1,VDL'XTRIAL ALYDENGISEERING CHEJIISTRY
May, 1930
Literature Cited
519
(9) hfarden and Rentschler, I X D . ENO.CHEM,,19, 97 (1927). (10) Moissan, Compf. rend., 113, 2 (1891). (11) Moissau, IDzcf., 116, 347 (1893). (12) l l o i s s a n , I b i d . , 122, 1088 (1896). (13) Moore, Trans. A m . Elecfrochem. Soc., 43, 317 (1923). (14) Peligot, Ann. chim. phys., [3]. 6, 5 (1842). (15) Pierle and Kahlenberg, J . P h y s . Chem., 23, 517 (1919). (16) Zimmerman, A n n . , 213, 290 (1882); 216, 1 (1883). (17) Zimmerman, Ber., 17, 2739 (1884).
(1) Aloy, Bull. SOC. chim., [3] 26, 344 (1901). (2) Aloy, A n n . chim. phys., 171 24, 412 (1901). (3) Burger, Dissertation Basel, p. 19 (1907). (4) Feree, Bull. SOC. chim., [3] 25, 622 (1901). ( 5 ) Fischer and Rideal, Z . anorg. Chem., 81, 170 (1913). (6) Fogg and James, I N D . ENG.CHEM., 18, 114 0 9 2 6 ) . (7) Giolitti and Tavanti, G a m chim. i f a l , , 38, 239 (1908). (8) Lely and Hamburger, Z . anorg. Chem., 87, 209 (1914).
Properties of Strontium-Tin Alloys' K. W. Ray DEPARTMENT OF CHEMISTRY, UNIVERSITY OF I o w a , IOWACITY,IOWA
E V E M L strontium-tin alloys have been prepared (3, 5 ) , but no systematic study of the properties of these alloys has been made. The thermal diagram of the magnesium-tin system ( 2 ) as well as the thermal diagram of a,,portion of each of the calcium-tin ( 1 ) and the barium-tin (G) systems have been worked out, but there is no record of any such work for the strontium-tin system. According to Tammann's rule ( 7 ) that an element forms a compound with all the elements of a natural group or with none of the members of the group, tin should form compounds with strontium, since it does with magnesium, calcium, and barium. However, the crystal structures of barium and of strontium are different ( 4 ) , and crystal form seems to be somewhat related to compound formation.
S
Figure 1-Current
The electrolysis was carried out a t the lowest temperature a t which the contents of the crucible could be kept liquid. The salt bath was usually entirely liquid a t 600" C., but in some cases the temperature had to be kept much higher than this to maintain the alloy in a molten condition. The alloys prepared in this way contained appreciable amounts of sodium, which was largely removed from all alloys containing less than 25 per cent strontium by remelting the crude alloy under a bath of pure strontium chloride. The extent of the purification is shown in the following case: An alloy as first made contained 20.04 per cent strontium and 0.21 per cent sodium, while after its fusion with strontium chloride it contained 18.95 per cent strontium and 0.04 per cent sodium. This remelting was done in a fire-clay crucible heated in a gas-fired furnace. The thermal diagram JTas based on the data obtained by methods of thermal analysis as well as by microscopic study of the alloys. In taking a cooling curve, the metal was placed in a Pyrex test tube which was wrapped with asbestos paper and then placed in a vertical electric tube-furnace. The temperature was raised to about 100" C. above the melting point of the alloy and the current shut off. The cooling rate was recorded automatically by a Brown electric recording pyrometer. A few drops of a paraffin oil were placed in the tube before heating t o preyent oxidization of the sample.
Efficiency
Even though strontium-tin alloys have no industrial use these alloys should have as much interest from the point of view of theoretical metallurgy as any other alloy system. They might also have sufficient bearing on problems of both theoretical and practical interest to justify their investigation. The purpose of this investigation, therefore, was to prepare a large number of strontium-tin alloys, to study their properties, and to construct as much of the thermal diagram as possible from the data obtained. Experimental Methods
The strontium-tin alloys were prepared and tested by methods similar to those used by Ray and Thompson (G) for the barium-tin alloys. The alloys were produced by the electrolysis of a mixture of fused sodium and strontium chlorides over molten tin, in a chromium-plated iron crucible. The molten tin was made the cathode and a carbon rod which extended into the salt bath served as the anode. Chlorine was evolved a t the anode while strontium was deposited in the liquid cathode metal. The composition of the bath varied from 60 to 90 per cent strontium chloride by weight, the remainder being sodium chloride. The crucible and contents were heated by one or more gas burners. 1
Received March 6, 1930.
