the MBYC method. If t'his empirical correction is made, the relative standard deviation of the resulting data will be increased as a result of the uncertainty of the correction factor. Similar bias was noted for samples that, conta.ined a smaller concentration of americium. Comparison of corrected data from this new method with that from the mass spectrometric method showed an agreement to within *5y0 at 17 ~ gLknl~43/ml. . ~h~ relative standard deviation a t this concentrat'ion was 8.07, (n = 8).
LITERATURE CITED
(1) Aron, P. M., Soviet J . At. Energy (English Transl.) 5, 1032 (1958). ~
~
~
$
~
~
$ ~ w ~ ~ 2~
CHEM.36,392 (1964). (4) Leuze, R. E., Baybarz, R. D., Weaver, Boyd, Sucl. Sci. Eng. 17,252 (1963). ( 5 ) Maddock, A, G,, Booth, A, H, (to U, S.At, Energy comm,), u, S,patent 2,952,511 (sept, 13, 1960). (6) Moore, F. L., ANAL.CHEM.35, 715 (1963). ( 7 ) Penneman, R. A., Keenan, T. K., "The Radiocffemistry of Americium and Curium, Rept. NAS-NS-3006 (1960). Available from Clearinghouse
,
for Federal Scientific and Technical Informatiion, ards, u, s, National Bureau of Commerce, of StandSpringfield, Va. $( ~~ ~ ~ ~ : l'&xx-gie Atomique, Report CEA-2354 (1963), (9) Wells, A. F., "Structural Inorganic Chemistry," 2nd ed., P. 142, Clarendon Press, Oxford, 1950. RECEIVED for review June 2, 1964. Accepted August 10, 1964. Division of Analytical Chemistry, 148th Meeting, ACS, Chicago, Ill., September 1964. Work under contract AT( 07-2)-1 with the U. S.Atomic Energy Commission.
(8L?d13;id27~,J.kYg,2;;;;iat~i
Infrared Spectra of Transition Metal AI koxides C. T. LYNCH, K. S. MAZDIYASNI, J. S. SMITH, and W. J. CRAWFORD Air Force Materials Laboratory, Wright-Patterson AFB, Ohio
b The infrared spectra of a number of transition metal isopropoxides and tetra-tert-butoxides have been obtained from 5000 to 2 8 5 cm.-' for the first time. Characteristic absorptions for the isopropoxy group have been found at 1 1 60 to 1175 ern.-' and 1 1 2 0 to 1 1 4 0 cm.-' They are assigned to kobranching vibrations. The isopropoxides exhibit a doublet at about 1375 and 1365 cm.-l characteristic of the gem-dimethyl structure. The major feature of the spectra is a very strong band in the 1 OOO-cm.-' region assigned as the C-0 stretch vibration, which is shifted by the influence of the specific metal atom on the C-0 vibration. The butoxides have four characteristic absorptions a t about 785, 900, 1010, and 1 1 90 cm.-' The band in the 1000-cm.-i region appears to b e the C-0 stretch vibration; the other bands are attributed to skeletal vibrations of the tert-butyl group. The typical C-H deformation of the tert-butyl group is observed at about 1360 cm.-' with a weaker band at 1380 cm.-' In the medium infrared region from 7 1 5 to 2 8 5 cm.-', a small number of very strong absorption bands are found for the tert-butoxides. The results suggest that the region would b e very satisfactory for characterizing ferf-butyl compounds.
