Amount Of Sintering Aids Research Articles

Vat photopolymerization of complex-shaped silicon nitride ceramics with high mechanical and thermal performance by optimization sintering aids and kinetics

In this study, the impact of sintering aid content and sintering time on the density, phase composition, microstructure, thermal conductivity, and mechanical properties of silicon nitride (Si3N4) ceramics through vat photopolymerization (VPP) was systematically investigated. The results revealed that an increase in sintering aid amount promoted the network distribution of the grain boundary phase along with densification, grain coarsening and microstructure uniformity. The extension of sintering time improved density, thermal conductivity, and mechanical properties of the material. Superior performance with density of 99.4%, thermal conductivity of 64.4W·m-1·K-1, flexural strength of 879 ± 37MPa, and hardness of 15.0 ± 0.4GPa was achieved in sample containing 8wt.% MgO/Y2O3 sintered for 12h. Finally, high-precision Si3N4 ceramic heat sink elements were successfully fabricated via VPP, opening up new prospects in thermal management applications associated with electronics and automotive industries.

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.

Role of liquid sintering aids in the synthesis of SiAlON materials

The synthesis of dense sintered sialon with external additives selected from the system Y2O3-AlN-SiO2 is described. The highest density (3.21g/cc) was achieved at 1750ºC at 90 min of sintering with 5 wt% additive. Non-oxide ceramic materials are increasingly coming out as a potential candidate in engineering applications and among them, sialon is one of the most important materials. β-Sialon was first to be discovered in this class of compounds. It has an excellent combination of thermal, mechanical and chemical properties. The degree of sialon substitution increased with the amount of liquids, the YSiO2N crystalline phase formed concurrently. Strength degradation occurred above 1000ºC.The fracture toughness of the material sintered with a lower amount of sintering aid remained relatively unchanged to 1200ºC.

Structural and Mechanical Properties of Alumina-Zirconia (ZTA) Composites with Unstabilized Zirconia Modulation

Zirconia toughened alumina (ZTA) ceramics are very promising materials for structural and biomedical applications due to their high hardness, fracture toughness, strength, corrosion and abrasion resistance and excellent biocompatibility. The effect of unstabilized ZrO2 on the density, fracture toughness, microhardness, flexural strength and microstructure of some Zirconia-toughened alumina (ZTA) samples was investigated in this work. The volume percentage of unstabilized ZrO2 was varied from 0% - 20% whereas sintering time and sintering temperature were kept constant at 2 hours and 1580°C. The samples were fabricated from nanometer-sized (α-Al2O3: 150 nm, monoclinic ZrO2: 30 - 60 nm) powder raw materials by the conventional mechanical mixing process. Using a small amount of sintering aid (0.2 wt% MgO) almost 99.2% of theoretical density, 8.54 MPam? fracture toughness, 17.35 GPa Vickers microhardness and 495.67 MPa flexural strength were found. It was observed that the maximum flexural strength and fracture toughness was obtained for 10 vol% monoclinic ZrO2 but maximum Vickers microhardness was achieved for 5 vol% ZrO2 although the maximum density was found for 20 vol% ZrO2. It is assumed that this was happened due to addition of denser component, phase transformation of monoclinic ZrO2 and the changes of grain size of α-Al2O3 and ZrO2.

Sinterability and Dielectric Properties of LiTaO3-Based Ceramics with Addition of CoO.

Lithium tantalite (LiTaO3) is a common piezoelectric and ferroelectric crystal, but the LiTaO3 polycrystalline ceramics have rarely been reported, and their refractory character presents difficulties in their fabrication. In this study, LiTaO3-based ceramics with different amounts of CoO were prepared by pressureless sintering at 1250 °C, and the effects of the amount of sintering aid on the sinterability, microstructure, and dielectric properties of the ceramics were investigated. The relative densities of the LiTaO3-based ceramics were significantly improved by the addition of CoO powder. The LiTaO3-based ceramics achieved the highest relative density (89.4%) and obtained a well-grained microstructure when the added amount of CoO was 5 wt.%. Only the LiTaO3 phase in the ceramics was observed, indicating that the ions Co diffused into the LiTaO3 lattices and mainly existed in two forms: Co2+ and Co3+. The effects of the added amount of CoO on the dielectric properties of the LiTaO3-based ceramics were studied thoroughly. Consequently, the dielectric constant was enhanced, and the dielectric loss decreased in the LiTaO3-based ceramics with the addition of CoO. The optimal value was obtained at 5 wt.% of CoO-added LiTaO3-based ceramics.

