There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Mechanical Alloying And Milling

ion. The oxidative addition mechanism was originally proposed22i because of the lack of a strong rate dependence on polar factors and on the acidity of the medium. Later, however, the electrophilic substitution mechanism also was proposed. Recently, the oxidative addition mechanism was confirmed by investigations into the decomposition and protonolysis of alkylplatinum complexes, which are the reverse of alkane activation. There are two routes which operate in the decomposition of the dimethylplatinum(IV) complex Cs2Pt(CH3)2Cl4. The first route leads to chloride-induced reductive elimination and produces methyl chloride and methane. The second route leads to the formation of ethane. There is strong kinetic evidence that the ethane is produced by the decomposition of an ethylhydridoplatinum(IV) complex formed from the initial dimethylplatinum(IV) complex. In D2O-DCl, the ethane which is formed contains several D atoms and has practically the same multiple exchange parameter and distribution as does an ethane which has undergone platinum(II)-catalyzed H-D exchange with D2O. Moreover, ethyl chloride is formed competitively with H-D exchange in the presence of platinum(IV). From the principle of microscopic reversibility it follows that the same ethylhydridoplatinum(IV) complex is the intermediate in the reaction of ethane with platinum(II). Important results were obtained by Labinger and Bercaw62c in the investigation of the protonolysis mechanism of several alkylplatinum(II) complexes at low temperatures. These reactions are important because they could model the microscopic reverse of C-H activation by platinum(II) complexes. Alkylhydridoplatinum(IV) complexes were observed as intermediates in certain cases, such as when the complex (tmeda)Pt(CH2Ph)Cl or (tmeda)PtMe2 (tmeda ) N,N,N′,N′-tetramethylenediamine) was treated with HCl in CD2Cl2 or CD3OD, respectively. In some cases H-D exchange took place between the methyl groups on platinum and the, CD3OD prior to methane loss. On the basis of the kinetic results, a common mechanism was proposed to operate in all the reactions: (1) protonation of Pt(II) to generate an alkylhydridoplatinum(IV) intermediate, (2) dissociation of solvent or chloride to generate a cationic, fivecoordinate platinum(IV) species, (3) reductive C-H bond formation, producing a platinum(II) alkane σ-complex, and (4) loss of the alkane either through an associative or dissociative substitution pathway. These results implicate the presence of both alkane σ-complexes and alkylhydridoplatinum(IV) complexes as intermediates in the Pt(II)-induced C-H activation reactions. Thus, the first step in the alkane activation reaction is formation of a σ-complex with the alkane, which then undergoes oxidative addition to produce an alkylhydrido complex. Reversible interconversion of these intermediates, together with reversible deprotonation of the alkylhydridoplatinum(IV) complexes, leads to multiple H-D exchange

Activation of c-h bonds by metal complexes

Hydrogen Production by Molecular Photocatalysis

Transition metal catalyzed oxidative functionalization of carbon-hydrogen bonds

A ferritic heat−resistant steel which comprises, in wt %, 1.0 to 13 % of chromium, 0.1 to 8.0 % of cobalt, 0.01 to 0.20 % of nitrogen, 3.0 % or less of nickel, 0.01 to 0.50 % of one or more elements selected from the group consisting of vanadium, niobium, tantalum, titanium, hafnium and zirconium, which form MX type precipitates, and 0.01 % or less of carbon, as constituting elements, the balance being substantially composed of iron and inevitable impurities, and has a metal structure wherein MX type precipitates are formed over the whole of grain boundaries and the surface within grains and M 23 C 6 type precipitates are present on grain boundaries in an area percentage of 50 % or less. The ferritic heat−resistant steel exhibits excellent creep characteristics even at a high temperature exceeding 600 ˚ C.

Ferritic heat-resistant steel and method for production thereof

The applicability of theoretical energy analysis to the evolution of microstructures in heat-resistant steels was explored by using the system free energy method to predict the precipitation of M23C6 and σ phase within grains in 18Cr–8Ni austenitic steels. The chemical free energy of Fe–C–Cr–Ni quaternary steel and the interfacial and elastic strain energies between austenitic (γ) matrix and the M23C6 and σ phase were estimated for the system free energy of microstructures wherein coherent or incoherent M23C6 and the incoherent σ phase precipitated within γ grains. By identifying the minimum-energy path through a determination of system free energy hierarchies, the precipitation initiation curves of precipitates in Fe–0.07C–18.95Cr–9.57Ni steel for temperatures between 823–973 K were theoretically predicted. The calculated curves agreed well with experimental results for Type 304H austenitic steels; this suggests that the system free energy method is suitable for predicting the evolution of microstructures in heat-resistant steels.

Prediction of Precipitation Sequences within Grains in 18Cr–8Ni Austenitic Steel by Using System Free Energy Method

The creep strength of advanced ferritic heat-resistant steels for ultra super critical (USC) power plants is significantly improved by the addition of Pd. It has been found by a detailed transmission electron microscopy (TEM) observation that fine precipitation of an Fe-Pd based L10-ordered phase within a lath-martensite grain possessing a certain crystallographic orientation relationship with the matrix is reponsible for the strengthening mechanism. Phenomenological calculation by combining the cluster variation method (CVM) with a Lennard-Jones (L-J) type pair interaction energy is herein attempted for the Fe-Pd binary system to evaluate L10-disorder phase equilibria as an initial step to investigate ternary systems. Some of the unknown parameters in the Lennard-Jones pair interaction energies are determined with the help of computations based on a combination of a thermodynamic database and experimental measurement of the latent heat for the L10-disorder transition, the latter from differential scanning calorimetry. The experimental L10-disorder transition temperature is well reproduced by incorporating a tetragonal distortion of the L10-ordered phase into the calculation. In addition, detailed atomistic information, which is indispensable in designing and controlling the morphology of the L10-ordered phase, is obtained by the present calculation.

L10-disorder phase equilibria in the Fe-Pd system investigated by phenomenological calculation

Energy issues enjoy an almost unprecedented public profile. Future sources of energy, the security of current supplies, energy conservation, and the related question of climate change and environmental emissions are all subjects of intense scientific and political debate. While the challenges are global, it is clear that a range of solutions, often local in character, will be required to address them.

Energy drivers for materials research and development

Carbon fiber reinforced SiC (C/SiC) and SiC fiber reinforced SiC (SiC/SiC) composites were fabricated by a chemical vapor infiltration (CVI) method to obtain the composites with minimized impurity contamination. The neutron activation analysis showed that 30 elements were detected as impurities. However total impurity concentrations in the C/SiC and SiC/SiC were lower than 14.5 wt ppm and 9.80 wt ppm, respectively. The evaluation of induced activity under the simulation of fusion neutron irradiation of 10 MW.y/m 2 was made based on the impurity concentration. The dose rates of both composites were assumed to decrease by about 6 orders of magnitude in one day cooling and by 9 orders of magnitude in several ten years. The results indicate that the present composites behave excellent in terms of low activation and the CVI is a potential process to obtain high-purity composites

https://www.tandfonline.com/doi/pdf/10.1080/18811248.1994.9735259

Fujio Abe

Papers

Ferritic heat-resistant steel and method for production thereof

Prediction of Precipitation Sequences within Grains in 18Cr–8Ni Austenitic Steel by Using System Free Energy Method

L10-disorder phase equilibria in the Fe-Pd system investigated by phenomenological calculation

Energy drivers for materials research and development

Impurities and evaluation of induced activity of SiC composites prepared with chemical vapor infiltration