CHAPTER-3 RESULTS AND DISCUSSION

Transcription

1 CHAPTER-3 RESULTS AND DISCUSSION

2 Initially, transition metal oxides (TMOs) chosen for the present study were fully characterized for their purity and particle size using different instrumental techniques. After complete characterization, the effects of TMOs on thermal decomposition of ammonium perchlorate were studied in detail. Based on the thermal behaviour of AP with TMOs, the selected TMOs were further incorporated in propellant formulation to study the effect of TMOs on mechanical, thermal and ballistic properties. The details of above finding are described in the following sections. 3.1 CHARACTERIZATION OF TRANSITION METAL OXIDES The different nano and micron sized transition metal oxides used in the present study were characterized by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES), NANOPHOX particle size analyzer, Cilas particle size analyser, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and powder X-ray diffractometer (XRD) Determination of purity of transition metal oxides The purity of the nano and micron sized TMOs was determined by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) using high temperature argon plasma. The percentage of metal content in nano-and micron sized TMOs was estimated. The results are presented in table 3.1. Table 3.1 Purity of transition metal oxides Sr. No. Metal oxide Form Purity (%) 1 Iron oxide Nano Fe 3 O Nano Fe 2 O Copper oxide Nano CuO 99.3 Micron CuO Cobalt oxide Nano Co 3 O Micron Co 3 O Chromium oxide Nano Cr 2 O Micron Cr 2 O Manganese oxide Nano MnO Micron MnO

3 Based on the metal content, the purity of nano and micron sized TMOs were found to be greater than 99.0%. The high purity of metal oxide is essential to ensure the better catalytic effect of particular metal oxide on thermal decomposition of AP and composite propellant formulation Determination of density of transition metal oxides The density of transition metal oxides was determined by gas pycnometer using helium gas at 30 C and results are presented in table 3.2 Table 3.2 Density of transition metal oxides Sr. No. Metal oxide Form Density (g/cc) 1 Iron oxide Nano Fe 3 O Nano Fe 2 O Copper oxide Nano CuO 6.31 Micron CuO Cobalt oxide Nano Co 3 O Micron Co 3 O Chromium oxide Nano Cr 2 O Micron Cr 2 O Manganese oxide Nano MnO Micron MnO Density of the nano and micron sized TMOs are found nearly identical Determination of particle size of nano sized TMOs by NANOPHOX particle size analyser. Before investigation of transition metal oxides in the decomposition study of AP and in composite propellant formulation, the particles size and surface area were confirmed. The particle size and surface area are inversely proportional to each other, i.e., if particle size increases surface area decreases and vice-versa. The particle size of nano sized metal oxides was determined by a NANOPHOX particle size analyser in presence of aqueous and isopropylalcohol medium by keeping five minutes of sonication. The results of surface mean diameter of the product and their distribution are presented in table

4 Table 3.3 Particle size and particle size distribution of nano sized metal oxides Sr. No Metal oxide Particle size (nm) Particle Size Distribution (nm) 1 Nano Fe 3 O Nano Fe 2 O Nano CuO Nano Co 3 O Nano Cr 2 O Nano MnO The particle size distribution of nano metal oxides obtained from NANOPHOX is presented in figures 3.1 (a) to 3.1 (f). The distribution pattern infers that all the nano powders show a narrow distribution. Although the data obtained from NANOPHOX are of a qualitative nature and provides a reasonable evaluation of the size distribution for the obtained powder Determination of particle size of micron sized TMOs by Cilas particle size analyser. The average particle size of micron sized TMOs was determined by laser based Cilas particle size analyser in presence of aqueous medium by keeping two minutes sonication. The results are shown in table 3.4. Table 3.4 Particle Size of micron sized metal oxides Sr. No Metal oxide (micron size) Particle size(µm) 1 CuO Co 3 O Cr 2 O MnO In the same way, the particle size distribution of micron sized TMOs were also determined and pattern indicates that the particle have narrow distribution. 73

5 cumulative distribution Q(x) / % particle size / nm density distribution q*(x) Figure 3.1(a) Particle size distribution of nano Fe 3 O 4 cumulative distribution Q(x) / % particle size / nm density distribution q*(x) Figure 3.1(b) Particle size distribution of nano Fe 2 O 3 74

6 cumulative distribution Q(x) / % particle size / nm Figure 3.1(c) Particle size distribution of nano CuO density distribution q*(x) cumulative distribution Q(x) / % particle size / nm density distribution q*(x) Figure 3.1(d) Particle size distribution of nano Co 3 O 4 75

7 100 9 cumulative distribution Q(x) / % particle size / nm density distribution q*(x) Figure 3.1(e) Particle size distribution of nano Cr 2 O 3 cumulative distribution Q(x) / % particle size / nm density distribution q*(x) Figure 3.1(f) Particle size distribution of nano MnO 2 76

8 3.1.5 Determination of specific surface area (SSA) Specific surface area of the nano and micron sized TMOs were determined using a BET Surface Area Analyser at liquid nitrogen temperature. The specific surface area of the nano and micron sized TMOs are presented in table 3.5 Table 3.5 Specific surface area of different transition metal oxides Sr. No. Metal oxide Form Specific Surface Area (m 2 /g) 1 Iron oxide Nano Fe 3 O NanoFe 2 O Copper oxide Nano CuO Micron CuO Cobalt oxide Nano Co 3 O Micron Co 3 O Chromium oxide Nano Cr 2 O Micron Cr 2 O Manganese oxide Nano MnO Micron MnO The catalytic effect of catalyst depends on the specific surface area. The result clearly shows that nano sized metal oxides have smaller particle size and high surface area compared to micron sized materials. Furthermore, the prepared nano Fe 3 O 4 have very high surface area compared to nano Fe 2 O Determination of particle size and surface morphology of TMOs The particle size and surface morphology of nano-and micron sized TMOs was determined by HR-TEM and SEM. The images obtained are presented in figures 3.2 to

