Reaction Sintering Process Research Articles

Induced 2H-Phase Formation and Low Thermal Conductivity by Reactive Spark Plasma Sintering of 1T-Phase Pristine and Co-Doped MoS2 Nanosheets.

Pristine and Co-doped MoS2 nanosheets, containing a dominant 1T phase, have been densified by spark plasma sintering (SPS) to produce a nanostructured arrangement. The structural analysis by X-ray powder diffraction revealed that the reactive sintering process transforms the 1T-MoS2 nanosheets into their stable 2H form despite a significantly reduced sintering temperature and time testifying to the fast kinetics of phase change. Together with the phase conversion, the SPS process promoted a strong texturing of the nanosheets, which drives additional scattering processes and alters the electronic and thermal transport properties. In the pristine sample, it produced one of the lowest thermal conductivities ever reported on MoS2 with a minimal value of 0.66 W/m·K at room temperature. The effect of Co substitution in the final sintered samples is not significant, compared to the pristine MoS2 sample, except for a non-negligible improvement of the electrical conductivity by a factor of 100 in the high-Co content (6% by mass) sample.

Estimating Ni valence with magnetometry in solid‐state reactive sintered yttrium‐doped barium zirconate

AbstractNi is known to have a significant impact on the sintering and microstructure evolution in yttrium‐doped barium zirconate (BZY) and yet details of its specific role remain unclear. The present study examined the valence state of Ni in solid‐state reactive sintered BZY prepared with different amounts of Ni, formulated for deliberate substitution of Ni for Zr : BaZr0.8−xY0.2NixO3−δ with x = 0.005, 0.01, 0.02, 0.03, 0.04 (approx. 0.1 wt%, 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%). Quenching from revealed transient BaY2NiO5 phase was present in the microstructure for all concentrations of Ni studied here. Energy‐dispersive X‐ray spectroscopy identified Ni segregation in grain‐boundary regions upon completion of the solid‐state reactive sintering process, and magnetometry is used to show that low‐spin Ni3+ predominantly substitutes for Zr4+.

Three-layer structure hot bending/diffusion bonding process of reactive sintering Ti-22Al-25Nb alloy and its load response at high temperature

Three-layer structure part as a ideal structure part, that had light weight and enough strength to be widely used, was prepared combining hot bending and diffusion bonding processes in this paper. The Ti-22Al-25Nb sintered alloy that owned better using temperature was applied to manufacture three-layer structure part. The forming processes of manufacturing three-layer structure was divided into hot bending forming of the core sheet and diffusion bonding of three layers sheets. Firstly, the hot bending of core sheet was performed at 1423K for 10MPa in a vacuum furnace. Secondly, the diffusion bonding of three layers sheets was carried out at 1473K for 120min and 10MPa. Furthermore, in order to evaluate the quality and performances of three-layer structure, the microstructure of bonding joint of three layers sheets was analyzed by SEM, and the properties of three-layer structure part were tested at 1073K by compressing test and three-point bending test. Compressing load and compressing strength were 9014N and 10MPa, respectively. Bending strength was up to 54MPa. In addition, the experimental results also indicated that three-layer structure that prepared using the Ti-22Al-25Nb sintered alloy owned good properties.

The role of Al in the reactive synthesis of porous Mo2Ti2AlC3 ceramics

The mixed powders of TiH2, molybdenum, aluminum and graphite with molar ratios of 2/2/n/2.85 (n ranges from 1.0 to 1.4 mol with an interval of 0.1 mol) were used as raw material powders for this work, and a novel porous Mo2Ti2AlC3 was synthesized via reactive synthesis. Through systematic research on the pore structure parameters of porous Mo2Ti2AlC3 prepared with different aluminum content, the results show that there is a clear correlation between the aluminum content and the pore structure parameters. With the aluminum content rising from 1.0 to 1.2 mol, the viscous permeability coefficient and pore size decreased, while the porosity increased; When the aluminum content increased from 1.2 to 1.4 mol, the pore structure parameters of porous Mo2Ti2AlC3 displayed an opposite trend. The reasons for the evolution laws of these pore structure parameters were also discussed in depth. In addition, the pore structure forming mechanism of porous Mo2Ti2AlC3 ceramics during the activation reaction sintering process has been explored. This work can provide an important reference for the subsequent preparation of quaternary porous MAX phase ceramics.

