I N D U S T R I A L A N D ENGINEERING CHEMISTRY
August 1950
TABLE 111. APPROXIMATE SPILLINDEXES (8.1.) FOR DIFFERENT LEVELSOF ACTIVITY $pproximate Level Less than 1 w. 1 w.-1 me. low frequency) 1 pc.-1 mc. {high frequency) 1 mc.-100 me. (low frequency) 1 mc.-100 me. (high frequency) 100 me.-1 0 . low frequency) 100 me.-1 c , lhigh frequency)
S.I. -3 5-6 7-8 7-8 9-10
9-10 11-12
D . I. 2 3-4 5-6 5-6 7-8 7-8 9-10
1475
facilities for “hot” laboratories is to be reduced. Such a surface should be smooth, nonporous, and, although chemically resistant, it should be possible to remove practically monomolecular layers without pitting or roughening the cleaned area. I n view of the fact that good reagent decontamination depends primarily on preventing surface reaction, water repellent properties should be high on the list of requirements for a decontaminable surface. SUMMARY
~~~
4
~
~
~
mate decontamination occabionally. These values should be interpreted as representative of what the base material itself can achieve. Superficial coatings of various kinds can be used to raise the activity capable of being handled adequately hy thc base material. The schedule presented in Table 111 has been used to estimate the spill index and the standard decontamination index that a material should have for work at different levels of activity. The data for Pyrex glass KO.774, lead, polished stainless steel No. 347, unpolished stainless steel No. 316, and two additional stainless steel samples KO.302 have been summarized in Table I. The authors consider that a difference of 0.5 unit in either the spill index or standard decontamination index is probably significant, and that a difference of 1 unit is certainly significant. Less specificity toward the radioelement is shown by Pyrex glass No. 774 than by either lead or stainless steel. All of the stainless steels are less satisfactory when used in conjunction with P 3 2 than with BalQ or 1 1 3 1 . Also, some specificity with respect to the type of stainless steel is shown toward both barium and iodine. The high standard decontamination index observed on lead is due primarily to the fact that the decontamination reagents attack the surface. In this, and similar cases, the quantity of activity removed per step does not necessaiily level off as fast as it does when the surface is not attacked. However, in the later stages of reagent decontamination, the fraction of the activity removed is not a t all commensurate with the degree to xhich the surface is eroded. A comparison of Table I11 with the data of Table Iindicates that any of these materials can be used routinely up to the inillicurie level of activity, although more vigorous treatment would be required to keep lead cleaned, and difficulty would be encountered when P 3 2 is used in conjunction with stainless steel. If these materials are used with higher activity levels, one must be prepared to include in each cleaning operation a procedure which removes some of the surface layers B possible exception may be the contamination of type 316 or 347 stainless steel with T h e very good results obtained in the decontamination of polished stainless steel are due largely t o the mirror finish; unfortunately the latter tends t o become tarnished by laboratory fumes and the net benefit hardly justifies the additional cost of polishing. Materials which arc cheaper, more easily fabricated, and more easily decontaminated must be found if the cost of satisfactory
The exchange of a radionuclide between surface and solutioii is inherently a slow process. The difficulty of decontaminating a surface depends largely on the removal of radionuclides which are firmly attached to the surface. Simple tests which permit comparisons between surfaces, decontamination reagents, and contaminating conditions have been developed. A few conclusions regarding the suitability of glass, stainless steel, and lead for radiochemical laboratory surfaces have been drawn. ACKNOWLEDGMENT
The authors gratefully acknowledge the assistance of H. A. Levy, D. S. Anthony, and W. T. Burnett for criticism and aid in the preparation of the manuscript, and C. W. Sheppard for his many helpful suggestions during the progress of this work. LITERATURE CITED
Argonne National Laboratory, Chicago, Ill., ANL-HLH-13 (Feb 23, 1948).
Boyd, G. E., Adamson, A. W., and Myers, L. S., J. Am. Chem. Soc., 69, 2836 (1947).
Browder, F., Oak Ridge National Laboratory ORNL 158 (Oct. 6, 1948).
Burnett, W. T., and Beyl, G., unpublished experiments, Biology Division, Oak Ridge National Laboratory, 1949. Buzhgh, A. von, “Colloidal Systems,” London, The Technicat Press, Ltd., 1937. Duffield, R. B., and Calvin, M., J. Am. Chem. Soc., 68, 557 (1 946).
