Ni-based Cermet Research Articles

Influence of Tertiary Phases Incorporated into Ni-based Cermets by Solution Precursor Plasma Spraying (SPPS) on Anode Stability

not Available.

Effect of partial substitution of Cr for Ni on densification behavior, microstructure evolution and mechanical properties of Ti(C,N)–Ni-based cermets

Four cermets of composition TiC–10TiN–16Mo–6.5WC–0.8C–0.6Cr 3C 2–(32 − x)Ni– xCr ( x = 0, 3.2, 6.4 and 9.6 wt%) were prepared, to investigate the effect of the partial substitution of Cr for Ni on densification behavior, microstructure evolution and mechanical properties of Ti(C,N)–Ni-based cermets. The partial substitution of Cr for Ni decreased full densification temperature, and the higher the content of Cr additive was, the lower full densification temperature was. The partial substitution of Cr for Ni had no significant effect of the formation of Mo 2C and Ti(C,N) and the dissolution of WC, and however, it had a significant effect on the dissolution of Mo 2C. Cr in Ni-based binder phase diffused into undissolved Mo 2C to form (Mo,Cr) 2C above 1000 °C at 6.4–9.6 wt% Cr additive, and a small amount of (Mo,Cr) 2C did not dissolve after sintering at 1410 °C for 1 h at 9.6 wt% Cr additive. In the final microstructure, Cr content in Ni-based binder phase increased with increasing the content of Cr additive, and however, regardless of the content of Cr additive, coarse Ti(C,N) grains generally consisted of black core, white inner rim and grey outer rim, and fine Ti(C,N) grains generally consisted of white core and grey rim. The partial substitution of Cr for Ni increased hardness and decreased transverse rupture strength (TRS). Ni-based binder phase became hard with increasing the content of Cr additive, therefore resulting in the increase of hardness and the decrease of TRS. TRS was fairly low at 9.6 wt% Cr additive, which was mainly attributed hardening of Ni-based binder phase and undissolved (Mo,Cr) 2C.

An H2S-Tolerant Ni-GDC Anode with a GDC Barrier Layer

The solid oxide fuel cell (SOFC) can operate effectively on a variety of fuels, such as coal-syngas and hydrogen. A Ni-based cermet is a cost-effective anode material for these fuels; however, H2S in the fuel can degrade cell performance by poisoning the Ni-based anode. In this research, nickel- gadolinium doped ceria (Ni-GDC) hybrid anodes were exposed to synthesized coal-syngas and H2 fuels with various concentrations of H2S at 800°C under constant current conditions. Some SOFC prototypes contained a ∼5 μm thick GDC barrier layer inserted between the Ni-GDC hybrid anode and the YSZ electrolyte. A reference electrode was incorporated in the cell to monitor changes in the anode and cathode polarization resistances. The tests showed that the cells with a GDC barrier layer were resistant to H2S at levels up to 1000 ppm in wet H2 and 100 ppm in syngas during long-term tests. Cells without the barrier layer had a significantly lower tolerance for the H2S impurity. This result, along with post-mortem analyses of the poisoned anode, lead to the hypothesis that the GDC barrier layer assists in the prevention of nickel oxidation at the anode/electrolyte interface by acting as an oxidation catalyst for the H2S.

Direct, In Situ Optical Studies of Ni−YSZ Anodes in Solid Oxide Fuel Cells Operating with Methanol and Methane

Near-infrared imaging and vibrational Raman scattering have been used to measure the susceptibility of Ni-based cermet anodes to carbon formation in solid oxide fuel cells (SOFCs) operating with methane and methanol fuels at 715 °C. These two complementary optical methods afford previously unavailable opportunities to monitor chemical and physical processes occurring in situ and in real time with molecular specificity and spatial resolution. Imaging and spectroscopic data show that when the cell is held at open circuit voltage carbon forms within one minute of methanol or methane being introduced to the anode chamber. Raman spectra identify these deposits as highly ordered graphite based on a single sharp feature in the vibrational spectrum near 1580 cm−1. While graphite formed from methane remains highly ordered regardless of exposure duration, graphite formed from sustained exposure to methanol begins to show evidence of structural disorder inferred from the appearance of a weak feature at 1340 cm−1. Th...