Effects of Matrix Material Particle Size on Mullite Whisker Growth

Understanding of effects of changes in the particle size of the matrix material on the mullite whisker growth during the production of porous mullite is crucial for better design of new porous ceramics materials in different applications. Commercially, raw materials such as Al2O3/SiO2 and Al(OH)3/SiO2 are used as starting materials, while AlF3 is added to fabricate porous mullite through reaction sintering process. When Al2O3 is used as a starting material, a porous microstructure can be identified, but a more developed needle shaped microstructure is identified in the specimen using Al(OH)3, which has excellent reactivity. The specimen using Al2O3/SiO2 composite powder does not undergo mulliteization even at 1,400 oC, but the specimen using the Al(OH)3/SiO2 composite powder had already formed complete mullite whiskers from the particle size specimen milled for 3 h at 1,100 oC. As a result, the change in sintering temperature does not significantly affect formation of microstructures. As the particle size of the matrix materials, Al2O3 and Al(OH)3, decreases, the porosity tends to decrease. In the case of the Al(OH)3/SiO2 composite powder, the highest porosity obtained is 75% when the particle size passes through a milling time of 3 h. The smaller the particle size of Al(OH)3 is and the more the long/short ratio of the mullite whisker phase decreases, the higher the density becomes.

Observations of multi-component boride precipitates in ultrahard boron carbide

Boron carbide (B4C) often consists of intrinsic secondary phase precipitates that are formed during the reaction-sintering process. These precipitates not only play an important role during the densification process but also affect the mechanical properties of B4C. In the present study, the structural determination of multicomponent secondary phases that are precipitated out in monolithic B4C was investigated using atomic resolution scanning transmission electron microscopy (STEM) and atom probe tomography (APT). Here we found two types (Type-I and II) of multicomponent boride nano-precipitates in B4C i.e. (i) elongated precipitates (type-I), identified as (Cr(1-x-y)-Fex-Wy)3B4 phase, rich in chromium (Cr), Iron (Fe), tungsten (W), and boron (B) (ii) equiaxial (type-II) precipitates that are rich in titanium (Ti), Cr, and B in form of Ti(1-x)CrxB2 phase. The estimated reduced modulus and hardness using depth sensitive nanoindentation on type-I precipitates were 335 ± 6 GPa and 32 ± 2 GPa and that in type-II precipitates were 268 ± 13 GPa and 22 ± 3 GPa, respectively. These results underscore the importance of multicomponent solid solution hardening in ultra-hard B4C material.

Room-temperature ferromagnetism in (K0.5Na0.5)NbO3-xBaNi0.5Nb0.5O3-δ ferroelectric ceramics with narrow bandgap

In this paper, a simple, reproducible and cost-effective solid-state reaction sintering process is developed to fabricate (K0.5Na0.5)NbO3-xBaNi0.5Nb0.5O3-δ (KNN-xBNN) ceramics with a narrow bandgap and room-temperature ferromagnetism. Here, we report a systematic investigation of the influence of the BaNi0.5Nb0.5O3-δ (BNN) concentration on the properties of KNN-xBNN ceramics. All ceramics form orthorhombic perovskite structures with a space group Amm2 and a weak peak at the wavelength of 550 cm−1 that is characteristic of the pillow shoulder of the orthorhombic phase. KNN-xBNN ceramics with x between 0.02 and 0.08 have a narrow bandgap of about 2.5 eV—much smaller than the 3.5 eV of its parent (K0.5Na0.5)NbO3 (KNN) ceramic—which is attributed to Ni2+-oxygen vacancy combinations (Ni2+-VO) raising the valence electron energy level of the KNN ceramic. Furthermore, doping BNN into KNN ceramics can significantly convert the magnetism from diamagnetism to ferromagnetism and the component of x = 0.08 achieves both maximum saturation magnetisation intensity (14 memu/g) and minimum coercive magnetic field (80 Oe). Our findings provide a systematic insight into the bandgap tunability and ferromagnetism induction at room temperature in lead-free perovskite KNN-xBNN ceramics, as well as demonstrate their potential applications in perovskite solar cells and multiferroic devices.

