摘要
为了提升硼粉的点火燃烧性能,采用高能球磨与喷雾干燥相结合的技术制备了4种微纳米B‑Fe‑Bi2O3@AP/PVDF复合物,根据其高热值和高燃烧效率的特点将四种复合物命名为μBHHc、μBHCe、nBHHc及nBHCe,并对其形貌结构、热反应性、点火延迟、质量燃速和凝聚相产物进行了表征分析。结果表明,μBHHc和μBHCe复合物在氩气中最大热值达9.7 kJ·
图文摘要
高能固体推进剂是未来导弹和航天技术发展的重要方向,一般采用添加金属/非金属/金属氢化物燃料和高能氧化剂来提升其能量水平。常用燃料主要有硼(B)、铝(Al)、镁(Mg)和三氢化铝(AlH3)。其中,硼因高质量热值和体积热值而备受青
目前改性硼可用的材料包括氟聚
此外,AP/PVDF含卤复合氧化剂体系已在铝改性中被广泛研
基于以上研究结果,本研究选用Fe在硼表面合金化处理后,将AP/PVDF含卤复合氧化剂包覆其表面,并引入Bi2O3作为催化剂,设计制备了四种微纳米B‑Fe‑Bi2O3@AP/PVDF复合物,根据其高热值和高燃烧效率的特点将四种复合物命名为μBHHc、μBHCe、nBHHc及nBHCe,并对其形貌结构、热反应性、点火延迟、质量燃速和凝聚相产物进行了表征分析。
实验材料:微米硼(粒径1~5 μm)由营口市辽滨化工有限公司提供,纳米硼(粒径500~700 nm)由湖北航天化学技术研究所提供。Fe(以团聚体形式存在,粒径1~9 μm,中值直径D50 2.6 μm)由广州市宏武新材料科技有限公司提供,Bi2O3(粒径100~300 nm,中值直径D50 224 nm)由贤信新材料科技有限公司提供,PVDF(平均分子量534000)由上海易恩化学技术有限公司提供,AP(100~125 μm)由西安近代化学研究所提供。
仪器:行星式球磨机(XQM‑2‑DW),长沙天创粉末技术有限公司;冷冻干燥机(FD‑100),上海田枫技术有限公司;喷雾干燥机(YC‑015),上海雅程仪器设备有限公司;扫描电子显微镜SEM(ZEISS sigma500),德国蔡司技术有限公司;激光粒度仪(Mastersizer 3000),马尔文设备有限公司;氧弹量热仪(ZDHW‑HN7000C),鹤壁市华能电子科技有限公司;热重‑差示扫描量热仪TG‑DSC(NETZSCH、STA‑692F5),德国耐驰仪器制造有限公司;激光点火测试平台,海御虹激光设备有限公司;新型多功能推进剂燃烧诊断系统,自研。
在微米硼中,由于表面氧化膜的存在导致其点火困难。在纳米硼中,还存在粒度不均匀的问题,需要将大颗粒除去。通过预处理,可除去微米硼中部分氧化膜,也可使纳米硼在除去部分氧化膜的同时优化粒径,不同材料预处理过程如下:
微米硼的预处理:在500 mL烧杯中加入300 mL去离子水,称量24 g NaOH并转移至烧杯中,配置浓度为2 mol·

