Dilatometer

A device that measures the expansion coefficient of solids, liquids, and gases. A widely used device is one that measures the change in length of a solid due to temperature (thermal expansion coefficient). The change in length can be measured directly with a microscopic microscope for materials with large expansion coefficients such as glass and metals, but generally, for materials with small expansion coefficients such as quartz glass, the change in length is transmitted to the outside of the heating device using a rod (called a transmission rod or push rod) made of a material with a known expansion coefficient, and the change in position is measured by mechanical expansion using an optical lever or rollers, or electrical expansion using a differential transformer or capacitor. In addition, for small samples or small changes, there are also methods that use laser light or optical interference.

The expansion coefficient of an irregularly shaped solid is measured by suspending the sample in a suitable medium and determining the change in buoyancy. If a solid with a known expansion coefficient is used, the expansion coefficient of a liquid can be determined. There is also a method of measuring by transmitting changes to the liquid, as in a liquid thermometer. Both methods are limited to certain media, making it difficult to measure high temperatures.

The volumetric expansion coefficient of a gas can be determined by calculating the change in volume when the gas pressure is kept constant and the temperature is changed, but this is a technically difficult procedure.

[Seizo Nagasaki April 17, 2015]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

固体、液体、気体の膨張率expansion coefficientを測定する装置。広く使われているのは、固体の温度による長さの変化（熱膨張率）を測る装置である。長さの変化は、膨張率の大きいガラスや金属などでは、測微顕微鏡で直接測ることもできるが、一般には、石英ガラスのように膨張率が小さく、膨張率既知の材料の棒（伝達棒とか押し棒という）で加熱装置の外に長さの変化を伝えて、その位置の変化を光てこ、ころによる機械的拡大や、差動変圧器、コンデンサーによる電気的拡大によって測る。また、小さい試料とか変化の小さい場合は、レーザー光を使うとか光の干渉を使う方法もある。

　異形の固体の膨張率の測定は、適当な媒体の中に試料を吊(つ)るして浮力の変化から求める。膨張率既知の固体を用いれば、液体の膨張率が求められる。液体温度計のように液体に変化を伝えて測る方法もある。いずれの方法も媒体が限定されるため、高温の測定はむずかしい。

　気体の体膨張率は、気体の圧力を一定に保ち温度を変化させたときの体積の変化を求めればいいが、技術的にむずかしい操作である。

［長崎誠三　2015年4月17日］

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