Y. He et al. /Ceramics Intemational 34(2008)1399-1403 equipment and process is simple and efficient. But the quality of the product is difficult to control because the supersaturation is infuenced by many factors, which makes the scale-up and ndustrial production of Mgo whiskers very complicated Besides, corrosive reactants and byproduct may be detrimental to the equipments. Conversion of magnesium hydroxide whiskers is a prospective way to produce magnesia whiskers industrially Though the shape of MgO whiskers by this method is rough and some whiskers are aggregated, single crystal structure can be preserved as verified by electron diffraction. Great care must be taken to keep the single crystal structure and avoid aggregating during heating and calcinations More studies should be made hopefully to compare the mechanical properties and strength ening effects of the whiskers References [1] Y.s. Yuan, M.S. Wong, S.S. Wang, Superconducting properties of MgO. whisker reinforced BPSCCO composite, Physica C: Superconduct. 250 Fig. 6. Electron diffraction pattern of Mgo whiskers obtained by conversion 2]A. Yamaguchi, S. Hashimoto, Growth of magnesia whiskers, Ceram. Int 18(5)(1992)301-305 more gas molecules are liberated, the more prone the surface of 3] B.D. Brubaker.(The Dow Chemical Company ) US patent 3 711 599, 13 precursor whiskers will be broken. More important, magnesium (41 Z Wei. H Qi, P. Ma, J. Bao, A new route to prepare magnesium oxide hydroxide crystal has a layered structure and the forces between whisker, Inorg. Chem. Commun. 5(2)(2002)147-140 layers of Mg(OH)2 are relatively weak hydrogen bonds. When [5] Q Wei, Synthesis, properties and applications of nanorods and nanowires. magnesium hydroxide whiskers are heated slowly, the water Ph. D. thesis of Harvard University, 2001, 23-29 vapor will be liberated easily through the channels between [6] B. Soylu, N. Adamopoulos, D M. Glowacka, J.E. Evetts, Composite layers in Mg(OH)2 without destruction of the needle shap reaction texturing of superconducting ceramic composites, Appl. Phys. Lett.60(25)(1992)3183-3185 Besides, only water vapor is formed in the conversion of [7 E.E. Schrier, H.M. Clark, Interaction in salt vapors and activity coeffi- esium hydroxide while some corrosive gases are often cients in the potassium chloride- magnesium chloride system, J. Phy serious corrosion to the equipment. Direct decomposition of 8S. Hayashi, H. Saito, Growth of magnesia whiskers by vapor phase magnesium hydroxide chloride whiskers will result in the [9] M.G. Kim, U. Dahmen, A W. Searcy, Transformations in the decom- destruction of the needle shape [11] position of Mg(OH)2 and MgCO3, J. Am. Ceram Soc. 70(3)(1987) 146-154. 4. Conclusions [10] N. Thangaraj, KH p ott, U. Dahmen, HVEM studies of the wo main methods for preparation of MgO whiskers were compared. Whiskers prepared by hydrolysis of melt have [11] S Xia, P Xing, S Gao, Studies on the basic compounds of magnesia cement: the thermal behavior of magnesium oxychlorides, Thermochim uniform diameter, straight stem and smooth surface. The Acta183(5)(1991)349-363more gas molecules are liberated, the more prone the surface of precursor whiskers will be broken. More important, magnesium hydroxide crystal has a layered structure and the forces between layers of Mg(OH)2 are relatively weak hydrogen bonds. When magnesium hydroxide whiskers are heated slowly, the water vapor will be liberated easily through the channels between layers in Mg(OH)2 without destruction of the needle shape. Besides, only water vapor is formed in the conversion of magnesium hydroxide while some corrosive gases are often evolved in conversion of other precursors, which may cause serious corrosion to the equipment. Direct decomposition of magnesium hydroxide chloride whiskers will result in the destruction of the needle shape [11]. 4. Conclusions Two main methods for preparation of MgO whiskers were compared. Whiskers prepared by hydrolysis of melt have uniform diameter, straight stem and smooth surface. The equipment and process is simple and efficient. But the quality of the product is difficult to control because the supersaturation is influenced by many factors, which makes the scale-up and industrial production of MgO whiskers very complicated. Besides, corrosive reactants and byproduct may be detrimental to the equipments. Conversion of magnesium hydroxide whiskers is a prospective way to produce magnesia whiskers industrially. Though the shape of MgO whiskers by this method is rough and some whiskers are aggregated, single crystal structure can be preserved as verified by electron diffraction. Great care must be taken to keep the single crystal structure and avoid aggregating during heating and calcinations. More studies should be made hopefully to compare the mechanical properties and strength￾ening effects of the whiskers. References [1] Y.S. Yuan, M.S. Wong, S.S. Wang, Superconducting properties of MgO￾whisker reinforced BPSCCO composite, Physica C: Superconduct. 250 (3–4) (1995) 247–255. [2] A. Yamaguchi, S. Hashimoto, Growth of magnesia whiskers, Ceram. Int. 18 (5) (1992) 301–305. [3] B.D. Brubaker. (The Dow Chemical Company), US patent 3 711 599, 13 April 1970. [4] Z. Wei, H. Qi, P. Ma, J. Bao, A new route to prepare magnesium oxide whisker, Inorg. Chem. Commun. 5 (2) (2002) 147–149. [5] Q. Wei, Synthesis, properties and applications of nanorods and nanowires, Ph.D. thesis of Harvard University, 2001, 23–29. [6] B. Soylu, N. Adamopoulos, D.M. Glowacka, J.E. Evetts, Composite reaction texturing of superconducting ceramic composites, Appl. Phys. Lett. 60 (25) (1992) 3183–3185. [7] E.E. Schrier, H.M. Clark, Interaction in salt vapors and activity coeffi- cients in the potassium chloride-magnesium chloride system, J. Phys. Chem. 67 (1963) 1259–1263. [8] S. Hayashi, H. Saito, Growth of magnesia whiskers by vapor phase reactions, J. Cryst. Growth 24–25 (1974) 345–349. [9] M.G. Kim, U. Dahmen, A.W. Searcy, Transformations in the decom￾position of Mg(OH)2 and MgCO3, J. Am. Ceram. Soc. 70 (3) (1987) 146–154. [10] N. Thangaraj, K.H. Westmacott, U. Dahmen, HVEM studies of the sintering of MgO nanocrystals prepared by Mg(OH)2 decomposition, Ultramicroscopy 37 (1–4) (1991) 362–374. [11] S. Xia, P. Xing, S. Gao, Studies on the basic compounds of magnesia cement: the thermal behavior of magnesium oxychlorides, Thermochim. Acta 183 (5) (1991) 349–363. Fig. 6. Electron diffraction pattern of MgO whiskers obtained by conversion. Y. He et al. / Ceramics International 34 (2008) 1399–1403 1403