» Se THESIS aac eat sL CRT) ee taa H, L. WATERBURY J. D. ROBERTS 1917 5 i? auy 1" yn An Investigation of . The Art of Rust - Proofing of Iron and Steel. » A Thesis Submitted to The Faculty of Michigan Agricultural College By -_ \ < pee 7 . . ‘ ae poe” ho + H. L. Waterbury J. D. Roberts ee Candidates for the Degree of Bachelor of Science June 1917. THESIS Iron and that form of iron called steel are being used increa-— singly as engineering materials. The tendency to rust is a character- istic inherent in the element iron impairing its usefulness both on ac- count of reduction of strength and the offending appearance of rusty esur- faces. It is probable that this rusting of iron and steel cannot be entirely overcome since no method is known by which to baniah the agents which cause corrosion. The elements of this agency are those necessary to life itself and society would hardly consent to their removal were it possible. Great expense falls annually upon manufacturers through the corrosion of iron and steel; great quantities of which are wasted through this baleful influence, The preservation of iron and steel is, there- fore, one of the problems of highest importance before the world at pres- ent. The industries concerned must learn how to preserve the present supply for future generations. It is known, however, that there is a great deal of difference between the manner and rapidity which different specimens and types of iron and steel and their alloys are affected by corrosion. Some metals are more susceptible to corrosion than others. The proper control of unavoidable impurities, their homogenous distribution and careful heat treatment, will improve the rust resisting qualities of metal whether it is called iron or steel, and regardless of the method by which it is made. As the result of recent researches by a number of investigators, it is now very generally admitted that a state of stress or strain in the met- al invites rapid corrosion. A similar effect is produced by a burnt condition of the metal leading to a high porosity and the presence of 103912 occluded gas and blow holes. The old hand forged metals are less easily corroded than are the modern metals. } In this Thesis an effort has been made to point out the causes of rust and the means and methods by which it may be prevented, Information was obtained by research on the various causes and prevention of rust, as outlined by experts, and an investigation was conducted on the so called Parker Method of Rust Proofing, The bibliography consulted for the purpose of securing in- formation comprised the following references: corrosion and Preservation of Iron and Steel, by Cushman and Gardner, Galvanizing and Tinning by Flanders. Metalurgy of Iron and Steel, by Bradley Stoughton. PART Tf. Theories of Corrosion. There have been three theories put forward to explain the corrosion of iron and steel; the carbonic aeid theory, the hydrogen peroxide theory and the electrolytic theory. The carbonic acid theory is the one which until recently was most generally accepted. The theory is best set forth in the words of a text book in analytical chemistry recently published. "The process of rusting is a cyclical one, three factors play an important part; an acid, water and oxygen. This process of rusting ie always started by an acid (even the week carbonic acid suffices); the acid changes the metal to a ferrous salt with evolution of hydrogen. 2Fe plus 2H2C03 = 2FeC03 plus 2Ho “Water and exygen now act upon ferrous salt causing the iron in this salt to separate out as ferric hydroxide, setting free the same amount of acid which was used in forming the ferrous salt. 2FeCO, plus 5H,0 plus 0 = 2Fe (0H), plus 2H,CO3 The acid which is set free again acts upon the metal forming more ferrous salt, which is again decomposed, forming more rust. Very small amount of acid, therefore, suffices to rust a large amount of iron. If the acid is lacking, the iron will not rust." The above theory is a plausible explanation for rusting, and in spite of the fact carbonic acid and other acids do act a part in the ordinary rusting of iron it has been proven by the experiments of Dunstan and coworkers that rusting does take place when carbonicasid is absent with extreme rapidity. Hence it is plain that the carbonic acid theory does not furnish a complete explanation of the phenomenon of corrosion, but it does tm express partial truth in as much as hydrogen ions must be present before the attach on the surface of the iron can be made. The fact that even pure water provides a sufficient number of hydrogen ions to start the action shows that the roll of carbonic acid is only contrib- utory and not the sole sxgm cause, The peroxide theory of corrosion is based on the scheme of oxidation processes advanced by Traube. Thus the chemical action con- cerned in the formation of