9 Figure 3.2 Transmission electron microscopy image of nano Fe 3 O 4 Figure 3.3 Scanning electron microscopy image of nano Fe 2 O 3 Figure 3.4 Transmission electron microscopy image of nano CuO 78

10 Figure 3.5 Scanning electron microscopy image of micron CuO Figure 3.6 Transmission electron microscopy image of nano Co 3 O 4 Figure 3.7 Scanning electron microscopy image of micron Co 3 O 4 79

11 Figure 3.8 Transmission electron microscopy image of nano Cr 2 O 3 Figure 3.9 Scanning electron microscopy image of micron Cr 2 O 3 Figure 3.10 Scanning electron microscopy image of nano MnO 2 80

12 Figure 3.11 Scanning electron microscopy image of micron MnO 2 The results of HR-TEM and SEM for particle size and surface morphology are summarised in table 3.6. The results of particle size and surface morphology indicate that all nano material is in the range of nm with surface morphology nearly spherical except nano MnO 2 which is cubic in nature. Further, the micron sized material shows surface morphology nearly spherical except micron Co 3 O 4 which is cubic in nature. Table 3.6 Results of particle size and surface morphology of TMOs Sr. No. Metal oxide Form Particle size Surface morphology 1 Iron oxide Nano Fe 3 O 4 20nm Nearly spherical Nano Fe 2 O 3 - Nearly spherical 2 Copper oxide Nano CuO 45 nm Nearly spherical Micron CuO - Nearly spherical 3 Cobalt oxide Nano Co 3 O 4 20 nm Nearly spherical Micron Co 3 O 4 - cubic 4 Chromium oxide Nano Cr 2 O 3 40nm Nearly spherical Micron Cr 2 O 3 - Nearly spherical 4 Manganese oxide Nano MnO 2 50 nm cubic Micron MnO 2 - Nearly spherical 81

13 3.1.7 Powder X-ray diffraction The nano and micron sized TMOs was characterized for the metal oxide and its phase using the powder XRD technique at a scanning rate of 2 deg/min in a continuous scanning mode and the obtained XRD patterns are presented in figures 3.12 to diffracted Intensity(a.u.) (2 2 0 ) (3 1 1 ) (4 0 0 ) (5 1 1 ) (4 2 2 ) (4 4 0 ) (6 2 2 ) B ra g g A n g le 2 T h e ta Figure 3.12 X- ray diffraction pattern of nano Fe 3 O 4 Diffracted Intensity (a.u.) (012) (113) (110) (104) (1010) (214) (116) (122) (024) B ragg angle 2Theta (300) Figure 3.13 X- ray diffraction pattern of nano Fe 2 O 3 82

14 Differacted intensity(a.u.) Bragg angle 2Theta Figure 3.14 X- ray diffraction pattern of nano CuO Diffrected intensity(a.u.) Bragg angle 2 Theta Figure 3.15 X- ray diffraction pattern of micron CuO 83

15 Differacted intensity(a.u.) Bragg angle 2Theta Figure 3.16 X- ray diffraction pattern of nano Co 3 O Differacted intensity(a.u.) Bragg angle 2Theta Figure 3.17 X- ray diffraction pattern of micron Co 3 O 4 84

16 Differacted intensity(a.u.) Bragg angle 2Theta Figure 3.18 X- ray diffraction pattern of nano Cr 2 O Differacted intensity(a.u.) Bragg angle 2Theta Figure 3.19 X- ray diffraction pattern of micron Cr 2 O 3 85

17 300 Differaction intensity(a.u.) Bragg angle 2 Theta Figure 3.20 X- ray diffraction pattern of nano MnO Differacted intensity(a.u.) Bragg angle 2Theta Figure 3.21 X- ray diffraction pattern of micron MnO 2 86

18 The two theta values were compared with standard data file (JCPDS Card NOs) to confirm the metal oxides are presented in table 3.7. Table 3.7 Two theta value of TMOs, JCPDS Card numbers and their reference Sr. No. Metal oxide Two theta value JCPDS Card numbers and references 1 Fe 3 O , 35.5, 43.5, 53.5, 57.1, 62.7, , Ai 1, Fe 2 O , 33.23, 35.5, 40.90, , Zhao 2, , 57.61, 63.09, 64.8, CuO 32.6, 35.57, 38.76, 48.83, 53.37, , Gao 3, , 61.60, 66.12, Co 3 O , 36.69, 38.89, 44.67, 56.20, , Makhlouf 4, , Cr 2 O , 33.80, 36.28, 41.54, 50.26, 54.86, 63.58, , Esparza 5a, 2011, Farzaneh 5b, MnO , 37.44, 41.24, 42.31, 46.06, 56.83, , Zheng 6, 2005 It is clear from table 3.7 that two theta values obtained from XRD patterns are matching with JCPDS standard data file confirms the identification of metal oxides. The results of XRD confirm that it is in well agreement with purity of standard metal oxides. Further, the XRD peaks pattern confirms that metal oxides are in crystalline phase. It is observed that, the crystallites must be sufficiently large so that a destructive interference occurs and the intensity returns to the background level. However, this condition is not met when crystallite size is too small, which causes few diffraction planes and broadens the reflection. The peaks in XRD pattern of nanomaterials are broaden which further indicate finer crystallite size EFFECT OF TMOs ON THERMAL DECOMPOSITION OF AMMONIUM PERCHLORATE After complete characterisation of transition metal oxides, the effect of selected TMOs on thermal decomposition temperature of ammonium perchlorate was studied in detail by using DSC and TGA technique. 87

