The effect of sintering conditions on the properties of WC–10wt%Co PIM compacts

The powder injection molding (PIM) process has an advantage of near net shaping of homogeneous micro structure and density at the complicate form. This study was investigated for microstructure and mechanical properties of WC–10%Co insert tool alloy fabricated by PIM process. The WC–10%Co feedstock mixed with wax binder was fabricated by two blade mixer. After WC–10%Co feedstocks were injection molded, debinding process was carried by two-steps methods with solvent extraction and thermal debinding. The binder was eliminated with normal hexane for 12 h at 50 °C by solvent extraction, and subsequently thermal debinding was examined for 1 h at the temperature 900 °C. After debinding process, the specimens were sintered at vacuum or N₂/H₂ mixed gas atmosphere at 1380 °C. The microstructure and phase were observed by FE-SEM. In the case of sintered at 1380 °C in vacuum atmosphere, the hardness was 1600 Hv, and the relative density of WC–10%Co was 92.5%. The density of WC–10%Co sintered at 1380 °C in mixed gas atmosphere was 87.5% and the hardness was lower than 1400 Hv. Residual carbon contents of sintered at vacuum and mixed gas atmosphere were 5.4 wt%.     

Nanosized bismuth titanate (Bi4Ti3O12) system drive through auto-combustion process by using suspension titania (TiO2)

Bismuth titanate (Bi₄Ti₃O₁₂) was developed by means of titanium oxide (TiO₂) suspension in auto-combustion process at 220 °C to get nanosized (20 ± 5 nm) bismuth titanate (Bi₄Ti₃O₁₂) powder. Complete piezoelectric phase (tetragonal) was obtained after calcination at 700 °C. Dilatometery of compacts was performed to find out sintering temperature. On the basis of shrinkage results, compacts were sintered at 750, 800, and 850 °C for 2 h. After sintering single phase was obtained with orthorhombic structure analyzed by X-ray diffraction and also investigated by Rietveld method. High-resolution scanning electron microscopy revealed that fine plate-like structure which is a characteristic of BIT powder can be obtained at 850 °C. Sintering results indicate that density and average grain size increase with the increasing temperature. A maximum of about 90 % of the theoretical density was achieved for the sintered product at 850 °C.     

Synthesis of porous Cu–Sn using freeze-drying process of CuO–SnO2/camphene slurries

Porous Cu–Sn with controlled pore characteristics was synthesized by a freeze-drying and sintering process. CuO and SnO₂ powders were selected as the source material, which are hydrogen-reduced to metallic Cu–Sn in the sintering stage. Camphene-based CuO–SnO₂ slurries were prepared by milling at 60 °C with a small amount of dispersant. Freezing of a slurry was done at ?40 °C with unidirectional control of the growth direction of the camphene. Pores were generated by sublimation of the camphene. The green bodies were sintered at 650 °C under a hydrogen atmosphere. The sintered bodies with Cu₃Sn, Cu₆Sn₅ and β-Sn phases showed macroscopic aligned pores with an average size of 200 μm. The internal wall of the macroscopic pores is also porous, and there are a number of many small pores in it. The formation of macroscopic and microscopic pores was discussed in terms of solidification behavior of the liquid with foreign particles.     

Characterization and Wear Behavior of Plasma Nitrided Nickel Based Dental Alloy

In the present work, the plasma nitriding behavior of a nickel based dental alloy was investigated. Plasma nitriding experiments carried out under constant gas mixture (15% H₂?C85% N₂) for different process parameters including time (4, 6, 10, and 20 h) and temperature (400, 450, 500, and 550 °C). Depending on nitriding parameters, it was found that triple or double layers formed on the surface of the samples. Increasing of treatment time and temperature has resulted in a double layer. ??_N1 layer was in formed all nitrided samples. However, ??_N2 layer is formed only at low temperatures and in short times. Layer growth of nickel based alloys increases until a critical time or a critical temperature reached. Above these critical values, it is observed that the layer thickness decreases. It was also found that plasma nitriding not only increases the surface hardness but also improves the wear resistance of nickel based dental alloy. The maximum wear resistance was observed at 400 °C for 10 h due to the high hardness and thickness of the nitride layers.     

