摘要
硼粉因其较高的质量热值、体积热值和洁净的燃烧产物,常被用作可燃剂,然而硼粉表面的氧化层使硼粉点火困难且燃烧效率低。为此,研究利用氧化硼在乙腈溶剂中易溶解的特性,以热乙腈为控制剂湿法球磨硼粉,去除其表面氧化膜得到活性较高的预处理硼粉;再以乙腈⁃正己烷为双控制剂,将其与高活性金属铝二次球磨得到硼铝质量比分别为10/90,20/80,30/70,40/60的硼铝复合粉。对预处理硼及硼铝复合粉的形貌特征、热重、点火与燃烧特性进行了测试。结果表明:预处理硼粉的表面氧化硼含量降低,在空气中加热时更容易与氧气反应,质量增加百分数比未处理的硼粉多25.6%;所得硼铝复合粉的表面氧化硼的含量降低,活性硼含量增高,点火燃烧性能显著得以改善,其中硼铝质量比例为60/40的复合粉在空气中加热质量增加93%,低加热速率下点火温度为738.1 ℃,颗粒燃烧时间为11.2 ms。
图文摘要
The boron powder was pretreated with acetonitrile, and then the composite powders of different mass ratio of boron and aluminum were successfully prepared using a wet‑milling method. Their thermal oxidation, ignition and combustion properties were systematically characterized. The effects of oxide layer and boral ratio on properties were analyzed.
含能材料是一类含有爆炸性基团的化合物或含有氧化剂与可燃物、能独立进行化学反应并输出能量的混合物。为了提高含能材料的能量密度,常向其中加入能量较高的金属/非金属燃料,如镁、铝、
为进一步提高硼粉的活性,改善其点火燃烧性能,在仅采用单一方法对硼进行改性的基础上,本研究先利用乙腈去除硼粉表面的氧化层,再采取双控制剂‑球磨法来制备硼铝复合粉,对所得硼铝复合粉进行形貌表征、点火实验与燃烧实验。研究乙腈预处理对硼粉表面氧化层的去除效果和乙腈预处理、铝粉含量对硼粉以及硼铝复合粉热重、点火与燃烧特性的影响规律。
原料及试剂:无定形硼粉(纯度98%,粒径<5 μm)、铝粉(粒径1 μm)、乙腈(色谱级,纯度99.9%)、正己烷(Q/CYTGJ 013‑2011),以上原料及试剂均由上海迈瑞尔化学技术有限公司提供。其中乙腈和正己烷可按体积比1∶3配置出制备硼铝复合粉所需的过程控制剂。
仪器:PMQ4L 全方位行星式球磨机,中国卓的仪器设备(上海)有限公司;NETZSCH TG 209F1热重分析仪,德国NETZSCH公司;G300扫描电镜,德国Carl Zeiss AG公司;FDR‑AX700索尼高速摄像机,中国索尼公司;Omega OS‑4000红外测温仪,温度覆盖范围为240~1500 ℃(240 ℃以下都直接默认为240 ℃),中国DwyerOmega公司。
实验时,先将硼粉和乙腈按质量比1∶3混合后进行球磨预处理,然后分别将经乙腈预处理的硼粉(boron‑treated)和未经乙腈预处理的硼粉(boron‑untreated)与铝粉按照不同质量比混合,制备出不同组分的硼铝复合粉(硼铝混合粉与过程控制剂质量比为1∶6)。
sample | wAl / % | wB / % |
---|---|---|
10Al/90B‑treated | 10 | 90 |
10Al/90B‑untreated | 10 | 90 |
20Al/80B‑treated | 20 | 80 |
20Al/80B‑untreated | 20 | 80 |
30Al/70B‑treated | 30 | 70 |
30Al/70B‑untreated | 30 | 70 |
40Al/60B‑treated | 40 | 60 |
40Al/60B‑untreated | 40 | 60 |
Note: wAl is aluminum content. wB is boron content. BPR(ball to powder weight ratio) is 10, milling time is 1 h.