1'
transition metal alkoxides have been investigated for application to the vapor deposition of oxides on refractory substrates such as graphit'e for protection against oxidation. The alkoxides of Group I11 I3 and IV B met'als decompose at 300" to 400" C. to t'he oxide, olefin, and alcohol (15). This reaction can be used to prepare fine particulates of high purity oxides. -4s a
part of this investigation the infrared spectra of a number of these compounds were obtained for the first time. The spectra have proved useful in checking the results of synthesis for completeness of reaction and product identification. The infrared spectra of a number of metal isopropoxides were studied by Bell, Heisler, Tannenbaum, and Goldenson (9.Characteristic absorptions were reported for the isopropoxy group a t 1175, 1138, and 1110 cm.-', and for the n-butoxy group a t 1150, 1125, and 1075 cm-I. Ory (18) associated the tertbutoxy group of various organic compounds with absorptions in the 720to 770-cm.-', 820- to 9 2 0 - ~ m . - ~1000, to 1 0 4 0 - ~ m . - ~and , 1155- to 1200-cm.-' regions. Only one alkoxide was included in this study, titanium tetratert-butoxide. Philpotts and Thain (19) reported a strong characteristic absorption for the tert-butoxy group in the 800- to 920-cm.-' region from a study of tertiary peroxides. Zeiss and Tsutsui (24) found the C-0 absorptions for primary, secondary, and tertiary alcohols in the 1050- to 1085cm.-l, 1085- to 1125-cm.-', and 1125to 1205-cm.-' regions. Other workers have reported characteristic absorptions for the isopropoxy group in the 1175to IllO-cm.-1 region from diisoamyl ether (20), diisopropyl methyl phosphonate ( I ? ) , and diisopropyl ether ( 2 ) .
HE
2332
ANALYTICAL CHEMISTRY
EXPERIMENTAL
The tetraisopropoxides of zirconium, hafnium, and thorium have been synthesized by the method of Bradlej (6): >IC14
+ 4ROH + 4XH3 e CsHs
where R is the isopropyl group.
Titanium, zirconium, and hafnium tetra-tert-butoxides were formed by ester exchange with tert-butyl acetate by the procedure of Mehrotra ( 1 6 ) . The tert-butyl acetate was made by the acetic anhydride method (10). The infrared spectrum of dried, redistilled tert-butyl acetate was almost identical to that reported by Ory (18). Gas chromatographic analysis showed only traces of impurities with an approximate purity of better than 99.9%. Isopropyl alcohol was dried over sodium hydroxide and redistilled over calcium hydride and calciuni sulfate. Benzene was dried over magnesium perchlorate. The tetrachlorides were used as received from Fairniont Chemical Co. Acetic anhydride was dried over sodium carbonate and calcium hydride and redistilled. The isopropoxides were recrystallized from anhydrous isopropyl alcohol. The crystalline product contains a small amount of bound isopropyl alcohol, which is greatest for the thorium tetraisopropoxide. The thorium compound is much more soluble in isopropyl alcohol, much less soluble in benzene, and insoluble in carbon disulfide and carbon tetrachloride, which are good solvents for the less ionic titanium, zirconium, hafnium, and yttrium isopropoxides. Yttrium isopropoxide was synthesized for use in stabilizing zirconia in the cubic modification in vapor deposition experiments. Attempts to prepare it by the trichloride-ammonia method were unsuccessful. Yttrium isopropoxide was synthesized by the method of =idkins and Cox ( 1 ) :
+ HgClz + 3ROH M(OR)3 + H g + 2HC1 +
AI
HZ ( 2 )
Xdkins and Cox found that for the synthesis of aluminum isopropoxide the reaction was exothermic and was complete after a 4-hour reflux. %th yttrium the reaction was slow and a 24-
hour reflux was needed for the reaction to go to completion. A better method for synthesizing thorium was found using sodium isopropoxide ( 7 ): ThC1,
+ 4NaOR
Table
(3)
(3) 2950 2915 2841 2618
2959 2915 2857
___f
+ 4KaC1
(3)
The infrared spectra in the 5000- to 625-mi.-' region were obtained on a Baird Model 13 infrared spectrophotometer with 0.135-mm. cell, and with a capillary film. I n the medium infrared 715- to 285-cm.-' region, a Perkin Elmer Model 21 double-beam spectrophotometer with a cesium bromide prism was utilized. Ai two-solvent system of carbon disulfide and carbon tetrachloride was used for the infrared spectra of zirconium, hafnium, titanium, and yttrium isoproposides; Nujol was used for the thorium compound. In the medium infrared region Sujol was used for all the isopropoxides except yttrium, which uas run in the two-solvent CS2-CCl4 system in this region. Approximately 10% concentrations in solvent were used. Titanium, zirconium, and hafnium tetra-tert-butoxides are colorless liquids a t room temperature. The liquids were run as capillary films. The tetra-tert-butoxide of thorium is a semisolid which was mixed with a little Sujol and run as a capillary film. All sample handling and loading into cells were done in a dry box. DISCUSSION AND RESULTS
The absorption frequencies of the metal isopropoxides are given in Table I. The bands due to Nujol or a solvent have been designated. For comparison the spectra given by Bell, Heisler, Tannenbaum, and Goldenson (3) for B(OR)3 and hl(OR)3 are listed. The spectra obtained in the present work for the isopropoxides of zirconium, thorium, and yttrium are given in Figures 1 through 3. The spectra for zirconium and hafnium isopropoxides are almost identical except for a band at 1186 em.-' for hafnium, and a t 2849 cm.-l for zirconium. Some small frequency shifts also occur, such as the major band at
Infrared Absorption
Al(OR)a
ROH
Th(ORj4
1.
