Table of Contents 19th International Symposium of Ballistics, 7–11 May 2001, Interlaken, SwitzerlandSPHEROIDAL PROPELLANT STABILIZER STUDIES A. Gonzalez1 and H. Shimm2 1 St. Marks Powder, A General Dynamics Company, P.O. 222, St. Marks, FL 323552 ARDEC, U.S. Army, Picatinny Arsenal, New Jersey 07806
The stabilization effectiveness of diphenylamine, ethyl centralite and arkadit IIis being evaluated in spheroidal propellant formulations ranging from 0 to 35%nitroglycerin. German stability, stabilizer depletion rates, pH, NO2/NO3 ionchromatography and microcalorimetry are being used to assess stabilizer effec-tiveness. INTRODUCTION
In a joint effort sponsored by the U. S. Army Mortar Program Management Office; the
U.S. Army Research Development and Engineering Center (ARDEC) and St. MarksPowder are evaluating the performance of various stabilizers in spheroidal propellants.
A matrix of nine propellant formulations is being extensively analyzed to evaluate and
compare the stabilizing effects of three stabilizers. Results to date are presented here. SAMPLES MATRIX
Three basic propellant formulations were selected, and each was manufactured with
the three selected stabilizers for a total sample matrix of nine propellants. The three for-mulations selected are:
I. Single baseII. Low nitroglycerin double base deterredIII. High nitroglycerin double base undeterred
Each of the three formulations was stabilized with diphenylamine (DPA), ethyl cen-
The nominal compositions for each of these three formulations are summarized in
“Table 1”. The sample matrix nomenclature used through out this report is depicted in“Table 2”. Table of Contents
Table 1. Nominal compositions of propellants formulations
EVALUATION TESTS
The sample matrix is being subjected to a battery of tests to evaluate the stabilization
properties of the three stabilizers for the varying formulations. The tests are being con-ducted at ARDEC, NSWC–Crane and/or St. Marks Powder.
Tests conducted and summarized here include:
German Heat Tests – A reference test for propellant stability. – Salmon Pink Time (135°C. for single base and 120°C. for double base samples). – Time to Explosion at (135°C. for single base and 120°C. for double base samples).
Stabilizer Depletion Rate – Stabilizer depletion rates are being measured at 65°C. over a period of 12 weeks.
Microcalorimetry – Heat flow microcalorimetry measurements are being made at 50°,65.5° and 80°C. TEST RESULTS
To date, tests have been completed on the DPA and EC stabilized samples (ID, IID, IE
and IIE). Evaluation of the high nitroglycerin undeterred samples is partially completed,and evaluation of the akardit stabilized samples is planned for 2001. Table of Contents Spheroidal Propellants Stabilizer StudiesGerman Heat Tests
Salmon pink test results are shown in “Table 3”. All samples tested exceeded the 300-
minute minimum explosion time criteria. Stabilizer Depletion Rates
Stabilizer depletion rates at 65.5°C for the DPA and EC stabilized samples were mea-
sured for a period of 12 weeks at St. Marks Powder and ARDEC. The St. Marks Powderresults are summarized in “Figures 1 and 2”. ARDEC results show similar depletion rates.
Figure 1. 65.5°C stabilizer depletion rates for the single base formulation – samples IDand IE. Table of Contents
Figure 2.65.5°C stabilizer depletion rates for low the NG, deterred double base formula-tion-samples IID and IIE.
DPA is reported as the combined total of DPA and daughter products using the for-
DPA = DPA + .854 NNDPA + .790 (2nDPA + 4nDPA)
Values were normalized to % using the formula:
Normalized % Stabilizer = Stabilizer (t)/Stabilizer (to) * 100%
Analyses were conducted using high-pressure liquid chromatography (HPLC).
pH and NO3/NO2 Ion Concentrations
Samples conditioned at 65.5°C storage were subjected to pH, and NO2 and NO3 ion
concentration analysis. Samples were stored for eight weeks at 65.5°C and analyzed atweeks 0, 1, 2, 3, 4 ,6 and 8.
All samples were held and analyzed for pH at the same time. The procedure was adap-
ted from an NSWC-Crane method for testing pH of propellants after accelerated agingstorage. The samples were ground to increase surface area and extracted with deionizedwater for 24 hours. The pH was taken directly from the water/propellant slurry.
No differences in pH were noted for the EC and DPA stabilized high NG formulations.
However the single base samples showed distinct pH differences between the EC andDPA stabilized samples. Likewise the NO2 anion concentration (measured by chromato-graphy) showed a marked difference of NO2 presence between the DPA and EC stabilizedsingle base propellants. Table of Contents Spheroidal Propellants Stabilizer Studies
“Figures 3 and 4” depict the pH and NO2 comparison for the single base propellants.
The DPA stabilized formulation shows higher pH and lower NO2 concentration as com-pared to the EC stabilized formulation. The pH drop and the presence of increased levelsof NO2 should be considered negative stability indicators.
Figure 3. pH shift as a function of 65.5°C storage time for the single base formulation.
Figure 4. NO2 ion concentration as a function of 65.5°C storage time for the single baseformulation.
