Low-temperature Sintering Behavior Research Articles

The Effect of TiO2 Addition on Low-temperature Sintering Behaviors in a SnO2-CoO-CuO System

Pure SnO2 has proven very difficult to densify. This poor densification can be useful for the fabrication of SnO2 with a porous microstructure, which is used in electronic devices such as gas sensors. Most electronic devices based on SnO2 have a porous microstructure, with a porosity of > 40%. In pure SnO2, a high sintering temperature of approximately 1300C is required to obtain > 40% porosity. In an attempt to reduce the required sintering temperature, the present study investigated the low-temperature sinterability of a current system. With the addition of TiO2, the compositions of the samples were Sn1-xTixO2-CoO(0.3wt%)-CuO(2wt%) in the range of x ≤ 0.04. Compared to the samples without added TiO2, densification was shown to be improved when the samples were sintered at 950C. The dominant mass transport mechanism appears to be grain-boundary diffusion during heat treatment at 950C.

(Cu1/3Nb2/3)4+ ionic substituting effects, low-temperature sintering behaviors, and improved temperature stability of Ba3Nb4Ti4O21 microwave dielectric ceramics

In this study, (Cu1/3Nb2/3)4+ complex cation and BaO–ZnO–B2O3 glass frit were adopted to solve the high sintering temperature and poor temperature stability of Ba3Nb4Ti4O21 ceramics. It is shown that pure Ba3Nb4Ti4O21 phase was formed when Ti site was partially replaced by (Cu1/3Nb2/3)4+ cation. The increasing number of dopants decreases the dielectric polarizability, correspondingly, the dielectric constant and temperature coefficient of the resonance frequency values are reduced consistently. The variation of the Q × f value is determined by internal ionic packing fraction and external sintering densification. The (Cu1/3Nb2/3)4+ cation effectively decreases the suitable sintering temperature from 1200 to 1050 °C while greatly improving the temperature stability. BaO–ZnO–B2O3 glass was used to further improve the low-temperature sintering characteristics of Ba3Nb4Ti4O21 ceramics. It is proven that the addition of glass frits effectively decreases the temperature to 925 °C with combinational excellent microwave dielectric properties: εr ∼55.6, Q × f ∼5700 GHz, τf ∼3 ppm/°C, making the Ba3Nb4Ti4O21 ceramics promising in the applications of low-temperature cofired ceramic technology.

Low-temperature sintering behavior of fly ash from hazardous waste incinerator: Effect of temperature and oxygen on ash properties

Hazardous waste incineration fly ash (HFA) is high risk for the environment due to heavy metals leaching and other pollutants. Sintering treatment potentially reduces the mass and volume of HFA and immobilizes heavy metals in ceramic-like bodies. However, HFA contains a large amount of heavy metals, thus sintering at too high a temperature will lead to the volatilization of heavy metals. The low-temperature sintering behavior of HFA at different temperature (450 °C, 670 °C and 900 °C) and different atmospheres (21% O2, 47.3% O2, 60.5% O2 and 100% O2) was investigated in this study. The mass loss, morphology, bulk density, elemental composition, heavy metal leaching rate, and mineral phase transformation of sintered ash were experimentally tested. With increasing sintering temperature, more mass of HFA was lost and the leaching rate of heavy metals decreased. For instance, sintered at 450 °C, 670 °C and 900 °C under air, the mass losses were 4.30%, 6.58%, and 17.96%, the leaching rate of Pb were 19.37%, 2.74%, and 0.65%, respectively. Sintered ash became denser and formed ceramic-like particle due to thermal agglomeration and chemical reactions. The bulk density significantly increased, which was favorable to reduce space occupancy for fly ash landfill. Oxygen-rich atmosphere could make the fly ash denser and inhibit the volatilization and leaching of Pb. The obtained findings are beneficial for deep understanding of the sintering behavior of HFA at low-temperature.

Low-temperature sintering behaviors in a titanium oxide–copper oxide system through two-step heat treatment

The low-temperature sinterability of TiO2–CuO systems was examined through a two-step sintering process. The first-step heat treatment was carried out at 900 °C for either 5 min or 1 h. The subsequent second-step sintering by reheating after cooling proceeded at 800 °C for various times. Micron-sized (2 µm) powders as received were used as the starting materials. In the present system, the densification behaviors through grain-boundary diffusion were similar to those in nanocrystalline ceramics at low temperatures. The difference in temperature sensitivity for densification or grain growth was thus exploited to enhance densification and hinder grain growth. As a result, enhanced densification without notable grain growth was achieved after second-step sintering, as opposed to conventional sintering at 800 °C. This implies that the grain-boundary diffusion contributing to densification was more active than the grain-boundary migration at 800 °C. In this regard, the current results show a trait of activated sintering as well.

