The second reason for zip fuel's abandonment was that the stuff itself proved disappointing.In jets, instead of burning completely, it produced a sticky residue which clung to turbine blades.Boron additives in rocket fuels also failed. The combustion process involved proved unexpectedly complex, and the promised additional energy was not forthcoming.The navy's notice suggests, though, that boron is back.The boffins behind it think that new physical forms of the element, known as allotropes, may offer ways around both the partial-combustion and the toxicity problems.Allotropes of an element can have very different properties from each other (graphite and diamond, for example, are both allotropes of carbon).The organisers suggest a novel boron allotrope, perhaps interlaced at the molecular level with a suitable oxidising agent,might yield a completely combustible, non-toxic fuel, and they are asking the country's chemists to bring them one.Whether such allotropes exist remains to be seen.But America is not the only place working on the idea of boron-powered jets and rockets. China is interested, too.A project involving gelled fuel that has particles of boron suspended in it is under way at the National University of Defence Technology, in Changsha.The objective is to develop fuel for ramjets, a type of engine that operates efficiently only above Mach 3.So far, the researchers involved have managed to produce one that is 40% boron and yet burns more or less completely.
废弃拉链燃料的第二个原因是这种燃料本身令人失望。在喷气机中，它不会完全燃烧，而是会产生粘在涡轮叶片上的粘性残留物。火箭燃料中的硼添加剂也失败了，其中涉及的燃烧过程出乎意料地复杂，而且所承诺的额外能量并没有到来。然而，海军的公告表明硼又回来了。研究人员认为，这种元素的新物理形式，即同素异形体，可能会提供解决部分燃烧和毒性问题的方法。一种元素的同素异形体可能彼此具有非常不同的性质(例如，石墨和金刚石都是碳的同素异形体)。组织者认为，一种新型的硼同素异象(也许在分子水平上与合适的氧化剂交错)可以产生一种完全可燃、无毒的燃料，他们正请求英国的化学家们给他们带一个。这种同素异形体是否存在还有待观察。但美国并不是唯一一个致力于硼动力喷气机和火箭的地方，中国也颇感兴趣。位于长沙的国防科技大学正在进行一个涉及悬浮硼颗粒的胶凝燃料的项目，目的是为冲压式喷气发动机(效率仅高于3马赫)开发燃料。到目前为止，参与研究的研究人员已经成功制造出了一种含有40%硼且几乎可完全燃烧的燃料。
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