Electrical conductivity of titanium pyrophosphate between 100 and 400 °C: effect of sintering temperature and phosphorus content

The synthesis of titanium pyrophosphate is carried out, and the material is sintered at different temperatures between 370 and 970 °C. Yttrium is added during the synthesis to act as acceptor dopant, but it is mainly present in the material in secondary phases. The conductivity is studied systematically as a function of sintering temperature, pH₂O, pO₂, and temperature (100–400 °C). Loss of phosphorus upon sintering above 580–600 °C is confirmed by energy dispersive spectroscopy and combined thermogravimetry and mass spectrometry. The conductivity decreases with increasing sintering temperature and decreasing phosphorus content. The highest conductivity is 5.3?×?10^?4 S cm^?1 at 140 °C in wet air (pH₂O?=?0.22 atm) after sintering at 370 °C. The conductivity is higher in wet atmospheres than in dry atmospheres. The proton conduction mechanism is discussed, and the conductivity is attributed to an amorphous secondary phase at the grain boundaries, associated with the presence of excess phosphorus in the samples. A contribution to the conductivity by point defects in the bulk may explain the conductivity trend in dry air and the difference in conductivity between oxidizing and reducing atmospheres at 300–390 °C. Slow loss of phosphorus by evaporation over time and changes in the distribution of the amorphous phase during testing are suggested as causes of conductivity degradation above 220 °C.     

Preparation process of a highly resistant wollastonite bioceramics using local raw materials

Wollastonite (CaSiO₃) is mainly used for traditional ceramics. In this study, wollastonite-based ceramics was obtained by solid state reaction. The starting powders were sintered at different temperatures (850–1,250 °C) for 2 h. Moreover, different amounts of B₂O₃ (0.5–5.0 mass%) have been added. A relative density of about 97% of the theoretical was reached for samples sintered at 1,050 °C for 2 h, containing 3 and 5 mass% B₂O₃. Excellent values of both three point flexural strength (343 ± 34 MPa) and micro-hardness (4.8 GPa) for samples containing 5 mass% B₂O₃, sintered at 1,050 °C for 2 h. Besides this, a relatively low mass loss ratio has been measured (1.1%) for wollastonite samples containing 5 mass% B₂O₃, sintered under the same conditions, after soaking in lactic acid for 9 days. Finally, the bioactivity of wollastonite by the possibility of formation of apatite on the surface of wollastonite immersed in simulated body fluid was confirmed.     

Microstructural properties of sintered Al–Cu–Mg–Sn alloys

A non-commercial Al4Cu0.5Mg alloy has been used for investigating the effects of the elemental Sn additions. Uniaxial die compaction response of the alloys in terms of green density was examined, and the results showed that Sn addition has no effect when compacting conducted under high pressures. In total, 93–95% green density was achieved with an applied pressure of 400 MPa. Thermal events occurring during the sintering of the emerging alloys were studied by using differential scanning calorimetry (DSC). First thermal event on the DSC analysis of the Al4Cu0.5Mg1Sn alloy is the melting of elemental Sn, whereas for Al4Cu0.5Mg alloy, it is the formation of Al–Mg liquid nearly at 450 °C. Also it is clearly seen on the DSC analysis that Sn addition led to an increase in the formation enthalpy of Al–Mg liquid phase. High Sn content and high sintering temperature (620 °C), therefore high liquid-phase content, caused decrease on the mechanical properties due to thick intergranular phases and grain coarsening. Highest transverse rupture strength and hardness values were obtained from Al4Cu0.5Mg0.1Sn alloy sintered at 600 °C and measured as 390 MPa and 73 HB, respectively.     

Neutron diffraction study of dehydrogenation of titanium carbohydrides TiC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

The possibility of the synthesis of hydrogen-nonstoichiometric cubic titanium carbide ТiС _х of high purity from powdery nonstoichiometric cubic titanium carbohydride ТiС _х H _y or nonstoichiometric titanium carbide with admixture hydrogen by annealing in a continuously maintained vacuum of no worse than 1.33 × 10^–3 Pa at temperatures of 600–750°C for several hours has been shown. Similar annealing at higher temperatures (T ≥ 800°C) does not lead to the complete removal of hydrogen from a sample due to intensive sintering. In this case, it seems that pores between sintered particles are hydrogen traps, and the release of hydrogen through the surface of sintered particles is hindered.     

