July, 1923
I N D U S T R I A L A.VD ENGINEERING CHEMISTRY
New Applications of Phenol Resins in the Chemical and Allied Industries
Laboratory Corrosion Tests By W. S. Calcott
By L. V. Redman BAKELITE CORPORATION, REDMANOL DIVISION,CHICAGO, ILL,
T
HE phenol resins continue to find wider applications in the industries on account of their physical and chemical properties, and these applications are in the allied fields rather than directly in the chemical industry. The most striking new application in the chemical field is the use of laminated phenol products-sold under such trade names as Bakelite-Dilecto, Bakelite-Micarta, Laminated-Redmanol, Formica, Condensite-Celeron and Fibrocfor the manufacture of octagonal plating barrels in cyanide solutions and nonconducting conveyor chains in cyanide plating. The laminated phenol products have sufficient resistance to cyanide solutions to give good life and wear in this mechanical-chemical application. The use of the pure phenol resins as a transparent medium for measuring cylinders and conductivity cells for hydrofluoric acid is of academic interest only. The pure resins are unaffected by hydrofluoric acid solutions, and furnish transparent vessels for this use. The laminated products made from phenol resins and woven fabrics are finding a new and extended use as pump valves and pump-valve disks in deep oil wells and in uses where corrosive animal by-products, such as slaughter-house refuse, are handled in pumps. These woven, laminated phenol-resin fabrics are also rapidly replacing other materials as silent gears in washing machines for household use and in power laundries. The’material is not only silent as a gear, but it resists the dampness and corrosive effects of cleaning materials. It is replacing rawhide gears wherever rodents are a possible menace-for example, in basements, mines, etc. These products are also used as accurate gears for vernier adjustments on radio, high-class phonograph motors, and on printing presses. Their use is also extending rapidly in the mechanical field for high-speed jigs, drills, lathes, etc., where a minimum of noise during operation is desirable. I n the automatic telephone, the laminated phenol-resin products have replaced or are replacing thin, hard rubber as the insulation used in the automatic piles, since the phenol resins when properly made have no “cold flow,” and the automatic piles when locked do remain firmly locked and do not rattle after months of use, as they would do if the insulation had a cold flow. These mechanical properties of rigidity or nonflo-vving under pressure from bolts and screws have given the phenol resins a very extended use in the radio industry. I n the radio it is not only necessary to have accuracy of dimensions in order to give satisfactory adjustment of the instrument, but it is also necessary that these accurate adjustments be maintained-in other words, that the material from which the set is made does not creep or fall out of alignment. The phenol resins fulfil this function admirably. I n the mechanical field these new chemical products are finding extended use in automatic pencil barrels, high-grade buttons for the clothing industry, door knobs and handles, elevator dashpots, mechanical parts on typewriters and adding machines, and a multitude of other uses which need not be mentioned here. One further interesting mechanical application that might be mentioned is the replacement of porcelain by phenol plastics wherever violent shock is liable to break porcelain, as in the discharge of high-power guns on battleships.
677
E. I.
DU
PONTDE NEMOURS & Co., WILMINCTON, DEL
HE laboratory corrosion test about to be discussed involves relatively little that is new, most of the points involved having already been brought out. It represents a combination of factors found necessary, in our experience, to obtain consistent and accurate results capable of being applied to plant design with some degree of confidence that the apparatus constructed will have the predicted life. The test evolved as the result of combining these factors has been found to give quite satisiactory results for the class of work for which it is intended-testing materials for their suhability for constructing plant and semiworks equipment. The general method employed for determining the rate of corrosion consists in exposing the specimen t o the action of the corrosive agent for a definite time and determining the loss of weight per unit area, the result obtained varying widely with slight variations in test conditions. While no published method gives sufficient detail to be used as a general method, the following method has been found to give results applicable to plant design, provided the exact plant conditions of temperature, concentration, impurities, movement of liquid, etc., are carefully taken into consideration. I n establishing this test, the chief sources of variation investigated and standardized were: shape of test piece, volume of solution, temperature, time of exposure, and method of cleaning test pieces. The effect of each of these variables was separately investigated in order to permit the establishment of definite and reproducible test conditions. The method of expressing results used, while somewhat novel, has been found to be extremely convenient fr’om the purely practical point of view. The test is made in the usual way, the corrosion rate being found as loss of weight per unit area per unit time. I n order to reduce the results to a comparable basis, however, so that data on materials of widely differing density, as, for instance, lead and aluminium, can be compared, the loss of weight is recalculated to the equivalent thickness of metal removed. The unit arbitrarily taken is inches penetration per month. This system has the further advantage that the corrosion rate itself gives an approximate idea of the probable life of a given piece of apparatus under a given set of conditions, as the thickness of metal divided by the corrosion rate gives the life of the apparatus in months. Where the metal under test pits badly, the simple loss of weight is, of course, not a fair measure of the effective rate of corrosion, as a small hole due to pitting can cause just as complete failure as a general thinning of the entire surface. In this case, the corrosion rate is estimated in this laboratory by grinding down the entire surface of the test piece until the bottom of the pits is just reached, this point being determined by microscopic examination. The combined loss of weight in the corrosion test proper, plus the loss in the subsequent grinding, is taken as the measure of the true or effective rate of corrosion.
