June, 1934
.
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 IS T R Y
by the change in rotatory power, was the single effect of heating only during the complete series a t 175" and the first period a t 230" C. The decarboxylation and dehydration which proceed concurrently with isomerization under the other conditions naturally affected somewhat the melting points and rotatory power of the reaction products. According t o Easterfield and Bagley, however, the optical power of the acid is independent of the presence of the carboxyl group (3). In most cases the products of heating were glassy rosins which, when heated in capillary tubes, fist sintered, then melted a t 107" to 112" C., and then began to recrystallize and finally remelted at 147" to 158" C., both melting points depending on the previous heat treatment. Similar observations were made by Easterfield and Bagley (3) and by Seidel (IO). The change in rotation was very gradual a t 175" C., but increased sharply with rising temperature, the greatest change occurring during the first hour of heating. Thus at 230°, 275", and 330" C. during the first hour when the degree of decarboxylation and anhydride formation was small compared with the extent of these reactions during the longer periods, the change in rotation was 81, 56, and 76 per cent, respectively, of the total change during the longer periods. This indicates that isomerization rather than the rotatory power of decomposition products was the chief
681
cause of the alteration in the optical rotation during these intervals. LITERATURE CITED (1) (2)
Dupont, BUZZ.soc. chim., [ 4 ] 35, 1209 (1924). Dupont, Rouin, and Dubourg, Bull. I'inst. pin, No. 38,
157
(1927).
(3) Easterfield and Bagley, J . Chem. SOC.,85, 1238 (1904). Eiseman, Weaver, and Smith, Bur. Standards J . Research, 8,
(4)
669 (1932).
( 5 ) Gerstacker, Farben-Ztg., 25, 1170 (1920); Herty and Cox, J. IND. ENG.CHEY., 1, 68 (1909); Herty and Dickson, Ibid., 6, 782 (1914); Lange, Oil, Paint Drug Reptr., 95, No. 11, 28 (1919); Schwalbe, 2. angew. Chem., 18, 1852 (1905); Stock, Farben-Ztg., 27, 2 2 1 (1921). (6) Hurd, C. D., "Pyrolysis of Carbon Compounds," p. 330,
Chemical Catalog Co., N. Y . , 1929. (7) Ibid., pp. 344-5. (8)
(9)
Knecht, J. SOC.Dyers Colourists, 39, 338 (1923); Knecht and Hibbert, Ibid., 35, 148 (1919); Rouin, Bull. I'inst. pin, No. 53, 2 2 1 (1928); Ruaicka and Pfeiffer, Helv. Chim. Acta, 8, 632 (1926) ; Ruzicka and Schina, Ibid., 6 , 662 (1923) : Ruaicka and Schina, Ibid., 6 , 833 (1923); Schkateloff, Moni. S c i . , 22, 217, 548 (1908); Schula, Chem.-Ztg., 41, 666 (1917). Ruzicka, de Graaf, and Muller, Helv. Chim. Acta, 15, 1300 (1932).
(IO) Seidel, Dissertation, Mannheim, 1913. (11) Steele, J. -4m. Chem. SOC.,44, 1333 (1922) RBCEIVED October 14, 1933.
Diffusion Coefficients in Gaseous Systems E. R. GILLILAND,Massachusetts I n s t i t u t e of Technology, Cambridge, Mass.
