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

The effect of tungsten–molybdenum (W–Mo) balance on creep life has been investigated for five heats of martensitic 9Cr steel with 1.5 % Mo equivalent (= 1/2W + Mo) at 600, 650 and 700°C. Th...

Effect of W–Mo balance on long-term creep life of 9Cr steel

The effect of W-Mo balance and boron nitrides (BN) on creep rupture ductility has been investigated for five heats of 9% Cr steel with 1.5% Mo equivalent, 0.003% boron and 0.05% nitrogen at 600oC, ...

Effect of W-Mo balance and boron nitrides on creep rupture ductility of 9Cr steel

The mechanisms responsible for lower creep strength of fine-grained heat-affected-zone (HAZ) than base metal, the microstructural evolution in the HAZ during heating and the suppression of Type IV fracture by boron have been investigated using simulated-HAZ specimens and welded joint specimens of Gr.92, Gr.122 and newly developed 9Cr steel with boron. Creep tests were carried out at 650°C for up to about 30,000 h. In Gr.122, the time to rupture has its minimum after heating the specimens to a peak temperature near AC3, while the hardness has its minimum after heating to a peak temperature near AC1. In Gr.92, the reduction of boundary and sub-boundary hardening in fine-grained HAZ is more important than the grain refinement for a significant decrease in time to rupture after the AC3 thermal cycle. The addition of boron without the formation of any boron nitrides suppresses the formation of fine-grained HAZ and produces substantially the same microstructure as the base metal, even after the AC3 ther...

Metallurgy of Type IV fracture in advanced ferritic power plant steels

The creep rupture ductility has been investigated for Gr.91 and Gr.92 at 550 to 700°C for up to 118,648.8 h. The degradation in the reduction of area (RA) is more significant in Gr.92 than in Gr.91...

Creep rupture ductility of Gr.91 and Gr.92 at 550°C to 700°C

The formation of SiC film by photo-chemical vapour deposition (CVD) using ArF excimer laser with a wavelength of 193 nm has been studied to establish a low-temperature and mild synthetic process for ceramic films. Photo-CVD was conducted using Si2H6 and C2H2 as source gases on quartz glass, molybdenum and graphite substrates at 508–623 K. The pressure ratio of Si2H6 to C2H2 was changed from 0.06 to 1.2. The laser was irradiated at 50 mJ cm−2 at 25 Hz. The films were identified using transmission electron microscopy and infrared spectrometry, and the chemical composition was determined using Auger electron specroscopy. The growth rate of SiC was measured with a step-height profilometer. s-SiC, with almost stoichiometric composition, was formed in the pressure ratio range, Si2H6/C2H2, of 0.06–1.2 at 508–623 K. Crystallization of the SiC film was observed with increasing Si2H6/C2H2 ratio. The film growth rate linearly depended on Si2H6 pressure but was independent of C2H2 pressure. The rate-determining step of film formation is assumed to be photolysis of Si2H6. The cross-section of photolysis calculated from the film growth rate was about 10−18 cm2 for the ArF laser.

Fujio Abe

Papers

Effect of W–Mo balance on long-term creep life of 9Cr steel

Effect of W-Mo balance and boron nitrides on creep rupture ductility of 9Cr steel

Metallurgy of Type IV fracture in advanced ferritic power plant steels

Creep rupture ductility of Gr.91 and Gr.92 at 550°C to 700°C

Microstructure and growth of SiC film by excimer laser chemical vapour deposition at low temperatures