摘要
为了探究高聚物黏结剂对奥克托今(HMX)相变行为的影响,使用压装成型工艺制备了含聚酯型聚氨酯(HMX‑Estane)、氟橡胶(HMX‑F2314)、硝化纤维素(HMX‑F2314‑NC)的HMX基高聚物黏结炸药以及纯HMX药柱,利用原位变温X射线广角散射(WAXS)技术和差示扫描量热法,研究了热刺激下样品中HMX的相变行为和机制。WAXS结果表明,HMX‑Estane(95∶5)、HMX药柱、HMX‑F2314(95∶5)、HMX‑F2314‑NC(95∶3∶2)的相变起始温度(Ti)分别为186 ℃、188 ℃、192 ℃、198 ℃。相比于HMX药柱,黏结剂中加入少量的NC(2%),Ti可提升10 ℃。真空条件下,4种样品从高温δ相降温至100 ℃保温,只有HMX‑Estane发生了δ→β逆相变且在3.5 h内δ相全部转变为β相,而其他样品均未发生相变,仍为δ相。β‑HMX在HMX‑Estane界面位置的溶解(升温过程)和析出(降温过程)可能是促进HMX‑Estane发生β→δ相变,及其逆相变的主要因素。
图文摘要
奥克托今(HMX)的β→δ相变或δ→β逆相变过程,会导致HMX炸药内部产生显著的损伤(孔洞、微裂纹、界面脱粘
晶粒尺寸、晶体品质以及黏结剂等多种因素均会影响HMX的相变行
为探究黏结剂对HMX相变的影响,制备了含聚氨酯、氟橡胶和NC三种典型黏结剂的高聚物黏结炸药以及不含黏结剂的纯HMX药柱,重点使用原位变温广角X射线散射(WAXS)技术,研究了真空条件下升温和降温过程黏结剂对HMX相变行为的影响。相比于多晶X射线衍射(反射式)、拉曼、红外等测试技
重结晶HMX晶体颗粒,密度为1.90 g·c
利用奥地利Anton Paar公司的SAXSpace散射仪测试样品的WAXS数据,工作电压和电流分别为40 kV和50 mA,X射线波长(λ)为0.154 nm,样品与探测器的距离为121 mm。使用分辨率为50 μm的Mythen2 R 1K探测器(瑞士,Dectris公司的)记录透过样品的X射线散射强度(I)和位置,通过散射几何和λ计算出I与散射矢量q(q=4πsinθ/λ,其中θ等于二分之一散射角)的关系。所探测的q值范围为0.45~18.5 n
采用水悬浮工艺制备HMX的模压成型造型粉:首先将HMX晶体颗粒投入60 ℃的去离子水中,然后搅拌,再缓慢滴加高聚物黏结剂溶液,随着有机溶剂的挥发,并在黏结剂的黏附及搅拌离心力作用下,HMX晶体颗粒逐步团聚成
对所有样品设置相同的控温程序,升降温速率为10 ℃·mi
为了验证Estane和F2314与HMX的热相容性,另设计了三组对比验证实验。取两份Esatne固体样品(尺寸约为20 mm×10 mm×2 mm)分别作为第一组和第二组,取一份F2314固体样品作为第三组。三组样品均加热到100 ℃,然后,分别在其表面撒少许平均粒径为5 μm的HMX晶体颗粒。第一组样品继续在100 ℃保温4 h,第二组和第三组样品则加热到180 ℃并保温1 h。
4种样品的原位变温WAXS实验结果如

a. HMX‑disc

b. HMX‑Estane

c. HMX‑F2314

d. HMX‑F2314‑NC
图1 升温过程4种样品的WAXS曲线图
Fig.1 WAXS curves of the four samples during heating

图2 4种样品的DSC曲线图
Fig.2 DSC curves of the four samples
已有理论计算表明,NC、F2314、Estane与HMX晶体的结合能分别为699、372、357 kJ·mo
HMX与Estane和F2314的热相容实验结果如

a. group 1

b. group 2

c. group 3

d. group 1 (100 ℃,4 h)

e. group 2 (180 ℃,1 h)

f. group 3 (180 ℃,1 h)
图3 HMX粉末与Estane(第一组、第二组)和F2314(第三组)的热相容实验光学照片
Fig.3 Optical photos of thermal compatibility experiments of HMX powders with Estane (groups 1 and 2) and F2314 (group 3)
4种样品从高温(δ相)降至室温后的W AXS实验结果如

a. HMX‑disc

b. HMX‑Estane

c. HMX‑F2314

d. HMX‑F2314‑NC
图4 4种样品从210 ℃(δ相)降至室温后的WAXS曲线图
Fig.4 WAXS curves of the four samples after cooling from 210 ℃ (δ phase) to room temperature

图5 4种样品从210 ℃(δ相)降至100 ℃保温的WAXS曲线图
Fig.5 WAXS curves of the four samples at 100 ℃ after cooling from 210 ℃ (δ phase)

图6 HMX‑Estane从210 ℃(δ相)降至100 ℃保温的WAXS曲线图
Fig.6 WAXS curves of HMX‑Estane at 100 ℃ after cooling from 210 ℃ (δ phase)
4种样品在相对湿度大于75%的空气环境中放置2 d后,其WAXS曲线中均只有β‑HMX的衍射峰,说明δ‑HMX已完全转变为β‑HMX(
结合
(1)原位变温WAXS结果表明,4种样品的Ti由大到小依次为:HMX‑F2314‑NC(198 ℃)>HMX‑F2314(192 ℃)>HMX‑disc(188 ℃)>HMX‑Estane(186 ℃)。
(2)在黏结剂中加入2%质量比的NC,即可显著抑制HMX的β→δ相变(Ti提升10 ℃);在真空环境中,从高温(δ‑HMX相)降温至100 ℃,只有HMX‑Estane发生了δ→β逆相变,3.5 h内所有δ相转变为β相。
(3)Estane既可促进HMX的β→δ相变,又可促进其逆相变,这可能源于升降温度过程β‑HMX在HMX‑Estane界面位置的溶解、析出特性。
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