Figure 2-Thermal
Diagram
hlost of the alloy samples were studied microscopically (1) as chill-cast; ( 2 ) after annealing several hours a t 240" C.; and (3) after annealing a few hours near the melting point followed by rapid cooling. It was found necessary to seal the samples in Pyrex tubes before annealing to prevent oxidation. The specific gravity was determined only on the chill-cast alloys. A section of the ingot prepared by pouring the molten metal into a steel mold was smooth-polished on a fine emery wheel. The piece mas then weighed in air, and
pigure ~ - - B . I u % strontium. A"mated a t Z I U ' C . White, Sn; Dark, s n s r . x IOU
9--iz.an% strontium, A,). nealed a t 350' C. and Quenched Sa and Sn&. X 100
FiQure 8-12.687 Strctntium Anncaledaf 24U3C. 8 e l y SnaSr Prebent in Phofofiraphed Section. x SUO
these alloys for longer periods of t i m e disappearance of either thr bin or tlie Rn&. The specific gravities of tlic alloys are sliown in Figure 3. The calculat,ed values, taking tire specific gravity of tin tis 7.30 and of strontium as 2.60, are also plotted. Evidcntly there is a slight coiit,rat:tioii in voliinie when alloys containing less than 6 per cent strontirinr are rriadc, wliile an expansion occurs i n the formation OS alloys containing more tlian '3 per cent. The Iiardrms of tlie alloys itii:rea rapidly with increasing ariiouii1.s ofstrontiorn until t i l e first emiipounrl is furint:d, after wliieli thra tiunlm:ss inereiisvs nnicli iiiore slo~l-ly. T1,e h a r h x of tlic drillc i u t alloys is sliown in 'Palile IT. Tlrc ront,aioirig iiiorc than stroritiiiirr werc so hrithe in the llriiiell tests. tilo slmealcli sallijrlcs was not siiidied, biit it was iiiiich 2I.llsF; Srruntium. May of Sn,Sr and SnSr. x grr!atcr than thtlt of tile corr~:qx~liding drill-cast alloy in all cast's where tlic content of strontiuni was less tlraii 19 jicr cent. This was iliic, of coiirse, t,o the prcseiirr i d Sn&, wliioli was very niorli harder t,lirtli tin. caii~1~ the 1
Figure 10- 11.585: Sfrontium, Annealed for 2 Hours a( 24u" Whiic,
c.
Sn: mark. Sn,,Sr: and LiChf, Sn.Sr.
x
100
Figure 1 1 Re Eufecfic
suo
'Cable II--llsrdncm
. o., o.o....
11.1
4
i OR
17.0
8
--2x
+
1
of Sfrontium-Tin Alloya
13.~5 17.58
ti ! 1
21 8
10
16
20.23
!3 11s
as.O
12
40
25.81
84.4
14
82
29.06
12 86
3x.3
45.6
Sa*"pk
broke Saiaplc
broke
Sainple
broke
16
21
78 9%
36
110
32
11,5 '
40
118
Strontium-tiii alloys corrode very rapidly in rlamp air alii1 water, but much more slowly in dry air. Strontium
I A . DUSTRIAL AXD EXGINEERING C H E - I S T R Y
522
hydroxide forms in the presence of moisture, and the tin is left in the form of sponge. In dry air the alloy tarnishes only superficially with a coating which seems to be a mixture of the oxide and carbonate. Table I11 gives some corrosion data for an alloy containing 18 per cent strontium. Table 111-Rate
of Corrosion of 18 Per C e n t Strontium-82 Per C e n t T i n Alloy a t Z O O C. IN AIR SATDWITH
EXPOSURE WATERVAPOR
IN DRYAIR
Days 10 20 30 40 50
Gain in weight Gram per sq cm. 0 07 0 18 0 31 0 45 0 62
Gain in weight. Gram per sq cm. 0 0013 0 0024 0 0033 0 0048 0 0051
60 85
0.85 1.42
0,0060 0.0081
I N WATER Hydrogen evolved per sq cm. surface
Hours 10 24 34 46 58 65
Cc. 52 106 154 202 264 Completely disintegrated
Vol. 22, No. 5
All the chill-cast alloys containing more than 12 per cent strontium were practically non-malleable and non-ductile. Alloys containing from 12 to 18 per cent strontium were coarsely crystalline, as shown by the fracture, and the alloys still higher in strontium were about as brittle as glass. Strontium-tin alloys might be used as de-oxidizing agents for bronze, or they could be used to introduce tin and strontium into many other alloys if this were found to be desirable. Literature Cited (1) (2) (3) (4) (5) (6) (7)
Donski, 2 anorg Chem., 67, 213 (1908) Grube, I b t d . , 46, 76 (1905). Jellinek and Wolff,Ibid , 146, 329 (1925). King and Clark, J . A m . Chem. Soc., 61, 1709 (1929). Ray, Metals and Alloys, 1, 112 (1929). Ray and Thompson, Ibzd , 1, 314 (1929) Tammann, “Textbook of Metallography,” p. 228, Chemical Catalog, 1925.
