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Homogeneous nucleation of bis(1,2-cyclohexanedionedioximato)palladium(II)
1060
Short communications
high purity nickel oxide and nickel wire. The results for the oxide were NiO, 100.7%; 100.8%; 100.7 %; 1006%: for the nickel wire they were Ni, 99.7%; 99.6%; 994%. These and many other results gave a relative standard deviation of 0.1% for the method in this concentration region, which demonstrates that the method is very useful for the precision spectrophotometric determination of nickel. Acknowledgement-The authors wish to thank Mrs. I. G. Asscher-Wolanska, larger part of the experimental work.
who carried out the
Laboratory for Analytical Chemistry University of Amsterdam Amsterdam, The Netherlands
G. H.
DEN
BOEF
POPPA
Summary-The determination of nickel with pyridine-2,6-dicarboxylic acid by means of differential spectrophotometry at 1025 rnp is described. At the Ni concentration level of 2 mg/ml the relative standard deviation is 0.1 ‘A. Only a few elements interfere. Zusammenfassung-Die Bestimmung von Nickel mit Pyridin-2,6dicarbonsiiure durch Differenz-Spektrophotometrie bei 1025 mn wird beschrieben. Bei Nickelkonzentrationen urn 2 mg/ml ist die relative Standardabweichung 0,1x. Nur wenige Elemente stdren. R&rm&-On d&it le dosage du nickel par l’acide pyridine 2,6dicarboxylique au moyen dune spectrophotometrie diff6rentielle a 1025 m,u. Au niveau de concentration en Ni de 2 mg/ml l’&trt type relatif est de 0,l ‘A. Seuls quelques elements g&rent. REFERENCES 1. R. Bastian, Anal. Chem., 1951,23,580. 2. G. Svehla, Talanta, 1966, 13, 641.
Talanta, 1968, Vol. 15, pp. 1060 to 1062. Pergamon Press.
Prmted in Northern Ireland
Homogeneous nucleation of bis(l,2-cyclohexanedionedioximato)palladi~(II) (Received 15 January 1968. Accepted 19 April 1968) droplet technique, first described by Vonnegut, 1 has been used with considerable success in the study of homogeneous nucleation of a large variety of substances. %-* This method involves the subdivision of the sample under study into a very large number of non-communicating droplets. The foreign particles capable of acting as nucleation catalysts in the original sample are presumably sequestered by incorporation into a small fraction of the droplets, which will undoubtedly exhibit heterogeneous nucleation. However, most of the droplets should remain catalyst free, so homogeneous nucleation is expected to occur in them. In most droplet experiments the supersaturation required to induce nucleation has been attained by gradually lowering the temperature of the system. In 1966 Hileman,? and Thompson and Gordon,8 while studying the nucleation of metal chelates, utilized the technique of precipitation from homogeneous solution as the means of achieving supersaturation in the droplets. This paper describes recent studies on the nucleation of bis(l,2-cyclohexanedionedioximato)palladium(II) in which supersaturation was obtained by reaction between 1,Zcyclohexanedione and hydroxylamine in the presence of palladium ions. EXPERIMENTAL Solutions containing palladium(H), hydrochloric acid, hydroxylamine hydrochloride and 1,2cyclohexanedione were prepared by mixing, in the order given, various amounts of their stock solutions. Immediately after the last reagent was added the solutions were dispersed in mineral oil. The dispersions, which consisted mostly of droplets of about 20 ,u in diameter, were then examined with a polarizing microscope and the crystallization occurring in the droplets was recorded photographically. RESULTS AND DISCUSSION THE
From the photographs the nucleation rate was obtained, and plotted as a function of time. The results of the experiments are demonstrated in Fig. 1.
Short communications
1061
To X v
(a) I
E-~
1.5
rr~
1.0 E-~
0.5 v
,,lJli ,I,
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0 0
6
9
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|
18
15
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REACTION TIME (rain)
T0
(b) ~
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~
~
1.O
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TIME
15
I
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18
21
(rain)
(e)
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~
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,,i,,I,,I, 9
6
12
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REACTION TIME (min)
FIG. 1 .--Nucleation rate
vs.
reaction time for the palladium chelate.
