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

Alkanes are catalytically dehydrogenated to alkenes with RhCl(CH2=CH2)(PMe3)2 (λmax 416 nm) under visible light irradiation in the presence of ethylene. The reaction proceeds smoothly even at room temperature; the quantum yield of cyclooctane dehydrogenation was 0. 10 at 25 °C.

Visible light-assisted dehydrogenation of alkanes catalyzed by the rhcl(ch2=ch2)(pme3)2-hv system

Irradiation hardening and ductility loss of a low-activation 9Cr-1V ferritic steel at low temperatures

The steam oxidation resistance of 80Ni-20Cr coatings on modified 9Cr-1Mo steel has been evaluated in the temperature range of 600 °C to 750 °C. High-velocity oxyfuel (HVOF) spray was used for the coating process. The steam-oxidized specimens exhibited the diffusion of iron from the substrate to the coating and diffusion of nickel from the coating to the substrate. Nickel diffusion to the substrate adjacent to the coating induced the microstructural changes. Micro X-ray diffraction (XRD) studies and energy-dispersive spectroscopy (EDS) point analysis on these transformed zones revealed that the newly formed phases are the austenite in the high-Ni-concentration region and the martensite in the low-Ni-concentration region. Microhardness studies showed higher hardness values in the martensite zones.

Steam oxidation of 80Ni-20Cr high-velocity oxyfuel coatings on 9Cr-1Mo steel: Diffusion-induced phase transformations in the substrate adjacent to the coating

High-Temperature Annealing for Maximization of Dissolved Boron in Creep-Resistant Martensitic 9Cr Steel

In our previous study, we reported the adhesive strength of thermal sprayed Ni–Cr coatings on modified 9Cr–1Mo steel after a long-term aging at 750 °C for 3000 h In this paper, the effect of thermal cycling on the adhesive strength has been evaluated for the 80Ni–20Cr and 50Ni–50Cr coatings sprayed by a high-velocity oxyfuel (HVOF) spraying process on modified 9Cr–1Mo steel substrate The rapid heating and air-cooling were performed to simulate the thermal cycling condition of the thermal power plants where the coatings are targeted to use ASTM C-633 type tensile test was adopted to evaluate the adhesive strength of the coated and thermal-cycled specimens The specimens exposed to thermal cycling test for 100 and 300 cycles did not show significant change in their adhesive strength values compared to as-coated condition The 80Ni–20Cr specimens aged for 3000 h at 750 °C exposed to thermal cycling test for 300 cycles also showed similar performance; the tensile specimen broke within the resin The 50Ni–50Cr coatings aged for 3000 h showed a significant reduction in adhesive strength The coatings were delaminated from the substrate during the tensile test Thermal cycling on aged 50Ni–50Cr specimens resulted in similar performance of coating delamination under the tensile test and the adhesive strength values remained unchanged The results suggest that there is only limited probability for the coating exfoliation due to thermal cycling when Ni–Cr coatings are used to protect the boiler component against steam oxidation

Fujio Abe

Papers

Visible light-assisted dehydrogenation of alkanes catalyzed by the rhcl(ch2=ch2)(pme3)2-hv system

Irradiation hardening and ductility loss of a low-activation 9Cr-1V ferritic steel at low temperatures

Steam oxidation of 80Ni-20Cr high-velocity oxyfuel coatings on 9Cr-1Mo steel: Diffusion-induced phase transformations in the substrate adjacent to the coating

High-Temperature Annealing for Maximization of Dissolved Boron in Creep-Resistant Martensitic 9Cr Steel

Effect of thermal cycling on the adhesive strength of Ni–Cr coatings