Performance Deterioration of Ni-based Cermet Induced by Electrochemically-generated Steam in Anode

Nickel-yttria stabilized zirconia (Ni-YSZ) cermet is a conventional anode for use in solid oxide fuel cells, and its composition and microstructure are carefully controlled to achieve high performance and long-term stability. In this study, the performance stability of electrolyte-supported cell (Ni-YSZ | YSZ | LSM) was examined at 1000ºC by feeding humidified fuel, x% H2O-(100-x)% H2. The influence of cermet composition on deterioration was also studied. The deterioration behavior was significantly dependent on the fuel humidity and cermet composition. In the case of Ni-YSZ with a volumetric ratio of 50 to 50, peculiar phenomena were observed. When the fuel of 30% H2O-70% H2 was supplied to anode and the terminal voltage was fixed at 0.7 V, the current density decreased gradually soon after the discharge up to 70 h. Then a sudden drop in current density occurred. After the subsequent open-circuit holding, the performance was partially recovered in discharge operation. This behavior of deterioration-recovery was reversibly repeated upon discharge-open-circuit holding operation.

Methane Oxidation at the Ni1-XCoX-Samaria-doped Ceria Cermet Anode

Substitution of Co atoms for Ni atoms in the Ni-based cermet anode resulted in a decrease in the anodic overvoltage and interfacial resistance between the anode and electrolyte. This effect has been confirmed for a samaria-doped ceria (SDC) electrolyte and a scandia-stabilized zirconia (ScSZ) electrolyte. The results of electrochemical measurements revealed that the enhancement of the direct oxidation of methane was caused by the modification of microstructure in the cermet anode.

Correlation between Crystalline Phase of ScSZ and Carbon Deposition Behavior Over Ni-ScSZ Anode for Internal Reforming of Solid Oxide Fuel Cells

The influence of preparation condition of Ni-ScSZ (scandia-stabilized zirconia) cermet on the tolerance to carbon deposition was investigated in the wide temperature range of 800-1000ºC. The mixture of NiO-ScSZ was subjected to pre-heat treatments prior to use as a cermet electrode. Although the inhibitory effect of ScSZ in Ni-based cermet for carbon deposition is well-known, the present study revealed that the preparation method and firing condition affected the carbon deposition behavior. The Ni-ScSZ cermet obtained from the oxide mixture heated at 1400ºC showed peculiar behavior to carbon deposition. The initial carbon deposition rate at 800-900ºC for this sample was larger than that at 1000ºC, whereas other samples exhibited a reduction in deposition rate with decreasing temperature. The cubic phase stabilization in ScSZ was confirmed for the sample treated at 1400ºC, though ScSZ was in the rhombohedral phase before the heat-treatment with NiO. These results suggested that a strong interaction between NiO and ScSZ was induced by the high-temperature heat-treatment.

Performance Deterioration of Ni-based Cermet Induced by Electrochemically-generated Steam in Anode

not Available.

Chlorine Poisoning of SOFC Ni-Cermet Anodes

Poisoning effects by chlorine compounds, including and HCl, to typical electrolyte-supported solid oxide fuel cells (SOFCs) with Ni–scandia-stabilized zirconia cermet anodes have been evaluated. The degradation rate of cell voltage poisoned by was estimated to be ca. . Chlorine degradation rate increased with increasing concentration. Microstructural change associated with the formation of nickel nanoparticles on zirconia grains, probably via sublimation, was observed after poisoning tests, whereas a partial recovery of cell voltage by removing chlorine from the fuels indicates that the chlorine poisoning is partially reversible. Thermochemical calculations, microstructural analysis, and electrochemical characterizations have revealed that the poisoning phenomena for Ni-based cermet anodes caused by chlorine compounds can be explained by the mixed adsorption-type and sublimation-type poisoning mechanism.

