Resistivity as a Tool for Characterizing Point Defects in Nonstoichiometric Metallic Ceramics

1995 ◽  
Vol 411 ◽  
Author(s):  
Wendell S. Williams
Keyword(s):  
Chemical Composition ◽  
Point Defects ◽  
Residual Resistivity ◽  
Slow Cooling ◽  
Conduction Electrons ◽  
Hard Materials ◽  
Ordered Phases ◽  
Scattering Centers ◽  
Metal Ratio ◽  
Metal Ratios

ABSTRACTCompounds of IVb and Vb transition metals and carbon are electronically conductive, hard materials that crystallize in the NaC1 structure but are very nonstoichiometric (carbon-poor), as in TiCx, where x is the carbon/metal ratio and is less than unity. Carbon atom vacancies are randomly located in the fcc carbon sublattice and act as scattering centers for conduction electrons. Data on the electrical resistivity as a function of the concentration of these point defects could be used in the opposite sense–i.e., to determine the defect concentration, (l-x), through a measurement of resistivity. The chemical composition (carbon/metal ratio) is then given directly by x. The random vacancies can be ordered by slow cooling from high temperatures, thereby eliminating the residual resistivity. The carbon/metal ratios of these ordered phases are either 3:4, 5:6 or 7:8 and thus can specify the chemical composition precisely.

Studies of the Late Bronze Age copper-based ingots found in Greece

2000 ◽  
Vol 95 ◽  
pp. 207-217 ◽  
Author(s):  
Helen Mangou ◽  
Panayiotis V. Ioannou
Keyword(s):  
Chemical Composition ◽  
Bronze Age ◽  
Atomic Absorption Spectroscopy ◽  
Pure Copper ◽  
Late Bronze Age ◽  
Slow Cooling ◽  
Metallographic Examination ◽  
Aegean Region ◽  
Chemical Content ◽  
Different Origin

Seven bun type, one slab type, and 44 oxhide type Late Bronze Age ingots found in the Aegean region, Crete and Mainland Greece have been analysed for their chemical content (twelve elements) by atomic absorption spectroscopy. The results show that the ingots contain variable amounts of oxygen as copper(I) oxide. The oxhide ingots are made of purer copper, the bun type are of relatively pure copper and bronze, while the slab type is bronze. The oxhide ingots from Crete may have a different origin from those found in the Aegean and in Mainland Greece because they have a different chemical composition. The metallographic examination of twenty ingots, three of bun and seventeen of oxhide type, revealed that they have been cast in open moulds, followed by slow cooling. Microanalyses of inclusions in fifteen ingots revealed the presence of copper(I) sulphide, copper(I) oxide, copper-iron and copper-iron-sulphur and their origin is discussed. Hardness measurements on fourteen ingots of various types revealed that they are somewhat harder for a cast object than control alloys and likely explanations are given.

Microstructural Dependence of Magnetization and Magnetostriction in Fe-20at.%Ga

2016 ◽  
Vol 703 ◽  
pp. 100-105
Author(s):  
Yue Ming Shi
Keyword(s):  
Room Temperature ◽  
Single Phase ◽  
Cooling Water ◽  
Magnetic Domain ◽  
Saturation Magnetostriction ◽  
Magnetic Domain Wall ◽  
Slow Cooling ◽  
Heat Treated ◽  
Ordered Phases ◽  
Combination Study

A combination study of magnetic and magnetostrictive properties in directionally cast and differently heat-treated Fe-20Ga(at.%) samples has been carried out at room temperature. Slow cooling leads to an increase in the occupation of [200] easy magnetic axes; however, a structural ordering of Ga atoms into a metastable D03 phase decreasesthe saturation magnetostriction (λs) and the saturation magnetization (Ms), and increases coercivity (Hc).Our results confirm the contribution of D03 ordering to magnetic and magnetostrictive properties due to their pinning effects against magnetic domain wall motions. As compared to slow cooling, water quenching suppresses the formation of metastable (D03) or stable (L12) ordered phases and preserves the A2 single phase structure down to room temperature, leading to enhanced magnetostriction and magnetization.