图1 处理后微纳米硼的粒径分布图
Fig.1 Particle size distribution of micron and nano boron after processing
纳米硼的预处理:将纳米硼溶于乙醇溶液中,静置10 min使其自然分层,分层后将上层溶液用移液管进行分离,并将分离后的溶液抽滤。将产物冷冻干燥12 h后得到处理后的纳米硼。对处理后的纳米硼进行激光粒度测试,发现其D10为131 nm,D50为175 nm,D90为240 nm(
高能球磨法和喷雾干燥法是常用的制备改性硼基复合物的方法。通过高能球磨可将各类材料粉末按比例机械混合,并在磨球介质的反复冲撞下,经受碰撞冲击而不断挤压变形。高强度较长时间的研磨可使各类粉末充分细化,最终成为均匀分布的复合粉
高能球磨制备B‑Fe‑Bi2O3复合物的制备:在行星式球磨机上,加入9.7 g预处理后硼粉、0.1 g Fe、0.2 g Bi2O3及100颗钢制小球后倒入25 mL的正己烷,以200 r·mi
喷雾干燥制备微纳米B‑Fe‑Bi2O3@AP/PVDF复合物的制备:将AP和PVDF在N,N‑二甲基甲酰胺溶液中混合,室温磁搅拌2 h,再加入高能球磨制备出的B‑Fe‑Bi2O3复合物,室温磁搅拌2 h,制得的悬浮液用于喷雾造粒。最后,采用喷雾干燥技术制备硼基复合物。喷雾干燥参数:进料孔直径为1 mm,入口温度125 ℃,风机速度35转,流体流速为8 mL·mi
采用激光粒度仪对复合物粒度进行分析,测试条件为:200 mL乙醇分散,测试前超声5min;采用扫描电镜对复合物微观结构进行分析,测试条件为:工作距离8.5 mm,加速电压15 kV。采用热重‑扫描量热仪测定复合物的热反应性,测试条件为:空气环境,样品以10 ℃·mi
采用激光点火平台对复合物的点火延迟进行分析。测试系统主要由同步触发的水冷CO2激光发生器、光纤光谱仪及高速相机组成。光谱仪(积分时间3 ms)与CO2激光发生器同步触发,记录整个燃烧过程的光谱数据,计算位于547 nm处BO2的特征光谱峰强度达到其最强辐射度10%的时间,该时间与触发点火的时间间隔即为待测样品的点火延迟时间。在开放环境(1 atm,25 ℃)中测试,待测样品为粉末
采用多功能燃烧诊断系统对复合物的火焰结构、燃烧温度、质量燃速等参数进行分析。该系统主要包括高压燃烧器(配蓝宝石和有机玻璃视窗各一个)、控压系统、控制系统(负责传达点火、充/放气、电磁阀开/关和数据采集指令)、高速相机和高速红外热像仪。点火指令下达后,利用两端接有24 V电源的镍铬点火丝(Φ=0.5 mm)引燃复合物粉末(500 mg,平铺在石英坩埚表面,并压实),采用iX Cameras高速相机记录燃面退移过程(曝光时间10 μs,帧率250 fps),将第一次与最后一次出现火苗的时间间隔作为复合物的燃烧时间,并通过复合物质量除以燃烧时间计算质量燃
本研究基于高热值和高燃烧效率进行配方设计,首先对B/AP复合物(机械研磨制备)进行热值及燃烧效率测试,得到热值和燃烧效率最高的B/AP复合物配方;其次使用PVDF部分替换AP,对B/AP/PVDF(机械研磨制备)进行热值及燃烧效率测试,最终得到高热值高燃烧效率的B/AP/PVDF复合物配方。
对B/AP复合物(机械研磨制备)进行热值及燃烧效率测试,发现当B∶AP投料比为1∶4时复合物爆热最大达8.2 kJ·

a.

b.

c.

d.
图2 热值和燃烧效率随B/AP/PVDF体系中AP含量变化的Gauss拟合图
Fig.2 Gauss fitting plot of calorific value and combustion efficiency with changes of AP content in B/AP/PVDF system
根据2.1中配方设计结果以1.2.2中制备方法对μBHHc、μBHCe、nBHHc和nBHCe四种复合物进行制备,对所制备的μBHHc、μBHCe、nBHHc及nBHCe复合物进行了热值测量,并计算了它们的燃烧效率,结果如
atmosphere | complex | mass calorific value / kJ· | normalization / kJ· | combustion Efficiency / % | density / g·c | volumetric calorific value / kJ·c |
---|---|---|---|---|---|---|
Ar | μBHHc | 9.7 | 31.6 | 55.2 | 2.12 | 20.6 |
Ar | nBHHc | 9.9 | 32.2 | 56.1 | 2.11 | 20.8 |
O2 | μBHHc | 14.6 | 51.5 | 89.9 | 2.12 | 31.2 |
O2 | nBHHc | 14.8 | 52.3 | 91.3 | 2.11 | 31.3 |
Ar | μBHCe | 9.1 | 37.9 | 66.2 | 2.11 | 19.2 |
Ar | nBHCe | 9.3 | 39.5 | 68.9 | 2.10 | 19.5 |
O2 | μBHCe | 12.3 | 53.5 | 93.3 | 2.11 | 26.1 |
O2 | nBHCe | 12.6 | 55.7 | 97.2 | 2.10 | 26.5 |
对原材料与制备的μBHHc、μBHCe、nBHHc及nBHCe复合物进行形貌结构表征,结果如