NO3 analysis did not yield conclusive results for the single base samples, and the dou-
ble base sample results were skewed by the presence of NG, which interfered with NO2and NO3 quantification. Microcalorimetry
Microcalorimetry provides a measure of the total heat generation rate of a material.
Propellant chemical stability is determined by the rates of denitrification reactions of ni-trate esters. If these denitrification reactions are the predominant source of heat genera-tion in aging propellant, then microcalorimetry can provide a good indication of relativestability. Table of Contents
Extensive heat flow microcalorimetry analyses are being conducted by NSWC-Crane
Division. Heat generation rates are being measured at 50°C, 65.5°C and 80°C, to gatherinformation about the relative stability of the samples.
Microcalorimetry measurements for the single base samples ID and IE show similar
heat flows at 50°C. The 65.5°C tests show the DPA stabilized sample (ID) has a lower rateof heat generation for the first 10 weeks. After approximately 10 weeks the heat genera-tion curves for samples ID and IE intersect, and the EC stabilized sample shows a lowerrate of heat generation at 65.5°C. Results at 80°C show similar trends as those at 65.5°C.
The low nitroglycerin deterred samples (IID and IIE) show almost equivalent heat ge-
neration rates at the three temperatures tested (50°C, 65.5°C and 80°C.).
“Figures 5 and 6” depict the total heat generation as a function of time at 80°C. for the
otal Ener
Figure 5. Total energy released at 80°C. As a function of time for the single base samplesID and IE. otal Ener T
Figure 6. Total energy released at 80°C. As a function of time for low nitroglycerindeterred samples IID and IIE. Table of Contents Spheroidal Propellants Stabilizer StudiesCONCLUSIONS
All data on the stabilizer test matrix evaluation is not available. As testing is ongoing,
no definitive conclusions have yet been drawn.
However from the available data the following observations and preliminary conclu-
In multiple sampling of all formulations, the EC stabilized samples demonstrate alower Salmon pink time than their DPA stabilized counterparts.
With the exception of the microcalorimetry test, all of the stability indicators evalua-ted (salmon pink time, pH, ion chromatography and stabilizer depletion rates) point toDPA as more suitable for single base formulations than EC. No conclusions are drawnfrom the microcalorimetry results of samples ID an IE, as further interpretation andanalyses are required.
For the low NG deterred formulation (samples IID and IIE) the stability indicatorsevaluated do not show significant differences between the stabilization effects of DPAand EC. ON-GOING/FUTURE WORK
Work is ongoing to complete the testing of the sample matrix described in “Table 1”:
Completion of the high nitroglycerin and akardit samples (IA, IIA, IIIA, IIID andIIIE) evaluation is planned for 2001.
Ballistic evaluations will be conducted with selected samples.
Future areas of planned work include an evaluation of the effects of potassium flash
suppressants (KNO3, K2SO3) on the chemical stability of single and double base propel-lants. ACKNOWLEDGEMENTS
The ARDEC Surveillance Group and NSWC-Crane are acknowledged for their con-
Table of Contents
IBS 2001 19 th International Symposium on Ballistics
IS01 The Ballistics of Hornussen
IS02 The History of Explosives in Switzerland
IB01 Insensitive High Energy Propellants
IB02 Advanced Cartridge Design for the Term-KE Round
IB03 High Performance Propulsion Design for
IB04 Ballistic Shelf Life of Propellants for Medium
IB05 Development and Validation of a Comprehensive Model
IB06 Comparison of 0D and 1D Interior Ballistics Modelling
IB07 Two-phase Flow Model of Gun Interior
IB08 Interior Ballistic Principle of High/Low Pressure
IB09 Factors Effecting the Accuracy of Internal Ballistics,
IB10 ATwo-Dimensional Internal Ballistics Model for Modular
IB11 Investigations for Modeling Consolidated Propellants
IB12 Burning Characteristics of Foamed Polymer
IB13 The Analysis of Gun Pressure Instability
IB14 Influence of Different Ignition Systems on the Interior Ballistics
IB15 ALeading-Detonation-Tube Ignitor and Its Firing Results
IB16 Functional Lifetime of Gun Propellants
IB17 Spheroidal Propellant Stabilizer Studies
IB18 Applicability of the Hydrogen Gas Erosion Theory to
IB19 Experimental Investigation of Heat Transfer in a 120 mm Gun
IB20 Analysis of ETC or Classical Manometric Closed Vessel Tests
IB21 Variation in Enhanced Gas Generation Rates
IB22 Plasma Ignition of Consolidated Propellants
IB23 Plasma Ignition and Combustion
IB24 Discussion on Emission Spectroscopy Measurements
LD01 Sabot Discard Model for Conventional and
LD02 Experimental and Simulation Analysis of Setback
LD03 Measurements of Muzzle Break Effectiveness
LD04 Transitional Motion of KE Projectile and Governing
LD05 Numerical Simulation of Intermediate Ballistics
LD06 Multistage Method for Acceleration of
LD07 Computation of Muzzle Flow Fields Using Unstructured
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