Hahn, O., “Applied Radiochemistry,” Ithaca, N. Y . , Cornel1 University Press, 1936. Hawes, W., Naval Radiological Defense Laboratory, AD-48 ( C ) , (November 1948). Mackintosh, A. D., Nucleonics, 5, 48 (November 1949) McKay, H. A. C., Nature, 142, 997 (1938). Mayer, S., Naval Radiological Defense Laboratory, AD-47 (C) (September 1948). Parker, G. W., personal communication. Sullivan, W. H., and Schwob, C. R., Naval Radiological Defense Laboratory, AD-I33 (L)(June 1949). Tompkins, Paul C., U. S. Naval Medical Bulletin (Suppl.) (March-April 1948). U. S. Atomic Energy Commission, Isotopes Division, “Radioisotopes Catalog,” September 1947. RECEIVED August 26, 1949. Presented before the Division of Paint, VarCHBMInish, and Plastics Chemistry at the 117th Meeting of the AMERICAN SOCIETY,Detroit, Mich. This paper is based on work done in tiit>Biology Division, Oak Ridge National Laboratory under Contract No. W. 7408-Eng-26 for the Atomic Energy Commission. CAL
(Working Surfaces for eadiochemical Laboratories)
PAINTS, PLASTICS, AND FLOOR MATERIALS PAUL C. TOMPKINSl, OSCAR M. BIZZELL, AND CLYDE D. WATSON Oak Ridge National Laboratory, Oak Ridge, Tenn.
A S Y inaterials which are commonly used in radiochemical laboratories have proved difficult, if not practically impossible, t o clean once they have become contaminated with a radioactive element. This has led to the general conclusion that radioactive decontamination and surface erosion are practically synonymous. Therefore considerable emphasis has been placed 1 Present address, Naval Radiological Defense Laboratory, San Francisco, Calif.
on a search for materials which are resistant to chemical corrosion and abrasion, with much of the emphasis being placed on properties permitting replacement of sections which are highly contaminated. Complete reliance on the use of expendable materials for permanent fixtures is less satisfactory in many instances than the use of more permanent surfaces if these can be satisfactorily decontaminated by ordinary reagent .techniques. Also, many
1476
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 42, No. 8
The methods for testing the susceptibility of a surface to conpersons in relatively small institutions do most of their work a t tamination and its subsequent ease of decontamination with variactivity levels low enough to permit proper maintenance by the ous reagents have been described (1). The susceptibility test cheaper decontamination procedures. For these reasons, a measures the apparent adsorption of the radioelement by the sursystematic study of the problems involved in reagent decontamiface u,hen a small drop is allollTed to stand in contact with the nation has been initiated a t Oak Ridge National Laboratory in surface for an hour. The decontamination test measures the total amount of contamination that may be removed a t the end collaboration with the Isotopes Division of the Atomic Energy of the second decontamination step (1) when a small drop of Commission. radioactive solution is dried on the surface under controlled condiExtensive preliminary experiments with several materials and tions and then removed, first by soaking with the standard reagents led to the develo~mentof simple, empirical tests by reagent alone, and then by standard reagent plus scrubbing. The standard reagents which the susceptibility used are given in- the of different materials to preceding paper. contamination, and their A beginning has been subsequent ease of demade toward evaluating T h e susceptibility of various paints, plastics, and floor the efficacy of less corcontamination could be materials to contamination and their subsequent ease rosive reagents, such as compared under conof decontamination have been determined by simple detergents, which would trolled conditions ( 1 ) . empirical tests. The degree of decontamination possible be the ones used in practice. These would for P32, BaI4O, and I'31spilled on seventy-five surfaces is This paper reports the be expected to vary in reduced to numerical terms and the efficacy of approxiiesults obtained by the efficiency from one mately twenty commercial detergents in decontaminating standard test on different material t o a n o t h e r . lucite and various selected resins is tabulated. AddiThe solutions of the deresins (paints and strip tergents used were pretional information on the probable usefulness of these c o a t s ) , p l a s t i c s , and pared in accordance with materials in radiochemical laboratories and attendant flooring m a t e r i a l s . the specifications of the facilities is indicated by chemical corrosion tests with manufacturer and a 1% (The inclusion or exclusolution was used except common laboratory reagents. The feasibility of using sion of specific materials as otherwise specified. some of these materials to advantage in place of glass, in these tests does not CORROSIOKT E S T S . stainless steel, or lead is discussed. The various