图3 原材料、μBHHc、μBHCe、nBHHc及nBHCe复合物的SEM图
Fig.3 SEM images of raw materials and μBHHc, μBHCe, nBHHc and nBHCe composite
对制备的μBHHc、μBHCe、nBHHc及nBHCe复合物(
在空气中以升温速率10 ℃·mi

图4 μBHHc、μBHCe、nBHHc及nBHCe复合物在升温速率10 ℃·mi
Fig.4 TG‑DSC curves of μBHHc, μBHCe, nBHHc and nBHCe in air at the heating rate of 10 ℃·mi
Complex | CB / % | WAPl / % | WBg / % | TAPt / ℃ | TAPl / ℃ | TAPh / ℃ | TBo / ℃ | Hr / kJ· |
---|---|---|---|---|---|---|---|---|
μBHCe | 14.3 | 88.7 | 13.8 | 249.9 | 308.4 | 348.4 | 757.5 | 3.0 |
μBHHc | 20.0 | 82.6 | 24.8 | 247.7 | 307.1 | 342.3 | 749.1 | 3.5 |
nBHCe | 14.3 | 83.6 | 16.0 | 250.4 | 299.8 | 337.9 | 595.9 | 3.4 |
nBHHc | 20.0 | 79.7 | 17.6 | 250.4 | 296.1 | 330.5 | 595.7 | 3.7 |
Note: CB means effective boron content, WAPl means AP decomposition quality loss, WBg means boron oxidation weight gain, TAPt means AP transition temperature, TAPl means AP low‑temperature decomposition temperature, TAPh means AP high‑temperature decomposition temperature, TBo means modified boron oxidation temperature, and Hr means heat release.
由
值得注意的是,这4种复合物AP分解质量损失均达到了80%左右,其中μBHCe复合物质量损失最高达88.7%。结合文献[
利用1.3节介绍的思路和方法对μBHHc、μBHCe、nBHHc及nBHCe复合物的点火性能进行探究,4种复合物的光谱强度变化趋势如

a. μBHCe

b. μBHHc

c. nBHCe

d. nBHHc
图5 μBHHc、μBHCe、nBHHc及nBHCe复合物光谱强度趋势图
Fig.5 Trend of spectral intensity of μBHHc, μBHCe, nBHHc and nBHCe
4种复合物最大辐射位置处200~1100 nm之间的光谱如

a. spectra

b. peak radiance‑ignition delay time
图6 μBHHc、μBHCe、nBHHc及nBHCe复合物最大辐射处200~1100 nm光谱和μBHHc、μBHCe、nBHHc及nBHCe复合物BO2峰辐射度随点火延迟的关系
Fig.6 Spectra of the maximum radiation at 200-1100 nm for μBHHc, μBHCe, nBHHc and nBHCe composite, and relationship between peak radiance of BO2 and ignition delay time for μBHHc, μBHCe, nBHHc and nBHCe composite
利用燃烧诊断法对μBHHc、μBHCe、nBHHc及nBHCe复合物进行火焰结构及传播特性燃烧探究实验,4种复合物燃烧过程如