Fabrication and characterization of Tb3Al5O12 magneto-optical ceramics by solid-state reactive sintering

Terbium aluminum garnet (TAG) transparent ceramics were fabricated by solid-state reactive sintering in vacuum combined with hot isostatic pressing (HIP) post-treatment using tetraethoxysilane (TEOS) as sintering aid. The influences of TEOS amount on the densification, microstructure and optical properties of TAG ceramics were investigated. The in-line transmittance of the TAG ceramic with 0.2 wt% TEOS additive, which was fabricated by pre-sintering at 1700 °C for 20 h and HIP post-treating at 1700 °C for 3 h, can reach about 66% in the visible and near-infrared regions. With appropriate amount of sintering aid, the transmittance of TAG ceramics in the visible wavelength range can be improved significantly by prolonging the holding time.

Effect of low-melting-point sintering aid on densification mechanisms of boron carbide during spark plasma sintering

A densification creep model was proposed to analyze the densification mechanism involved in spark plasma sintering (SPS) of boron carbide containing low-melting-point sintering aid. This model incorporated the effect of the sintering aid on relative density as well as the actual internal stress during SPS of boron carbide ceramics. The internal stress bias caused by sintering aid was considered and a more accurate effective stress was used to investigate the kinetics during SPS. The proposed model explains why an increase of sintering aid amount decreases the sintering activation energy and promotes densification.

Enhancing sinterability and electrochemical properties of Ba(Zr0.1Ce0.7Y0.2)O3-δ proton conducting electrolyte for solid oxide fuel cells by addition of NiO

The influence of NiO on the sintering behavior and electrical properties of proton conducting Ba(Zr0.1Ce0.7Y0.2)O3-δ (BZCY7) as an electrolyte supporter for solid oxide fuel cells is systematically investigated. SEM images and shrinkage curve demonstrate that the sinterability of the electrolyte pellets is dramatically improved by doping NiO as a sintering aid. The sintering aid amount and sintering temperature are optimized by analyzing the linear shrinkage, grain size and morphology for a series of sintered BZCY7 electrolyte pellets. Almost full dense electrolyte pellets are successfully formed by using 0.5–1.0 wt% NiO loading after sintering at 1400 °C for 6 h. The linear shrinkage of 0.5 wt% NiO modified BZCY7 sample is about 14.25% higher than that without NiO addition (4.81%). Energy dispersive X-ray spectroscopy analysis indicate that partial NiO might dissolve into the perovskite lattice structure and the other NiO react with BZCY7 to form BaY2NiO5 secondary phase as a sintering aid. Excessive NiO is especially detrimental to the electrical properties of BZCY7 and thus lower the open circuit voltage. The electrochemical performance for a series of single cells with different concentration NiO modified BZCY7 electrolyte are measured and analyzed. The optimized composition of 0.5 wt% NiO modified BZCY7 as an electrolyte support for solid oxide fuel cell demonstrates a high electrochemical performance.

The Effect of Fabrication Conditions for GDC Buffer Layer on Electrochemical Performance of Solid Oxide Fuel Cells

Abstract A Gd-doped ceria (GDC) buffer layer is required between a conventional yttria-stabilized zirconia (YSZ) electrolyte and a La-Sr-Co-Fe-O3 (LSCF) cathode to prevent their chemical reaction. In this study, the effect of varying the conditions for fabricating the GDC buffer layer, such as sintering temperature and amount of sintering aid, on the solid oxide fuel cell (SOFC) performance was investigated. A finer GDC powder (i.e., ultra-high surface area), a higher sintering temperature (∼1290°C), and a larger amount of sintering aid (∼12%) resulted in improved densification of the buffer layer; however, the electrochemical performance of an anode-supported cell containing this GDC buffer layer was poor. These conflicting results are attributed to the formation of (Zr, Ce)O2 and/or excess cobalt grain boundaries (GBs) at higher sintering temperatures with a large amount of sintering aid (i.e., cobalt oxide). A cell comprising of a cobalt-free GDC buffer layer, which was fabricated using a low-temperature process, had lower cell resistance and higher stability. The results indicate that electrochemical performance and stability of SOFCs strongly depend on fabrication conditions for the GDC buffer layer.

