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

Response of Fe-Cr-Mn austenitic alloys to thermal aging and neutron irradiation

Effects of alloying elements of W and Co on a creep strength of full annealed 15Cr ferritic steel whose chemical composition is Fe-01C-15Cr-1Mo-3W-02V-005Nb-007N-0003B has been investigated Increases in creep strength with increase in W content and addition of Co have been obviously observed About 10 times and 30 times longer time to rupture than that of the base steel have been obtained at 923K-100MPa by increase in W content from 3 mass% to 6 mass% and addition of 3 mass% of Co, respectively Moreover, significant improvement of creep strength has been observed by the combination of increase in W content and addition of Co Time to rupture of the steel strengthened by 6 mass% of W and 3 mass% of Co is 100 times longer than that of the base steel at 923K-100MPa Creep rupture strength of the steel containing 6 mass % of W and 3 mass% of Co is almost the same as that of ASME T92 steel Since Cr content of conventional ferritic creep resistant steels is less than 12 mass%, oxidation resistance of the 15Cr ferritic steel investigated in this study is better than those of conventional ferritic creep resistant steels It has been concluded that a full annealed 15Cr ferritic creep resistant steel should be one of the candidate materials for new Ultra Supercritical (USC) power plant in the 21st century

Development of High Strength 15Cr Ferritic Creep Resistant Steel with Addition of Tungsten and Cobalt

The precipitation of σ-phase in the cold rolled specimens of an Fe–10Cr–30Mn steel was investigated by transmission electron microscopy after aging at 923 K. The specimens were prepared as a reduced activation austenitic steel for fusion reactor structures. During the aging, recrystallisation and discontinuous precipitation of σ-phase occurred simultaneously in the specimens with > 30% cold working (CW). The recrystallising interfaces moved toward the deformed and supersaturated solid solutions, leaving the precipitates of σ-phase behind the new recrystallised grains. The nucleation and growth behaviour of σ-phase is discussed.MST/779

Discontinuous precipitation of σ-phase during recrystallisation in cold rolled Fe-10Cr-30Mn austenite

Precipitation strengthening is important to improve creep strength of heat resisting steels at elevated temperatures. Especially, in the high-Cr ferritic steels recently developed for Ultra Super Critical Power Plants, precipitation behavior is complicated and should be clarified because the correlation between various strengthening factors are still not well understood. In this study, we focus on the change in precipitation behavior of MX type carbonitrides in model steels with different heat treatment conditions. It is found that dominant precipitation behavior has been changed with cooling rate from normalization temperature before tempering and better creep properties have been obtained in the steel quenched rather than in the one air-cooled. It is confirmed that precipitation of M 23 C 6 is suppressed and total fraction of MX is relatively increased by the quenching procedure. It is thought that better creep resistance is mainly due to fine distribution of MX that is achieved by suppressing typical co-precipitation of MX such as Nb(C, N)-VN during cooling after normalization and tempering.

Effect of Heat Treatment on Precipitation Kinetics in High-Cr Ferritic Steels

The creep strength by a fine distribution of titanium carbides in 9Cr heat resistant steel has been investigated. In order to distribute titanium carbides finely, the concentration of nitrogen was decreased to avoid large titanium nitrides remaining after normalising, and the normalising temperature was raised to 1573 K to dissolve titanium carbides into the matrix. The rise of the normalising temperature to 1573 K causes an increase of the amount of δ phase, which has a bad influence on toughness, and hence the composition of the steel was adjusted and the holding time at normalising was shortened to repress the growth of δ phase. In the developed steel, very fine titanium carbides precipitated densely, and the creep strength of the steel increased remarkably. It is presumed that the movement of dislocations was obstructed by fine titanium carbides in the form of laths in the matrix.

Fujio Abe

Papers

Response of Fe-Cr-Mn austenitic alloys to thermal aging and neutron irradiation

Development of High Strength 15Cr Ferritic Creep Resistant Steel with Addition of Tungsten and Cobalt

Discontinuous precipitation of σ-phase during recrystallisation in cold rolled Fe-10Cr-30Mn austenite

Effect of Heat Treatment on Precipitation Kinetics in High-Cr Ferritic Steels

Improvement of creep strength by fine distribution of TiC in 9Cr ferritic heat resistant steel