Studies in Heat Transmission’ I-Measurement of Fluid and Surface Temperatures A. P. Colburnl and 0. A. Hougen DEPARTMENT
OF
CHEMICAL ENGINEERING. UNIVERSITY OF WISCONSIN, MADISON, WIS
The accuracy of experimental data on heat transmission depends upon exact measurements of temperatures of surfaces and fluid streams. The serious errors introduced by improper use of thermocouples are demonstrated. Methods are given for the following temperature measurements with thermocouples: ( 1 ) Measurement of the average temperature of a given cross section of a fluid stream or of a given surface area by a single observation by means of a special multiplejunction thermocouple. (2) An accurate method of measuring surface temperatures of metals. This method consists in imbedding the
wires in a narrow slot in the metal surface in a line of zero temperature gradient for a distance of about 1 inch in each direction from the junction. The junction is soldered in place and made flush with outer surface of metal. The rest of the couple in the groove is packed flush with surface with glycerol-litharge cement providing excellent thermal contact but poor electrical contact except at the junction. (3) Method of minimizing temperature fluctuations of couples in fluid streams so as to facilitate readings. A review and criticism of previous methods are given.
I
will be the average of the individual circuit e. m. f.’s. If the resistances are not the same, the individual temperatures will be weighted by the relative conductances of the junction circuits in determining the reading of the single wires. A proof of these statements follows. The relation of the e. m. f . of the single wires to.the e. m. f .’s of the individual thermocouples can be shown theoretically from Kirchoff’s laws. Let the individual junctions and wires be represented by sources of e. m. f . (el, e2, . . . e,) and by electrical conductances (e1, c2, . . . en). (Figure 1) By Kirchoff’s first law the total e. m. f., E, across the main wires bears the following relationship t o the individual e. m. f.’s, where il, i2, , , i, are the currents flowing in the individual circuits:
N DETERMINING the heat-transmission coefficients of
the various fluid films in an experimental tubular gas condenser, a preliminary study was made of the technic of temperature measurements in such a heat exchanger. For convenience and precision thermocouples were used which required special arrangements for the following conditions: (1) to measure the average temperature of an area over a given cross section of a fluid stream or over a given surface; ( 2 ) to measure the temperatures of surfaces; and (3) to minimize the fluctuations of thermocouple temperatures which would prevent precise balancing of the potentiometer. Measurement of Average Temperature of Areas
To measure the average temperature of fluid streams and of surfaces a multiple-junction single thermocouple was devised. This consists essentially of several very short thermocouples connected in parallel to a common pair of thermocouple wires. These short branch thermocouples are all of equal length (3 or 4 inches), just long enough t o reach the common thermocouple wires. If the resistance in each small branch circuit is the same the e. m. f. indicated by the common wires Received February 10, 1930. Abstracted from a forthcoming bulletin of the Chemical Engineering Department of the University of Wisconsin. Present 2 Fellow in Chemical Engineering, University of Wisconsin. address, Experimental Station, E. I. du Pout de Nemours & Company, Wilmington, Del. 1
E
= el
E
= e2
- il -
or E
c1
= el
c1
-
il
GI’ a2
- -,
or E cz = e2 c2 - i~
61
E = e,,
=
5 or E
c,, = e,, c,, -
i,
cn’
By summing up the (n) equations for the (n) junctions and by Kirchoff’s second law, placing it + i * . . . . +in = 0
+.
the following equation results:
