THE: CKYSTAI, STlLU(:TtiItl', OF COPPER E1,ECTRODEPOSITEU IN THE PRESENCE OF GELATINE
___
BY H. KERSTEN*
Introduction Electrodeposited metals are usually more microcrystalline when the baths [rum which they .we deposited contain colloids. l n the case of copper plated from an acid bath containing gelatine it has been shown' that some of the gelatine is deposited with the copper. Fig. I shows that such copper is more brittle than that obtained from the same bath without the addition of gelatine. The two kinds of OODM?~ .. shown were plated on stainless steel (to which most electmdeposits adhere poorly) and partly stripped to show t,he difference in brittleness. In view of these differrnces in physical properties one might expect a differenoe in the crystsl structure of the deposits. Trillat" cxamined such sampls by means of x-rays and found apparent, but not conclusive, evidence for a difference in the length D, Fig 2 , of the edge of the unit crystal lattice for the two kinds of copper. This . pawr . describes a new determination which shows that any difference in th,e length of the unit lattice for the two kinds of copper must be less than 0.01 Bnastrijm. Experimental The x-rays. were supplied by a Siegbabn-Hadding type of x-ray tube having a copper target. A special camera shown in Fig. 3 was constructed, in which the x-rays passed through the slits in the ends of the tube A and struck the samples B and C nearly at a tangent. Them samples were electroplated on gold-plated brass tubes so that if any x-rays were diffracted by the under metal this fact could be not,iced in the picture because the distance D of Fig. 2 for gold is much different from that, of copper. The samples B and C were of the same outside diameter and fitted snugly over the pin D. This made the distance from the slit to the film the same for both samples. The * Dcpt. of Ptrysies, University of Cincinnati, Cincinnati, Ohio.
' Muller and Rahntje: Z. Elektrochemie, 12, 3'7 ZTrillat:Rev. Mbtnllurgie, 25, 286 (isza).
(lgo6).
.1
s
paper cnvclopp and held on the circuniferuriw of rliu Sext. to the film was plirced a picec of 0 . 0 2 iriiii lilter giving npproximstely rnonochronralic l,i.:ims, Thc~plnce where the t w o samples joined was aligned with the p:rriilion 1' which prtiventrd the diffracted beams from one of the samples crossing OVIY to ?be piwt of ilrr iilrn whirh was intended to receive the beams from thn other s:trr~plr~.:In ml;irpd ptiotogrnph, taken xvith this camera, is sl~ownin Vig. 4 . mclosed
iii it
The other bath had the same coniposition except that it contained IOO gm of gelatine. The baths were connected in series and since the cathodes hsd the =me area, the current density was z amp per dm' for each sample. The temperature wa8 kept constant a t z 5 C by placing tho beakers wntaining the electrolyte in a water-bath. A sufficiently thick deposit wae obtained in one hour.
Theoreticat To show that the difference in the length of the edge of the unit lattice must be less than o . o r i for the two kinds of copper, Bragg's law is used nh =
2
k D sin 0,
n. KERSTEN
3646
where : n = order of the reflection ( I , 2 , 3, etc.), X = wave length of the x-ray beam, k = a factor which when multiplied by D gives the distance between corresponding planes (for the I I I planes k = 0.5 j7), D = length of the unit crystal edge (Fig. 2 ) , 0 = angle between the incident x-ray beam and the diffracting plane. From this, 8 is computed for the various planes which may caus: diffraction, assuming the $stance D for copper to be its usual value of 3 . 6 ~ 4 as , well as 3.60 and 3.504. The theoretical positions of the lines thus determined are plotted in Fig. 5 from the computed values given in Table I. RANtS
X,
SO
80
80
70
ee
I10
1oQ
IZO
130
l e
I N DEGREES
FIG.j Theoretical positions of the lines for various values of D.
TABLE I Values of
2 0
for various values of D z
Planes I11 200 220
3'1 222
400
331
e for D
=
3 61
43O 50' 74' 90' 950 117' 137'
89' 50' 95' 2'
116' 46' 136' 14'
In the computations, X was taken as
3 50
3 60
43' 16' 50' 24' 74' 2 '
I . 53
24'
44' 4 2 '
32' 16' 6' 21'
6' 76' 46' 93' 2 8 ' 99O 2 '
16'
I 2 2 O 52'
2'
52'
146'
20'
jh.
From the table and from Fig. 5 it is evident that the greatest difference in the positions of the lines occurs on the right-hand end. Turning to Fig. 4, the difference between the positions of the 331 lines is not !a great as that between the same lines in Fig. 5 for D = 3.61 and D = 3.60 A. Hence we conclude that any difference in the unit crystal lattice edge is less than O.OI.&.
