effect of BaCu(B2O5) on the sintering and microwave dielectric properties of Ca0.4Li0.3Sm0.05Nd0.25TiO3 ceramics

The sintering behaviors and microwave dielectric properties of the Ca0.4Li0.3Sm0.05Nd0.25TiO3 (abbreviated CLSNT) ceramics with different amounts of BaCu(B2O5) addition were investigated in this paper. Adding BaCu(B2O5) to CLSNT lowered its sintering temperature from 1300°C to 925°C. No secondary phase was observed in the CLSNT ceramics and complete solid solution of the complex perovskite phase was confirmed. The CLSNT ceramics with small amounts of BaCu(B2O5) addition could be well sintered at 925°C without much degradation in the microwave dielectric properties. Especially, the 1.75wt.% BaCu(B2O5)-doped CLSNT ceramic sample sintered at 925°C for 3h had optimum microwave dielectric properties of εr=93.5±3.2, Q×f=6486±434GHz, and τf=5±1.5ppm/°C (at 3–4GHz), enabling it a promising candidate material for LTCC applications. Obviously, BaCu(B2O5) could be a suitable sintering aid to facilitate the densification and microwave dielectric properties of the CLSNT ceramics.

Screening Sintering Aids for (K0.5Na0.5)NbO3 Ceramics

Searching for suitable sintering aids for ceramic materials is important and tedious work. In this study, we introduce a simple and effective method, named liquid phase screening method (LPSM), for rapidly screening sintering aids for KNN ceramics. By measuring the structure and properties, we demonstrated that the suitable sintering aids for KNN can be quickly determined by LPSM. The new sintering aids found by this method, GeO2 and borax which have not been reported before, lead to improved properties.

Pressureless sintering of ZrB2–SiC composite laminates using boron and carbon as sintering aids

A processing method common to composite ceramics with very different ZrB2/SiC ratios was developed in order to exploit ZrB2–SiC laminates comprising alternate layers with different compositions for thermal protection systems of re-entry vehicles. Ceramic laminates were made using SiC, ZrB2 and composites with a SiC/ZrB2 ratio ranging from 100 vol.-%SiC to 100 vol.-%ZrB2. The preparation was performed by tape casting of a slurry, layer stacking, debinding and pressureless sintering. Boron and carbon proved to be suitable sintering aids for SiC laminates as well as for composite laminates containing SiC. In the case of composites with a ZrB2 matrix, the second phase of SiC acted as a sintering aid. This process obtains very similar densification for specimens with very different compositions (ranging from 100%SiC to 80ZrB2–20SiC). The stiffness of ZrB2–SiC laminates increased with the ZrB2 content increase, while the bending strength was not affected by the ZrB2/SiC ratio.

Effect of Cerium Oxide on Sinterability, Microstructure and Properties of Anorthite-Based Glass/Ceramic Composites

The properties of anorthite-based glass/ceramic with different amounts of CeO2 addition had been investigated in this paper. The glass/ceramics with small amounts of CeO2 addition could be well sintered at 850~900°C. The water absorption was examined to evaluate the sintering behavior of the samples. The crystalline phase,microstructure, dielectric properties, thermal expansion and bending strength were characterized by X-Ray diffraction (XRD), scanning transmission electron microscope (SEM), impedance materials analyzer, thermal expansion analyzer and flexural strength analyzer. The results showed the 1wt % CeO2-doped glass/ceramics sintered at 900 °C have optimum properties of ε = 6.282, tanθ = 2.18×10-3 at 1 MHz and a thermal expansion coefficient of 3.32×10-6 °C-1 (25~500 oC) matched with silicon chip (3.4×10-6 °C -1). Obviously, CeO2 could be used as a suitable sintering aid that improves densification of the glass/ceramic composites.

Preparation of BCB Powder and its Effects on the Sintering Behaviour and Microwave Dielectric Properties of MCT Ceramics

The BCB (BaCu(B2O5)) powders were synthesized by solid state reaction method and its effects on the microstructures, the phase formation and the microwave dielectric properties of MCT (Mg0.95Ca0.05TiO3) ceramics were investigated. BaO and B2O3 first forms BaB2O4, and then BaB2O4 reacts with CuO forming BCB. The sintering temperature of MCT ceramics with as-synthesized BCB addition can be effectively lowered from 1450°C to 1100°C due to the liquid phase effect. The formation of second phase (MgTi2O5) was restrained. The 3wt% BCB-doped MCT ceramics sintered at 1100°C for 3h have optimum microwave dielectric properties of Kr=21.5, Q×f=28000GHz, and TCF=-3.3ppm/°C. Obviously, BCB could be a suitable sintering aid that improves densification and microwave dielectric properties of the MCT ceramics.

