Effect Of Transition Metal Additives Research Articles

Electrical resistivity and flexural strength of mullite‐bonded porous SiC: Effect of transition metal additives

AbstractThe influence of various transition metal (Mo, Co, Ni, and Fe) additives on the electrical and mechanical properties of mullite‐strengthened SiC sintered in the range of 1100–1500°C under an Ar atmosphere was investigated. Kaolin was added as a low‐temperature sintering aid in the designed formulations. The addition of metal additives reduced the electrical resistivity, enhanced the mechanical strength, and produced samples with an approximately 40% porosity. The decrease in electrical resistivity was attributed to the in situ formation of electrically conductive metal silicides, whereas the conversion of kaolin to mullite enhanced the mechanical properties. The comparative study shows that at the same metal‐additive content (15 wt%), Fe was the most effective element to reduce the electrical resistivity and increase the flexural strength, which were recorded as 8.0 × 100 Ω cm and 20 ± 2 MPa, respectively, of the samples sintered at merely 1300°C.

Effect of Transition Metal Additives on the Catalytic Performance of Cu–Mn/SAPO-34 for Selective Catalytic Reduction of NO with NH3 at Low Temperature

The adsorption of NO, NH3, H2O, and SO2 gaseous molecules on different transition metal oxides was studied based on density function theory (DFT), and three better-performing transition metal elements (Fe, Co, and Ce) were selected. Cu–Mn/SAPO-34 catalysts were prepared by impregnation method and then modified by the selected transition metals (Fe, Co, and Ce); the SO2 resistance experiments and characterizations including Brunner−Emmet−Teller (BET), X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM), and thermal gravity analysis (TG)-differential thermal gravity (DTG) before and after SO2 poisoning were conducted. The results showed that the deactivation of the Cu–Mn/SAPO-34 catalyst is ascribed to the deposition of lots of ammonium sulfates on the surface, depositing on the active sites and inhibiting the adsorption of NH3. After the modification of Fe, Co, and Ce oxides, the SO2 resistance of the modified Cu–Mn/SAPO-34 catalyst was significantly enhanced due to the less formation of ammonium sulfates. Among all these modified Cu–Mn/SAPO-34 catalysts, the Cu–Mn–Ce/SAPO-34 exhibited the highest SO2 resistance owing to the decreased decomposition temperature and the trapper of ceria for capturing SO2 to form Ce(SO4)2, further inhibiting the deposition of ammonium sulfates.

Hydro-Liquefaction of Tile-Like Barzas Coals in the Presence of Some Transition Metal Additives

Using a laboratory micro-autoclave (of ~ 20 cm3 volume), the effects of transition metal additives (MoO3, Fe2O3 and commercial AlCoMo catalyst) on the thermal transformations of tile-like Barzas coals (sapromixites) in a hydrogen medium at T ~ 475°C and P ~ 6.0-7.5 MPa have been studied. It has been shown that catalytic additives under investigation somewhat suppress gas formation processes, facilitating the increase in H/C atomic ratios and in the amount of alkyl-containing structures in resin-like solid products of Barzas coal hydro-liquefaction. Maximal yields of “coal liquids” (maltenes + asphaltenes) (~ 35 wt.%, daf basis) were obtained during the heat treatment of sapromixites in the presence of bb1 wt.% MoO3.

Effect of transition metal addition on microstructure and hardening behavior of two-phase Ni3Al-Ni3V intermetallic alloys

The comprehensive mechanisms for the hardening of two-phase Ni3Al-Ni3V intermetallic alloys by transition metal addition were presented, based on the microstructural observation, alloying behavior and lattice properties of the additives in the constituent phases. The alloys to which 2 at.% Ti, Nb and Ta were added in different substitution manners for Ni, Al and V, respectively were studied by scanning electron microscopy, electron probe microscopic analyzer, X-ray diffraction and hardness test. The alloys in which the additives were substituted for Al exhibited microstructures with finer and cuboidal Ni3Al precipitates. Nb and Ta addition resulted in larger lattice expansion in the two constituent phases than Ti addition. The hardness increase by the Nb and Ta addition was larger than that by the Ti addition. Also, the hardness increase was larger in the substitution manner of the additives for Al than in those for Ni and V. The hardening behavior was explained in terms of solid solution hardening mechanism in which the mixture rule in the volume fraction of the two constituent phases and the atomic size misfit evaluated from the changes of the lattice parameters were incorporated. Consequently, the hardening for the alloys in which the additives were substituted for Ni and V was wholly attributed to solid solution hardening. On the other hand, the hardening for the alloys in which the additives were substituted for Al was attributed to the hardening due to microstructural refining in addition to the solid solution hardening.

