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An optical dilatometer is a non-contact device able to measure thermal expansions or sintering kinetics of any kind of materials, unlike traditional push rod dilatometer, it can push up to the dilatometric softening of the specimen. It is a device for measuring changes in the dimensions of a specimen, optically, the achieved resolution can result in greater values than those of a conventional pushrod dilatometer. A monochromatic light source, such as a laser, illuminates the specimen. Some of the light is reflected by the specimen and interferes with the incoming light, creating optical interference fringes. As the specimen contracts or expands, there is a proportional movement of the interference fringes, which can be measured using a camera system. The measurement resolution is determined by the wavelength of the light, and is typically 0.5 μm for blue light. Optical dilatometers are used to measure thermal expansion. The optical dilatometer is in fact complementary to the traditional higher resolution push rod dilatometer when it comes to measure dimensional changes of materials, as a function of temperature, and no contact between specimen and instrument is required. == Structure and types == The most recent types of optical dilatometer use a direct-beam system so as to avoid contact-related problems by measuring the image that the specimen projects on an image sensor, when irradiated by a light beam. By using a single beam of light with short wavelength and a very high resolution image sensor it is possible to achieve good resolutions, although not comparable to those of the standard dilatometers. For example, using a blue light with a wavelength below 1500 micrometers, it is possible to achieve images with an actual resolution of nearly 1500 micrometers/pixel of the camera (not an interpolated resolution but an actual resolution). By using two light beams, which illuminate two small portions of material at the extremities of the sample, set perpendicularly to the beams direction, it is then possible to achieve an absolute measurement of longitudinal variation while heat-treating the specimen. There are two major types of optical dilatometers which are currently in use: * ''(Horizontal Optical Dilatometer: ) '' the rod-specimen is laid horizontally on the sample holder and, during the thermal treatment in the oven, it is completely free to expand and contract. The displacement of the sample holder is not relevant for the result of the measurement because the optical system follows the horizontal movements of small portions of the specimen at its extremities. * ''(Vertical Optical Dilatometer: ) '' the rod-specimen is set vertically on the sample holder (alumina thin plate) and while one camera “watches” the top of the plate the other follows the vertical displacements of the sample’s top edge. This system has been used so far to find the characteristic temperatures (phase transitions, maximum sintering speed, swelling, etc.) of ceramic materials. In fact, phase transitions are always associated to dimension variation of the material: sintering is accompanied by high shrinkages, related to the decrease of porosity -swelling usually appears at high temperatures. After sintering occurs and the viscosity of the ceramics formulation strongly decreases and trapped gas is then free to exit. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Optical dilatometer」の詳細全文を読む スポンサード リンク
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