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e s e a r c h the mass has particle diameter less than d 0.5 ). The results showed that there was a marked difference in dissolution time of the various aluminas; in fact more than one order of magnitude. The best dissolution behaviour was observed for the ‘normal’ metal grade alumina, as shown in Figure 9. In this case relatively short dissolution times were observed, similar to those previously observed for commercial aluminas in cryolite. The longest dissolution times were observed for crushed MG alumina, calcined at 1,600°C, where the dissolution time was of the order of 5 to 20 minutes in the alumina concentration range of 1 to 2 wt-% (see. Fig. 9). Even crushed MG alumina pre-dried to 300°C, showed dissolution times 4 to 10 times higher than the ‘normal’ grade alumina in this concentration range. In view of the observations made in these experiments it appears that the fineness of the alumina is a determining factor for the dissolution process. A high content of the alpha phase seem to have an additional detrimental effect, i. e. it increases the time of dissolution. It has previously been found that high alpha alumina dissolves somewhat more slowly than the gamma phase alumina in cryolitic melts at 1,030°C [2] and it is possible that this difference is enhanced in lowmelting baths, where the solubility of alumina is lower. However, no simple relationship could be found between Type, description Term d 0.5 /µm Metal grade, commercial alumina MG 82.95 A-152, fine, 1 µm, highly calcined alumina, from Alcoa A152 1.86 Crushed MG * alumina, calcined at 1600°C CMG 1600 4.51 Crushed MG alumina, pre-dried at 300°C * MG – Metal Grade CMG 300 5.45 Table 3: Materials tested and cut sizes (see text) these parameters and the time of dissolution. For example, the slowest dissolving alumina in these experiments was the CMG 1600 material. Table 3 shows that 50% of the mass of this material has particles with diameter 4.5 µm or less (d 0.5 =4.507 µm), compared to 1.86 µm for the A152 material. These materials have both been calcined at 1,600°C and have thus been converted to 100% α-alumina, but the finer A152 (d 0.5 =1.86) dissolves more rapidly than the coarser CMG 1600 (d 0.5 =4.5 µm). conclusion It can be concluded from this investigation that if the only selection criterion is the rate of dissolution in low-melting baths, the normal industrial grade alumina is the best choice. The main concern will probably be the ability to operate the bath at near saturation concentration with respect to alumina. Hence, the problem of maintaining slurry and avoiding forming sludge, i. e. alumina deposits, must be given high priority, and operating with fine-grained alumina might be Fig. 9: Results from three parallel runs with ‘normal’ MG alumina in low-melting bath. Time observed to obtain transparent melt after addition of batches of 0.5 wt-% alumina. Time plotted as a function of the concentration of alumina dissolved in the bath, determined from bath samples taken before the addition the only option. In that case finely ground low-calcined alumina appears to be the best choice. acknowledgement Permission to publish given by Golden Northwest Alumunum Holding Company, is gratefully acknowledged. references [1] E.J. Frazer and J. Thonstad, “Alumina solubility and diffusion coefficient in lowtemperature fluoride electrolytes”, to be published. [2] J. Thonstad, F. Nordmo, J. B. Paulsen, “Dissolution of Alumina in Molten Cryolite”. Met Trans. 1972, pp. 403-408. [3] J. Thonstad, A. Solheim, S. Rolseth, O. Skaar, “The Dissolution of Alumina in Cryolite Melts”, Light Metals 1988, pp. 655-661. [4] T. Beck and R. J. Brooks. “Non-Consumable Anode and Lining for Aluminum Electrolytic Reduction Cell”, United States Patent No. 5,284,562, 1994. [5] S. Rolseth, R. Hovland, O. Kobbeltvedt, ”Alumina Agglomeration and Dissolution in Cryolitic melts”, Light Metals 1994, pp.351-357. [6] O. Kobbeltvedt, S. Rolseth and J. Thonstad, “On the Mechanism of Alumina Dissolution with Relevance to Point Feeding Aluminium Cells”, Light Metals 1996, pp. 421-427. [7] R. G. Haverkamp, B. J. Welch and J. B. Metson, ”An Electrochemical Method for Measuring the Dissolution Rate of Alumina in Molten Cryolite”, Bulletin of Electrochemistry, Vol.8, pp.334-340, 1992. authors S. Rolseth, H. Gudbrandsen, K.S. Osen and J. Kvello are from SINTEF Materials and Chemistry, Trondheim, Norway. J. Thonstad is from Department of Materials Technology and Electrochemistry, Norwegian University of Science and Technology, Trondheim, Norway. 56 ALUMINIUM · 9/2009