The influence of sintering aids for Nd(Mg 0.5Ti 0.5)O 3 microwave dielectric ceramics properties

The influence of various sintering aids on the microwave dielectric properties and the structure of Nd(Mg 0.5Ti 0.5)O 3 ceramics were investigated systematically. B 2O 3, Bi 2O 3, and V 2O 5 were selected as liquid-phase sintering aids to lower the sintering temperature. The sintered Nd(Mg 0.5Ti 0.5)O 3 ceramics are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microwave dielectric properties. The sintering temperature of Nd(Mg 0.5Ti 0.5)O 3 microwave dielectric ceramics is generally high, about 1500 °C. However, the sintering temperature was significantly lowered about 175 °C from 1500 °C to 1325 °C by incorporating in 10 mol% B 2O 3 and revealed the optimum microwave dielectric properties of dielectric constant ( ɛ r ) value of 26.2, a quality factor ( Q × f) value of 61,307 (at 9.63 GHz), and τ f value of −45.5 ppm/°C. NdVO 4 secondary phase was observed at 10 mol% V 2O 5 addition in the sintering temperature range of 1300–1325 °C, which led the degradation in microwave dielectric properties. The microwave dielectric properties as well as grain sizes, grain morphology, and bulk density were greatly dependent on sintering temperature and various sintering aids. In this study, it is found that Nd(Mg 0.5Ti 0.5)O 3 incorporated with 10 mol% B 2O 3 with lower sintering temperature and excellent dielectric microwave properties may be suggested for application in microwave communication devices. The use of liquid-phase sintering, the liquid formed during firing normally remains as a grain boundary phase on cooling. This grain boundary phase can cause a deterioration of the microwave properties. Therefore, the selection of a suitable sintering aid is extremely important.

EFFECTS OF V2O5 ADDITION ON MICROWAVE DIELECTRIC PROPERTIES OF 16CaO-9Li2O-12Sm2O3-63TiO2 CERAMICS

Effects of V 2 O 5 addition on the microwave dielectric properties of 16 CaO -9 Li 2 O -12 Sm 2 O 3-63 TiO 2 (abbreviated CLST) ceramics prepared by conventional mixed oxides method were investigated as a function of V 2 O 5 content and sintering temperature. All the specimens were sintered between 1100°C and 1250°C. The sintering temperature of the CLST ceramics was lowered by 100°C with V 2 O 5 addition. With the changing content of V 2 O 5, the dielectric constants lie between 88.6 and 108.2, while the Q × f values are between 3275 and 6573 GHz. Especially, the specimens doped by 0.75 wt% V 2 O 5 sintered at 1200°C and 1250°C for 3 h show good microwave dielectric properties with Kr =100.4-108.2, Q × f >4500 GHz , and TCF=7-8 ppm/°C. Obviously, V 2 O 5 could be used as a suitable sintering aid that could improve densification and microwave dielectric properties of the CLST ceramics.

Low temperature firing of CaO–Li 2O–Sm 2O 3–TiO 2 ceramics with BaCu(B 2O 5) addition

The sintering behavior and dielectric properties of the 16CaO–9Li 2O–12Sm 2O 3–63TiO 2 (abbreviated CLST) ceramics with different amounts of BaCu(B 2O 5) (abbreviated BCB) addition were investigated in this paper. The sintering temperature of the CLST ceramics was efficiently lowered by 250 ∘C. The CLST ceramics doped by small amounts of BaCu(B 2O 5) could be well sintered at 1050 ∘C and possesses good dielectric properties. Especially, the 4 wt% BaCu(B 2O 5)-doped CLST ceramics sintered at 1050 ∘C for 2 h have optimum dielectric properties of Kr=81.4 and tan δ = 0.0212 . Obviously, BaCu(B 2O 5) could be used as a suitable sintering aid that could improve densification of the CLST ceramics at very low temperature.

Low‐Sintering High‐k Materials for an LTCC Application

High‐k LTCC tapes with ultralow sintering temperatures were developed from lead‐free perovskite powders. Lowering of the sintering temperature from 1250°C down to 900°C has been achieved by means of ultrafine ceramic powders in combination with suitable sintering aids. The tape‐casting process has been optimized for ultrafine powders with an enhanced sintering activity. Low‐sintering high‐k tapes of a thickness down to 40 μm, suitable for LTCC processing, were obtained. The sintering behavior of these high‐k tapes has been studied and compared with other LTCC materials. Dielectric properties of the high‐k material have been investigated on a multilayer test structure consisting of up to 20 dielectric layers. After metallization with an Ag conductor, the green tapes were stacked and laminated. Sintering of these multilayer stacks at 900°C gives dense ceramic samples. Permittivities up to 2000 have been obtained, together with low dielectric losses. Material compatibility with several Ag/Au‐thick‐film‐paste systems has been tested.