T
SHAPEOF TESTPIECE The shape of test piece has already been investigated t o some extent, but was reinvestigated in this laboratory for the especial purpose of determining the effect of slight variations such as m a y occur between different test pieces. A s an edge is exposed to attack from two directions, while a plane surface is exposed from only one, the rate of corrosion should be somewhat greater in the case of the test piece with the larger ratio of edge to surface. This was verified
IAVDUSTRIALA N D E-VGIMEERING CHEiIlISTRY
678
by exposing cast-lead test strips to the action of 20 per cent hydrochloric acid a t 26" C., when it was found that the rate of corrosion increased slightly (from 5.8 to 6.2 mils) as the ratio of edge to surface increased from 3 to 8. Ratio Length of Edge Area
Corrosion In./Mo.
0,0068 0.0062 0,0055 0.0062
3.17 3.88
5.56 8.52
The effect was, however, quite small, so that a considerable variation in this factor is permissible.
VOLUMEOF SOLUTION Another factor obviously entering into the equation is the volume of solution as compared with the surface exposed to action. If enough metal dissolves to a l t e r the composition of the test solution appreciably, the resulting corrosion rate may be greatly affected. The magnitude of the affection depends on the degree of alteration of the corroding liquid, but may easily amount t o 100 per cent. For instance, a lead test piece in 100 cc. of dilute acetic acid showed a corrosion rate of 0.0035 in., and in 400 cc. a rate of 0.0066 in. Volume of
LEADDISSOLVED
Solution
IN
80 per 80 per 80 per 98 per 98 per 10 per 10 per
cent cent cent cent cent cent cent
Acetic Acetic Acetic Acetic Acetic (Satd. with PbAcz)
HC1 HCl (Satd. wlth PbAcd
Cc. 100 200 400 250 250 250 250
Corrosion Rate In./Mo. 0 0035 0.0065 0.0066 0.0006 0,0024 0,0138 0,0105
For moderate rates of corrosion (less than 0.01 in.) this factor was therefore standardized a t 250 cc. per test piece of 4.6 sq. in. area, as with this amount of solution the change in composition due to dissolved metal is insufficient to alter the rate of corrosion perceptibly. For higher rates an error is, of course, introduced, but in this case, as the rate would be too high to permit of plant use of the material under test, the error is for practical purposes of minor importance.
TEMPERATURE The exact temperature of the test has also been found t o be of extreme importance. Experimentally, it has been found that the effect of temperature upon the rate of solution can be expressed by the following equation within the range 20" to looo C.: log C = A
+ BT
dC dT
or - = 2 303BC,
C
=
EA f
dC - = KC dT
BT
From this, the change in the rate of corrosion with changing temperature should be an exponential function of the temperature. Our experiments indicate a change in the rate of corrosion of from 1 to 3 per cent per degree centigrade, a variation of sufficient magnitude to necessitate very accurate temperature control.
TIMEOF EXPOSURE I n investigating the effect of time on exposure, an unexpected result was found. The rate of corrosion, calculated to a comparable basis, was found to be a function of the time of exposure. Generally speaking, the corrosion rate calculated from a short exposure was found to be greatly in excess of that calculated from a long one. This point is illustrated by the figures obtained on mild steel in 93 per cent sulfuric acid a t 22" to 27" C.