The Effect of Fabrication Conditions for GDC Buffer Layer on Electrochemical Performance of Solid Oxide Fuel Cells

A Gd-doped ceria (GDC) buffer layer is required between a conventional yttria-stabilized zirconia (YSZ) electrolyte and a La-Sr-Co-Fe-O3 (LSCF) cathode to prevent their chemical reaction. In this study, the effect of varying the conditions for fabricating the GDC buffer layer, such as sintering temperature and amount of sintering aid, on the solid oxide fuel cell (SOFC) performance was investigated. A finer GDC powder (i.e., ultra-high surface area), a higher sintering temperature (∼1290°C), and a larger amount of sintering aid (∼12%) resulted in improved densification of the buffer layer; however, the electrochemical performance of an anode-supported cell containing this GDC buffer layer was poor. These conflicting results are attributed to the formation of (Zr, Ce)O2 and/or excess cobalt grain boundaries (GBs) at higher sintering temperatures with a large amount of sintering aid (i.e., cobalt oxide). A cell comprising of a cobalt-free GDC buffer layer, which was fabricated using a low-temperature process, had lower cell resistance and higher stability. The results indicate that electrochemical performance and stability of SOFCs strongly depend on fabrication conditions for the GDC buffer layer.

The effect of cation type, intergranular phase amount and cation mole ratios on z value and intergranular phase crystallization of SiAlON ceramics

The chemical resistance of SiAlONs is controlled by various factors such as z value, microstructure, type and amount of sintering additives, and intergranular phase nature (amorphous or crystalline). In this study, the relationship between z value and intergranular phase crystallization of αı:βı-SiAlON composites reinforced with TiN (17wt%) was investigated by using various dopant systems (Y:Sm:Ca, Yb:Sm:Ca, and Er:Sm:Ca) and various amounts of intergranular phase. The effect of TiN on densification, phase assemblage and microstructural evolution of composites was systematically investigated. Further, the effects of variations in the sintering aid amount and cation mole ratios on density, hardness and fracture toughness were determined in relation to z values. It was found that high z value (>0.5), crystalline intergranular phase and appropriate mechanical properties can be achieved by selecting the type of sintering additive, its amount and ratio.

Preparation of Low-Temperature Sintered Ba<sub>2</sub>Ti<sub>9</sub>O<sub>20</sub> Ceramics Doped with B<sub>2</sub>O<sub>3</sub> by Different Method

Ba2Ti9O20 ceramics were prepared with different additives of B2O3 by liquid coating method and solid phase mix method. The sintering behavior, phase structure and dielectric properties of ceramics were investigated by X-ray diffraction, scanning electron microscopy and inductance-capacitance resistance analysis. The liquid coating method can reduce the amount of sintering aid and minimized the negative impact of sintering aid on dielectric properties. A ceramic composite which could be sintered well at 900°C for 3h and showed good dielectric properties of εr=42,tanδ=0.002 and TCF=-4ppm/°C（1MHz）was obtained when 1.0mol/l H3BO3 was added to the Ba2Ti9O20 ceramic.

Sintering Behavior and Dielectric Properties of BZN Ceramics Coated by Precursor Solution of CuSO<sub>4</sub>

(Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 (BZN) ceramic samples were prepared by solid state reaction, In order to reduce the sintering temperature of BZN ceramic we have used liquid coating technology to dope CuO by precursor solution of CuSO4. The sintering behavior, microstructures, phase structures, and dielectric properties were studied. The process reduces the amount of sintering aid and minimized the negative impact of sintering aid on dielectric properties. A ceramic composite which could be sintered well at 900°C and showed good dielectric properties of εr=161,tanδ=0.005 and TCF=-398ppm/°C（1MHz）was obtained when 0.5mol/l CuSO4 was added to the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 ceramic.