19 3.2.1 Differential scanning calorimeter (DSC) Prior to evaluation in composite propellant formulations, the catalytic effect of nano and micron sized TMOs were studied with AP by varying the catalyst concentration from 0.25 to 1% using DSC and TGA. The DSC and TGA samples were prepared by blending AP and ballistic modifiers in mortar and pestle. The DSC study indicates that pure ammonium perchlorate has distinct thermal decomposition pattern in which it changes the phase from orthorhombic to cubic at 240 C followed by strong peaks at 300 C and 463 C, respectively and presented in figures 3.22 to The figure clearly indicates that on addition of nano and micron sized burning rate modifier, the decomposition temperature of ammonium perchlorate decreases in comparison to that of the pure AP. The data presented in table 3.8 indicate that effect is stronger for the nano size burning rate modifier. Table 3.8 Effect of different concentration of TMOs on thermal decomposition temperature of ammonium perchlorate Sr. No. Metal oxide Form Thermal decomposition temperature of AP with catalyst Concentration ( C) 0.25% 0. 50% 0.75% 1.00% 1 Pure Ammonium -- Perchlorate Iron oxide Nano Fe 3 O Nano Fe 2 O Copper oxide Nano CuO Micron CuO Cobalt oxide Nano Co 3 O Micron Co 3 O Chromium oxide Nano Cr 2 O Micron Cr 2 O Manganese oxide Nano MnO Micron MnO

20 Figure 3.22 Effect of nano Fe 3 O 4 on decomposition of ammonium perchlorate Figure 3.23 Effect of nano Fe 2 O 3 on decomposition of ammonium perchlorate 89

21 Figure 3.24 Effect of nano CuO on decomposition of ammonium perchlorate Figure 3.25 Effect of micron CuO on decomposition of ammonium perchlorate 90

22 Figure 3.26 Effect of nano Co 3 O 4 on decomposition of ammonium perchlorate Figure 3.27 Effect of micron Co 3 O 4 on decomposition of ammonium perchlorate 91

23 Figure 3.28 Effect of nano Cr 2 O 3 on decomposition of ammonium perchlorate Figure 3.29 Effect of micron Cr 2 O 3 on decomposition of ammonium perchlorate 92

24 Figure 3.30 Effect of nano MnO 2 on decomposition of ammonium perchlorate Figure 3.31 Effect of micron MnO 2 on decomposition of ammonium perchlorate 93

25 The presented thermo-grams (fig 3.22 to 3.31) and data on thermal decomposition reveal that the addition of catalyst decreases the thermal decomposition temperature of AP and shift it towards lower temperature. All the studied TMOs are found effective in lowering the decomposition temperature of AP and as concentration increases the decomposition temperature also shifts further towards lower temperatures. Furthermore, if the nano sized catalyst used in place of micron sized catalyst, the decomposition temperature at same concentration of nano sized catalyst was found to be more effective to reduce thermal decomposition temperature of AP. At 0.5 % concentration level, the findings of decomposition temperatures of the studied TMOs are presented in table 3.9 based on their application in composition. Table 3.9 Data on thermal decomposition temperature of AP containing 0.50% Concentration of TMOs Sr. No. Metal oxide Form Thermal decomposition temperature of AP with 0. 50% Concentration of TMOs ( C) 1 Pure AP Iron oxide Nano Fe 3 O Nano Fe 2 O Copper oxide Nano CuO 316 Micron CuO Cobalt oxide Nano Co 3 O Micron Co 3 O Chromium oxide Nano Cr 2 O Micron Cr 2 O Manganese oxide Nano MnO Micron MnO The data presented in the table 3.8 indicates that nano copper oxide is most effective in lowering the thermal decomposition temperature of AP whereas micron sized chromium oxide is least effective in reduction of thermal decomposition 94

26 temperature of AP at 0.5% concentration level. The effectiveness of the nano sized TMOs on thermal decomposition of AP at 0.5 % concentration level can be summarized as below Copper (II) oxide > cobalt (II, III) oxide> manganese (IV) oxide >chromium (III) oxide>iron (II, III) oxide >iron (III) oxide Thermo gravimetric analysis (TGA) The thermo gravimetric analysis of pure ammonium perchlorate and samples containing micron and nano sized TMOs was carried out on thermo gravimetric analyser, Mettler-Toledo make and presented in the figures 3.32 to TGA study indicates that pure ammonium perchlorate shows two stage weight loss in the temperature range of 256 to 343 C and 343 to 447 C, which is approximately 23% and 76 % respectively. On incorporation of burning rate catalyst in the ammonium perchlorate weight loss takes place in single or two stages and at low temperature. As concentration of the catalyst increases decomposition of pure ammonium perchlorate shifted further towards the lower temperature. Furthermore, the pure ammonium perchlorate with nano sized burning rate catalysts shows weight loss towards the lower temperature compared to micron sized burning rate catalysts at the same concentration level. The results obtained are presented in figures 3.32 to 3.41 and also summarised in table 3.10 Table 3.10 TGA data of ammonium perchlorate containing nano and micron sized TMOs Sr No Metal oxide Form Conc. (%) Temp. range % WL Temp. range % WL Temp. range % WL ( C) ( C) ( C) Nano Fe 3 O Iron oxide Nano Fe 2 O

