Amorphous atomic size

Figure 10.6 Tracer diffusivities in glassy NisoZrso of various solute atoms as a function of their size (as measured by their metallic radii) [25]. Reprinted, by permission, from H. Hahn and R.S. Averback, "Dependence of tracer diffusion on atomic size in amorphous Ni-Zr," Phys. Rev. B, Vol. 37, p. 6534. Copyright 1988 by the American Physical Society.

Atomizers nozzle (air, pressure position, number) rotary, etc. Shape/size, size distribution of drops Trajectory of drops Flow rate/pressure drying air Temperature air inlet/outlet Flow rate/temperature product Powder yield (TS), sticking Water content, aw composition, retention, degradation,% surface structure (amorphous, crystallized) Size, density, wettability, flowabiUty, surface state Temperature, Tg, MP... 

It has been shown that all the properties of T, Hy, 0 and electrical resistivity at room temperature (Prt) for the Al-R amorphous alloys were essentially independent of the atomic number of the R metals. The atomic size of the R metals varies systematically with the atomic number and hence the atomic size factor also seems to have little effect on the above-mentioned properties. On the other hand, it is generally known that the inherent chemical nature of the lanthanide metals results from 4f-electrons which lie at the inner side in their atoms. Although the number of 4f-electrons varies systematically with the atomic number, the electrons are screened by 5s - and 5p -electrons which lie at the outer side of the atoms, resulting in a similarity in chemical properties of the lanthanide metals. Accordingly, it may reasonably be assumed that the independence of the properties of the Al-R amorphous alloys as a function of atomic number is due to the unique electronic structure in which the 4f-electrons are screened by 5s- and 5p-electrons. 

It is shown in sect. 3.1 that Mg-based amorphous alloys are obtained in Mg-Ni—R and Mg-Cu-R and that glass formation is independent of the kind of R element. It is important to know the influence of the atomic size of R on the Vickers hardness (H ) of Mg-R-M amorphous alloys. Figure 75 shows the change in of the amorphous Mg65Cu2sRio alloys with the kind of R element, together with the data of their atomic radii (S.G. Kim 1992). Although exceptional values are observed only for Eu and Yb, which also have significantly different atomic sizes, there is a tendency for to increase from about 180 for R=La to about 310 for the R element with the smallest atomic radius. 

Figure 105 summarizes the changes in the as-quenched phase and the atomic diameter in the Zn55Mg4oRs alloys with the R elements. We note a systematic change dependent on the atomic size of the R elements. The as-quenched structure exhibits the amorphous phase when it contains La, Ce, Pr or Eu, and the icosahedral phase wdien it contains Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or Y. It seems that the atomic size of the R element is an important factor for the formation of amorphous and icosahedral phases. The alloys containing an R element with an atomic diameter larger than 0.366 nm, except Yb, form... 

The atomic sizes of the constituent elements in the ternary R-Al-M amorphous alloys differ significantly. Therefore, the interpretation of the total radial distribution function (RDf) obtained by the ordinary X-ray diffraction method is complicated, and it is extremely hard to obtain structural parameters for each independent pair of elements. By using the anomalous X-ray scattering (AXS) method with which the structural environment around a particular constituent element can be determined, it is expected that this difference is observed and the structural environment around Ni in the amorphous La55Al25Ni2o alloy is estimated in as-quenched, annealed (in the supercooled liquid region) and crystallized states. From these systematic AXS measurements, the structural changes due to crystallization were discussed. 

The results of SAXS (small-angle X-ray scattering) profile analysis yield the size distribution and frequency of particles and are plotted in Fig. 10.4. Particles with radius of about 1 nm were formed in as-MA powder and heat-treated powder below 800°C, even though the results of XRD measurements showed that the oxide complex particles were not detected at those temperatures. This result is quite surprising, but it is supposed that amorphous atomic clusters of 1 nm size were formed at temperatures below 800°C. Therefore, the oxide complex particles in crystalhne stmcture grow in size with broad size distribution with increasing temperature between 960 and 1200°C. 

X-ray diffraction consists of the measurement of the coherent scattering of x-rays (phenomenon 4 above). X-ray diffraction is used to determine the identity of crystalline phases in a multiphase powder sample and the atomic and molecular stmctures of single crystals. It can also be used to determine stmctural details of polymers, fibers, thin films, and amorphous soflds and to study stress, texture, and particle size. 

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