504
T H E J O C ' R N A L OF IiVDL-STRZAL A S D E-VGINEEKIiVG C H E M I S T R Y
did t h e zinc oxide, or t h e lead a n d t h e oxide mixed. Later results, however, do not substantiate this. Another series of determinations were made b y t h e a p p a r a t u s shown i n Fig. 2 , t h e essential differences being in t h e nature of t h e drying chamber a n d t h e usc of a U-tube t o take out a n y carbon monoxide which m a y have accidentally been present in t h e air. T h e drying bottle was a large acid carboy which contained 50 strips of glass plates in. wide by 18 in. in length. which were coated a n d so spaced as t o leave their surfaces free a n d exposed t o t h e air drawn through. -1 p a r t of t h e inside surface of t h e bottle w a s also coated with t h e drying films. T u b e Xo. 3 contained fresh iodine pentoxide, while t u b e No. 11 was a n old t u b e which h a d ceased t o give off a n y iodine on being heated. T h e air was drawn through at t h e same r a t e a s in t h e other tests. R u n s were made with ( I ) linseed oil alone a n d ( 2 ) linseed oil a n d basic white lead. ( I ) 2 3 grams of linseed oil alone gave off 1.05 per cent as carbon dioxide, and 0.13 per cent as carbon monoxide ( 2 ) 3 0 . 2 1 grams of white lead in 26.79 g. of oil evolved 1 . 1 6 per cent of oil as carbon dioxide and 0.108 per cent as carbon monoxide. In each of the above cases the film dried 15 days. F r o m these results i t would appear t h a t t h e oil itself gives off a b o u t , if not fully, as much of these t w o gases when drying alone as when mixed with some pigment. I n order t o see t h e effect of sublimed white lead upon t h e a m o u n t s of these t w o gases set free a third w drying chamber was used (see = (i Fig. 3). This was a large cylinder, some six inches in diameter a n d three feet high, which was filled with carefully spaced glass plates about three or four inches wide a n d running t h e length of t h e cylinder. This was connected t o t h e same kind of arrangement as in Fig. 2 . 25.6 grams of sublimed white lead in 35.4 grams of linseed oil set free 0.43 per cent of the oil as carbon dioxide, and 0.047 per cent as carbon monFIG. 3 oxide, the films drying during six days. This would show t h a t sublimed white lead does n o t differ very much from either of t h e other pigments used. I n order t o ascertain if this evolution of gases continues for a long period of time these chambers have been retained filled with t h e dried films a n d will be opened a n d tested for t h e presence of these gases from time t o time over a period of a t least one year. T h e evidence points t o t h e presence of carbon monoxide as one of t h e products given off i n t h e drying of paint films. There is no basis for a statement especially favorable t o a n y one pigment i n this respect, as very small amounts of this gas appear t o be produced in t h e presence of all those so far investigated. It is also t o be conceded t h a t t h e a m o u n t is so very small t h a t great caution should be exercised in claiming i t t o be t h e agent effective as a poison. If t h e q u a n t i t y
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3-
Vol. 7 ; N o . 6
mentioned in t h e above results is fairjy well distributed with respect t o i t s r a t e of liberation during t h e entire drying period of several days, as appears t o be t h e case, n o serious danger would be likely t o arise in dwellings, as t h e gas would undoubtedly be t o o highly diffused a n d removed t o o rapidly t o cause a n y h a r m . CHEMICAL LABORATORIES, STATEAGRICULTURAL COLLEGE MANHATTAN, K A N S A 5
PAINTS TO PREVENT ELECTROLYSIS IN CONCRETE STRUCTURES 1 B y HEXRYA. GARDXER
T h e use of protective paints upon metal t h a t is t o be embedded i n concrete structures, in order t o prevent a n y damage which might be caused b y electrolysis, has been heretofore proposed. No tests have been made, however, as f a r as t h e writer is aware, which h a r e determined what t y p e of coating is best suited for t h e purpose. It would appear from first consideration t h a t a paint capable of forming a film of high electrical resistance would be most efficient. Such films, however, generally present a high gloss surface a n d are a p t t o prevent t h e proper bonding of t h e concrete with t h e painted metal, t h u s doing more h a r m t h a n good. I t is chiefly for this reason t h a t engineers have not generally adopted t h e use of paint upon reinforcing metal. I n t h e experiments presented herein, a method for overcoming this objectionable feature of insulating paints is described, a n d d a t a are presented on t h e relative insulating a n d bonding values of