27 2 Copper oxide 3 Cobalt oxide 4 Chromium oxide 5 Manganes e oxide Nano CuO Micron CuO Nano Co 3 O 4 Micron Co 3 O 4 Nano Cr 2 O 3 Micron Cr 2 O 3 Nano MnO 2 Micron MnO

28 Figure 3.32 Effect of nano Fe 3 O 4 on decomposition of ammonium perchlorate Figure 3.33 Effect of nano Fe 2 O 3 on decomposition of ammonium perchlorate 97

29 Figure 3.34 Effect of nano CuO on decomposition of ammonium perchlorate Figure 3.35 Effect of micron CuO on decomposition of ammonium perchlorate 98

30 Figure 3.36 Effect of nano Co 3 O 4 on decomposition of ammonium perchlorate Figure 3.37 Effect of micron Co 3 O 4 on decomposition of ammonium perchlorate 99

31 Figure 3.38 Effect of nano Cr 2 O 3 on decomposition of ammonium perchlorate Figure 3.39 Effect of micron Cr 2 O 3 on decomposition of ammonium perchlorate 100

32 Figure 3.40 Effect of nano MnO 2 on decomposition of ammonium perchlorate Figure 3.41 Effect of micron MnO 2 on decomposition of ammonium perchlorate 101

33 This finding further infers that the nano sized burning rate modifier has a very good catalytic effect on thermal decomposition of ammonium perchlorate due to the high specific surface area in comparison to micron sized burning rate modifiers. Nano particles of Cobalt and Copper oxides are found to be most effective catalysts for decomposition of AP which shifts % weight loss at lower temperature compared to other TMOs. The data obtained on effect of nano transition metal oxide on thermal decomposition of AP is in well agreement with data reported by Gurdipet al 8, EFFECT OF TMOs ON THERMAL DECOMPOSITION OF BINDER (GUM STOCK) The binder without filler is known as a gum stock. The gum stock study helps in the evaluation of mechanical properties and also the thermal behaviour over a period. In view of this, the thermo gravimetric analysis of binder and binder containing nano and micron sized TMOs were carried out and data obtained are presented in table The TGA plots of binder with nano-and micron sized burn rate modifiers are presented in figures 3.42 to The TGA study indicates that the pure binder shows weight loss in the range of 135 to 534 C in two stages, i.e., C and C and % weight loss is approximately 29 % and 69 % respectively. Further, the weight loss takes place nearly at same temperature on incorporation of burning rate catalysts in the binder. Also, the binder with nano and micron sized burning rate modifiers shows nearly same weight loss pattern. Data on binder decomposition study infer that there is slightly change in percentage weight loss pattern and decomposition temperatures on incorporation of TMOs in the binder. The binder with nano- and micron sized TMOs shows nearly same weight loss pattern. Further, nano sized TMOs shifts decomposition towards lower temperature compared to micron sized TMOs and nano CuO and Nano Fe 3 O 4 found most effective for thermal decomposition of binder. The TGA thermo-gram obtained for the gum stock is similar to the thermo-gram reported by Bazaki 10. Data obtained from TGA study of binder decomposition indicate that TMOs inhibit the decomposition of binder similar result also observed by Kishore

34 Figure 3.42 Thermal decomposition of pure binder Figure 3.43 Effect of nano Fe 2 O 3 and nano Fe 3 O 4 on decomposition of binder 103

35 Figure 3.44 Effect of CuO (nano and micron) on decomposition of binder Figure 3.45 Effect of Co 3 O 4 (nano and micron) on decomposition of binder 104

36 Figure 3.46 Effect of Cr 2 O 3 (nano and micron) on decomposition of binder Figure 3.47 Effect of MnO 2 (nano and micron) on decomposition of binder 105

37 Table 3.11 TGA data of binder containing nano and micron sized TMOs Sr. No Metal oxide Form Con c. Temp range % WL Temp. range % WL (%) ( C) ( C) 1 Gum stock Iron oxide 3 Copper oxide 4 Cobalt oxide 5 Chromium oxide 6 Manganese oxide Nano Fe 3 O Nano Fe 2 O Nano CuO Micron CuO Nano Co 3 O Micron Co 3 O Nano Cr 2 O Micron Cr 2 O Nano MnO Micron MnO EFFECT OF NANO AND MICRON SIZED TMOs ON HTPB/AP/Al BASED COMPOSITE PROPELLANT FORMULATION Effectiveness of nano sized TMOs on thermal decomposition of AP at 0.5 % concentration level is as given below Copper (II) oxide > cobalt (II, III) oxide> manganese (IV) oxide >chromium (III) oxide>iron (II, III) oxide >iron (III) oxide Based on this, nano and micron sized TMOs were evaluated in composite propellant formulations to study their effect on mechanical, thermal and ballistic properties in detail The formulation details of composite propellant HTPB/AP/Al based composite propellant formulation having 86% of solid loading and 14% of binder was selected as standard composition. The selected TMOs 106