I
by gases, in fundamental airNDUSTRY is exerting everNew data are presented on diffusion coeficonditioning and n u m be r 1e s s increasing pressure upon the cients for various organic vapors and f o r mercury other cases. If sound design engineer to reduce costs. in air at one atmosphere at temperatures f r o m must wait until data are availI n achieving this, one of the 25.9" to 341' C. Data from the literature o n most attractive possibilities is able on each individual operadiffusion coeficients f o r a large number of tion, the engineer will wait till the reduction of the element of doomsday for the facts he needs. fixed charges by increasing the gaseous systems have been collected and plotted. capacity of given equipment. Fortunately, however, the genI t is found that the data are better correlated by The engineer too f r e q u e n t l y eralizations of the physicist put the groups of the original Maxwell equation fails to appreciate the fact t h a t one in a position to solve these than by the Sutherland modification, and that diffusional problems by the use the limiting factor which conthe mass of data m a y be represented within the of limited data properly genstitutes the bottle neck of capacity is not infrequently the diferalized. The purpose of this accuracy of the experimental methods by the fusion of the reacting substances. article is to make an additional Maxwell equation with a n empirical constant. The dearth of engineering attencontribution in this direction in The resulting equation is given as Equation 6 . tion directed to this toDic in the the special field of gaseous difpast is convincing evidence of the fusion. The fundamental differential equations for the diffusion engineer's lack of appreciation of its importance. The time has come to place this matter on an engineering basis which of gases, derived originally by Maxwell ( I ? ) and Stefan (.e,+), must be integrated for the individual situations arising in any is not only broad but sound. Two methods of attack are available: the use of empirical given engineering operation.' However, the equations contain experimental data obtained for each individual case, or the the diffusion coefficient of the gaseous mixture under condevelopment of dependable generalizations which will make sideration and cannot be used without a knowledge of its possible a sound synthesis of each individual problem. numerical value. Maxwell, recognizing the importance of The multiplicity of problems involved is convincing evidence this point, proposed the following equation : that only the second method of attack is adequate. Thus, one must keep in mind the fact that diffusion is a necessary and frequently a controlling factor in the rate of every interaction between gases in which there is present any nonB = ordinary mol. weights of the two gases reacting constituent or in which any substance is synthesized where M A , M P = totalpressure at one point and eliminated from the zone of reaction a t the S = distance between the centers of the two unother. Gas diffusion plays its part in the combustion of like molecules at collision (or sum of the radii of the two unlike molecules) solid and liquid fuels, in the roasting of sulfide ores, in every D = diffusion coefficient of the system acceleration of gaseous reactions by solid or liquid catalysts, T = abs. temp. in every operation of rectification, in the selective absorption A = aconstant of gases by liquids, in the removal of volatile constituents I For integrations see Colburn and Hougen ( 3 ) . Hanks and McAdams (7), from the liquids by steam distillation, in the drying of solids and Lewis and Chang ( l e ) .
682
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 26, No. 6
TABLEI. SOURCES O F PUBLISHED DATAFOR VARIOVS SYSTEMS TEMP.
SYSTEX
RANGE O
c.
PRESSURE R-ANGE
REFERENCE
TEMP.
SYSTEM
c.
OASES
Air-Hz Air-COz Air-Os Oz-HI
ORGANIC E S T E R 3
OPNZ
18-22 0-61 0 0-61 12-61
1 1 1 1
orco
M I
1 1 1 1 1
os-COI CO-Hz
1
0 0 0 0-6 1
co-coz Hz-COz
Hz-Nz HI-SO? Hs-Nz0 Hs-CHI Hz-CsHd Cos-Nz0 COz-Nz COz-CzH4 CO~CHI
1
0-61 0 0 0
1 1 1
NHrAir He-A Air-HsO Hz-HzO Cos-HsO ORGANIC ESTERS
Air-methyl formate Air-met!gyl acetate H*-methvl acetate COruiethyl acetate
1
11-99 10-51 20-46 20-46
1
1 1
Air-ethyl formate Hz-ethyl formate COa-ethvl formate A i r m e t h y l propionate Hz-methyl proprionate COrmethylproprionate
11-50 20-46 20-46 15-70 46-67 46-67
Air-ethyl acetate Hz-eth 1 acetate COz-etXyl acetate Air-propyl formate Hz-propyl formate Con-propyl formate
10-70 46 46 2(t80 46-67 46-67
1
Air-methyl butyrate Ht-methyl butyrate COI-methvl butvrate Airlme;h?:liso-b;tyrste H1-rneth 1 iaobutyrate Cot-metgrl isobutyrate
22-99 67-92 67-92
1 1
1 1 1
1
1 1
1
1 1 1
1
1
ii-80
1
1 1
49-67 49-67
Numerous rederivations and modifications of Maxwell’s original equation have been proposed. Jeans (10) gives the same relation but with a slightly different constant, 8/3n times that given by Maxwell. Chapman’s derivation ( 2 ) leads to a constant three-fourths as large as that obtained by Maxwell. This type of equation predicts no variation of the diffusion coefficient with the relative amounts of the two gases present. Meyer (18) has proposed an equation which indicates large variations in D as the relative percentages of the two gases are varied. The work of Lonius ( I d ) , Schultze (M), Jackman (9),and Deutsch (4) indicate that such variations are very slight, and probably within the experimental accuracy; consequently the Maxwell type of equation is used in preference to that of Meyer. The most important modification of the Maxwell equation is due to Sutherland (d6), who introduced the factor (1 C / T ) in the denominator of the right-hand side of Equation 1:
+
drA+ re S2P + E>
A‘T3l2
D =
1
PRESSURE RANGE REFERENCE Atm.