coatings necessarily constitute an mere also applied to endorsement or rejection rounded rods 3 / , inch of a product.) in diameter by 5inches Since these materials long of soft wood or aluminum. Separate experiments with each reagent were made are used to coat either porous or corrodible items, the best by immersing test rods a t room temperature for a period of 1 surfaces would be built up as follows: week in 3 i1/1 solutions of nitric acid, hydrochloric acid, sulfuric 1. First layer, seal coat: This coat must penetrate the porous acid, sodium hydroxide, and in hexone (methylisobutyl ketone material to some depth (several millimeters on concrete or wood) which was selected as a typical organic solvent). Failure of the coating was indicated if the reagent became badly and fill all the pores with a homogeneous, chemically resistant discolored, if the coating became soft, or if "bleed through" was body. indicated by discoloration of the test rod a t a level of 0.5 em. 2. Second layer, permanent surface coat: This is preferably a above the immersion level. homogeneous extension of the seal coat. I t should be resistant The ccptings were rated as follows (see Tables I and 11): to those conditions to which it is destined to be exposed, and E. Passed all tests. should have a low adsorption value for the radioelements of S. Satisfactory for hydrochloric acid, nitric acid, sulfuric acid, inter&. and sodium hydroxide. 3. Third layer, final surface coat: This may be varied to suit A S . Satisfactory for acids, failed with sodium hydroxide. A;**. Failed with sodium hydroxide and with one acid, conditions. (In the case of flooring material, an exterior wax SX*. Satisfactory for sodium hydroxide, failed with one acid. finish is often used.) In addition to the requisite chemical and F. Failed with sodium hydroxide and two acids. physical properties, it should have a low susceptibility to contamination, and a large decontamination index (1) for all the This classification embodies not. only the data obtained in the authors' laboratory, but also data obtained by them under other radioelements of interest, and the moat important contaminating conditions, as well as data obtained by others. There was inconditions encountered. These data are of a preliminary nature sufficient information on some materials to permit such classifito the extent that a wider range of elements and contaminating cation and these have been left blank. conditions must be explored before a full evaluation can be made. The purpose of this investigation is to explore the extent to which protective coatings can be used with ordinary structural MATERIALS AND METHODS materials such as wood, transite, concrete, etc., so that reagent decontamination procedures can be used for their maintenance. PREPARATION OF THE COATINGS.The various coatings were A systematic attempt has been made to develop the information applied to 2.5 X 2.5 inch plaques as nearly as possible in the in such a way that it will contribute to the ultimate constructlion manner and to the type of material recommended by the manuof standard tables so that decontamination properties may be facturer. They were cured in a dust-free atmosphere with a d e included among the physical and chemical properties of a product. quate ventilation for the prescribed time or longer. Those which required heat curing were baked under the conditions prescribed by the manufacturer. RESULTS AND DISCUSSION The finished plaques were stored individually and examined carefully before use. Only those which presented a smooth, CHENICALRESISTAKCETESTS.Previous studies ( 1 ) have nonporous appearance were selected in an effort to obtain data shown that when a decontamination solvent is applied to a surunder the best possible conditions. face contaminated with a radionuclide, practically all of the conSome of the materials were submitted in sheet form. Plaques of the proper size were cut from these sheets, and the edges taminant that can be removed in a reasonable time is removed rounded to minimize adsorption. These materials are indicated very rapidly. The very tenacious retention of the residual acby an asterisk in tables. tivity (so well known to workers in the field) has been shown to ADSORPTION AND DECOKTAMINATION TESTS.Carrier-free arise in part from a sIow rate of exchange between the surface solutions of P 3 2 , Ba140,and 1 1 3 1 were used in the form and concentrations provided by the Operations Division of Oak Ridge and the solvent. The removal of this slowly exchanging fracXational Laboratory (9). (No isotopic carrier added deliberately tion, as well as of atoms irreversibly attached to the surface, can during production. The total solids were of the general order of be accomplished only by a process of surface erosion, preferably 1 mg. per 25 ml.) Approximately 100 to 200 microcuries of acby the removal of successive monolayers. tivity were applied as contamination in each case.
