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

Effect of specimen size on the ductile-brittle transition behavior and the fracture sequence of 9Cr-W steels

Microscopic deformation behavior upon abrupt stress loading at high temperature and the effects of microstructural factors on the behavior were investigated in 9% chromium martensitic steels with a variety of microstructures. Anelastic deformation occurs upon abrupt stress loading in steels with a martensitic lath structure. The anelastic deformation originates from the lath structure; that is, the cell structure independent of the presence of a high dislocation density, precipitates, or solute atoms of W or Mo. The lath boundaries, which correspond to sub-boundaries, elastically bend under applied stress, and the motion of the lath boundary requires time due to its complicated structure. This is the reason for the anelastic deformation in the martensitic lath structure. The anelastic strain of extremely low-carbon 9% Cr steel is smaller than that of conventional 9% Cr steels, indicating the difficulty of lath boundary motion in the low-carbon steel. The many MX precipitates present at the lath boundaries effectively retard the elastic bending of the lath boundary in the extremely low-carbon 9% Cr steel. The difficulty of lath boundary motion expected from the analysis of anelastic strain can reasonably explain the improvement of creep strength in extremely low-carbon 9% Cr steel reported in the literature.

Mechanical response of 9% Cr heat-resistant martensitic steels to abrupt stress loading at high temperature

In order to develop reduced-activation ferritic/martensitic steels potentially suitable for fusion reactor applications, the effect of principal alloying elements Cr, W and V on the micro- structural evolution, toughness and high-temperature creep strength was systematically investigated for relatively simple Cr-W-V steels. Based on the results on the simple steels, two kinds of martensitic 9Cr steels with low and high levels of W were alloy-designed: 9Cr-1WVTa and 9Cr-3WVTa. They exhibited excellent toughness and high-temperature strength. Irradiation hardening was the smaller for the reduced-activation 9Cr-1WVTa and 9Cr-3WVTa steels than for the conventional 9Cr-lMoVNb and it was smaller for the low W steel than for the high W steel. It is concluded that from the aspect of toughness the 9Cr-1WVTa steel is the most promising alloy for the first wall and blanket structures which will be operated at low temperatures below 773 K (500°C). Another 9Cr-3WVTa steel is the most promising in terms of high- temper...

https://www.tandfonline.com/doi/pdf/10.1080/18811248.1994.9735152

Development of reduced-activation martensitic 9cr steels for fusion reactor

Oxide dispersion-strengthened (ODS) ferritic steels have a good radiation resistance, high creep strength and a good swelling resistance. In such alloys, Zr is used to improve the creep properties by stabilizing the grains boundaries. The influence of the zirconium on the microstructure will be discussed is this study. The addition of Zr reduces strongly the number density of the inclusion distribution. The reduction factor is between 4 (transverse direction) to 15 (longitudinal direction). The addition of Zr reduces the formation of Al and Y oxides (micro scale). The carbide composition is also different according to the material composition. Zr-free material forms W/Ti carbides and Zr-added material forms Zr/Ti carbides without formation of W carbides (free enthalpy). Zr addition may be considered as very good in term of strength and corrosion resistance.

Effects of Zr Addition on the Microstructure of 14%Cr4%Al ODS Ferritic Steels

Boundary and sub-boundary hardening is shown to be the most important strengthening mechanism for creep of martensitic 9Cr steel and is enhanced by fine dispersions of precipitates along boundaries. Based on the boundary and sub-boundary hardening, new martensitic 9Cr steel has been alloy-designed for application to thick-section boiler components, such as main steam pipes and headers, with steam temperature of 650°C maximum in coal-fired power plants. Boron stabilizes fine distributions of M 23 C 6 carbides along prior austenite grain boundaries in a 9Cr-3W-3Co-0.2V-0.05Nb steel for up to long times during exposure at 650°C, which increases the creep strength at low stresses and long times. Boron also suppresses the degradation in creep strength due to brittle Type IV fracture in the heat-affected zone of welded joints at 650°C. The addition of nitrogen causes the precipitation of nanometer-size MX nitrides, which significantly increases the creep strength. The addition of boron and nitrogen without any formation of boron nitrides during normalizing heat treatment exhibits not only much higher creep rupture strength of base metal than conventional martensitic steels Gr.91, Gr.92, and Gr.122 but also substantially no Type IV fracture in welded joints at 650°C. This is a new martensitic 9Cr steel MARBN ( mar tensitic 9Cr steel strengthened by b oron and MX n itrides), which contains 120–150 ppm boron and 60–90 ppm nitrogen. MARBN also exhibits enough creep rupture ductility, larger than or the same as Gr.91, because of low nitrogen concentration. The formation of protective Cr 2 O 3 -rich oxide scale is achieved on the surface of MARBN by pre-oxidation treatment in argon gas, which significantly improves the oxidation resistance in steam at 650°C.

Fujio Abe

Papers

Effect of specimen size on the ductile-brittle transition behavior and the fracture sequence of 9Cr-W steels

Mechanical response of 9% Cr heat-resistant martensitic steels to abrupt stress loading at high temperature

Development of reduced-activation martensitic 9cr steels for fusion reactor

Effects of Zr Addition on the Microstructure of 14%Cr4%Al ODS Ferritic Steels

New martensitic steels