RANQB
Atm.
1
(1
The Sutherland constant, C, for the system depends only on the natures of the two kinds of molecules and is obtained from the individual values of C for each gas, which are in turn obtained preferably from viscosity data on the pure gases. Methods of estimating C for any gas system are discussed bv Arnold ( 1 ) . The radii of the‘molecules may be obtained in several
(ContinUed) 1
Air-ethyl propionate Hz-ethyl ropionate COz-ethyppropionate Air-propyl acetate Air-isobutyl formate Air-methyl valerate
10-92 67-90 67-90 10-99 25-85 45-100
Air-ethyl butyrate Hz-ethyl butyrate COz-thy! butyrate Air-ethyl isobutyrate Hz-ethyl isobutyrate COsethyl isobutyrate
42-100 67-96 67-96 59-100 67-96 67-96
Air-propyl propionate Hz-propyl ropionate Cos-propyypropionate Air-butyl acetate Hf-butyl acetate C O r b u t y l acetate
53-100 96 96 50-100 67-98 67-98
Air-amyl formate Air-ieoamyl form ate Air-ethyl valerate Hz-ethyl valerate COz-ethyl valerate
37-99 49-100 50-99 9s 98
Air-propyl butyrate Hz-propyl butyrate COz-propyl butyrate Air-propyl isobutyrate Hz-propvl isobutyrate Cot-propyl isobutyrate Air-isopropyl isobutyrate
50-100 98 98 56-100 97 97 50-100
Air-isobutyl propionate Hz-isobutyl propionate COz-isobutyl ropionate Air-propyl vaferate Hz-propyl valerate Cor-propyl valerate
66-100 98 98 70-100 98 98
1
Air-isobutyl butyrate Hz-isobutyl butyrate COz-isobutyl butyrate Air-isobutyl isobutyrate Hz-isobutyl isobutyrate Cot-isobutyl isobutyrate
75-100 98 98 75-100 98 98
1 1 1 1 1 1
Air-isobutyl valerate Hz-isobutyl valerate CO-isobutyl valerate Air-amyl butyrate Air-amyl isobutyrate Hz-amyl isobutyrate COz-amyl is0butyrat.e
80-100 98 98 50-100 84-100 98 98
1 1
1
1
1
1 1 1
1 1 1
1 1 1 1 1
1
1
1
1
1 1 1 1 1
1
1
1 1 1
1 1
1
1 1 1
1 1 1
1 1
ways (e. g., viscosity data, x-rays, etc.) ; but, since data from these sources are rather limited, it seems better to use the empirical relation developed by Titani who found that the molal volume of a liquid a t its normal boiling point is proportional to the cube of the radius of the molecule. Equations l and 2 then become: I
.
(3) B’T3f2
D = (VA1’3
+
.,/&
VB1/3)7
+ M1g
(
P 1
+
3
(4)
-
where V A ,V B = molal volumes a t the normal boiling point B, B‘ = constants
The constants in the Equations 3 and 4 can be calculated as has been done by Arnold ( 1 ) ; but, since these calculations involve the use of Titani’s empirical constant, it seems better to compare the groups suggested by the above equations with the actual experimental data to obtain the most suitable values of B and B’. Several hundred determinations of experimental diffusion coefficients have been reported in the literature. The principal methods of obtaining these coefficients are briefly as follows: EVAPORATION OF LIQUIDS IN NARROW TUBES. One of the two components, in the liquid state, is placed in a small glass tube,
June, 1934
INDUSTRIAL
AND
ENGINEERING CHEMISTRY
683
TABLE I (Continued) SYSTEM
TEMP. RAXGE e
c.