iron rust should be written. | F, plusv0g plus H20 = F,0 plus H,02 2F_0 plus Ho0. = Feo Og (OH) 4 ® Feo 03 =, Hg0 The excess of hydrogen peroxide immediately reacts with the iron, form ing a further quantity of rust Fe plus H202 8 F,0 plus Ho0 | 2FeO plus Ho02g = Feo02 (OH)2 = F,°3 » H,0 The theories of this explanation are interesting but they have never proved themselves or have they been supported by facts. Thus a further search must be made for a true explanation of the corrosion of iron. The electrolytic theory is the one which has finally been ac- cepted, as the true explanation of corrosion. In order to understand thé above theory it will be necessary to give some attention to the theory of solution. All soluable substances have a solution pressure which forces that substance into solution being opposed only by the osmotic pressure of the water, When the two balance the disolving stops. Solution pres- sure varies over the surface of a piece of iron or steel causing some points to go into solution and rust while other portions remain bright. This rusting is an electrolytic action produced by positive and negative ions of solution. For instance, if we place a piece ofiron in pure water, the iron has a definite solution tension, especially at certain points on the surface, which are electro positive to other poihts. The iron enters the solution as positive ferrous ions, the corresponding negative charges being assumed by hydroxyis. But immediately the oxygen of the air changes the ferrous ions to a ferric condition resulting in the hydrolytic formation of the insoluble ferric hydroxide or rust. Thus it appears that in order for rust to be formed iron mst go into solu- tion and hydrogen must be given off in the presence of oxygen or some other oxidizing agent. This presumes an electrolytic action as every iron ion that appears at a certain spot demands the dissapearance of a hydrogen ion at another, with a consequent formation of gaseous hydrogen. The gaseous hydrogen is rarely visible in the process of rusting, owing to the rather high solubility and great diffusive power of this element. Substances which increase a concentration of hydrogen ions, such as acids and acid salts, stimulate corrosion, while substances which increase the concentration of hydroxyls inhibit it. It is further seen that solution tension is modified by im- purities or additional substances contained in the metal and in the solvent. The effect of the slightest segregation of the metal or even unequal etresses or,strains in the surface, will throw that surface out of equi- librium, and the solution tension will be greater at some points than at others. The points or nodes of maximum solution pressure will be electro-positive to those of minimum pressure, and a current will flow, provided the surface points are in contact through a conducting film. If the film is water, or is in any way moist, the higher its conductiv- ity the faster will iron pass into solution in the electro-positive areas, and the faster corrosion precedes, By the use of ferroxyl, a solution for the indiétion of pos- itive poles as well as negative poles, it was shown that the solution tension of iron is higher at certain points on the surface than it is at others, Or, in other words, certain surface points are, be it ever so slightly, electro-positive to others. Theseeffects which are pro- duced in the ferroxyl indicator constitutes a visible demonstration of the electrolytic action taking place on the surface of iron and causing rapid corrosion at the positive nodes. The ferroxyl test in the hands of a number of investigators has brought out with clearness a considerable body of evidence to show that the electrolytic theory is in accord with the observed facts when iron is undergoing corrosion. ‘Samples of rusted iron under the microscope show the formation of craters and mounds indicating the two poles of action in the electro- lytic process. That is, when a posttive center is surrounded by a neg- ative area and when a negative center is surrounded by positive area. In the first case we find the metal is piled up in a crater formation, the metal being eaten out in the center. In the second case, the hydroxide is piled up in the center while the surrounding area is eaten away. The foregding examples confirm the conclusion that rusting is altogether a matter of electrolysis, Hence the iron that is most nearly free from other metals which will produce a difference in potential and hence an electrolytic action are the ones which will hold out the longest against rust. For instance there is a metal on the market at the present time which contains only five hundreths percent impurities which approaches in rust resistance the pure iron of our forefathers. Care should be - taken, however, that in getting pure iron the metal be notspoiled by heat