A new microencapsulation was established in which small microcapsules with a hydrophilic polymeric wall could be fabricated, capsulizing the water‐soluble content. The new microencapsulation is based on an emulsion interfacial reaction technique that combines the characteristics of an interfacial reaction and conventional emulsion processes. In this technique, hydrophilic polymers [poly(vinyl alcohol) and chitosan] were used as the wall material of the microcapsules. The microencapsulation process was composed mainly of the following steps: preparation of a water/oil (w/o) emulsion 1 containing hydrophilic polymers and a water‐soluble core material and w/o emulsion 2 containing a water‐soluble crosslinking agent and catalyst; the formation of microcapsules by mixing emulsion 1 and emulsion 2; and washing and drying the formed microcapsules. In the new technique an insoluble polymer film was formed easily by the fast crosslinking reaction on the surface of tiny emulsified polymer solution particles in contact with the emulsified crosslinking agent solution particles under mixing with high speed agitation. Thereby, small stable microcapsules were formed. The emphasis in this study was on the establishment of the microencapsulation process by which microcapsules were formed and controlled. The microencapsulation was characterized by analysis of the size distribution of microcapsules fabricated with process conditions. The clarification of the effect of the preparation conditions was also made on the morphology and diameter of the microcapsules. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1645–1655, 2000
Fig. 4-Electron micrographs of the alloy aged at 823 K for 20 min: (a) BF (b ) An SADP taken from an area covering (␣ ϩ B2) particle and -carbide lamella. The foil normals of the ␣ and -carbide are [001] ␣ and [011] , respectively (hkl ϭ ␣, hkl ϭ B2, and (hkl) ϭ carbide). (c) and ( d ) 100carbide and 100 B2 DF images, respectively. 15. T.
Roll processing technology has recently made great advancements to meet the demands for enhanced surface properties of rolled products and diversified consumer needs. Continuous efforts also have been made to improve the quality of work rolls, specifically in wear resistance, strength, fracture toughness, and thermal fatigue properties. [1,2,3] The prime objectives in the development of advanced work rolls are to improve the surface quality of rolled products and to extend the life of rolls themselves. To achieve these objectives, it is essential to understand fracture properties that directly affect the surface roughness, spalling, failure, etc.Fracture toughness, which is used to evaluate the structural stability of materials, is one of the most important material properties to be considered when designing structures and selecting structural materials. To improve fracture toughness, systematic studies on its correlation with the microstructural characteristics are highly required; specifically, clarification on the microfracture mechanism based on the microstructural control of each material concerned should proceed. [4] For example, fracture toughness in ductile materials is strongly affected by the presence of secondphase particles that induce the dimple formation by void initiation and propagation. When the second-phase particles are coarse and very brittle, they often induce cleavage fracture and deteriorate the material properties. Thus, the improvement of fracture toughness can be achieved by clarifying each microstructural factor involved in each microfracture mechanism. Work rolls can be fractured unexpectedly by spalling or thermal fatigue caused by the growth of internal cracks or by the roughening of the roll surface. This results from the repeated formation of thermal-fatigue cracks due to the abrupt temperature rise arising from the contact with high-temperature rolled plates and the ensuing drop in temperature by cooling water, and from the repeated impact load and the increased rolling load caused by abrupt intrusion of rolled plates. [5][6][7][8] Accordingly, analyses of the microstructural factors determining fracture properties are critical in establishing the overall rolling conditions, such as the roll surface roughness and the roll life.The present study aims at providing the basic data for the establishment of using conditions of work rolls by investigating the microstructure, hardness, and fracture tough-GWIHWAN BYUN, Section Manager, is with the Hot Rolling ness of the five currently commercialized work rolls and by clarifying their respective fracture mechanisms. They are high speed steel roll (HSS roll), high chromium cast iron roll (Hi-Cr roll), Ni-grain cast iron roll (Ni-grain roll), Adamite roll, and ductile cast iron roll (DCI roll). The microfracture behavior was observed by using an in situ loading stage installed inside a scanning electron microscope (SEM) chamber, while simultaneously measuring apparent fracture toughness. These experiments enable evaluation and interpretation...
Two types of Pd nanoparticle catalysts were prepared having 2-4 nm particle size using silica gel and porous polymer beads as solid supports. 2-Pyridinecarboxaldehyde ligand was anchored on commercially available 3-aminopropyl-functionalized silica gel followed by Pd metal dispersion. Bead-shaped cross-linked poly(4-vinylpyridine-co-styrene) gel was prepared by an emulsifier-free emulsion polymerization of 4-vinylpyridine, styrene and divinylbenzene in the presence of ammonium persulfate and subsequently dispersing the Pd metal on the synthesized polymer. These catalysts were characterized by SEM, TEM and ICP techiniques with respect to appearance, size and possible leaching out, respectively. Furthermore, the reactivity of these catalysts was tested on hydrogenation of various α,β-unsaturated carbonyl compounds using aqueous solvent under a hydrogen balloon (1 atm). The results showed that the Pd dispersed on silica was a more efficient catalyst than Pd dispersed on polymer and the former could be recycled more than 10 times without considerable loss in activity.
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