Catalytic Effect of Nanoparticles on Primary and Secondary Phase Nucleation

2013 ◽  
Vol 765 ◽  
pp. 250-254 ◽  
Author(s):  
Michael P. de Cicco ◽  
John H. Perepezko
Keyword(s):  
Secondary Phase ◽  
Zinc Alloy ◽  
Secondary Phases ◽  
Metal Matrix Nanocomposites ◽  
Secondary Phase Formation ◽  
Droplet Emulsion ◽  
Phase Nucleation ◽  
Equiaxed Grains ◽  
Matrix Nanocomposites ◽  
Primary Aluminium

Nanoparticles were shown to catalyze nucleation of primary and secondary phases in metal matrix nanocomposites (MMNCs). This catalysis is important as it contributes to the mechanical property enhancement in the MMNCs. Primary aluminium grain refinement was demonstrated in A356 matrix nanocomposites. Various types and sizes of nanoparticles (SiC, TiC, γ-Al2O3; 10-96 nm) were used to make these MMNCs and in all cases the MMNCs had smaller, more equiaxed grains compared to the reference A356. Using the droplet emulsion technique, undercoolings were shown to be significantly reduced. Undercoolings in the MMNCs were in good general agreement with the undercooling necessary for free growth, suggesting the applicability of this model to nucleation on nanoscale catalysts. Secondary phase nucleation catalysis was demonstrated in a zinc alloy AC43A MMNC and a binary Mg-4Zn MMNC. In AC43A, secondary phase nucleation was catalyzed with the addition of various nanoparticles (TiC, SiC, γ-Al2O3). The secondary phase nucleation catalysis in AC43A coincided with ductility enhancement. In Mg-4Zn, SiC nanoparticle addition changed the secondary phases that formed. MgZn2 was formed in the MMNC at relatively high temperatures consuming the Zn and reducing the amount of the low temperature Mg2Zn3 phase that formed in the reference alloy. The change in secondary phase formation coincided with significant enhancement in strength and ductility.

PH3 Effects on the Electrochemical Degradation of SOFC Anode

2011 ◽  
Author(s):  
Huang Guo ◽  
Gulfam Iqbal ◽  
Bruce S. Kang
Keyword(s):  
Electrochemical Performance ◽  
Secondary Phase ◽  
Anode Surface ◽  
Electrochemical Degradation ◽  
Secondary Phases ◽  
Nickel Phosphate ◽  
Secondary Phase Formation ◽  
Cell Anode ◽  
Fuel Cell Anode ◽  
Ppm Level

Solid Oxide Fuel Cell anode is readily degraded by trace amount of Phosphine (PH3) contaminant that is found in coal-derived syngas. PH3 interacts with the anode material and affects its electrochemical performance by forming secondary phases. In this paper, the influence of the ppm level of PH3 with moisture is investigated on the formation of secondary phases and hence on anode electrochemical performance degradation. Nickel yttria-stabilized zirconia (Ni-YSZ) anode shows immediate and severe electrochemical degradation due to PH3 in moist hydrogen condition attributed to the nickel-phosphate secondary phase formation. Whereas in dry hydrogen condition, nickel-phosphide is preferred to form on the anode surface that shows less deleterious effects on SOFC performance as compared to nickel-phosphate.

Identification of Secondary Phases Formed During Unsaturated Reaction of UO2 with EJ-13 Water

1989 ◽  
Vol 176 ◽  
Author(s):  
J. K. Bates ◽  
B. S. Tani ◽  
E. Veleckis ◽  
O. J. Wronklewicz
Keyword(s):  
Phase Formation ◽  
Secondary Phase ◽  
Yucca Mountain ◽  
Solution Chemistry ◽  
Spent Fuel ◽  
Secondary Phases ◽  
Secondary Phase Formation