B(ORh
1471 1422 1397 1389 1377 1333 1325 1256 1174 1136 1124 953 839
685 662 a
1464
Y(0R)a 2941 2857 2825 2604 1550b 1466
1389 1374 1361 1351 1333
1387 1372 1359 1339
1245 1206 1179 170 134 121 032 958 859 834
Frequencies of
Metal lsopropoxides
(Cm.-l)
Zr(OR)4 2950 2899 2849 262.5 1550l 1464 1449
Hf(OR)a
2638 1563b 1475 1460
2667
1391 1381 1370
1370 1360
1379 1364
1377n 1364
1328
1333
1348
1337
Ti(0R)r 2959 2924 2857 2604 1462 1451 1425
Th(OR),
2941 2882
2899& ~
1468b
1248 1176
1159
1166
1186 1170
1164
1139 1013
1124 1000
1136 1007 958 945
1140 1020 983 946
1138 996 973 943
843 817
847 823
980
958
950
836 828
852
7 69 698 676
840 - ~. 826 7220
Nujol. Solvent.
1007 cm.-l for zirconium isopropoxide and at 1020 em.-' for the hafnium compound. The similarity of the spectra of the isopropoxides of titanium, zirconium, hafnium, and thorium is seen in Table 1. While the bands for thorium isopropoxide appear a t about the same frequency as those for the titanium, zirconium, and hafnium compounds, the relative intensities are markedly different. Some difference might be expected from the more ionic character of the thorium derivative. The splitting of the band at 1449 to 1475 ern.-' is found for zirconium, hafnium, and titanium, but not yttrium isopropoxide, and is masked in thorium isopropoxide
because of the strong Nujol band at 1468 em.-' It is difficult to dry thorium isopropoxide to remove all the adsorbed isopropyl alcohol. A st,rong broad band due to the hydroxyl group appears at 3200 to 3300 em.-' but is not found when the thorium isopropoxide is purified by sublimation (at 200" to 210" C. and 0.1 mm. of Hgj. The zirconium, hafnium, and thorium isopropoxides exhibit, four strong absorptions in the 990- to 810-cm.-I region. In part t,hese are assigned to skeletal vibrations ( I d , 18). The 817and 9 4 5 - ~ m . - ~bands for Zirconium isopropoxide decreased in intensity on distillation of the alkoxide, removing a
WAVELWCTH IN MICRONS
Figure 1 .