several different t y p e s of paint. C O R R O S I O N causEs-Before describing these tests, i t might be well t o review briefly, for t h e benefit of those not thoroughly familiar with t h e subject, some of t h e conditions upon which metal corrosion depends. T h e ordinary forms of iron corrosion have been found t o be due t o auto-electrolysis, t h e presence of segregated impurities being responsible for differences in potential a t certain areas, which set up galvanic action a n d cause solution a n d t h e formation of rust a t t h e positive nodes. =\ similar b u t more rapid action takes place when a n electric current is passed through an iron anode immersed i n a n electrolyte; e. g., salt water. When d a m p cement contains a n embedded iron anode, t h e cement acts as a n electrolyte a n d t h e same rusting action takes place, regardless of t h e fact t h a t concrete contains sufficient lime t o inhibit corrosion when no electrical currents are present. With t h e electrolytic change of metal into oxide comes a n increase in volume of t h e products of reaction, a n d there is developed a n enormous expansive force or mechanical pressure, which is sufficient t o crack t h e strongest forms of c0ncret.e. S O U R C E O F cuRREsrs-Corrosion m a y therefore be expected, with its a t t e n d a n t results, when sufficiently high-voltage direct currents enter t h e i r o n . of a new concrete building, either through contact with conductors of light a n d power circuits, contact with water or gas pipes carrying direct currents from grounded power lines, through defective insulation of electrical wiring, or f r o m similar sources. T h a t t h e damage is 1 Presented before the Master Painters' Association of Pennsylvania. Philadelphia, Jan. 12, 1915.
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June, 1915
T I i E J 0 7 ~ R X . I l .O F I ~ V D b - S ? ' R I . I L ; l K D B X G I S E E K I X C C11EAMIS7'KY
greatcsr t o new structures is due t o t h e fact t h a t t h e concrete is then d a m p and a better electrolyte t h a n when i t has become d r y from age. That examples of reinforced concrete structures damaged from stray currents are not more common m a y he due t o t h e fact t h a t in many localities enginccrs are active in their endeavors t o prevent high voltage currents from runninr: wild. This fact, howcvcr, docs not justify a disregard of what might happen iii the future a n d wliat may now Ijc hiippening t o some structures which have not Iiccii carefully guardcil itgainst stray current electrolysis. T h a t much of this damagc may he prevcnted b y t h e adoption of suitablc forms of foundation waterproofing, exterior insulating joints f o r pipclines, isolation of lead-co\~credcahlcs entering biiildings, and other insulating devices is shown b y Rosa, M c Collum, and I'etcrsl in what is probably t,he most valuahlc coiitrihiition t o t h e subject of reinforcement electrolysis t h a t has ever been published. Of equal importanw.; howeveP. should he t h e safeguarding of t h e metal w i t h suitahlc insirlating a n d bonding paints, before i t is einheddeii in cement. T h e adoption of this precaution, if followcd by t h e usc of the safety devices noted above, will guard against t h e causes wlrich contribntc t o electrolysis a n d t h u s render our modern concrete structures safe from destruction by reinforcement corrosion. RXPERIMENTAE
slinII(s 1-----The writer's
invcstigations were made upon t w o separate series of concrete test cylinders. T h e first series were made by embedding, in concrete cylinders, painted iron rods 1 1 3 in. in diameter and i z in. long. Previous t o painting, t h e rods were thoroughly cleaned from scale a n d rust. Two Coats of paint were then applied, :illowing a wcek's time for drying hetween coats. T h e paintcri rods \vere then placed in molds in a n upright position, about I in. npart zind I in. from t h e bottom of the molds. Cement mortar, prepared from one part of Portlrind cenicnt and t w o parts of sand, was poured around t h e rods and t s m p c d into vlacc. ?.iter two d a w ' time the molds werc removed a n d the tcst pieces wcrc repaired ivitli cement mortar wherever ilefccts were siiown. "sanded"
I S G SR?FACFS---In making up t h e speciincns for test. it occurred to t h e writcr t h a t ion t o using paints which dry upon metal to :I gloss surfacc a n d whirl1 prevent proper hondin:! oi thc cement, might lie overcome by applying t o t h e pxinted surface. whilc i t is still tiicky (not dry), sli:irp particlcs of sand or similar matcrinl. Emcry powder; alirasives, a n d fine qiizi-tz sand wcrc among 1 " J : ~ ~ ~ ~ ~ o IinY concrete:' S~S 'recilnoiogic xo. is, E. s. BUTW
o< Standards.
