Co-precipitation preparation and burning performance test of delay composition containing barium chromate

QI Yi, WANG Jin-ying, ZHANG Xin, YU Shuo, YU Hui-qin,2

(1. School of Environment and Safety Engineering, North University of China, Taiyuan 030051, China;2. Dept. of Civil Engineering, Changzhi Vocational and Technical College, Changzhi 046000, China)

0 Introduction

Barium chromate not only can be used as fuse and pyrotechnic agent, but also can be used to make pigments, ceramics, etc, especially in making the mixed delay composition. Barium chromate has a high decomposition temperature and can absorb heat when it is decomposed, which makes barium chromate multifunctional when used as a delay composition in combination with different combustible agents and acted as an oxidizer or a flame retardant[1]. Therefore, it has a great influence on the burning performance of delay composition.Many investigators have studied the formula, burning performance, and the factors that affect the delay precision[2]of boron[3-6], tungsten[7-8]and silicon type[9]delay composition. Co-precipitation method has greater advantages compared with the traditional mechanical mixing method: First, the co-precipitation method can make the ingredients mix more evenly; Besides, using the traditional mechanical mixing method appears pharmaceutical powder. It is harmful to work in the environment chronically with the great toxicity of barium chromate and other agents. The preparation process of co-precipitation method is basically no dust, which is conductive to industrial hygiene[3].

In this paper, the preparation conditions of barium chromate are optimized firstly. On the basis of this, the S/BaCrO4/KClO4delay composition is prepared by co-precipitation method and the burning performance is tested.

1 Experiment

1.1 Experimental materials and equipments

Barium chloride, analytical grade, Tianjin Tianli Chemical Reagent Co., Ltd;Sodium dichromate, analytical grade, Tianjin Kaitong Chemical Reagent Co., Ltd;Sodium hydroxide, analytical grade, Tianjin Dalu Chemical Reagent Factory;Sulfur powder, analytical grade, Wenzhou, Zhejiang Dongsheng Chemical Reagent Factory;Potassium perchlorate, analytical grade, Tianjin Sailboat Chemical Reagent Technology Co., Ltd;Methanol, analytical grade, Tianjin Kaitong Chemical Reagent Co., Ltd.

SPY glass thermostatic water bath, Gongyi Yuhua Instrument Co., Ltd;DW-3 digital electric mixer,Gongyi Yuhua Instrument Co., Ltd;HL-2S constant current pump, Shanghai Yue Ming Scientific Instrument Co., Ltd;SHZ-D(Ⅲ)Circulating water pump, Hangzhou Ruijia Precision Scientific Instrument Co., Ltd;1700 Fourier transform infrared spectrometer, the United States Perkin-Elmer company;JSM-6700F scanning electron microscope, Japan Electronics Co., Ltd;FCY-1A Fire point tester, Hebei Xintai Hi-Tech Instruments Manufacturing Co., Ltd.

1.2 Preparation of barium chromate

The reaction formula for the preparation of barium chromate is 2BaCl2+Na2Cr2O7+H2O→ 2BaCrO4↓+2NaCl+2HCl. In the experiment, the flask containing barium chloride solution was placed in a thermostatic water bath, and sodium dichromate solution was added dropwise to the barium chloride solution by a constant current pump. Stired the solution and kept warm for10 min after adding dropwise. Then removed the flask to be cooled to room temperature and remain for 30 min so that barium chromate can precipitate completely.In order to investigate the effect of different conditions on the yield and morphology of barium chromate, an orthogonal experiment L9(43) was designed.

1.3 Coprecipitation preparation of S/BaCrO4/KClO4 delay composition

The ratio of S, BaCrO4and KClO4was 7.5∶83∶8. The weighed sulfur powder and potassium perchlorate together with the BaCl2solution were placed in a three-necked flask, and then added an appropriate amount of methanol to make the sulfur sink to the bottom in the flask. The three-necked flask was fixed in a thermostatic water bath at 45 ℃ and stirred for 20 min to thoroughly mix the contents in the flask. Subsequently, the Na2Cr2O7solution was dropped into a three-necked flask under the action of a constant current pump, and the mixed solution was naturally cooled to room temperature while dripping, and stir was continued for 10 min after the dropwise addition. Finally, the three-necked flask was removed and kept for 20 min. Suction filtered and washed repeatedly with distilled water. The product was put in an oven and dried.

1.4 Burning performance test of delay comp-osition

According to GJB772A-97 method 606.1，the ignition temperature of 5 s delay time was tested. The burning time of delay composition was tested by photoelectric method[10].

2 Results and discussion

2.1 Optimization of preparation of barium chromate

The L9(43) orthogonal experiment for preparing barium chromate is shown in Table 1.

Table 1 Orthogonal test of preparation of barium chromate

According to the orthogonal table, set yield rate as an indicator of range analysis, the order of the four factors is D>B>A>C, and the optimal combination is A2B2C2D3. Namely, the conditions for obtaining the highest yield of barium chromate are as follows: the dripping speed is 1.17 ml/min, the concentration is 0.8 mol/L, the temperature is 45 ℃ and pH is 7.

