Effect of 1,1-diamino-2,2-dintroethene(FOX-7)on properties of CMDB propellants①

FAN Xue-zhong，FU Xiao-long，SHAO Chong-bin，LIU Xiao-gang，LI Ji-zhen

(Xi’an,Modern Research Institute,Xi’an　710065,China)



Effect of 1,1-diamino-2,2-dintroethene(FOX-7)on properties of CMDB propellants①

FAN Xue-zhong，FU Xiao-long，SHAO Chong-bin，LIU Xiao-gang，LI Ji-zhen

(Xi’an,Modern Research Institute,Xi’an710065,China)

In order to decrease the sensitivity of CMDB propellants,several propellant formulations containing 1,1-diamino-2,2-dinitroethene(FOX-7)were studied.The effects of FOX-7 on the sensitivity properties,combustion characteristics and thermochemical properties of the CMDB propellants were investigated by the impact sensitivity apparatus,the thermal video systems and DSC instrument,et al.It was found that FOX-7 not only decrease the sensitivity properties obviously(Impact sensitivity 20.4 cm,Friction sensitivity 4%),enhance the combustion characteristics at low pressure by 39.49 % and accelerate the decomposition of the CMDB propellants,but also maintain the advantage of RDX/CMDB propellant for high energy,low signature and good mechanism properties.It is indicated that FOX-7 can be used in weapon as high energetic and insensitive material by theoretical calculation and experiment.

material chemistry；FOX-7；CMDB propellant；sensitivity；combustion characteristics；thermal behavior

0　Introduction

CMDB propellants containing AP and Al(AP/Al/CMDB propellants)have been widely used in rocket and missile weapons,because of their high specific impulse,good mechanical properties and low cost[1].1,1-Diamino-2,2-dinitroethylene(FOX-7)is generally considered to be an useful high energetic material with high density combining comparatively high performance and low sensitivity[2-3].FOX-7 has been found to be less sensitive to friction and impact than cyclotrimethylene trinitramine(RDX),while energetic properties of FOX-7 are comparable to RDX[4-6].Due to these advanced characteristics,FOX-7 has been extensively studied as a promising energetic material for insensitive munitions(IM)or propellants[7].In the past decades,the standard molar special heat capacity(Cp)of FOX-7[8]and energetic parameters of the smokeless propellants containing FOX-7 were studied[9-10].However,most of these studies concerning the properties of the propellants with FOX-7 were theoretical evaluation.Also,there is little publication on AP/Al/CMDB propellants.In order to decrease the sensitivity of AP/Al/CMDB propellants,FOX-7 is added in the propellant partially instead of RDX in this work.The effects of FOX-7 on the properties,such as sensitivity,energetic properties,combustion characteristics and mechanical properties,of the CMDB propellants are investigated in details,and the thermal decomposition behavior,flame structure and quenched surface of the CMDB propellants are also examined in order to indicate the effects of FOX-7 on the properties of CMDB propellants.

1　Experimental

1.1Materials and formulations

1,1-Diamino-2,2-dinitroethylene(FOX-7,≥99.8%,d50=180 μm,andρ=1.85 g/cm3),nitrocellulose(NC,N%12.0,purity is over 99.6%),nitroglycerin(NG,≥99.3%),aluminum powder(Al,≥99.4%),cyclotrimethylenetrinitramine(RDX,≥99.5%),ammonium perchlorate(AP,≥99.5%),N-nitrodihydroxyethylaminedinitrate(DINA,≥99.5%).The formulations of the five different propellants are as follows:

(1)RDX-CMDB:AP/10%,Al/5%,NC/24%,NG/33%,DINA/3%,RDX/20%,C2/5%.

(2)F5-CMDB:FOX-7/5%,AP/10%,Al/5%,NC/24%,NG/33%,DINA/3%,RDX/15%,C2/5%.

(3)F10-CMDB:FOX-7/10%,AP/10%,Al/5%,NC/24%,NG/33%,DINA/3%,RDX/10%,C2/5%.

