Corrosion of Metal Fastenings in ZincChloride-Treated Wood R. H. BAECHLER, Forest Products Laboratory, Madison, Wis. INCE zinc chloride is the
.
driven into the wood. They were At the present stage of the tests it appears arranged in six vertical rows of water-soluble preservative that the corrosion of wire nails in wood lreated ten units (Figure 1). The first most widely used in the and fourth rows each contained with zinc chloride and exposed to a moderately U n i t e d States, the total conten No. 4 wire nails, the second humid interior or to outside conditions such as and B t h rows each contained ten sumption being greater than that No. 6 1.5-inch (3.8-cm.) brass prevail at Madison, Wis., is not appreciably of all other preservative salts screws, and the third and sixth combined, reliable information greater than the corrosion occurring in untreated rows each contained ten 1.5-inch about its effect on the corrosion galvanized iron nails. The top wood, provided the treated wood is seasoned before three wire nails and brass screws of metal f a s t e n i n g s i n wood the nails are driven. Nails driven into wet of each row were weighed to treated with it is highly desirwithin 10.01 gram, with a view treated wood and exposed to the foregoing condiable. Tests w e r e s t a r t e d at to obtaining a quantitative exlions corrode rapidly during the drying period. this laboratory in 1928 t o obp.ression for the extent of corrosion. P r e l i m i n a r y t e s t s had tain authentic information on the It s e e m inadvisable to use wire nails in zincshown that the wire nails and c o r r o s i o n of steel, brass, and chloride-treated wood that is to be exposed to very brass screws could be driven into galvanized iron fastenings in the wood and withdrawn with no humid conditions. Corrosion of wire nails in wood treated with zinc chloride appreciable loss in weight, but the wood treated with zinc chloride apparently is galvanized nails could not beand exposed to: (a) a dry incause of the c h i p p i n g of t h e not modiJied greatly by painting the wood or by terior, (b)an interior of moderate zinc coating. The left half of h u m i d i t y , (c) a n e x t r e m e l y adding sodium dichromate to the treating solueach piece containing rows 1, 2, humid interior, (d) outdoor conand 3 was given three coats of tion. The corrosion of brass and galvanized iron paint including a priming ditions. The tests are to extend fastenings in wood treated with zinc chloride is coat; the right half was left unover a p e r i o d of 20 y e a r s or painted. probably slight under all conditions of humidity. until 1948. The data obtained EXPOSURE. The pieces were during the first five gears, howt h e n r e a r r a n g e d i n t o fortv ever, &e considered -of sufficient interest t o be given here groups of five pieces. Each group contained one piece from each of the four treatments and one untreated piece. Ten groups were as a progress report. loosely piled in a room kept a t a relative humidity of 30 per cent and a temperature of 80" F. (26.7' C.). Ten groups were piled CONDITIONS OF TESTS in a room kept at 65 per cent relative humidity and 80" F. PFLESERVATIVE TREATMENT.The wood selected for the tests Ten groups were piled in a room kept a t 90 per cent relative was chiefly the sapwood of air-dried ponderosa pine, a species that humidity and 80" F. The remaining ten groups were placed out is fairly easy to impregnate with liquids, The wood was sawed of doors on a fence at Madison, Wis. into two hundred pieces, 2 X 10 X 18 inches (5.1 x 25.4 X 45.7 cm.) in size, and divided into INSPECTION. I n making inspections, one five groups, four of which were treated with group of test pieces was removed from each p r e s e r v a t i v e . The fifth group, comprising of the 30, 65, and 90 per cent r e l a t i v e pieces that contained some heartwood, was left humidity rooms and one group from the untreated to serve as control. All treated pieces were weighed before and after treatment so fence. The removed pieces were then split that the amount of salt in each piece was known; along the rows of nails and screws so that the pieces that took a treatment considerably the fastenings could be pried loose and exdifferent from the average were discarded. amined for signs of c o r r o s i o n . The top The first group was Treated with 3.37 per cent zinc chloride solution, an average net rethree wire nails and screws from each row tention of 1.41 ounds of dry salt per cubic foot were rubbed with a coarse eraser to remove of wood (22.6 per cubic meter) being obcorrosion deposits. It was sometimes necestained. The treating solution was then diluted sary to use sandpaper t o remove firmly adto 1.78 per cent and the second group treated. An average net retention of 0.74 pound of salt hering rust spots, and, although this was per cubic foot of wood (11.8 kg. per cubic meter) done as carefully as possible, a little unwas obtained in this group. The third group corroded metal was doubtless lost. The was treated with 3.66 per cent zinc chloride heads of the fastenings that were painted solution and an average net retention of 1.51 pounds of zinc chloride per cubic foot of wood were immersed in chloroform for about an (24.2 kg. per cubic meter) was obtained. The hour, after which the paint was scraped off. fourth group was treated with a solution conThe weights of the wire nails and the brass taining 2.4 per cent zinc chloride and 1.2 per screws were then taken and compared with cent sodium dichromate. An average retention of 1.51 pounds of mixed salt per cubic foot the original weights. of wood was obtained. The determination of the loss in weight After treatment, the first and second groups shown by the upper three wire nails and were laid in open piles under cover and allowed screws was supplemented by an observation to dry until they had returned to approximately their original moisture content. This of the general appearance of all of the nails drying period required about 6 months. The and screws. In this way corrosion that third and fourth groups were not dried after FIGURE 1. ARRANGEMENT OF was within the error of weighing could be treatment, NAILS AND SCREWSIN A r e p o r t e d ; f o r example, fastenings whose FASTENINGS. Nails and screws were then TYPICAL TEST PIECE
S
E,.
