Thin slab

A comprehensive history of ferrous scrap recycling ia the United States beginning ia 1646 has beea pubUshed (3). Some selected eveats of iaterest iaclude the first opea-hearth steel produced (1868) the first commercial direct-arc electric furnace steel produced ia the United States (1906) the first large iaduction furnace iastaHed ia the United States (1914) the first basic oxygen steel produced ia the United States (1954) the rise of continuous casters and scrap-based minimills (1965) the first thin-slab continuous caster at a minimill (1989) U.S. exports and imports of ferrous scrap at record highs (1990) and the end of production of open-hearth steel (1991). 

For various reasons, including financial ones, the United States was slower than Japan and Europe to install continuous slab casters for the production of sheet. Electric melters cast billets continuously from about 1975 onward. Casting was done cmdely at first but the sophistication increased rapidly, culminating in the operation of a thin-slab caster at one of Nucor s plants. This opened up another avenue of attack on sheet markets, once the province of integrated mills. 

This logical extension of thin slabs to cast direcdy to sheet in the 1-mm range is a possibiUty long recogni2ed but difficult to reali2e. Progress in both stainless and carbon steel has been rapid and early prototypes are expected by the year 2000. Several schemes have been tried in laboratories all over the world. 

Dry Ice. Refrigeration of foodstuffs, especially ice cream, meat products, and frozen foods, is the principal use for soHd carbon dioxide. Dry ice is especially useful for chilling ice cream products because it can be easily sawed into thin slabs and leaves no Hquid residue upon evaporation. Cmshed dry ice may be mixed directly with other products without contaminating them and is widely used in the processing of substances that must be kept cold. Dry ice is mixed with molded substances that must be kept cold. For example, dry ice is mixed with molded mbber articles in a tumbling dmm to chill them sufficiently so that the thin flash or rind becomes brittle and breaks off. It is also used to chill golf-ball centers before winding. 

Gas impingement from slots, orifices, and nozzles at 10—100 m/s velocities is used for drying sheets, films, coatings (qv), and thin slabs, and as a secondary heat source on dmm dryers and paper (qv) machine cans. The general relationship for convection heat transfer is (13,14) ... 

Air impingement is commonly employed for drying sheets, film, thin slabs, and coatings. Another application in which it is used is as a secondary heat source on drum and can diyers (see Fig. 12-46). 

In the early days of TEM, sample preparation was divided into two categories, one for thin films and one for bulk materials. Thin-films, particularly metal layers, were often deposited on substrates and later removed by some sort of technique involving dissolution of the substrate. Bulk materials were cut and polished into thin slabs, which were then either electropolished (metals) or ion-milled (ceramics). The latter technique uses a focused ion beam (typically Ar+) of high-energy, which sputters the surface of the thinned slab. These techniques produce so-called plan-view thin foils. 

When fracture is confined to a single plane of the lattice, the net solution collapses to the nail solution. Consider an atomically thin slab of dimension V = AL, where A is unit area and L is a bond length, the strain energy stored is U = a AL/lE and the energy dissipated is U = DoE p — / c). The VP model then predicts that Gic o- such that... 

Long, thin slabs, separate or in the form of tongues, are formed as a result of this process. The decreasing thickness of the slabs becomes stable when it reaches the Batchelor microscale "... 

A thin slab of solid material dries first by evaporation from the top surface and then by diffusion from the interior of the solid. The water movement is approximated by the diffusion equation... 

Pyroelectric detectors depend on the use of a thin slice of ferroelectric material (deuterated triglycine sulfate [DTGS], Figure 5.6, is the standard example) - in which the molecules of the organic crystal are naturally aligned with a permanent electric dipole. The thin slab is cut and arranged such that the direction... 

Let us now consider a thin slab for which L < I (Fig. 26b). Here the bulk of the crystal is no longer electrically neutral and the bands are less bent than in the preceding case for the same surface charge density. The Fermi level both in the bulk and on the surface is shifted compared with the preceding case. It can be shown that as the slab becomes thinner, the potential difference between the surface and the center of the crystal decreases and the bands gradually straighten out. 

For a sufficiently thin slab when L 1 (Fig. 26c) the bands may be considered completely straightened and the entire volume of the semiconductor uniformly charged. We shall confine ourselves to this limiting case and consider .+ = e,+ = e+ or e, = = e. The position of the Fermi level... 