Infrared spectra of zirconium isopropoxide VOL. 36, NO. 12, NOVEMBER 1964
2333
small amount of bound 2-propanol. (The spectrum shown for zirconium isopropoxide is after distillation.) The diminution of the two bands indicates that the bands are partly due to skeletal vibrations from the bound 2-propanol. The hydroxyl absorption band at about 3200 em.-' almost disappears on distillation. In the 1000- to 800-cm.-' region the titanium compound has two major bands. Apparently these two strong bands observed as skeletal vibrations have shifted to a higher frequency and are located one a t 852 em.-' and the second as a part of the 1000-cm.-l band. The same two bands are ob-
Table II. Characteristic Absorption of lsopropoxy Groups (Crn.-l)
R
=
(CH8)ZCH-
Com-
pound B(OR)n
Characteristics 1174 1136 1124 ~ i ( o R j 1170 ~ 1134 1121 P(OR)3 1176 1139 1110 Y(OR), 1176 1139 1 1 ( 0 R ) r 1159 1134 Z r ( O R ) r 1166 1136 HfiORlr 1170 1140 Th1OR')a 1164 1138
Ref. (3)
(sj (3)
served in the thorium compound, at 840 and 973 em.-', respectively. ,111 of the isopropoxides exhibit a doublet at about 1375 and 1365 cm.+ characteristic of the gem-dimethyl structure (3). Characteristic absorptions appear at 1160 to 1175 em.-' and 1120 to 1140 em.-' These are assigned to the isobranching vibrations ( 3 ) . The yttrium isopropoxide spectrum differed from the spectrum of aluminum isopropoxide reported in the literature. The bands in the 1050- to 800-cm.-' region are shifted to lower frequencies and the aluminum isopropoxide bands a t 769, 698, and 676 cm.-l were not observed in the yttrium isopropoxide spectrum. These bands, however, may be due to the partial hydrolysis of the aluminum isopropoxide. K e have found absorption bands in the 600- to 800em.-' region for partially hydrolyzed yttrium and zirconium isopropoxides. Intermediate oxy-alkoxide compounds such as ZrO(OR)n are formed in the decomposition to the oxides. In the spectra of the isopropoxides of boron arid phosphorus several bands a1.o are reported in this region. At least one band for boron has been attributed to a R-0 deformation vibration. This
m cw
WAVENUMBERS
3
4
(NoCI PLUU. C H M IOOU-101
I b WAELEN6H IN M C U W
WAVEWMIRS IN
7
Figure 3.
2334
ANALYTICAL CHEMISTRY
band appears at 7 0 em.-' for the BIO isopropoxide and a t 665 cm.-' for the 13" isopropoxide (12). These vibrations would be found a t lower frequencies for heavier metals such as yttrium. The characteristic absorptions of the isopropoxide group as given by Bell et al. (3) are listed in Table 11, with the absorption bands observed in the present work. Only two of the three absorption bands they suggested as characteristic have been found for these isopropoxides. Only the phosphorus compound has a distinct "middle" band at 1139 em.-' The bands Bell et nl. (3)report for boron and aluminum isopropoxides a t 1136 and 1134 em. -1 are weak shoulders on the 1124- and 1121-cm.-l bands, respectively. The two bands observed for yttrium, titanium, zirconium, hafnium, and thorium isopropoxides at 1124 to 1140 cin.-l and 1159 to 1176 em.-' correspond to the 1110- to 1124-cm.-' and 1170- to 1176-cin.-l bands for boron, aluminum, and phosphorus isopropoxides and are listed accordingly in the table. The difference found for phosphorus may be due to differences in symmetry arising from having a pair of unbonded valence electrons.
8
*
10
II
CM.1
It I3 WAVELW6H IN MICRONS
Infrared spectra of yttrium isopropoxide
14
IS
lb
Figure 4.
An absorption band at 2604 to 2667 ern.-' was repeatedly observed in the alkoxides when the a-carhon, referring to the ether linkage, had a hydrogen attached to it. If the a-carbon had a methyl or alkyl group attached to it, this band was absent. A similar observation has been previously reported (21). I t is felt that the band is the carbon-hydrogen stretch vibration of the a-hydrogen. The apparent reason for the shift is the decrease in the strength of the bond of the 0-hydrogen to the carbon, causing a shift to a lower frequency. As would be predicted, this band was not observed in the spectra of the tert-butoxides. A spectrum of aluminum sec-butoxide reported in Sadtler Standard Spectra (No. 15298C-4) showed a band at 2625 cm.-l, which agrees with this assignment. The spectra of the tert-butoxides are expected to be significantly different from the isopropoxides. Because of the size of the tert-butyl group, there is a steric blocking to intermolecular association of the butoxides (6). The compounds are much more volatile than the isopropoxides. The spectra for zirconium tetra-tert-butoxide and thorium tetra-tert-butoxide are shown in Figures 4 and 5.
