Thermoelectrics：Every little helps

　　HERE is a thought: approximately 60% of the energy converted in power generation is wasted. The price of energy is high, both in terms of the actual cost to the consumer and the consequences of the climate change that generating power from fossil fuels causes. If even a small proportion of this wasted heat could be converted to useful power, it would be a good thing.
　　At this week's meeting of the American Physical Society, in Baltimore, Mercouri Kanatzidis of Michigan State University proposed such a scheme. He advocates attaching thermoelectric devices that convert heat into electricity to chimney stacks and vehicle exhausts, to squeeze more useful energy from power generation.
　　The technology to do so has existed for years. If one end of an electrical conductor is heated while the other is kept cool, a small voltage is created between the two. Placing two dissimilar metals, or other electrically conductive materials, in contact with each other and then heating them also generates a voltage. Such devices, called thermocouples, are nowadays usually made using semiconductors. They are widely used as thermometers. But if they could be made cheaper, or more efficient, or both, they could also be employed to generate power.
　　Dr Kanatzidis is developing new thermoelectric materials designed to be capable of converting up to 20% of the heat that would otherwise be wasted into useful electricity. The challenge lies in finding a substance that conducts electricity well and heat badly. These two properties define what physicists call the "figure of merit" of a thermoelectric substance, which describes the power a device made of that substance could generate. Dr Kanatzidis's group aims to make materials with higher figures of merit than those attainable with today's semiconductors.
　　Since the electrical properties of solids depend on their crystal structures, his group is experimenting with new atomic lattices. In particular, they are working on a group of chemicals called chalcogenides. These are compounds of oxygen, sulphur, selenium and tellurium that are thought to be particularly suitable for thermoelectric applications because their structure allows electric currents to flow while blocking thermal currents. They thus have a high figure of merit. Dr Kanatzidis's group is developing new ways of making these compounds crystallise correctly.
　　But even existing devices could become economically useful as fuel prices rise, Dr Kanatzidis argues. In America, transport accounts for a quarter of the energy used. Fitting small thermoelectric devices to the exhaust pipes of vehicles could squeeze another 10% from the fuel-a saving that would be especially relevant in hybrid petrol/electric devices where the battery is recharged in part by recycling energy that would otherwise be dissipated by energy-draining activities such as braking. Similarly, attaching thermoelectric devices to the flues of power plants could generate more useful power.
　　And thermoelectric devices could be used in other areas. They could work alongside solar cells and solar heating systems. They could also be used in geothermal and nuclear power plants. Dr Kanatzidis argues that wherever heat is generated as part of power generation, thermoelectric devices could help extract more useful energy. Waste not, want not.

　　译文

　　热电学：每一小部分都是有用的

　　有人认为，在发电过程中，其中大约有60%的能量在其转化成电能时被浪费掉。无论从消费者的实际花费， 还是从用化石燃料发电所引起的气候变化的角度而言，使用能源的代价都是很高的。如果把浪费掉的很小的一部分热能转换为有用的能量，这都是件好事。
　　美国物理学会本周在巴尔的摩举行的例会上，密歇根州立大学的Mercouri Kanatzidis建议，把热电转化装置安装在烟囱和车辆排气管上，从而获得更多可用能源。
　　这项技术已经研发出好多年了。如果电导体一段加热，另一端不加热，就会在电导体两端产生少量的电压。把两种不同的金属或其他非金属电导体连在一起，进行加热，也会产生一定的电压。这样的装置被称为热电偶，现在通常由半导体材料制成。这些热电偶被广泛用作温度计。如果它们的造价再低一些，或效用再高一些，或同时降低造价、提高效用，就可以用它们来发电了。
　　Kanatzidis博士正在研发的一种新型热电材料，可以将原本会浪费掉的热能中的20%转化为电能。他目前面临的困难是，要找到一种物质，同时是很好的电导体又是热的不良导体。这两种属性决定着热电材料的“品质因数”。“品质因数”是用来描述用热电材料所制成的元器件的输出功率的单位。Kanatzidis博士团队的目标就是研制出“品质因数”更高的热电材料。
　　由于固体的导电性能由其晶体结构所决定，Kanatzidis博士团队于是实验新的原子晶格。具体来说，他们就是在研究一种叫做“硫系化合物”的化学品，其成分包括氧、硫、砷、碲。这些元素被认为很适于热电应用，因为它们的结构能够在阻挡热流的同时允许电子流通过。因此，它们具有很高的“品质因数”。Kanatzidis博士团队正在研究能够使这些化合物适当结晶的方法。
　　Kanatzidis博士认为，随着化石燃料价格上涨，即便是当前的热电装置，也可以变得更经济实用。在美国，交通运输所需能源占能源消耗总量的四分之一。在机动车排气管上安装小型的热电装置，可以节省另外10%的燃料。这部分燃料所包含的能量，在混合燃料发动机或电动发动机运转的过程中，通过位于发动机上的电池充电，被部分的再次利用，成为循环能量，从而不至于在诸如刹车这样的能量流动过程中白白流失。同理，在发电厂的烟囱上安装热电装置，就可以收集更多的能量，从而发更多的电。
　　热电装置还可以用于其他领域，比如太阳能电池和太阳能加热系统。除此以外，还可以用在地热发电厂和核电站。Kanatzidis博士认为，热电装置可以收集发电过程中产生的热能，并将其转化为其他可用能量。俭以防匮。