Brief review of silver sinter-bonding processing for packaging high-temperature power devices

Silver sintering is receiving increasing attention due to its novel die-attach technique for high-temperature power electronics. Excellent thermal conductivity, high melting point/remelting temperature and low-temperature sintering behaviors of the silver sintered attachment meet the requirements of high-temperature applications for power devices, specifically SiC devices. The merits and demerits of the existing pressure-assisted sintering and pressure-less sintering techniques using nano-scale, micro-scale and micro-nano-scale hybrid silver sintered materials are separately presented. The emerging rapid sintering approaches, such as the electric-assisted approach, are briefly introduced and the technical outlook is provided. In addition, the study highlights the importance of creating a brief resource guide on using the correct sintering methods.

Study on Low-Temperature Sintering Behavior of 90W-7Ni-3Fe Alloys: The Influence of Sn Addition

In this work, we investigate low-temperature sintering behavior of the 90W-7Ni-3Fe alloy by introducing Sn. The 90W-7Ni-3Fe alloy with different Sn contents (0, 0.5, 1.0 and 1.5 wt.%) was fabricated via vacuum sintering at 1300 °C for 90 min. When 1 wt.% Sn was added, the liquidus temperature of the 90W-7Ni-3Fe alloy decreased from 1477 to 1265 °C, resulting in rapid densification (relative density increased from 77.77 to 98.59%) and an homogeneous liquid-phase sintered microstructure. Electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) observations revealed that, apart from W and the γ-(Ni, Fe) phase, a new Ni3Sn2 phase appeared in the matrix phase. Furthermore, we discuss in detail the formation of the Ni3Sn2 phase based on element selection theory, which can be associated with the larger atomic radius of Sn and with the negative enthalpy of mixing Sn and Ni. Excessive Sn content (1.5 wt.%) led to the increase in Ni3Sn2 phase, and this deteriorated the relative density and tensile strength of the alloy. The 90W-7Ni-3Fe alloy with the addition of 1 wt.% Sn exhibited a maximum tensile strength value (710 MPa), which was much higher than that of the 90W-7Ni-3Fe alloy that was obtained at 1300 °C. Our findings shed light on further research directions and developed a 90W-6.3Ni-2.1Fe-1Sn alloy for low-temperature sintering.

Investigation on low-temperature reactive viscous flow sintering behavior of lanthanum-borate glass-ceramic with BaTi4O9 ceramic filler

In this paper, the sintering behavior of the lanthanum-borate (B2O3-La2O3-MgO-TiO2,BLMT) glass-ceramic with BaTi4O9 filler composite was investigated in terms of the wetting behavior, interfacial reaction, sinter-shrinkage process, sintering activation energy, as well as phase and microstructure evolution with change in filler contents and sintering temperature. Our research suggested that the glass is unable to wet the filler material within a temperature up to 1000 °C, indicating that the densification process of composites is dominated by viscous flow of glass matrix. The increase in filler content that performs as a rigid particle in composite causes the rise in the sinter-shrinkage-onset and -end temperature, thereby proving that the viscous-flow densification of the composites with x≤ 30 wt% filler content is accomplished before the crystallization of BLMT glass, whereas the composites with x≥ 40 wt% cannot. After densification, a chemical reaction that almost synchronizes with the glass crystallization occurred between glass and ceramic, which not only imposes significant influence on the crystallization behavior, but eradicates the closed pore formed by the viscous flow and the induced crystallization porosity. The densification process of the BaTi4O9 filler-BLMT glass composite was referred to as two-stage reactive assisted viscous flow sintering process which consists of viscous flow of glass, of the crystallization process of glass, and/or of the chemical reaction between glass and filler.

The effect of Y2O3 on the grain growth and densification of W matrix during low temperature sintering: Experiments and modelling

In this work, the effect of Y2O3 addition on the grain growth and densification of W matrix was explored from a kinetic perspective by comparing the low temperature sintering behavior of W-Y2O3 composite nanopowder system with that of pure W nanopowder system. By combining nonisothermal sintering experiment with the power law of grain growth, it was found that grain boundary diffusion is responsible for the mass transport mechanism in both systems. The inhibition of W grain growth after Y2O3 addition is closely related to the lower surface diffusivity of W skeleton. The densification rate of W skeleton in these two systems were modelled using a periodic 3D arrangement of identical particles and a much smaller grain boundary diffusivity of W skeleton was obtained for W-Y2O3 sample. Firstly, it is the decrease in dihedral angle of W matrix after Y2O3 addition that causes a decrease in thermodynamic driving force for densification. Secondly, from the view of atomic mobility, the inhibited W grain growth caused by limited surface diffusivity is one of the reasons impeding densification. Besides, Y2O3 grains distributed at W grain boundary coarsen through wetting W grain boundary, which also has an inhibition effect on the W skeleton densification.