1477
1478
,
.. ,
August
1950
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
TABLE 11. SUSCEPTIBILITY OF VARIOUS STRUCTURAL MATERIALS, TAPES, AND STRIPCOATS Corro-
S
Adsorbed in 1 HOE Pas Ba140 1121 0.1 0.3 0.03
S
0,001
0.007
0.004
S
0.08
0.05
0.07
S**
0.009
0.03
0.01
SIOn
Material and Mfr. Liquid S.C. 553-45A American Resinous Chemicals Corp. Brevon, black S . C . Atlas Powder Co. Polyken tape* Bauer & Black Div. Bisonite No. 751, white S.C. Biaonite Go. Concrete*, special floor sa,mple, ORNL Carbide & Carbon Chemicals Corp. Geon latex 31X B. F. Goodrich Co. Cocoon S C R. M. Hoilinmhead Corp O.D. No. 68 tape* Industrial Tape Cow. Jonflex No. 66 tape* Industrial Tape Corp. Acetate film tape* Industrial Tape Corp. Copeel liquid plastic Maas & Waldstein Co. Mica S.C blue Midland i'ndustrial Finibhea Co. Research sample No. J-653 (S.C.) Monsanto Chemical Co. Spraylat S.C.-1054 Spraylat Corp. Plywood* United States Plywood Cow. Tygofilm, clear S.C. The United States Stoneware C o . Aluminum' Structural steel* Transite*
Rating
. ..
95.4
90.3
20.2
P
21.0
21.0
6 0
S
0.4
0.3
4.7
AS**
9.9
43.1
41.1
AS
0.5
18.0
0.2
F
0.1
0.1
0.01
S
0.001
0.03
0.2
S
0.03
0.04
0.03
E
0.07
0.4
0.3
AS**
0.1
0.3
0.3
48.0
82.0
41.0
... s
... ... ...
0.004
0.5 76.6 95.0
0.008
0.04 9.3 98.0
0.02 0.05 0.1 9.7
Therefore, it is desirable to find a solvent which may be used as the final step in the decontamination process which would attack t h e surface very slowly and yet not soften it significantly. This characteristic, aa well aa general chemical resistance, is important i n considering the results of the corrosion tests. The following discussion concerns only the protective coatings. Fluorothene, polythene, Duralon No. 35, and Monsanto research sample 5-653 (vinyl butyral dispersion D-1000) which is a strip coat, withstood all of the corrosion tests. The baked Shell enamel and Unichrome B-124-1 successfully withstood the hexone but failed in the presence of the alkali. The Devon resin K 5925 withstood the hexone for 24 hours and all of the aqueous reagents for the full week. Hexone might provide a good reagent for the final removal of contaminating radioelements from the Devon resin. However, this point has not been investigated. Twenty-eight coatings successfully withstood the aqueous reagents for a period of one week, but did not withstand the hexone. They are: Amercoat No. 31 Amercoat No. 44 Amercoat, No. 55 Liquid atrip 553-45A Brevon 535-2-353 (S.C.) Bisonite M-101 Corrosite plastic, gray Corrosite plastic. 8228 Acanal. a r m .ylrt t e
Gordon Laoey J 220F Gordon Lace A 898 Cocoon (s.c."~ Copeel liquid plastic Pyroflex white Pyroflex' ray Pyroflex' back Silicone h3X222 Mica (S. C.), blue Penkote Proxcote 19-70-3 Prufcoat Ucilon-400-9 Tygofilm, clear (S.C.)
