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Selective corrosion in a hot hydrochloric acid service was noted in a narrow band of the heat affected zone of a commercially fabricated zirconium weldment. Little attack was present on the weld proper or the parent stock. The selective attack has been found to be intergranular in nature and associated with the presence of a precipitated phase in the grain boundaries. The particular precipitated phase required for this attack has been duplicated in bulk samples by specific heat treatment, as well as in experimental weldments. Two methods of prevention of this localized attack near welds have been evaluated; namely: (1) Use of high purity zirconium, and (2) heating of commercially pure zirconium weldment at 1800 F followed by a water quench. Possible mechanisms for the microstructural changes and for the corrosion attack are discussed. 6.3.20, 3.2.2, 4.3.2, 3.7.3

Vol. 43, No. 7 boron oxide and the various boric acids, and from the high intensity of the light scattering observed, it can be concluded that the heterogeneities must be quite large, perhaps of the order of 1000 a.u. across. Therefore, if these heterogeneities do indeed exist, they must be quite disordered in internal structure. In this connection, it is interesting to note that the molten glasses of high water content are also strong scatterers of light. Evidently, rather large regions of the crystalline precursor of the glasses, orthorhombic metaboric acid," are retained in disordered form rather than being broken up at the low preparation temperatures employed. This type of behavior has been noted for vitreous S O z by Florinskaya and Pechenkina.I6 It is expected that much of the speculative nature of the conclusions concerning the heterogeneity of the glasses under consideration will be removed on completion of a quantitative light-scattering study in this laboratory. IV. Conclusions.-HYDROGEN * -BORON 0 -OXYGEN Fig. 4. Schematic diagram of proposed structure of BzOa-H20 glass showing region of high hydrogen bond density embedded in &Oa matrix.The triangular coordination of oxygen around boron, characteristic of vitreous BzOa, is, for the most part, retained in glasses with compositions corresponding to B203. 0.42H20, B203.0.50H20, and Bz03.0.63Hz0. I t is highly probable that these glasses of high water content are heterogeneous, containing disordered regions of high hydrogen bond density embedded in a matrix very similar to vitreous BZ03. B a 3 in composition and bonding, as is shown schematically in Fig. 4. From the breadth of the halos on the diffraction patterns i t is clear that no extensive regions with a degree of order approaching crystallinity exist in the glasses. However, from what is known of the refractive indices of vitreousThe effect of water content on the corrosion resistance of a proprietary borosilicate glass is discussed. Several glass smelting methods were employed to produce an alkali borosilicate glass with various amounts of water within the body of the glass. Infrared studies in the region 2.7 to 3.0 p showed that a decrease in the 0-H groups in the glass resulted in a decrease in the amount of absorption in this region. The corrosion resistance of these glasses was measured in the vapor phase over boiling 20% hydrochloric acid. A correlation between water content and corrosion resistance is shown.