INDUSTRIAL AND ENGINEERING CHEiMIxTRY
16
sented by a horizontal line a t 20.2 per cent free water. Data were obtained on the moisture gradients in the same slab after 166, 383, and 1152 hours, and are represented by t8he three solid curves on Figure 8. By graphical integration of the area under the third curve the average free-moisture concentration a t that time was 13.1 per cent; E is therefore 13.1/20.2 or 0.65. The theoretical moisture-gradient curve (from Figure 2) corresponding to a value of E of 0.65 is shown
VOl. 21, No. 1
by the dashed line on Figure 8. The actual gradient curve is therefore seen to be much flatter than the theoretical curve for the same conditions. This may be explained as being due to the lower vaIues of the diffusion constant K a t the Iower moisture concentrations-i. e., near the faces. Where K is low a steeper gradient curve is necessary to cause the water to diffuse than in the center where the moisture concentration and consequently K are greater.
Lead =Tin-Cadmium as a Substitute for Lead-Tin Wiping Solder' Earle E. Schumacher and Edward J. Basch BELLTELEPHONE LABORATORIES, 463 WEST ST., N E W YORE, N. Y.
Data are presented which show that certain lead-tin-cadmium alloys may be advantageously substituted as solders f o r lead-tin alloys. Data are given showing the physical and chemical properties of these alloys. HE high cost of tin is stimulating investigation of means
T
for curtailing its use. Since large quantities of tin are used in wiping solder, the satisfactory substitution of a ternary alloy containing less tin for the present lead-tin alloy would result in a considerable saving of this metal. A review of the literature indicated that alloys of lead, tin, and cadmium offered good possibilities as substitutes. A phase diagram for these alloys has been prepared by Stoffel.2 Burgess and Woodward3 state that cadmium appears as a promising substitute for part of the tin in solders. This is not because cadmium is cheaper than tin, but because it allows the use of a higher percentage of lead. Physical properties of several lead-tin-cadmium solders are given by . S c h w a r t ~ . ~Since the previous work did not include any examination of the behavior of these alloys as wiping solders, it seemed desirable to continue the work and examine their properties in this respect. The results discussed in this paper were collected from laboratory tests. Field tests have not yet been made with these solders, and until their behavior under actual operating conditions has been ascertained it is, of course, unwise to make any statement regarding their practical value. Properties of a Wiping Solder
1-The melting point of the solder should be somewhat below that of the parts being joined. 2-The solder should have a solidification range of a t least 50" C. in order to provide adequate time in which to mold it easily into the shape desired. 3-Joints made with the solder should be readily unwiped; that is, the solder comprising the joint should be readily removable. The parts being joined should not be harmed during the unwiping procedure. 4-The solder should not change in composition when subjected to prolonged heating in the melting pot at temperatures ranging from 300" to 400" C. 5-Joints made with the solder should have tensile and shear strengths greater than the parts being joined. 6-The solder should have no injurious effects on the parts being joined and should readily tin them. Received August 18, 1928. BS, 137 (1907). Bur. Standards, Tech. Paper 109, 8 (March, 1919). 6 Am. Inst. Min. M e t . Eng. Tech. Pub. 86 (1928). 1 2
7-The joints must be non-porous when joining cables in order to prevent damage to the insulation of the cable by the introduction of moisture. 8-The joint should not deteriorate with age. Procedure
SELECTION OF ALLOYSTo BE TEsTm-The main objective of this investigation was to find a wiping solder that would be a t least as satisfactory as and cheaper than the 62 per cent lead-38 per cent tin alloy which today is generally used for wiping purposes. (This alloy is referred to hereafter as standard solder.) Since lead is by far the cheapest of the constituents of lead-tin-cadmium solders, and cadmium and tin are about the same price,5 any cheaper solder in this system must contain a higher percentage of lead. (Figure 2) PREPaRATION O F ALLOYS-High-purity constituents were used in preparing the test alloys. Bunker Hill and Doe Run leads, containing less than 0.01 per cent impurities, were used. The cadmium was 99.5 to 99.9 per cent pure; the tin, 99.9 per cent. The constituents of the alloys were carefully weighed with a maximum possible error of +0.1 per cent. The lead was melted in a graphite crucible under a covering of palm oil to prevent oxidation. As soon as the lead was molten, the tin and cadmium were added. Most of the melts were cooled in the crucible but those from which tensile specimens were to be cast were heated to about 50" C. above the liquidus and poured into moIds only slightly cooler. Experimental
PHASEDIAGRAM-cooling curves of lend- tin-cadmium alloys containing a high percentage of lead showed arrests which agreed closely with those previously found by Stoffe12 and S c h w a r t ~ . ~From Stoffel's diagram (Figure 1)the cooling ranges and the percentages of primary, binary, and ternary solidifications of the alloys given in Table I were calculated. I n the range of compositions satisfactory as wiping solders the lead-tin-cadmium alloys have a longer cooling range than the lead-tin. WORKABILITYCHARACTERISTICS-Standard solder was arbitrarily chosen as having satisfactory workability; that is,
