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1 NRC Publications Archive Archives des publications du CNRC Measurement of the Salt Content of Air at Corrosion Sites Across Canada Foran, M. R.; King, W. L. M. For the publisher s version, please access the DOI link below./ Pour consulter la version de l éditeur, utilisez le lien DOI ci-dessous. Publisher s version / Version de l'éditeur: Internal Report (National Research Council Canada. Division of Building Research), NRC Publications Record / Notice d'archives des publications de CNRC: Access and use of this website and the material on it are subject to the Terms and Conditions set forth at READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. L accès à ce site Web et l utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D UTILISER CE SITE WEB. Questions? Contact the NRC Publications Archive team at PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to the authors directly, please see the first page of the publication for their contact information. Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

2 NATIONAL RESEARCH COUNCIL OF CANADA DIVISION OF BUILDING RESEARCH MEASUREMENT OF THE SALT CONTENT OF AIR AT CORROSION SITES ACROSS CANADA Part I : Part II: General Discussion and Comment Some Experiments on the Determination of Atmospheric Chlorides near Halifax by M.R. Foran and WoLoM. King Report No o 122 of the Division of Building Research Ottawa June, 19.57

3 PREFACE The Divisipn of Building Research has established eight exposure sites across Canada and maintains these for the work of the Associate Committee on Corrosion of the National Research Council. These sites, which are administered by the Divlsion$ are also used in its own projects involving exposure of materials to representative Canadian atmospheres, and can be used by arrangement by others having need of such facilities. It is of value in interpreting the results obtained by exposure at various locations to have, in addition to the usual climatic data, quantitative measurements on certain other characteristics of the atmosphere such as the occurrence of sulphur dioxide and of chlorides. Routine measurements on sulphur dioxide are already being made at the various sites, but there has been no accepted simple method by which the salt content of the air might be satisfactorily measured on a routine basis o The Division was therefore pleased to be able to arranged in co-operation with the Associate Committee on Corrosion and the Nova Scotia Research Foundation for the employment of a summer student Mr o WoL.M. King to work under Dr. MoR. Foran on an initial study of possible methods of measuring atmospheric chlorides o Dr. Foran's assessment of the problem together with the results of the summer 9s work carried out by Mr. King are now reported. Ottawa, June g NoB. Hutcheon 9 Assistant Director.

4 MEASUREMENT OF THE SALT CONTENT OF AIR AT CORROSION SITES ACROSS CANADA by p a r t G i GENERAL DISCUSSION AND COMMENT by MoR. Foran In the spring of 1956 the Nova Scotia Research Foundation arranged with the Division of Building Research of the National Research Council of Canada to have a summer research student investigate some of the methods which might be used to determine the salt content of the air at corrosion sites where no electrical power was available and where there was no continuous supervisione Mr. W.L.Mo King, a very capable and intelligent medical student was engaged to do the worko Although he had almost no training in quantitative analysis g Mro King worked industriously at the very tedious and exacting analytical procedures required for the measurement of traces of chloride and mastered them well enough to obtain the results in the attached report o Before he began his experimental work he reviewed a great deal of the カ ゥャ literature for methods and specific procedureso A general review of the problem and some of the requirements for its solution will be attempted here in order to show the difficulties. A survey of the corrosion literature did not reveal any conclusive facts about the size of the salt particles which must be measured in order to relate the corrosion of metals to the salt content of the airo The apparent salt content of air depends very much upon the method of measurement since some methods are more suitable for large particles and others collect even the very fine particles. オウ The following is a list of some of the methods which have been 1 0 BUbbling air through chloride-free water, 2 0 Drawing air through chloride-free ヲゥャエ イウ 3. Drawing air through refrigerated tubes (dew tubes)z