PRE~EURE
SYSTEM
RANQE
Atm.
O
O R Q A N I C ACIDS
65-85 65-85 65-85 62-99 66-99 66-99
1
Air-propionic Hz-DroDlonlo COzlpiopionic Air-butyric Hz-butyric COz-butyric
51-99 93-99 93-99 75-100 99 99
1 1
Air-isobutyric HP-isobutyric COz-ieobutyric Air-valeric
78-100 98 98 82-100
1 1
Air-isovaleric Hz-isovaleric COz-isovaleric Air-caproic Air-isocaproic
71-100 99 91 82-100 82-100
1
.4ir-propylbenzene Air-isopropylbenzene Air-mesitylene Air-ethylbenzene Air-o-xylene
1
1 1 1
1
Air-propyl Hz-propyl COzTpropyl Air-isopropyl
10-84 67-84 07-84 15-60
REFERENCE
Atm.
52-99 60-99 60-100 50-100 50-100
1
42-67 25 25 25 99
1
21-63 20-52 31-100 50-79
1
Air- n-butylamine Air-isobutylarnine Air-diethylamine Nz-mercury
61-63 19-62 10-51 19
1 1
Nz-iodine Air-iodine Air-o-chlorotoluene Air- n-chlorotoluene Air-p-chlorotoluene
19 0-30 65-98 65- 98 60-100
1 1 1
I
Air-m-xvlene
1
1 1 1
Air-chlorobenzene Air-diphenyl Air-aniline Air-naphthalene Air-anthracene
1
1 1
1 1
coz-cs*
1 1 1 1
Air-toluene Air-n-octane Air-benzidine Hz-CCh
1 1
Air-propyl bromide, Air-isopropyl bromide Air-propyl iodide Air-isopropyl iodide
1
1 1
1
60-100 99 99 60-99 21
1
Air-n-amyl Hz-n-am yl Con-n-amvl .~&neth$ethyl ethanol Hz-methyl ethyl ethanol
99 99 99 99 99
1
Air-n-hexyl Hz-n-hexyl COz-n -hexyl
99 99 99
1
1
Air-benzene Hz-benaene 02-benzene COI-benzene
1
Air-butyl H?-butyl COzYbutyl Air-isobutyl Air-tert-butyl
1 1 1
Air-CSz Hz-CSz
ALCOHOLS
10-50 25-50 25-50 10-67 40-57 4&67
RANQE
c.
MISCELLANEOUS
Air-formic Hz-formic COz-formic Air-acetic Hracetio COracetic
Air-methyl Hz-methyl COrmethyl Air-ethyl Hz-e t h yl COz-ethyl
PRESSURE
TEMP. RANQE
1 1
1
Air-safrole Air-isosafrole Air-eugenol Air-isoeugenol
1 1 1
1 1 1 1
1 1
1
filling the tube within 1 to 5 cm. of the top. The tube and liquid are held a t constant temperature, and the second gas is passed over the top of the tube. The rate of diffusion is obtained by measuring the rate of fall of liquid in the tube. This technic, devised and developed by Stefan, is perhaps the best and most widely used of the experimental methods. It is limited, however, to a fairly narrow temperature range for any one system, since one of the components must be liquid, and the precision is poor a t very low or very high vapor pressures. This method has been used by Stefan ($4, Griboiedow (5), LeBlanc and Wuppermann (12),Vaillant (SO), Trautz and Ries (29), and extensively by Winkelmann (32) and Pochettino (21). UNSTEADY-STATE INTERDIFFUSION OF Two GASES. The two gaseous components are placed in separate sections of a tube, and diffusion is allowed to take place by removing the partition separating the sections. After a definite time interval the gas from various portions of the tube is analyzed and the results are compared with an integrated form of the following diffusion equation:
(5) This method has been widely used for systems of the permanent gases but gives results somewhat less reliable than those obtained by the first method. Von Obermayer (go), Lonius (14), Schultze (23), Jackman (9),Deutsch (4), Loschmidt (15), Waitz (SI), Toepler (87), and Wintergest (33) were the principal users of this method. MISCELLANEOUS METHODS. Diffusion coefficients for iodine in air have been obtained by measuring the rate of evaporation of a small sphere of iodine suspended in air. It seems probable that convection currents in the air make this method unreliable. Mullaly and Jacques (19)placed iodine and mercury, respectively, a t the two ends of a tube filled with nitrogen at low pressures. The diffusion coefficient of both iodine and mercury were calculated from the measured amount, composition, and location
0.00259-0.00745 1 0.0087-0.018
(81) (81) (19) (21)
1
(19) (11, 16, 88)
1
($1)
1 1
(21) (81 1
TABLE11. DIFFUSIONCOEFFICIEXTS DETERMINED EXPERIMENTALLY
(Barometric pressure, 1 atmosphere) SYSTEM TEMP. O
Air-water vapor Air-%-butyl alcohol -4ir-t oluene Air- sec-butyl alcohol Air-ethyl acetate Air-sec-amyl alcohol Air-chlorobenzene Air-aniline Air-diphenyl Air-mercury Air-isopropyl alcohol
c.