(4)F15-CMDB:FOX-7/15%,AP/10%,Al/5%,NC/24%,NG/33%,DINA/3%,RDX/5%,C2/5%.

(5)F20-CMDB:FOX-7/20%,AP/10%,Al/5%,NC/24%,NG/33%,DINA/3%,C2/5%.

1.2Preparation

All the samples involved in this investigation are mixed by a planetary vertical mixer of 5L capacity(Germany).Each batches are prepared by a slurry vaccum casting process.The propellants are cured at 70 ℃ for 3 days in a water jacketed oven.

1.3Characterization

1.3.1Surface morphology

The surface morpholoy of FOX-7 is measured by field-emission scan electron microscope(Netherlands,FEI company).

1.3.2Ideal energetic properties

The energetic properties of CMDB propellants with FOX-7 are calculated by NASA-Chemical Equilibrium and Applications(NASA-CEA)program which was established by NASA Lewis Flight Propulsion Laboratory[11].

1.3.3Sensitivity test

Impact sensitivity is analyzed by employing the fall hammer method(5.0 kg drop hammer) in Model WL-1 impact sensitivity apparatus(China) with sample mass of 30 mg and reference sample of standard RDX.Impact sensitivity is expressed by critical height of 50% probability of explosion(H50,cm).

Friction sensitivities are obtained by a Model WM-1 friction sensitivity apparatus(China) with pendulum angle of 66°,sample mass of 20 mg,sample of standard tetryl.Friction sensitivity is expressed by probability of explosion(P,%).

1.3.4Burning rate test

The burning rate is tested with the Crawford measurement method in the pressure range of 2～22 MPa.The sample strands with dimensions of 150 mm×5 mm×5 mm are coated with polyethylene alcohol and ignited by 0.1 mm nickel wire.Burning rates are determined for 100 mm measuring distance by disruption of 0.1 mm nickel wires drawn through the strands.

1.3.5Mechanical properties test

The mechanical properties of the propellants are measured by INSTRON 4505(USA)tensile tester.The propellants are cut into slices with 10 mm×10 mm×120 mm,and the slices are made into JANNAF dogbones.The tests are carried out at 20 ℃ with 100 mm/min cross-head speed.

1.3.6Thermal decomposition test

Differential Scanning Calorimeter(DSC) analysis is carried out on a Model TA DSC 910S(USA) differential scanning calorimeter in static nitrogen atmosphere with sample mass of 2.0 mg at a heating rate of 5 ℃/min and in static nitrogen atmosphere with pressure of 0.1 MPa.

1.3.7Flame structure test

The Thermal Video Systems(China) is introduced to test the combustion flame zone.The uncoated sample(dimension,5 mm×5 mm×15 mm) is placed vertically on the ignition rack,and the rack is fixed in a combustion chamber with vitreous window.The chamber is filled with continuous flow of argon atmosphere from bottom to top achieving a definite pressure.The nickel-chrome wire is used to ignite the propellant samples,in this way the flame pictures are obtained.

1.3.8Quenched surface test

The quenched surface is analyzed by scanning electron microscope(Netherlands,FEI Company).The sample of propellants is put on the copper cylinder,and ignited in nitrogen atmosphere.Then the burning sample is quenched,and the quenched surface are obtained by means of SEM.

2　Results and discussion

2.1Surface morphology of FOX-7

The surface morphology of pure FOX-7 is measured by field-emission scan electron microscope(FE-SEM)and the photographies are shown in Fig.1.

It is observed from Fig.1 that the FOX-7 sample is plated with grain size in the range of 100～500 μm.

(a)100×　　　　(b)200×

2.2Sensitivity

The mechanical sensitivities of the pure FOX-7 and RDX are listed in Table 1,and the mechanical sensitivity of the CMDB propellants with FOX-7 are listed in Table 2.

