Reaction Sintering Process Research Articles

Reactive sintering study of a novel cemented carbide hard alloy (W 0.5Al 0.5)C 0.5–Ni

Cemented carbides hard alloy (W 0.5Al 0.5)C 0.5–13.3 vol% Ni was successfully prepared by reactive sintering of carbon, nickel powder and W 0.5Al 0.5 alloy powder. The novel cemented carbide hard alloy has superior mechanical properties. The influence of sintering time and temperature on the microstructure, mechanical properties and density of the specimens are well described. Interestingly, both sintering time and temperature have amazing influence on the mechanical properties, density and microstructure of the specimen. During the reactive sintering process, Ni was the binder phase for sintering (W 0.5Al 0.5)C 0.5–Ni cemented carbide, and it also accelerated the reaction rate of synthesizing (W 0.5Al 0.5)C 0.5. The reactive sintering is a good method for preparing cemented carbide hard alloy (W 0.5Al 0.5)C 0.5–Ni. Another phenomenon is that no WNi/W 3Ni 3C/NiC x type phases are found in the bulk specimens, although it was prepared by reactive sintering the carbon, nickel powder and W 0.5Al 0.5 alloy powder directly and the carbon vacancy reach to the astonished 50% value.

Thermoelectric Performance of Half-Heusler TiNiSn Alloys Fabricated by Solid-Liquid Reaction Sintering

A new fabrication process was proposed for half-Heusler type TiNiSn thermoelectric alloys. Based on the result that the TiNiSn phase can be formed easily at the Sn(Liquid)/TiNi(Solid) interface, the liquid-solid reaction-sintering process was developed using TiNi and Sn powders. The TiNi compound powders were prepared by the atomization method using argon gas atmosphere. We have fabrictaed nearly single-phase TiNiSn alloys and evaluated their thermoelectrical properties; the presnt TiNiSn alloys have large electrical power factor of about 3.5 mWm-1K-2, and the maximum value of dimensionless figure of merit, ZT = 0.67, can be achieved at around 700 K even without tuning of the carrier concentration through alloying elements.

Ni 4Nb 2O 9 ceramics prepared by the reaction-sintering process

Fabrication of Ni 4Nb 2O 9 ceramics via a reaction-sintering process was investigated. A mixture of raw materials was sintered into ceramics by bypassing calcination and subsequent pulverization stages. Ni 4Nb 2O 9 phase appeared at 1300 °C and increased with increasing soak time. Ni 4Nb 2O 9 content was found >96% in 1350 °C/2 h sintering pellets. A density of 5.71 g/cm 3 was obtained for pellets sintered at 1350 °C for 2 h. This reaches 96.5% of the theoretical density. As the sintering temperature increased to 1350 °C, an abnormal grain growth occurred and grains >100 μm could be found. ɛ r of 15.4–16.9 are found in pellets sintered at 1200–1300 °C. Q × f increased from 9380 GHz in pellets sintered at 1200 °C to 14,650 GHz in pellets sintered at 1250 °C.

Effect of reactive sintering conditions on microstructure of Fe–Al–Si alloys

Abstract In this work, the dependence of microstructure of Fe–Al–Si alloy on conditions of reactive sintering was studied. It was shown that heating rate strongly affects the structure of this alloy. The microstructure consisting of uniformly distributed Al 2 Fe 3 Si 3 particles in Al 2 FeSi matrix can only be obtained in this material by rapid heating (over 300 K min −1 ). Sufficient reactive sintering temperature to obtain Al 2 Fe 3 Si 3 –Al 2 FeSi two-phase structure is 750 °C. Further increase of the reaction temperature reduces porosity but causes a growth of Al 2 Fe 3 Si 3 particles. Reactive sintering process is completed during less than 10 min in the investigated material. Temperatures over 1050 °C produce material composed of FeSi, FeAl and Al 2 Fe 3 Si 3 phases. However, strongly exothermal reaction of FeSi formation causes melting of the sample.

Effect of Mo/B atomic ratio on the microstructure and mechanical properties of Mo2FeB2 based cermets

Abstract Four series of Mo 2 FeB 2 based cermets with the Mo/B atomic ratio in the range from 0.8 to 1.1 were prepared by reaction sintering process. The microstructure and crystalline phases were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results indicate that the transverse rupture strength (TRS) of the cermets increases with an increase of Mo/B atomic ratio and shows a maximum value of 1.9 GPa at a Mo/B atomic ratio of 0.9. At a higher atomic ratio the TRS decreases. The hardness of the cermets decreases monotonically from 90.8 HRA to 88.8 HRA with an increase of Mo/B atomic ratio. In Mo-rich cermets with an atomic ratio of Mo/B above 1.0, a new M 23 B 6 type phase (M 23 B 6 , where M represents a metal) is found. This phase has a lattice parameter a = 1.09 nm containing Mo, Fe, Cr and B with an atomic ratio close to 16:6:1:6 and is precipitated at the interface of Mo 2 FeB 2 grains or at the Mo 2 FeB 2 grain boundaries.