25.9 39.4 59.0 25.9 39.4 59.0 25.9 39.4 59.0 25.9
3.9 .. 4 -
59.0 26.9 39.4 59.0 25.9 39.4 59.0 25.9 39.4 59.0 25.9 39.4 59.0 218 341 25.9 39.4 59.0
0760
Sp. cm./sec. 0.258 0.277 0.305 0.087 0.092 0.104 0.086 0.002 0.104 0.089 0.096 0.108 0.057 0.094 0.106 0.071 0.076 0.086 0.074 0.079 0.090 0.074 0.079 0.090 0.160 0.473 0.099 0.107 0.121
of the deposit of mercurous and mercuric iodides formed. Special methods of this type are useful only for special types of systems.
The published results collected total some five hundred determinations, covering the various systems indicated by Table I. I n addition, experimental determinations were made on a number of vapors including diphenyl and mercury
INDUSTRIAL AND ENGINEERING CHEMISTRY
684
Vol. 26, No. 6
50
I .o
0.5
0.
0 .o IO
50
100
woo 1 4 m
loo0
500
4-
T G K
TtV&t+ P ( V j t vi)
Pi">+ V t ) ' ( I i C / l )
'
FIGURE 2. DIFFUSION COEFFICIENT us. GROUPSUCGESTED BY EQUATION 4
FIGURE 1. DIFFUSION COEFFICIENT us. GROUPSUGGESTED BY EQUATION 3
a t elevated temperatures in air, using the evaporative technic. These new data are summarized in Table 11. The experimental apparatus was similar t o that used by previous investigators (12, 21, 24, 39). Small glass tubes 2 mm. in diameter and 10 cm. lon were etched in millimeter divisions and filled within 1 to 5 cm. o? the to with the liquid to be tested. Tubes containing the liquid were pgced vertically in a constanttemperature bath, and air at the temperature of the bath was passed slowly across the top open ends of the tubes. The heat requirements were small since the rate of evaporation was low. In the low-tern erature experiments a thermostatically controlled water bat\ was used; this was replaced by a condensing vapor bath when operating at higher temperatures. The liquid level in the tubes was recorded a t e ual time intervals, and the diffusion coefficient calculated from $e ordinary integrated form of the Stefan equation. The data from the literature, together with the new data of Table 11, are plotted in Figures 1 and 2 using as abscissa the groups suggested by Equations 3 and 4, and the experimentally observed diffusion coefficients as ordinates. I n calculating the group plotted as abscissa in Figure 2, the values of C were obtained as suggested by Arnold (I), using values of C for the pure gases obtained from viscosity determinations, or, where th&e were lacking, values estimated from the empirical relation:
was narrow, being only from 0" to 100" C., except for a few points, so that it is not possible to show whether the poorer correlation with the Sutherland group is due to the temperature function being incorrect, or to the use of the incorrect value of C in calculating the groups plotted. Without discarding some of the experimental data, it would be difficult to obtain a much better correlation than that of Figure 1, as the percentage deviations in this figure are of the same order of magnitude as the deviations in the actual experimental data as obtained by the different investigators for the same systems under similar conditions. I n obtaining an empirical relation, the first plot is the more satisfactory from a practical point of view, since it not only shows a better correlation of the data but is simpler to use and does not involve the uncertain quantity, C. Figure 1 shows the empirical constant to be 0.0043, and the relation is, therefore:
dFA+
0.0043T3/2 1
+
D =
(VA'13 VB"*)*P where D = diffusion coeofficient,sq. cm./sec. T = abs. temp., K. P = total pressure, atm.