Effect of Transition Metal Addition in the Bioactivity of Borate Bioglass Dental Materials

Objectives: The basic structure and some physical properties of a bioactive borate glasses doped with transition metals were prepared and investigated with the same molar composition as 45S5 glass but with all the silicon dioxide (SiO2) replaced by boron trioxide (B2O3). Methods: The biodegradability was explored and estimated by soaking the samples into simulated body fluid (SBF) at 37ºC for 30 days. The pH changes of solution were measured during the soaking periods in order to explore the ionic change processes. The structural changes in the crystalline phases obtained in the glass matrix before and after immersion in SBF were recognized by means of X-ray diffraction (XRD) and Fourier transform infrared analysis (FTIR). The surface modification was explored by means of scanning electron microscope (SEM). Results: All obtained results support the aggregation and formation of hydroxyapatite (Hap) layer with different amounts that depend on the type of transition metal added to the glass matrix. Conclusions: The biodegradation data and spectral analysis of different samples may consider the material to be a good candidate for use as dental biomaterials.

Effects of transition metals on the oxidation behavior of ZrB2 ceramics

The effects of transition metal additives on the oxidation behavior of ZrB2 ceramics at 1600°C were investigated. Additions of W, Mo, or Nb improved the oxidation resistance of ZrB2 even after evaporation of the protective B2O3 layer. The oxide layers were composed of an outer layer that was porous and had light color and an inner layer that was dense and appeared dark. Additions of Mo or Nb were more effective than W at improving the oxidation resistance of ZrB2 at 1600°C due to a lower evaporation rate for B2O3 glasses containing Nb and Mo compared to W.

Effect of transition metal additives on composite cobalt catalyst for NO x reduction with CH4

The CoH-BZZ and CoH-BMZ catalysts have good catalytic activity in the selective catalytic reduction of NO (NO-SCR) by methane, but have less selectivity at the reaction temperatures above 600°C. It was found that the addition of different transition metals to CoH-BZZ took different effect on SCR of NO by methane. Besides, Zn additives improved effectively the selectivity of methane towards NOx reduction. The nature of the active sites is characterized by diffuse reflectance H2-TPR and XPS. These techniques show that in both CoZn-BZZ and CoZn-BMZ catalysts the cobalt is present as mononuclear Co2+ species, and the bind energy also decreased compared with CoH-composites (-BZZ and -BMZ). Reactivity of both CoZn-BZZ and CoZn-BMZ is much higher than that found on Co based catalysts in temperature range between 500 and 650°C.

Effects of transition metal additives on redox stability and high-temperature electrical conductivity of (Fe,Mg)3O4 spinels

Abstract Magnetite-based spinels are considered as promising oxide materials to meet the requirements for ceramic consumable anodes in molten oxide pyroelectrolysis process, a breakthrough low-CO2 steel technology aimed to overcome the environmental impact of classical extractive metallurgy. The present work focuses on the assessment of phase relationships, redox stability and electrical conductivity of Fe2.6Me0.2Mg0.2O4 (M = Ni, Cr, Al, Mn, Ti) spinel-type materials at 300–1773 K and p(O2) from 10−5 to 0.21 atm. The oxidation state of substituting transition metal cation, affecting the fraction of Fe2+ in spinel lattice, was found to be a key factor, which determines the electronic transport and tolerance against oxidative decomposition, while the impact of preferred coordination of additives on these properties was less pronounced. At T > 650 K thermal expansion of Fe2.6Me0.2Mg0.2O4 ceramics exhibited complex behaviour, and, in highly oxidizing conditions, resulted in significant volume changes, unfavourable for high-temperature electrochemical applications.

Effects of transition metal addition on sintering and electrical conductivity of La-doped CeO2 as buffer layer for doped LaGaO3 electrolyte film

Abstract Effects of transition metal additives (0.5 at.% Fe, Mn, and Co) on densification, microstructure, crystal structure, and electrical conductivity of Ce 0.6 La 0.4 O 2 (LDC) were investigated. The power generation property of a single cell using LDC with the transition metal addition as buffer layer was measured. The addition of Co decreased the sintering temperature of LDC to 1373 K and increased the grain size when the sintering was performed at 1623 K. No impurity phase appeared by the addition of transition metals. The total conductivity of the Co-LDC sample sintered at 1373 K was even higher than that of LDC sintered at 1623 K, and Co-LDC sintered at 1623 K exhibited a conductivity of around 0.01 S cm − 1 at 973 K for the high density and large grain size. The single cell using an LSGM electrolyte film and Co-LDC buffer layers showed an open circuit voltage (~ 1.1 V) close to the theoretical value and the maximum power density of 974, 353, and 84 mW cm − 2 at 973, 873, and 773 K, respectively. Thus, Co-LDC is a promising buffer layer for enhanced sintering density and decreasing the ohmic resistance in anode supported SOFCs using LSGM electrolyte films.