Infrared spectra of zirconium tetra-terf-butoxide
Table IV in accordance with the tabulation of Ory (18). The 785-crn.-' vibration for zirconium tert-butoxide has been assigned to a symmetrical skeletal vibration of the tert-butyl group (23). The 902-cm.-' band has been attributed to a skeletal vibration of the tertbutyl group (19). Ory attributes the band a t 1010 em.-' to a C-C vibration
The absorption frequencies of the metal butoxides and tert-butyl acetate are given in Table 111. The spectra for zirconium and hafnium tert-butoxides are almost identical. dll the spectra are similar except for the thorium compound. The characteristic frequencies for selected tert-butoxides are given in
Table 111.
Ti(OR), 2976
Infrared Absorption Frequencies of Metal Butoxides (Crn.-l)
WORh 2976 2924 2865
Hf(OR)4 2985 2914 2890
1481 1468 1393 1368 1242 1190 1008
1553 1471 1458 1381 1359 1230 1186 1002
1567 1475 1466 1387 1362 1235 1190 1015
1208 971
909
90 1
904
883
797 783 744
785
787
2914 1600
Th(OR)4 2899 2817
tertBuilc 2988 2924
1460 1370 1348
753
1739 1481 1458 1391 -1366 1256 1171 1020 940 917 841 761
67 1
VOL. 36, NO. 12, NOVEMBER 1964
2335
WAZ
NVMsERS
IN CM-'
4w
WAVELENGTH IN MICRONS
Figure 6.
Medium infrared spectra of zirconium tetra-tert-butoxide
within the tert-butoxy groups and a band at 1190 cm.-l as a C- 0 stretch vibration [based on earlier work ( 2 4 ) ] . From a conqideration of alkane spectra in general, it is felt that the band in the region of 1170 to 1210 em.-' is a skeletal stretching of the tert-butyl group. The band in the 1000-cni.-' region appears to be the C-0 stretch vibration rather than the llBO-cm.-' band as Ory reports. Ory (18) felt that the bonding
Table IV.
Compound ROK CHsCOOR Si(ORL Al(ORj3 Ti(ORL Zr(OR); Hf(OR)4 TNORh Table V.
of the tert-butyl group to an oxygen attached to a transition metal would cause a lowering of the C-C vibration to the lOOO-ci~i.-~region. But as Eellamy point5 out ( 4 ) , the tert-butyl group is not very sensitive to changes in its immediate environment and frequency shifts are ordinarily very small. The tert-butyl group is consistently characterized by strong absorptions at about 1200 and 1250 cm.-', with the
Characteristic Absorption of Butoxy Groups (Cm.-l)
R = (CH3)sC_______Characteristics 1194 1174 1199
1024 1015 1022
1190 1186 1190 1208
1008 1002 1015 971
Ref.