5 Exposure of wet, chloride-free cloths; 5. Exposure of wet, chloride-free cylinders ("wet-candle" method), 6. Determining the salt content of rainwater; 1. Collection of artificial dew on cold flasks, X Counting salt crystals on exposed slides; 9. Collecting salt by impactors or jets; 10. Thermal precipitation of particles onto a glass slids e The first seven methods all depend upon the accurate determination of small traces of chlorides by chemical methods. In each case, all surfaces, chemicals, solutions and materials must be free from chlorides at the beginning of a measurement. This requires the development of an antichloride technique for all stages of the preparation, handling, and transfer of the atmospheric chloride to the analytical vessels. These methods are therefore laborious and exacting since only a very few milligrams of chloride can be collected unless large volumes of air or large surfaces are used e Another factor to be considered is whether the chloride found by any of these methods comes from sodium chloride. Sugawara et al (1) and Ambler (2) found that in rainwater near the sea the' ratio of H n K I (C1-) = 008S t which is approximately the ratio in sea water. In mountain fog, sea fog, inland rain, and other types of atmospheric precipitation they found that the ratio varied from 0.48 to For this reason the results should be given in terms of chloride ion alone. The last three methods enumerated above are physical methods and t he salt particles generally have to be counted under a microscope. These are not suitable for the routine measurement of atmospheric chlorideo As these methods collect オウエ spores, all types of airborne salts, and liquid droplets of various kinds it would be very difficult to isolate the chlorides o In addition to the requirement that a Canadian method should require no electrical power and no supervision between occasional visits to the site, it must also be able to withstand severe climatic changes, be continuous in ッー イ エゥッョ unaffected by wind velocity and direction, and capable of collecting all types of chloride particles which are significant for corrosion. A systematic examination of the ten methods listed above shows that no one of them is entirely suitable.

6 - 3 - Bubbling air through chloride-free water is not feasible in our climate but a study of relatively non-volatile solvents for sodium chloride might be made o The lack of electrical power on the sites might be circumvented by the installation of winddriven, six-volt generators with storage batteries floating on the lineo These would operate small blowers or pumpso Air might be drawn through dry filters if the abovementioned power supply system was considered feasible e The pore size of the filters could then be chosen to collect all slzes of particle considered significant to corrosion. Cold tubes for the continuous collection of salt in dew hardly seem feasible where electrical refrigeration is not available. Exposure of wet-cloths has been found to require constant attention and they give no better results than the "wet-candle" method which requires little attention if freezing and too rapid evaporation can be avoided (2). The exposure of moist cylinders has been found fairly suitable in the tropics (2) but no specific measures to prevent a too rapid rate of evaporation are mentioned in the literature. In order to use them in Canada they would have to be suitable for freezing temperatures o A study of antifreeze solutions in conical or cylindrical metal flasks could be made.. Glycerine has been found (3) to prevent undue rates of evaporation from the flasks but makes the analysis for chlorides somewhat more complicated. This method is known as the "wet-candle" method because gauze is wrapped around a tube to form a candleo The amount of chloride collected is quite small and the preparation of a chloride=free assembly is tediouso The chloride analysis is quite time consuming because of the washing of the gauze.. Atmospheric soot and grime increase the difficulty of the analysiso For general Canadian conditions the flasks and tubes should be made of Hastelloy or some non-reactive metal or of a ーャ ウエゥ セャゥォ ーッャケ エィケャ ョ The Nova Scotia Research Foundation has had dustfall or rainfall cans of standard design exposed at twelve different locations in Halifax and Dartmoutho These were generally less than half a mile from the harbouro The chloride content of the water collected during one winter month and four summer months is shown in Table 110 For comparison Table I shows results obtained by the wet-candle method during the same summer months o Three stations have been selected because their exposure was comparable or identical to that of the dustfall cans.

7 - 4 - TABLE CHLORIDES COLLECTED BY WET-CANDLES AT HALIFAX (Quantitives are in Mg o of chloride/m2/day) Station A B C Average. Federal Building York Redoubt Technical College I - - TABLE II CHLORIDES COLLECTED BY RAINFALL CANS IN h a l i セ AREA (Quantities shown 'are in Mg o chloride ion/m 7day) Station No. Dec e 9 25 June 9$6 Ju1y IJ56 Aug v$6 Sept IJ S , ge04 110$ $ $ 3 $ ,, $ $ < $ 70$ $