Comparison of structure and catalytic performance of Pt–Co and Pt–Cu bimetallic catalysts supported on Al2O3 and CeO2 synthesized by electron beam irradiation method for preferential CO oxidation

In order to investigate the effect of transition metal addition to platinum with different support materials on preferential CO oxidation, structure and chemical properties of supported bimetallic catalysts prepared by electron beam irradiation method were correlated to the catalytic performance. On Al2O3, decoration of Pt by small amount of Co (Co/Pt ∼ 0.03) drastically increased CO and O2 conversions while addition of equimolar Cu to Pt increased them only above 100 °C, where the rate-controlling factor was suggested to change from oxygen transport to CO activation. On CeO2, either addition of Co or Cu to Pt had minor or negative effect on high O2 conversion inherent to high oxygen transport at Pt–CeO2 interface. On Pt–Cu/CeO2, however, metal-CuOx interface dominates the reaction characteristics to give improved selectivity, which is suitable for deep CO removal in excess O2/CO condition. The order of selectivity above 100 °C, Pt–CoOx > Pt(alloy)–CuOx > Pt–CeO2 interfaces, was derived from structural analysis and catalytic tests.

Effect of transition metal additives on the catalytic stability of Mo/HZSM-5 in the methane dehydroaromatization under periodic CH 4–H 2 switch operation at 1073 K

Eight 0.5 wt%M–5 wt%Mo/HZSM-5 catalysts (M = Cr, Mn, Fe, Co, Cu, Zn, Ru or Pd) prepared by co-impregnation method were tested for the non-oxidative methane dehydroaromatization at a practically required severe condition of 1 atm, 1073 K and 10,000 mL/g/h in periodic CH 4–H 2 switch operation mode. The aim was to investigate promotional effects of these transition metal additives on the activity and stability of Mo/HZSM-5 and find out a really effective promoter for the title catalytic system. While Fe, Co, Ru and Pd additions were found to enhance the catalyst's CH 4 conversion activity, only Fe was observed to remarkably improve the activity stability, and therefore another two Fe-modified catalysts with 0.3 and 1.0 wt% of Fe were prepared and tested to make further confirmation. Ascribed to the second group of metal additives, Cr, Mn, Cu and Zn additions exhibited little influence on the CH 4 conversion activity, and Cr and Mn caused even slight decreases in the activity stability. Similar tests were also conducted with the samples of 0.5 wt%M/HZSM-5s to confirm the negligibly low activities of all but Pd metal additive themselves. Then, all spent catalyst samples were subjected to TPO, TG, SEM and BET measurements to gain an insight into the promotion mechanisms of Fe additive. Consequently, the TPO and TG measurements revealed that the addition of all metals except Ru enhanced coke accumulation and only Fe induced the formation of a new type of coke. Well consistently, the SEM observations confirmed considerable amounts of carbon nanotubes formed in all Fe-containing spent samples, whereas no single carbon nanotube in all other spent samples. Furthermore, the BET measurements also confirmed that all Fe-containing spent samples had obviously higher BET surface areas and micropore volumes than all other spent catalyst samples. While all these, in addition to the test results, strongly suggest that the promotional effect of Fe additive is closely related to Fe-induced carbon nanotube formation and growth at the tested condition, three possible promotion effects were proposed in the article to explain all observations.

