铝热剂具有极高的活化能,使其在室温下稳定且难以点燃。点火需要达到约 1,300 °C (2,400 °F) 的温度。这通常不是通过直接火焰来实现的,而是借助中间高温引发剂(例如燃烧的镁带或专门设计的烟火引信)来实现的,这些引发剂可提供引发反应所需的局部能量。

铝热剂具有极高的活化能,使其在室温下稳定且难以点燃。点火需要达到约 1,300 °C (2,400 °F) 的温度。这通常不是通过直接火焰来实现的,而是借助中间高温引发剂(例如燃烧的镁带或专门设计的烟火引信)来实现的,这些引发剂可提供引发反应所需的局部能量。
铝热剂的高燃点直接源于其反应机理,即固态反应。与气相或液相反应(反应物可自由移动且混合)不同,在铝热剂中,铝和金属氧化物颗粒最初呈固态。反应开始时,原子必须获得足够的动能,以克服扩散和颗粒界面键重排的能垒。这需要大量的热能输入,这决定了铝热剂具有较高的活化能。
A simple match or propane torch does not provide a sufficiently high temperature or energy density to initiate the self-sustaining reaction. The standard method involves using a material that burns at a very high temperature. Magnesium ribbon is a classic initiator, as its combustion in air ([latex]2Mg + O_2 \rightarrow 2MgO[/latex]) reaches temperatures of about 2,200 °C, well above thermite’s ignition point. Other initiators include sparklers (which contain metal powders and oxidizers) or mixtures like potassium permanganate and glycerin, which react hypergolically. Once a small portion of the thermite mixture is ignited, the immense heat it releases is transferred to the adjacent material, causing the reaction to propagate in a wave-like front through the entire mixture. The speed of this propagation depends on factors like stoichiometry, particle size, and packing density. Finer powders with greater surface area react faster, while denser packing improves thermal conductivity, aiding propagation. This high activation energy is a crucial safety feature, preventing accidental ignition while allowing for deliberate and controlled use.
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铝热剂的点火和传播
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