Table 1　Mechanical sensitivities of FOX-7 and RDX

Table 2　Effect of FOX-7 on the sensitivities of the CMDB propellants

It is found from Table 1 that the pure FOX-7 is more insensitive than RDX.It is noticed from Table 2 that the sensitivity of the RDX-CMDB propellant decreases with increase of FOX-7 when RDX is partialy replaced by the FOX-7 in the CMDB propellants,especially for the friction sensitivity decreases from 40% to 4% when RDX is replaced completely by FOX-7 in the propellant.The results suggest that the addition of FOX-7 in the CMDB propellant fromulation can decrease the mechanical sensitivity of propellant significantly.

2.3Energetic properties

The energetic properties of the CMDB propellants with and without FOX-7 are calculated by NASA-CEA programme. The ideal specific impulse(Isp)and characteristic velocity (C*) of the propellants with FOX-7 are shown in Table 3.

Comparing the ideal specific impulse of the RDX-CMDB propellant with those of the F20-CMDB propellant,the ideal specific impulse and the characteristics velocity of the RDX-CMDB propellant are marginally decreased 1.76% and 1.63%,respectively. It is indicated that the energetic properties of the FOX-7 substituted-CMDB propellants are close to those of RDX-CMDB propellants.

Table 3　Energetic properties of the CMDB propellants

2.4Combustion characteristics

The burning rate and pressure exponent of the CMDB propellants with FOX-7 are listed in Table 4.

It is observed from Table 4 that the burning rates of the CMDB propellants increase with increase of the mass fraction of FOX-7 in the formulations.For example,the burning rates of the RDX-CMDB propellant are increased 39.49 % at 2 MPa and 3.06 % at 22 MPa when the formulation F20-CMDB was tested. Meanwhile, the pressure exponent decreases from 0.88 to 0.75 in this case. The results reveal that the variation tendencies in the combustion characteristics of the CMDB propellants containing FOX-7 with pressure are the same as those of the RDX-CMDB propellants. FOX-7 exerts much effort on the combustion properties of the CMDB propellants at low pressure such as 2 MPa.

Table 4　Effects of FOX-7 on the combustion characteristics of the CMDB propellants

The typical combustion structures of the CMDB propellants with FOX-7 at different pressures are shown in Fig.2.

(a1)RDX-CMDB(2 MPa)　　　(a2)RDX-CMDB(4 MPa)

(b1)F5-CMDB(2 MPa)　　　(b2)F5-CMDB(4 MPa)

(c1)F10-CMDB(2 MPa)　　　(c2)F10-CMDB(4 MPa)

(d1)F15-CMDB(2 MPa)　　　(d2)F15-CMDB(4 MPa)

(e1)F20-CMDB(2 MPa)　　　(e2)F20-CMDB(4 MPa)

The simulations of combustion flame model of the CMDB propellant with FOX-7 are shown in Fig.3.

From both Fig.2 and Fig.3,it is found that the combustion flame structures of the CMDB propellants with FOX-7 are typical heterogeneous flame structure,which is composed of dark zone,fizz zone and flame zone.With the increase of FOX-7 mass fraction in the formulations,the flame of F20-CMDB is more fierce than that of RDX-CMDB.

Fig.3　Flame model for combusion of the CMDB propellants

2.5Mechanical properties

In order to analyze the effects of FOX-7 on the mechanical properties for the CMDB propellants,the maximum tensile strength(σm)and the maximum elongation(εm)of CMDB propellant containing FOX-7 are determined and listed in Table 5.

It is shown from Table 5 that the maximum tensile strength and the maximum elongation of the CMDB propellants containing FOX-7 are higher than those of RDX-CMDB propellant at 20 ℃.When RDX is completely substituted for FOX-7,σmis increased 2.32% and theεmis increased 12.73%.The mechanical properties of the CMDB propellants containing FOX-7 meet the needs of rocket motors at 20 ℃[12-13].

Table 5　The mechanical properties of CMDB propellants containing FOX-7

2.6Thermal decomposition behavior

The thermal decomposition curves of the CMDB propellants with FOX-7 are shown in Fig.4.

