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. TABLE 111. SUMMARY OF VALUESAND RULES EL~MIQNT 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
ATOMIC VOL. 14.8 24.6 37.0 3.7 27.0 25.6
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) C h a p m a n , 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) H a n k s a n d h l c b d a m s , IND. ENO.CHEX,21,1034 (1929). (8) Houdaille, Thesis, Paris, 1896. (9) J a c k m a n , 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 a n d Wuppermann, 2.physik. Chem., 91, 143 (1916). (13) Lewis a n d 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 a n d 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) T r a u t z a n d Ries, Ann. Physik, 8,163 (1931). (30) Vaillant, J. phys. radium, 1, 877 (1911). (31) W a i t s , 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
1 N D U S T R I A L A N D E N G I N 13 E 1< I N G C H E M I S T R Y
686
B
A
X 50
B.
X 500
C.
OF 1)URL:
C.
D.
2.
bfICROSTRucTURE OF COMMEHClAL
45.6 per Cent tin: 48.5, lead: 3. antimony 49.5 L"'cent tin' 49.5 lead' 1 copper 60-50 solder oontkining'o.25 be; cent nickel 49.5 per eent tin: 49.5. lead: 1, areenio
D.
h n
SOLDERX
Poured hot and omlad too slowly; X 220
whose Inass is about eiglit times tliat of the bar which it produced. Pure 50-50 solder is preferably poured a t 525" to 575" F. At liiglier temperatures there is uirtiue oxidation of t,lie metal, and at lower temperatures the appearance of the bar is nnsatisfactory. The contraction crack down the center of the bar is practically free from frost, arid the bar is smooth and shiny. Wlieii pore solder is prepared under t,liesc conditions, the microstructure a t 50 magnifications appears exceedingly uniform, liomogeneous, and free from dendrites (Figure ] A ) . At, liiglicr magnifications one can detect tlie light eutectic and the dark mixt.ure of lead and solid solution (Figure 1B). Just as in the case of otlier metals, the microstructure of pure solder depends largely on blie manner in which it is treated. If pure solder is poured into a mold a t too low a temperature so that tlie solder does not flow freely to the end of the mold, the bar will be frosty and the microstructure at 50 magnificat,ions will reveal many dendrites (Figure 1C). If, on the other hand, tlie metal is poured into a hot mold and allowed to cool slowly, the microstructure will again reveal large dendrites of lead and solid solution and the beautifully laminated structure of the eutectic (Figure ID). Ac-
F FIOURE
B.
TIN-hXI)
B
E
A.
50-30
Poufed too