ABSTRACTA set of experiments, wherein UO2 has been contacted by dripping water, has been conducted over a period of 182.5 weeks. The experiments are being conducted to develop procedures to study spent fuel reaction under unsaturated conditions that are expected to exist over the lifetime of the proposed Yucca Mountain repository site. One half of the experiments have been terminated, while one half are ongoing. Analyses of solutions that have dripped from the reacted UO2 have been performed for all experiments, while reacted UO2 surfaces have been examined for the terminated experiments. A pulse of uranium release from the UO2 solid, combined with the formation of schoepite on the surface of the UO2, was observed between 39 and 96 weeks of reaction. Thereafter, the uranium release decreased and a second set of secondary phases was observed. The latter phases incorporated cations from the EJ-13 water and include boltwoodite, uranophane, sklodowskite, compreignacite, and schoepite. The experiments are continuing to monitor whether additional changes in solution chemistry or secondary phase formation occurs.

scholarly journals The Importance of Secondary Phases in Glass Corrosion

1990 ◽  
Vol 212 ◽  
Author(s):  
William L. Ebert ◽  
John K. Bates
Keyword(s):  
Computer Simulations ◽  
Reaction Times ◽  
Microscopic Analysis ◽  
Secondary Phase ◽  
Secondary Phases ◽  
Reaction Behavior ◽  
Glass Corrosion ◽  
Model Glass ◽  
Secondary Phase Formation

ABSTRACTThe analytical expression used to model glass reaction in computer simulations such as EQ6 is compared to the results of experiments used to support the simulations. The expression correctly predicts the acceleration observed in experiments performed at high glass surface area/1eachant volume ratios (SA/V) upon the formation of secondary phases. High resolution microscopic analysis of reacted glass samples suggests that the accelerated nature of the reaction after secondary phase formation is due to changes in the reaction affinity (i.e., is a solution effect) and not a change in the glass reaction mechanism. The composition of solutions in contact with reacted samples reflect the effects of the secondary phases predicted in the model. Experiments which lead to the generation of secondary phases within short reaction times can be used to identify important secondary phases which must be Included in the data base of computer simulations to correctly project long-term glass reaction behavior.

The behavior of unirradiated UO2and uraninite under repository conditions characterized by Raman

MRS Advances ◽  
2016 ◽  
Vol 1 (62) ◽  
pp. 4157-4162 ◽  
Author(s):  
L. J. Bonales ◽  
J.M. Elorrieta ◽  
C. Menor-Salván ◽  
J. Cobos
Keyword(s):  
Raman Spectroscopy ◽  
Spent Nuclear Fuel ◽  
Secondary Phase ◽  
Storage Conditions ◽  
Oxidation Products ◽  
Deep Geological Repository ◽  
Secondary Phases ◽  
Secondary Phase Formation ◽  
Geological Repository ◽  
Spectroscopy Studies

ABSTRACTRaman spectroscopy studies have been performed on one hand to identify different materials related to spent nuclear fuel (SNF), and on the other hand to study the behavior of SNF at different storage conditions. Specifically, the expected oxidation of the SNF matrix under dry storage conditions and the formation of secondary phases (SP), as a result of corrosion of SNF in a deep geological repository, have been studied. In order to perform these experiments, two protocols based on the Raman spectroscopy technique have been developed. The results show U4O9/U3O7and U3O8as oxidation products of UO2powder at high temperatures in air, and the secondary phase formation (rutherfordine, UO2(CO3), soddyite, (UO2)2SiO4•2H2O, uranophane alpha Ca(UO2)2(SiO3OH)2•5H2O and kasolite, PbUO2SiO4•H2O), due to uraninite corrosion under the conditions of Sierra Albarrana (Spain).

Metallurgical, mechanical and tribological behavior of Reinforced magnesium-based composite developed Via Friction stir processing

2021 ◽  
pp. 095440892110630
Author(s):  
Prem Sagar ◽  
Amit Handa ◽  
Gitesh Kumar
Keyword(s):  
Friction Stir Processing ◽  
Rotational Speed ◽  
Tribological Behavior ◽  
Secondary Phase ◽  
Tool Rotational Speed ◽  
Metal Matrix Nanocomposites ◽  
Friction Stir ◽  
Base Matrix ◽  
Matrix Nanocomposites ◽  
High Plastic