Phase evolution and electrical properties of BaO–SrO–TiO2–SiO2–Al2O3-based glass ceramics prepared by sol–gel process

Crystallization of BaO–SrO–TiO₂–SiO₂–Al₂O₃-based glass ceramics, prepared by sol–gel process, was evaluated in terms of the effect of sintering temperature on phase evolution and electrical properties. The characterization of the samples was performed by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) studies and impedance spectroscopy analysis. The XRD results demonstrate that fresnoite phase starts to crystallize at 700 °C and perovskite phase appears at 900 °C. The glass ceramic samples sintered at high temperatures contained three crystalline phases, including perovskite, feldspar and fresnoite. In addition, SEM observation showed that the average grain size increased and the porosity decreased with increasing sintering temperature. Furthermore, the measurement of impedance spectroscopy suggests that there is a minimum value of the activation energy associated with the sintering temperature of the glass ceramics. The possible explanation of the sintering temperature dependence was discussed.     

Sol-Gel Microsphere Pelletisation Process for Fabrication of (U,Pu)O2, (U,Pu)C and (U,Pu)N Fuel Pellets for the Prototype Fast Breeder Reactor in India

A “dust-free” sol-gel microsphere pelletisation (SGMP) process has been developed for fabrication of (U,Pu)O₂, (U,Pu)C and (U,Pu)N fuel pellets containing around 15% plutonium for the forthcoming prototype fast breeder reactor (PFBR) in India. The objective was to produce homogeneous sintered pellets of ∼85% T.D. with a predominantly open-pore structure. Hydrated gel-microspheres of UO₃+PuO₂ and UO₃+PuO₂+C have been prepared from nitrate solutions of uranium and plutonium by the “ammonia internal gelation” process, using hexamethylene tetramine (HMTA) as an ammonia generator and silicone oil at 90±1°C as gelation bath. For oxide fuel pellets, the hydrated UO₃+PuO₂ gel-microspheres were calcined at around 700°C in Ar+8% H₂ atmosphere to produce “non-porous”, “free-flowing” and coarse (around 400 micron) microspheres which could be directly pelletised at 550 MPa to green pellets. The mixed oxide pellets were subjected either to low temperature (∼1100°C) oxidative sintering (LTS) in N₂+air containing ∼1500 ppm O₂ or to high temperature (1650°C) sintering, (HTS) in Ar+8% H₂. For monocarbide and mononitride pellets, hydrated gel-microspheres of UO₃+PuO₂+C were subjected to carbothermic synthesis in vacuum (∼1 Pa) and flowing nitrogen (flow rate: 1.2 m³/h) in the temperature range of 1450–1550°C respectively. The monocarbide and mononitride microspheres thus produced were relatively hard and required higher compaction pressure (∼1200 MPa) for making reen pellets which could be sintered to 85% T.D. in Ar+8% H₂ at 1700°C. The sintered oxide, monocarbide and mononitride pellets had a “blackberry” “open” pore microstructure with fine grain size. The microspheres retained their individual identity in the sintered pellets because during sintering densification took place mainly within and not between the microspheres.     

The effect of calcination on morphology of phosphate coating and microstructure of sintered iron phosphated powder

Carbonyl iron powder was coated with phosphate layer using phosphating precipitation method. The phosphated powder was dried at 60 °C for 2 h in air and heat treated by calcination at 400 and 800 °C for 3 h in air. Cylindrical specimens density of ~6.5 g.cm^?3 based on iron phosphated powder calcined at 400 °C were sintered at 820, 900, 1110 °C in N₂ + 10%H₂ atmosphere and 1240 °C in vacuum for 30 min. The morphology and phase composition of the phosphate coating and sintered compacts were studied by scanning electron microscopy, atomic force microscopy (AFM) and X‐ray diffraction (XRD) analysis. Gelatinous morphology of dried phosphate coating (thickness of ~100 nm) containing nanoparticles of iron oxyhydroxides and hydrated iron phosphate was observed. From XRD, diffractogram indicated the presence of goethite α‐FeOOH, lepidocrocite γ‐FeOOH and ludlamite Fe₃(PO₄)₂.4H₂O. The calcined phosphate coating (thickness of ~ 400 nm) contained non‐homogeneous consistency of α‐Fe₂O₃ layer on iron particles, an inter‐layer of amorphous FePO₄ and Fe₃O₄ top layer. The transformation to crystalline FePO₄ structure occurred during calcination at 800 °C with the presence of α‐Fe₂O₃ forming a light top zone (rough morphology). The microstructure of compacts sintered in solid state at temperatures up to 900 °C has retained composite network character. A fundamental change in microstructure due to the liquid phase sintering occurred after sintering at temperatures of 1100 and 1240 °C. It was confirmed that the microstructure complex consists of spheroidized α‐Fe and α‐Fe₂O₃ phases surrounded by solidified liquid phase consisting various phosphate compounds. Copyright © 2013 John Wiley & Sons, Ltd.     