38 were added in the standard composition by partial replacement of ammonium perchlorate by keeping other ingredients at constant. The details of composition are presented in the table The different compositions were prepared using selected TMOs as per method described in chapter II under preparation of composition. Table 3.12 Formulations containing nano and micron sized catalyst Sr. Ingredients Standard Developed Compositions No. Composition Comp. 1 Comp. 2 Comp. 3 Comp Binder 14% 14% 14% 14% 14% (HTPB+TDI+DOA) 2. AP Coarse (300µm) % % % % % 3. AP Fine(50 µm) 15.5% 15.5% 15.5% 15.5% 15.5% 4. Al(P) 18.00% 18.00% 18.00% 18.00% 18.00% 5. Catalyst nano/micron 0.00 % 0.25% 0.50% 0.75% 1.00% Prior to curing, the end of mix (EOM) viscosity of prepared composite propellant slurry was determined by Brookfield viscometer on incorporation of TMOs. The cured propellant grains were used for evaluation of mechanical, thermal and ballistic properties. The density of cured propellant grain was determined by helium gas pycnometer by taking 25 mm 25 mm 25 mm samples based on gas volume replacement principle. The cured propellant grains were cut into dumb bell shape using dumb bell cutter for the evaluation of mechanical properties as per ASTM D 638 type-iv. The dumb bell specimens were presented in figure To evaluate ballistic properties such as burning rate and pressure exponent, burning rate of solid strand of known dimensions (6 x 6 x 140 mm) were determined in nitrogen gas using acoustic emission technique as per pressure requirement (60 to 80ksc). The details of findings of each TMO are described in the following sections. 107

39 Figure 3.48 Specimen of dumbbell shaped cured propellant grains 3.5 EFFECT OF NANO AND MICRON SIZED COPPER (II) OXIDE ON HTPB/AP/Al BASED COMPOSITE PROPELLANT FORMULATION Fully characterized nano and micron sized copper oxide was evaluated in standard composite propellant formulation based on HTPB/AP/Al having 86% solid loading by varying the concentration from 0.25% to 1 % level on partial replacement of AP. The details of composition are presented in the table Table 3.13 Formulations containing nano and micron CuO Sr. Ingredients Standard Developed Compositions No. Compositi Comp. 1 Comp. 2 Comp. 3 Comp. 4 on 1. Binder 14 % 14 % 14 % 14 % 14 % (HTPB+TDI+DOA) 2. AP Coarse(300 µm) % % % % % 3. AP Fine (50 µm) 15.5% 15.5% 15.5% 15.5% 15.5% 4. Al(P) % % % % % 5. Nano/ micron CuO 0.00 % 0.25 % 0.50 % 0.75 % 1.00 % The effect of nano and micron CuO on different properties of compositions is discussed in detail. 108

40 3.5.1 Effect of nano CuO and micron CuO on viscosity built up The different composite propellant composition were prepared to study the end of mix (EOM) viscosity by varying the nano CuO and micron CuO concentration formulation from 0.25% to 1.0% keeping the solid loading constant (86%) using Brookfield viscometer by inserting T-C spindle at 2.5 rpm. The data on EOM of composite propellant formulation by varying the nano CuO and micron CuO concentration are presented in table The data on EOM clearly indicate that as concentration of copper oxide in composition increases the EOM of propellant slurry increases in comparison to standard composition without CuO. Furthermore, it was observed that in case of nano CuO, EOM viscosity of propellant slurry is on higher side compared to the composition containing micron CuO. This difference in EOM may be due to finer particle size and higher specific surface area. The enhancement in viscosity with nano TMOs having high surface area may be due to low wetting of ingredients in comparison to standard /micron sized TMOs as percentage of DOA is constant throughout the experiment. The low wetting is not found effective as blanketing agent between -OH group of HTPB and -NCO group of TDI. This causes enhancement of the reaction between -OH group of HTPB and -NCO group of TDI which ultimately enhances the viscosity built up 12a.The findings of viscosity built up data are well supported by the literature 12b. Table 3.14 Data on EOM of composite propellant formulation Sr. No. Composition 40 C (Poise) 1 Standard composition HTPB/AP/Al(14/68/18), % Nano CuO Micron CuO

41 3.5.2 Effect of nano CuO and micron CuO on mechanical properties The effect of nano CuO and micron CuO on mechanical properties such as tensile strength (TS), % elongation and elastic modulus (E-mod) of the cured propellant sample was determined on Hounsfield universal testing machine (UTM) using dumbbells conforming to ASTM-D-638 type IV at a cross head speed of 50 mm/min at ambient temperature for all the studied compositions as well as base composition having 86% solid loading. The data on effect of nano CuO and micron CuO on mechanical properties are presented in table The results reveal that as the percentage of nano CuO increases in the composition, TS and E-mod also increases accordingly while percentage elongation decreases compared to micron- CuO. The findings of the base composition for TS and E-mod were 6.3ksc and 35ksc, respectively while elongation was 45%. The findings of this study are as per expectation and clearly reveals the effect of particle size on elongation which is mainly affected by fine particles in the composition 13,14. Table 3.15 Effect of nano CuO and micron CuO on mechanical properties Sr. No. Composition TS (Kgf/cm 2 ) E-Mod (Kgf/cm 2 ) Elongation (%) 1 Standard Nano CuO, 0.25% Nano CuO, 0.50% Nano CuO, 0.75% Nano CuO, 1.00% Micron CuO, 0.25% Micron CuO, 0.50% Micron CuO, 0.75% Micron CuO, 1.00%