The 1 700 Fourier transform infrared spectrometer is used to analyze the infrared spectra of barium chromate prepared by the optimal conditions. The FT-IR of the barium chromate is shown in Fig.1.

a: Standard spectrum of barium chromate; b: Spectrum of prepared barium chromateFig.1 Infrared spectrum of purity analysis of barium chromate

2.2 SEM analysis of S/BaCrO4/KClO4 co-precipitation delay composition

The morphologie of S/BaCrO4/KClO4delay composition prepared by co-precipitation method is analyzed by JSM-6700F scanning electron microscope. The SEM photographs of S/BaCrO4/ KClO4delay composition and the prepared barium chromate are shown in Fig.2.

Fig.2 SEM photographs of S/BaCrO4/KClO4 delay composition and barium chromate

From Fig.2(a), it is observed that there are some spherical particles on the surface of the irregular cakes. The size of the particles is under 1 μm, which is consistent with that of barium chromate in Fig.2(b). The sulfur powder used in the experiment is an irregular shape with a particle size of about 35 μm, and the potassium perchlorate is square with a particle size of about 15 μm. It is speculated that the larger irregularities in Fig.2(a) are that sulfur and the potassium perchlorate adheres to the outside of spherical particles. It shows that the innermost layer of the delay composition prepared by the co-precipitation method is sulfur powder, barium chromate absorbs on the surface of sulfur and potassium perchlorate adheres to barium chromate.

2.3 Results of burning performance of delay composition

The ignition temperature of 5 s delay time of S/BaCrO4/KClO4delay composition prepared by co-precipitation method and traditional mechanical mixing method are 392.6 ℃ and 347.6 ℃ respectively. The igniting temperature mainly depends on the ignition point of the combustible agent in the explosive agent. The ignition point of the sulfur powder in the delay composition is 230 ℃, while the barium chromate has a higher ignition point. It is speculated that the delay composition prepared by co-precipitation has a higher ignition point, which is due to barium chromate is wrapped on the surface of sulfur powder.

Press the delay composition into a delay tube with inner diameter of 6.9 mm and wall thickness of 0.8 mm in three times. Ignite the delay composition with 5 W laser light.The results of burning time and burning rate of S/BaCrO4/KClO4delay composition prepared by co-precipitation method and traditional mechanical mixing method are shown in Table 2.

As seen from Table 2, the standard deviation of burning time prepared by the co-precipitation method is 0.75, the average burning rate is 2.22 mm/s; while the standard deviation of the burning time mixed by the traditional mechanical mixing method is 1.96, the average burning rate is 2.04 mm/s. The delay time of the former is more uniform and the burning speed is faster, indicating that the three components in the delay composition prepared by co-precipitation method are mixed more uniform and the burning time is more accurate.

Table 2 Burning rate of S/BaCrO4/KClO4 delay composion

3 Conclusion

1) In this paper, the preparation process of barium chromate is optimized by L9(43). The optimized preparation conditions are as follows:the drpping speed is 1.17 mL/min, the concentration is 0.8 mol/L, the temperature is 45 ℃ and the pH is 7.

2) Based on the optimized conditions of barium chromate, S/BaCrO4/KClO4delay composition is prepared with barium chromate as the precipitator. The SEM photographs show that barium chromate is on the surface of sulfur powder and potassium perchlorate is adhered on barium chromate.

3) Comparing the burning properties of delay composition prepared by coprecipitation method with traditional mechanical mixing method, it is concluded that the S/BaCrO4/KClO4delay composition prepared by co-precipitation method has higher ignition temperature, faster burning rate and higher burning time precision.

[1] Xiao H, Ding S S, Xu X, et al. Controlled synthesis of barium chromate microcrystals. Crystal Research and Technology, 2014, 49(11): 919-925.

[2] Han T F. Experimental study on influencing the precision of the delay composition. Huainan: Anhui University of Science and Technoilogy, 2015.

[3] Li S J. Study on formula and preparation technology of high precision boron/barium chromate delay composition. Taiyuan: North University of China, 2011.

[4] Ma H W. Study on the performance of high presition boron serises delay composition. Huainan: Anhui University of Science and Technoilogy, 2009.

[5] Wu S Z, Shen R Q, Ye Y H, et al. Combustion characteristics of boron delayed composition. Chinese Journal of Energetic Materials, 2008, 16(5): 502-506.

[6] Hui Y L. Study on burning rate and reaction Kinetics of boron delay composition. Nanjing: Nanjing University of Science and Technology, 2008.

[7] Zhang Y. Study on the manuafeturing and combusting meehanism of thngsten type delay composition. Nanjing: Nanjing University of Science and Technology, 2005.

[8] Lu K T, Yang C C, Ko Y H. Investigation of the burning properties of slow-propagation tungsten type delay compositions. Propellants, Explosives, Pyrotechnics, 2008, 33(3): 219-226.

[9] Ren Q G, Qiao X J, Li W C, et al. Co-precipitation preparation and properties of silicon delay composition. Chinese Journal of Energetic Materials, 2012, 20(4): 409-413.

[10] Cheng C L, Liu Y C, Li S J, et al. Relationship between delay time and charging density of B/BaSO4/BaCrO4. Chenmical Intermediate, 2013, (3): 52-55.