CuBe alloy

Figure 12.20 shows the structure of the side-window circular cage type and linear focused head-on type of photomultiplier which are both preeminent in fluorescence studies. The lower cost of side-window tubes tends to favor their use for steady-state studies, whereas the ultimate performance for lifetime studies is probably at present provided by linear focused devices. In both types internal current amplification is achieved by virtue of secondary electron emission from discrete dynode stages, usually constructed of copper-beryllium (CuBe) alloy, though gallium-phosphide (GaP) first dynodes have been used to obtain higher gains. 

FIGURE 24 (A) Schematic drawing of the pressure cell. Hardened CuBe alloy is used for... 

Greater amounts of copper increase the proportion of needles or stars of Cu Sn in the microstmcture. Increase in antimony above 7.5% results in antimony—tin cubes. Hardness and tensile strength increase with copper and antimony content ductiUty decreases. Low percentages of antimony (3—7%) and copper (2—4%) provide maximum resistance to fatigue cracking in service. Since these low alloy compositions are relatively soft and weak, compromise between fatigue resistance and compressive strength is often necessary. 

An electron microscope picture of dislocation lines in stainless steel. The picture was taken by firing electrons through a very thin slice of steel about lOOnm thick. The dislocation lines here ore only about 1000 atom diameters long because they have been chopped off where they meet the top and bottom surfaces of the thin slice. But a sugar-cube-sized piece of ony engineering alloy contains about 10 km of dislocation line. (Courtesy of Dr. Peter Southwick.)... 

In 1951Castaing8 published results to show that an electron microscope could be converted into a useful x-ray emission spectrograph for point-to-point exploration on a micron scale. The conversion consisted mainly in adding a second electrostatic lens to obtain a narrower electron beam for the excitation of an x-ray spectrum, and adding an external spectrometer for analysis of the spectrum and measurement of analytical-line intensity. Outstanding features of the technique were the small size of sample (1 g cube, or thereabouts) and the absence of pronounced absorption and enhancement effects, which, of course, is characteristic of electron excitation (7.10). Castaing8 gives remarkable quantitative results for copper alloys the results in parentheses are the quotients... 

The following simplified treatment is presented to illustrate some roughly quantitative aspects of the theory. The value of 0 is taken to be constant, with AO = 120°. The interaction constant p is taken as 0.36 yaV22ipiARi, in which pt is the fraction of ions i in the crystal and ARt is the change in radius. The quantity v v, the cube of the average valence for the metal or alloy, is an approximate representation of the force constant k of the bonds, which enters linearly in the expression for V. The coefficient z has the value +1 for M+ and —1 for M. The number 0.36 has been introduced to give agreement with the observed... 

The absence or very low intensity of 111, 311, 331, 333 and 511 indicates that clusters of atoms, perhaps 13-20, occupy the centres of the hexakaidecahedra, around iij and so on. There are also smaller clusters, probably of four atoms, inside the pentagonal dodecahedra, increasing the number of atoms in the 25.73-A cube to between 1,120 and 1,176. The composition of the alloys may be changed from MA16 by these additional atoms. 

Fabry-Perot cavity, 14 849, 850 Fabry-Perot etalons, 11 151, 152 Face-centered cube lattice, 8 114t Face-centered cubic (FCC) crystal structure in Ni-base alloys, 13 512 of spinel ferrites, 11 60 Facial makup, 7 846-847 Facial preparations, 7 842t Facial tridendate ligand, 7 578 Facihtated transport, 15 826-827 carrier, 15 845-846... 

Figure 3.31. cF16-MnCu2Al type structure (representative of the Heusler type alloys). The unit cell is shown in (a), an eighth of the cell is shown in (b). It degenerates into a cP2-CsCl type cell if the atoms at the cube comers (Mn and Al) are equivalent. If all the atoms were equivalent there would he a further degeneration into the cI2-W type. 

Difluorides such as PbF2 with the fluorite structure exhibit fast ion conduction due to facile F ion transport (Section 6.4.5). An interesting structure showing Li" conduction is that of LijN (Rabenau, 1978). Conduction is two-dimensional. Cooperative basal plane excitations involving the rotation of six Li ions by 30 about a common ion to edge positions (positions midway between ions in the Li2N layer) seem to be responsible for conduction in this nitride. In the fluorite structure, a rotation by 45 of a single cube of F ions seems to be involved. The Zintl alloy LiAl is also a lithium-ion conductor. 

Other alloys that may be placed in this class are CuBe, AgZn, AgCd, AgMg, AuZn, and Ag Al. 

The [Bai4CaN6] cluster can be considered as a Ca-centered Bas cube with each face capped by a Ba atom, and the six N atoms are each located inside a Bas tetragonal pyramid, as shown in Fig. 12.6.6. The stmcture can be viewed alternatively as a cluster composed of the fusion of six N-centered BasCa octahedra sharing a common Ca vertex. In the synthesis of this type of cluster compounds, variation of the atomic ratio of the Na/K binary alloy system leads to a series of compounds of variable stoichiometry Bai4CaN6]Na,v withx = 7,8,14,17,21... 

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