438
ICUAN-HAN SUN AND MAURICE L. HUGGIXS
ENERGY ADDITIVITY I N OXYGEN-CONTAINING CRYSTALS AND GLASSES. 11’ KUAK-HAK SUN* A N D MAURICE L. HUGGINS Kodak Research Laboratories, Rochester, New York Received September 17, 1946
In recent papers (2, 3) it has been shown that the energies of dissociation of simple and complex oxides into the gaseous ions of their component elements are approximately additive, conforming to the relationship
where
is the “ionic dissociation energy” of the compound (or glass) . . * 0, and zy is a constant characteristic of element M. This constant may be thought of as the average contribution of one gram-atom of element M to the total energy of dissociation into gaseous ions of compounds or glasses in which each M atom is surrounded by a shell of oxygen atoms. No assumption regarding the nature of the forces (ionic or covalent) holding the M atoms to these oxygens is involved. Differences in the number of oxygens around each M in different compounds or glasses produce departures from strict additivity, but the deviations are not great. A large part of the magnitude of each % value can be attributed to the energies of formation of the gaseous ions, ill+” and 0-?,from the uncharged gaseous atoms, M and 0. In studying other factors affecting the magnitudes of the energy constants, it is of interest to subtract the contributions of these atomic ionization energies-in other words, to compute and compare energy constants, 4,for dissociation into gaseous uncharged atoms, rather than ions. The 4 values are related to the % values by the following equation: Ei
M,M:,Ml,,
i
+
- WM, gas1 + l i ~ j ~ gas1 --, O ~ OW, I I = % + Qj[M+u,gas] - of[M, gas] - 83 v = %
gas1
c ~ f [ ~ + v ,
(2)
Here u is the valence of the atom M in the compounds or glasses being considered and Qf designates the heat of formation, obtainable from Bichowsky and Rossini’s valuable tabulation (1). Table 1lists values of e& together with the values of eM from which they were computed by means of equation 2. Some additional €4values are included, for elements for which the data on ionization energies of the gaseous elements required for the computation of % are not available. The equation used for Communication No. 1107 from the Kodak Research Laboratories. address: Research Laboratory, Westinghouse Electric and Manufacturing Company, East Pittsburgh, Pennsylvania.
* Present
439
ENERGY ADDITIVITY I N CRYSTALS AND GLASSES
TABLE 1 Ionic and atomic dissociation constants* M kg
Monovalent: H. i n M(OH)*........................... H, i n MHCOI . .................... H , in MHSO, ........................... H, in H,M,O, . . . . . H, average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Li . . . . . . . . . . . . . . . . . . . . . . . . . . . Na. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . K....................................... Rb. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cu . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ag . . . . . . . . . . . . . . . . . . Rh .............
T1 . . . . . . . . . . . . .
NH, . . . . . . . . . . . . . . . Divalent: Be. ........................
........................... Ca ...................................... ........................... Ba ...................................... Zn ..............
Cd ......................................
.................. .................. ..................
co . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cu ...................................
Xi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..601.
515 501 490 489 500 351 322 299 295 288 295 346 316 309 151 - c
250 222 257 256 260 144
907
978 882 829
68 240 196 189 171 166 146 198 161 200 145
2047 1878 1793 1721
356 402 317 245
901 895 919 1118 929 860
i
Y.......................................
118 104 93 92 103 144 120 115 115 114 131 88 154 250 68 . C’
1141 912 839 800 768 941 883
Rh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.............................. Sn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trivalent: B............... . . . . . . . . . AI, in M,Al,O . . . . . . . . . . . . . . . . . AI, in M,AI,Si,O . . . . . . Al, in M,M:(SOc) . . . . . . . . . . Al, average . . . . . . . . . . . . . . . . sc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
kg.-col
119
1i9i
321
1563 1566
362 399 406 267 259 187
La. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1827 1722 1734
440
WAN-EfAN
SUN AND MAURICE L. WWPTS
TABLE 1-Continued M
4Y
_ _ _ _ _ ~
Trivalent-Continued
kg.-cd.
ka.-cal.
2565 1767 1614 1526 1691 1695
194 193 164 147 337 279 233 287 239 223 241 171
4208 3172 - 123Nsi 3128 2882 2637
471 466 - 123Nsi 424 435 485 516 278 232 393 406 457 593 249 269 309 289 286
:
N ......................................
Cr ......................
.............................
Fe .................................... Ni ..................................... Rh. ..........................
........................
Tetravalent:
....................
Si, average. .......
Ti, ................
.....................
2769 2835
.................. Ru . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pentavalent: N .....................................
v................................. As . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sb.., . . ......................... Bi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hexavalent:
6831 4870 - 530 Np 4720 4564 4507 4250
276 575 - 530 IVp 425 449 349 339 281
7195
439 443 553 622 725 349 407
Cr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . w... ...............................
u . .....................................