Effect of transition metal additives on electrical conductivity for La-excess-type lanthanum silicate

Influences on electrical property and phase relationship of oxyapatite-type solid electrolytes based on lanthanum silicate (LSO) were investigated by addition of a small amount of transition metal elements. It was revealed that a very small amount of 3d-transition metal additives into the La-excess-type, i.e., oxygen-excess-type Al-doped LSO, La 10(Si 5.8Al 0.2)O 26.9, changed its electrical conductivity. Some metals such as iron and chromium showed a positive effect for an increase in conductivity. The specimen with a nominal composition of 0.995{La 10(Si 5.8Al 0.2)O 26.9}–0.005(FeO γ ), showed the maximum electrical conductivity among the specimens measured in this study. Formed phases of oxygen-excess-type Al-doped LSO based materials were found to be altered even by addition of a small amount of transition metal oxides. La-rich impurity phases such as La(OH) 3 and La 2SiO 5 are usually detected in the oxygen-excess-type LSO, whereas no formation of La-rich impurity phases was confirmed in the case of iron addition. These results suggest that the enhancement of electrical conductivity by iron addition is due to a disappearance of the La-rich impurity phases as insulators and/or an increase in the concentration of oxygen interstitial carriers within the LSO phase.

Effect of Transition Metal Additives on Electrical Properties for La-Excess-Type Lanthanum Silicate-Based Solid Electrolytes

not Available.

Effect of transition metal additions on the electrochemical properties of a MgNi-based alloy

Mg–Ni metastable alloys (amorphous and/or nanocrystalline) are promising candidate materials to be used as anode in Ni–MH batteries. In the present work, Mg–50 at.% Ni and Mg–45 at.% Ni–10 at.% TM alloys (where TM = Co, Zr, V, Cr, Ti and Nb transition metals) were processed for 72 h of mechanical alloying in a planetary ball mill. After milling, the alloys were characterized by X-ray diffraction and submitted to galvanostatic cycles of charge and discharge. All samples were nanostructured and presented the highest discharge capacity at the 1st cycle. The Zr, Cr and Nb alloying elements increased the maximum discharge capacity from 221 mA h/g (of the binary alloy) to 293, 246 and 276 mA h/g, respectively. Additions of Co and Ti decreased the maximum discharge capacity to 136 and 117 mA h/g, respectively. Concerning the cycle of life of the electrodes, the best results were obtained for the Mg–Ni–Cr and Mg–Ni–Co alloys.

Solid solution softening in bcc Mo alloys: Effect of transition-metal additions on dislocation structure and mobility

The electronic origin of solid solution softening (SSS) in bcc molybdenum alloys was investigated in the framework of a combined approach that includes atomistic dislocation modeling with first principles parametrization of interatomic interactions. The softening additions are found to locally change the chemical bonding which results in a decrease of the generalized stacking fault (GSF) energy and atomic row shear resistance. Using the atomic row model, we show that the isotropic core of the screw dislocation in Mo tends to a ``split'' (planar) core under alloying with softener solutes (Re, Os, Ir, Pt). The generalized Peierls-Nabarro model for a non-planar core was employed to link the reduction in GSF energy with the enhancement of double kink nucleation and dislocation mobility. Our study appears to explain the experimental dependence of the alloying effect on the atomic number of the addition and to provide an understanding of the electronic reasons for SSS in Mo alloys.

The Effect of Transition Metal Additions on the Microstructure and Properties of Nanocomposite Pr–Fe–B Permanent Magnets

Permanent magnets with the general composition Pr/sub 9/(Fe/sub 0.95/Co/sub 0.05/)/sub 85.5/M/sub 0.5/B/sub 5/, where M denotes a transition metal, have been produced by melt spinning. The effect on the microstructure and magnetic properties of eight different alloying elements has been examined. The grain size and distribution have been correlated to the maximum energy product obtained. The grain size of the Pr/sub 9/(Fe/sub 0.95/Co/sub 0.05/)/sub 85.5/B/sub 5/ control alloy was determined to be 17.5 nm, and it was found that the grain size was not significantly reduced compared to the control alloy by any of the additions. However, some additions resulted in significant increases in grain size, notably Cu, Ti, and Cr, which had grain sizes between 26 and 36 nm, and an increase in the grain size distribution. The increase in grain size resulted in a loss in hysteretic squareness, leading to reduced energy products in these alloys. In other alloys, fine grain size did not always correlate to improved maximum energy products. For example, the Mo-added alloy had the finest grain size but a decreased maximum energy product, likely due to solute segregation to grain boundaries that inhibited intergranular exchange interactions. In general, Group VB additions had a more positive effect on the microstructure and magnetic properties than did other alloying additions. This paper will summarize the overall effects of the additions on the microstructures and magnetic properties, enabling further alloy design efforts in nanocomposite alloy systems.