A Study of Toughness Degradation in CA6NM Stainless Steel

2010 ◽  
Vol 654-656 ◽  
pp. 2515-2518 ◽  
Author(s):  
Yoshitaka Iwabuchi ◽  
Isao Kobayashi
Keyword(s):  
Stainless Steel ◽  
Chemical Composition ◽  
Intergranular Fracture ◽  
Prior Austenite ◽  
Martensitic Stainless Steel ◽  
Carbide Precipitation ◽  
Isothermal Heating ◽  
Slow Cooling ◽  
Austenite Grain ◽  
Prior Austenite Grain

The mechanism of toughness degradation during slow cooling in the austenite range was studied in CA6NM stainless steel, 13% Cr-4% Ni soft martensitic stainless steel. The variation of toughness, fracture mode and microstructural features were examined by means of cooling rate and isothermal heating in the austenite range together with chemical composition. Toughness degradation was referred to as the increases of FATT and intergranular fracture when those steels were cooled slowly after austenitizing and isothermally heated in the austenite range. The embrittlement was found to be related the intergranular fracture and the precipitation of carbide along prior austenite grain boundaries. Its fracture surface was characterized by mosaic-like markings when the carbide precipitation got to increase. Reducing carbon, silicon and phosphorus and increasing molybdenum improve the toughness degradation.

scholarly journals SMM behaviour and magnetocaloric effect in heterometallic 3d–4f coordination clusters with high azide : metal ratios

2017 ◽  
Vol 46 (45) ◽  
pp. 15661-15665 ◽  
Author(s):  
Sebastian F. M. Schmidt ◽  
Marcel P. Merkel ◽  
George E. Kostakis ◽  
Gernot Buth ◽  
Christopher E. Anson ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Magnetocaloric Effect ◽  
Synthesis And Characterization ◽  
Metal Ratio ◽  
Metal Ratios

We present the synthesis and characterization of heterometallic compounds with a very large azide to metal ratio and fascinating magnetic properties.

Heat of interaction of oxygen with dysprosium and yttrium

1988 ◽  
Vol 53 (10) ◽  
pp. 2412-2417 ◽  
Author(s):  
Slavoj Černý ◽  
Milan Kovář
Keyword(s):  
Solid Solution ◽  
Rare Earth ◽  
Sorption Capacity ◽  
Room Temperature ◽  
Rare Earth Metals ◽  
High Reactivity ◽  
Oxygen Species ◽  
Low Oxygen ◽  
Metal Ratio ◽  
Metal Ratios

Heat of interaction of oxygen dosed to vacuum-evaporated films of dysprosium and yttrium were measured in a calorimeter at room temperature. The high and rapidly produced heat, and the attained oxygen-to-metal ratio indicate high reactivity of these rare earth metals towards oxygen molecules which obviously undergo dissociative sorption. The energy of bonding of the formed oxygen species to the metal was estimated to 723 kJ/mol (173 kcal/mol) and 780 kJ/mol (186 kcal/mol) for Dy and Y, respectively. A markedly higher sorption capacity of Y film compared to Dy film was observed. The heat produced by the first admitted doses of oxygen may suggest formation of a solid solution of oxygen species in Dy and Y at very low oxygen-to-metal ratios.

scholarly journals A systematic metallicity study of DustPedia galaxies reveals evolution in the dust-to-metal ratios

2019 ◽  
Vol 623 ◽  
pp. A5 ◽  
Author(s):  
P. De Vis ◽  
A. Jones ◽  
S. Viaene ◽  
V. Casasola ◽  
C. J. R. Clark ◽  
...  
Keyword(s):  
Star Formation ◽  
Grain Growth ◽  
Stellar Mass ◽  
Mass Ratio ◽  
Local Conditions ◽  
Metal Ratio ◽  
Stellar Masses ◽  
Dust Grain ◽  
Dust Grain Growth ◽  
Metal Ratios

