FeCo

FeCo - in particular with a 2 % V addition - has found widespread use as a magnetically soft material with a high saturation induction, e.g. as electromagnet pole tips, and the respective alloys are known as Permendur alloys (Chen, 1961 Kouvel, 1967 Dietrich, 1990). These alloys also exhibit a high, positive magnetostrictive co- 

The mechanical behavior of FeCo has been studied intensively since the order-disorder transition allows a direct study of the effects of ordering on the mechanical properties including creep, fatigue and 

Ordered FeCo-2V exhibits a more homogeneous deformation and a higher 

Finally, it may be noted that alloying Fe and Co with precious metals leads to the phases FePt, CoPt, and FePd with an LIq structure, which is an ordered f.c.c. structure with tetragonal distortion (see Fig. 1). These phases have been of importance for applications as permanent magnetic materials, and in particular CoPt, which is used in the only partially ordered state, excels because of isotropy, ductility, easy machinability and resistance to corrosion and high temperatures (Jellinghaus, 1936 Kouvel, 1967 Chin and Wernick, 

1986 Fiepke, 1990 Leroux et al., 1991 Watanabe, 1991). However, CoPt alloy magnets are seldom used now since these alloys have been replaced by the rare earth magnets with superior magnetic properties. 

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To simplify FECO evaluation, it is conmion practice to experimentally filter out one of the components by the use of a linear polarizer after the interferometer. Mica bireftingence can, however, be useftil to study thin films of birefringent molecules [49] between the surfaces. Rabinowitz [53] has presented an eigenvalue analysis of birefringence in the multiple beam interferometer. 

Partial reflections at the iimer optical interfaces of the interferometer lead to so-called secondary and tertiary fringe patterns as can be seen from figure B 1.20.4. These additional FECO patterns become clearly visible if the reflectivity of the silver mirrors is reduced. Methods for analysis of such secondary and tertiary FECO patterns were developed to extract infonnation about the topography of non-unifonn substrates [54]. 

Figure Bl.20.4. Cross-sectional sideview of a syimnetric, tliree-layer interferometer illustrating the origin of primary, secondary, tertiary and gap FECOs. (Reproduced with pennission from [54].)...

Instead of an absorbing dye layer between the mica. Levins et al [57] used thin metallic films and developed a method for FECO analysis using an extended spectral range. 

The preparation of the reflecting silver layers for MBI deserves special attention, since it affects the optical properties of the mirrors. Another important issue is the optical phase change [ ] at the mica/silver interface, which is responsible for a wavelength-dependent shift of all FECOs. The phase change is a fimction of silver layer thickness, T, especially for T < 40 mn [54]. The roughness of the silver layers can also have an effect on the resolution of the distance measurement [59, 60]. 

Another interesting extension of the FECO teclmique, using a capillary droplet of mercury as the second mirror, was developed by Flom etal [6f]. The light from this special interferometer is analysed in reflection. 

Each of the systems has an optimum distance for which the SNR has a maximum. For Tb—FeCo this is at about 220 K (50),... 

Carbonates. Iron(II) carbonate [563-71-3] FeCO, precipitates as a white soHd when air-free solutions of alkah metal carbonates and iron(II) salts are mixed. The limited tendency of [Fe(H20)g] to hydroly2e is illustrated by the lack of carbon dioxide evolution in this reaction. The soHd rapidly... 

Figure 3.7 Siderite (FeCOs) nodules inside a tubercle revealed by breaking open the magnetite shell. (Courtesy of National Association of Corrosion Engineers, Corrosion 89 Paper No. 197 by H. M. Herro.)...

Fig. 8. (ii) Geometry and interferometry in the SFA. The distance between the surfaces is determined from the wavelengths of FECO. (a) The PECO fringes when the surfaces are in contact. The separation profile, D versus r, can be measured from the fringe profile, and compared to that predicted by the JKR theory of contact mechanics, (b) The FECO when the surfaces are separated. By measuring the wavelengths of the fringes when the surfaces are in contact and when they are separated, we can determine the distance between the two surfaces. 

Hence 0.771 - 0.059161og,o(10 ) = 0.771 - 1.301 = -0.530 V Thus by making the solution alkaline the sign of has been reversed and the susceptibility of Fe (aq) to oxidation (i.e. its reducing power) enormously increased. This is why white, precipitated Fe(OH)2 and FeCOs are rapidly darkened by aerial oxidation and why Fe in alkaline solution will reduce nitrates to ammonia and copper(II) salts to metallic copper. 

Calcium carbonate (CaCO,) calcium sulfate or gypsum (CaSOJ and iron(II) carbonate (FeCO ) are the most common types of scales formed in drilling. If hydrogen sulfide is present, then there is a possibility of iron sulfide (FeS) scale depositing. 

Carbon dioxide was once thought essential for the rusting of ferrous metals (viz. the carbonic acid theory of rusting) but is now considered of relatively minor importance . However, basic zinc carbonate is frequently found in the corrosion products of zinc and small amounts of siderite (FeCOs) are found in ferrous rusts. 

Montano (89) developed matrix Mossbauer spectroscopy to the point of being able to identify FeMn, FeCo, FeNi, and FeCu bimetallics. In these combinations, an increase in the electron density at the Fe nu-... 

Spherical rollers were machined from AISI 52100 steel, hardened to a Rockwell hardness of Rc 60 and manually polished with diamond paste to RMS surface roughness of 5 nm. Two glass disks with a different thickness of the silica spacer layer are used. For thin film colorimetric interferometry, a spacer layer about 190 nm thick is employed whereas FECO interferometry requires a thicker spacer layer, approximately 500 nm. In both cases, the layer was deposited by the reactive electron beam evaporation process and it covers the entire underside of the glass disk with the exception of a narrow radial strip. The refractive index of the spacer layer was determined by reflection spectroscopy and its value for a wavelength of 550 nm is 1.47. 

Fig. 15—A schematic diagram of the optical system based on FECO technique for the gap measurement.

Fig. 16—A sketch of samples and fringes of FECO. (a) Mica sheets, silver films, and the light path, (b) Fringes before and after shift.

Other, similar methods for measuring surface-surface interactions, which come under the generic heading of surface force apparatus, include the crossed-filament method. This utilizes a beam deflection technique similar to that now being used in some AFMs for the measurement of surface displacement [94]. Another technique for displacement measurement used in a similar SFA is that of a capacitance transducer. Both techniques suffer the criticism that separation is not measured at the point of interest, i.e., the gap between the two surfaces as measured in the FECO technique. 

The physical meaning of our final equation is best seen on eqn 39. The term containing w is essentially the self-energy correction introduced by Mulliken in his analysis of electronegativities to account for the average repulsion of electrons occupying the same orbital. In order to get an idea of the orders of magnitude, let us apply eqn 39 to a model computation of FeCO, made to compare the ClPSl results of Berthier et al. [11] with those of a simple orbital scheme. Consider one of the two x systems of FeCO, treated under the assumption of full localization (and therefore strict cr — x separation)... 

Table 1 Source data and dP/drir for the average x system of FeCO...

FeCOs) of Mn-carbonates varies widely in a range of 10 -10 mole fraction. Siderite from Au-Ag vein-type deposits (Ohmori) contains appreciable amounts of zinc (0.8-5.8 wt% as ZnO) (Shikazono, 1977b). 

Glaesemann KR, Gordon MS, Nakano H (1999) A study of feCO+ with correlated wavefunctions. Phys Chem Chem Phys 1 967... 

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