918 843 841 901 909 901 904 883
753 762 727 797 785 787
(18)
(18) (18) (18)
*-
ureand skeletal vibrations in the 1250- to lllO-cm.-' region. The medium infrared spectra of zirconium tetra-tert-butoxide is shown in Figure 6. The spectrum for tert-butyl acetate has seven major peaks, which suggests that the region would be very satisfactory for characterizing aliphatic est>ers( I S ) . The absorption frequencies of the isopropoxides in t'he medium infrared region are listed in Table 17. Those for the tert-butoxides are listed in Table VI. The data for tert-butyl acetate haye been added for comparison. The marked differences in the spectra in this region are particularly useful for identification and analysis. The ester exchange react,ion between an isopropoxide and tert-butyl acetate can be followed. As the reaction proceeds, the tertbutoxide peaks appear and those for tert-butyl acetate (and the isopropoxide) , of course, disappear. The simplicity of the medium infrared spectra makes t,his analysis possible. The infrared of these comspectra (5000 to 625 pounds cannot readily be used in this manner. If the spectra of a l u n ~ i n u n yttrium, ~, titanium, zirconium, hafnium, and thorium isopropoxides are examined together, a very strong absorpt>ionband is found in all the compounds in the region of 1020 to 990 em.-] In the boron compound no band is observed in this region. 111 the present work, it has been found that as the zirconium isopropoxide hydrolyzes, the band at
1007 cm.-l disappears from the spectrum. A band a t 745 em.-’ for zirconium oxide has been reported (14). X band found a t 1035 cm.-I for divinylzinc has been attributed to a carbon-oxygen-zinc vibration from the oxidation of divinylzinc ( I 1 ) . Recent work on dialkyltin dialkoxides ( 8 ) is in agreement with the assignment of the C-0 stretch vibration to the very strong. band in this region. Thus the 1020- to 990-cni.-1 band is apparently shifted by the influence of the specific metal on the C-0 vibration. There is no definite correlation of the mass of the metal atom and the degree of shift observed. The lowest frequency band at, 996 em.-’ was for the isopropoxide of the heaviest metal, thorium. For aluminum and yttrium the band is at 1032‘and 1013 cm.-l, which is in agreement with the mass effect. But the results for titanium, zirconium, and hafnium are reversed, with the titanium isopropoxide having the lowest Yrequency for this vibration. Properties of t,he metal atom such m covalent radius and electronegativity do not seem to yield a consistent explanation. For many alkoxides a surprising order of volatilities attributed to changes in intermolecular association has been found-Hf > Zr > Ti > T h
(6). This is consistent with the observed frequency changes of the C-0 stretch vibration. ACKNOWLEDGMENT
The authors acknowledge the sistance of Robert L. Hentrich, in preparing the alkoxides and of D. Smithson in obtaining some of spectra.
asJr., Lee the
LITERATURE CITED
(1) Adkins, H., Cox, J., J . A m . Chem. Soc. 60, 1151 (1938). ( 2 ) Barnes, R. B., Gore, R. C., Liddel, U., U illiams, Y. Z., “Infrared Spectroscopy,” Reinhold, New York, 1944. (3) Bell, J. Y.)Heisler, J., Tannenbaum, H., Goldenson, J., ANAL.CHEM.25, 1720 (1953). (4) Bellamy, L. J., “Infrared Spectra of Complex Molecules,” 2nd ed., p. 25, Wiley, New York, 1958. (5) Bradley, D. C., Record Chem. Progr. (Kresge-Hooker Scz. Lib.) 21, 179 ( 1960). (6) Bradley, D. C., Mehrotra, R. C., Wardlaw, W., J . Chem. SOC. 1952, 4204 _ _ _-
(7) Bradley, D. C., Saad, M. A., Wardlaw, W., Ibid., 1954, 1091. 18) . , Bradlev, D. C., Wardlaw,. W.,. Ibid.. 1951, 208. (9) Butcher, F. K., Gerrard, W., Mooney, E. F., Rees, R. G., Willis, H. A., Spectrochim. dcta 20, 51 (1964). (10) Homing, E. C., Organic Syntheses,”
Collective T’ol. 111, p. 141, Wiley, New York. 1955. (11) Kaesz, ‘H., Stone, F., Spectrochzm. Acta 15, 360 (1959). (12) Lehmann, W. J., Weiss, H. G., ShaDiro. I.. J . Chem. Phvs. 30, 1226 (19$9).’ ’ (13) Lucier, J. J., Bentley, F. F., Spectrochim. Acta 20, 1 (1964). (14) McDevitt N., Baun, W., Air Force Materials Laboratory, Wright-Pstterson AFB, Ohio, ASD TDR 63-789 (September 1963). (15) Mazdiyasni, K. S., Lynch, C. T., Zbid.. ASD TDR 63-322 (March 1963). (16) Mehrotra, R. C., j. Chem. SOC. London 76, 2266 (1953). (17) Meyrick, C. I., Thompson, H. W., Zbzd., 1950, 225. (18) Ory, H. A., ANAL. CHEM.3 2 , 509 (1960). (19) Philpotts, A. R., Thain, W., Ibzd., 24, 638 (1952). (20) Randall, H. M., Fowler, R. G., Dangle, J. R., Fuson, N., “Infrared Determination of Organic Structures,’? Xew York, Van Nostrand, 1949. (21) Seubold, F. H., J . Org. Chem. 21, 157 (1956). (22) Sheppard, N., Trans. Faraday SOC. 46, 527 (1950). (23) Sheppard, N., Pimpson, D. M., Quart. Revs. (London) 7 , 19 (1953). (24) Zeiss, H. H., Tsutsui, M., J . Am. Chem. SOC.75, 897 (1953). RECEIVED for review February 28, 1964. Resubmitted March 30, 1964. Accepted September 14, 1964. Division of Analytical Chemistry (in part), 145th Meeting, ACS, New York, N. Y., September 1963.
