356
Vol. 66
NOTBS
STUDIES ON THE SOLGEL TRANSFOItMATION OF THE FERRO- AND FERRICY-4NIDES OF SOMS METALS. PART 111. GELATION IN CHROMIC FERROCYANIDE BY WAHIDU. MALIKAND Flisrrr A. SIDDIQI Chemical Laborotorcea, M w k m Untowatt$(,Aligarh, Jndia Received August 99, 1981
During the course of the work on heavy metal ferrocyanides we came across an unusual reaction, viz., that between chromic chloride and potassium ferrocyanide, where iinlikc other metal ferrocyanides a soluble complex (reddish brown in color) of the composition1v2KCr11TFe1rCy6is formed. On carrying out the reaction a t 80' an insoluble complex, highly viscous in nature and showing a tendency to gelatinize, is obtained. A study of some colloidal aspects of this compound was undertaken. Experimental The chromir ferrocyanide 801 did not reveal vulnerability toward electrolytes as is grncrally the case with typical hydrophobic sols. However, intcresting results were obtained on keeping it in the electrophoresis tube. Thus with a mixture of CrCI3 and K,FeCye (concn. 0.075 and 0.025 M , respectively) of molar ratio Cr*+/FeCy$'- of 3: 1 , wclldcfined rings in the cathodic limb were formed; the liquid in the anodic limb depressed to about 1 cm. in about one hr. 15 min. (potential applied:150 v.; current 2 to 5 mamp.). hlixtures of the molar ratio 1 : 3 (concn. CrC4 = 0.016 111 and K4FeCys 0.05 M ) underwent movement toward the anode; with thc equilibrium mixture (concn. 0.05 M of each reactant) there was no perceptible movement toward cither of the electrodes. The time of wtting of chromic ferrocyanide grl a8 influenced by the Cra+/FtCy6'- ratio was studied by Fleming's method3 with the followng four sets of mixtures. (i) 3.5 cc. of 0.78M K,FeCys mixed with 1.0, 1.5,2.0. . . . . . . . .6.0, 6.5 cc. of 1 2 5 M CrC1.. Total volume made UD to 10 cc. (Molar ratio vuriedfrom 0.45: 1 to 2.97: 1.O); (ii) 5.0 cc. of 0.78 M IGFeCya mixed with 1.0, 1.2, . . . . . . . . .4.2, 1.5 ec. of 1.25 M-CrCI,. Total volume made 11 to 15.0 cc. (Molar ratio varied from 0.32:l to I . 8 : l . O ) . l i i ) 2.8 cc. of 0.58 M K,FeCya mixed with 0.96,1.2,1.28,. . .. . , -3.06, 3.2 cc. of 1.25 M CrC4. Total volume made up to 10 cc. (51olai ratio varied from 0.53:l.O to 1 . 8 3 : l . O ) ; (iv) 1.8 cc. of 0.78 M K,FeCye mixrd with 0.6, 0.8,. . .2.0, 2.2 cc. of 1.25 M CrC13. Total volume made u to 10 cc. (Molar ratio varied from 0.534:l to 2.0: 1.0). 8 h e results are depicted in Figs. 1 and 2 (curves 1, 2, 3 and 4, respectively). The t.imeof gelation, besides being influenced by the Cra+/ l'eCy~4-also wae found to be dependelit upon the concentration of the reactants. Thus the time of gelation of the mixt,iire containing 3.5 cc. of 0.78 K,FeCye and 2.5 C.C. of 1.25 M CrCI3 (molar rptio 1.1:l.O)increased from 12 min. to 15, 17, 28, 60,156 min., respectively, on diluting the rcactnnts to 4/5th, :J/5th, 2/5th, l.5/5th and 1/6th of the original concentration.
.
3
I.
2
2.4
4
R.
16
i 2.1
6 %
o 1.5 *
.I
1
53 0.9 H
CI
0.3
Loj 1. at5
0
50
I?$
75
100
IX
150
:is
200
T', min. (Set i).
is
250
Fig. l . - S e t i and ii.
2.0 c'
A
U, 1.6
k 2
6 1.2
a C
E 0.8
3
2
I
0.4
50
. .
100
150
200
T,min. (Set iii).
Fig. 2.-Set
250
iii and iv.
ions; (iii) slow movement in the electrophoresis tube and indistinct separation of the phases at the interface; (iv) the tendency of the particles to assume a positive as well as negative charge (depending upon the excess of chromic or ferrocyanide ions). That the two types of gel-forming mixtures exist can be seen from the results on the time of gelation. Thus with the increasing concentration of the chromic ioiis a continuous decrease in the time of gelulion is not realized. On the uthcr hand, after reaching a minimum value for the equimolar mixture gradual increase in the time of gelation takes Discussion place (Figs. 1 and 2 ) . However, in both cases the The results on t~hesol-gel transformation of chro- time of gelation is highly dependent upon the Cr3+/ mic ferrocyanide reveal many points of dissimilarity FeCyE4- ratio. The behavior, vi?., decrease in the time of gelawith other metal ferrocyanides.* These are (i) lesser solubility of the complex with increasing tion for mixtures of minimum gelation time (molar temperature, optimum condit.ion for gelation being ratio 1.1:1.0) with increase in the concentration of reached in the vicinity of 80'; (ii) non-destructi- (,he reactions is not unexpected since with ,concenbility of the colloidal state by the addition of foreign trated solutions the degree of supersaturation increases and chances of gelation are enhanced. (1) W.U. Malik. J . Sci. Ind. Research (India), 18, 463 (1959). A plot of log M against log 1' gives a pair of ( 2 ) W. U. hlalik, ibid., 20B.6, 213 (1961). ( 3 ) Fleming, 2. Phyaik, 41, 427 (1902). straight lines. The exponential nature of the curves (4) K. Nasiruddin, W. U. hialik and A. K. Bhattaoharya, J . Phya. can be represented by the empirical relationship
. .. . .. .