505
tcsted. Whcn allowed l o drain upon n painted rod, t h e particles become attached t o t h e paint and d r y with it t o form a rough surface resembling coarsc sandpaper (see Fig. I ) , After thoroughly drying, t h e particles are solidly embcdderl in t h e paint, which t h u s presents a dull rather t h a n a gloss film. Pine, elcan, whitc sand w a s found most useful. A R R A S G E M E S T OF T E S T S ~-rlftcragcing f o r a month, t h c pieces wrrc conncct,ed in parallcl and in scwics uvith
Pia. IS-AQRANCBMIENT OT SRBIES IS SPBCIXIBNS IMMIIRSBD lion molds lor forming specimens shown nt kit. Specimen removed irom jar shows suiiounding Iron cathode
rcsistancc t o reiiiicc the v o h g e from 1 x 0 to JO volts D. C . Current reitdings were made over ii pcriod of twenty-four hours. T h e current passing was small. T h e test cylinders were t h e n pliiccd in a shallow pan containing sufficient water t o immerse t h e lower 2 in. of each specimen. After a week's test, the cylinders were disconnected and removed from t h e pan for observation. A fcw of t h e specimens showed small cracks near t h e bottom, where t h e W C ~cement had condncted t h e current to the grcat.est extent. T h e cylinders were then placed in scparatc earthenware jars a n d again connected. up. T h e jars contained sufficient water t o immerse t h e specimens up t n within I inch of thcir t o p surfaces. They were left in circuit for ten d a y s and cnrrent readings were made e w r y twenty-four hours. Cracking u-as shown b y nearly every cylinder which current readings proved t o he carrying m y appreciaiile amount of current. T h e ry case started a t thc anode, extending radially to the cdge of the cylinders a n d parallel t.o t h e elect.rode, gradually opening up as t h e tests were continued. l'hc specimens wcre finally disconnected and rcmovcd for examination. (Set, Table I a n d Pigs. 111 and I!',) Those which had been cracked by the electrolytic corrosion of thc mctal wcre easily split into two sections, disclosing t,he containcd electrodes. The others. which did riot show a n y rmcking, were partcd with a chisel, in order t o niake a comparative examination of t h c condition of t h e embedded metal. SERIES 11 consisted of specimcns made b y embedding i n concrct,e cylindcrs painted anodes a/+ inch in dinmetcr a n d 1 2 inches in length. Previous t o painting, t h e rods werc thoroughly cleancd from scalc a n d rnst. They were painted w i t h two coats a i the same paints used in Series I . T h e rods rvere placed in molds 3 ' 1 2 X 8 in., in :in upright position, and t h e same kind of Portland cement mixture used in Scrics I tests was placed nronnd t.he rods and
job
7’1IE JOCRiV2LL O F IAVDCS7‘l), 751. New Meihod for T ~ s Paint ~ i Pilnln ~ ~and Preseivltive Coatings for Iron end Steel," W. C. S i d e . T H E J o o r a ~ r1 . ( I O l Z ) , 189.