Reinforced magnesium metal matrix nanocomposites (MMMNCs) have piqued the interest of scientific community in recent years. Friction stir processing (FSP) is a known process to achieve the highest level of secondary phase nanocomposites distribution in the base monolithic matrix. In this study, an attempt has been made to synthesize magnesium base AZ61A/n-TiC nanocomposites using FSP and the influence of tool rotational speed on the metallurgical, mechanical, and tribological behavior of the developed composites has been studied. Microstructural examination shows that as tool rotational speed increases, high plastic deformation occurs and heat is generated along with the concomitant shattering impact of rotation, which consequently develops larger grains in the stir zone. However, this also provides thrusts resulting in uniform distribution of the nanoparticles in the base matrix. Microhardness and ultimate tensile strength of the developed nanocomposite were found to be significantly improved when contrasted with the base metal. Lower wear rate was observed for the composite developed at 800 rpm along with the abrasive type of wear mechanism.

scholarly journals Prediction of Radioactive Waste Glass Durability by the Hydration Thermodynamic Model: Application to Saturated Repository Environments

1989 ◽  
Vol 176 ◽  
Author(s):  
Carol M. Jantzen ◽  
W. Gene Ramsey
Keyword(s):  
Free Energy ◽  
Dissolution Rate ◽  
Phase Formation ◽  
Thermodynamic Model ◽  
Functional Dependence ◽  
Secondary Phase ◽  
Deionized Water ◽  
Secondary Phases ◽  
Durability Test ◽  
Secondary Phase Formation

ABSTRACTThe effects of groundwater chemistry on glass durability were examined using the hydration thermodynamic model. The relative durabilities of SiO2, obsidian, basalt, nuclear waste glasses, medieval window glasses, and a frit glass were determined in tuffaceous (J–13) groundwater, basaltic (GR–4) groundwater, WIPP–A brine, and Permian Basin brine (PBB–3) using the monolithic MCC–I durability test. In the groundwater–dominated MCC–l experiments, the interaction of the glasses and the initial groundwater (leachant) caused the formation of unique assemblages of secondary phases. The secondary phase formation, in turn, controlled the final groundwater (leachate) pH and ionic strength, I[t].Correlations of the final leachate pH and I[t] with the Si release from the glass indicated that it is the influence of the secondary phase formation on the leachate pH and I[t] that controls the final dissolution rate of the glass. Since I[t] and the pH of the leachates are functions of the precipitation reactions, inclusion of the experimentally determined solution pH in the free energy of hydration model provides for the functional dependence of the dissolution rate on the secondary precipitation. Therefore, superposition of the linear equation for the groundwater and deionized water experiments occurs and the hydration free energy model can be used to compare glass durability in deionized water and in repository groundwaters.

Dopant-Site Determination in Y- and Sc-Doped (Ba0.5Sr0.5)(Co0.8Fe0.2)O3−δby Atom Location by Channeling Enhanced Microanalysis and the Role of Dopant Site on Secondary Phase Formation

2015 ◽  
Vol 22 (1) ◽  
pp. 113-121 ◽  
Author(s):  
Matthias Meffert ◽  
Heike Störmer ◽  
Dagmar Gerthsen
Keyword(s):  
Phase Formation ◽  
Electronic Conductivity ◽  
Site Occupancy ◽  
Secondary Phase ◽  
Secondary Phases ◽  
Oxide Formation ◽  
Separation Membranes ◽  
Secondary Phase Formation ◽  
Homogenization Temperatures ◽  
Cation Sites