Carbon Deposition over Ni–ScSZ Anodes Subjected to Various Heat-Treatments for Internal Reforming of Solid Oxide Fuel Cells

The influence of the preparation condition of Ni–scandia-stabilized zirconia (Ni–ScSZ) cermet on the tolerance to carbon deposition was investigated in the wide temperature range of . The mixture of NiO–ScSZ was subjected to preheat-treatments prior to use as a cermet electrode. Although the inhibitory effect of ScSZ in Ni-based cermet for carbon deposition is well known, the present study revealed that the preparation method and firing condition influenced the carbon deposition behavior. The Ni–ScSZ cermet obtained from the oxide mixture heated at showed peculiar behavior to carbon deposition. The initial carbon deposition rate at for this sample was larger than that at , whereas other samples exhibited a reduction in deposition rate with decreasing temperature. The cubic phase stabilization in ScSZ was confirmed for the sample treated at , though ScSZ was in the rhombohedral phase before the heat-treatment with NiO. These results suggested that a strong interaction between NiO and ScSZ was induced by the high-temperature heat-treatment.

Tribochemistry in sliding wear of TiCN–Ni-based cermets

The tailoring of cermet composition to improve tribological properties requires careful choice of the type of secondary carbide. To investigate this aspect, a number of sliding tests were carried out on baseline TiCN–20Ni cermet and TiCN–20wt%Ni–10 wt% XC cermets (X = W/Nb/Ta/Hf) at varying loads of 5N, 20N, and 50N against bearing steel. With these experiments, we attempted to answer some of the pertinent issues: (i) how does the type of secondary carbide (WC/NbC/TaC/HfC) influence friction and wear behavior, and is such influence dependent on load?; and (ii) how does the secondary carbide addition affect the stability and composition of the tribochemical layer under the selected sliding conditions? Our experimental results reveal that the added secondary carbides influence chemical interactions between different oxides and such interactions dominate the friction and wear behavior. A higher coefficient of friction (COF) range, varying from 0.75 to 0.64 was recorded at 5N; whereas the reduced COF of 0.46–0.52 was observed at 20N or 50N. The volumetric wear rate decreased with load and varied on the order of 10−6 to 10−7 mm3/Nm for the cermets investigated. The cermet containing HfC exhibited high friction and poor wear resistance. At low load (5N), the abrasion and adhesion of hard debris containing various oxides dominated the wear, and resulted in high friction and wear loss. In contrast, the more pronounced increase in friction-induced contact temperature (below 500 °C) and compaction of hard debris resulted in the formation of a distinct tribochemical layer at higher loads (20N and 50N). The formation of a dense tribolayer containing oxides of iron and/or titanium is responsible for the reduced friction and wear, irrespective of secondary carbides.

Electricity production from wastewater treatment via a novel biogas-SOFC aided process

A novel process for the treatment of municipal and industrial wastewater is developed, which leads to the direct production of electricity, and/or H 2, by an environmentally friendly way. Through this process, production of electricity is obtained by a novel direct-biogas-fuelled fuel cell, which is also developed here, that concerns a major subunit of the overall process. Both intermediate and high temperature solid oxide fuel cells (IT- and HT-SOFCs) based on 10mol% Gd 2O 3 doped CeO 2 (gadolinia doped ceria, GDC) and 8mol% Y 2O 3 stabilized ZrO 2 (yttria stabilized zirconia, YSZ) solid electrolytes, respectively, have been constructed and tested, while three different Ni-based cermets were used as anodic materials. The operation performances of these cells under direct feed of simulated biogas mixtures are comparatively discussed.