The remainder of the coatings failed in the presence of one or more of the aqueous reagents as well as hexone. Seven of these coatings failed all tests within 48 hours and are not considered
1479
suitable for arem where acids or organic reagents are used. These are : 615 Rubalt Corrosite aluminum Silicone 60.9 Unichrome B-121
Cotoid Black Plastic01 Ucilon No. 1601
The authors recognize the fact that resistance to corrosion depends very greatly on the preparation of the coating. Therefore, it is probable that in a few instances an apparent failure could be improved by applying the coating in a different way. STANDARD DECONTAMINATION A N D SUSCEPTIBILITY TESTS. Several strippable type paints were tested. These would Iogically be used under circumstances where reagent decontamination is not practical and, therefore, only their chemical resistance and susceptibility t o contamination were tested. The results are presented in Table 11. Unlike permanent surfaces, it is often desirable that these coatings hold all contaminants permanently so they will not rub off during the stripping process. The results of the standard decontamination tests are presented in Table I. The data are presented for each radioelement The fourth column gives the gross average of the spill indexes for all three elements. It is included only as an aid in locating the very good or very bad materials and has a semiquantitative significance-the larger the number, the better the material. If a spill occurs, and the radioactive solution is removed from the surface a t once, only a portion of the radioactive atoms will remain adsorbed on the surface as contamination. Much of this contamination can be removed by subsequent reagent decontamination. The spill index evaluates a surface with respect to two criteria, ( a ) susceptibility to contamination, and ( b ) ease of decontamination. From these two values, a single value can be obtained which will incorporate them both. It is designed to estimate the fraction of the total radioactive sample that is likely to remain tenaciously attached on the surface if a spill occurs and is decontaminated within an hour. However, this does not make a distinction as to whethey an apparently good material is useful because the adsorption is low, or because a very large fraction may be removed by reagent decontamination even after the surface has dried, or both. The specific spill indexes for each element are listed in the fifth column of Table I; the per cent adsorbed in 1hour and the standard decontamination index are also given in this table. These measure, respectively, the total decontamination possible after a spill, the susceptibility of the surface to contamination, and its ease of decontamination after drying. Since the decontamination procedure is done in two steps, the results for each step independently are shown in the last two columns. The tables for the most part are self-explanatory, Therefore, only a few points of general interest will be discussed specifically. 1. The susceptibility and decontamination properties of various types of resins and plastics showed little consistency corresponding to their chemical composition-i.e. , vinyls, methyl methacrylates, furfuraldehydes, phenolformaldehydea, etc. A more detailed knowledge of the chemical composition of fillers, solvents, plasticizers, etc., used by each producer would be necessary before a good correlation on this basis could be attempted. 2. The combination of the contaminating conditions, the surface material, and the decontamination reagent constitutes a system of three interdependent variables which leads to a high degree of specificity in cleaning efficiency. Therefore, extrapolations t o new situations are extremely uncertain, and it is difficult, if not impossible, to predict what will happen. 3. Since porosity and roughness were minimized in the selection of the materials, a so-called good surface could be correlated more directly with its water repellency than with any other one property. For example, the silicones, as a group, stand out because of their uniformly high spill index. A glance a t the tables shows that most of this comes from their uniformly low adsorption values. 4. The rather uniform pattern obtained with iodine is interpreted to mean that the is adsorbed very slowly as compared
1480
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE 111. D E C O N T A M I N A T I O N O F LUCITEWITH DETERGENTS AXD WETTIKG -AGENTS Cleaning Reagent and RIBr. 0.170 Nytron Allied Chemical & Dye Corp. 1% Kytron Allied Chemical & Dye Corp.
1% Sequestrene A..4. Alrose Chemical Co. 1% Amine 0 Alrose Chemical Co. 1% Rynsynol ltlrose Chemical Co. 1% Tergitol WA No. 4 Carbide & Carbon Chemicals Corp. 1% Solvadine E O Ciba Co., Inc. 170product QB E. I. du P o n t de Nemours & Co., Inc. 10% ChIS (E. I. du P a n t de Nemours & Co., Ino.) and lY0 S-189 lyOS-189 Jacques Wolf & Co. 1 7 BTC Ox& Oil & Chemical Co. 1% Phi-0-Sol Onyx Oil & Chemical Co. 1% D2-389 Rohm & Haas Co. 1% Triton 720 Rohm & Haas Co. 170 Triton 770 Rohm & Haas Co. 170Mulsor 224 Synthetic Chemicals, Inc.
