Small‐scale laboratory experiments were performed to analyze gas transport mechanics in PBX 9502, an insensitive high explosive (IHE) composition. Two independent investigations are reported here. First, gas permeametry and dynamic pycnometry techniques were used to measure the molecular flow (Knudsen) coefficient and the internally interconnected void fraction of pristine and thermally damaged samples in two uniaxial pressing orientations. The permeability of PBX 9502 was found to be unmeasurably low (of the same order of magnitude as PTFE) with gas transport being diffusion‐dominated. Secondly, a pressure vessel experiment was developed to measure quasi‐static and dynamic gas generation as the explosive was heated to self‐ignition (cookoff). The gas generation results and the permeability/diffusivity findings provide evidence that PBX 9502 remains impermeable until seconds prior to self‐ignition. At ignition, internal void‐pressure drives macro‐scale cracking and the sample becomes uniformly incorporated in the following deconsolidating deflagration. These results are discussed within the context of previous observations of pressure‐dependent cookoff behavior of PBX 9502 and provide a more complete description of thermal damage evolution in this explosive composition.

中文翻译：

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不敏感的易爆PBX 9502中的气体传输

进行了小型实验室实验，以分析PBX 9502（一种不敏感的高爆炸物（IHE）成分）中的气体传输机理。这里报告了两项独立的调查。首先，使用气体渗透法和动态比重瓶技术，在两个单轴压制方向上测量原始和热损伤样品的分子流量（Knudsen）系数和内部互连的空隙率。发现PBX 9502的渗透率非常低（与PTFE处于同一数量级），而气体传输以扩散为主。其次，开展了一个压力容器实验，以测量炸药加热至自燃时的准静态和动态气体生成（蒸煮）。气体生成结果和渗透率/扩散率发现提供了证据，表明PBX 9502直到自燃前几秒钟仍保持不渗透。着火时，内部空隙压力会导致宏观裂纹，并且样品在随后的解体爆燃中变得均匀。这些结果是在先前对PBX 9502的压力依赖性蒸煮行为的观察中讨论的，并提供了对该炸药成分中热损害演变的更完整描述。