A Novel Approach by Spark Plasma Sintering to the Improvement of Mechanical Properties of Titanium Carbonitride-Reinforced Alumina Ceramics

Ti(C,N)-reinforced alumina-zirconia composites with different ratios of C to N in titanium carbonitride solid solutions, such as Ti(C_0.3,N_0.7) (C:N = 30:70) and Ti(C_0.5,N_0.5) (C:N = 50:50), were tested to improve their mechanical properties. Spark plasma sintering (SPS) with temperatures ranging from 1600 °C to 1675 °C and pressureless sintering (PS) with a higher temperature of 1720 °C were used to compare results. The following mechanical and physical properties were determined: Vickers hardness, Young’s modulus, apparent density, wear resistance, and fracture toughness. A composite with the addition of Ti(C_0.5,N_0.5)n nanopowder exhibited the highest Vickers hardness of over 19.0 GPa, and its fracture toughness was at 5.0 Mpa·m^1/2. A composite with the Ti(C_0.3,N_0.7) phase was found to have lower values of Vickers hardness (by about 10%), friction coefficient, and specific wear rate of disc (Ws_d) compared to the composite with the addition of Ti(C_0.5,N_0.5). The Vickers hardness values slightly decreased (from 5% to 10%) with increasing sintering temperature. The mechanical properties of the samples sintered using PS were lower than those of the samples that were spark plasma sintered. This research on alumina–zirconia composites with different ratios of C to N in titanium carbonitride solid solution Ti(C,N), sintered using an unconventional SPS method, reveals the effect of C/N ratios on improving mechanical properties of tested composites. X-ray analysis of the phase composition and an observation of the microstructure was carried out.     

Phenolic resin as a carbon source for the synthesis of monometallic Mo and bimetallic CoMo carbides via carbothermal reduction route

It was the first time that phenolic resin (PR) was used as a carbon source for the synthesis of nanostructured monometallic Mo and bimetallic CoMo carbides via carbothermal reduction route. The results showed that phase-pure β-Mo₂C can be formed under an Ar atmosphere at 900°C or a H₂ atmosphere above 700°C. However, almost pure CoMo carbides (Co₃Mo₃C and Co₆Mo₆C) can be obtained only under a H₂ atmosphere at a low temperature of 630°C for 24 and 48 h, respectively. The role of PR in the preparation process has been investigated and a detailed formation mechanism was proposed based on the experimental results.     

Thermoelectric properties of n-type Bi2Te3 alloys produced by a combined process of magnetic pulsed compaction (MPC) and spark plasma sintering (SPS)

In this study, n-type 95 %Bi₂Te₃-5 %Bi₂Se₃ thermoelectric materials have been produced by a combined process of gas atomization with subsequent magnetic pulsed compaction and spark plasma sintering, and then we investigated the behavior of transport properties with sintering temperature. The microstructural observation was performed by optical microscopy and scanning electron microscopy. The crystal structures were analyzed by X-ray diffractometer. The mechanical properties were calculated by measuring the density and micro-Vickers hardness of the samples. It was found that with increasing sintering temperature the gaps between powder particles decreases and the grain sizes were coarsened. The mechanical properties shows higher values along the parallel direction compared to the perpendicular direction to the pressing. The transport properties of the thermoelectric material were investigated with variation of the sintering temperatures. The maximum power factor 1.7 × 10^?3 Wm^?1 K^?2 was measured at the sintering temperature of 450 °C.     

