Study on the effect of RDX content on the properties of nitramine propellant

Fen ZHANG,Deng-pn ZHU,Qiong LIU,Zhi-to LIU,Ping DU,*,1

aSchool of Chemistry and Engineering Nanjing University of Science and Technology,Nanjing 210094,China

bLiaoning Qingyang Chemical Industry Corporation,Liaoyang 111001,China

Study on the effect of RDX content on the properties of nitramine propellant

Fen ZHANGa,Deng-pan ZHUa,Qiong LIUb,Zhi-tao LIUa,Ping DUa,*,1

aSchool of Chemistry and Engineering Nanjing University of Science and Technology,Nanjing 210094,China

bLiaoning Qingyang Chemical Industry Corporation,Liaoyang 111001,China

A R T I C L E I N F O

Article history:

13 May 2017

Accepted 24 May 2017

Available online 26 May 2017

Nitramine propellant

RDX

Mechanical property

Combustion property

Four kinds of nitroamine propellants with different RDX contents(10%,20%,30%and 40%)were prepared to study the effect of RDX content on the mechanical properties and combustion properties of nitroamine propellant.The mechanical properties and combustion properties of nitroamine propellant at the normal temperature(20°C)and low temperature(-40°C)were test by using impact testing machine,drop hammer impact test machine and closed bomb vessel.The test results show that the impact strength of 30%RDX-contained nitramine propellant is maximum,but 40%RDX-contained nitramine propellant has the minimum impact strength.And the crushing height of propellant with 20%RDX-contained was the highest,but the crushing height of propellant with 40%RDX-contained the lowest.With the increase in RDX content in nitramine propellant,the energy of nitramine propellant increases and its burning rate reduces,but 40%RDX-contained nitramine propellant did not meet this trend at the low temperature because of its poor mechanical properties.

?2017 The Authors.Published by Elsevier Ltd.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

1.Introduction

High energy and high strength performances are the basic requirements of modern gun propellants,but the traditional propellants have been dif ficult to meet the requirements.Nitramine propellant was prepared byadding high-energy nitramine particles (RDX,HMX,etc.)to the double-based propellant.Nitramine propellant has received extensive attention and research in recent years because of its excellent thermal properties,such as high energy,low detonation temperature,lowaverage molecular weight of gas[1].The content and morphology of nitramine particles,such as RDX and HMX,affect the combustion performance of rocket solid propellants[2-4].Nitramine particles can be found to signi ficantly increase the burning rate of propellants and the particle sizes of nitramine particles.The burning rate of the larger propellant is lower.Also,some researchers have reported the use of nitramine particles in gun propellant[5-8],and found that nitramine particles can improve the gunpowder force of propellants,while propellant containing nitramine particles has a smaller ablation[9]. However,the current research is mainly to study the effect of nitramine particles on the combustion properties of propellant,but there have been a lack of reports on the mechanical properties and combustion performance of nitramine propellant.In the present study,the preparation of nitroamine propellants containing RDX, NC and NG was presented.The effect of RDX content on the mechanical properties and combustion properties of propellant was studied by changing the RDX content.

2.Experiment

2.1.Preparation of RDX-contained nitramine propellants

Four nitroamine propellants with 10%,20%,30%,and 40%RDXs were prepared by using same semi-solvent method,and the numbers of propellants were 1#,2#,3#and 4#.

2.2.Propellant performance test

The mechanical properties of the propellants were tested by using the simple beam impact testing machine and the drop hammer impact testing machine.The samples of propellants wereprepared according to GJB 770B-2005 standard,and the comparative tests at low temperature(-40°C)and room temperature (20°C)were adopted.The impact test sample was 60.0 mm tubular propellant,and the drop hammer impact test sample was 1:1 aspect ratio propellant.The weight of the drop hammer was 2.5 kg.

The combustion performances of propellants were tested by using closed bomb vessel.The volume of closed bomb vessel was 102.85 cm3,the charge density of propellant was 0.20 g/cm3,the ignition pressure was 10.0 MPa,and the 15/1 propellant was used. Thep-tcurves of nitroamine propellants were measured,and theupandL-Bcurves were obtained through data processing.

3.Result analysis and discussion

3.1.Mechanical properties of propellant

The mechanical properties of propellant are very important to the safety of the propellant.The dynamic mechanical properties of the propellants were tested to simulate the process of impact of the propellant in the chamber.The impact strengths of nitroamine propellants with different RDX contents at normal temperature (20°C)and low temperature(-40°C)were tested by using simple beam impact testing machine,and the impact strengths of the samples were calculated,as shown in Table 1.