Sulfur Tolerance and Hydrocarbon Stability of La0.75Sr0.25Cr0.5Mn0.5O3 ∕ Gd0.2Ce0.8O1.9 Composite Anode under Anodic Polarization

A (LSCM/GDC) composite electrode was developed and applied as a solid oxide fuel cell (SOFC) anode for the direct oxidation of sulfur-containing methane. The anode was fully activated in wet at and a constant potential of with respect to a Pt/air reference before the fuel was shifted to wet . In the sulfur-containing methane fuel, the anodic current dropped from to in a period, showing a performance degradation rate of ca. 1.4%/hr possibly due to sulfur poisoning. In the subsequent period, the anodic current tended to be relatively stable with a very small degradation rate of 0.017%/h, which is most likely attributed to the coarsening of the electrode microstructure. Though some impurities, such as , , and , were detected in the X-ray diffraction analysis of the anode after of stability test, the scanning electron microscopy micrographs and energy-dispersive X-ray analysis showed that no carbon and sulfur deposition was found on the cross-sectional surface of the anode. The results suggest that the LSCM/GDC composite is a promising candidate material for an anode and has much better hydrocarbon stability and sulfur tolerance under the anodic polarization than Ni-based cermets.

Electrochemical Activity of Ni1-XCoX-Based Cermet Anode for Methane Oxidation

Partial substitution of Co atoms for Ni atoms in the Ni-based cermet anode resulted in a decrease in the anodic overvoltage and interfacial resistance between the anode and electrolyte. This effect has been confirmed for yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ) electrolytes. The Ni1-XCoX-ScSZ (-YSZ) cermet anode showed an increase in the cell performance with increasing amount of Co content up to approximately 0.5. The decrease in the anodic overvoltage and the interfacial resistance contributes to an enhancement of the cell performance. The results of electrochemical measurements and microstructural characterization revealed that the enhancement of the direct oxidation of methane is caused by the modification of microstructure due to a solid- solutioning effect in the starting NiO-CoO binary system.

Crater wear mechanisms of TiCN–Ni–WC cermets during dry machining

Abstract TiCN–Ni-based cermets are attractive cutting tools because of the combination of high hardness and wear resistance with improved toughness and thermal shock resistance. The present work reports the effect of WC addition (0–15 wt.%) on the machining performance of TiCN–20 wt.% Ni cermets against boiler steel. The cutting force was measured on-line using dynamometer, with respect to varying cutting speed and feed rate, in dry and orthogonal cutting conditions. The principal aim of the present investigation is to evaluate the dominant mechanisms, responsible for material removal on the rake face of cermets, using SEM–EDS. The cutting performance of TiCN–Ni cermet is observed to improve with the addition of WC content upto 10 wt.%. While, the adhesion of tribochemical layer is dominant with limited WC content, the presence of abrasive grooves and pull-outs are observed for TiCN–20Ni cermets containing higher amount of WC (>10 wt.%).

Synthesis and characterization of a Ni/Ba 2In 0.6Ti 1.4O 5.7□ 0.3 cermet for SOFC application

Ni-based cermets were prepared and reduced from mixtures of NiO and Ba 2In 0.6Ti 1.4O 5.7□ 0.3. A cermet containing 18.7 vol.% of Ni exhibits promising characteristics: 40% of open porosity and a lower DC resistivity than a Ni/YSZ cermet with a larger Ni content (30 vol.%). Its thermal expansion coefficient is 11.4 × 10 − 6 K − 1 whereas that measured for Ba 2In 0.6Ti 1.4O 5.7□ 0.3 is 9.9 × 10 − 6 K − 1 . Electrical measurements vs. the Ni content have shown that the percolation threshold corresponds to 15.7 vol.% of Ni. By using saccharose as a pore former, the porosity of the electrode can be tuned. It is shown that the pore size is controlled by the particle size distribution of the pore former.

Catalytic and electrocatalytic behavior of Ni-based cermet anodes under internal dry reforming of CH 4 + CO 2 mixtures in SOFCs

A high temperature (700–900 °C) SOFC with yttria stabilized zirconia (YSZ) solid electrolyte was constructed and tested on direct feed of simulated biogas (CH 4 + CO 2) mixtures. Both catalytic, i.e. open-circuit, and electrocatalytic, i.e. closed-circuit, measurements were carried out. Open-circuit kinetic data showed that the rate of the catalytic reaction of the dry(CO 2)-reforming of methane is maximized at about equimolar CO 2/CH 4 feed ratio for all temperatures studied. Closed-circuit data showed that cell output characteristics (i.e. current and power densities) are also maximized for equimolar CO 2/CH 4 biogas composition. Power densities up to 51.6 mW/cm 2 (at V = 453 mV, i = 114 mA/cm 2, T = 875 °C) have been obtained. Long-term operation experiments demonstrated that the constructed biogas fuel cell has very stable behavior for all three different simulated biogas compositions fed, including poor, equimolar and rich methane constitutions.