1336
December. 1934
INDUSTRIAL AND ESGINEERING CHEMISTRY
loss in weight was recorded as zero could be described as being “bright as new,” “slightly rusty,’’ or “moderately rusty” as the case might be. Also the presence of pitting, which is probably of more practical significance than the total loss in w e i g h t , could be observed. The wire nails that were entirely or almost entirely covered with rust w e r e d e s c r i b e d as “very rusty,” those that were about half c o v e r e d with rust were “moderately rusty,” and those that had scattered rust spots with most of the surface of the n a i l uncorroded were “slightly rusty.” As might be expected, some of the nails could readily be placed in one of the three classes whereas others were on the border line.
1337
vanized nails and brass screws showed slight corrosion only under the most severe conditions of treatment and humidity. The addition of sodium dichromate had no marked influence on corrosion nor did the painting of the wood. .-. 0.04
0.0Z
0 O W 0.06
aoa
os2 0 0.08 056
,
,
,
,
,
,
rEJr ,
,
FENCE
,
,
,
,
,
,
RESULTS OF INSPECTIONS AFTER FIVEYEARS To date a total of six inspections has been made of the treated and untreated pieces containing the steel, brass, and galvanized iron fastenings. The condition of the wire nails a t each i n s p e c t i o n is shown in Table I. The first inspection was made 2 months after the pieces were s u b j e c t e d to the various exposures previously described. It was found that the nails and s c r e w s d r i v e n into untreated p i e c e s showed no corrosion when kept in the 30 and 65 per cent relative humidity rooms a n d o n l y slight corrosion when k e p t in t h e 90 per cent room and on the fence. All the wire nails in treated pieces s h o w e d corrosion, the severity of which increased w i t h t h e amount of zinc chloride in the wood and with the relative humidity to which the pieces were exposed. The corrosion of t h e wire nails i n t h e t r e a t e d wood was greater when the nails were driven into wet wood than when they were driven into wood that had been s e a s o n e d after treatment. The gal-
0
I TIMI
(“*:.I
5
FIGURE2. Loss IN WEIGHTOF WIRENAILS FROM UNTREATED AND FROM ZINCREMOVED CHLORIDE-TREATED WOOD (16 kg. per cubic meter = 1 pound per cubic foot)
The second inspection was made a t the end of 4 months and the third at the end of 6 months. These inspections qualitatively checked the findings of the first. The fourth inspection was made after 1 year and showed that corrosion had proceeded very slowly after the first 2 months, especially in the pieces kept in the 30 and 65 per cent rooms and on the fence. I n the 90 per cent room nails driven into untreated pieces were very rusty but unpitted, while those driven into treated pieces were very rusty and showed some pitting. The fifth inspection was made at the end of 2 years and the findings agreed with that of the year before. At this time the pitting of the nails in treated wood kept in the 90 per cent room had not progressed far enough to affect seriously the strength of the wire nails. The addition of sodium dichromate to the treating solution seemed to have reduced corrosion somewhat. The sixth inspection was made at the end of 5 years. At this time it was found that, except in the 90 per cent room, corrosion had proceeded at a negligible rate since the previous inspection and indeed since the 6rst inspection. The wire nails from treated pieces kept in the 30 and 65 per cent relative humidity rooms showed little or no pitting. The wire nails from the treated pieces on the fence, with the exception of a few nails that had been driven into wet treated wood, also showed little or no pitting. All the wire nails driven into the wood and kept in the 90 per cent humidity room showed marked rusting and those in the treated wood
I ND U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
1338
also showed pitting; some were so pitted that their cross sections were reduced 50 per cent in size. The corrosion of the brass screws and galvanized nails was slight except under the most severe conditions where it mas noticeable but not excessive. There was no marked difference between the fastenings removed from the painted and unpainted halves of the pieces. The sodium dichromate had an erratic effect; it seemed to have reduced corrosion slightly in the fastenings on the fence but not in those in the relative humidity rooms. The loss in weight of the wire nails is shown in Figure 2. Each point represents the average of the losses shown by six nails from one piece. I n the 30 and 65 per cent relative humidity rooms there was no loss in weight