8 M M M M M M セ M M M M N It appears that the dustfall or rainfall cans will give essentially similar rdsults to those of the wet-candle method in coastal areas" They.ere not tried in duplicate or triplicate at the same location so the spread of the results is not known" They are much easier to handle than the wet-candles and the analysis is much easier to perform e They seem to handle snow, ice and freezing conditions very well which the present form of the wet-candle apparatus was not designed to doe The dustfall cans appear to be the best method to try under the present conditions at the corrosion sites across Canada" As long as no electrical power is available at the sites it is impossible to test methods which blow or suck air through dry filters or other devices o This leaves modification of the "wetcandle" method as the only alternative among the proposed methods o So far the current research has not led to any very feasible methods which can meet the rigid limitations imposed by the atmospheres, the climate, the lack of power, and ウオー イカゥウゥッョ and the need for simplicityo REFERENCES s オァ キ イ K0 9 S. Oana, and To Koyamae Bullo Chemo Soco Japan, Vol o 22 9 Noo 47, (1949)0 (2 ) Ambler 9 HoRo, and AoAoJo Baine se, 43b, (1955)" Jo Applied Cheme Vole U (3) King, WeL"M" Some experiments on the determination of atmospheric chlorides near Halifax o National Research Council, Division of Building Research, Internal Report No" 122 (Part II) j) June 1957.

9 - 6 - PART II: SOME EXPERIMENTS ON THE DETERMINATION OF ATMOSPHERIC CHLORIDES NEAR HALIFAX by More than one method of collecting atmospheric chloride for its chemical determination was considered. A direct measurement of the chloride concentration was attempted by drawing very slowly a metered quantity of air through a tube packed with washed-glass wool o The results were unsatisfactory, no titratable amount of chloride being detected in the glass wool after cu o fto of air had been drawn through the tube over a 5 2/3-day period o The sampler used a converted automobile heater fan, running on a 6-volt battery, as a source of powero No field trials of the unit were made. Although an appreciable amount of chloride might be collected through the use of a highspeed sampler, one is faced with the fact that the results obtained at one location over a period of a day or so would not be comparable to that obtained elsewhere for a ゥヲヲ イ ョエ and also brief, period o If comparison between sites is to be made g it is necessary to run simultaneous and fairly lengthy testse Finally, there is the problem of finding a source of power for the high-speed sampler at the various siteso The wet-cloth method was considered to require more attention than it could be given. This method g which consists of exposing a cotton cloth kept wet with water or glycerine-water at 45 0 to the sea or the wind, was said by Ambler and Bain (1) to be in constant need of attention if the cloth were to be kept weto Another method suggested by Ambler and Bain was that of artificial dew o Dew is made to deposit on the surface of a glass container filled with ice, and the salt in the dew is then measured. Because this method appears to collect almost exclusively the finer salt particles not deposited on metal surfaces, it would be of little value for a corrosion study involving sea-side locationso Furthermore g since the method requires the use of low temperatures» it would be difficult to run a test over a long-term period at those sites which have no electrical power supp1ieso The wet-candia method appeared to be the most promising. The wet-candles were prepared as follows o Three strips of Noo 2 gauze bandage, 3 inches wide and about 28 inches long g folded alqng the length, were wrapped around that portion of a 5 3/4-