Total IsoD . I . for D.I. D.I.det tope Detergent Step 1 Step 2 D.I.8 6 . 0 2 . 9 2 . 1 -2.1 P32 3.5 -0.7 Ba140 4.0 0.5 1131 2.6 2.4 0.2 -0.3 2.2 -1.9 3.0 5.2 3.2 -1.1 0.4 3.6 2.5 2.8 0.3 -0.1 3.6 2.7 -0.8 6.3 1.6 2.8 4.4 -0.4 4.0 2.1 -1.0 6.1 1.8 3.1 fO.2 4.9 2.7 2.1 -2.3 4.8 1.2 3.0 -0.7 4.2 4.1 2.8 -0.2 6.8 1.9 2.2 -0.6 4.1
P32
Ba140 P32
Ball0 P32
Ba140 P32 Balio P32
Bald0 P32
~a140 P32
Ball0 P32
Ba140 113'
ly0 Mulsor
224 and 10% ChIS
V.4RIOCS
P32
Ba"0 11%'
5,7 3.6 4.4 4.2
3.5 0.9 2 6 1.7
2.2 2.7 1,s 2.3
-1.4 -1.1 -2.7 -0.7
7 2 3.3
4.1 2.1
3 1 1.2
+0.1 -1.1
4.4 2.7 4.7 3.4 5.3 3.4 4.4 3.6 5.0 3.1 5.0 4.0 5,4 4.0 3.1
2.5 1.0 2.7 1.1 2.7 0.8 2.6 1.2 2.9 .8 2.5 .7 2.7 1.1 2.8
4.9 3.7 3.0
3.2 2.0 2.7
1.9 1.7 2.0 2.3 2.6 2.6 1.8 2.4 2.1 2.3 2.5 3.3 2.7 2.9 .3 1.7 1.7 .3
-2.7 -2.0 -2.4 - 1.3 -1.8 -1.3 -2.7 -1.1 -2.1 -1.6 -2.1 -0.7 -1.7 -0.7 +0.2 -2.2 -1.0 +O.l
to Ba140and P32,but once attached to the surface it becomes very difficult to remove. This behavior is consist,ent with the fact that most of t,hese materials contain double bonds with which iodine can react irreversibly as it becomes oxidized by the air. Therefore, the use of plastics and paints with can be expected to lead to some difficulties. a. The results obtained on floor materials, which have been selected in the past because of their ouhtanding abrasion and chemical resistance, were uniformly poor. Reagent decontamination has little chance of success in their maintenance (see asphalt tile, Penkote). There is ample experience t,o prove that this conclusion is correct. However, other materials which have not yet been extensively used in radiochemical facilities show considerable promise since, on the basis of experimental results, they should compete favorably with some types of stainless steel, when judged only on their decontamination properties (see Duralon 35 and Sloane-Blabon flooring sample 386D). In order to compete favorably the material should have a spill index of 7 or higher and a s t a n d a d decontamination index of 6 or higher to be considered markedly superior. A spill index of 5 to 6 and a standard decont,amiiiation index of 4 to 5 is considered comparable. 6. Several of the materials examined have been shown to be basically superior in decontaminating properties t,o glass, lead, or stainless steel when used with P32or Balio. Many more are comparable. 7 . By comparison with the spill indexes and standard decont,aniination indexes that should be used for different activity levels, it is concluded that, a very wide range of plastics and resins can be used efficient,ly in laboratories using 1 millicurie or less activity in the total sample. A smaller number are basically capable of efficient use up to approximately 100 millicuries. The authors consider that efficient routine use depends on t,he ability to reduce a surface contaminant to a level near "tolerance" by reagent methods without resorting to surface erosion. A ' smooth, homogeneous material from which the superficial (monomolecular) layers can be dissolved Tr-ithoutsignificant pene-
Vol. 42, No. 8
