/'
small samplcs on u hot stage with a rnicroscopc ufiing tho tcchnique described by McCrone.l This tcchnique made it possiblc t o determine the sequence witjh which the vuriouB phases crystullized a# the, sample cooled, A comparison method also was used i n which four t,oeight fivc-g. samples of only slightly different composition were melted simultaneously in s forced air oven. The oven was allowed to cool slowly so that it was possible to determine the sequence in which crystallization started in the Yet of samples chosen. No temperatures were dctermincd by this method. Only the relation between sample freezing point and composition was determined. This technique had the advantage over the hot stage fusion method in that evaporation of aminonium nitrate from the system was minimized; hence, the composition ctiangc was considerably less.
Results and Discussion The results obt>ainedfrom tho cooling curyes arc shown in Tables I and 11. The liquidus curves 7.6 7.9 8.2 8.5 8.8 obtained from these data clearly indicated that the Ionization energy, e.v. system did not have a simple eutectic; however, Fig. 1. there was a small region lying between 6.8 and 8.2 forin and recrystallizing. Phtlialimitle was purified by re- mole yo that was very difficult to resolvc by thc crystullizing from alcohol. Jlydrorarhons were piirificd hy cooling curve techniques. This camc about becausc methods described beforcx.5 Merclc G . R. quality chloro- the liquidus curve in this region remained within a form was used without further piirihcation. Absorption in(lasurenients were made with it I k k m a n spcctrophotoni- t,empcraturc range of about 1O , which was approxietw Model DU. lI1gh conccntrstrons of both accc~ptore matcly the accuracy of the measurcmcnts. Conseanti donors were u s d , a n d a t that concentration the com- quently, the resolution of this part of the liquidus ponents had absorption a t the wave length whcre the curve was not good. The cooling curves indicated a charge-transfer hand was locatrd. This was eliminated short region of solid solution formation. It apcithrr by balancing the mixture against the componrnt, or 3.0I 73
/
by subtracting the optical density of the components from the total optical density.
Thanks are due to Professor S. Basu for his helpful suggestions. (5) Bhattaoharys and Bssu, Tians. Faraday Soc., 64, 1286 (1958).
A PHASE DIAGRAM STUDY O F THE SYSTEM AMMONIUM NITRATE-I~MMONIUMPERClILORATE B Y A.
GREENVILLE
WHI'r?'AKER'bAND DAVIDc. BARHAM
Sandia Laboratory, Albuquerque, New Mexico Received June 9. 1961
In the course of some studies on the combustion of solid material, it became riecessary to know somcthing about phase behavior of the system ammonium nitrate-ammonium perchlorate. Since this was not an important part of t.he study, only a brief trcatmerit of the system was carried out. Unfortunat,ely, the completc diagram was not possible to obtain because the liquidus t,ernperature at 12% ammoiiium perchlorate was high enough to cause rapid decomposit>ionof ammonium nitrate.
TABLE I FREEZING AXD >fELTING P O I N T 6 O F THE SYSTEM AMMONI~JM ~ I ' I X . l T E - A M M O N I U M PERCHLORATE
Mole
%
of NH4C104 0.00 0.50 0.76 0.90 1.00 1.25 1.50 2.00 3.00 4.00 5.00 6.00 7.00 7.25 7.50 7.75 8.00 8.25 8.50 9.00 9.50 10.00 10.60 11.00
No. of runs 2 2 2 2 2 1 1 2 3 3 4 1 4 2 2 2 4
4 2 7 1 4 2 1
A"
*o. f
1
.o
f .1
*
.05 .2
a .
.