treatment. The physical properties of the iron may be changed to such an extent that the metal will be worthless or else it will have ab- sorbed so much gas, principally hydrogen, that it will rust as readily, if not more readily, than it would have under the other conditions. Experiements show that good homogeneous iron and steel rust about equally and that where iron and steel are connected together, the iron protects the steel which is negative to the iron. Alloys of iron with other metals such as nickel, chroniun, vanadium, tungsten, and silicon are all known to be resistant to corrosion, while manganese, if present in a large quantity, is resistant but if in combination with sulphur in small quantity it helpe corrosion. PhospKor- us retards corrosion and the fact that common iron does not rust as rap- idly as the better grades has been attributed by some to the greater pre- centage of phosporus in it, Owing to the nature of corrosion it is probably true that no satisfactory accelerating test for corrosion resistance can be devised, Corrison, in the natural process of rust formation, that is to say, in very slightly acid media, is a question of comparitively slow growth under special conditions and any effort to hasten the action changes all the conditions of equilibrium, producing an éntirely different order of phenomena. PART Il | Preservation of Iron and Steel. The probdém of preservation has two phases. First, the manufacturing of a metal highly resistant to corrosion which has been discussed in the previous chapter. Second, protective coatings such as zinc, tin and lead, or oils, paints, varnishes, and bituminous na- terials and finally the production of a higher oxide on the surface. Some authorities state that hich carbon will protect the steel; that is, as the metal is eaten away the cemetite will come to the sur- face and protect it. However, there has not been sufficient experi- mentation and there is not enough data known to make this a positive statement. Highly alkaline solution prohibits corrosion if it has an ac- cess of hydroxyl ions but if the solution ise only dilutely alkaline rusting progresses very rapidly. . As has been stated before, oxygen is necessary in the water to cause rusting. Now if something provents the oxygen from reaching the iron through the wka water, then no rusting will take place, thus natural water may contain properties which will prohibit rusting through preventing the oxygen from reaching the iron. Thus it is plain how in many cases iron will corrodue faster in clear water than in sewage, the amount of free oxygen is less and hence, the action is less, This theory also explains why it is that iron and steel immersed in water or imboded in the earth below where the free oxy- gen from the air can reach it will last indefinitely without corroding to any great extent. - Any process for the prevention of rust requires that there be a clean surface on which to work and the cleaning of materials may be accomplished in three ways, pickling, tumbling and sand blast. Pickling means the removing of scale or other foreign sub- stances by the action of acids, sulphuric, muriatic and hydrofloric acids are all valuable agents for this purpose. Sulphuric 4¢id golu- tions are used generally of strengths of one part sulphuric acid to twenty parts water at 150 deg. Fahrenheit. Muriatic acid is used in smaller plants in place of sulphuric *£k¥? one part to four parts water. Care must be taken against ovetpickling which leaves the work seamed. Hydroflouric acid is very satisfactory for removing sand since it does ndt act on the metal. The formula for use is eix gal- lons of hydroflouric acid, four gal. of muriatéic acid and forty gallons of water. This should be used warm not hot. In order to obtain good results the work must be agitated in the liquid, being done to a large extent by hand, but mechanical power is coming into use with better results. The tumbling process is a mechanical means of removing scale and dirt. The water rolling process produces a smoother surface than the other processes. The castings are rolled in a tumbling drum loaded with stars and gravel and filled three fourths full of water. To this mixture is added fifteen pounds of muriatic acid, two pounds of grey ground sal amoniac. The whole is rolled from two and a half to five hours, The dry tumbling process polishes the casting as well as cleans them. In loading the drum put in first a layer of shot then a layer of castings and continue in this manner. One third shot and two thirds castings is about the right proportion for ordinary ‘tumbling. The simplest definition of sand blasting is a stream of sand and air under pressure. The cutting value of the flow is preat- er when it strikes the object slant wise rather than straight. Dif- ferent kinds of apparatus can be purchased for use in this