Low-temperature firing and microwave dielectric properties of 16CaO–9Li 2O–12Sm 2O 3–63TiO 2 ceramics with V 2O 5 addition

The sintering behaviors and microwave dielectric properties of the 16CaO–9Li 2O–12Sm 2O 3–63TiO 2 (abbreviated CLST) ceramics with different amounts of V 2O 5 addition had been investigated in this paper. The sintering temperature of the CLST ceramic had been efficiently decreased by nearly 100 °C. No secondary phase was observed in the CLST ceramics and complete solid solution of the complex perovskite phase was confirmed. The CLST ceramics with small amounts of V 2O 5 addition could be well sintered at 1200 °C for 3 h without much degradation in the microwave dielectric properties. Especially, the 0.75 wt.% V 2O 5-doped ceramics sintered at 1200 °C for 3 h have optimum microwave dielectric properties of Kr = 100.4, Q × f = 5600 GHz, and TCF = 7 ppm/°C. Obviously, V 2O 5 could be a suitable sintering aid that improves densification and microwave dielectric properties of the CLST ceramics.

Sintering and piezoelectric properties of KNN ceramics doped with KZT

This paper investigates the effect of K(1.94)Zn(1.06)Ta(5.19)O(15) (KZT) addition on the sintering behavior and piezoelectric properties in lead free piezoelectric ceramics of (K(0.5)Na(0.5))NbO(3) (KNN). The apparent density of sintered KNN ceramics was increased with KZT addition, and a relative density of above 96.3% was obtained with the doping of over 0.5 mol% KZT. The maximum dielectric and piezoelectric properties of epsilon(T)(3)/epsilon(0) = 590, d(33) = 126 pC/N, k(p) = 0.42, and P(r) = 18 microC/cm(2) were obtained from 0.5 mol% KZT-doped KNN ceramics. A small amount of KZT (about 0.5 mol%) was effective for improving the sintering behavior and piezoelectric properties, but KZT addition exceeding 1.0 mol% was effective only for densification. A small amount of KZT was effective for densification of KNN ceramics by promoting K(5.75)Nb(10.8)O(30) liquid phase formation. However, even though KNN with 1.0 to approximately -2.0 mol% KZT had a relative density of >98.5%, the piezoelectric properties were inferior to those of 0.5 mol% KZT-doped KNN, presumably due to the smaller grain size and excess liquid phase of the KNN ceramics doped with higher amounts of KZT. It is believed that a small amount of KZT could be one of the suitable sintering aids to obtain highly dense KNN based piezoelectric.

Densification behaviour and microstructure of gel-derived phase-pure mullite in the presence of sinter additives

Gels with high pure mullite composition have been synthesized using aluminum nitrate nanohydrate and ethyl silicate. Pure mullite has been sintered to 88.5% of the T.D., when sintered at 1600°C for 3 h. Suitable sintering aids such as SrO (0.5 wt.%) and clay (2 wt.%) have tremendous effect in promoting the densification behavior of mullite to attain density to 98 and 95% of T.D. respectively at relatively low temperatures by pressureless sintering. SrO promotes the densification of pure mullite via liquid phase sintering and also does clay assist the viscous flow sintering. Clear differences found in the microstructures of mullite could be related to the different sintering aids, which have apparent effect on the densification behavior. SrO doped samples show a duplex microstructure of fine equiaxed and elongated grain morphology, while the clay doped samples show equiaxed and acicular morphology.

Low temperature pressureless sintering of sol-gel derived mullite

Mullite of stoichiometric composition has been synthesized by sol-gel process. Aluminium nitrate and ethyl silicate are used as the starting materials to prepare the single phase mullite powder. DTA shows that the mullitization starts at 971°C. It is observed from XRD analysis that the amorphous mullite completely transforms to orthorhombic crystalline mullite at 1300°C. Wet milling operation has enhanced the sintering density of pure mullite by 12% more than that of dry milling. The naturally available raw material, clay has been identified as one of the suitable sintering aids for mullite. The addition of clay to the mullite powder enhances the density up to 95% of TD even at a very low temperature, 1450°C by pressureless sintering. A viscous flow sintering mechanism during densification is one of the main criteria to achieve good densification.

Processing of pressureless-sintered SiC whisker-reinforced Al2O3 composites

Silicon carbide whisker-reinforced Al2O3 Composites were prepared using a processing scheme in which the constituents were dispersed in nonaqueous media, then colloid-pressed and pressureless-sintered under an inert atmosphere. Novel oligomeric and polymeric dispersants were used to sterically stabilize the SiC whiskers in the presence of the Al2O3 powder. The sintering studies indicated that in the absence of a suitable sintering aid, the whiskers significantly inhibited densification of the Al2O3 matrix. Doped composites containing yttrium isopmpoxide as a sintering aid were pressureless-sintered to final densities 95% of theoretical.