10 セ 7 - inch test-tube protruding above the rubber or cork stopper in which it was standing (Fig. 1)0 Any chloride in the gauze had been removed by boiling in distilled watero The stopper was fitted into a 500 ml wide-mouth glass flask containing 500 ml of a glycerine-distilled water solution which was 20 per cent glycerine by volumeo Two sides of the stopper were recessed a bit, allowing the gauze tails to dip into the ァャケ イゥョ セキ エ solution o The apparatus was covered with a sloping roof for protection from rain and suno According to Ambler and Bain, this method gives the same magnitude of results as does the wet-cloth methodo Its advantages, as far as use in corrosion research is concerned, are two. f ゥイウエャケ it is suitable for long-term tests, and secondly, it gives an indication of the quantity of salt likely to be deposited on a surface, which is apt to make it even more useful from a standpoint of corrosion than a method which gives the absolute concentration of atmospheric chloride o Some modifications of the wet-candle method, as outlined by Ambler and Bain, were tested o Fiber glass tape was tried in the place of gauze bandage, but was found to be no improvement. Its chief fault was that it did not remain wet o The method, as Ambler and Bain discussed it, called for no glycerine Q Because, without it, it is necessary to add water weekly at some sites 6 it was decided to add glycerine to slow down the rate of evaporation of the liquid in the flask and make it possible to continue the tests during winter weather, if desired, with less danger of broken flaskso Twenty per cent of glycerine 9 by volume, was found to be a suitable concentration for summer conditionso No tests were made at freezing temperatureso In the first エイゥ ャウ for the chemical determination of the amount of chloride deposited on the キ エセ ョ ャ the contents of the flask, including the ァ オコ キ titrated with silver nitrate w This was thought to be unsuitable from a standpoint of オイ ケ a blank titration requiring too much silver nitrateo Thus, the mercurimetric method, which had seemed promising, was tried o In titrating mercurimetrically9 complicating factors were encountered o Because the end-point is represented by a faint but permanent turbidity, colloidal organic ュ エエ イ frequently present, interfered o Organic matter, ィッキ カ イ along with sulphites g which also interfere in titrations with mercuric nitrate, were oxidized with an excess of potassium permanganate, the excess being SUbsequently reduced with hydrogen peroxide 6

11 = 8 = Finally, mention should be made or the mould which appeared inside the flasks containing glycerine about two weeks after the 'flasks had been set outo Very little 9 however, if anyd was seen in each or the flasks fitted with rubber, rather than ッイォ stopperso This mould 9 the presence of which did not prove too troublesome, obviously lived on the glycerine» the decomposition of which was indicated by the appearance of a yellow colour in the glycerine-distilled water solutiono Mould was much more prevalent with cork stoppers probably because either a poorer fit was being obtained or the mould was originating rrom spores in the cork o The routine involved in the mercurimetric titration of the chloride collected by a キ エセ ョ ャ is as follows.. Following the careful removal of the gauze strips from the エ ウエセエオ their submersion in the glycerine-water solution in the flask, and the washing of the test-tube surface into the flaskd the contents or the flask were boiled.. The liquid in the flask was then poured into a beaker and distilled water was added to the gauze in the flasko After boiling, the supernatant liquid was poured into the beaker o The gauze was then washed repeatedly in boiling water until all the chloride was removed o Now the mixture that had collected in the beaker was boiled down to a volume or about 200 ml, after filtering, an excess or potassium permanganate was added and the mixture was allowed to stand for at least fifteen minuteso One ml of hydrogen peroxide was now added to reduce the excess permanganate o More hydrogen peroxide can be added if the peroxide is ィャッイゥ セヲイ and there is no worry about increasing the volume of mercuric nitrate necessary in the back エゥエイ エゥッョ but ir this is not the cased and all of the permanganate has not been reduced 9 boiling can be employedo Boiling permanganate auto-decomposes itl' manganese dioxide acting as a catalyst o Arter filtering to remove the manganese dioxide.\> the mixture was again boiled down to about 200 ml and then made up to 250 ml in a volumetric flasko Two ッョ セィオョ イ ml portions were taken and acidified with nitric acid (about 1 ml of concentrated nitric acid)o Following the addition to each aliquot of 2 ml of sodium nitroprusside indicator» and SUbsequent filtering if there was any エオイ ゥ ゥエケ the aliquot was セゥエイ エ slowly with standardized mercuric nitrate until a faint but permanent turbidity appeared o A dilute N mercuric nitrate solution was used, since the chloride i11 the mixture being titrated was of such low concentration.. It was because the mercuric nitrate solution was so dilute that 2 ml of indicator were used o It was discovered that observation of the first sign of permanent turbidity could best be made by setting the flask on a black background and looking down into the flask through the mouth» while wrapping the hands around that portion of the flask above the level of the mixture o