Reaction thickness between diamond and silicon under 5 GPa

The thickness of the silicon carbide layer around diamond grains in the reaction sintering process of diamond/SiC composites starting from diamond and silicon was investigated at 1100–1400 °C and 5 GPa using two different sample assemblies. Dense silicon carbide layers with thicknesses from 60 nm to 350 nm were observed using energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis. This demonstrated that the thickness of the silicon carbide layer increased with increasing sintering temperature and time. The surface morphology of diamond grains/single-crystal diamond wafers eroded by liquid silicon was analysed by field emission scanning electron microscopy (FESEM), and it was found that SiC growth was controlled by the diffusion of silicon and carbon atoms through the existing layer of SiC.

Enhancing oxygen permeation of solid-state reactive sintered Ce0.8Gd0.2O2-δ-FeCo2O4 composite by optimizing the powder preparation method

Dual phase membranes with mixed ionic-electronic conductivity exhibit promising properties for applications in pure oxygen separation under harsh atmospheres. The conductivity of an individual phase within dual phase membranes is often attenuated by the blocking effects from the other phase(s). Here, facile but effective ways are reported to alleviate such effects by optimizing the powder preparation method for a solid-state reactive sintering process. Powder mixtures with a nominal composition 85 wt% Ce0.8Gd0.2O2-δ:15 wt% FeCo2O4 were prepared by traditional wet ball milling method, as well as a moderate dry mixing approach. Using a modified wet ball milling procedure, homogenous powder mixtures with fine particle size are obtained and the synthesized membrane shows a fine and homogenous microstructure that realizes high oxygen permeance. Besides, a novel “dual phase” membrane having one ionic conductive monophase zone and one mixed ionic-electronic conductive multiphase zone was sintered using dry-mixed powder mixtures. With individual mesoscale percolations, two phase zones provide relatively straight paths for ionic conduction and electronic conduction, respectively, which contributes to achieving the highest oxygen permeance among all the sintered membranes.

Insights into the reactive sintering and separated specific grain/grain boundary conductivities of Li1.3Al0.3Ti1.7(PO4)3

Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a promising candidate as solid electrolyte and Li+ conductive component in the composite electrodes of all-solid-state Li-ion batteries. For both applications, reducing the sintering temperature of LATP while preserving its electrochemical properties is highly desired. This work is dedicated to reducing the sintering temperature of LATP from conventionally around 1000 °C to a low temperature of 775 °C with adding an extra 10 wt % of Li2CO3 to the precursors by a reactive sintering process. Comparative investigations with the stoichiometric LATP prepared by the same sintering method indicate that the combination effect of reactive sintering and Li2CO3-excess promotes the liquid phase sintering within LATP yielding a high relative density of 95.3%, whereas the stoichiometric LATP can only achieve a comparable relative density at 875 °C. Furthermore, the reactive sintering assisted Li2CO3-excess LATP exhibits a significantly higher ionic conductivity of 0.65 mS cm−1 at 25 °C and lower total activation energy of 0.334 eV compared with that of the stoichiometric LATP. Correlative studies on the microstructure and the separated specific grain/grain boundary conductivities for the two samples reveal that the improvement of Li+ conductivity for Li-excess LATP is attributed to its smaller total grain boundary thickness.

Microstructure evolution and mechanical properties of Al-8wt. % Si semi-solid billet fabricated by powder metallurgy liquid phase reaction sintering

Abstract The Al-8wt. % Si semi-solid billets were successfully prepared by a new liquid phase reaction sintering process with Al and Si elemental powders. The reaction mechanism of the Al and Si elemental powders was investigated, and the thermodynamics and dynamics of the reaction process were studied. The effect of the microstructure evolution on the mechanical properties was analyzed. In the reaction process, the reaction product Al(Si)(L) liquid phase wets the Al particles well, and the liquid phase content increased with increasing reaction temperature and time. It was found that the kinetic model given by ψ = 4.6 × 105exp(-1.05 × 105/RT)t1/3 can accurately predict the actual liquid phase formation fraction. With increasing reaction temperature, the viscosity of the liquid phase decreases and the Si atom diffusion coefficient increases. This will increase the formation rate of the liquid phase and decrease the length of lath Si. The increased liquid phase content increases the strength of the billet and decreases its elongation. The shear crack is the main reason for the instability of the billets during the deformation process. Acting as a crack source, Si particles accelerate the generation and propagation of cracks, and promote the instability fracture of the billet.