Observations of evolution in the dust-to-metal ratio allow us to constrain the dominant dust processing mechanisms. In this work, we present a study of the dust-to-metal and dust-to-gas ratios in a sub-sample of ~500 DustPedia galaxies. Using literature and MUSE emission line fluxes, we derived gas-phase metallicities (oxygen abundances) for over 10 000 individual regions and determine characteristic metallicities for each galaxy. We study how the relative dust, gas, and metal contents of galaxies evolve by using metallicity and gas fraction as proxies for evolutionary state. The global oxygen abundance and nitrogen-to-oxygen ratio are found to increase monotonically as galaxies evolve. Additionally, unevolved galaxies (gas fraction >60%, metallicity 12 + log(O∕H) < 8.2) have dust-to-metal ratios that are about a factor of 2.1 lower (a factor of six lower for galaxies with gas fraction >80%) than the typical dust-to-metal ratio (Md∕MZ ~ 0.214) for more evolved sources. However, for high gas fractions, the scatter is larger due to larger observational uncertainties as well as a potential dependence of the dust grain growth timescale and supernova dust yield on local conditions and star formation histories. We find chemical evolution models with a strong contribution from dust grain growth describe these observations reasonably well. The dust-to-metal ratio is also found to be lower for low stellar masses and high specific star formation rates (with the exception of some sources undergoing a starburst). Finally, the metallicity gradient correlates weakly with the HI-to-stellar mass ratio, the effective radius and the dust-to-stellar mass ratio, but not with stellar mass.

scholarly journals Mechanical Spectroscopy Investigation of Point Defect-Driven Phenomena in a Cr Martensitic Steel

Metals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 870 ◽  
Author(s):  
Alessandra Fava ◽  
Roberto Montanari ◽  
Alessandra Varone
Keyword(s):  
Point Defect ◽  
Cooling Rate ◽  
Point Defects ◽  
Martensitic Steel ◽  
Nucleation Mechanism ◽  
Hydrogen Attack ◽  
Mechanical Spectroscopy ◽  
Hydrogen Atoms ◽  
Slow Cooling ◽  
Cr Concentration

The paper presents and discusses results of mechanical spectroscopy (MS) tests carried out on a Cr martensitic steel. The study regards the following topics: (i) embrittlement induced by Cr segregation; (ii) interaction of hydrogen with C–Cr associates; (iii) nucleation of Cr carbides. The MS technique permitted characterising of the specific role played by point defects in the investigated phenomena: (i) Cr segregation depends on C–Cr associates distribution in as-quenched material, in particular, a slow cooling rate (~150 K/min) from austenitic field involves an unstable distribution, which leads to Cr concentration fluctuations after tempering at 973 K; (ii) hydrogen interacts with C–Cr associates, and the phenomenon hinders hydrogen attack (HA) because hydrogen atoms bound by C–Cr associates are not able to diffuse towards grain boundaries and dislocation where CH4 bubbles may nucleate, grow, and merge to form the typical HA cracks; (iii) C–Cr associates take part in the nucleation mechanism of Cr7C3 carbides, and specifically these carbides form by the aggregation of C–Cr associates with 1 Cr atom.

Determination of the activation enthalpy for migration of dislocations in plastically deformed 8006 Al-alloy by positron annihilation lifetime technique

2016 ◽  
Vol 30 (18) ◽  
pp. 1650110 ◽  
Author(s):  
Mohammed Salah ◽  
M. Abdel-Rahman ◽  
Emad A. Badawi ◽  
M. A. Abdel-Rahman
Keyword(s):  
Plastic Deformation ◽  
Positron Annihilation ◽  
Point Defects ◽  
Isothermal Annealing ◽  
Activation Enthalpy ◽  
Hydraulic Press ◽  
Al Alloy ◽  
Slow Cooling ◽  
Positron Annihilation Lifetime

The activation enthalpy for migration of dislocations of plastically deformed 8006 Al-alloy was investigated by positron annihilation lifetime technique. Plastic deformation using a hydraulic press produces mainly dislocations and may produce point defects. The type of defect was studied by isochronal annealing which determines the temperature range of recovery of each type. Only one type of defect (dislocations) was observed for the investigated sample and was found to be recovered within the range 455–700 K. Isothermal annealing by slow cooling was performed through this range and used in determination of the activation enthalpy of migration of dislocations which was found to be 0.26 ± 0.01 eV.

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