SOLDERS AND BABBITTS Routine Spectrographic Analysis A. W. IkiNKO
ASD
G . W.WIENER, Westinghouse Electric Corporation, East Pittsburgh, Pa.
A spark spectrographic method for the analysis of lead, copper, antimony, and tin in tin-base solders and babbitts and lead-tin solders has been developed. The percentage ranges of anal>-sisinclude copper from 0.10 to 7.50, antimony 0.10 to 2.50, lead 0.10 to 2.00, and tin in lead-tin solders from 25.0 to 70.0. Copper, antimony, and lead w-orlring curves are plotted in the usual fashion of log intensity against log concentration. The high percentage tin is calculated from a graph by plotting log intensity against 76 (Pb Sn). The method as developed is rapid and of suitable accuracy for routine control of solders and babbitts. Segregation effects are reduced by the superimposition technique and the leadtin difference function permits the analysis of high percentage tin with an accuracy of *2.009'~ of the amount present.
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D
URING the past year, the Spectrochemical Laboratory has conducted an extensive investigation of a spectro-
Table 11. Analytical Line Pairs
graphic method for the analysis of solders and babbitts used in the manufacturing operations of the company. This development was prompted by the need of a rapid method for the quality control of these alloys and of reducing the rejection rate of electrical equipment due to the use of solders and babbitts of improper composition. Approximately 200 pots currently used in the plant require chemical control. These pots vary in capacity from 50 to 2000 pounds of molten metal. The spectrographic method developed had to be of sufficient accuracy to meet the chemical requirements of the process specifications. Table I lists the types and typical compositions of the solders and babbitts currently analyzed spectrographically a t this laboratory. There are tn-o different classes of alloys, the tin-base solders and babbitts and the lead-base solders. The spectrographic analysis of these materials has not been extensively discussed in the literature. Smith ( 7 ) and Scribner (6) described a technique for the spectrographic analysis of low amounts of copper, lead, and other metal$ in pure tin. Dull and Hibbert ( 3 ) described a method for the spectrochemical analysis of lead-base metals. h modification of these methods was developed to analyze the compoiit ionlisted in Table I.
Element Line
2.O'kax. 2.00 5.00 8.00 2.00max. 2.00max. 2 , O O max.
Sb
...
2 . 0 max. 8.00
10.00 8.00 2 . 0 0 rnax. 1 . 0 0 max. 2 , O O max.
Pb 0 . 5b'Aax. 0 . 5 0 max. 0.50 max. 0.50 max. Balance Balance Balance
Sn 9 9 . 7 5 min. Balance Balance B a 1a n ce Balance 65.0 35.0 45.0
Lead-Base Alloys P b 2628.26 P b 2628.26 P b 2628.26 P b 2628.26 P b 2388.77
0.20-4.00 0 . 15 0 - 01 . 75 50 1.00-3 . O O 25.0-76.0
oi 0.66 kv.-amp., 1.44 mh. inductance, 75 volts (primary voltage),
and a 5-mm. gap. The spectrum is free from background and gives an adequate number of lines for the elements in the rangec: required. All exposures are 30 seconds, taken through a 20micron slit. For the tin-base alloys, the exposure is continuous: but for the lead-tin solders, two 15-second exposures, one taken from the top of the disk and one taken from the bottom, are superimposed. Hemispherically tipped 0.6-cm. (0.25-inch) carbons are used as the counter electrodes. The photographic plate is developed in D-19 for 3 minutes, cleared in rapid x-ray fixer, washed, and dried. The line pairs used are listed in Table 11. The copper lin? 2824.4 is used for the complete percentage range of that element. Other lines were tried for shorter ranges a t the higher percentage?, but they gave no better accuracy than the one listed. The plate is calibrated by sparking a high purity iron block for *SO seconds, 30 seconds being the prespark and 20 seconds the exposure a t 1.3 kv.-amp., 0.09-mh. inductance, 50 primary volts, and 3-mm. gap. The procedure used is a modification of the tKo-line method described by Churchill ( 2 ) . The wage lengths of two iron lines measured are 3083.72 and 3091.58 A.
A cast disk 3.75 em. (1.5 inches) in diameter and 1.25 em. (0.5 inch) thick is used. The molten alloy in the pot is thoroughly mixed manually, after which a sample is withdrawn in a small ladle, poured into an open steel mold, and alloived to cool in air.
Cu
Cu 2824,37 Sb 2628.54 S b 2877.92 Sb 2769.94 Sn 2380.74
0.10-7.50 00.10-1.50 .10-1.00
SPECTROGRAPHIC PROCEDURE
SAMPLING
Type Tin solder A Tin solder B Tin babbitt A Tin babbitt B Tin babbitt C Tin-lead solder Lead-tin solder A Lead-tin solder B
Tin-Base Alloys Sn 2761.78 Sn 2761.78 Sn 2761.78
.I satisfactory spectrum is obtained with a high voltage spark
EQUIPMEST
Typical Solders and Babbitts
Cu 2824.37 P b 2873.32 Sb 2877.92
Percentage Rango
The tin-base samples are prepared for sparking by grinding either side on a belt grinder. The lead-base solders are machined on the top side of the disk and then ground smooth on both \ides. The sparking surfaces are cleaned with alcohol.
The spectrograph employed is a large G>ertner prism instrument set to photograph the 2350 to 3300 A. range on a 4 X 10 spectrum analysis Xo. 1 plate. An A.R.L.-Dietert high voltage spark unit furnishes the excitation. Other equipment includes a constant temperature developing machine and a Vincent and Sawyer type of nonrecording densitometer.
Table I.
Internal Standard Line
Theoretically ( 4 , 5 ) ,for accurate analysis, calibration lines and analytical line pairs should be in the same spectral region. HOKever, in practice the reproducibility and precision of the results obtained by the above procedure are Tell within the limits required to meet the specifications of these materials. STANDARD SAMPLES
Because it was impossible to purchase standard samples, they were prepared by the metallurgical section. To facilitate the 1178
1179
V O L U M E 2 0 , NO. 1 2 , D E C E M B E R 1 9 4 8 Table 111. Saniple
Segregation Studies of Tin-Base Alloys % Copper 5% Lead yo Antimony
Chem.
Spec.
0.38 0.40 1 1R ....
12 Top
1.18 1.11 1.09 1.09 1.09
Chem.
Spec.
Chem.
Sper.
0.21 0.23
0.28 0.28
0.... s i
n
0.66 0.61 0.61 0.60 0.63
to have a considerable number of results as much as * 0.25Cc from the true analysis, but even with this large deviation the method was sufficient for control purposes. Table IV is a comparison of routine spectrographic analysic with routine chemical analysis. A study of this table indicates a complete range of analyses, typical of those encountered in routine work. The method as developed is not sensitive t o antimony belon- 0.10%. Hon-ever, results reported as less than this amount in solders are acceptable to inspection department.
....
57
0 59 0.57 0.55 0.57 0.57
Table IV.
R Lead % Antimony Sample N o . Spec. Chem. Spec. Chem. Spec. Chem. 0.41 0.38 0.24 0.23 16 0.28 0 28 13 0.54 0.55 0.55 0.99 0.96 0.53 10 0.63 0.83 1.53 1.68 0.82 0 69 5 1.27a 1 27 1.39 2.60 2.69 1.39 16-9 2.17 2.24
