Cerium(III) sulfide (Ce 2 S 3 ) powder was synthesized via the sulfurization of ceria (CeO 2 ) powder using carbon disulfide gas. Single-phase ␣-Ce 2 S 3 could be formed via sulfurization at 973 K for 28.8 ks. The preparation of ␣-Ce 2 S 3 became feasible at low temperature, in comparison to sulfurization using hydrogen sulfide gas. According to the fact that the formation of ␣-Ce 2 S 3 was accelerated by the addition of carbon black to the CeO 2 powder, carbothermic reduction was considered to become a dominant reaction, as the temperature increased. To obtain the activation energy for the densification of ␤-Ce 2 S 3 powder, which was prepared by vacuum heating ␣-Ce 2 S 3 , the data of densification by hot pressing was analyzed by a kinetic equation that was proposed by other researchers. As a result, the sintering behavior could be best explained by a grain-boundarydiffusion mechanism that had an apparent activation energy of 382 kJ/mol.

No abstract

No abstract

Instead of the conventional sol-gel process in which heat treatment is used to form a dense composite film after dipping/withdrawing a substrate into/from the sol, a new solgel process incorporating ultraviolet (UV) irradiation at ambient temperature has been attempted to improve the alkaline corrosion resistance of aluminum. A sol-gel film prepared by UV irradiation at ambient temperature indicated that alkaline corrosion resistance is superior in the range of 2.4 times to 2.6 times that of the conventional composite film heated at 573 K. The densification of the coating layer due to the elimination of residual organics induced by photoexcitation was responsible for the improvement in alkaline corrosion resistance. The high alkaline corrosion resistance of the irradiated film may be attributed to the formation of a dense coating layer and the self-repairing action caused by repetition for preparation and dissolution of the reactant in the penetrating path of NaOH solution into the composite film.

The classification and acidic leaching behaviors of phosphor sludge have been examined to establish the recycling system of rare earth components contained in fluorescent lamp waste. At first, separation characteristic of rare earth components and calcium phosphate in phosphor sludge was investigated by pneumatic classification. After pneumatic classification of phosphor sludge, rare earth components were leached in various acidic solutions and sodium hydroxide solution. For recovery of soluble component in leaching solution, rare earth component was recovered by treatment processes such as hydroxide and oxalate precipitations. The experimental results obtained are summarized as follows:(1) In classification process, rare earth components in phosphor sludge were concentrated to 29.3 % from 13.3 %, and its yield was 32.9 %.(2) In leaching process, sulfuric acidic solution was more effective one as a leaching solvent of rare earth components than other solutions. Yttrium and europium in phosphor sludge were dissolved in sulfuric acidic solution of 1.5 kmol / m 3 concentration, and other rare earth elements were rarely dissolved in leaching solution. The leaching degree of yttrium and europium were respectively 92 % and 98 % in following optimum leaching conditions ; sulfuric acid concentration is 1.5 kmol / m 3 , leaching temperature 343 K, leaching time 3.6 ks and pulp concentration 30 kg / m 3 . (3) In recovery process, yttrium and europium could be recovered to above 99.1 % by means of hydroxide treatment and oxalate precipitation method.(4) Yttrium and europium from phosphor sludge contained in fluorescent lamp waste were recovered effectively by three processes of pneumatic classification, sulfuric acid leaching and oxalate precipitation methods. Their recovery was finally about 65 %, and its purity was 98.2 %. KEY WORDS : Fluorescent Lamp, Phosphor, Pneumatic Classification, Sulfuric Acid Leaching, Rare Earth Elements, Separation and Recovery