Chsm.. 69, 488 (1955); W. U. hlalikand A. K . Bhattacharya, ibid., 69, 400 (19%).
(T
- crM")(T - g'5f-n)
=0
Fcb., 1002
3t57
NOTES
M
bcing mo1n.r ratio and T the time of gelation, where a,B, n and m are constants. Their values for t h e foiir sets are a = 5 3 , 19.9, 18.6, 10.0; B 19.05, 14.2, 17.78,X.l4; IL = 3.4,5.0, 6.9, 6.22 i t ~ d m = 2.01, 2.68, 4.16 and 4.68. The fact that the values of the conrtants are not the same may be due 5
to the varying influcnce of factors like solubility, degree of supersaturation, cxtciit of hydration and dilution during gelation. Acknowledgment.-Thanks are due to Dr. A. It. Kidwai for providing facilities and to C.S.I.R. (India) for the award of a fellowship to F.A.S.
2.4 I*
ii 20 1.2 .m
Y
E
4E 0.6 A rl
STUDIES ON THE SOL-GEL TRANSFORMATION OF THE FERRO- AND FERRICYANIDES OF SOME METALS. PART IV. VARIATIONS I N VISCOSITY AND HYDROGEN ION CONCENTRATION DURING THE GELATION OF CHROMIC FERROCYANIDE BY WAMDU. MALIKAND FASIH A. SIDDIQI
4
104T . e15
3:s
0’15
50
C*VW ~
1.75
la 225
150 200 250 T, min. Fig. l , - C u r v e la, T us. M ; curve lb, log T us. log M ; curve 2, strength of CrCls us. log ( q t - ~ o ) / v o . 100
setting for the gelation mixturcs of molar ratios 0.50:1,0, 1.O:l.O and 2.0:l.O being 25, 17, 85 minutes, respectively, by Fleming’s method and 120, 28 Chamkal Laboratm‘cs, M w l i m Uniombitu, Aligarh, India and 120 minutes, reapectivcly, by the viscosity Recoined A w a t #Se 1881 method), provided due allowance is given to the disThe conductivity method, which was successfully turbances experienced by the gel-forming mixturc employed’ earlier in studying gelation of Prussian during its movement through the capillary; ( 2 ) and Turnbull’s blues, did not give any useful in- similar types of curves are obtained by the two formation here, and hence the methods based on the methods on plotting the time of setting against the variations in viscosity and pH werc adopted. The molar ratio (Fig. l), confirming thereby the existlatter method was particularly chosen with a view ence of two types of gels in chromic ferrocyanide to ascertain the hydrolytic effects operative during (Part 111); (3) a straight line is obtained on plotting log (qt - qo)/qo (for abrupt change) against the congel formation. centration of chromic chloride (Fig. 1, curve 2 ) Experimental (Crs+ concn. for sets I to VII), which indicates a Viscosity measurements were carried out at 80 0.1’ thixotropic behavior of chromic ferrocyanide gcl (a (Fisher Unitized constant temperature oil-bath) with the help of an Ostwald viscometer after applying a vacuum of 1 linear rclationship log 6 = A - Bc, where 0 is the cm. (manometer tube sirpplicd with koppeos viscometer time of setting and c is the concentration of the u n i t was used for this purpose) a t the head of the viscometer electrolyte and A and B are constants, \va$ found by tube. Beckinan pI-1 meter (model H2) was used for pH Freundlich,2 Schalek and Szegvaria for thc gelation measurements. Seven sets were studied, containing 0.25 M of ferric oxide sol). &FeCys and varying concn. of CrC4 (0.083, 0.125,0.18, The results on p1-E measurcmcnts, besides con0.25,0.375,0.50 and 0.625 M ) in the reaction mixture. Thc results arc summarized in Table I. firming the results on viscometry (the time whcn constancy in pH value is reached being taken as the TABLE I time of setting), throw some light on the nature of Time Value the chromic ferrocyanide gel. As cxpected the interval Change in of for abrupt ’I during (at mixtures containing excess of chromic ions have change in this r)a)/qo a t p H change viscwity r) interval abrupt during lower pH values and those containing excess of Seb Crs+/FeCyd- (min.) (centipoise) change gelation potassium ferrocyanide have highcr pH values. I 0.33:l.O 218-250 0.70-2.4 0.75 4.0-7.25 But with lapse of time the pH of the mixtures havI1 0.5:l.O 120-140 0.95-2.7 0.90 3.8-6.8 ing Cra +/FeCye4>1 continuously decreases, I11 0.75:l.O 72-80 1.15-4.8 1.10 3.6-4.0 while for those having Cr3f/l;rCyb4-