T hermoanalysis of Some Inorganic Fluorides a nd Silicofluorides ELI S.
FREEMAN’ and VIRGINIA D. H O G A N
Basic Chemical Unit, Pyrotechnics laboratory, Picatinny Arsenal, Dover, N . J .
b
Differential thermal and thermogravimetric analyses were conducted on several inorganic fluorides and silicofluorides: potassium fluoride dihydrate, calcium fluoride, lead fluoride, ammonium silicofluoride, sodium si Iicofluoride, magnesium si Iicofluoride hexahydrate, calcium silicofluoride dihydrate, and zinc silicofluoride hexahydrate. The experiments were carried out in air at 1-atm. pressure over the temperature range 25” to 800” C. The decomposition reactions are characterized and a previously unreported crystalline transition for Na2SiFG is indicated by the experimental data. The activation energy and order of reaction for decomposition were also determined from the thermogravimetric curve for the sodium silicofluoride.
minations, differential thermal analysis, and x-ray analysis. Differential thermal analysis and thermogravimetry were used to investigate the thermal behavior of several inorganic fluorides and silicofluorides in air a t I-atm. pressure over the temperature range 25” to 800” C. The compounds examined were potassium fluoride dihydrate, alpha-lead fluoride, ammonium silicofluoride , magnesium silicofluoride hexahydrate, calcium silicofluoride dihydrate, and zinc silicofluoride hexahydrate. Calcium fluoride and sodium silicofluoride were also investigated but over different temperature ranges than previously considered ( 4 , 6). The other substances had not been previously studied. EXPERIMENTAL
D
Machin, and Allen ( 4 , 6 ) studied the stability in dry and moist atmospheres of some alkali and alkaline earth metal fluorides, fluosilicates, fluotitanates, and fluozirconates using isothermal weight loss deterEADMORE,
Reagents. For purposes of confirmation, all of t h e following materials, except t h e reagent grade calcium fluoride and potassium fluoride dihydrate, were identified by x-ray diffraction: calcium fluoride, potassium fluoride dihydrate, reagent (Fisher
Scientific Co.); lead fluoride, purified, anhydrous (City Chemical Corp.); ammonium silicofluoride, magnesium silicofluoride hexahydrate, zinc silicofluoride hexahydrate, samples (Davison Chemical Corp.) ; calcium silicofluoride dihydrate, special, technical, sodium silicofluoride reagent (Fisher Scientific CO.).
Instrumentation and Procedures. T h e differential thermal analysis (DTA) apparatus has been described (7, 8). The temperature difference between the sample and an inert reference material is recorded as a function of the temperature of the reference material. Chrome1 - Xlumel thermocouples protected by borosilicate glass wells are embedded in the sample and reference materials which are contained in borosilicate glass test tubes. The test tubes are inserted into holes drilled in a metal block which is heated in a crucible-type furnace. I n this investigation 0.5-gram samples were u3ed
Present address, Physical Chemistry Research, I I T Research Institute, 10 West 35th St., Chicago, Ill. VOL. 36, NO. 12, NOVEMBER 1964
2337