I I
Se . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Te . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6886 6167
441
ENERGY ADDITIVITY IN CRYSTALS AND GLASSES
TABLE l 4 o n c l u d e d M
1
Heptavalenl: c1, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >In, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I..,. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I Octavalent: os . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I ~
kg.-cal. kg’-caL ~
9948 ~
353 405 357 452
* c denotes the heat
of formation of NH: (gas) from hypothetical NH, metal. c’ denotes the heat of formation of NHI (gas) from hypothetical h”,metal. YE,denotes the ratio of silicon atoms to oxygen atoms in the compound or glass. Np denotes the ratio of phosphorus to oxygen atoms in the compound or glass.
computing e I
from the c;?r data for a simple crystalline oxide (M,O,) is
1
elf = - Qf[M,O,,
m
=
-1 Qf[M,O,,
m
crystal]
n m + n ~ ~ - QIM,gasl - m Qf[O, gasl - ___ m
crystal]
- Qf[M, gas] + 2 9 . 3 ~- 0.6
(3)
For a complex oxide, the equation is similar but slightly more complicated. Just as approximate ionic dissociation energies, Ei, may be computed additively from the eM values by equation 1, so atomic dissociation energies, E,? may be computed additirely from the ;e values. Mathematically expressed:
E, =
c m,ed
(4)
M
The e; values are all much lower than the corresponding eM values, a result of the fact that large amounts of energyare required to remove the valence electrons from the more metallic atoms and add them to oxygen atoms, forming 0-- ions. Dissociation of an oxide into isolated neutral atoms requires less energy than dissociation into isolated ions. The e; values for Groups I to IV of the Periodic Table are plotted in figure 1. The most striking regularity is the regular increase in eM with increase in valence, measuring the increase in attraction energy for oxygen as the kernel charge is increased. Another generalization, obvious from the figure, is that with increasing atomic number e:, decreases within the b subgroups and increases within the a subgroups (except in Subgroup Ia, in which it remains practically constant). The decrease in the b subgroups may be related to the decrease in binding energy as the atomic number increases. For these elements, which tend (more than do the a subgroup elements) t o form covalent bonds, the coordination number is practically independent of atomic number. For the elements in the a subgroups, however, the binding is largely ionic, and increasing atomic number is accompanied by increasing size and increasing coordination number. This more
442
WAN-HAN SUN AND MAURICE L. W C I O I N S
than counteracts the probable decrease in attraction energy per oxygen neighbor as. the atomic number increases within each group. The constants for the elements of higher valence change less regularly with atomic number than do those for the elements represented in the figure, for various remons. The experimental data are more sketchy. The tendency to
Fig. 1. Atomic dissociation constants for elements in Groups I to IV of the Periodic Table, when exhibiting their normal valences.
form covalent bonds is strong, resulting in the formation of groups of atoms (ions) and more variation in energy content from compound to compound. The electronic structures of the atoms play a greater r8le. Because of these complications, further discussion of the dissociation energy constants for the higher valence elements will not be attempted a t this time. For similar reasons, discussion of the data for the transition elements and for atoms in states other than those in which they exhibit their normal valence will also be omitted.
STABILITY OF SYNTHETIC RUBBER DISPERSIONS.
443
I
SUrdbfmY
Energies of dissociation of simple and complex oxides into their component atoms, like the corresponding ionic dissociation energies, are approximately additive. A table of characteristic constants for use in computing these atomic dissociation energies is presented. Certain relationships to the Periodic Table are noted: in. particular, the increase in the magnitude of the constant with increase in valence and its regular increase and decrertse with atomic number in the a and b subgroups, respectively. REFERENCES
( I ) BICHOWSKY, F. R., AND ROSSINI,F. D.. The Thermochemistry of the Chemical Substances. Reinhold Publishing Corporation, New York (1936). (2) HUGGINS, M. L., AND Suls, K.-H. : Trans. SOC.Glass Tech. 28,463 (1944); J. Am. Ceram. SOC.28,149 (1945). (3) HUGGINS, M. L . , A N D SI:N, K-H.: J. Phys. Chem. 60,319 (1946).
STABILITY O F SYNTHETIC RUBBER DISPERSIONS.
I
LOW-TEMPERATURE THICKENING OF NEOPRENELATEX',^ H. K. LIVINGSTON Jackson Laboratory, E . I . du Pont de Nemours and Company, Wilmington, Delaware Received October I , 1946 INTRODUCTION
Neoprene latex of 50 per cent neoprene concentration is quite fluid and deviates only slightly from the ideal or Newtonian flow characteristics. The viscosity of Neoprene Latex Type 571 a t 25°C. is 7-9 centipoises, but if the latex is cooled into the temperature range 0-10°C., a t some point in this temperature range (the exact temperature depending on factors to be discussed) an abrupt change in the character of the latex takes place. The latex becomes of a paste-like consistency with a very high yield point and viscosity. Typical data showing this transition, as given in an earlier paper (S),are reproduced in table 1. In view of this marked change in viscosity, Neoprene Latex Type 571 cannot be considered to be stable below 10°C., if "stability" is defined in the broad sense. However, the instability is not of the type that produces coagulation of the colloidal system. This is in contrast to the behavior of synthetic rubber latices cooled below 0°C. At sub-zero temperatures, instability takes the form of 'Contribution S o . 53 from Jackson Laboratory, E. I. du Pont de Nemours and Company. *Presented a t the Symposium on the Stability of Colloidal Dispersions, which was held under the auspices of the Division of Colloid Chemistry at the 110th Meeting of the American Chemical Society, Chicago, Illinois, September, 1946.
