. Typical cases of the deterioration of muntz metal (60:40 brass) by selective corrosion. . e filled by the pulverulent copper which resulted from thecorroded /3 crystals. In the bolts described (type 1), the attack,though similar, is very different in regard to the rate at which thecorrosion of the a phase follows that of the /3. The attack of thisconstituent follows almost immediately that of the (3 grains, theintermediate layer in which only the 0 is attacked averaging mm in depth. The same is true of the condenser tube(type 3a); the deterioration of the a follows very quickly that
. Typical cases of the deterioration of muntz metal (60:40 brass) by selective corrosion. . e filled by the pulverulent copper which resulted from thecorroded /3 crystals. In the bolts described (type 1), the attack,though similar, is very different in regard to the rate at which thecorrosion of the a phase follows that of the /3. The attack of thisconstituent follows almost immediately that of the (3 grains, theintermediate layer in which only the 0 is attacked averaging mm in depth. The same is true of the condenser tube(type 3a); the deterioration of the a follows very quickly thatof the 0. 3. BEHAVIOR OF « BRASS UNDER SIMILAR CONDITIONS The behavior of a brass—that is, brass in which the copper ishigh enough so that the /3 constituent is entirely absent—whenplaced in comparable conditions is of interest. Fig. 10b illus-trates how this behavior differs from that of metal containingboth phases. The material here shown is from brass bolts which B Jour. Inst, of Metals, 1914, XI, p. 235; ibid., 1915, XIII, p. 80. i6 Technologic Papers of the Bureau of Standards. a /;,,<•** ???? t: ^ /.• - \ - * wJ-yi . ~^. .^ I „-:#; . ., ,<-i? • ^S^itC^i ?.--i:V*- • \4l* P$MiB i^^p^^v«^ ui ^Sk\-»- Fig. io.—Method of dezincification (a) Method of attack within the /3 crystals. The attack here as shown by the large central & grain is nota gradual one but abrupt and complete. (X500.) Etching, ammonium hydroxide and hydrocenperoxide. (6) Corrosive attack of a brass. The material (bolts) was used in a water rheostat. The attack inducedby the external emf is very complete and shows a slightly greater rate of attack at the crystalboundaries. (X500.) Etching, ammonium hydroxide and hydrogen peroxide. Deterioration of Muntz Metal 17 were used in the construction of a water rheostat. The macro-scopic appearance is very similar to that of attacked Muntz 106 shows, however, that the method of attack is very dif-ferent. The normal (i. e., unchanged)
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