Low-Temperature Sintering Behavior of Aluminum Nitride Ceramics with Added Copper Oxide or Copper

Low-Temperature Sintering Behavior of Aluminum Nitride Ceramics with Added Copper Oxide or Copper

Low-firing, temperature stable and improved microwave dielectric properties of ZnO[sbnd]TiO2[sbnd]Nb2O5 composite ceramics

This article presents low-firing, low-loss and temperature stable ZnOTiO2Nb2O5 microwave dielectric composite ceramics with the assistance of lithium borosilicate (LBS) and zinc borosilicate (ZBS) glass frits. There is a liquid phase (eutectic mixture) generated by LBS (ZBS) glass, and solid particles could be wetted and dissolved. Therefore, the migrations and rearrangements of particles could be performed. Besides, compared with ceramics undoped with glass frits, lower activation energies (Ea) of ceramics doped with LBS and ZBS glass suggest that the low-temperature sintering behavior is easier to carry out. The results indicated that LBS and ZBS glass both are effective sintering aids to accelerate the sintering process and improve the microwave dielectric properties of composite ceramics by controlling the phase compositions under low temperature. Combination great properties of ZnOTiO2Nb2O5 ceramics were obtained when sintered at 900 °C for 4 h: εr = 36.7, Q × f = 20,000 GHz, τf = 7 ppm/oC.

Crystal structure, microwave dielectric properties and low temperature sintering of (Al0.5Nb0.5)4+ co-substitution for Ti4+ of LiNb0.6Ti0.5O3 ceramics

The phase composition, microstructure, microwave dielectric properties of (Al0.5Nb0.5)4+ co-substitution for Ti site in LiNb0.6Ti0.5O3 ceramics and the low temperature sintering behaviors of Li2O-B2O3-SiO2 (LBS) glass were systematically discussed. XRD patterns and EDS analysis result confirmed that single phase of Li1.075Nb0.625Ti0.45O3 solid solution was formed in all component. The increase of dielectric constant (εr) is ascribed to the improvement of bulk density. The restricted growth of grain has a negative influence on quality factor (Q×f) value. The τf value could be continuously shifted to near zero as the doping content increases. Great microwave dielectric properties were obtained in LiNb0.6Ti(0.5-x)(Al0.5Nb0.5)xO3 ceramics (x = 0.10) when sintered at 1100 ℃ for 2 h: εr = 70.34, Q×f = 5144 GHz, τf = 4.8 ppm/℃. The sintering aid, LBS glass, can effectively reduce the temperature and remain satisfied microwave performance. Excellent microwave dielectric properties for x = 0.10 were obtained with 1.0 wt% glass: εr = 70.16, Q×f = 4153 GHz (at 4 GHz), τf = -0.65 ppm/℃ when sintered at 925 ℃ for 2 h.

Low-Temperature Sintering Behavior (≤ 400°C) of Micro-sized Silver Particles Decorated by Silver Nanoparticles Through Surface Iodination

This paper introduces a facile and effective route to decorate micro-sized silver particle surfaces with Ag/AgI nanoclusters through a wet chemical reaction at room temperature using iodine and ethanol as reactant and solvent, respectively. Photosensitivity of AgI is utilized in the route, and AgI decomposes into Ag upon contact with sunshine, forming Ag/AgI nanoclusters. The modified micro-sized Ag particles showed sinterability even at 200°C and formed rigid electrical conductive networks at 350°C. Moreover, sintered film containing the modified Ag particles reached the best conductivity, 9.35 mΩ/sq, after sintering at 350°C for 20 min, while the film with untreated control Ag particles obtained its best conductivity at 400°C. The excellent sinterability should be attributed to the nanoclusters which served as a sintering aid during the heating process. However, increase of sintering temperature and time destroyed densification and conductivity of the sintered film containing the modified particles.