work. The pressure of the air used in the sand blast is maintained at about 60 pounds per sq. in. It has long been known that if iron has been made the anode in an electrolytic circuit it will not rust, providing the current passing is sufficient to protect it. Zinc is electro-positive to iron, and when the two metals are in contact and wet with a corroding medium, zinc will pass into solution and the iron will be protected. There are three methods of galvanizing or plating with zinc, hot geig dipping process, "cold" or electro process, and sherardizing. The hot dipping process is a process by which the materials are coated by dipping in a hot bath of spelter or slab zinc. After the work comes from the cleaning processes it goes thru the inspection and then is dipped in muriatic acid one to one liquid measure. The work is then dried either in an oven or on plates over the fire, The dry- ing place should be near the dipping kettle as care must be taken not to dry too long or get too hot as it will burn the muriatic acid off and the piece will have to be dipped again. When properly dried the salts of muriatic acid should show on the surface of the work as a white powder. The work is dipped directly after drying and should not be allowed to get cold or stand over night as oxidation and rusting will again attack the clean surface. The most important thing about a galvanizing process is the firing of the kettles. A layer of about six inches of lead is placed in the bottom for the protection of the kettle; above this is the molten spelter and at the top a flux of salamoniac. The temperature of the zinc cannot have definite rules laid down. These things must be learned by experiment and practice. The temperature ranges from 750 deg. to 925 deg. F. The article to be dipped ie dropped thru the flux into the molten zinc and kept there until it is the temperature of the zine, It is then ringed or washed around in the metal in such a way that the flux will come in contact with all parts of it. When the article is thoroughly coated clear a space on the surface of the metal with the skimmer, sprinkle on a little dry sala- moniac and draw the article slowly from the metal, Hold the article in such a position as to cause the surplus metal to flow to one point and just as the drop starts to harden remove it with a stiff brush or old file. Expose the article to the air until crystals appear Lightly with a brush wet with clear water. Do not dip 1@ght castings in water. The Shoop metal spray process has been perfected by three stages of development; the liquid metal process, involvine a tank for hot metal weighing about one ton was non-portable; the next stage con- sisted of anparatus which was portable and galvanizing was accomplished by spraying zinc dust thru a flame. The metal in the pastic con- dition produced a coating and is yet the most economical method of coating with zinc; the last invention is the gun, weighing about four pounds, which is fed by means of a metal wire and sprays the hot molten -~10- metal upon the surface to be plated. The thickness of a single coat- -ing is about one thousandths of an inch. The operator easily can distinguish the places where there is no coat also the difference be- tween the first and second coat. Two thousandths of an inch well impacted on a surface is just as effective as a thicker coat and since the cost increases as the thickness, care should be taken not to put on more than necessary. For metal spraying the work. should be thoroughly cleaned and pores opened by preliminary sand blasting, since the action of the metal spray, with the exception of the few cases when there is chemical affinity, is a purely mechanical one and reetricted to superficial pores of the object. However, with a thoroughly cleaned opened surface, a durable, adherent protective coating is obtained. In general the application of the metal spray process may be divided into five groups; protective coatings, bonding or junction coatings, electrical coatings, decorative coatings, detachable coatings or copies of the objects. The tinning of objects is a hot dip process similar to gal- vanizing. All work must be cleaned by some one of the methods as hith- erto described. All paint or grease must be removed before processing. The sand blast may be used for this or a strong solution of caustic soda or soda ash, Immerse the object in the hot liquid and when free from matter remove and rinse. This process should precede pickling. When the work has been made perfectly clean from sand, scale, rust, grease or paint by some one of the treatments described, it is ready for the final operations. It should now be put in the alkali -ll- solution and be allowed to remain there for several minutes. From the alkali solution the work is to be passed into the rinsing tank, where care should be taken that all traces