Time
Hrs.
Rate In./Mo.
Vol. 15, No. 7 Time Hrs.
.
Rate In./Mo.
I n this case, the rate of corrosion decrcased from an initial rate of 0.0308 in. to a final steady rate of 0.001,5 in., a decrease of 95 per cent from the rate of the first hour and 75 per cent from that of the first 24 hrs. This high initial rate is not uniformly encountered. Aluminium in nitric acid, for instance, shows a nearly uniform rate of corrosion from the beginning. The effect is probably due t o initial electrochemical surface phenomena, complicated by the slow formation, in some cases, of a protective coat. The phenomenon occurs with sufficient frequency, however, so that the results of a short test (less than 48 hrs.) are likely to be seriously in error. For accurate work i t has been found advisable to run the test for two periods of 48 and 96 hrs., respectively, the difference between the two weight losses, calculated on the 48-hr. bahis, being taken as the true rate of corrosion. This figure will frequently differ materially from that obtained over the short period, sometimes by several hundred per cent, and in general will be somewhat different.
PREPARATION OF TESTPIECE The method of preparing the test piece has been found to be of relatively little importance, provided tool marks and deep scratches are removed before testing. Polishing seems to be unnecessary or even disadvantageous, through altering the surface composition of the metal. The final cleansing can be done either by treating the test piece with a solvent for t h e corrosion product but nobfor the metal, or by cleaning with a mild abrasive. The second method is of more general applicability than the first.
PROCEDURE The test as actually used, incorporating these points, follows : REAGENTSAND APPARATUS-corroding Solution. Use 250 cc. of the corroding solution per test piece of given area (4.6 sq. in.) for fairly rapid corrosion rate (0.01 in. penetration per month). The volume should be increased in proportion for pieces of greater area. PREPARATION OF THE S A M P L E - M e t a l Test Piece. Size 2 x 1 x 0.1 in. (area 4.6 sq. in.). Dimensions should be accurate to 0.01 in. in order t o save time of measurement and area calculated in the laboratory. Other shapes may be 'used within a range of ratio of length of edge to total area of test piece between 4 and 8. Preparatioa. The strip of indicated size may be cut from flat sheet metal or turned from pipe. Tool marks should be removed by successive use of file and emery. Exceedingly fine finishes are unnecessary, but, the surface should be clean and reasonably smooth. DETAILEDPROCEDURE-8tUndaTd 8 t d C COTrOSiOn Test. Place the corroding solution in a flask or wide-mouth bottle and bring to the temperature of the test. Maintain this temperature to a t least 1 C. in a carefully regulated thermostat. Suspend the test piece upoa a glass hook from a stopper of such a size as to fit the flask or the bottle loosely. The stopper must be made of a material which will be unaffected by the corroding solution. Immerse the test piece in t h e solution when it reaches the proper temperature, closing the bottle or flask with the stopper. If the test is being made a t a high temperature, a reflux condenser must be used, taking care to prevent the condensate from running directly onto the test piece.
INDLTXTRIALAXD ENGINEERING CHEMIXTRY
July, 1923
The highest accuracy is desirable. Expose the test piece for 48 hrs. to the corroding solution. Remove from the . solution, wash thoroughly in a stream of water, and remove any coating. This cleaning may be done by dissolving off the coating (lead sulfate in ammonium acetate solution, lead chloride in hot water, etc.), or by rubbing and scouring with or without a soft powder as a mild abrasive. Do not adopt any method of cleaning until the error due to its use has been determined. Weigh the test piece after thoroughly drying, especially wiping out the hole by which it was suspended on the glass hook. Immerse the test piece in the corroding solution for a second 48-hr. period. Care should be taken that while drying and making the first weight no oil or grease is allowed to get on the test piece by handling, since this would give low results. After the second 48-hr. immersion, clean and weigh again, as described above. From the loss during the last 48 hrs. calculate the average rate of corrosion ( t = 48 hrs.) as indicated under “Calculations.” Run a check test simultaneously. Never place test pieces of different metals in the same container. It is permissible to place two pieces of the same metal in the same container, but they should not be in contact. In case the metal develops pitting, this factor must be in-
679
cluded in the results, since failure in any case will occur when a pit has entirely penetrated the metal. Determine the magnitude of this effect by grinding down on a metallographic-grinding set until all the pits have just disappeared and solid metal is reached. The loss in weight during this grinding is determined and the pitting calculated as indicated. CALCULATIONS If W = loss in weight in grams OF test piece during second 48-hr. immersion A = area of test piece in square inches S = density of metal in grams per cubic centimeter t = time of exposure in hours ( t = 48) then C = rate oE chemical corrosion expressed as inches penetrated per month = 24 X 30 X W W (2.f14)~ASt Or 43’9 A T
In order to calculate the pitting corrosion, let P = loss in weight in grams due t o grinding out pits, then D = rate of penetration of metal by both normal corrosion over the entire surface and local action due to pitting, W + P D = 43.9 X AS^
T h e Simultaneous Combustion of Hydrogen and Carbon M on oxi d e”2 By R. T. Haslam >f ASSACHUSETTS INSTITUTE OF
TECHNOLOGY, CAMBRIDGE.