ALUMINIUM CHINA 2009 exceedingly successful Those who attended ALUMINIUM CHINA 2009 some weeks ago, the fifth time that the event has taken place in China, could be forgiven for thinking that the industrial downturn and economic crisis have never spread as far as China. Shanghai is still buzzing with exhilarating business activities, entertainment and the spending spree mentality, and the world’s most important aluminium industry gathering of the year, ALU- MINIUM CHINA, was attended by 8,786 qualified trade visitors and over 4,000 exhibiting staff from 61 countries and regions, a recordbreaking result despite the difficult economic situation. ALUMINIUM CHINA 2009 brought together 265 exhibitors from 30 countries and regions, and 8,786 trade visitors, including 480 VIPs and 30 delegations from 32 provinces in China and 61 countries around the world. The number of visitor was up by 30% compared with the 2008 event and also a record compared to 2007 when the industry was at its peak. 47% of the visitors were from aluminium applications industries such as building and construction, transportation, electronics and machinery manufacturing, while nearly 66% of visitors had purchasing recommendation and decision-making authority. Leading the exhibitors this year were some of the industry’s top companies such as the Aluminium Corporation of China, Nanshan Aluminium, Dubal, Novelis, SMS Metallurgy, Siemens VAI, Wagstaff, Pyrotek, Jieru Heavy Industry Equipment, Fata Hunter, Achenbach, Toshiba Mitsubishi-Electric Industrial Systems and others, who presented the latest products and leading technologies and, taken together, inspired the Asian and the global community with confidence in an imminent recovery. The performance of the show in Shanghai generated superb feedback from participants, and three-quarters of the international hall space had already been booked for the 2010 trade fair by the end of the event. The ALUMINIUM · 9/2009 on-site exhibitor survey showed that more than 92% of the exhibitors were satisfied or completely satisfied with their participation, 86% were satisfied with the number of visitors, while 87% are satisfied with the visitor quality. The marketing manager from Emmegi China commented: “We received a huge number of professional visitors this year, who were genuinely interested in our products. We rebooked our stand for 2010 as soon as we could and expect to expand our market activities even more next year.” The on-site visitor survey showed the same encouraging results, with 97% of those attending being content with their visit this year. The deputy plant manager for the casting unit of the Chinalco Luoyang branch declared: “I was able to achieve all my goals this year: to meet old friends, find out about the latest technologies, and reach agreements with a number of suppliers at the show.” The associated 2009 China Aluminium Fabrication Forum, organised by the China Non Ferrous Metal Industry Association along with China’s aluminium information and consultancy provider Antaike, was moderated by experts and senior executives from IAI, AA, JAA, London Metal Exchange and provided important information on the latest trends in More than 8,700 business people visited the AluMiniuM ChinA 2009 fair Schweißen & Schneiden 2009 Die ganze Welt der Schweißtechnik steht im Mittelpunkt der Fachmesse „Schweißen & Schneiden. Vom 14. bis 19. September 2009 präsentiert die international wichtigste und umfassendste Messe der Branche in Essen einen lückenlosen Überblick zu aktuellen Entwicklungen und Innovationen rund um das Fügen, Trennen und Beschichten. Alle namhaften Hersteller sowie die Anbieter von Dienstleistungen werden ihre Inno the global aluminium market. In light of the positive feedback from exhibitors, organiser Reed Exhibitions has confirmed that ALUMINIUM CHINA 2010 will again be held at the Shanghai New International Expo Centre, from 9 to 11 June. ■ vationen vorstellen. Zur mittlerweile 17. Auflage dieser Messe werden rund 1.000 Aussteller aus über 30 Nationen erwartet. Aus circa 90 Ländern werden die Fachbesucher nach Essen reisen, um sich über das Weltmarktangebot zu informieren und Investitionen zu realisieren. Kontakt: Messe Essen GmbH www.messeessen.de E v E N t S 57 Reed Exhibitions
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