Document kDKQwE85kJZxVpg8a30w46gOb

w& [Quantitative Evaluation of Corrosive Conditions 1_____ 6y W. F. Sonwitt1 and I. Eisen uW-W' ilTAOft - *. V fllufC1 j Synopsis faces of each end`of the foil and fixed to the Transite base. = It was found possible to calibrate the effect of natural corrosion and of several artificial accelerated corrosion procedures on a metal by observation of the electrical resistance of a thin foil ribbon of the metal. With copper as the experimental sample, a linear relation was found between the dura tion of exposure to the corrosive procedure and the increase of resistance of the sample. This linear relation, which held true for natural corrosion and for all of the artificial procedures investigated, made it possible to develop a constant expressed as percentage increase in resistance per unit `time for the effect of each corrosive procedure. From the data collected this corrosive effect constant was computed for each of the corrosive procedures investigated. The constant obtained for each process is significant, of course, only for the particular metal used for the foil. It is believed that `.further experiments will show whether this method can be applied "to other -metals and more complex conditions and to the quantitative evaluation ' of corrosive atmospheres present in various locations. . . ..._ i Procedure - -- - -Five test samples as described were prepared. Before assembly each foil ' was cleaned with carbon', tetrachloride. Following assembly the length of foil between measuring points and the area of untinned foil exposed to "corrosion were determined. Several resistance measurements were taken over an ex tended period to establish the initial resistance of each sample. A standard measuring current of 0.1 amp. was used giving a current density of 100 amp. per sq. in. for the initial cross-sectional area of 0.001 sq. in. This current density was sufficiently various artificial pro accelerated corrosion test procedures low so that the heating effect of the cedures have been used in tests designed with each other,-and with atmospheric current could be neglected. Measure to simulate the effects of natural cor corrosion. -Bather, all previous work ments of resistance were made at stand rosion at an accelerated rate as a means was concerned with a specific corrosive ard conditions with a Leeds & North- for determining comparatively quickly condition-as it would affect a particular nip precision Kelvin bridge. the, probable effects of natural corrosion metallic sample. . .iSince accelerated test - After stable values for the resistance on a sample under test. - There is little methods are used more and more, a of the foil strips had been obtained in basis, however, on which quantitative -quantitative basis for -comparison of . repeated measurements,>4he foils were comparisons can be .made between different procedures .seems essential. subjected to various corrosive proce various artificial procedures and natural The first step was to select a test dures, as described below. corrosive processes. The - purpose of sample 'of such a ;nature as to provide: . Foil No. 1 was exposed to open air the work described was to investigate (-1) sensitivity-to a wide range of de-. j| conditions (industrial atmosphere) in a sensitive means for making such com grees of -corrosive, effect, and (2) a New York City. Resistance of this foil parisons. Tn this -project the relative significant,- accurate, quantitative de (V was measured at one-week intervals. severity of a natural corrosive process termination of corrosive - effect as a "Toil No. 2 was subjected to a 24- and of three artificial procedures was change .-in a .-physical characteristic, hr.. cyclic accelerated corrosion pro determined. The .rate of corrosion of after short increments of exposure time. cedure. Each cycle consisted of 7 hr. metals has previously. been measured It was found practicable to measure exposure, in a test chamber at room by the increase of the .electrical resist corrosive effect .in .terms of increase of temperature, to the mist' produced by ance of the metal. -Bums and Camp electrical resistance corresponding to atomizing a 10 per cent aqueous sodium bell,1 for instance, reported in 1929 on reduction in cross-sectional area caused chloride solution with filtered air, the use of this-method for observing by corrosion of a corrosion-sensitive followed by heating in an air oven for the corrosive deterioration of lead by conductor. In order to provide taaxi- 45 min. at 125 O., followed by slow acetic acid vapors. Snelling2 used the mum surface area with minimum cross- ' cooling to room temperature in the oven resistance increase of a metallic layer to sectional area, the test sample selected for the remainder of the 24-hr. cycle. detect perforation of a paint coating was a metal foil ribbon.- -With such a --This -foil was measured at five-cycle coveringthemetal,andthuscomparedthe --sample,"-significant increases of,resist- intervals. relative qualities of. protective coatings ance were obtained for small reductions Foil No. 3 was -eubjected to a dif exposed to corrosive media. It was also., in cross-section. ferent 24-hr. cyclic accelerated cor foundthat adefmiterelationship seemed The corrosion-sensitive. test sample rosion ' procedure! ^Each cycle con- to exist between the resistance, diam- used -was a. strip.-of copper foil 0.001 r^sisted of 7 hr.^exposure, in a test cham - eter, find length of .exposure of copper . in. thick, 1 in. wide, and approximately ber-at'38-<3.,ti)<the Bpray and mist . wires to atmospheric corrodon.* ^>55 in. long.- i This copper foil ribbomwas ^^jprodiiced Sjy ^atomizing a 20 per cent . ^oweverj^e-aiithqre-are aot aware wound' 'bac'k and' f*ort"h around' .two par j iaqueous sodium chloride solution with ofj any -previous attempt to compare . allel rows of pyrexglass rods mounted on U qjreheated, saturated -air, `followed by quantitatively the severity of various _ a_Transite; jbpse. For measurement ^I Seating-in an air oven for 45 min. at TOTE.-^biecnssroN iof this taper .is purposes, current-was fed into the cop ! ^125'C., followed by slow cooling to per foil through . ' . the don xjitlift author. A.ddreM &11 - fommuni- ~T3nounted"St each end of tlm'lHinfflte soQjjhe ^24^hr. -cycle. This stMjase which ..clamped around the . ends ;|Jg|fo5i^was AlsoJfaheasured aat ..five-cycle ^bf.the foiL'^Toprevent conp$dn^;l andrthe.foil `j3Pet<Siitiid - .jiH:. itAttjtbelabomtory mm DSW 587043 STLCOPCB4092378