Thermal,structural, and impedance analysis of nanocrystalline magnesium chromite spinel synthesized via hydrothermal process

Nanocrystalline magnesium chromite spinel was synthesized through hydrothermal reaction of metal nitrate solutions in stoichiometric amount at different pH, temperature and time intervals. The synthesized products were characterized for crystallinity, phase identification, and surface morphology by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD patterns showed that as-synthesized product remained amorphous up to 250 °C. However, well-crystallized magnesium chromite spinel structure is formed after calcination at 850 °C. Rietveld refinement study confirms the formation of single-phase cubic structure MgCr₂O₄ with lattice parameter a = 8.3347 Å, and Fd3m space group. The as-processed MgCr₂O₄ products showed extensive XRD line broadening, and the mean crystallite size of such crystals was found to be mainly in size range of 85–124 nm. Surface SEM images of calcined specimens revealed that the matrix is uniform, and no separation of secondary phase was detected. Thermal stability was examined by thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry. TG/DTA reveals that MgCr₂O₄ is thermally stable above 700 °C. Fourier transform infrared (FTIR) spectra studies shows two strong bands, one around 600 cm^?1 which is attributed to the intrinsic vibrations of tetrahedral and other at 400 cm^?1 is due to octahedral one. FTIR confirms the formation of metal oxides. The bandgap energy was estimated by absorption spectroscopy in ultraviolet–visible range and was found to be 0.693 eV for MgCr₂O₄ specimen sintered at 1,000 °C. Isothermal shrinkage characteristic and coefficient of thermal expansion were determined by dilatometry. The powder specimens showed excellent densification at 1,250 °C temperature and uniformly fine grain sintered ceramics (>90 % relative density) with submicron grain size (2–5 μm) were obtained after sintering at 1,000–1,250 °C. Impedance studies were carried out at room temperature and equivalent circuit model (R ₁ Q ₁) (R ₂ Q ₂) (R ₃ Q ₃) is used to explain different relaxation processes. We report largest impedance values i.e., 6.74 × 10⁸ Ω, reduced dielectric constant (≈1.0), and low tangent loss (0.8) for MgCr₂O₄ sintered at 1,250 °C.     

Improved molten salt synthesis and structure evolution upon cycling of 0.5Li2MnO3·0.5LiCoO2 in lithium-ion batteries

The Li-rich cathode material Li_1.2Co_0.4Mn_0.4O₂(=0.5Li₂MnO₃·0.5LiCoO₂) was prepared by an improved molten salt method. The effects of sintering temperature and time on the physical and electrochemical properties of Li_1.2Co_0.4Mn_0.4O₂ were investigated. With increasing sintering temperature, excellent crystallinity and a stable structure are obtained, which lead to excellent electrochemical properties. However, the sample sintered at 900 °C has poor performance because its large powder diameter prolongs the transportation length of Li⁺ ions. Higher specific surface areas are obtained when samples are sintered at 850 °C for a shorter time, which leads to more activity and excellent charge/discharge capacity. The evolution of a derivative peak at about 3.0 V in the differential capacity (dQ/dV) curves is observed along with the formation of a spinel-like phase, which is verified by analysis using a high-resolution transmission electron microscope. Therefore, it is a simple and quick method to characterize the structure evolution upon cycling of Li-rich cathode materials by means of analysis of the derivative peak.     

Thermal studies for preparation of Nb10Hf1Ti Alloy

The aim of this work is to evaluate the feasibility of preparation of Nb10Hf1Ti alloy by magnesiothermic reduction of its oxides. DTA studies were conducted to identify the reduction temperature for co reduction of the mixed oxides of Nb₂O₅, HfO₂, and TiO₂ by magnesium under reducing atmosphere. Based on DTA analysis, experiments were carried out to prepare Nb10Hf1Ti alloy by magnesiothermic reduction of their oxides at 750 °C. The reduced product was analyzed for its phases by X-ray diffraction. The excess Mg was leached out, the alloy mixture was vacuum dried, pelletized, sintered, and electron beam melted to get a consolidated alloy of the required composition. The alloy was characterized using different techniques such as optical microscopy, scanning electron microscopy, and chemical analysis. Microstructural observations revealed the formation of coarse grain structure in the consolidated alloy. The alloy product was also evaluated for its micro hardness.     