Z. anoyg. Chem.,
6 At the time of writing cadmium and tin are both selling for approximately 60 cents a pound.
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1929
Table I-Solidification
ALLOY
1 2 3 4 5 6 7 8 9 10
11 12
13 14 15 16 17 1s 19 20 21 22
-
COMPOSITION
Pb
Sn
Cd
%
%
%
TOTAL
SOLIDIFICATION
RANGE
O
c.
129.5 107 103
110
103.5 91.5 94.5 87.5 85.5 97 90 85 87 82.5 78.5 77.5 79.5 58 72.5 27 48.5 0
17
Ranges and Phase Compositions of Some Lead-Tin-Cadmium Alloys PRIMARY
BINARYSOLIDIFICATION
SOLIDIFICATION remp. of Pr. beginlmary ning crystals
OC.
%
275 252 248 255 249 237 240 233 231 242 235 230 232 22s 224 223
SO 60 63 68 64 7.8 56 40 23.7 54.5 52 37 50 47.2 36.6 23
239 218 20s
4b:7 42 21.9
...
... ...
.. ..
TERNARY SOLIDIFICATION Temp.
Composition Pb Sn Cd OC. 194 216 193
... ...
?$:-
%
..
. . . . . .
233
86:2
7k:7
::
2413
216 160
30 56.3 17.7
68 71 34
.. 66
32 29
190
29
88.
150 182 202 225 181
23.4 47 82 59.3
65 67 69 72.5 36
7811 50
36 68
.194 .. ... ...
iSi
194
..
. . . . . .
..
..
::
3i'
. . . . . . . . 35 . . 33 . . 31
2:s
. .
..
.
.
27.5
64
.
64
,
.
.. . .
.
32
.
.
.
Ternary eutectic
Composition Pb Sn Cd
c.
%
%
%
%
145.5 145.5 145.5 145.5 145.5 145.5 145.5 145.5 145.5 145.5 145.5 145.5 145.5 145.5 145.5 145.5 145.5
10 10 20 32 36 6 44 30 20 27.8 48 34 50 50 40 30 18
32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32
50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50
18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18
1ik:5
58
32
144:5 145.5
50 100
32 32
0
10 30 16
Of
.. ..
..
18
50 is . . . . . . 50 50
IS
18
i t is sufficiently plastic and coherent to allow the easy forma- tained.) The oxide that accumulated was removed every tion of joints. Alloys having possibilities as substitute solders half hour; the samples were cooled and weighed every hour. were submitted to experienced splicers and their wiping Samples for analysis were removed from the pots before each properties compared with those of the standard. Alloys weighing. The d a h , given in Tables I1 and 111, show that that, in the opinion of the splicers, worked as well as, or better oxidation losses for the test solder are of the same order as than, standard solder were considered to be satisfactory from standard solder. Neither alloy changed appreciably in comthe workability standpoint. When wiping characteristics position during the heating. of lead-tin solder were classified as good by the splicer, it was of Some Molten Lead-Tin and Leadnoticed also that the joints were generally non-porous. The Table 111-Rate of Oxidation Tin-Cadmium Solders" data obtained are given in Table IV and show that certain 1 FIRSTHOUR I SECOND HOUR I THIRDHOUR I .,.--.. lead-tin-cadmium alloys within a rather well defined area of IN the phase diagram (Figure 1) are satisfactory from the worka- SPLDER , : : : i Temp. ko;:t, Temp. if;o$, Temp. LOSS WEIGHT bility standpoint. This point will be discussed later. UNWIPING A JOINTMADE WITH LEAD-TIN-CADMIUM 70 70 O C . o c . % 11 1.15 347 0.97 355 1.36 398 3.45 SOLDER-Joints made from lead-tin-cadmium solders are 11 0.95 350 1.12 350 1.97 400 3.99 1s 0.86 348 1.12 400 1.5s 350 unwiped by the same method as joints made from lead-tin 3.77 18 1.14 355 0.93 351 1.01 395 3.05 solders. Molten solder is poured over the joint until its The solder pot used had an inside diameter of 41/2 inches. temperature is raised above 145" C., the eutectic temperature. The solder comprising the joint then becomes soft and may TENSILE STRENGTH-Tensile-strength measurements were be wiped away with a wiping cloth. 