11th CAD/PAD Technical Exchange Workshop May 2016

Transcription

1 The Effect of H 2 O and Moisture on the Chemistry of B-KNO 3 (BKNO 3 Pellets) with respect to Delay-Times and Thermal-Energy Output 11th CAD/PAD Technical Exchange Workshop May 2016 Dr. S.M. Caulder* Mr. J.A. Mackey Dr. V.J. Bellitto Mr. J.M. Kelley

2 Objective For BKNO 3 (B-KNO 3 ) and Boron Powder Used in Igniters/Delay-Compositions: To determine the major factors that influence the ballistic properties (e. g.; ignition-delay, thermalenergy output, and aging) of BKNO 3 pellets. To determine the effect of moisture and H 2 O on the chemical reactivity of Boron powder used in Igniters and Delay-Compositions. 2

3 BKNO 3 Physical Properties Property Virgin Pellets Clumped Pellets Weight, 15 pellets (g) Calc. Density (g/cm 3 ) Calc. Surface Area (m 2 /g) x Meas. Density (g/cm 3 ) ± ± Meas. Surface Area (m 2 /g)

4 BKNO 3 -Related Physico-Chemical Properties Property Material Value Temp. Specific Heat (cal/ C/g) Boron Specific Heat (cal/ C/g) DH v (cal/g) DH v (kcal /mole) DH Decomposition (kcal /mole) DH Decomposition (kcal /mole) H 2 O H 2 O H 2 O H 3 BO 3 KNO * C 185 C 400 C (decomp.) 337 C (m. p.) * KNO 3 K 2 O + N O 2 B + O 2 Exothermic reaction 4

5 Findings Pristine BKNO 3 : As-Received. 5

6 Findings Clumped BKNO 3 : As-Received. 6

7 Findings Clumped BKNO 3 : As-Received. 7

8 Findings Clumped BKNO 3 : As-Received. 8

9 Findings Clumped BKNO 3 : Dried at 100 C. 9

10 Boric Acid on Surface of BKNO 3 Pellet 10

11 SEM: Virgin vs. Aged BKNO 3 Pellets 11

12 Boric Acid (H 3 BO 3 ) - Reference Material Surface crystals identified as primarily Boric Acid, H 3 BO 3. 12

13 BKNO 3 Pellet - Inner vs. Surface Significant crystal cover on cylinder face and sides. FTIR spectrum of surface vs. inner regions differ significantly. Spectrum of inner region consistent with that of virgin pellets. Surface crystals identified as primarily Boric Acid, H 3 B

14 Deconvoluted XPS Spectrum of Boron 1s Region Prewashed Sample Boron B 2 O 3 B x O y 14

15 XPS Spectrum of Boric Acid (SPEX Standard) B1s region B(OH) 3 ~6eV shift due to charging effects 15

16 Boric Acid - Experimental Weight, Initial Weight after C Weight-Loss ( C) % Weight-Loss g g g 33.6 % Weight after additional C 179 C (added C) % Weight-Loss g g % Weight-Loss, Cumulative (150 C and 179 C): % Weight-Loss after 48 Hr g 43.6 % 16

17 Energy-Consuming (Endothermic) Reaction Pathway of Boric Acid and Boron Oxide H 3 BO 3 H 2 O HBO 2 H 2 B 4 O 7 B 2 O 3 + (BO) x compound M. P. Meta-Boric M. P. Tetra-Boric M. P. M. P. 179 C Acid 236 C Acid 250 C 450 C B 2 O 3 + H 2 O H 3 BO 3 B + O 2 B 2 O 3 (exothermic) Boron (found in the form of compounds; never as elemental Boron) is manufactured by reduction of B 2 O 3 with Magnesium: B 2 O 3 + Mg B + B 2 O 3 + Mg + MgO In nature, a self-limiting reaction with O 2 occurs due to formation of B 2 O 3 film. This film evaporates above 1,000 C: B + B 2 O 3 BO (1,050 C) 17

18 DELTA TEMPERATURE ( C) 6 Boric Acid C M.P. H 2 B 4 O C 222 M.P. HBO M.P. 187 H 3 BO 3-6 REF TEMPERATURE ( C) 18

19 DELTA TEMPERATURE ( C) 8 Boric Acid C C -8 REF TEMPERATURE ( C) 19

20 DELTA TEMPERATURE ( C) 12 KNO 3 C 3/31/ C REF TEMPERATURE ( C)

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28 Conclusions Boric Acid covered about 25% of the analyzed BKNO 3 pellet surfaces. The Boric Acid did not infiltrate the interior (i. e.; the bulk) of the pellets. Boron reacts slowly with atmospheric O 2 to form B 2 O 3 films on high surface-area Boron particles. Drying the clumped BKNO 3 pellets increased the thermal output of the pellets (i. e.; dt/dt, dp/dt). Moisture caused an increase in the particle-size of the KNO 3 and may be responsible for the clumping of the BKNO 3 pellets, thus hindering flame-spreading during ignition. Magnesium reacts with O 2 to increase the thermal-energy output of the BKNO 3 pellets and/or Boron powder (5.9 kcal/g). 28