Reaction conditions, [HCI], M [Pd(II)], M (a) (b) (c)
1 "0 1"0 1"0
0"1 0"1 0"1
[NH,OI-I.HCI], M 0"7 0"7 0"3
[C6H802], M 0-2 0"1 0"1
1062
Short communications
One point of very high nucleation rate was observed for each of the three sets of concentrations employed. The position of this point was reproducible and occurred 11.5, 140 and 155 min after mixing the reagents (see Fig. 1). Filtering the reagent solutions through membrane filters of various pore sizes before the preparation of the dispersion did not alter the results. Gravimetric analysis* showed that when the reagents were mixed in the proportions corresponding to the set of concentrations listed under Fig. la, the precipitate was produced at a constant rate of 0.38 mg.ml-l.min-l. At this rate the concentration of monomers in the droplets should rise to about 10-BM after 11.5 min of reaction. Spectrophotometric analysis showed that the palladium content of a saturated solution of the chelate in 1M hydrochloric acid was about 1O-5M. This implies that the supersaturation existing in the droplets at the point of maximum nucleation rate was lOa. According to the Volmerlo theory of homogeneous nucleation the rate of nucleation is expressed as log,, J = log,!) A -
167raSv2 3(2.303kT)3(loglo s)*
where J is the nucleation rate, A is the kinetic constant, 0 is the interfacial free energy, v is the molecular volume of the solid solute, k is the Boltzmann constant, T is the absolute temperature at which the experiment was carried out, and S is the supersaturation ratio. J was found to be of the order of lo8 nuclei.cm-3.sec-1. Assuming A = lOa cm-s.sec-l, o was found to be 47 erg.cm-2 for the chelate. Several expressions have been derived which relate the supersaturation of a crystalline solid to the interfacial free energy and the particle size .I1 One such expression is the Gibbs-Thomson equation which was originally derived for vapours but has also been found applicable to small particles in solution. We shall use it in the form r * = 2ov/2.303kT log,, S, where r* is the size of the critical radius and the other symbols have the same meaning as before. The calculated value of r* for the palladium compound was about 11 A. J. A. VELAZQLJEZ Department of Chemistry 0. E. HILEMAN, JR. McMaster Hamilton Ontario
University
Summary-Precipitation from homogeneous solution has been applied to the drop technique for the study of the homogeneous nucleation of bis(l,2-cyclohexanedionedioximato)palladium(II). It was found that under the experimental conditions employed the interfacial energy of the chelate was 47 ergs.cm-a and the critical radius size 11 A. Zusammenfassun8-Auf die Tropfenmethode zur Untersuchung der homogenen Keimbildung von Bis(l,2-cyclohexandiondioximato)palladium(I1) wurde die Fallung aus homogener Losung angewandt. Unter den Versuchsbedingungen war die GrenztIachenenergie des Chelats 47 erg cm+ und der kritische Radius 11 A. R&m&-On a applique la precipitation en solution homogene a la technique a la goutte pour l’etude de I’amorcage homogene du bis(l,2cyclohexanedionedioximato)palladium(II). On a trouve que, dans les conditions experimentales employees, l’energie interfaciale du chelate est de 47 ergs/cm-a et la dimension du rayon critique 11 A. REFERENCES 1. B. Vonnegut, J. ColIoid Sci., 1948, 3, 563. 2. E. Baer, J. A. Koutsky and A. G. Walton, BUN. Am. Phys. Sot., 1966, 11, 247. 3. R. L. Cormia, F. P. Price and D. Turnbull, 1. Chem. Phys., 1962 37, 1333. 4. E. K. Bigg, Proc. Phys. Sot., 1953, 66B, 688. 5. G. M. Pound and V. K. La Mer, J. Am. Chem. Sot., 1952, 74,2323. 6. D. Turnbull and R. L. Cormia, J. Chem. Phys. 1961,34,820. 7. 0. E. Hileman, Jr., Talanta, 1967, 14, 139. 8. S. Thompson and L. Gordon, ibid., 1967, 14, 137. 9. J. Velazauez and 0. E. Hileman, Jr.. Unnublished work. 10. M. Volmer, Kinetik der Phasenbildu&, Edwards, Ann Arbor, 1945. 11. B. V. Entistiin and J. Turkevich, J. Am. Chem. Sot., 1960, 82,4502.