As shown in the DSC curve of the RDX-CMDB in Fig.4,it is inferred that NC/NG decomposes at 175.24 ℃,and RDX decomposes at 200.32 ℃ in the CMDB propellants.The small endothermic peak at 244.51 ℃ is related to crystal transformation of AP.AP and the centralite are completely consumed in the range of 310～ 322 ℃.

FOX-7 has one endothermic peak at 164 ℃,and two exothermic peaks at both 232.5 ℃ and 284.2 ℃[14].In the DSC curve of F20-CMDB,the weak endothermic peak at about 124 ℃ is ascribed to the crystal transformation peak of FOX-7.NC/NG decomposes at 176.32 ℃,and the decomposition peak at 193.02 ℃ is related to the first decomposition stage of both FOX-7 and RDX.The small endothermic peak at about 248.47 ℃ is the crystal transformation peak of AP.The AP,FOX-7 and the centralite decompose completely from 314 ℃ to 350 ℃.It is concluded that FOX-7 can accelerate the decomposition of the CMDB propellants from the analysis of the main decomposition peak temperature.

Fig.4　Thermal decomposition behavior of the CMDB porpellants with FOX-7

2.7Quenched surface

The quenched surfaces and the analysis results of surface elements of both RDX-CMDB and F20-CMDB propellants are shown in Fig.5 and Table 6.

From Fig.5,it can be seen that there are mainly carbon layers,balled Al2O3and unburned RDX/AP/FOX-7 distributedd in the quenched surface.From Table 6,it is noticed that the main elements of the quenched surface is carbon coming from the products of the burning propellants.The content of carbon in the RDX-CMDB(0% of FOX-7)is relative less than that of F20-CMDB(20% of FOX-7),and the oxygen content in RDX-CMDB is more than that of F20-CMDB.It is indicated that with the increase of FOX-7,the combustion of a propellant is more surfficent.To summary,the elements of quenched surface are composed of unburned propelllant and the residues resulted from burned propellant.

Fig.5　Quenched surface of CMDB propellant with FOX-7

Samplesw/%CONAlothersRDX-CMDB(2MPa)32.2623.9220.3521.162.31F20-CMDB(2MPa)29.1128.7721.1418.032.95

3　Conclusion

(1)The addition of FOX-7 in the CMDB propellant fromulation can obviously decrease the mechanical sensitivity of propellant,especially for the friction sensitivity decreases from 40% to 4% when RDX is replaced completely by FOX-7 in the propellant.

(2)FOX-7 exerts much effort on the combustion properties of the CMDB propellants for 39.49 % at 2 MPa.

(3)FOX-7/CMDB propellant can maintain the advantage of RDX/CMDB propellant for high energy,low signature and good mechanism properties according to the study of energetic properties,thermal decomposition behaviour,mechanical properties and quenched surface.

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(编辑：薛永利)

FOX-7对CMDB固体推进剂性能的影响

樊学忠，付小龙，邵重斌，刘小刚，李吉祯

(西交近代化学研究所，西安710065)

为有效降低高能CMDB推进剂体系的危险性，研究了1，1-二氨基-2，2-二硝基乙烯(FOX-7)在CMDB推进剂中的应用，采用感度仪、热像仪及DSC等测试分析了FOX-7对其感度、燃烧特性及热性能的影响。研究表明，FOX-7不但明显降低CMDB推进剂的感度(摩擦感度4%，撞击感度20.4 cm)，大幅提高CMDB推进剂低压下的燃速(约提高39.49 %)，促进了CMDB推进剂的热分解，且保持了CMDB推进剂的高能量、低特征信号和较好的力学性能等优点。理论计算和实验表明，FOX-7可作为高能钝感含能组分在武器型号中推广应用。

材料化学；FOX-7；CMDB推进剂；感度；燃烧性能；热行为

date：2014-12-04；Revised date：2015-02-05。

V512Document code：AArticle ID：1006-2793(2016)02-0201-06

10.7673/j.issn.1006-2793.2016.02.009

Biography：FAN Xue-zhong(1962—)，male，researcher，speciality：solid propellant.