0 4
c
= 1.47 Tb
where
Tb = normal boiling point,
0.3 O
K.
Each plot shows a wide band of points, with considerable deviation from a mean line. This is to be expected from the rather poor precision obtained by the experimental methods so far developed for obtaining diffusion coefficients. There is, however, no definite trend with molecular weight or with pressure, both of which were varied over wide ranges in the data plotted. Comparison shows Figure 1 to give better correlation than Figure 2. The temperature range covered
I-CHLOROBLHLENE
0 2
D780
01 0 08
0 08 0 01 0 06 0 05
Kg1
20
40
50
60
80
100
P DL
FIQURE 3. DATAOF TABLE I1 COMPARED WITH EQUATION 6
Figure 3 shows the data of Table I1 compared with Equation 6. Sutherland (26),on a n a l y z i n g certain of von Obermayer's data for several pairs of gases, found a greater variation in B' than in B. For six pairs of gases he found B to vary from 0.0038 to 0.0047. Lines corresponding to the calculated constants of Maxwell, Jeans, and Chapman are drawn in Figures 1 and 2. I n using Equation 6, values of V should be obtained in the same way as were those employed in preparing Figure 1. For this plot the values of V were obtained using Kopp's law of additive columns, with the rules and values for each element given by LeBas, as out-
June, 1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
lined by Arnold (I). These values and rules are summarized for convenience in Table 111. Equation 6 is recommended for use in estimating values of D where no good experimental data exist. Reliable experimental data are, of course, to be preferred to an estimation obtained from such an empirical equation. TABLE111. SUMMARY OF VALUESAND RULES EL~MIQNT
ATOMIC VOL. 14.8 24.6 37.0 3.7 27.0 25.6
Carbon Chlorine Iodine Hydrogen Bromine
Sulfur
Oxygen in: Aldehydes and ketones Methyl estere Methvl ethers Hieher estera and ethers Acida Ni troaen: Double-bonded I n primary amines In aecondary amines
7.4 9.1 9.9 11.0 12.0 15.6 10.5 12.0
Deduct.15 for benzene ring formation: deduct 30 for naphthalene ring formation. For example: .Molar volume of C2Hg = 2 X 14.8 6 X 3.7 51.8.
+
-
LITERATURE CITED (1) Arnold, IND. ENO.CHEM.,22, 1091 (1930). (2) Chapman, Trans. Roy. SOC.(London), 211.4, 433 (1912); 216.4, 279 (1916);217-4,115 (1917). (3) Colburn and Hougen, Wis. Eng. Bull. 70 (1930). (4) Deutsch, Inaugural dissertation, Halle, 1907; Ann. Physik, 29,664 (1909). (5) Griboiedow, J. Russ. Phys.-Chem. Soc., 25, 36 (1893).