Microstructure and oxygen permeability of a La0.6Sr0.4Fe0.9Ga0.1O3−δ membrane containing magnesia as dispersed second phase particles

Dense mixed-conducting membranes of La_0.6Sr_0.4Fe_0.9Ga_0.1O_3−δ (LSFG) with various contents of MgO as second phase particles were prepared to evaluate the influence of magnesia inclusions on LSFG stoechiometry, microstructure and oxygen permeation. XRD and EDS investigations on sintered pellets revealed that magnesia inclusions were quite inert with the LSFG matrix phase, the composition of which remained identical whatever the magnesia content. LSFG pure phase material was synthesized through a solid-state route and sintered between 1250 and 1350 °C. Sintering temperature strongly affected microstructure of the LSFG membrane since rapid grain growth and decreasing density were observed when temperature increased. Small amounts of fine particles of magnesia, from 2 to 10 vol%, were found to significantly reduce grain size of sintered samples and made it possible to obtain a high density on a large sintering temperature range. Average grain size experimental data of LSFG in function of the amount of second phase magnesia were also compared with numerical models from literature. Oxygen permeation rates of pure LSFG and composite LSFG/MgO dense membranes were measured in an air/argon gradient, in a temperature range from 825 to 975 °C and results were discussed to explain the flux improvement of composite membranes.     

Inclusion of W in electroless Ni–B coating developed from a stabilizer free bath and investigation of its tribological behaviour

In the present study, tribological and corrosion behaviour of electroless Ni–B–W (ENB-W) coatings prepared from stabilizer-free baths and deposited on AISI 1040 steel substrates were examined. Three distinct coating bath temperatures (85 °C, 90 °C, and 95 °C) were varied for coating deposition. The coatings showed nodular morphology. Thermogravimetric study of ENB-W coatings revealed improved thermal stability attained at 95 °C bath temperature. The microhardness of ENB-W coating was 645, 690, and 720 HV₁₀₀ at bath temperatures of 85 °C, 90 °C, and 95 °C respectively. The inclusion of W to Ni–B coating enhanced the hardness by ∼150 HV₁₀₀. On a pin-on-disc tribometer, wear test was conducted. The precipitation of Ni (111) and its borides occurred post sliding wear at high temperatures (300 °C). Ni (111) crystallite size decreased because of high temperature sliding wear at 300 °C with an increase in coating bath temperature. With a reduction in crystallite size at high temperatures, both wear rate and COF decreases. The scratch hardness and first critical load of failure of the coatings was determined using a scratch tester. Using potentiodynamic polarization, corrosion resistance of ENB-W coatings in 3.5% NaCl was investigated. ENB-W coatings could provide shielding to AISI 1040 steel from corrosion. Though the corrosion resistance is poor with respect to lead stabilized coatings.     

Pyrolysis of Hailar lignite in an autogenerated steam agent

An in situ pyrolysis process of high moisture content lignite in an autogenerated steam agent was proposed. The aim is to utilize steam autogenerated from lignite moisture as a reactant to produce fuel gas and additional hydrogen. Thermogravimetric analysis revealed that mass loss and maximum mass loss rate increased with the rise of heating rates. The in situ pyrolysis process was performed in a screw kiln reactor to investigate the effects of moisture content and reactor temperature on product yields, gas compositions, and pyrolysis performance. The results demonstrated that inherent moisture in lignite had a significant influence on the product yield. The pyrolysis of L _R (raw lignite with a moisture content of 36.9 %, wet basis) at 900 °C exhibited higher dry yield of 33.67 mL g^?1 and H₂ content of 50.3 vol% than those from the pyrolysis of the predried lignite. It was also shown that increasing reaction temperature led to a rising dry gas yield and H₂ yield. The pyrolysis of L _R showed the maximum dry yield of 33.7 mL g^?1 and H₂ content of 53.2 vol% at 1,000 °C. The LHV of fuel gas ranged from 18.45 to 14.38 MJ Nm^?3 when the reactor temperature increased from 600 to 1,000 °C.