42 3.5.3 Effect of nano CuO and micron CuO on thermal properties All propellant compositions containing nano and micron sized copper oxide along with base composition were studied for their effect on thermal properties by DSC and TGA technique Evaluation of thermal properties by DSC technique Thermal properties of the reference sample were first evaluated by using DSC technique. The DSC thermo-gram shows three distinguishable peaks.the first endothermic peak at C corresponds to phase change of ammonium perchlorate and remaining two exothermic peaks at 304 and 403 C are of double decomposition of composite propellant. All composite propellant formulations containing nano sized burning rate catalysts and micron sized burning rate catalysts were studied for thermal properties. The DSC thermo-grams obtained are presented in figures 3.49 to 3.50 for nano CuO and micron CuO respectively and data obtained from figures is presented in table 3.16 Table 3.16 Data on thermal decomposition of propellant formulations containing nano and micron sized copper oxide Sr.No. Composition Thermal decomposition temperature, ( C) 1 Standard composition 403 HTPB/AP/Al(14/68/18), % Nano CuO Micron CuO

43 Figure 3.49 Effect of nano CuO on thermal decomposition of composite propellant formulation Figure 3.50 Effect of micron CuO on thermal decomposition of composite propellant formulation 112

44 The results can be concluded as 1. On incorporation of burning rate catalyst exothermic peaks at 304 and 403 C are of double decomposition of base composite propellant formulation shifted towards the lower temperature. 2. As concentration of the catalyst increases double decomposition of composite propellant shifted further toward the lower temperature. 3. The propellant formulation with nano sized burning rate catalysts shows double decomposition of composite propellant towards the lower temperature compared to micron sized burning rate catalysts at same concentration level Evaluation of thermal properties by TGA technique The thermo gravimetric analysis carried out for propellant sample containing nano and micron sized copper oxide burning rate catalysts. TGA plots of composite propellant formulation with nano-and micron sized copper oxide are presented in figures 3.51 and 3.52 respectively. The data obtained from TGA plots are also presented in table 3.17 Table 3.17 TGA Data on thermal decomposition of composite propellant formulations containing nano and micron sized copper oxide Sr. Form Conc. Temp. % WL Temp. % WL Temp. % WL No % range ( C) range ( C) range ( C) 1 Nano CuO Micron CuO

45 Figure 3.51 Effect of nano CuO on thermal decomposition of composite propellant formulation Figure 3.52 Effect of micron CuO on thermal decomposition of composite propellant formulation 114

46 From the above data, it is concluded that 1) TGA study indicates that base composition shows two stage weight loss in the temperature range of 247 to 327 C and 327 to 415 C, which is approximately 15 % and 53 % respectively. 2) On incorporation of TMOs two stage weight loss of base composition shifts towards lower temperature. 3) As concentration of the catalyst increases, double decomposition of composite propellant shifted further towards the lower temperature. 4) The propellant formulation with nano sized burning rate catalysts shows double decomposition of composite propellant towards the lower temperature compared to micron sized burning rate catalysts at same concentration level. The findings of thermal study are also well supported by literature 15. Similar study and findings on thermal decomposition of propellant containing copper oxide have been reported by Fuente D. Let al Effect of nano CuO and micron CuO on ballistic properties All propellant compositions containing nano and micron sized copper oxide along with base composition were studied for their effect on following ballistic properties Effect of nano CuO and micron CuO on density The density of composite propellant formulation influences the performance parameter such as mass flow rate and density-impulse. The density of the cured propellant sample was determined by gas pycnometer using helium gas at 30 C. The density of base composition was found in the range of to 1.77 g/cc whereas density of the nano CuO and micron CuO based formulations showed almost same density as per base composition. The data on effect of nano CuO and micron CuO on density are presented in table However, there was marginal improvement in density observed when concentration of TMOs beyond 0.5% due to higher density of CuO compared to ammonium perchlorate. The observed data of density is in well agreement with data reported in the literature 16. These findings further infer that studied formulations possess good homogeneity and packing, leading to wide applications in futuristic propulsion systems Effect of nano CuO and micron CuO on calorimetric value (cal-val) The effect of nano CuO and micron CuO on cal-val was determined by bomb calorimeter for all the studied composition as well as base composition having 86% 115

47 solid loading. The calorimetric value measures the energy content of the propellant in presence of inert atmosphere. Generally higher is the cal val of the composition, higher the performance. The data on effect of nano CuO and micron CuO on cal-val are presented in table The cal-val of base composition was found to be 1550 cal/g whereas on incorporation of nano CuO and micron CuO it decreases slightly. The decrease in cal-val is attributed to inertness of nano CuO and micron CuO. The observed data of calorimetric value (cal-val) is in well agreement with data reported in the literature. 16, Effect of nano CuO and micron CuO on burning rate The propellant formulations were processed by incorporation of nano CuO and micron CuO up to the extent of 0.25 to 1.0 % level by replacing coarse ammonium perchlorate. Solid strand burning rate (SSBR) samples (6 X 6 X 140 mm) were prepared from the cured propellant and burning rates were determined by acoustic emission technique in the presence of inert atmosphere at various pressures 17 and data obtained are given in table It is clear from the table that as the percentage of nano copper oxide increases in the composition burning rate also increases accordingly 18. The table 3.18 also reveals that 36% increase in burning rate was observed with nano CuO in comparison to micron CuO at 1.0% concentration level. It is also clear from the table 3.18 that the increase in burning rate was high with nano CuO at 1.0 % level and beyond this concentration generally burning rate modifiers are not used in the composition because it replaces the active ingredients which in turns decreases the performance. However, in case of micron CuO, the burning rate continuously increases up to 1% level. This study further reveals that 0.25% nano CuO is found more effective to enhance burning rate compared to 1% micron CuO in the composition. The burning rate enhancement using nano and micron sized CuO in the composition clearly infers that as concentration of catalyst touches the concentration level of 1%, the burning rate enhancement gets saturated indicates the optimum concentration and therefore beyond 1 % concentration level it was not incorporated in the formulation. This also infers that less quantity of nano CuO can provide same burning rate in comparison to micron CuO at higher level. Thus, the use of less quantity of catalyst can further help in enhancing the performance of composition. The increase in burning rate may be due to high specific surface area of 20, 21 nano CuO in comparison to micron CuO 116