145" C. is the lowest temperature a t which joints composed of alloys of lead-tin- made on some lead-tin-cadmium alloys. The alloys were cadmium can be unwiped, and is 36" C. lower than the corre- tested as cast in a 600-pound (272-kg.) Amsler testing machine, whose speed was 0.4 inch per minute per foot (0.3 meter) sponding temperature for alloys of the lead-tin system. of free length, The data given in Table V show that most of these alloys have tensile strengths comparable with that of Table 11-Composition Changes of Alloys 11 and 18 when Heated for Different Time Intervals at Temperatures above Their Melting standard solder and reference to Figure 2 shows some of them Points to be economically attractive. These alloys were therefore INITIAL AFTER HEATING AFTERHEATING A THIRD selected for further testing. HOURAT 400' C. TENSILE STRENGTH OF WIPEDJOINTS-It is not sufficient Pb Sn Cd that the tensile strength of the solder compares favorably with that of standard solder, but the strength of the joints made from this solder must be greater than that of the parts being joined. The samples for tensile testing were prepared in the following manner: Two sections of lead cable were connected OXIDATION LOSSESOCCURRING IN SOLDERS DURING PRO- by a lead-tin sleeve. The two necessary joints were wiped LONGED HEATIKG-SinCe a satisfactory solder should not with those alloys that appeared most promising. Tensile change in composition when subjected to prolonged heating loads were applied to the two ends of the sample. Since, in a t temperatures between 300" and 400" C., the lead-tin- every test (Table I, alloys 11 and 19) it was the sleeve that cadmium solder, which compared most favorably in other ruptured i t follows that the cadmium solder tins satisfactorily ways with standard solder, was tested for resistance to heating and probably has no injurious effects. losses. Two circular pots 4l/2 inches (11.4 cm.) in diameter, "TIKKING" OF SoLDms-Since there is no established one containing 6 pounds (2.7 kg.) of standard solder and the method of measuring "tinning," the lead-tin-cadmium alloys other containing the same amount of 68 per cent lead-23 that were being considered for wiping solders were in all per cent tin-9 per cent cadmium solder, were heated to 350" cases evaluated for this property by comparison with standC. for 2 hours, and to 400" C. for an additional hour. (These ard solder. All the alloys tested seemed to tin an alloy comtemperatures are about 25" and 76" C. higher, respectively, posed of 99 per cent lead-1 per cent, antimony as satisfactorily than the temperature a t which solder pots should be main- as standard solder and a t a lower temperature.
1
1
O C .
O
I
L V l n l
~
IND USTRIAL AND .ENGINEERISG CHEMISTRY
18
Vol. 21, No. 1
been used in preparing the 68 per cent lead-23 per cent tin9 per cent cadmium alloy. The high-bismuth lead decreases somewhat the ease of working the alloy; the southeastern Missouri lead seems to act about the same as high-purity lead, although it may make the solder slightly more workable. Joints made with solders containing the commercial leads were satisfactory from the porosity standpoint. When the copper content of the solder is increased t o above 0.1 per cent, joints made with the solder show a tendency t o be porous. Table V-Tensile ALLOY
Figure 1-Lead-Tin-Cadmium
Phase Diagram
CORROSION OF SOLDERS-The resistance of standard solder and the 68 per cent lead-23 per cent tin-9 per cent cadmium alloy to corrosion by saturated lime-water, distilled water, and 0.001 A' acetic acid was measured by the following method: Samples of the two alloys, each with a total area of 1 sq. dc., were immersed in the corrosive liquids and maintained a t 25' C. At various intervals the samples were cleaned with 1:5 acetic acid, dried with alcohol, and weighed. The results indicated that the corrosion of the lead-tin-cadmium alloy was of the same order as that of the standard solder.