M.4SS
it seems strange that relaRXCTICALLY all In contrast to the views of other investigators, a study of the simultively little is known about our industrial fuels taneous combustion of hydrogen and carbon monoxide shows that them. On the other hand, between 900’ and l5OO0 C. both reactions are trimolecular: --coal, producer gas, when one considers the water gas, fuel oil, etc,2co 0 2 = 2c0, speed of these reactions, the decompose in the course of 2H2 02 = 2H20 temperature produced by burning to form carbon 4% The ratio of the velocity constants for these two reactions is the large amount of heat dioxide, water vapor, cartco evolved, the marked effect bon monoxide, and hydro= 2.86, showing that hydrogen burns 2.86 times as fast as carbon of catalyzers (surfaces), gen. Any hydrocarbons monoxide. and the difficulty of conpresent in the early stages There is considerable evidence that the mechanism of combustion trolling mixing, the lack of of combustion are conof either hydrogen or carbon monoxide alone. with or without cataexact data is not surprising. sumed first, so that after a lytic surfaces, is diflerent from the combustion of a mixture of these Owing to turbulence it is very brief interval the only two gases in the ordinary industrial furnace where both gases are to measure even difficult combustible gases remainburning simultaneously. the exact time the combusing are hydrogen and carThe possibility of obtaining a lower stack loss on an overburdened tible gases have been burnbon monoxide.’,* In burngas-fired furnace or increasing production by the use of a gas with ing with the oxygen. The ing coal, for example, a increascd hydrogen content is pointed out. literature indicates that combustion chamber six little is known quantitatimes the size reauired to burn all the hyirocarbons may be needed to consume tively of the rates of these reactions, either actual or relative the last traces of hydrogen and carbon monoxide.2 The to one another, and that there is serious doubt as to their scientific design of a combustion space depends, therefore, order-i. e., whether bimolecular or trimolecular. on an exact knowledge of the combustion of carbon monoxide PREVIOCS INVESTIGATIONS and hydrogen, since they are the controlling factors in designing the smallest combustion space to give a predetermined Falk, after investigating the ignition temperatures of hydrogen, stack loss. carbon monoxide, and mixtures of these gases with oxygen, In view of the fact that the reactions states that the reaction between hydrogen and oxygen is bimolec-
P
+
+
2H2
+
0 2
= 2H20 and 2CO
+
0 2
= 2C02
are industrially of the greatest importance, a t first glance Pre.ented before the Section of Gas and Fuel Chemistry a t the 64th Meeting of the American Chemical Society, Pittsburgh, P a , September 4 t o 8, 1922 2 Contribution N o 33 from Department of Chenmal Engineering * Numbers In text and table refer t o bibliography a t end of article 1
ular-i. e., one Hz molecule reacts with one 0 2 molecule, presum0-and ably to form H 2 0 2 , which in turn is broken down to HzO that the reaction between carbon monoxide and oxygen is 0 2 = 2C02). trimolecular (2CO B~denstein,~ on the other hand, measuring the reaction velocity directly, concluded t h a t a t 600” C. the combustion of 0 2 = 2H20), and that the hydrogen was trimolecular (2Hz rate of the reaction was proportional to the ratio of surface of the container to its volume.
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