Effects of Transition Metal Addition on the Solid-State Transformation of Molybdenum Trioxide to Molybdenum Carbides

Direct conversion of MoO3 to molybdenum carbides by temperature-programmed reaction (TPR) with a reacting gas mixture of CH4/4H2 has been studied in the presence of a transition metal selected from Pt, Pd, Ni, Co, Cu, and pre-synthesized Mo2C loaded on MoO3. Loading of the metals reduced the temperatures of MoO3 reduction and increased the specific surface area of produced carbides. However, the obtained phase of molybdenum carbides differed depending on the employed transition metal; Pt, Pd, or Ni produced cubic α-MoC1-x, while Co, Cu, or pre-synthesized Mo2C formed hexagonal β-Mo2C, which was the same phase as that produced from the direct transformation of MoO3 itself without any metal loading. The nature of transition metals loaded on MoO3 also led to different TPR patterns for the transformation to molybdenum carbide, suggesting that different reaction routes were involved. Thus, MoO3 loaded with Co, Cu, or Mo2C showed TPR patterns similar to that of MoO3 itself, except for slightly lower temperatures for the initiation of the reduction. With these metals, the transformation of MoO3 to carbides followed a nontopotactic route involving the MoO2 intermediate phase. By contrast, loading of Pt, Pd, or Ni to MoO3 drove MoO3 reduction into a topotactic transformation through a MoOxCy intermediate phase. However, unlike the well-established topotactic MoO3 → Mo2N → α−MoC1-x transformation, the pseudomorphism was only partly maintained in this metal-promoted, direct MoO3 → α-MoC1-x transformation.

Rhenium containing binary catalysts for ammonia synthesis

The rhenium nitride was prepared and applied for ammonia synthesis. Under the synthesis conditions (623 K, 0.1 MPa), the nitride was partly decomposed (Re 3N+Re) but the activity was stable and higher (179 μmol h −1 g −1 at 623 K under 0.1 MPa) than the other transition metal nitrides (VN, NbN, Mo 2N, and W 2N), although the BET surface area was immeasurably low. The active phase was considered to be Re 3N. The effect of transition metal addition to the rhenium catalyst for ammonia synthesis was investigated. Cobalt and iron were effective, but nickel, chromium, and copper were not effective. The best combination was Co-Re (1:4) (492 μmol h −1 g −1 at 623 K under 0.1 MPa, expressed as Co-Re 4 catalyst). NH 3 treatment of Co-Re 4 at 973 K gave a new XRD pattern (probably some kind of rhenium nitride phase), which was suggested to be responsible to the high activity of Co-Re 4 catalyst. The ammonia synthesis rate over Co-Re 4 catalyst was increased under high pressure (2372 μmol h −1 g −1 at 623 K under 3.1 MPa), however, the rate overshot above 1.1 MPa. The kinetic analysis indicated that Re surface was strongly covered either by hydrogen or by nitrogen (ammonia). By the addition of cobalt, the degree of nitrogen (ammonia) poisoning was weakened, but at the same time, the degree of hydrogen poisoning was strengthened.

Effect of transition metal addition on liquid phase sintering of tungsten-copper : T.H. Ihn et al (National University of Korea, Seoul, Korea), Powder Metallurgy, vol 37, no 4, 1994, 283–288

Effect of transition metal addition on liquid phase sintering of tungsten-copper : T.H. Ihn et al (National University of Korea, Seoul, Korea), Powder Metallurgy, vol 37, no 4, 1994, 283–288

Effects of transition metal addition to CoMo/ γ-Al 2O 3 catalyst on the hydrotreating reactions of atmospheric residual oil

The effects of transition metal addition to a commercial CoMo/ γ-Al 2O 3 catalyst on the hydrotreatment of atmospheric residual oil were investigated using a continuous flow fixed bed reactor operated at 420°C and 6.9 MPa. Nickel, ruthenium and tungsten were used as an additive to the catalyst. Catalyst performances were evaluated in terms of activities and initial deactivation rates in sulfur removal, conversion of heavier to lighter oil fractions, and removal of asphaltenes. Among the metal additive-modified CoMo/ γ-Al 2O 3 catalysts, NiCoMo/ γ-Al 2O 3 and WCoMo/ γ-Al 2O 3 showed a more improved reaction performance than commercial CoMo/ γ-Al 2O 3 whereas RuCoMo/ γ-Al 2O 3, did not. The performance improvements observed after addition of nickel or tungsten were thought to be mainly a result of the promotion effect on the catalytic activity in hydrodesulfurization. Significant improvements of catalyst performance were obtained by the addition of a small amount of tungsten (0.5 wt.-%). Tungsten was considered to be promising as a secondary promoter of CoMo/ γ-Al 2O 3.