48 Effect of nano CuO and micron CuO on pressure exponent (n) The pressure exponent (n) was calculated by the Saint Robert and Ville s method.the pressure exponent (n) was determined using SSBR data at different pressures by plotting a curve of lnr b vs. ln p and calculated the pressure exponent from the slope of the curve. The pressure exponent of a propellant is zero when burning rate is totally independent of pressure. However, when it is substantial positive, the rocket will over pressure and may explode. A pressure exponent of less than 0.5 is necessary for a propellant to be acceptable for use in rocket propulsion sub-systems. 19 The burning rate data were generated at 60, 70 and 80 ksc for all composite propellant formulations. The data on effect of nano CuO and micron CuO on pressure exponentare presented in table The pressure exponent of the base composition was found to be 0.35 whereas on addition of nano CuO and micron CuO the pressure exponent value decreases compared to base composition. In the literature copper compounds are well-known for their property of pressure exponent reducer for composite propellant formulation 22. The pressure exponent values are found less in case of nano sized copper oxide compared with micron sized copper oxide.the plot on pressure exponent vs. % concentration of copper oxide is presented in figure Furthermore, as concentration of nano CuO and micron CuO increases the pressure exponent values decreases, at the same time nano CuO found to be most effective to reduce pressure exponent. The observed data on pressure exponent is in well agreement with data reported in the literature 20, 21, 22, Pressure Exponent (n) Micron CuO Nano CuO Concentration (%) Figure 3.53 Pressure exponents vs. % concentration of copper oxide 117

49 Sr. No. Table 3.18 Effect of nano CuO and micron CuO on ballistic properties Composition Solid strand burning rate Density Pressure Cal-Val (mm/s) (g/cc) Exponent (cal/g) (n) 1 Standard Nano CuO, 0.25% Nano CuO, 0.50% Nano CuO, 0.75% Nano CuO, 1.00% Micron CuO, 0.25% Micron CuO, 0.50% Micron CuO, 0.75% Micron CuO, 1.00% EFFECT OF NANO AND MICRON SIZED COBALT (II, III) OXIDE ON HTPB/AP/Al BASED COMPOSITE PROPELLANT FORMULATION Fully characterized nano-and micron size cobalt (II, III) oxide was evaluated in standard composite propellant formulation based on HTPB/AP/Al having 86 % solid loading by varying the concentration from 0.25 % to 1 % level on partial replacement of AP. The details of composition are presented in the table Table 3.19 Formulations containing nano and micron sized Co 3 O 4 Sr. Ingredients Standard Developed Compositions No. Composition Comp. 1 Comp. 2 Comp. 3 Comp Binder 14 % 14 % 14 % 14 % 14 % (HTPB+TDI+DOA) 2. AP Coarse(300 µm) % % % % % 3. AP Fine(50 µm) 15.5% 15.5% 15.5% 15.5% 15.5% 4. Al(P) % % % % % 5. Nano/ micron Co 3 O % 0.25 % 0.50 % 0.75 % 1.00 % 118

50 The effect of nano Co 3 O 4 and micron Co 3 O 4 on different properties of compositions are discussed in detail Effect of nano and micron sized cobalt (II, III) oxide on viscosity built up The different composite propellant composition were prepared to study the end of mix (EOM) viscosity by varying the nano Co 3 O 4 and micron Co 3 O 4 concentration in propellant formulation from 0.25 % to 1.0 % keeping the solid loading constant (86 %) using Brookfield viscometer by inserting T-C spindle at 2.5 rpm. The data on EOM of composite propellant formulation by varying the nano Co 3 O 4 and micron Co 3 O 4 concentration are presented in table The data on EOM clearly indicate that as concentration of Co 3 O 4 in composition increases the EOM of propellant slurry increases in comparison to standard composition without cobalt oxide. Furthermore, it was observed in case of nano Co 3 O 4 that EOM values of propellant slurry at higher side compared to the composition containing micron sized Co 3 O 4. This difference in EOM may be due to finer particle size and higher specific surface area. The enhancement in viscosity with nano-tmos having high surface area may be due to low wetting of ingredients in comparison to standard /micron-sized TMOs as percentage of DOA is constant throughout the experiment. The low wetting is not found effective as blanketing agent between -OH group of HTPB and -NCO group of TDI. This causes enhancement of the reaction between -OH group of HTPB and -NCO group of TDI which ultimately enhances the viscosity built up 12a. The findings of viscosity built up data are supported by the literature 12b. Table 3.20 Data on EOM of composite propellant formulation Sr. No. Composition viscosity@ 40 C (Poise) 1 Standard composition HTPB/AP/Al(14/68/18), % Nano Co 3 O Micron Co 3 O

