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  • UNCLASSIFIED

    AD 403 804

    DEFENSE DOCUMENTATION CENTERFOR

    SCIENTIFIC AND TECHNICAL INFORMATIONCAMERON STATION. ALEXANDRIA, VIRGINIA

    UNCLASSIFIED

  • NOTICE: ibhen goverment or other drawings, speci-fications or other data are used for any purposeother than in connection with a definitely relatedgovernment procurement operation, the U. S.Government thereby incurs no responsibility, nor anyobligation whatsoever; and the fact that the Govern-ment may have foruaated, furnished, or in any waysupplied the said drawings, specifications, or otherdata is not to be regarded by implication or other-wise am in any manner licensing the holder or anyother person or corporation, or conveying any rightsor permission to manufacture, use or sell anypatented invention that may in any way be relatedthereto.

  • 403 804, COPY NO.

    PICATINNY ARSENAL TECHNICAL REPORT 3046

    . DIFFERENTIAL THERMAL ANALYSIS

    OF POTASSIUM PERCHLORATE

    DAVID A. ANDERSON

    ELI S. FREEMAN

    alA 1 MARCH 1963

    OMS 5010.11.838001 DA PROJECT 599-25-001

    PICATINNY ARSENAIDOVER, NEW JERSEY

  • [he findings in this Report are not to be construed asAn official Department of the Army poJsition.

    DISPOSITION

    Destroy this report when it is no longer needed.Do not return.

    ASTIA AVAILABILITY NOTICE

    Qualified requesters may obtain copies of this reportfrom ASTIA.

  • DIFFERENTIAL THERMAL ANALYSIS OF POTASSIUM PERCHLORATE

    by

    David A. AndersonEli S. Freeman

    March 1963

    Feltman Research LaboratoriesPicatinny Arsenal

    Dover, New Jersey

    Technical Report 3046 Approved by:

    OMS 5010.11.838001 .,4O, I2S. Sage

    DA Project 599-25-001Chief, PyrotechnicsLaboratory

  • ACKNOWLEDGEME NT

    The authors wish to acknowledge the assistance of R. Croom whoconducted the chemical analysis.

    !1

  • ABSTRACT

    Differential thermal analysis and thermogravimetric analysis experi-ments were carried out on potassium perchlorate. The thermogramsclarify conflicting reports in the literature concerning details of decom-position and elucidate the thermodynamics of this reaction.

    2

  • DISCUSSION

    In a paper by Gordon and Campbell published in 1955 (Ref 1), the dif-ferential thermal analysis of potassium perchlorate is illustrated fromthe point of view of the characterization of this compound rather than thedetails of its decomposition. In this work, for which the differentialthermal analysis was carried out in a test tube in an open furnace, a largeendotherm following the initial exotherm after fusion was observed. Later,Markowitz and Boryta (Ref 2) became interested in the details of decom-position as revealed by differential thermal analysis and pointed out thatthis endotherm is due to the molten sample rising up the sides of thetube resulting in separation of the sample from the thermocouple. Thisgives rise to an apparent endotherm at that point. These authors attemptedto oaercome the thermal effects which accompany the separation of thesample from the thermocouple by carrying out the thermal analysis in aclosed furnace system. Although the endotherm in question is not ob-served under these conditions, the details of the decomposition aremissed, undoubtedly because a large mass of sample was used in theseexperiments and heat transfer conditions in the closed furnace systemwere poor.

    The approach in conducting the differential thermal analysis experi-ments in the present work is to adjust the mass of the sample and thedimensions of the sample container so that the decomposing gases willnot force the reacting mass up the tube. Thus, intimate contact of thesample with the thermocouple is maintained throughout the entire reaction,which is, after all, the best condition for the differential thermal analysisexperiment. It was found that when 500 mg or less of potassiumperchlorate is contained in a test tube with an inside diameter of 16 mm,separation of the sample from the thermocouple does not occur. Theseexperiments show that it is possible to obtain detailed differential thermalanalysis curves for decomposition reactions which are accompanied byviolent foaming and bubbling by adjusting sample weight and geometricparameters. In this work, the detailed differential thermal analysiscurve for the decomposition of KC10 4 is presented for the first time.

    It reveals two exothermal processes, one occurring during decomposi-tion prior to the precipitation of KCl and the other occurring simultane-ously with the precipitation of KC1. This was determined in differentialthermal analysis experiments carried out in a metal block in whichprovision was made for observing the sample as it was heated (Ref 1).

    3

  • Figure 1 shows curves for both differential thermal analysis andthermogravimetric analysis carried out simultaneously on an 86-mgsample of KC10 4 The sample mass used in these experiments is less

    than 1/50 as great as that used by the referenced authors. The differen-tial thermal analysis curve is essentially identical to the dta curvesobtained with 500-mg samples using the furnace block. It shows anendotherm due to melting with a peak at approximately 6060. After thesample melts, the reaction becomes exothermal. The exothermicitydecreases as the temperature approaches approximately 6380. At 6380,a sharp rise in exothermicity occurs, with a peak at 6410 followed by therapid decay of the exotherm.