Effect of Sintering Aid on Microstructure and Mechanical Properties of TiB<sub>2</sub>/TiN Tool Materials

TiB2/TiN composites with various content of Ni and Mo as sintering aid were hot-pressed at 1530°C. Effect of the content of sintering aid on microstructure and mechanical properties is investigated. Experimental results show that the fracture toughness of the composites increases consistently with an increase in the sintering aid content, however, the flexural strength gets to the maximum when the content of sintering aid is 10vol%. A new eutectic phase of MoNi can be found in the composites by X-ray diffraction (XRD) when the amount of sintering aid is over 7vol%. Scan electron microscope (SEM) analysis shows that the density of the composites increases consistently with the increasing of the sintering aid. But the abnormal-growth grains can be found and deteriorates the flexural strength in the composite No.4 because of the excessive sintering aid.

Proton-conducting yttrium-doped barium cerate ceramics synthesized by a cost-effective solid-state reactive sintering method

Ceramic pellets of the prototypical proton conductor BaCe 0.8Y 0.2O 3 − δ (BCY20) were synthesized using the recently developed solid-state reactive sintering (SSRS) method [J. Tong et al., Solid State Ionics, 2010, 181, 496–503] from inexpensive raw materials of BaCO 3, CeO 2, and Y 2O 3 with less than 2 wt.% NiO as a sintering aid. The sintering aid amount, sintering temperature, and sintering time were optimized by analyzing the crystal structure, relative density, and morphology for a series of as-sintered BCY20 ceramic pellets. High-quality, fully-densified BCY20 ceramic pellets were successfully prepared using 1.0 wt.% NiO loading at a sintering temperature of 1400 °C for 12 h. In order to examine the fate of the NiO addition in the as-fabricated (oxidized) pellets and under reducing conditions, the microstructure of several as-sintered and reduced BCY20 ceramic pellets were investigated in detail by EDS mapping and compared with as-sintered and reduced control BCY20 ceramic pellets obtained from polymeric sol–gel powder. Upon reduction, nanosized nickel particles were accumulated in grain boundary regions of the NiO-modified BCY20 pellets, while Y 2O 3 second-phase impurities were identified in the sol–gel BCY20 control pellets. The conductivities of both the NiO-modified SSRS and sol–gel control BCY20 ceramic pellets were investigated from 150 to 650 °C under H 2O saturated (P H 2O ~ 0.025 atm) atmospheres of UHP Ar and 5 vol.% H 2 + 95 vol.% Ar. The NiO-modified SSRS-fabricated BCY20 pellets demonstrated significantly higher conductivities than the sol–gel fabricated control BCY20 pellets.

Sintering Behavior, Microstructure, and Mechanical Properties: A Comparison among Pressureless Sintered Ultra-Refractory Carbides

Nearly fully dense carbides of zirconium, hafnium, and tantalum were obtained by pressureless sintering at 1950°C with the addition of 5–20 vol% of MoSi2. Increasing the amount of sintering aid, the final density increased too, thanks to the formation of small amounts of liquid phase constituted by M-Mo-Si-O-C, where M is either Zr, Hf, or Ta. The matrices of the composites obtained with the standard procedure showed faceted squared grains; when an ultrasonication step was introduced in the powder treatment, the grains were more rounded and no exaggerated grains growth occurred. Other secondary phases observed in the microstructure were SiC and mixed silicides of the transition metals. Among the three carbides prepared by pressurless sintering, TaC-based composites had the highest mechanical properties at room temperature (strength 590 MPa, Young's modulus 480 GPa, toughness 3.8 MPa·m1/2). HfC-based materials showed the highest sinterability (in terms of final density versus amount of sintering aid) and the highest high-temperature strength (300 MPa at 1500 °C).