of the alkali are removed, When this is accomplished the work is to be given a few min- utes immersion in muriatic acid and water. The object of this dip is to remove any trace of rust that may have formed in the work. After this dip muriatic acid and water, which should never be omitted, the work is to be dipped in muriate of zinc, which is the last dip previous to dipping in molten tin. If roughing and finishing kettles are to be used remove the work from the muriate of zinc solution and put directly into the roughing kettle. After the work has remained in the roughing kettle take the wire by which the work has been handled in the left hand and with a skimmer in the right hand, clear a space on the surface of the tin large enough to permit the wire full of work being removed without any of the dross or flux adhering to it. Remove the wire full of work and immeree it in the second kettle. Allow the work to remain in the second kettle for a fraction of a minute until the heat of the work attained in the first kettle is reduced to about the temperature of the tin in the second kettle, which, for most purposes should be about 400 deg. Fahrenheit. When the work has about reached thehsat of the metal draw it quickly from the tin and after a few rapid swinging motionsto free it of surplus metal plunge it into a tank of kerosene oil. It should be allowed to remain in the oil long enough to set the layer of tin, It should then be immersed in water and thrown in dry sawdust to dry and remove the oil, For special design objects such as wire and the like there are special contrivances used but this gives the method of tinning as it has been developed, - l2 « The art of electro galvanizing and its industry is not the result of an invention but was simply created within the last twenty years. The force of necessity in protecting such articles as springs, small wire nettinzs, screws, bolts, nuts and the like which could not up to that day be satisfactorily galvanized by the hot process brought about electro galvanizing. The cold galvanizing has its advantages being suitable for treating the larger objects especially plus 6H. ~ 17 - PART fIII Four samples of metal, tool steel, cold rolled, cast iron and wrought iron were selected and sent to the Parker Co, to be rust proofed. Upon being treated these samples were broken and the sur- faces buffed and placed under a microscope. No satisfying results were to be obtained from the microscopic structure as to any change in the surface of these samples. The sample of wrought iron was then etched with sulphuric acid without any result. After again polishing the sample, iodine was used to etch the sxu surface for a phosphorus test. The result of which is shown in cut one. No satisfying results were to be obtained by this treat- ment. Either the iron phosphate forms in such a thin layer at the outer surface of the sample that it is not made apparent by this test or else the phosphate combinations are not formed. By means of a file a thin layer of the outer surface of the samples was removed. One portion of these filings was diesolved in nitric acid (Sp. gr. 12) until it went into solution, The volume was increased three times with water and brought almost to the boiling point. 5 grms. Pbg 0, was added cautiously and boiled for about 5 minutes. The mixture was then allowed to stand in the dark. The lead settled to the bottom while the liquid above became dark purple showing the presence of manganese in large quantities. Another portion of the filings was dissolved in a solution of nitric acid and evaporated to nearly dryness, then made strongly acid again with nitric acid and boiled down as before. ‘The solution was then diluted with water to the original volume and warmed. A oe | Figure One. few C. C. of ammonium molybdate was added and a yellow precipitate (NH4)3 PO, 12 M04) was formed denoting the presence of iron phos- phate in large quantity. Two samples which were rust proofed by Parker Co, for ex- hibition purposes were tested for their rust resisting qualities, One piece was placed half immersed in water, The other in the open air only, The test, covering two months duration, showed that the piece half immersed in water rusted while the piece in air was free from rust. . The conclusion then from our limited observation is that the phosphate and manganese compounds are formed only to an exceed- ingly thin depth at the other edge and that rusting action does take place to a more or less degree. Thus where conditions for rusting are favorable the outer surface is soon eaten away and rusting action will progress very rapidly. The Parker method, therefore, though not being proved ab- — solutely inadequate by such limited experiments, should be irivestigated further by those interested before adopting the method for use very extensively. ER iit i. 93 031 “tii 1