Effects of mechanical alloying on the characteristics of a nanocrystalline Ti–50at.%Al during hot pressing consolidation

Two different powder metallurgy processes, i.e., reactive and non-reactive sintering, were investigated for the production of titanium aluminides. Ti–Al intermetallics have been successfully produced by mechanical alloying and hot pressing of powders with a nominal composition of Ti–50 at.%Al. A Ti(Al) solid solution was formed at the early stage of milling that transformed to an amorphous phase at longer milling times. On further milling, the amorphous structure transformed to a supersaturated hcp-Ti(Al) solid solution with trace amounts of TiAl after 80 h of milling, which was completely transformed to TiAl, Ti3Al, and TiAl3 intermetallic compounds after additional milling up to 100 h milling with particles of about 200 nm. Blended elemental powders and 100 h MA-ed powders were used for the reactive and non-reactive sintering processes, respectively. The results showed that the HP-ed pre-alloyed powder had better properties in terms of density, hardness, homogeneity of microstructure, yield stress, and ductility than that produced by reactive sintering. The major contribution to the yield stress of the sintered pre-alloyed powder comes from the nanometer-sized grains of intermetallics in accordance with the Hall–Petch relation.

Effect of Mn content on the microstructure and mechanical properties of Mo2FeB2 based cermets

Abstract Five series of Mo2FeB2 based cermets with Mn addition between 0 and 10 wt% in 2.5 wt% increments were prepared by reaction sintering process. The effect of Mn content on the microstructure and crystalline phases was investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD). Hardness (HRA) and transverse rupture strength (TRS) were also measured. Mn addition improved the wettability of the Fe binder phase on the Mo2FeB2 hard phase, which resulted in a decrease in porosity and Mo2FeB2 grain size and an increase in phase uniformity. No Fe–Mn intermetallic compounds or other intermetallic compounds were detected with increasing Mn content. The TRS increased with increasing Mn content until it reached the maximum value at 10.0 wt% Mn addition. The hardness slightly increased with increasing Mn content firstly and then turned to decrease with increasing Mn content. The highest hardness was obtained for cermets with 5.0 wt% Mn addition.

Preparation and Luminescence of Eu3 + -Activated Ca9ZnLi ( PO4 ) 7 Phosphor by a Solid Reaction–Sintering

A red-emitting phosphor, -doped , was synthesized by the solid reaction–sintering process. The morphological features of the phosphor were investigated by scanning electron microscopy. The photoluminescence excitation and emission spectra, fluorescence decay curves, and the dependence of luminescence intensity on temperature were investigated. The phosphor can be excited by near-UV wavelength radiation to realize an intense red luminescence (613 nm) corresponding to the electric dipole transition of ions. The crystallographic site occupations of the ions were investigated by the site-selective excitation spectra and the fluorescence decay in the region under a pulsed, tunable, narrow band dye laser. The potential application of this phosphor for light-emitting diodes was evaluated by the dependence of luminescence and the color coordinates on temperature.

Preparation of β-Sialon/ZrN bonded corundum composites from zircon by nitridation reaction sintering process

β-Sialon/ZrN bonded corundum composites were synthesized using fused white corundum, alumina micro powder, zircon and carbon black by nitridation reaction sintering process. Phase composition and microstructure of the synthesized composites were investigated by X-ray powder diffraction and scanning electronic microscope, and the formation process of the composites was discussed. The results show that the composites with different compositions can be obtained by controlling the heating temperature and contents of zircon and carbon black. The proper temperature to synthesize the composites is 1 773 K.

A low-temperature reactive sintering process for the 5Li 2O–1Nb 2O 5–5TiO 2 microwave dielectric ceramics

The B 2O 3-doped 5Li 2O–1Nb 2O 5–5TiO 2 composite microwave dielectric ceramics prepared by conventional and low-temperature single-step reactive sintering processes were investigated in the study. Without any calcinations involved, the Nb 2O 5 mixture of Li 2CO 3 and TiO 2 was pressed and sintered directly in the reactive sintering process. More uniform and finer grains could be obtained in the 5Li 2O–1Nb 2O 5–5TiO 2 ceramics by reactive sintering process, which could effectively save energy and manufacturing cost. And relatively good microwave dielectric properties of ɛ r = 41, Q × f = 9885 GHz and τ f = 43.6 ppm/°C could be obtained for the 1 wt.% B 2O 3-doped ceramics reactively sintered at 900 °C.