tration of the underlying surface by the solvent makes it possible to remove even the surface-bound contaminants rather efficiently by reagent methods. If the proper solvent could be found for generally unsuitable mateiials such as asphalt tile, Penkote, etc., their useful range could be improved markedly. Further developments along these lines should push the range of their efficient use into the Ioiv curie region. USE OF DETERGEhTS
The preliminary studies reported elseir-here ( 1 ) demonstrated that other reagents were just as effective as the standard (most effective) reagents for removing a paiticular element from a particular surface. Therefore, a further study of the decontamination properties of a number of commercial detergents is presented in this paper. Since lucite was readily available and had proved to be a good material from the standpoint of decontamination under the standard conditions, the ability of several different classes of detergents to remove P32and Bal-O after air diying on lucite was studied. The iesults are presented in Table 111 showing the decontamination index for the detergent, the separate indexes at each step in the procedure, and the comparative results with the standard decontamination index TThich nas obtained by the use of the standard reagent. The decontamination efficiency of the detergent as compared to that of the standard reagent is shown in the last column. Since the efficiency of each reagent is reported numerically in the logarithmic form, the ielative efficiencies are measured by subtracting the decontamlnation index of the standard reagent (D.1 from that of the detergent (DZ.det). A positive value indicates that the detergent was a better cleaning agent than the standard reagent, while a negative value indicates that it was a poorer reagent. When the diffeience falls between $0 5 and -0.5, the two are considered to be essentially equal in efficiency. The results sholv that the only two detergents (Nytron and llulsor) tried with were just as good as 56% hydrogen iodide in removing the contaminant. Two reagents (Tergitol WA 4 and S-189, Jacques Wolf & Company, plus Du Pont CMS protective colloid) were just as effective as 3 S nitric acid-3 S phosphoric acid in removing P 3 2 . Several mere almost as good as 6 N nitric acid in removing Ba1400. The protective colloid (Du Pont C X 3 ) was tried in conjunction with an anionic detergent (S-189, Jacques Wolf & Company) and with a nonionic detergent (Mulsor 224) on both lucite and glass.
TABLE IV. DECOST.4SIIKATION O F S E L E C T E D RESINSW I T H MULSOR224 Cleaning Reagent and Mfr. llmercoat N o . 31 American Pipe & Construction Co.
Total D.I. D.I.dd130D.I. for tope Detergent Step 1 Step 2 D.I.8 P32 3.9 2.6 1.3 -1.2 Ba140 3.0 1.2 1.8 -1.5 1131 2.4 2.1 0.3 -0.8 0.5 0.7
I131
0.4
0.3 0.4 0.3
0.2 0.3 0.1
-1.9 -2.2 -2.4
Polythene E. I. du Pont de Nemours & Co., Inc.
P32
4.0 3.1 1.8
1.9 0.5 1.6
2.1 2.6 0.2
-1.4 -2.9
Shell enamel E. I. du Pont de Nemours & Co., Inc.
Pa2 Ba'40
4.7 4.2 1.8
3.4 0.7 1.6
1.3 3.5 0.2
-0.2 -1.5 -0.2
4.7 3.7 1.7
3.3 1.8 1.6
1.4 1.9 0.1
-0.2 - 1.O -0.5
3.7 3.4 1.9
3.1 1.4 1.8
0.6 2.0 0.1
-2.8 -2.8 -0.8
1.2 0.9 0.4
0.4 0.3 0.4
0.8
-1.3 -1.7 -1.2
Asphalt tile flooring Armstrong Cork Co.
A-248-B Gordon-Lacey Chemical Products Co. Silicone No. 333 Interchemical Corp.
P32
Bald0 Bald0 1131
1131
P32
Bald0 I131 p32
Bit140
I131
Iioroseal tile flooring Sloane-Blabon Corp.