Short communications
high purity nickel oxide and nickel wire. The results for the oxide were NiO, 100.7%; 100.8%; 100.7 %; 1006%: for the nickel wire they were Ni, 99.7%; 99.6%; 994%. These and many other results gave a relative standard deviation of 0.1% for the method in this concentration region, which demonstrates that the method is very useful for the precision spectrophotometric determination of nickel. Acknowledgement-The authors wish to thank Mrs. I. G. Asscher-Wolanska, larger part of the experimental work.
who carried out the
Laboratory for Analytical Chemistry University of Amsterdam Amsterdam, The Netherlands
G. H.
DEN
BOEF
POPPA
Summary-The determination of nickel with pyridine-2,6-dicarboxylic acid by means of differential spectrophotometry at 1025 rnp is described. At the Ni concentration level of 2 mg/ml the relative standard deviation is 0.1 ‘A. Only a few elements interfere. Zusammenfassung-Die Bestimmung von Nickel mit Pyridin-2,6dicarbonsiiure durch Differenz-Spektrophotometrie bei 1025 mn wird beschrieben. Bei Nickelkonzentrationen urn 2 mg/ml ist die relative Standardabweichung 0,1x. Nur wenige Elemente stdren. R&rm&-On d&it le dosage du nickel par l’acide pyridine 2,6dicarboxylique au moyen dune spectrophotometrie diff6rentielle a 1025 m,u. Au niveau de concentration en Ni de 2 mg/ml l’&trt type relatif est de 0,l ‘A. Seuls quelques elements g&rent. REFERENCES 1. R. Bastian, Anal. Chem., 1951,23,580. 2. G. Svehla, Talanta, 1966, 13, 641.
Talanta, 1968, Vol. 15, pp. 1060 to 1062. Pergamon Press.
Prmted in Northern Ireland
Homogeneous nucleation of bis(l,2-cyclohexanedionedioximato)palladi~(II) (Received 15 January 1968. Accepted 19 April 1968) droplet technique, first described by Vonnegut, 1 has been used with considerable success in the study of homogeneous nucleation of a large variety of substances. %-* This method involves the subdivision of the sample under study into a very large number of non-communicating droplets. The foreign particles capable of acting as nucleation catalysts in the original sample are presumably sequestered by incorporation into a small fraction of the droplets, which will undoubtedly exhibit heterogeneous nucleation. However, most of the droplets should remain catalyst free, so homogeneous nucleation is expected to occur in them. In most droplet experiments the supersaturation required to induce nucleation has been attained by gradually lowering the temperature of the system. In 1966 Hileman,? and Thompson and Gordon,8 while studying the nucleation of metal chelates, utilized the technique of precipitation from homogeneous solution as the means of achieving supersaturation in the droplets. This paper describes recent studies on the nucleation of bis(l,2-cyclohexanedionedioximato)palladium(II) in which supersaturation was obtained by reaction between 1,Zcyclohexanedione and hydroxylamine in the presence of palladium ions. EXPERIMENTAL Solutions containing palladium(H), hydrochloric acid, hydroxylamine hydrochloride and 1,2cyclohexanedione were prepared by mixing, in the order given, various amounts of their stock solutions. Immediately after the last reagent was added the solutions were dispersed in mineral oil. The dispersions, which consisted mostly of droplets of about 20 ,u in diameter, were then examined with a polarizing microscope and the crystallization occurring in the droplets was recorded photographically. RESULTS AND DISCUSSION THE
From the photographs the nucleation rate was obtained, and plotted as a function of time. The results of the experiments are demonstrated in Fig. 1.
Short communications
1061
To X v
(a) I
E-~
1.5
rr~
1.0 E-~
0.5 v
,,lJli ,I,
Z
0 0
6
9
]2
|
18
15
21
REACTION TIME (rain)
T0
(b) ~
~.5
~
~
1.O
_g~
,-4
~
"< rJ
0.5
v
,I,i I
Z
o
6
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REACTION
To
o [-4 <
M 0 z
TIME
15
I
I.
18
21
(rain)
(e)
× v
]2
1.5
7 ~
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.~,
0.5
,--~
v
~
0 0
,,i,,I,,I, 9
6
12
15
I
]8
21
REACTION TIME (min)
FIG. 1 .--Nucleation rate
vs.
reaction time for the palladium chelate.