Reaction Processing of Ultra‐High Temperature W/Ta2C‐Based Cermets

A reactive processing method was used to produce dense (>99.5% relative density) W/Ta2C/Ta2WO8 cermets from Ta2O5, WC, TaC, and phenolic resin. The powder compacts were reacted under vacuum at 1450°C and then densified at 1850°C. The microstructure of the cermets was examined using scanning electron microscopy and found to contain fine grains on the order of 1–3 μm in diameter. X‐ray diffraction, transmission electron microscopy, and parallel energy electron loss spectroscopy were used to identify the composition and structure of the phases in the composites. The composites were found to contain approximately 47.5 wt% W, 47.3 wt% Ta2C, and 5.2 wt% Ta2WO8. Crack‐free and dense W/Ta2C‐based cermets were prepared by an in situ reactive sintering process without the application of pressure during densification.

Effect of CuO on CaTiO 3 perovskite ceramics prepared using a direct sintering process

Effect of CuO on CaTiO 3 (CT) ceramics prepared using a direct sintering process (reaction-sintering process) was investigated. The mixture of raw materials was pressed and sintered into ceramics without any calcination stage involved. Pure CT could be obtained. The degree of densification in CT via reaction-sintering process is lower than traditional oxide route but the grains grew easier in CT via reaction-sintering process. A density 3.63 g/cm 3 (90.3% of ρ th) is obtained in CT pellets after 1500 °C/16 h sintering. With 3 wt.% CuO addition, density 3.92 g/cm 3 (97.5% of ρ th) is obtained after 8 h sintering at 1500 °C due to the liquid phase sintering. The liquid phase at grain boundaries appeared significantly at a lower sintering temperature for longer soak time.

Crossover from Antiferroelectric to Normal Ferroelectric Behavior in Lead Zirconate—Lead Nickel Niobate Ceramics Prepared by the Reaction Sintering Process

The lead zirconate—lead nickel niobate ceramics, (1-x)PbZrO3—xPb(Ni1/3Nb2/3)O3 (PZ-PNN) with x = 0.00–0.10, have been prepared by reaction sintering. Without any calcination involved, the mixture of raw materials was pressed and sintered directly. The PZ–PNN ceramics could be obtained after 6 h sintering at 1,100–1,250°C. The crystal structure data obtained from XRD indicate that the PZ-PNN, where x = 0.00–0.10, successively transforms from orthorhombic to rhombohedral symmetry with an increase in the PNN concentration around x = 0.08. The antiferroelectric phase (AFE) → ferroelectric phase (FE) transition occurs in compositions of 0.0 ≤ x ≤ 0.08. The AFE → FE phase transition shifts to lower temperatures with higher compositions of x. The FE phase temperature range width increases with increased PNN.

Preparation of Lead Zirconate-Lead Nickel Niobate Ceramics by the Reaction Sintering Process

The perovskite structure of lead zirconate – lead nickel niobate ceramics, (1-x) PbZrO 3 –xPb(Ni 1/3 Nb 2/3 )O 3 (PZ – PNN) at x between 0.00–0.50, has been prepared by the reaction-sintering process. The specimens were prepared directly from a mixture of their constituent oxide without any calcination step. The PZ – PNN ceramics could be obtained after 6 h sintering at 1,100–1,250°C. Crystal structure and phase transition of PZ-PNN were investigated by x-ray diffraction (XRD). XRD indicated that the structure of PZ-PNN ceramics is orthorhombic for a composition where x = 0.00, rhombohedral for compositions where x = 0.10 ≤ x ≤ 0.40 and pseudo-cubic for a composition where x = 0.50. The dielectric properties of the ceramics were measured as functions of both temperature and frequency. The results indicated that the transition temperature decreases with increasing PNN concentration. Furthermore, morphology and grain size evolution have been determined via a scanning electron microscope (SEM)

Finite-difference model for the reaction sintering of oxide ceramics by direct oxidation of intermetallic powder compacts

A kinetic model for the reaction sintering of oxide ceramics in the system Al2O3–SiO2–ZrO2 using mixtures of intermetallic compounds is presented. A 2D finite-difference model is developed to describe the exothermic gas-solid reactions taking place during the firing of ZrAl3/ZrSi2 powder compacts. The model accounts for the oxidation kinetics of the powder particles, as well as the consumption and diffusion of gaseous oxygen through the porous matrix. Additionally, possible changes in the pore structure of the green body due to the oxidation reactions and sintering effects are incorporated in the model. The resulting differential equations are coupled with a two-dimensional Fourier heat balance equation leading to a system of nonlinear partial differential equations, which is solved by the numerical method of lines. The influence of different processing parameters like sample composition and heating cycle on the reaction sintering process is investigated and the model-predicted reaction behaviour is compared to experimental results.