图1 颗粒点火实验装置示意图
Fig.1 Schematic diagram of particle ignition experimental device

图2 颗粒燃烧实验装置示意图
Fig.2 Schematic diagram of particle combustion experimental device
为了分析硼粉以及硼铝复合粉的形貌学特征,研究采用扫描电镜对硼粉(boron‑treated/ boron‑untreated)以及硼铝复合粉中的40Al/60B‑untreated和40Al/60B‑treated样品进行了形貌学测试,电子束的加速电压为2 kV,结果如

a. boron‑untreated

b. boron‑treated

c. 40Al/60B‑untreated

d. 40Al/60B‑treated
图3 样品扫描电镜图
Fig.3 Scanning electron microscopy images of sample
为了研究硼粉以及硼铝复合粉的热分解性能,对2种硼粉(boron‑treated/ boron‑untreated)以及8种硼铝复合粉在空气中的热重性能进行了测试。其中硼粉的测试温度范围为35~700 ℃,硼铝复合粉的测试温度范围为35~950 ℃,升温速率皆为5 ℃·mi

a. mass variation curves

b. mass variation rate curves
图4 boron‑treated和boron‑untreated的质量变化曲线和质量变化速率曲线
Fig.4 Thermo‑gravimetric curve and mass variation rate curve of boron‑treated and boron‑untreated powders

a. mass variation rate curves

b. mass gain curves
图5 不同硼铝质量比的样品在空气中加热的热重曲线
Fig.5 Thermo‑gravimetric curve of samples with different B/Al mass ratios heated in air
为了探究乙腈预处理以及硼铝比例对复合粉点火温度的影响,研究对硼铝复合粉的点火温度进行了测试,硼铝复合粉在不同加热速率下的点火温度如

图6 复合粉的点火温度图
Fig.6 Ignition temperature diagram of composite powder
通过分析高速相机拍摄的样品点火过程的图像,可以准确确定样品的点火时刻。为了探究乙腈预处理以及硼铝比例对复合粉点火过程的影响,研究对硼铝比例分别为90/10和60/40的复合粉在低加热速率下的点火图像进行了分析,如

a. 10Al/90B‑untreated(Tig=840.1 ℃)

b. 10Al/90B‑treated(Tig=775.7 ℃)

c. 40Al/60B‑untreated(Tig=760.8 ℃)

d. 40Al/60B‑treated (Tig=738.1 ℃)
图7 不同复合粉在低加热速率下的点火图像
Fig.7 Ignition images of different composite powders at low heating rates

a. 40Al/60B‑untreated(Tig=805.1 ℃)

b. 40Al/60B‑treated(Tig=797.7 ℃)
图8 40Al/60B‑untreated和40Al/60B‑treated在高加热速率下的点火图像
Fig.8 Ignition images of 40Al/60B‑untreated and 40Al/60B‑treated samples at high heating rates
通过分析光电倍增管记录的发光信号曲线中的脉冲持续时间可以得到颗粒的燃烧时间。

图9 样品颗粒燃烧时典型的发光信号曲线(700 nm)
Fig.9 Typical luminescence signal curve of sample particle during combustion(700 nm)

图10 复合粉燃烧时间随硼铝比变化图
Fig.10 Change of composite powder combustion time with the ratio of boron to aluminum
为了改善硼粉的点火及燃烧性能,研究采用以热乙腈为控制剂的湿法球磨方法去除硼粉表面氧化膜,获得了活性较高的预处理硼粉,并制备了不同比例的高活性硼铝复合粉。对硼粉以及硼铝复合粉进行了热重分析、点火和燃烧试验。研究结果表明:
(1)通过以热乙腈为控制剂的湿法球磨方法能够使硼粉表面的氧化层厚度变薄,提高硼粉中活性硼的含量。在空气中加热后,boron‑untreated增重56.1%,boron‑treated增重81.7%。
(2)当样品中的硼粉经过乙腈预处理后,点火延迟时间缩短,且复合粉中铝粉含量越高,复合粉的点火延迟时间越短,颗粒点火发光区域越大,点火温度越低。各样品中40Al/60B‑treated点火温度最低,在高、低加热速率下分别为797.7 ℃和738.1 ℃。
(3)硼铝复合粉在加热的情况下,铝粉先被点燃,放出的热量为硼粉的点火和燃烧提供热量,从而致使硼更容易点火。经过乙腈预处理的样品燃烧时间始终长于同种硼铝比下未经乙腈预处理的样品,且随着铝粉含量的增加,燃烧时间逐渐增长。所有样品中硼铝质量比为40/60的样品燃烧时间最长,40Al/60B‑untreated为10.9 ms,40Al/60B‑treated为11.2 ms。
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