Chemical time delays, devices that burn over specific times from under a millisecond to several seconds, are widely used in mining as well as civilian and military pyrotechnics and generally are composed of environmentally hazardous materials. Reactive nanolaminates are energetic materials composed of two or more reactants organized in an alternating layered structure, which may be fabricated with environmentally friendly components. Many traits of reactive nanolaminates are desirable for time delay applications, including their long shelf life and their highly repeatable and finely tunable reaction velocities. However, their reaction velocities are generally too high to be broadly applicable in chemical time delays. In this work, we use polymer mesh substrates to produce a constrained network of reactive particles, which reduce the reaction velocity of Al/Ni multilayers approximately 100× from a range of 2.8 to 7 m s^–1 to a range of 7 to 90 mm s^–1. This is accomplished via an interrupted reaction mechanism wherein individual particles on the coated mesh react rapidly but exhibit a delay before igniting neighboring particles due to the required heat transfer at the particles’ interfaces. We present the macroscale reaction velocities as a function of substrate composition and size, as well as reactive coating thickness and bilayer spacing. We employ high-speed videography to probe the ignition delays and finite element analysis simulations to aid in explaining the observed trends. Through selection of substrate and coating properties, time delays spanning a large range of delay times can be packaged into standard form factors.

中文翻译：

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基于反应性纳米层压板间断反应的环保化学时延

化学时间延迟（在特定时间范围内从一毫秒到几秒燃烧的设备）已广泛用于采矿以及民用和军用烟火中，并且通常由对环境有害的材料组成。反应性纳米层压板是由两种或多种反应物组成的高能材料，这些反应物以交替的层状结构组织，可以与环境友好的组件一起制造。对于延时应用而言，反应性纳米层压板的许多特性是理想的，包括它们的长期保存期限以及高度可重复和可微调的反应速度。然而，它们的反应速度通常太高而不能广泛应用于化学时间延迟中。在这项工作中，我们使用聚合物网状基材来产生反应性颗粒的约束网络，^–1到7至90 mm s的范围^–1。这是通过中断的反应机理来实现的，在该机理中，由于颗粒界面处所需的传热，涂覆的筛网上的单个颗粒反应迅速，但在点燃相邻颗粒之前表现出延迟。我们提出了宏观反应速度，作为底物组成和尺寸的函数，以及反应性涂层的厚度和双层间距。我们使用高速摄影术来探测点火延迟，并使用有限元分析模拟来帮助解释观察到的趋势。通过选择基材和涂层特性，可以将跨越大范围延迟时间的时间延迟打包为标准形状因子。