Investigation on reactive sintering process of boron carbide ceramics by XRD

Boron carbide ceramics were simultaneously synthesised and densified from B and C elemental powders by a spark plasma sintering method. The reactive sintering process was investigated, and two stages of large shrinkage corresponding to synthesis and densification of boron carbide were observed. At stage I (1300–1700°C), B reacted with C and the product in phase of free C and B rich boron carbide (B4+xC) was synthesised. With increasing the sintering temperature, C atoms diffused into the B4+xC lattice, resulting in the reduction in free C content and the decreasing in lattice parameters of B4+xC. At stage II from 1700 to 1900°C, the densification of the synthesised boron carbide occurred. The product was densified gradually and a high relative density (95%) was obtained by spark plasma sintering at 1900°C.

Effect of reaction sintering process on the microwave dielectric properties of Ba 2Ti 9O 20 materials

The pre-reaction step, which is the holding time at 1000 °C in reaction-sintering process, was observed to influence the characteristics of the Ba 2Ti 9O 20 materials profoundly. For the materials possessing high sintered density and of pure Hollandite-like structure, the uniformity of granular structure is the prime factor, altering the microwave dielectric properties of the samples. Utilizing the BaTi 4O 9 + BaTi 5O 11 mixtures to replace for the 2BaTiO 3 + 7TiO 2 ones pronouncedly improved the uniformity of the microstructure and thus markedly increased the Q × f-value for the Ba 2Ti 9O 20 materials. The possible explanation for such a phenomenon is that the B-series mixture forms the Ba 2Ti 9O 20 Hollandite-like phase in a simpler way and results in more uniform microstructure then the A-series mixture. The microwave properties of B-series materials are superior to those of A-series ones, achieving K = 38.2 and Q × f-value = 36,000 GHz for the samples, which were pre-reacted at 1000 °C for 6 h and were sintered at 1410 °C for 4 h by reaction-sintering processes.

Fabrication and evaluation of solid-oxide fuel cell anodes employing reaction-sintered yttria-stabilized zirconia

Abstract This paper reports on the fabrication and performance of solid-oxide fuel cell (SOFC) anodes utilizing yttria reaction-sintered zirconia (YRSZ). Through the reaction-sintering process, the technical-grade YSZ commonly used in the Ni–YSZ anode cermet is replaced with lower-cost ZrO2 and Y2O3 materials. When sintered in the presence of nickel oxide, ZrO2 and Y2O3 form cubic-phase YSZ at temperatures characteristic of SOFC processing (1400–1550 ° C). Reaction sintering enables the formation of YSZ during cell fabrication, reducing SOFC anode raw-materials cost and the number of SOFC-fabrication processes. This paper reports the results of a broad range of characterization and performance measurements to evaluate the YRSZ material, including (1) crystal structure, (2) morphology, (3) pore-size distribution, (4) electronic resistivity, (5) fracture strength, (6) gas transport and catalytic activity, and (7) electrochemical performance. Material properties and performance are found to be comparable to or better than equivalent materials fabricated by conventional processes.

A simple and effective process for fabrication of Gd 0.1Ce 0.9O 1.95 solid electrolyte ceramics

Ce 0.9Gd 0.1O 1.95 ceramics were prepared using a simple and effective process in this study. Without any prior calcination, the mixture of raw materials was pressed and sintered directly. The reaction of the raw materials occurred during the heating up period by passing the calcination stage in the conventional solid-state reaction method. More than 99.5% of theoretical density was obtained for Ce 0.9Gd 0.1O 1.95 sintering at 1500–1600 °C. Fine grains (<1 μm) formed in pellets sintered at 1450 °C. The homogeneity of grains increased with the sintering temperature. The grains grew to >4.5 μm in pellets sintered at 1600 °C. The reactive-sintering process is proved to be a simple and effective method in preparing Ce 0.9Gd 0.1O 1.95 ceramics for solid electrolyte application.

Low-temperature synthesis of BiNbO 4 ceramics using reaction-sintering process

Low-temperature synthesis of BiNbO 4 ceramics using reaction-sintering process was investigated. Orthorhombic BiNbO 4 phase together with minor triclinic BiNbO 4 phase were found in the pellets. The phase transition temperature in BiNbO 4 with 0.5 wt% CuO addition was lowered from 960 °C via traditional route to 880 °C when the reaction-sintering process was used. After 920 °C sintering for 4 and 6 h, densities 6.8–6.85 g/cm 3 (94% of the theoretical value) were obtained. The abnormal grain growth in BiNbO 4 via traditional route was not observed in this study.