Low cost Ti\u2013Si intermetallic compound membrane with nano-pores synthesized by in-situ reactive sintering process

A low cost Ti–Si intermetallic compound membrane with nano-pores was successfully prepared by an in-situ reactive sintering process. The all synthesized membrane shows the presence of Ti, Ti5Si3, TiSi and TiO2 phases, and the Ti:Si atomic ratio of membrane is about 1.9. Two different synthesized granule configuration zones on membrane are observed. Membrane synthesized on the surface of Ti particles contains the mean sizes of both 631 nm nano-particles and 238 nm nano-pores, which is considerably different from that of membrane growing on top of the micro-pores of Ti matrix, 238 nm nano-particles and 80 nm nano-pores, respectively.

Sintering behavior, phase structure and microwave dielectric properties of CeO2 added CaTiO3-SmAlO3 ceramics prepared by reaction sintering method

Novel 0.695CaTiO3-0.305SmAlO3+xwt% CeO2 (x = 0, 0.5, 1.0, 1.5) ceramics were fabricated using a reaction-sintering (RS) approach. The crystal structure, morphology, and microwave dielectric properties of ceramics were systematically studied. The addition of CeO2 could effectively improve the sintering behavior of 0.695CaTiO3-0.305SmAlO3 (CTSA) ceramics. When x = 0.5 wt%, the ceramics exhibited optimal microwave dielectric properties, with εr = 43.9, Q×f = 48 779 GHz, and τƒ = −0.24 ppm/°C, thereby indicating that the samples prepared via the RS route possess superior dielectric properties compared to those prepared by the conventional solid phase reaction. The results demonstrate that CaTiO3-SmAlO3 ceramics can be prepared simply and efficiently through a reaction-sintering process.

Solid-state reactive sintering of dense and highly conductive Ta-doped Li7La3Z2O12 using CuO as a sintering aid

Cubic-phase garnet-type Li7La3Z2O12 is a promising candidate for an electrolyte of all-solid-state lithium-ion batteries; however, its poor sinterability due to Li sublimation during firing has impeded large scale development. This study demonstrates a solid-state reactive sintering (SSRS) process with added CuO as a sintering aid to enable enhanced materials processing at lower temperatures. Applying the SSRS process with the addition of 1 wt% CuO decreased the sintering temperature for 0.5 mol%Ta-doped LLZTO pellets having over 90% relative density from 1250 to 1100 °C to reduce Li loss. The 1 wt% CuO addition did not lead to secondary phase formation as detected by XRD, nor to appreciable electronic conduction below 100 °C as measured by four-point probe method. The 1 wt% CuO-mixed LLZTO pellet exhibited high conductivity of approximately 3.0 × 10−4 S·cm−1 (bulk) and 5.45x10−5 S·cm−1 (grain boundary). The mechanism of CuO function as a sintering aid is presumed to be enabling liquid-phase sintering along with enhancing the decomposition of LiOH. The combined SSRS process along with optimized CuO sintering aid addition is a one-step process that is a practical technique to enhance the preparation of LLZO-based electrolyte for all-solid-state lithium-ion batteries.

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.

Process optimisation enhancing thermoelectric and mechanical performance in reactive in-situ spark plasma sintered Mg2(Si,Sn)

Rapid, reactive in-situ spark plasma sintering was employed for the fabrication of n-type Mg2(Si,Sn) material via optimising the sintering temperature. This reaction sintering process resulted in an excellent thermoelectric and mechanical performance in the Mg2(Si,Sn) alloy, which is recognised as a good earth-abundant, non-toxic, and low-cost, intermediate- temperature-application thermoelectric material. The phase structure and composition of the synthesised alloy were investigated employing X-ray diffraction, field emission scanning electron microscopy, and energy-dispersive spectroscopy. The optimized figure of merit (ZT) ≃ 0.4 associated with a high hardness ∼450 Hv and a high fracture strength ∼1.4 MPa√m were achieved in spark plasma sintered Mg2(Si,Sn) material. This work also reports the thermoelectric and mechanical properties of Mg2(Si,Sn) material and correlates them with the processing parameters.

Fabrication of Ti-Si intermetallic compound porous membrane using an in-situ reactive sintering process

A low-cost and effective in-situ reactive method to produce Ti-Si intermetallic compound porous membrane is achieved for the first time using titanium powders and quartz tube (SiO2) as raw materials. Ti-Si porous membrane with small pores was fabricated on the surface of Ti porous substrate. The pore size of Ti-Si porous membrane is less than 0.5 µm with the thickness of ～2 µm. The Ti-Si intermetallic compound particles and nanopores of membrane on the substrate are well distributed, and a good metallurgy bonding between the particles of Ti-Si membrane and Ti substrate indicates an effective sintering process. The in-situ reactive sintering process was an effective technology for the fabrication of Ti-Si intermetallic compound porous membrane as well as the modification of the surface morphology of porous metals.