The mean diffusion distance over the cooling period subsequent to Tc is proportional to (fD where the integration is from the time of Tc to the time of room temperature. The concept of Tc dictates that mid-diffusion distance (fDdty subsequent to Tc is significantly smaller than the half-thickness of a thin slab (one-dimensional diffusion), or the radius of a sphere or long cylinder. Denote the half-thickness and radius as a. Therefore,... 

Figure 5-12 Fraction of mass loss due to diffusion in a thin slab with half-thickness a (solid curve) and a solid sphere with radius a (dashed curve) for uniform initial concentration and zero surface concentration with no growth. Some specific values are as follows (Fi for slab F2 for sphere) ...

Compared with one-dimensional diffusion in a plane sheet, for the same a value (such as a = 0.5), the fraction of mass loss is much larger for the solid sphere (T=0.9484) than for the planar slab (7=0.5622). To reach the same degree of mass loss (such as 50%), a smaller value is needed for the sphere (a = 0.0305) than for the thin slab = 0.1963). The difference in terms of is a factor of 6.4. Because the definition of is jD(f)df/a, by comparing with Equation 5-67b, we see that is proportional to 1/G. The difference in the value of for the same degree of mass loss for spherical and plane sheet shapes roughly explains the difference between G values (55/8.65 = 6.4) for spherical and plane sheet shapes. 

Plane sheet bounded by two parallel surfaces For the case of one-dimensional diffusion in a thin slab with half-thickness of a, the diffusion equation is... 

Measurement of the transmittance and reflectance of a slab for light at near-normal incidence. The samples must be sufficiently transparent for measurable transmission in thin slabs, but not as transparent as required in method 1. 

Consider the waves scattered by isotropic dipole oscillators in the thin slab of matter shown in Fig. 9.3 only part a is of concern at the moment. These waves add vectorially at point P to produce the resultant forward-scattered wave s the important point, which is by no means obvious yet, is that this resultant scattered wave is phase shifted 90° relative to the incident wave (in addition to the phase shift between the oscillators and the incident wave). The background necessary to show this has been presented in Chapter 3 Fig. 3.8 is similar to Fig. 9.3 except that in the former the scatterers were arbitrary particles. The transmitted field t at P is the vector sum of the incident field and the fields scattered by all the oscillators. If we assume that the direction of vibration of the incident wave is not rotated as it propagates through the slab, the transmitted field is given by (3.39) ... 

Faxvog, F. R., and D. M. Roessler, 1981. Optical absorption in thin slabs and spherical particles, Appl. Opt., 20, 729-731. 

When a polymer is initially in the dry state, solvent must penetrate into the network by diffusion. When the polymer is rubbery, this diffusion process is rate limiting. If the polymer is in the form of a thin slab, then solvent uptake will initially be correlated with the square root of time [30,31]. When the polymer is in an initially glassy state, swelling kinetics become more complicated [30, 32-34]. While solvent diffusion into the polymer still initiates the swelling... 

Fig. 9. Illustration of moving front model for swelling of a glassy polymer gel. Gel assumed to be thin slab. t0 Initially dry glassy state. t, At early and intermediate times after immersion in swelling solution gel contains glassy core and swollen rubbery periphery, with fronts separating the two phases. Core constraints swelling of periphery to occur only normal to front. t2 After fronts meet, swelling constraint vanishes, and swelling permitted in all directions. [Adapted with permission from Ret 24. Copyright CRC Press, Inc. Boca Raton, FL]...

Characteristic product shape thin slab extrusion granules spherical drops grains -in. particles... 

The principle of the mechanical measurement of the friction coefficient of a gel is schematically shown in Fig. 1. A thin slab of a gel of thickness d is held in... 

The residue insoluble in H2S04 is fused with Na202 poured into thin slabs and cooled. Ir is oxidized in the fusion of IrC>2, which is insoluble in H2O, Ru and Os form soluble sodium salts and are separated from the Ir by filtration, The insoluble Ir02 is dissolved m aqua regia, and ammonium hexachloroiridate(lV) is precipitated by the addition of NH4CI. Calcining yields pure Ir sponge. 

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