SynopsisMineralogical study of LD converter slag was carried out by means of microscopic and EPMA examinations and phosphorus was found to exist only in dicalcium silicate as solid solution. This led to the study of separation of dicalcium silicate from LD converter slag in order to remove phosphorus.When liquid slag was solidified slowly, most dicalcium silicate particles accumulated in the top part of the crucible and fewer in the bottom. The phenomena can be interpreted as follows; on solidification, dicalcium silicate is crystallized primarily and floats up owing to the difference of density between dicalcium silicate and residual liquid. By using this phenomena, we can separate LD converter slag into two layers, top and bottom in a vessel. As a result of slow cooling, CaO, Si02 and P205 are enriched in the top, and FeO, Fe203 and MnO in the bottom.Dicalcium silicate is apt to separate more efficiently with higher total iron content in slag, and at higher start temperature of cooling, close to liquidus temperature. The efficiency of separation was improved by blowing oxygen into the molten slag before cooling.
ABSTRACT:Static and dynamic swelling properties of cylindrical poly(N-isopropylacrylamide) (PNIPA) gels in water as well as in liquid paraffin (non-solvent for PNIPA gels) have been investigated by using a laboratory-made magnetic force-driven rheometer. In static tests (under a constant stress), the length and diameter of the gel sample in water increase with time due to stress-induced swelling. Relaxation times of the stress-induced swelling in both directions are identical within experimental error. The Poisson ratio decreases from $0:5 to $0:2 with time just after the application of the magnetic force. The dynamic tests (under sinusoidal forces) reveal large differences in the swelling behavior of the gels in water and liquid paraffin. In liquid paraffin, amplitudes of strains parallel and perpendicular to elongation
The kinetics of the shrinking of polymer gels induced by ultracentrifugal fields is investigated. A theory is proposed to describe the diffusion process of polymer networks under centrifugal fields. The initial shrinking rate is proportional to the ratio of the centrifugal force to the frictional force of networks. The shrinking attains the stationary state as a result of the balance between the centrifugal force and the swelling force of networks. The characteristic time for shrinking is of the order of a2/D where a and D are the stationary displacement and diffusion constant, respectively. We also present the experimental data for the shrinking of the poly(acrylamide) (PAAm) gels under ultracentrifugal fields. The shrinkage increases linearly with time in the initial stage whereas it reaches the steady state in the long time limit as expected by the theory. Each of longitudinal elastic modulus and friction coefficient of the PAAm gels is evaluated from the data on the basis of the theory.
KEY WORDSPolymer Gel / Swelling / Poisson's Ratio / Dynamic Viscoelasticity / Polymer gels in solvent show an interesting response to external stimulus. For example, a gel changes the volume when mechanical stress is applied to the gel, and the rate of volume change strongly depends on the sample dimension. The volume change responding to the applied stress originates from the fact that the polymer network and solvent molecules form a thermodynamical semi-open system, and this phenomenon has been considered to be a typical example of the stress-diffusion coupling. 1 Studies on swelling kinetics of the polymer gels after the application of mechanical stimulus have been made by employing so-called static methods, 2-5 such as continuous monitoring of the gel dimension after imposition of a step stress, and have shown that in the long time region the volume change can be written by a single exponential function; i.e., a single characteristic (or, relaxation) time governs the volume change to a new equilibrium state under deformation in that time region. 2-5 On the other hand, little is known on the swelling kinetics for the gels at short times, where a multi-exponential character is considered to become dominant for the volume change. 3,6 Studies in terms of dynamic viscoelasticity will be very useful to give the full picture of the swelling kinetics of the polymer gels. Conventional rheometers, however, cannot be used for this purpose; the rheometers require relatively large gel specimens to detect the mechanical response but the large specimens move the relaxation time far away from the measurable frequency range of the rheometers. A new type of rheomter, applicable to very small gel specimens, is needed to investigate the dynamic swelling properties of polymer gels. In this study we have made a new apparatus to observe the dynamic swelling behavior of polymer gels, and examined the frequency dependence of the dynamic Poisson ratio for a poly(N-isopropylacrylamide) (PNIPA) gel. A phenomenological theory of linear viscoelas- † To whom correspondence should be addressed. ticity to analyze the dynamic swelling behavior is also described briefly in this paper.Consider a time (t) profile of strain in response to an applied elongational stress (σ) of the following form
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