1 5 6 7 8 9 11 14 15 16 17 18 19 20 21 a
Data on Some Lead-Tin-Cadmium Alloys" ULTIMATE STRENGTH
COMPOSITION Pb
Sn
Cd
%
%
%
90 75 75 70 70 70 68 65 65 65 65 62 60 50 50
5 18 3 22 16 10 23 25 20 15 9 38 29 50 25
5 7 22 8 15 20 9 10 15 20 26 0 11 0 25
Average
Maximum
Minimum
Lbs. Kg. Lbs. Kg. Lbs. K e . . -in.' in.2 mm.2 in.2mm.i 4370 5450 6790 5950 4580 4910 6200 6510 5390 5520 5805 5385 7270 6300 6620
3.1 3.9 4.8 4.2 3.2 3.5 4.4 4.6 3.8 3.9 4.1 3.8 5.1 4.4 4.7
4400 5540 6930 6670 4665 5561 6500 6610 6042 7100 5980 5800 7310 6510 7190
3.1 3.9 4.9 4.7 3.3 3.9 4.6 4.7 4.3 5.0 4.2 4.1 5.1 4.6 5.1
4350 5280 6400 5400 4495 4500 5200 6460 4730 4710 5660 5170 6890 6180 5550
mm.2 3.1 3.7 4.5 3.8 3.2 3.2 3.7 4.5 3.3 3.3 4.0 3.6 4.8 4.4 3.9
Four samples of each alloy were tested
EFFECTOF SMALL CHANGES IN COMPOSITION OF THE 68 PER CEXT LEAD-23 PER CEXT TIN-9 PERCEXTCADMIUM SoLDER-If lead is added to the 68 per cent lead-23 per cent tin-9 per cent cadmium solder, the resulting alloy is more difficult to wipe, and is less reliable. Some of the joints wiped with a solder containing 69 per cent lead were porous. Additional tin makes the solder less coarse, as in the case of Table IV-Porosity and Wiping Characteristics of Various Solders standard solder, and joints wiped with it are not porous. SPLICERS' COMPOSITION Solder containing even 1 per cent additional cadmium appears COMMENTS AS No. No. ALIMPURITIESTO WIPING JOINTS JOINTS to oxidize appreciably more a t high temperatures and is more LOY CHARAC- WIPED POROUS Pb Sn Cd difficult to work. TERISTICS Discussion
7 0 7 0 %
17
75 75 70 68 68 67.9 67.8 67.5 67.75 67.6 67.9 68 68 68 66 65 65
18 3 22 27 23 23 23 23 23 23 23 23 23 17 25 25 9
18 23 24 25 26
62 62.6 63 64 65
38 37.4 37 36 35
5 6 7 10 11
11-1 11-2 11-3 11-4 11-5 11-6 11-7 11-8 12 13 14
a b
7 22 8 5 9 9 9 9 9 9 9 9 9 15 9 10 26
0 0 0 0 0
Coarse Not workable Fair Good Good Good 0.17~ cu Good 0.27, cu Good 0 . 5 % CU Fair 0.25Y Sb Coarse 0.470'Sb Fair ZiiFFpba Coarse S. E. Missoui-i Pbb Good Coarse 0 Good 0 Good 0 h-ot workable 0 0 0 0 0 0
0 0
0 0 0
ismuth content o verage copper con
Good Fair Fair Fair Coarse
8
8
8 2 58 15 2 2 2 2 10 10 2 3 8
3 1 0 1 1 1 0 0 1 0 0 2 0 0
4 6 6 10 4
0 3 3 8 4
..
2
..
Several lead-tin-cadmium alloys have physical and chemical properties comparable with those of standard solder. The
iigh-bismuth lead averages 0.155 per cent. of southeastern Missouri lead is 0.07 per cent.
It
POROSITY MEAsUREMENTS-h this work a soldered joint was considered t o be non-porous if i t could withstand an internal air pressure of 30 pounds per square inch (2100 grams per square centimeter) without leaking. The data obtained on porosity are given in Table IV and show, among other things, that an alloy composed of 68 per cent lead-23 per cent tin-9 per cent cadmium is satisfactory from the porosity standpoint. EFFECT OF IMPURE LEADS-TWO commercial leads, a highbismuth lead containing 0.155 per cent bismuth and a southeastern Missouri lead containing 0.07 per cent copper, have
Figure 2-Lead-Tin-Cadmium
Solders.