I
... -1: .o
* rt *
.4
.G .2
...
rt .8
*
.o
I .2 ,1 ==! . 2 .7 i .2 f1.4
* +
...
lt3.0 10.4
Freezrng point 1G9.7 169.4 169.1 169.1 168.4 168.2 167.7 165.6 163.5 IG1.1 158.9 156.2 153.8 154.6 154.5 154.8 154.0 155.6 155.9 159.5 162.2 165.4 108.6 171.3 178.2
No. of runs 2 2 2 2 2 2 1 2 3 3 4 1 4 2 2 2 4 4 2
G 1 4 1 1
bleltAm fO.l f .1 f .05 f .06 f .3 .4
*
...
199
point 169.7 169.1 168.5 1G8.5 151.5 150.0
153.0 152.1 f .4 153.2 .5 163.0 f .2 154.0 ... 152.7 Et . 8 153.8 .1 154.4 .2 153.6 zt . O 154.3 f .5 153.2 f .4 154.5 .2 153.4 k .9 153.8 , , 151.7 & .4 153.8 , , 154.3 ... 153.7 ... 153.9 Composition, mole % 6 . 8 NHICIOI 8 . 1 NHd2101 7 . 0 NHICXOI
* .4 * *
*
*
. .
Experimental 1 12.00 1 Reagent grade materials were used in this study without M.P., further purification. The samples were repared by weigh"C. ing out appropriate amounts on an anafyt,ical balance and 153.5 Eutectic no. 1 mixing the components as dry powders. Most of the dat,a 154.0 IEutectic no. 2 were obtained by the conventional cooling curve method; 154.5 New coinpound Cooling rates were used that ranged between 0.12 to 0.25 per minute. Because of frequcnt super-cooling tendencies, a Average deviation in dcgrees for a group of runs of a the lower cooling rates were uscd most frequently. The given composition. accuracy of thc points averaged about 3 ~ 0 . 5 ' . X-Ray powclcr patterns wcrc talcen of both fused and unfrised mix- pcarrd that the solid solution boundary ran quite tures using a Gemcral Electric X-ray unit. Powder pat>terns were taken on compositions which cover t,he entire section close to thc liquidus curve up to upproximately of the phase diagram studied. Critical regions of the phase 0.5 mole % ammonium perchlorate and then diagram were studied by watching the crystallization of dropped rather quickly to the eutectic line. This ______.
(1) (a) Work pcrforiricd under the auspices of the I:. S. Atomic Energy Coinmiasion : (b) Aerospaec Corporntiori Laboratorios Di&$on 2400 Ewt IC1 Segrrndo Blvd., El Scgiindo, Califomin.
regioii
WRS
notj investigated in detail.
Table 11
(2) W.C. MrCrone, Jr., "Fusion AIethods in Cliemioal Microacopy." Intersrirncc Publislicrs, Inr., Nrw York, N. Y.,1967,p. 148.
Feb., 1962
NOTES TABLE
11
TRANSITION 1'OINTS O F ~ ~ M O N I U M NrmArrY-AMMONIUM PERCH LOR AT^ SYRTEM O f W 8 0 ,
0 .oo 0.50 0 75 1 .oo
2.00 5 00 6 00
Transitiiin ten1p.
126 5 124.2 124.2 122.7 123.3 123.7 123.3
Mole yo of NH4C104
Trnneition
temp.