图7 μBHHc、μBHCe、nBHHc及nBHCe复合物高速相机拍摄图
Fig.7 High speed camera captures images of flame structures of μBHHc, μBHCe, nBHHc and nBHCe composite
由
complex | flame growth time / ms | duration of combustion / ms | flame attenuation time / ms | total combustion time / ms | mass burning rate / g· |
---|---|---|---|---|---|
μBHCe | 280(44.3%) | 228(36.1%) | 124(19.6%) | 624 | 0.80 |
μBHHc | 212(39.4%) | 260(48.3%) | 66(12.3%) | 538 | 0.93 |
nBHCe | 100(27.8%) | 96(26.7%) | 164(45.5%) | 356 | 1.40 |
nBHHc | 72(26.5%) | 84(30.9%) | 116(42.6%) | 272 | 1.84 |
Note: The flame growth time is defined as the time from the appearance of the flame to the formation of the mushroom cloud flame cluster. The duration of combustion is defined as the duration of the mushroom cloud flame. The flame decay time is defined as the time from the weakening of the mushroom cloud flame to the disappearance of the flame. The mass burning rate is defined as the mass of B‑based fuel divided by the total combustion time of B‑based composite, the percentage in parentheses refers to the percentage of this time to the total combustion time.
除此之外,利用红外摄像机获得了4种复合物达到最高燃烧温度时的燃烧波结构,结果如

图8 μBHHc、μBHCe、nBHHc及nBHCe复合物达到最高温度时红外拍摄图
Fig.8 Infrared images of μBHHc, μBHCe, nBHHc and nBHCe when the composites reach their highest temperature
μBHHc、μBHCe、nBHHc及nBHCe复合物凝聚相燃烧产物(CCPs)的显微镜照片如

图9 μBHHc、μBHCe、nBHHc及nBHCe复合物燃烧产物的显微镜照片
Fig.9 Microscopic photos on the combustion products of μBHHc, μBHCe, nBHHc and nBHCe composite
μBHHc、μBHCe、nBHHc及nBHCe复合物燃烧产物的凝聚相燃烧产物(CCPs)的物相组成如

图10 μBHHc、μBHCe、nBHHc及nBHCe复合物燃烧产物的显微镜照片
Fig.10 Microscopic photos on the combustion products of μBHHc, μBHCe, nBHHc and nBHCe composite
由
在这4种复合物中,AP分解产生N2,H2O,Cl2和O2等气体,PVDF分解产生气态HF和固态C。HF与硼表面氧化膜B2O3反应生成气态BF3和H2O,因此,覆盖在硼表面的氧化膜很容易被去除,便于硼与氧直接接触。当硼表面的氧化膜除去后,裸露的硼会与PVDF分解产生的碳和体系中的氧发生反应,硼与碳反应生成B4
以微纳米硼、AP、PVDF、Fe、Bi2O3为原材料,采用高能球磨与喷雾干燥相结合的工艺,成功制备了4种微纳米B‑Fe‑Bi2O3@AP/PVDF复合物,根据其高热值和高燃烧效率的特点将4种复合物命名为μBHHc、μBHCe、nBHHc及nBHCe,并对其形貌结构、热反应性、点火延迟、质量燃速和凝聚相产物进行了表征分析。主要研究结论如下:
(1)当B‑Fe‑Bi2O3/AP/PVDF质量配比为15∶53∶7时,其热值最高;质量配比为10∶53∶7时,其燃烧效率最高。μBHHc复合物最大爆热达9.7 kJ·
(2)μBHHc和μBHCe复合物氧化温度集中在750~760 ℃,AP的低温分解峰集中在307~308 ℃;nBHHc和nBHCe复合物氧化温度集中在595~600 ℃,AP的低温分解峰集中在295~300 ℃。nBHHc和nBHCe复合物热反应活性较μBHHc和μBHCe复合物高。
(3)4种硼基复合物的最高燃烧温度在1954~2011 ℃之间,其中nBHHc复合物的点火延迟最短(26 ms),且质量燃速最高(1.84 g·
(4)4种硼基复合物燃烧产物主要由B2O3、B4C及少量未完全燃烧的硼组成,其形貌包含5~10 μm的球体及10~20 μm的片状产物。
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