    The thermogravimetric analysis curve shows that weight loss due todecomposition occurs simultaneously with the endotherm for melting andis complete at the peak of the final exotherm. This curve shows a single,smooth, sigmoidal-shaped weight loss curve with no inflections corres-ponding to the thermal changes which occur during the reaction. Decom-position occurs throughout melting as well as in the exothermal regionsof reaction. Before the final exothermal band was reached at 6380, thesample underwent 67% decomposition. Observations made in separateexperiments show that, after melting and during the first exothermalstep of decomposition following melting, the decomposing mass is clear.The final exothermal band is observed to occur during the precipitationof potassium chloride.

    Since the net decomposition of KC10 4 to form chloride liquid and

    oxygen is reported to be endothermal (Ref 2), the fact that an exothermalreaction occurs prior to 6380 in the clear molten mass remains to beexplained. This is not easy since, in spite of the fact that the decomposi-tion of KC1O4 has been studied, the mechanism of reaction is not well

    understood (Refs 3, 4, 5). It was found from additional differentialthermal analysis experiments that, from the peak of the endotherm tothe end of the first exothermal side band at approximately 6380 C, theC10 3 - ion concentration is relatively constant compared to the formation

    of C1- ion. The C103- ion concentration decreased from approximately

    19% to 12% and the CI" ion concentration increased from 2% to 24%. Theoverall reaction since,the C103- ion is present in an approximatelysteady state concentration, is:

    KC10 4 (liquid) > KC1 (liquid) + 20 2 (g)

    4

  • The most reasonable explanation for the exothermal side band from6060 to 6380 is that the liquid state reaction is exothermal, contrary topreviously reported conclusions (Refs 2, 6) concerning this liquid statedecomposition reaction. Thermodynamic calculations at 6180 show that,unless the existing heat of formation, heat of transition, and heat capacityvalues are grossly incorrect, this reaction should be exothermal byapproximately -_-8 Kcal/mole. The values used for this determinationare A Hf (KC1) 7 solid at 250C = -104.2 Kcal/mol, L Hf7 (KC10 4 ) solid at250C = -103.6, specific heat at 1000C for KC18 = 0.17 cal/goC, specificheat for KC1048 at 300C = 0.9 cal/gOC, n H for crystalline transition+ fusion 6 for KC104 = 5. 5 Kcal/mole, A H8 fusion (KC1) = 5. 5 Kcal/mole.In these calculations, the heat capacity was taken as constant up to6180C since data on the change in heat capacity as a function of tern-perature was not available for KC104. However, this should not alterthe results appreciably, or change the conclusions.

    EXPERIMENTAL PROCEDURE

    Two series of differential thermal analysis experiments were con-ducted. In the first series, the apparatus, which is described in Refer-ence 1, consisted of a metal block in which test tubes containing thesamples and reference materials were located. The metal block washeated at a rate of 100C per minute, and the differential temperature vssample temperature was recorded on a Moseley Autograph, Model 3 X-Yrecorder. A West Gardsman proportioning controlled was used to moni-tor the rate of heating. In these experiments, bare 28-gage chromel-alumel thermocouples were located in the sample and in the referencematerial. The sample weight was approximately 500 mg and, in bothseries of experiments, doubly recrystallized Fisher scientific reagentgrade KC10 4 was used.

    The second series of experiments involved obtaining both the differen-tial thermal analysis and the thermogravimetric analysis curves simul-taneously on about 86 mg of KClO4 . The apparatus used consisted of ananalytical balance which was adapted for automatic recording by meansof a linear differential transformer. A rod supported on one end of thebalance beam and standing in a vertical position above the balance wasused to support the sample and reference materials which were containedin 16 mm test tubes approximately 1 1/2 inches long. The sample andreference materials were mounted one above the other. Chromel-alumel,38-gage thermocouples were placed in both the sample and referencecompounds. The furnace was lowered over the test tubes. Weight changes

    5

  • and differential temperature were simultaneously recorded in a Brownstrip chart recorder. The heating rate was programmed at 100C perminute. In all cases, replicate experiments were conducted. Thechloride was determined gravimetrically by precipitation with a standardsilver nitrate solution. The chlorate was first reduced to chloride byformaldehyde and the solution was then treated with silver nitrate. Theperchlorate was calculated by difference.

    6

  • REFERENCES

    1. Gordon, S. and Campbell, C., Anal. Chem. 27, 1102 (1955)

    2. Markowitz, M. M. and Boryta, D. A., J. Phys. Chem. 64, 1711(1960)

    3. Harvey, A. E., Wassink, C. J., Rodgers, T. A. and Stern, K. H.Ann. N. Y. Acad. Sci. 79, 971 (1960)

    4. Simchen, A. E., J. Phys. Chem. 65, 1003 (1961)

    5. Bircumshaw, L. L. and Phillips, T. A., J. Chem. Soc. 142, 703(1952)

    6. Markowitz, M. M., J. Phys. Chem. 61, 505 (1957)

    7. F. D. Rossini, et al, "Selected Values of Thermodynamic Proper-ties," National Bureau of Standards, Washington, D. C. (1947)

    8. Handbook of Chemistry and Physics, 40th Ed., Chemical RubberPublishing Co., Cleveland, Ohio (1958-1959)

    7

  • 574 5950

    0 641,

    IAW(5mg)64T

    63e

    593

    IAT(5C)

    6*

    38(70% DECOMPOSITION)

    1 641*48 50 52 54

    TIME(min)Fig 1 Simultaneous thermogravimetric analysis (I) anddifferential thermal analysis (II) curves for an 86-mg sam-ple of KC10 4 heated in air at a rate of 1 00 Ca/min

    8

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