7.00 7.60 8.00 9.00
122.3 123.9 123.8 123.4
10 00 11 .oo
123.8 124.0
shows the results obtaincd on the solid phasc transition, which in ammonium nitrate corrrsponds to the transition from cubic to rhombohedral. This transition persisted across the entire part of the phase diagram studied. The transition temperature droppcd rather sharply (about 2") over the first half mole per cent. of ammonium perchlorate added. After this, it remained constant within the error of thc measurements. This slight drop in the transition temperature corresponded to the region of solid solution formation. On the ammonium nitratc side of the diagram, the cooling curves remained a t a constant temperature during the transition. As more ammonium perchlorate was added, the transition occurred over a temperature range rather than a t a particular temperature. This tempcrature range increased with the ammonium perchlorate content. The temperatures given in Table I1 correspond to the highest temperature of thc transition temperature range. The X-ray diffraction apparatus was modified so that the samples could be held a t approximately 135 i 5' during the diffraction experiment. This put the samples above the transition temperature but below the melting point a t any place on the diagram. The cquilibrated samples showed new lines with d-spacings of 2.34, 2.80 and 3.60 8. The first two lines were weak; the third was very strong. Thcsc lines did not occur in either of the pure components, nor did they occur in any of the mixturrs that mere not equilibrated by melting. In addition to these lines, the principal ammonium nitrate lines for d-spacings of 3.10 and 4.39 8. were always strong even though the rest of the ammonium nitrate lines became weaker as the ammonium nitrate concentration decreased. Ammonium perchloratc lines also appeared in the patterns of the equilibrated samples. It was found, however, that these lines practically could be eliminated by cooling the samples very slowly. This behavior indicated that thc compound must be rather highly diwociated at its melting point and that even rather slow cooling does not allow time for the equilibrium to reverse completely. Powder patterns were obtained for the pure components and for compositions containing 3, 6, 7.6 and 10 mole yo ammonium perchlorate. Only the stroiigcst new line appcarcd in the composition containing 3% ammonium perchlorate. All the lincs appeared in the patterns for the rest of the samples, and their intensities increased as the concentration of ammonium perchlorate increased.
355
In ail attempt to clttrify the questionable rcgion of thc phase diagram, a hot stage microscope was employed l o makc a more cxrcfiil stndy of thc sequence with which the various p h a ~ nppcarcd s as u system crystallized. These observations indicated that a pcritcctic may cxist in this rcgion. Vnfortunately, the results were of somewhat dubious valuc bccause cooling rates could not be controlled adequately and the ammonium nitrate vapor pressure was high enough to cause considerublc evaporation of this component during the observations. This meant that samplcs of unknown composition were being observed. Because of this, a comparison method was developed using considerably larger samples, This minimized the effect of ammonium nitrate evaporation. Also, it was possible to get much lower cooling rates in the comparison method apparatus. The results obtained by this method indicatcd that there was a small hump in the phase diagram a t about 7.6 mole yo ammonium perchlorate with a eutectic quitc close by on either side. Since the maximum height of this hump from the lowest eutectic to its top was only about lo,and its width was only about 1 mole %, it was quite difficult to investigate this region and be sure of all the details. If all the results are considered to have equal reliability it is difficult to decide the actual phase bchavior of the system. The differential freezing point method seemed quite reliable and indicated a new compound a t 7.6 mole yo ammonium perchlorate, but this interpretation does not seem to be compatible with the fact that the ammonium nitrate solid phasc transition extends past 7.6 mole yo ammonium perchlorate. However, the persistence of the, strong ammonium nitrate lines a t 3.10 and 4.39 A. may indicate that, this compound may be ammonium nitrate-like in structure to the extent that some of its d-spacings are the same and a cubic to rhombohedral transition still is possible. On the other hand, the X-ray data indicate the exisknce of a pcritmtic a t about 8.2 mole % ammonium perchlorate. Howcver, thc cooling curves do not show holds a t the expected temperature of about 155' for this composition and greater. The X-ray studies showed that the new compound is rather slow to form; therefore, it is possible that the cooling rates were too high to allow cquilibrium conditions to be approached, thus causing the cooling curve holds to be missed. The increasc in Xray intensity of thc new compound lincs up to 10 mole Yo ammonium perchlorate is difficult to describe on any ground othcr than tho formation of a ic. This may be the clinching argument for concluding that thc system is best described as having a peritectic at about 8.2 mole yo ammonium perchlorate. There is not much possibility that the results are confused by decomposition products. Tests for chloride ion were always negative. It is doubtful that water from ammonium nitratc decornposition mould accumulat~ significantly a t the tcmpcratures involvcd. All the rest of the possible decomposition products would leave the system rather quickly.