51 3.6.2 Effect of nano Co 3 O 4 and micron Co 3 O 4 on mechanical properties The effect of nano Co 3 O 4 and micron Co 3 O 4 on mechanical properties such as tensile strength (TS), % elongation and elastic modulus (E-mod) of the cured propellant sample was determined on Hounsfield universal testing machine (UTM) using dumbbells conforming to ASTM-D-638 type IV at a cross head speed of 50 mm/min at ambient temperature for all the studied compositions as well as base composition having 86 % solid loading. The data on effect of nano Co 3 O 4 and micron Co 3 O 4 on mechanical properties are presented in table The results reveal that as the percentage of nano Co 3 O 4 increases in the composition, TS and E-mod also increases accordingly while percentage elongation decreases compared to micron Co 3 O 4. The findings of the base composition for TS and E-mod were 6.3ksc and 35 ksc, respectively while elongation was 45 %. The findings of this study are as per expectation and clearly reveals the effect of particle size on elongation which is mainly affected by fine particles in the composition 13,14. Table 3.21 Effect of nano Co 3 O 4 and micron Co 3 O 4 on mechanical properties Sr. No. Composition TS (Kgf/cm 2 ) E-Mod (Kgf/cm 2 ) Elongation (%) 1 Standard Nano Co 3 O 4,0.25% Nano Co 3 O 4,0.50% Nano Co 3 O 4,0.75% Nano Co 3 O 4,1.00% Micron Co 3 O 4,0.25% Micron Co 3 O 4,0.50% Micron Co 3 O 4,0.75% Micron Co 3 O 4,1.00%

52 3.6.3 Effect of nano and micron sized cobalt (II, III) oxide on thermal properties All propellant compositions containing nano and micron sized cobalt oxide along with base composition were studied for their effect on thermal properties by DSC and TGA technique Evaluation of thermal properties by DSC technique Thermal properties of the reference sample were first evaluated using DSC technique. The thermo-gram shows three distinguishable peaks. The first endothermic peak at C corresponds to phase change of ammonium perchlorate and remaining two exothermic peaks at 304 and 403 C are of double decomposition of composite propellant. All composite propellant formulations containing nano sized burning rate catalysts and micron sized burning rate catalysts were studied for thermal properties. The DSC thermo-grams obtained for nano Co 3 O 4 and micron Co 3 O 4 are presented in figures 3.54 and 3.55, respectively. The data obtained from DSC thermo grams are presented in table 3.22 Table 3.22 Data on thermal decomposition of propellant formulations containing nano Co 3 O 4 and micron Co 3 O 4 Sr. No. Composition Thermal decomposition temperature, ( C) 1 Standard composition 403 HTPB/AP/Al(14/68/18), % 2 Nano Co 3 O 4 3 Micron Co 3 O

53 Figure 3.54 Effect of nano Co 3 O 4 on thermal decomposition of composite propellant formulation Figure 3.55 Effect of micron Co 3 O 4 on thermal decomposition of composite propellant formulation 122

54 From the above data, findings can be summarized as- 1. On incorporation of burning rate catalyst exothermic peaks at 304 and 403 C are of double decomposition of base composite propellant formulation shifted towards the lower temperature. 2. As concentration of the catalyst increases double decomposition of composite propellant shifted further towards the lower temperature. 3. The propellant formulation with nano sized burning rate catalysts shows double decomposition of composite propellant towards the lower temperature compared to micron sized burning rate catalysts at same concentration level Evaluation of thermal properties by TGA technique The thermo gravimetric analysis carried out for propellant sample containing nano and micron sized cobalt oxides burning rate catalysts. TGA plots of composite propellant formulation with nano and micron sized cobalt oxides are presented in figures 3.56 and 3.57, respectively and data obtained from figures is presented in table 3.23 Table 3.23 Data on thermal decomposition of propellant formulations containing Sr. Form No 1 Nano Co 3 O 4 2 Micron Co 3 O 4 nano Co 3 O 4 and micron Co 3 O 4 Conc. Temp. % WL Temp. % WL Temp. % % range range Range WL ( C) ( C) ( C)

55 Figure 3.56 Effect of nano Co 3 O 4 on thermal decomposition of composite propellant formulation Figure 3.57 Effect of micron Co 3 O 4 on thermal decomposition of composite propellant formulation 124

56 From the above data, findings can be summarized as- 1. TGA study indicates that base composition shows two stage weight loss in the temperature range of 247 to 327 C and 327 to 415 C, which is approximately 15 % and 53 % respectively. 2. On incorporation of TMOs two stage weight loss of base composition shifts towards lower temperature. 3. As concentration of the catalyst increases, double decomposition of composite propellant shifted further towards the lower temperature. 4. The propellant formulation with nano sized burning rate catalysts shows double decomposition of composite propellant towards the lower temperature compared to micron sized burning rate catalysts at same concentration level. The findings of thermal study is also fully supported by literature Effect of nano and micron sized cobalt (II, III) oxide on ballistic properties All propellant compositions containing nano and micron sized cobalt oxide along with base composition were studied for their effect on following ballistic properties Effect of nano Co 3 O 4 and micron Co 3 O 4 on density The density of composite propellant formulation influences the performance parameter such as mass flow rate and density-impulse. The density of the cured propellant sample was determined by gas pycnometer using helium gas at 30 C.The density of base composition was found in the range of to 1.77 g/cc where as density of the nano Co 3 O 4 and micron Co 3 O 4 based formulations showed almost same density as per base composition. The data on effect of nano Co 3 O 4 and micron Co 3 O 4 on density are presented in table However, there was marginal improvement in density observed when concentration of TMOs beyond 0.5 % due to higher density of Co 3 O 4. The observed data of density is in well agreement with data reported in the literature 16. These findings further infer that studied formulations possess good homogeneity and packing, leading to wide applications in futuristic propulsion systems. 125