Effect of Ca substitution on the microwave properties and the inhibition of Ag diffusion in Ba1-xCaxMoO4 ceramics

Ba1-xCaxMoO4 (0 ≤ x ≤ 0.20) ceramics were prepared from powders to form solid solutions by a solid-state reaction sintering process. The influence of the Ca2+ content on the microstructure, sintering, densification, microwave dielectric properties and chemical stability of BaMoO4-based ceramics with Ag metal was discussed in detail. The sintering temperatures of the Ba1-xCaxMoO4 ceramics were effectively reduced to less than 950 °C by the formation of the solid solutions. Structural analysis indicates that the Ba1-xCaxMoO4 ceramics belong to the class of tetragonal scheelites. The crystal grain size begins to decrease and become more regular as x increases from 0 to 0.12. However, as x continues to increase, a liquid phase begins to appear, and the grain boundaries are no longer clear. The εr value increases from approximately 8.6 to 9.8 as x increases from 0 to 0.2. The Ba0.92Ca0.08MoO4 sample possesses the best microwave dielectric performance, namely an εr = 9.3 and the maximum Q × f value of 33593 GHz. The addition of 15 wt% TiO2 or 10 wt% CaTiO3 can effectively change the τf values of the Ba1-xCaxMoO4 ceramics to approximately 0. The Ba1-xCaxMoO4 ceramic samples can coexist with silver during the LTCC cofiring process.

Construction of TiP2O7 nanosheets/rGO hierarchical Flower-like heterostructures for superfast and ultralong lithiation/delithiation process

Despite significant progress in lithium-ion batteries (LIBs), the commercialization and performance improvement of anode materials are impended by their inferior stability and sluggish kinetics. Herein, a modified strategy, involving the one-step solvothermal reaction and subsequent sintering process, is proposed to synthesize the TiP2O7/reduced graphene oxide (rGO) microsphere, which serves as a Li-ion storage material. Profiting from the stable chemical characteristics of pyrophosphate and unique structure framework, the TiP2O7/rGO composite exhibits extraordinary electrochemical performance, especially in long-term cycling (over 4000 loops at a ultrahigh rate of 2000 mA g−1). In this hierarchical architecture, the three-dimensional TiP2O7 microflowers are intimately wrapped by the interlinked rGO nanosheets, constructing a well-designed conductive network with favorable electrochemical kinetics. Moreover, the dynamic changes of impedance and phase evolutions are further verified by in-situ electrochemical impedance spectroscopy (EIS) measurement. Based on the detailed analysis of kinetic features, enhanced pseudocapacitance effect could boost the rate of Li-ion transferring, leading to the superior rate capability (460.7, 372.1, 327.0, 280.9, 235.6, 176.8, 127.5 mAh g−1 at 40, 80, 200, 400, 800, 2000, 4000 mA g−1). This work provides an effective strategy to realize high performance of pyrophosphate-based materials for Li-ion storage.

A dynamic analysis of the aluminum titanate (Al2TiO5) reaction-sintering from alumina and titania, properties and effect of alumina particle size

Aluminum titanate Al2TiO5 materials were successfully processed from different fine commercial powders and characterized. Particularly, two calcined aluminas were compared through a multitechnique approach including differential thermal analysis and dilatometry together with structural, microestructural, and mechanical characterization. This allowed the description of all the thermochemical processes during thermal treatment. Developed phases were established. Relatively dense ceramics were obtained, and complex microstructures were described with interlocked grains and an interconnected microcrack matrix that do not jeopardize the material integrity. Multistep sintering and reaction sintering processes were observed in both samples. The first stage consists of the sintering of the starting powders (alumina and titania). A second sintering stage of the starting powders was observed for both samples as well. Once advanced, the second one is overlapped with Al2TiO5 formation that starts at 1380 °C and finishes at 1440 °C. They affect crack development and, in consequence, the thermal behavior. The lower alumina particle size enhances the sintering and reaction advance processes. In the technological temperature range (room temperature—1000 °C), low or even negative thermal expansion behaviors were observed in the developed materials. This, together with the mechanical behavior, encourages structural applications with high thermomechanical solicitations of Al2TiO5 based materials.