Curves of Equal Cost
January, 1929
IA\-D USTRIAL ALVDE,YGINEERIXG CHE-MISTRY
s compositions
of the alloys tested are marked in Figure 1. Those best suited for wiping purposes were found to fall on the line drawn from the lead vertex of the equilibrium diagram to the ternary eutectic point. These alloys, during equilibrium cooling, form no binary eutectic. The cooling is therefore very similar to that of a lead-tin solder. Several of these lead-tin-cadmium solders have longer cooling ranges than standard solder. This gives the splicer more time to wipe the joint. Of the satisfactory lead-tin-cadmium alloys that composed of 68 per cent lead-23 per cent tin-9 per cent cadmium is the cheapest. The substitution of this solder for the standard
19
62 per cent lead-38 per cent tin may effect a saving of several cents a pound. Conclusions
I-The addition of cadmium makes Possible the use of higher Percentages of lead in satisfactory solders. 2-These lead-tin-cadmium wiping solders are generally cheaper than corresponding lead-tin solders. 3-A solder containing 68 per cent lead-23 per cent tin, and 9 per cent cadmium is satisfactory as a substitute for standard 62 per cent lead-38 per cent tin solder.
Protection of Underground Pipe from Corrosion‘ A Method Used in Southern California E. 0. Slater SMITH-EMERY COMPANY, 920 SASTEEST.,Los AXGELES,CALIF.
HE distributing systems of gas and water companies represent 65 to i 5 per cent of their invested capital and a large proportion of oil companies’ capital investment. The proper protection of this tremendous mileage of underground pipe-over 150,000 miles with its capital value of $1,500,000,000-is of vital and growing importance. The enormous annual repair bill represented by pipe-line corrosion mill probably increase rather than decrease, as a large amount of this pipe has been in the ground long enough for accumulated deterioration to demand attention. The average expenditure for protection is 1.6 cents per foot of pipe for each inch in diameter. This is a very small amount when compared with the cost of reconditioning or replacement while endeavoring to maintain efficient and dependable service. The methods suggested for protecting against corrosion are :
T
(1) Manufacture of corrosion-resistant pipe Progress is being made in this direction by the use of an all-alloy pipe or an ordinary pipe with a resistant shell, although costs, so far, are prohibitive. (2) Modification of the condition of soil, as placing the pipe in Portland cement or lime. (3) Use of protective coatings, This is the method most in use.
The rate of corrosion is determined in a broad way by the character or the soil and the soil mater. Therefore, any coating, t o be effective, must keep the soil and water from contact with the pipe. As one eminent chemist puts it, “Pipe will not corrode if you keep the moisture from it.” As soil corrosion falls within the scope of electrochemical theory, it follows that, if the pipe in only known bad soils is protected, then the rest of the line, even in good soil, will be more or less affected. Therefore, the whole line should be protected. Old lines or products of corrosion should not be placed in proximity t o the new lines, as electrochemical action is stimulated. There are several methods of determining the corrosive power of soil. Among these are chemical analysis; ability to conduct electric current; rate of giving off gas when mixed with iron; and loss of weight of iron placed in the soil. These tests are of value when checks are run a t the same time on soils of known corrosive power. 1
Received August 21, 1928.
Method of Application of Coating
If the protective coating is expected t o preserve the pipe, it must be applied t o a clean, hard surface with which it can form a permanent bond and to which it will adhere tenaciously. The surface of the metal must be cleaned of all mill scale, rust, dust, and all traces of oil, grease, and moisture. Mill scale is electronegative to iron and steel and this tends inevitably to stimulate pitting. Even on new pipe mill scale is only a thin, brittle, loose covering, and if painted over will crack off because of the different coefficient of expansion between it and the pipe. Pipe may be cleaned by wire brushing, scratching, filing, hammering, pickling, and sandblasting. Sand-blasting is the only method that gives a really clean surface with the least damage to the pipe. The cost of sand-blasting, as shown in a paper2 by Fred Benson, of Los Angeles Gas & Electric Company, runs less than 2 cents per lineal foot of pipe 4 inches in diameter. The unit cost reduces as the diameter increases. Note-Since this article was written one of the large companies has installed a plant especially equipped for sand-blastlng pipe commercially, which charges one cent per square foot of surface
The application of the protective coating is usually the last thing done t o the pipe before lowering into the ditch and backfilling. For this reason the job is hurried by the men and slighted by the contractor and the result is generally little protection. Quoting D. R. Hiskey, of the Engineering Department of the Southern California Gas Company, “If we cannot afford to apply properly, why try to protect a t all?” Pipecleaning and -coating crews should be hand-picked men who could be trained and relied upon to keep up the standard of the work. This part of the work should be dignified as an art for skilled labor as much as welding and should take its place as one of the important parts of pipe-lining. Inspection should be rigid and made by men familiar with the product being used. Types of Coatings
Protective coatings available for underground pipe lines are : (1) Bituminous, as native and residuum asphalts, coal-tar pitches, and gilsonite. These are applied cold as paint or hot by dipping or pouring.
* Western
Cas, 4 (May, 1928).