Reaction conditions, [HCI], M [Pd(II)], M (a) (b) (c)
1 "0 1"0 1"0
0"1 0"1 0"1
[NH,OI-I.HCI], M 0"7 0"7 0"3
[C6H802], M 0-2 0"1 0"1
1062
Short communications
One point of very high nucleation rate was observed for each of the three sets of concentrations employed. The position of this point was reproducible and occurred 11.5, 140 and 155 min after mixing the reagents (see Fig. 1). Filtering the reagent solutions through membrane filters of various pore sizes before the preparation of the dispersion did not alter the results. Gravimetric analysis* showed that when the reagents were mixed in the proportions corresponding to the set of concentrations listed under Fig. la, the precipitate was produced at a constant rate of 0.38 mg.ml-l.min-l. At this rate the concentration of monomers in the droplets should rise to about 10-BM after 11.5 min of reaction. Spectrophotometric analysis showed that the palladium content of a saturated solution of the chelate in 1M hydrochloric acid was about 1O-5M. This implies that the supersaturation existing in the droplets at the point of maximum nucleation rate was lOa. According to the Volmerlo theory of homogeneous nucleation the rate of nucleation is expressed as log,, J = log,!) A -
167raSv2 3(2.303kT)3(loglo s)*
where J is the nucleation rate, A is the kinetic constant, 0 is the interfacial free energy, v is the molecular volume of the solid solute, k is the Boltzmann constant, T is the absolute temperature at which the experiment was carried out, and S is the supersaturation ratio. J was found to be of the order of lo8 nuclei.cm-3.sec-1. Assuming A = lOa cm-s.sec-l, o was found to be 47 erg.cm-2 for the chelate. Several expressions have been derived which relate the supersaturation of a crystalline solid to the interfacial free energy and the particle size .I1 One such expression is the Gibbs-Thomson equation which was originally derived for vapours but has also been found applicable to small particles in solution. We shall use it in the form r * = 2ov/2.303kT log,, S, where r* is the size of the critical radius and the other symbols have the same meaning as before. The calculated value of r* for the palladium compound was about 11 A. J. A. VELAZQLJEZ Department of Chemistry 0. E. HILEMAN, JR. McMaster Hamilton Ontario
University
Summary-Precipitation from homogeneous solution has been applied to the drop technique for the study of the homogeneous nucleation of bis(l,2-cyclohexanedionedioximato)palladium(II). It was found that under the experimental conditions employed the interfacial energy of the chelate was 47 ergs.cm-a and the critical radius size 11 A. Zusammenfassun8-Auf die Tropfenmethode zur Untersuchung der homogenen Keimbildung von Bis(l,2-cyclohexandiondioximato)palladium(I1) wurde die Fallung aus homogener Losung angewandt. Unter den Versuchsbedingungen war die GrenztIachenenergie des Chelats 47 erg cm+ und der kritische Radius 11 A. R&m&-On a applique la precipitation en solution homogene a la technique a la goutte pour l’etude de I’amorcage homogene du bis(l,2cyclohexanedionedioximato)palladium(II). On a trouve que, dans les conditions experimentales employees, l’energie interfaciale du chelate est de 47 ergs/cm-a et la dimension du rayon critique 11 A. REFERENCES 1. B. Vonnegut, J. ColIoid Sci., 1948, 3, 563. 2. E. Baer, J. A. Koutsky and A. G. Walton, BUN. Am. Phys. Sot., 1966, 11, 247. 3. R. L. Cormia, F. P. Price and D. Turnbull, 1. Chem. Phys., 1962 37, 1333. 4. E. K. Bigg, Proc. Phys. Sot., 1953, 66B, 688. 5. G. M. Pound and V. K. La Mer, J. Am. Chem. Sot., 1952, 74,2323. 6. D. Turnbull and R. L. Cormia, J. Chem. Phys. 1961,34,820. 7. 0. E. Hileman, Jr., Talanta, 1967, 14, 139. 8. S. Thompson and L. Gordon, ibid., 1967, 14, 137. 9. J. Velazauez and 0. E. Hileman, Jr.. Unnublished work. 10. M. Volmer, Kinetik der Phasenbildu&, Edwards, Ann Arbor, 1945. 11. B. V. Entistiin and J. Turkevich, J. Am. Chem. Sot., 1960, 82,4502.