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Combustion of Mg and composite Mg·S powders in different oxidizers

机译：Mg和Mg·S复合粉在不同氧化剂中的燃烧

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Micron-sized, spherical magnesium powders were ignited by a CO2laser beam and by injecting them in the products of air–C2H2and air–H2flames. The same experiments were performed with composite Mg·S powders prepared by mechanical milling magnesium and elemental sulfur powders. The non-spherical Mg powder used to prepare composites was also explored in selected combustion tests. Flow conditions were varied in experiments performed in air with all materials. The combustion products were collected for particles burning in air; the products were studied using electron microscopy. Optical emission produced by burning particles was recorded using filtered photomultipliers. The emission pulses were processed to recover the particle burn times and their temperatures. Fine Mg particles burn in air very rapidly, with the burn times under 1 ms for particles finer than ca. 10 µm. The apparent trend describing burn time as a function of the particle size for such particles ist∼d0.5. The particles burn without generating a detectable standoff flame zone or producing smoke; combustion products are particles of MgO with dimensions comparable to those of the starting Mg powder particles. Both the particles burn times and their measured flame temperatures decrease slightly when particles are carried by faster air flows. The present experimental results is interpreted qualitatively assuming that the reaction occurs at or very near the boiling Mg surface and its rate is affected by both surface kinetics and the inward diffusion of oxygen. It is further proposed that the fine, solid MgO particles form either directly on surface of Mg droplet or in its immediate vicinity. Deposition of MgO crystals on liquid Mg causes little change in the particle burn rate. Combustion of Mg in air–C2H2and air–H2flames occurs much slower than in air. Combustion of composite Mg·S particles follows a two-step process. In the first step, sulfur is evaporated. When the particles are heated by a CO2laser beam, rapid evaporation of sulfur leads to a sudden change in the particle velocity. Once sulfur is removed, the particles burn similarly to the pure Mg.
机译：微米级球形镁粉被二氧化碳激光束点燃，然后将其注入到空气–C2H2和空气–H2火焰中。对通过机械研磨镁和元素硫粉制备的Mg·S复合粉进行了相同的实验。在选定的燃烧测试中还探索了用于制备复合材料的非球形镁粉。在空气中对所有材料进行的实验中，流动条件有所不同。收集燃烧产物以在空气中燃烧颗粒。使用电子显微镜研究产物。使用过滤的光电倍增管记录由燃烧颗粒产生的光发射。处理发射脉冲以恢复粒子燃烧时间及其温度。细的Mg颗粒在空气中燃烧非常迅速，对于细于约ca的颗粒，燃烧时间在1µms以下。 10μm。描述这种颗粒的燃烧时间随粒度变化的表观趋势为ist〜d0.5。粒子燃烧时不会产生可检测到的对峙火焰区或产生烟雾；燃烧产物是MgO颗粒，其尺寸可与起始Mg粉末颗粒相比。当颗粒由较快的气流携带时，颗粒的燃烧时间和其测得的火焰温度都会略有降低。假设反应发生在沸腾的镁表面或非常接近沸腾的镁表面，并且其速率受表面动力学和氧的向内扩散的影响，则定性解释本实验结果。进一步提出，固态的MgO细颗粒直接在Mg液滴的表面上或其附近形成。 MgO晶体在液态Mg上的沉积几乎不会改变颗粒燃烧速率。 Mg在空气-C2H2和空气-H2火焰中的燃烧比在空气中燃烧慢得多。复合Mg·S颗粒的燃烧遵循两步过程。第一步，将硫蒸发。当粒子被CO2激光束加热时，硫的快速蒸发导致粒子速度突然改变。一旦去除了硫，颗粒的燃烧与纯Mg相似。

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