P32 Ball0 1131
0.6 0.01
-1.4
August 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
It caused a marked improvement in the action of the anionic product, but had no apparent effect on the nonionic product. This observation is consistent with the anticipated specificity of detergent action which a t present is based on the thought that the reaction of the detergent with the surface material contributes far more to its cleaning efficiency than does a reaction between the reagent and the radioelement. Additional evidence pointing in the same direction is the fact that Sequestrene A.A. which is a chelating reagent was much better for removing P3*, with which there should be no chemical combination, than it was for removing Ba140,with which it forms a complex ion, thus displacing the barium ion equilibrium toward the solution. I n the second experiment air-dried P32,BaI40, and 1131 were removed from a representative group of materials by Mulsor 224 which had proved t o be a n average detergent in the previous experiment. The results, presented in Table IV, show that Mulsor can compete with the standard reagent in only a few instances, most of these being in the removal of I13l. It should also be noted that on a particular material, one or another of the elements may be removed more efficiently than the others. There is no consistent relation between the indexes for the different elements when one uses the same detergent for removing contamination from different surfaces. The same observation was made with respect t o the removal of P32,BaI4o,and from glass, stainless steel, and lead, again pointing up the fact that reagent decontamination involves the interaction of a t least three major variables-the surface, the radioelement, and the decontamination reagent. The development of detergents which have outstanding cleaning properties promises to be a matter of fitting the reagent t o a specific job, a t least until the mechanism of the action is better understood. Despite the unfavorable comparison of many detergents with the standard reagent, the first experiment demonstrated that a detergent may be found that is just as good as the standard reagent for removing a particular element from a particular surface material. Also, a large number of cleaning problem exist for which a decontamination index of 3 or 4 is quite adequate, and
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Mulsor, a n average detergent when used with lucite, gave an index of this magnitude on several of the materials. Mulsor on asphalt tile and on Koroseal tile was virtually useless. If these materials are selected for use in a radiochemical laboratory t o take advantage of their proved wearing qualities, one should be prepared to adopt a maintenance policy of replacing the contaminated areas. SUMAIA R Y
The corrosion resistance and decontamination properties of several available paints, plastics, and resins have been studied under standardized conditions. It is concluded that some of these may be used to advantage in place of glass, stainless steel, or lead for many common functions, and that they may often be decontaminated by mild reagents, such as detergents. The combination of the contaminating conditions, the surface material, and the decontamination reagent are interdependent variables which leads to a high degree of specificity in cleaning efficiency. ACKNOWLEDGMENT
The authors gratefully acknowledge the assistance of Maryann Huddleston and George A. West for aid in performing these tests. They also wish to acknowledge Arthur D. Little, Inc., for making available to them some information obtained during their extensive studies of materials to be used in the construction of some of the new Atomic Energy Commission facilities. LITERATURE CITED
(1) T o m p k i n s , P. C., a n d Bizsell, 0. M., IND.ENG.CHEM., 42, 1469 (1950). (2) U. S. Atomic E n e r g y C o m m i s s i o n , Isotopes Division, “ R a d i o isotopes C a t a l o g , ” S e p t e m b e r 1947. RECEIVED August 26, 1949. Presented before the Division of Paint, VarCnExInish, and Plastics Chemistry a t the 117th Meeting of t h e AMBRICAN CAL SOCIETY,Detroit, Mich. This paper is based on work done in the Biology Division, Oak Ridge National Labmatory under Contract No. W7405-Eng-26 for the Atomic Energy Commission.
Solid-Fluid Heat Exchange in Moving Beds WILLIAM D. MUNRO AND NEAL R. AMUNDSON University of Minnesota, Minneapolis 14, M i n n .
A solution of the problem of heat exchange between solid and fluid is presented for parallel or counterflow exchangers. It is assumed that the solid consists of uniform spheres. The resistance to heat transfer by conduction in the spheres is taken into consideration. Heat generation within the spheres may occur either at a constant rate or as a linear function of the temperature. An exact solu-
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ECAUSE of its great industrial application, the general problem of heat exchange between a fluid and a solid has received widespread treatment in the literature. The fluid usually moves through the exchanger in a single direction. The solid, on the other hand, may be stationary, moving in a direction parallel, either concurrent or countercurrent, t o the fluid, or moving in almost random motion as in a fluidized bed. The fixed-bed operation has received the most attention because of the use of checker-brick regenerators and because all of the older catalytic processes were of this type. A rather complete bibliography of the theoretical work in this field is given by
tion of the theoretical equations is obtained by means of the Laplace transformation. Numerous special cases are obtained, among which is the use of the equations in catalytic reactor design for a simple reaction. Numerical examples are included for comparison with approximate treatments. The examples show that approximate treatments predict exchangers whose transfer area is too small.
Thiele ( 1 4 ) in a review article. The case of heat release in a fixed-bed catalytic converter was considered by Brinkley (a), Wilhelm, Johnson, and Acton ( I T ) , and Wilhelm and Singer (18). Other treatments of heat transfer in packed beds are those of Arthur and Linnett ( I ) , Damkohler ( 4 , 6), and Grossman (10).
The problem of a solid moving countercurrent to a fluid has received some attention because of its importance in blast furnace operations, kiln-type heaters, and the newly developed catalytic processes for cracking petroleum. Furnas (7-9) discussed this problem in an approximate manner. Love11 and Karnofsky