~,,*
special types of oil coatings which g a v c p o c l results in Series I and IT. ~ I ~ ~ r 1 i~ io~ +xw L EFILM S P O K O S I T Y A S U i:Li s l s ~ ~ ~ - Tsmall h c current flow s]3own ijy of +,he specimens in the t e s t may in p a r t b e attributed t o their impcrvious charactcr. Paints which form porous
. films allow t h e passage of water which m a y contain various electrolytes. Such films offer b u t small resistance t o t h e passage of electrical currents. P a i n t s which form highly impermeable films keep water a w a y from t h e underlying iron a n d offer great resistance t o t h e passage of electrical currents. Investigations u-hich have det rmined t h e actual degree of porosity % shown b y various t y p e s of paint films h a v e previously been m a d e b y A. M . Muckenfuss’ a n d b y t h e writer.2 These tests have already afforded useful information t o t h e designer of paints a n d might be studied with
composed of collodion a n d gutta-percha, respectively, dried t o a flat surface which accounts for t h e good bond tests shown. Among t h e oil paints, No. 1 6 , which also h a d t h e property of drying t o a flat surface, gave a much better bond t h a n paints of a similar composition which dried t o a gloss surface. T h e good bonding tests shown b y several of t h e water paints is readily explainable, t h e wet concrete exerting a solvent action upon such paints, which gave opportunity for direct contact with t h e steel. Some paints which gave excellent results in t h e insulating tests gave
FIG. VII-AMPER&-HOURCHARTS FOR SERIES I1
profit in t h e production of paints for t h e prevention of electrolytic corrosion. B O N D I K G TESTS-some paints gave good bonding tests, b u t failed t o act as insulators. Among these m a y be mentioned Nos. 1 2 , 19 a n d 2 0 (water paints) a n d Kos. 18 a n d 2 1 (lacquers). T h e l a t t e r t w o , 1 “Report on a Permeability Test for Paints and Varnishes,” A. M. Muckenfuss, THISJOURNAL, 6 (1913), 535; Proc. Amer. SOC.for Test. Malm., 14, I1 (1914), 361. * “Excluding and Water-Resisting Properties of Paint Films for the Protection of Iron and Steel,” H. A. Gardner, Bull. 18, Scientific Section, Paint Mfrs. Assn. of U. S., p , 17.
conversely poor results i n t h e bonding tests. Amtlng these m a y be mentioned Nos. 7 a n d 8 , composed of sandarac a n d shellac, respectively. Most of t h e oil-pigment paints made with raw linseed oil gave poor or only fair results. It is probable t h a t t h e r a w oil fails t o d r y h a r d , a n d , although apparently well dried, remains in a semi-oxidized condition. T h e oil films would in such cases be rather porous a n d therefore inefficient as insulators. Such films would be readily acted upon b y t h e hydrogen evolved b y electrolysis. Much better results were obtained with boiled linseed
T H E J O U R N A L OF I N D 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 oil, a product t h a t dries t o a harder, less porous, a n d more fully saturated film. T h e value of t h e “sanded surface” method is shown b y comparing t e s t No. 2 7 with test No. 1 5 , t h e paints used being of t h e same composition. T h e sanded surface of No. 2 7 gave much better insulating values a n d i t s bonding strength was double t h a t of t h e unsanded specimen. Another instance of t h e value of t h e “sanded surface” method is shown b y a comparison of specimens Nos. 2 8 a n d 14. U S E O F PIGMEXTS-It is quite likely t h a t t h e nature of t h e pigment used i n a paint designed t o prevent electrolysis of embedded metal will have some bearing upon t h e results obtained from its use. T h e addition of a pigment t o a n oil usually increases t h e resistance t o moisture a n d makes a more impermeable film. Theoretically, pigments which are of a non-conducting n a t u r e should be preferable. T h e inert pigments are examples of this t y p e (asbestine, china clay, silica, etc.). There should, however, be present in a paint a sufficient q u a n t i t y of rust-inhibitive pigment (basic pigments or pigments of t h e chromate t y p e ) t o produce a passive condition of t h e steel, similar t o t h e condition t h a t is produced b y t h e basic lime compounds in cement. Prominent among t h e protective compounds t h a t gave t h e best results are Nos. 2 a n d 9, composed of processed a n d heat-treated t u n g oil (Chinese wood oil). These compounds dried t o a h a r d , non-porous film of a saturated nature. H a d t h e y been sanded, t h e y undoubtedly would have given still better results. Distinction should also be accorded t o Nos. 17, 2 7 a n d 2 8 , although t h e good results obtained with t h e last t w o should be largely credited t o t h e sanding of t h e surfaces during drying. CONCLUSIONS
T h e corrosion of metal embedded in concrete structures, b y s t r a y currents of high voltage, is often productive of serious effects. T h e use of properly made paints upon such metal constitutes a safeguard t h a t should not be neglected b y t h e engineer. Such paints m a y be prepared as follows: I-The vehicle should contain: I-Boiled or bodied oils or products which d r y t o fairly s a t u r a t e d films. 2-Oils which d r y b y semi-polymerization rather t h a n b y oxidation. 3-Oils which d r y t o a flat r a t h e r t h a n a high gloss surface. 11-The solid portion should contain a percentage of : I-Pigments which are coarse a n d which therefore t e n d t o form films having a rough surface. 2-Pigments which a r e inert a n d which d o n o t a c t as conductors of electricity. 3-Pigments which are either basic or of t h e chromate type. 111-The painted metal should be “sanded” if possible. T h e writer wishes t o acknowledge t h e very valuable assistance throughout these tests of Mr. Leland P. H a r t , INSTITUTE OF INDUSTRIAL RESEARCH WASHINGTON, D. C .