12 "" 9 = Despite efforts to overcome it, unwanted turbidity persisted in some mixtures which were to be titratedo Six of twelve flasks set out on July 20 and taken in on August 10 gave acceptably close figures for the titrations of the two 100-ml aliquots" The data obtained from those six flasks are given below" An example of the method used for the single calculations is as ヲッャャッキウ With the titration figures being 3057 ml and 3054 ml for the two 100-ml aliquots drawn from the 25Q-ml total volume of オョォョッキョ and 0062 ml and セ for the two 100-ml aliquots drawn from the R U P セュ volume of blank solution, the total volume of mercuric nitrate needed to react with all the chloride in the total volume of unknown = ( ) + (3054 = 0061) x 5/4 = 7036 ml o Then, ウセョ one ml of N mercuric nitrate reacts with P P T R mg chloride ion, the total amount of chloride ion deposited on the gauze surface equals 7036 x = mg o TABLE AMOUNT OF CHLORIDE ION DEPOSITED ON WET-CANDLES DURING PERIOD, JULY 20 - AUG 0 10i 19$6 9 AS DETERMINED MERCURlMETRICALLY III Total amount of chloride ion g in ュァ deposited in 21 days Mgo of chloride ionl sq meter/day Candle A Candle B A B Federal Building Roof 3,, York Redoubt 2,,60 x lo90 x l3000 x 9050 x Sackville (in garden opposite end of paved 1 lo27 x Beaver Bank r ッ セ 6035 x x Signifies a rubber stopper o If no asterisk is present g a cork stopper was used o The surface area of the gauze on a test tube mounted in a rubber stopper is the sum of the surface areas of the eylinder p sq em, and of the gauze resting on the top or in the recesses in the side of the stopper p 5092 sq emo t ィオウ the total surface area is 9502 sq em or square meters o SimilarlY9 the surface area of the gauze when cork is used is the sum of sq cm and sq em, which equals 9104 sq cm or square

13 meters e The difference found with the different types of stoppers is due to the fact that the cork stoppers had more depth and, consequently, exposed less length of test-tube, but at the same time exposed more cork above the lip of the flask and so ーイ ウ ョエ more gauze on its own sides than did the イオ セ stopper. Because the mercurimetric method of titration had proved somewhat difficult, a ヲオイエィ ᄋ examination of the titration with silver nitrate was made, with pleasing results e As with the mercurimetric method, there was extraction of the chloride by boiling, イ セ エゥッ of the volume by boiling, filtering, addition of an excess of permanganate (5 ml)g standing, addition of 1 cc hydrogen peroxide, boiling if necessary, filtering, reduction of the volume to about 200 ml by boiling, dilution to 250 mig and the pipetting out of two 100-ml ャゥアオッセウ The aliquots, however, were put in white evaporating dishes to faoilitate observation of the end-point during titration. After 1 cc of 5 per oent potassium chromate had been added to each aliquot, titration was made with silver nitrate p I co of which precipitated 0.5 mg chloride ion. The data provided by the fifteen flasks which sat out from August 10 to August 24are given on the following page. With distance ヲセッ the sea, within the coastal area 9 quite a rapid decrease in the atmospheric content of salt particles subjeot to deposition has been shown by the "wet-candle" method. REFERENCE (1) Ambler, HoR o g and AoAoJo Baino Jo Appl. Chem. Vol. U No. 431 (1955)0

14 TABLE IV AMOUNT OF CHLORIDE ION DEPOSITED ON WET-CANDLES DURING PERIOD AUG o 10-24, 1956, AS DETERMINED AROENTlMERTICALLY o - Total amount of chloride ion, Mgo of chloride in mg, deposited in 14 days ion/sq meter/day Candle A Candle B Candle C A B C Federal Bldg. Roof x x York Redoubt Sackvi11e, NoS Mining Bldg NoSoT.Co Chebucto Rd., 135' from sea x denotes rubber stopper Mgo of chloride ion (sq meter day (average) Federal B1dg o 17065:6049 York Redoubt 12049:3082 Sackvi11e i NoS. 6027!300S Mining B1dgo, N.SoToC o 11079±203S Chebucto Head Light 20S08S! Standard Deviation = r3=-- D 2 '1/": n-1

15 Figure 1. "Wet Candles" exposed at NRC corrosion site at York Redoubt near Halifax. DBR INTERNAL REPORT NO. 122