Low temperature sintering behavior and microwave dielectric properties of LaNbO4 ceramics with BaCu(B2O5) additive

In this paper, LaNbO4 ceramics with BaCu(B2O5) additives were prepared via the conventional solid state reaction method. The effects of BaCu(B2O5) on sintering behavior, phase structure and microwave dielectric properties of LaNbO4 ceramics were investigated. The optimum sintering temperature of LaNbO4 ceramics could be lowered from 1325 °C to 925 °C with the addition of BaCu(B2O5) due to liquid phase sintering. X-ray diffraction patterns showed that single-phase LaNbO4 could be achieved when BaCu(B2O5) content is ≤ 1 wt%. However, with further increase in BaCu(B2O5) content, small amount of second phases such as BaNb3.6O10 and Ba6Nb2O11 would be found. The variation trends of εr and Q×f value were similar to that of bulk density, the temperature coefficient of resonant frequency (τf) could be affected by additives. Typically, LaNbO4 ceramics with 1 wt% BaCu(B2O5) sintered at 925 °C for 4 h possessed dense structure and exhibited enhanced microwave dielectric properties: εr = 21.2, Q×f = 22600 GHz and τf = 10.01 ppm/°C.

Low-temperature Sintering Behavior of TiO2 Activated with CuO

In TiO₂-CuO systems, low-temperature sinterability was investigated by a conventional sintering method. Sintering temperatures were set at under 950℃, at which the volume diffusion is inactive. The temperatures are less than the melting point of Ag (961℃), which is often used as an internal conductor in low-temperature co-fired ceramic technology. To optimize the amount of CuO dopant, various dopant contents were added. The optimum level for enhanced densification was 2 wt% CuO. Excess dopants were segregated to the grain boundaries. The segregated dopants supplied a high diffusion path, by which grain boundary diffusion improved. At lower temperatures in the solid state region, grain boundary diffusion was the principal mass transport mechanism for densification. The enhanced grain boundary diffusion, therefore, improved densification. In this regard, the results of this study prove that the sintering mechanism was the same as that of activated sintering.

Low-temperature sintering behavior and properties of monoclinic-SrAl2Si2O8 ceramics prepared via an aqueous suspension milling process

In this work, by an aqueous suspension milling process, boric acid (H3BO3), calcium hydroxide [Ca(OH)2], strontium carbonate (SrCO3) and barium hydroxide octahydrate [Ba (OH)2·8H2O] are mixed with strontium carbonate (SrCO3) and kaolin (Al2O3·2SiO2·2H2O) to prepare SrAl2Si2O8 ceramics with a sintering temperature of 950 °C. According to chemical compositions of flux agents B2O3, CaO·2B2O3, SrO·2B2O3 and BaO·2B2O3, raw materials boric acid, calcium hydroxide, strontium carbonate and barium hydroxide octahydrate were introduced to the suspension slurries of strontium carbonate and kaolin to decrease the densification sintering temperature of SrAl2Si2O8 ceramics. In addition, the Sr element in SrAl2Si2O8 ceramics are partly substituted with Ba and Ca elements, respectively, to investigate the low-temperature sintering behavior of partly substituted SrAl2Si2O8 ceramics. The results indicated that the addition of flux agents to SrAl2Si2O8 ceramics can availably achieve the densification sintering of SrAl2Si2O8 ceramics at 950 °C, whereas the substitution of Sr with Ca or Ba have a great effect on sintering behaviors and dielectric properties of SrAl2Si2O8 ceramics. Additionally, main crystal phases of the SrAl2Si2O8 ceramics are monoclinic- SrAl2Si2O8 and small quartz, but the evolution of crystal phases also depend on flux agents.

Structure and asymmetric ferroelectric loops of (K0.48Na0.52)NbO3–1mol%CuO–xmol%Co2O3 ceramics with low-temperature sintering

Lead-free piezoelectric ceramics, (K0.48Na0.52)NbO3–1 mol%CuO–x mol%Co2O3 [KNN–Cu–xCo hereafter], were prepared by a conventional solid-state sintering method, and the low-temperature sintering behavior and ferroelectric property of Co2O3 doped (K0.48Na0.52)NbO3 piezoelectric ceramics were investigated. It was found that CuO and Co2O3 additions are very effective to improve the density and sintering behavior of KNN ceramics. KNN–Cu–0.1Co ceramics with the highest density (ρ ∼ 4.38 g/cm3) could be prepared at such a low sintering temperature of 930 °C. Hard ferroelectrics KNN–Cu–xCo show an asymmetric P–E hysteresis loop, attributing to an internal bias field Ei. The improvement measures of Ei was discussed through the analysis on its affected factors, including doped level, sintering temperature, and measuring frequency. The results also suggested that mechanical quality factor Qm has similar variation trend with Ei as the variation sintering temperature or composition. KNN–Cu–0.5Co ceramics sintered at 980 °C obtain the excellent properties: Qm ∼ 577, kp ∼ 30% and d33 ∼ 83 pC/N.

