摘要
为了研究2,6‑二氨基‑3,5‑二硝基吡嗪‑1‑氧化物(LLM‑105)的结晶成核过程,利用CrystlScan多通道结晶仪测量了不同过饱和度比下LLM‑105反溶剂结晶成核诱导期。采用诱导期测量法研究了过饱和度对LLM‑105成核的影响并结合经典成核理论计算了成核的重要参数。结果表明,LLM‑105反溶剂结晶的诱导期随过饱和度的增大而降低。当过饱和度比S<2.53时,主要发生异相成核,界面张力γ值为6.67717×1
图文摘要
The influence of supersaturation on the nucleation of LLM‑105 was investigated based on the induction period measurement method. The nucleation induction periods of LLM‑105 with different supersaturation ratios were obtained by measuring the turbidity. Based on the results of anti‑solvent crystallization experiments and the classic nucleation theory, the nucleation and growth mechanisms of LLM‑105 were determined.
溶液结晶广泛应用于炸药晶体的制备,不仅在炸药分离和纯化过程中起重要作用,而且在炸药晶体的颗粒大小和形貌控制方面起至关重要的作用。炸药晶体颗粒的大小和形貌不仅影响炸药本身的物化性能和安全性能,而且与浇注、压装等装药工艺的流变性、成型性、安全性以及装药固含量等密切相关,显著影响炸药的起爆、传爆性能,决定了炸药应用的广度和深
成核是结晶过程的第一步,也是关键的一步,影响晶体的形貌、尺寸及其分布、多晶型和晶体产物的纯度
2,6‑二氨基‑3,5‑二硝基吡嗪‑1‑氧化物(LLM‑105)是通过分子设计成功合成的波形层状晶体结构,层内有强的分子内和分子间氢键,层间是π‑π作用,这种独特的分子结构,使得LLM‑105表现出优异的能量和安全性
根据经典成核理论,物质在特定的温度下在溶剂里的溶解度是恒定的,当溶液达到过饱和时,溶液处于不平衡状态,整体吉布斯自由能降低,形成临界尺寸的晶核,成核速率和过饱和度比关系如
(1) |
式中,A为指前因子;ΔGc为临界成核自由能;γ为界面张力,J·
过饱和度是溶液结晶的驱动力,对于反溶剂结晶,通过加入反溶剂降低溶质在溶液中的溶解度从而达到过饱和,反溶剂的加入使溶液达到过饱和的同时也在稀释溶液,因此,反溶剂结晶过饱和度可以定义为溶质加入反溶剂前后浓度差值,过饱和度比可以简化
(2) |
式中,C为溶液浓度,g·m
诱导时间是描述成核速率的一个重要参数,并且和成核速率成反
(3) |
因此,可以将
(4) |
式中,K为无量纲的经验常数,根据
(5) |
在特定温度和溶液组合下溶质结晶界面张力γ可以从斜率B中获
(6) |
根据界面张力γ,可以通过下式进一步求得表面熵因子f
(7) |
这些参数的定义与
对于经典均相成核理
(8) |
根据
(9) |
临界成核数量可以由(10)式计算:
(10) |
LLM‑105原料由中国工程物理研究院化工材料研究所提供(纯度>99%),DMSO、乙酸乙酯,天津致远化学试剂有限公司,均为分析纯直接使用,超纯水,自制。
Crystal SCAN多通道结晶仪(E1320,United Kingdom He.,Ltd.),其原理可参看文献[

图1 诱导期测定试验装置图
Fig.1 Sketch of the apparatus for determination of inducing time
根据LLM‑105在DMSO中的溶解度曲
通过测量LLM‑105溶液在结晶过程中的浊度变化情况来确定诱导期。

图2 LLM‑105溶液浊度与时间关系曲线
Fig.2 Curve of turbidity VS induction time in LLM‑105 anti‑solvent crystallization
在相同的反应温度、初始浓度、搅拌速度实验条件下,研究了过饱和度对LLM‑105结晶过程中的成核诱导期的影响。

图3 LLM‑105反溶剂结晶过程中过饱和度比与诱导期的关系
Fig.3 Relations between induction time and supersaturation ratio of LLM‑105 anti‑solvent crystallization

图4 不同饱和度比下浊度随时间变化曲线
Fig.4 Curves of various turbidity over time at different saturation ratios
由
首先,根据经典成核理论,采用获得的成核诱导期实验数据,根据

图5 LLM‑105反溶剂结晶l
Fig.5 Dependence of l
经计算,两条直线的交点所对应的过饱和度比S值为2.53,因此可以判定过饱和度比在S<2.53范围时,LLM‑105反溶剂结晶为异相成核,过饱和度比在S>2.53范围,LLM‑105反溶剂结晶为均相成核。根据
S is the supersaturation ratio. K is the intercept. B is the slope.
两条直线的相关系数
再根据公式(
S is the supersaturation ratio. J is the nucleation rate. r is the the radius of the critical nucleus. i is the number of molecules in the critical nucleus.

图6 过饱和度比与成核速率的关系图
Fig.6 Curve of supersaturation ratio VS nucleation rate

图7 过饱和度比与临界晶核半径和临界成核数量的关系图
Fig.7 Curve of supersaturation ratio VS radius of nucleus and the number of molecules in the critical nucleus.
(1)在LLM‑105反溶剂结晶过程中,过饱和度显著影响LLM‑105的成核。成核诱导期随着过饱和度比的增大而降低,当过饱和度比为1.83~2.67时,诱导期随过饱和度比的增加降低趋势比较明显,当过饱和度比为2.67~4.33时,诱导期随过饱和度比的变化比较平缓。
(2)基于获得的成核诱导期实验数据,结合经典成核理论进行计算,结果表明,当过饱和度比S<2.53时,主要发生异相成核;当S>2.53时,主要发生均相成核。当过饱和度比S<2.53时,界面张力γ值为6.67717×1
(3)基于获得的成核诱导期实验数据,结合经典成核理论,进一步计算得到了不同过饱和度比条件下LLM‑105的成核速率J,临界晶核半径r和临界成核数量i等成核参数。结果表明,均相成核时,成核速率随着过饱和比的增加而增加,临界晶核半径和临界成核数量均随着过饱和度比的增加而减小。
(责编: 高 毅)
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