Abstract(Ba0.5Sr0.5)(Co0.8Fe0.2)O3−δ(BSCF) is a promising material with mixed ionic and electronic conductivity which is considered for oxygen separation membranes. Selective improvement of material properties, e.g. oxygen diffusivity or suppression of secondary phase formation, can be achieved by B-site doping. This study is concerned with the formation of Co-oxide precipitates in undoped BSCF at typical homogenization temperatures of 1,000°C, which act as undesirable nucleation sites for other secondary phases in the application-relevant temperature range. Y-doping successfully suppresses Co-oxide formation, whereas only minor improvements are achieved by Sc-doping. To understand the reason for the different behavior of Y and Sc, the lattice sites of dopant cations in BSCF were experimentally determined in this work. Energy-dispersive X-ray spectroscopy in a transmission electron microscope was applied to locate dopant sites exploiting the atom location by channeling enhanced microanalysis technique. It is shown that Sc exclusively occupies B-cation sites, whereas Y is detected on A- and B-cation sites in Y-doped BSCF, although solely B-site doping was intended. A model is presented for the suppression of Co-oxide formation in Y-doped BSCF based on Y double-site occupancy.

scholarly journals Fabrication and Characterization of the Modified EV31-Based Metal Matrix Nanocomposites

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 125
Author(s):  
Seyed Kiomars Moheimani ◽  
Mehran Dadkhah ◽  
Mohammad Hossein Mosallanejad ◽  
Abdollah Saboori
Keyword(s):  
Thermal Expansion ◽  
Mechanical Strength ◽  
Metal Matrix ◽  
Coefficient Of Thermal Expansion ◽  
Structural Effect ◽  
Metal Matrix Nanocomposites ◽  
Mechanical Stirring ◽  
Specific Strength ◽  
The Matrix ◽  
Matrix Nanocomposites

Metal matrix nanocomposites (MMNCs) with high specific strength have been of interest for numerous researchers. In the current study, Mg matrix nanocomposites reinforced with AlN nanoparticles were produced using the mechanical stirring-assisted casting method. Microstructure, hardness, physical, thermal and electrical properties of the produced composites were characterized in this work. According to the microstructural evaluations, the ceramic nanoparticles were uniformly dispersed within the matrix by applying a mechanical stirring. At higher AlN contents, however, some agglomerates were observed as a consequence of a particle-pushing mechanism during the solidification. Microhardness results showed a slight improvement in the mechanical strength of the nanocomposites following the addition of AlN nanoparticles. Interestingly, nanocomposite samples were featured with higher electrical and thermal conductivities, which can be attributed to the structural effect of nanoparticles within the matrix. Moreover, thermal expansion analysis of the nanocomposites indicated that the presence of nanoparticles lowered the Coefficient of Thermal Expansion (CTE) in the case of nanocomposites. All in all, this combination of properties, including high mechanical strength, thermal and electrical conductivity, together with low CTE, make these new nanocomposites very promising materials for electro packaging applications.

scholarly journals Wettability in Metal Matrix Composites

Metals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1034
Author(s):  
Massoud Malaki ◽  
Alireza Fadaei Tehrani ◽  
Behzad Niroumand ◽  
Manoj Gupta
Keyword(s):  
Metal Matrix Composites ◽  
Metal Matrix ◽  
Aluminum Matrix ◽  
Interfacial Strength ◽  
High Strength ◽  
Aluminum Matrix Composites ◽  
Matrix Composites ◽  
Metal Matrix Nanocomposites ◽  
Aerospace Applications ◽  
Matrix Nanocomposites

Metal matrix composites (MMCs) have been developed in response to the enormous demand for special industrial materials and structures for automotive and aerospace applications, wherein both high-strength and light weight are simultaneously required. The most common, inexpensive route to fabricate MMCs or metal matrix nanocomposites (MMNCs) is based on casting, wherein reinforcements like nanoceramics, -carbides, -nitrides, elements or carbon allotropes are added to molten metal matrices; however, most of the mentioned reinforcements, especially those with nanosized reinforcing particles, have usually poor wettability with serious drawbacks like particle agglomerations and therefore diminished mechanical strength is almost always expected. Many research efforts have been made to enhance the affinity between the mating surfaces. The aim in this paper is to critically review and comprehensively discuss those approaches/routes commonly employed to boost wetting conditions at reinforcement-matrix interfaces. Particular attention is paid to aluminum matrix composites owing to the interest in lightweight materials and the need to enhance the mechanical properties like strength, wear, or creep resistance. It is believed that effective treatment(s) may enormously affect the wetting and interfacial strength.

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