Feasibility of Ni-based cermet anode for direct HC SOFCs: Fueling ethane at a low S/C condition to Ni–ScSZ anode-supported cell

The feasibility of a Ni-based cermet anode for direct hydrocarbon (HC) SOFCs was investigated with ethane fuel as a step towards utilizing higher HCs such as propane and butane. The possibility of stable operation of SOFCs with ethane fuel at a low steam/carbon (S/C) ratio of 1.2 mol% H 2O–98.8 mol% C 2H 6 was investigated with anode-supported SOFCs utilizing a scandia stabilized zirconia (ScSZ) electrolyte and a Ni–ScSZ anode. Severe carbon deposition was observed around the anode especially at the fuel injection port during the cell tests at T = 973 K. The amount of deposited carbon became smaller with decreasing operation temperature, and a stable cell operation was achieved at T ≈ 823 K without severe carbon deposition over a week. However, at a low fuel utilization rate ( U f) around 20%, nickel was heavily disintegrated accompanied by severe carbon deposition even at T ≈ 823 K. With increasing U f, the disintegration became less, and a stable cell operations were achieved only with a small amount of deposited carbon for over a week at high U f > 46%.

Solid-Solutioning Effect of the Ni-Based Cermet on the Electrochemical Oxidation of Methane

A new electrocatalyst which enhances the activity for methane oxidation at the anode was investigated. The solid solutioning of cobalt into nickel, whose starting oxide solid solution was prepared by co-precipitation from a mixed solution of oxalic acid and metal nitrates, resulted in an increase in the cell performance, particularly for the direct methane use. The partial oxidation of methane probably takes place at the active sites of the Co 0.5 Ni 0.5 alloy surface. The enhancement of the anodic oxidation of methane depends on a crystallographically oriented microstructure along the (111) crystal planes, which was not observed for the nickel particles. The cell performance was evaluated by the anodic polarization resistance and the production rates of CO, CO 2 and H 2 - The activation mechanism is discussed in terms of the formation of surface active sites for the electrochemical oxidation of methane.

Effect of Mo on microstructure and mechanical properties of TiC—Ni-based cermets produced by combustion synthesis—impact forging technique

The effect of Mo additions on the microstructure and mechanical properties of TiC-30 wt.% Ni cermets produced by the combustion synthesis-impact forging technique was investigated. The Mo content was varied between 0 and 10 wt.%, in 2 wt.% increments. Cylindrical tiles 6.35 cm in diameter and 1.27 cm thick were produced with apparent densities above 99%. Microscopically, the addition of Mo resulted in a decrease in the number of microstructural defects such as interphase debonding and binder microcracking. The microstructure consisted of a spheroidal carbide phase with a high degree of contiguity (decreasing with increasing Mo content). The Mo additions did not have a profound effect on the carbide phase morphologies (faceted vs. spheroidal), mean apparent particle diameters (3.5 μm–4.5 μm), or particle size distribution. Energy-dispersive X-ray analysis revealed Mo preferentially in the carbide phase, with trace amounts in the Ni alloy binder. A significant amount of Ti was found in solution with Ni. Vickers' microhardness did not vary significantly with Mo content and was approximately 13 GPa. Compressive strength, transverse rupture strength, fracture toughness, and Young's moduli increased with increasing Mo content; the mean values for the 8 wt.% Mo material were approximately 3400 MPa, 1300 MPa, 22 MPa m 1/2, and 340 GPa respectively. The beneficial effect of Mo is due to the improved wettability of the Ni alloy binder on the carbide phase. Improved wettability results in a decrease in detrimental microstructural defects and an increase in the interphase bond strength and phase uniformity.