For the four nitramine propellants with different RDX contents, the impact strength increases and then decreases with the increasein RDX content.When the content of RDX is 30%,the impact strength of the propellant is 14.08 kJ/m2at normal temperature and 5.92 kJ/m2at low temperature,and the impact strength is the highest at room temperature and low temperature.The impact strength of the nitramine propellant with 40%RDX was 8.89 kJ/m2and 4.46 kJ/m2,respectively,at room temperature and low temperature.

Table 1 Experimental results of impact properties of propellants.

The low-temperature crushing-falling tests and the statistics of crushing degree of gunpowder at a certain falling height were carried out,and the impact strengths of nitramine propellants with different RDX contents were measured by using the drop hammer test machine.

Drop hammer hit the surface of propellant at a certain height of free fall,and the drop height of propellant was the height at which the breakage probability of propellant is 80-100%,as shown in Table 2.4#propellant with the highest RDX content has the lowest crushing height at low-temperature and impact energy per unit area,and the crushing height of 2#propellant with 20%RDX-contained was the highest,the crushing height increases and then decreases with the increase in RDX content.The mechanical properties of 20%RDX-contained nitramine propellant are the best, and the mechanical properties of 40%RDX-contained nitramine propellant are the worst.

3.2.Combustion performance of propellant

The combustion properties of RDX nitramine propellants were measured by using closed bomb vessel.Thep-tcurve was measured,andu-pandL-Bcurves and the constant-volume combustion parameters of propellants were calculated,as shown in Fig.1 and Table 3.

Four nitramine propellants with different RDX contents at room temperature and low temperature,the maximum pressure of combustion increased with increasing RDX content in Table 3 and Fig.1.Because the energy of RDX is higher than that ofnitrocellulose,the energy of nitramine propellant increases as the RDX content increases.

Table 2Experimental results of low temperature drop weight test of propellants.

Table 3Constant volume combustion characteristic parameters of propellants.

Fig.1.p-tcurves of nitramine propellants containing RDX.

Fig.2.u-pcurves of nitramine propellants containing RDX.

Table 4 The relative gradient(RQ)of propellant.

Burning rates of four nitramine propellants weredecreased with the increase in RDX content at normal temperature,and the burning rate pressure index was less than 1%of nitramine propellant in Table 3 and Fig.2.And at low temperature,the burning rate curve of 40%RDX-contained propellant coincided with that of 30% RDX-contained propellant.The pressure index increases with the increase in RDX content,but 40%RDX-contained propellant deviates from this trend.The results show that the addition of RDX reduces the burning rate of propellant and increases the pressure index of propellant.And the relative gradient value(RQ)of the propellants at low temperature relative to room temperature was calculated from Eq.(1).The calculated results are listed in Table 4:

The relative gradient values of four different RDX-contained nitroamine propellants are all less than 1,which mean it obey to the normal combustion law at low temperature.The RQ value of 20%RDX-contained nitramine propellant is the smallest,which means that the possibility of abnormal combustion was low at low temperature,and the RQ value of 40%RDX-contained nitramine propellant was the highest.

40%RDX-contained nitramine propellant showed poor mechanical properties at low temperature,its burning rate and burning rate index were abnormal,and the relative gradient of combustion was higher.20%RDX-contained nitramine propellant had good mechanical properties at low temperature,and its RQ value was low.The results show that the combustion performance of nitramine propellant is related to the mechanical properties. When the mechanical properties of nitramine propellant are poor, the possibility of abnormal combustion is increased at low temperature.

4.Conclusions

1)The impact strength of nitramine propellant increases first and then decreases with the increase in RDX content.The impact strength of 30%RDX-contained propellant is the biggest. For 20%RDX-contained nitramine propellant,the drop height and the impact energy per unit area of drop hammer test at low temperature were the largest.

2)With the increase in RDX content,the maximum combustion pressure,burning rate and combustion pressure index all increased,However,the burning rate and burning rate pressure indexof 40%RDX-contained nitramine propellant deviated from this rule.The combustion performance of nitramine propellant is related to the mechanical properties.When the mechanical properties of nitramine propellant are poor,the possibility of abnormal combustion is increased at low temperature.

Acknowledgements

This paper was completed under the supported by National Natural Science Foundation of China(NO.51506093).

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29 January 2017

*Corresponding author.

E-mail address:zhangfen_31@163.com(P.DU).

Peer review under responsibility of China Ordnance Society

1Present/permanent address.351 buildings,Nanjing university of science and Technology,200th xiaolingwei street,Xuanwu borough,Nanjing city,Jiangsu province,China.

http://dx.doi.org/10.1016/j.dt.2017.05.020

2214-9147/?2017 The Authors.Published by Elsevier Ltd.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

in revised form