685
(6) Guglielmo, Attiaccad. sci. Tortho, 17, 54 (1881). (7) Hanks and hlcbdams, IND. ENO.CHEX,21,1034 (1929). (8) Houdaille, Thesis, Paris, 1896. (9) Jackman, Inaugural dissertation, Halle, 1906; Ann. Physik, 29, 664 (1909). (10) Jeans, “Dynamical Theory of Gases,” 3rd ed., 1921. (11) Langmuir, Phys. Rev., 12,368 (1918). (12) LeBlanc and Wuppermann, 2.physik. Chem., 91, 143 (1916). (13) Lewis and Chang, Trans. Am. Inst. Chem. Engrs., 21, 127 (1928). (14) Lonius, Ann. Physik, 29,664 (1909). (15) Loschrnidt, Sitz. Akad. Wiss. Wien, Abt. I I , 61, 367; 62, 468 (1870); 65,323 (1872). (16) Mack, J . Am. Chem. Soc., 47, 2468 (1925). (17) Maxwell, PhiI. Mag., 35, 185 (1868). (18) Meyer, “Kinetic Theory of Gases,” 1899. (19) Mullaly and Jacques, Phil. Mag., 48,1105 (1924). (20) Obermayer, von, Sitz. Akad. Wiss. Wien, Abt. 11, 81, 1102 (1880);85,147 and 748 (1882);87,188 (1883); 96,546 (1887). (21) Pochettino, Nuovo cimento, 8,No.7,5 (1915). (22) Schmidt, Z. Physik, 8, 152 (1922). (23) Schultze, Ann. Physik, 6,303 (1901). (24) Stefan, Sitz. Akad. Wiss. Wien, Abt. IT, 62, 385 (1870); 63, 63 (1871): 65. 323 (1872): 68.385 (1873): 77. 371. 78. 957 (1878); 79, 161 (1879); 98,6i6, 14i8 (1889); ‘Ann:Physik. 41,723 (1890). (25) Summerhays, Proc. Phys. SOC.(London), 42, 218 (1930). (26) Sutherland. Phil. Maa., 38, 1 (1894). (27) Toepler, Ann. Physik, 58, 549 (1896). (28) Topley, Whitlow, and Gray, Phil. Mag., 4, 875 (1927). (29) Trautz and Ries, Ann. Physik, 8,163 (1931). (30) Vaillant, J. phys. radium, 1, 877 (1911). (31) Waits, Ann. Physik, 17,201 (1882). (32) Winkelmann, Ibid., 22, 1, 154; 23, 203 (1884); 26, 105 (1885): 33,445(1888); 36,93 (1889). (33) Wintergest, Ibid., 4, 323 (1930). R E C E I Y January ~D 12, 1934.
Solder Effect of Impurities on Its Appearance and Microstructure CLIFFORD L. BARBER, Kester Solder Company, Chicago, Ill.
T
HE solder industry has for a long time judged the quality and purity of 50-50 tin-lead solder by the
physical appearance of a poured bar. Many contend that a smooth, shiny bar is indicative of quality, and that the presence of metallic impurities is reflected in a generally rough or frosty looking bar. One aim of the solder manufacturer is to produce a bar which is clean and smooth, and the occasional persistent roughness which sometimes prevails is always the source of much concern. This roughness is variously attributed to antimony, copper, nickel, arsenic, or other impurities whose effects have never been experimentally demonstrated. Needless to say, conclusions in these cases are based largely on whim, fancy, or tradition rather than on experimental evidence. At first thought it would appear that such points could easily be settled by chemical analysis. Very often, however, an exhaustive chemical investigation on samples of smooth and rough bars fails to reveal any essential differences. It is the purpose of this investigation to determine the effects of small amounts of common known impurities on the physical appearance and the microstructure of 50-50 bar solder. The first publication of an investigation of the surface appearance of solders seems to have been by Bannister and Tabor in 1909.l These authors, however, did not emphasize the practical significance of the influence of extremely small amounts of impurities such as concern the manufacturer of 1
J . Inst. Metals, 2, No. 2 (1909).
high-quality solders. I n most cases such a manu acturer is concerned with traces of impurities which defy c-iemical detection in routine analytical work. I n view of the many diverse and contradictory opinions held on this subject, it was thought advisable to investigate this question a little further, repeating a t the same time much of the work of Bannister and Tabor.
TESTSON SOLDER When tin and lead are fused together in equal proportions by weight and poured into an iron mold of appropriate thermal capacity, there results a smooth, shiny bar of solder which has a slight contraction crack extending down the center of the bar and throughout the greater part of its length. I n best grades of commercial 50-50 bar, which totals usually from 0.03 to 0.07 per cent impurity, there is always a faint, rough line extending along the contraction crack or portion which freezes last. For the following work the total impurity content of the metal, which is the purest commercially obtainable, was approximately 0.03 per cent, and in the resulting 50-50 bar, the faint ‘‘frost line” was practically negligible. Alloys of known impurity content were made by alloying such solder with known amounts of different elements, and a bar was made from each alloy. Each bar was then examined visually for frost, roughness, etc.; a short cross section about a centimeter long was then taken from the bar for metallurgical examination. After carefully filing the