Low sintering BaNd 2Ti 4O 12 microwave ceramics prepared by CuO thin layer coated powder

Recently, BaO–Nd 2O 3–TiO 2 systems are widely studied for microwave applications because of their high dielectric constant and high quality factor. However, pure BaNd 2Ti 4O 12 ceramics without additives have to be sintered above 1300 °C to achieve densification. Copper oxide has been known as a good sintering aid for electronic ceramics and less reactive toward silver. We have introduced the CuO into BaNd 2Ti 4O 12 by modifying the surface of BaNd 2Ti 4O 12 by CuO thin layer on the calcined powder instead of mixing CuO directly with BaNd 2Ti 4O 12 powder. The process reduces the amount of sintering aid and minimized the negative impact of sintering aid on dielectric properties such as quality factor. The CuO precursor solution of Cu(CH 3COO) 2, Cu(NO 3) 2 and CuSO 4, were used to prepare CuO thin layer. They were investigated individually to determine their effects on the densification, crystalline structure, microstructure and microwave dielectric properties of BaNd 2Ti 4O 12. The CuSO 4 coated BaNd 2Ti 4O 12 sintered at 1150 °C has exhibited better dielectric properties than those of CuO doped BaNd 2Ti 4O 12 ( k, 62.5 versus 61.2; Q × f, 11,500 GHz versus 10,500 GHz). The thin layer dopant coating process has been found to be a very effective way to lower ceramic sintering temperature without scarifying its dielectric properties.

Piezoelectric properties of (K0.5Na0.5)(Nb1−xTax)O3−K5.4CuTa10O29 ceramics

( K 0.5 Na 0.5 ) ( Nb 1 − x Ta x ) O 3 (KNNT)-based ceramics have been synthesized via a solid-state reaction. In this study, KNNT-based ceramics were sintered at atmospheric pressure by adding small amounts of sintering aid [0.38mol% K5.4Cu1.3Ta10O29]. The (K0.5Na0.5)NbO3 (KNN) ceramics which synthesized by using the K5.4Cu1.3Ta10O29 showed “hard” piezoelectric characteristics such as a high mechanical quality factor (Qm=1300) and low tanδ (0.4%). The quantitative effects of Ta on the electrical properties of (K0.5Na0.5)(Nb1−xTax)O3–K5.4Cu1.3Ta10O29 ceramics were also examined. Ta substitution provides “soft” piezoelectric characteristics and a large electrostrictive effect for KNN, which resulted in an improvement in kp, εr, strain, and d33 of KNNT ceramics depending upon the Ta content. Especially, (K0.5Na0.5)(Nb0.7Ta0.3)O3 showed the maximum strain and d33 values of 0.11% (at 40kV∕cm) and 270pm∕V (at 30–40kV∕cm), respectively. This strain level is comparable to that of hard Pb(Zr,Ti)O3 ceramics.

Low Temperature Densification of SOFC Electrolytes Using Manganese Oxide and Boron Oxide

To reduce the sintering temperature of yttria-stabilized zirconia (8YSZ) the influence of the addition of a pre-reacted mixture from manganese oxide and boron oxide on the densification behaviour was analyzed. The experiments were carried out on pressed pellets as well as on tubular SOFCs from Siemens Fuel Cells. Different sintering aid contents were investigated using sintering temperatures from 1200 up to 1400 °C and a dwelling time of 5 h, respectively. With all sintering aid contents, a distinct increase in the density of the pellets could be observed. In contrast to that, the addition of low amounts of the sintering aid in the electrolyte coatings results in no noticeable increase in the density. Additions of higher amounts of sintering aid leads to an increase of the density after comparable sintering. No evidence of an undesired compaction of the cathode leading to a low polarization in the cathode was observed.

Sintering of AlN Using CaO‐Al2O3 as a Sintering Additive: Chemistry and Microstructural Development

The densification of aluminum nitride using Ca12Al14O33 as a sintering aid has been studied with emphasis on the effect of using coarse or fine powder, the amount of sintering aid, the sintering temperature, and embedding. Both crystalline and amorphous grain boundary phases were observed. Significant weight losses were observed for coarse‐grained samples, and if suitable embedding was not used. Porous and coarse‐grained ceramics with high contiguity and minor amounts of secondary phases were obtained by enhanced evaporation while dense ceramics were obtained limiting the evaporation. High weight losses in the graphite environment resulted in formation of a dense AlN surface layer.