within the error of gram-of nails in the pieces that were weighing-*O.Ol seasoned after treatment. When the wire nails mere driven into wet treated pieces there was no loss after the first 4 months. Pieces of this size require about 6 weeks to dry from a water-logged state to a condition in equilibrium with air a t 65 per cent relative humidity. The wire nails in the fence showed a greater loss than those in the 65 per cent room but considerably less than those in the 90 per cent room. The wire nails in the wood treated with 1.51 pounds of zinc chloride per cubic foot, seasoned after treatment, and kept on the fence, showed less corrosion than did the wire nails in an untreated piece kept in the 90 per cent
Vol. 26, No. 12
room, which again shows the dominating effect of a high humidity. The mean annual relative humidity for the area in which the fence is located, as given by the weather reports, is 74 per cent, while for the winter months it is 82 per cent. The moisture content of the pieces kept on the fence was, of course, affected periodically by rain and snow. The rate of loss in weight in the dried pieces placed in the 90 per cent room tended to approach that of the undried pieces after the first 4 months. The wire nails from the piece treated with the mixture of zinc chloride and sodium dichromate and kept in the 90 per cent room showed the highest average loss-namely, 0.28 gram. These nails had originally weighed 1.59 grams; thus the loss represented 17.6 per cent of the original weight. The loss in weight of the brass screws in nearly all pieces kept in the 30 and 65 per cent rooms and on the fence was within the error of weighing. As to the pieces kept in the 90 per cent room, the screws from the untreated wood showed no loss in weight. Those from the treated wood showed a maximum loss of 0.10 gram from an original weight of 2.55 grams.
ACKNOWLEDGMEXT The tests reported here were started in cooperation with the Grasselli Chemical Company. RBCEIVBD September 28, 1934.
Pump for Delivering Liquids a t Low Constant Rates HANS TROPSCH AND w.J. MATTOX, Universal oil Products Company, Riverside, 111.
T
HE pump shown diagrammatically in Figure 1 has been f o u n d v a l u a b l e in this laboratory for delivering gasolines a t constant rates from 100 to 400 ml. per hour and should prove useful for other purposes where an accurate, constant flow is desired. The construction is simple and consists of a s m a l l c o n s t a n t speed motor which, t h r o u g h a reduction gear, operates a 1-inch (2.5-cm.) copper bellows. The rate is regulated by the length of the stroke which is in turn varied by means of an adjustable stop, or stroke regulator. /N The valves consist of 0.25-inch (0.635-cm.) stainless-steel b a 11s seating on groundglass seats. Ten-mm. Pyrex glass tubing was constricted t o the shape shown in Figure 1 and then ground with a Pyrex glass r o d s h a p e d similarly to the constricted tubing. Va 1v e s constructed in this way show no tendency to leak after months of use with extremely corrosive samples of gasoline.
D/5CHARGE
S%A/NLE55 BALL VAL
\
i
rate to vary slightly and is removed by filling with water and boiling. Filling the bellows with water also makes it unnecessary to clean the bellows when changing samples. The flow through the pump is necessarily in pulses but a steady flow is obtained after passing the liquid through the device shown in Figure 2: The liquid enters at A , rises in B, and issues dropwise from capillary C into coil D, the capillary being of such size that all the liquid does not drain from B before the next stroke of the pump. The same capillary is s u i t a b l e for a wide range of feed rates, since at higher rates the increased height of the liquid in B causes an increased pressure at C and a corresponding increased flow through C. E serves to equalize the pressure over the liquid. Fluctuations in flow at F are not noticeable.
u !F
A i r in t h e bellows causes t h e
FIGURE 1. PUMPFOR DELIVERING FlGURE2. FLOW EQUALIZER LIQTJIDSAT Low, CONSTANTRATES
The pump is capable of delivering a t atmospheric pressure any volume up to 500 ml. per hour a t a very constant rate. For periods of 12 hours a t a rate of 200 ml. per hour the deviation was *2 ml. per hour. The B a r b e r - C o l e m a n shaded pole motor mounted on a gear box for reducing the speed to 1.5 r. p. m. was purchased from the MerkIe-Korff Gear Company, Chicago, for less than 5 dollars. The authors wish to acknowledge the considerable assistance obtained in the dev e l o p m e n t of t h i s p u m p from Hugh Rodman and Harry Munn of the mechanical department. RECEIVED September 28, 1934.