Vol. 7, No. 6
PAINT VEHICLES AS PROTECTIVE AGENTS AGAINST CORROSION‘ B y MAXIMILIAN TOCH
A careful search of t h e literature of t h e past t w e n t y years has failed t o reveal anything like a systematic investigation of t h e relative value of different vehicles used in t h e manufacture of paints for structural steel a n d t h e prevention of corrosion. There are a few isolated cases in which boiled linseed oil,* K a u r i linseed oil varnish3 a n d spar varnish as protective coatings o n structural steel were studied. For many years past much has been written a n d many investigations have been made on t h e protective quality of t h e pigments, b u t no one has apparently made a n y s t u d y of t h e vehicles. I t is quite obvious t h a t without a rehicle a pigment is useless, a n d I know of no instance where a pigment could be used alone, with perhaps t h e single exception of Portland cement, if t h a t m a y be classed as a pigment; even then, Portland cement would be useless unless water were used a s a vehicle. I hardly need make t h e experiment of taking a dry pigment a n d using water as a vehicle t o show you t h a t when t h e water evaporated i t would leave t h e pigment, a n d t h e pigment in t u r n would leave t h e metal; a n d yet, t o t h e best of m y knowledge, nobody has paid a n y attention t o t h e very important role t h a t is played by t h e vehicle itself. There is a n old proverb which says, “ O n e h a n d is useless, for one h a n d washes t h e other,” a n d i t strikes m e t h a t t h e same is t r u e with reference t o vehicle a n d pigment, for one is of little value without t h e other, a n d if a n y value is t o be attached t o either of t h e m t h e vehicle has b y f a r t h e advantage, because, as I will show you, there are some vehicles which protect for a considerable length of time. With this end in view exposure tests were made in 1913, in which fifty-two steel plates (in duplicate) were carefully freed from grease b y washing with benzol, dried, sanded, a n d rubbed clean with pumice, a n d t h e n coated with all t h e paint vehicles or protective vehicles t o t h e extent of fifty-two in number, many of which, of course, are seldom, if ever, used alone, a n d some of which are failures a short time after t h e y are p u t on. However, I wanted t o d o this thing thoroughly, a n d for this purpose I selected t h e same quality of steel, known as cutlery steel, which I have been using for many years for m y exposure tests. I t is a steel which rusts very rapidly a n d of which I have several samples here. I must eliminate those plates which have shown no rusting in t h e year a n d five months t h a t t h e y have been exposed. These were coated with t h e paraffin or machinery oil compounds, a n d i t would be poor advice t o a n y engineer t o coat steel with paraffin compounds, for t h e method of cleaning before t h e application of a n y good paint would have t o be very carefully followed o u t , since n o protective paint would hold on steel t h a t retained t h e least trace of a paraffin 1 P_aper ptesented before the New York Section of the Society of Chemical Industry, Chemists’ Club, April 23, 1915. 2 C. Vdn Kreybig, Farben Zfg., 17, 1 7 6 6 8 ; J. N. Friend. Carnegie Scholarhsip Report, Iron and Steel Inst., May, 1913, Pp. 1-9. 8 Address of Prof. A. H. Sabin before American Society of Civil Engineers, Nov. 4, 1896, reported in Engineering News, July 28, 1898.