Low temperature sintering behavior of La-Co substituted M-type strontium hexaferrites for use in microwave LTCC technology

The La-Co substituted Sr1-xLaxFe12-xCoxO19 (x=0-0.5) ferrites with appropriate Bi2O3 additive were prepared by conventional sintering method and microwave sintering method at low sintering temperatures compatible with LTCC (low temperature co-fired ceramics) systems, and their sintering behavior was chiefly investigated, including the crystal structure, saturation magnetization Ms, magnetic anisotropy field Ha, intrinsic coercivity Hci, and Curie temperature TC. Experiment results clearly showed that the pure M-type crystal phase was successfully obtained when the La-Co substitution amount x did not exceed 0.3. However, the single M-type phase structure transformed to multiphase structure with further increased x, where the M-type phase coexisted with the non-magnetic phase such as α-Fe2O3 phase, La2O3 phase, and LaCoO3 phase. Appropriate La-Co substitution improved the Ms (>62 emu/g), Ha (>1400 kA/m), and Hci (>320 kA/m) for the ferrites with x varying from 0.1 to 0.3, but the TC decreased with increasing substitution amount. Moreover, the microwave sintered ferrites could provide larger Hci and similar Ms compared with the conventional sintered ferrites.

Low temperature sintering behavior of 11Li2O-3Nb2O5-12TiO2 microwave dielectric ceramics

Low temperature sintering behaviors, microstructures, and microwave dielectric properties of 11Li2O-3Nb2O5-12TiO2 (LNT) ceramics with Li2O-B2O3-SiO2 (LBS) glass additions were investigated. The XRD patterns reveal two phases, the “M-phase” and “ss-phase” Li2TiO3 solid solution phases. The results suggest that small amount of LBS glass could effectively decrease the sintering temperature of LNT ceramic from 1100 to 900 °C without reducing its microwave dielectric properties. However, decrease in microwave dielectric properties of LNT ceramic occurred when excess LBS glass added. Typically, LNT ceramics with 0.5 wt.% LBS glass possessed excellent microwave dielectric properties: er = 47.94, Q × f = 9290 GHz (f = 4.67 GHz), and τf = 49.63 ppm/°C were obtained when sintered at 900 °C.

Ni–Ti equiatomic co-substitution of hexagonal M-type Ba(NiTi)xFe12−2xO19 ferrites

Ionic substitution is considered the most effective way to expand the operational frequency of barium hexaferrites. So far, little attention has been paid to high level substitutions and their impacts on low temperature sintering behavior. Here, co-substituted equiatomic Ni–Ti M-type barium ferrites of nominal compositions Ba(NiTi)xFe12−2xO19 (x = 0.30, 0.60, 0.90, 1.20) were prepared by a solid state reaction method and studied for their structural, and static and high frequency magnetic properties. It was found that the phase purity of M-type hexagonal barium ferrite does not depend upon the amount of Ni–Ti substitution investigated here. Concomitantly, Bi2O3 additives are shown effective in lowering the sintering temperature of hexaferrite materials. For low temperature processed samples, the addition of Bi2O3 enables improved densification from localized liquid phase formation and restricted grain growth from its colocation at grain boundaries. By comparing samples and process conditions, the effect of grain growth and sintering aid upon sample microstructure, bulk density (ρ), saturation magnetization (Ms), coercivity (Hc) and magnetic permeability (μ′ and μ″) is made clear.

Low-Temperature Sintering Behavior and Dielectric Properties of Li2O-Nb2O5-TiO2 Ceramics with Li-B-Si-O Glass

This paper reports an investigation of the low-temperature sintering behaviors, microstructures, and microwave dielectric properties of Li1.0Nb0.6Ti0.5O3 (LNT) ceramics fired with addition of different amounts of Li2O-B2O3-SiO2 (LBS) glass. The results suggest that addition of LBS glass can effectively reduce the sintering temperature of LNT ceramic from 1100°C to 900°C without detriment of its microwave dielectric properties. However, addition of excess LBS glass leads to rapid grain growth and therefore decreases the density and microwave dielectric properties of the LNT ceramic. Optimized specimens with 1.0 wt.% LBS glass sintered at 900°C possessed excellent microwave dielectric properties of er ≈ 66.17, Q × f ≈ 5170 GHz (f = 4.32 GHz), and τf ≈ 19.2 ppm/°C.