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A simple structure of a dilatometer for the measurement of the thermal expansion of liquids and solids

A dilatometer is a scientific instrument that measures volume changes caused by a physical or chemical process. A familiar application of a dilatometer is the mercury-in-glass thermometer, in which the change in volume of the liquid column is read from a graduated scale. Because mercury has a fairly constant rate of expansion over normal temperature ranges, the volume changes are directly related to temperature.

## Applications

Dilatometers have been used in the fabrication of metallic alloys, compressed and sintered refractory compounds, glasses, ceramic products, composite materials, and plastics.[1]

Dilatometry is also used to monitor the progress of chemical reactions, particularly those displaying a substantial molar volume change (e.g., polymerisation). A specific example is the rate of phase changes.[2]

Another common application of a dilatometer is the measurement of thermal expansion. The thermal expansivity is defined as:

$\alpha = \frac{1}{V} \biggl(\frac{\partial V}{\partial T} \biggr)_{p}\$

and is an important engineering parameter.

## Types

There are a number of dilatometer types:

• Capacitance dilatometers possess a parallel plate capacitor with a one stationary plate, and one moveable plate. When the sample length changes, it moves the moveable plate, which changes the gap between the plates. The capacitance is inversely proportional to the gap. Changes in length of 10 picometres can be detected.[3]
• Connecting rod (push rod) dilatometer, the sample which can be examined is in the furnace. A connecting rod transfers the thermal expansion to a strain gauge, which measures the shift. Since the measuring system (connecting rod) is exposed to the same temperature as the sample and thereby likewise expands, one obtains a relative value, which must be converted afterwards. Matched low-expansion materials and differential constructions can be used to minimize the influence of connecting rod expansion [4] [5]
• High Resolution - Laser Dilatometer Highest resolution and absolute accuracy is possible with a Michelson Interferometer type Laser Dilatometer. Resolution goes up to picometres. On top the principle of interference measurement give the possibility for much higher accuracy's and it is an absolute measurement technique with no need of calibration.[6][clarification needed]
• Optical dilatometer is an instrument that measures dimension variations of a specimen heated at temperatures that generally range from 25 to 1400 °C. The optical dilatometer allows the monitoring of materials’ expansions and contractions by using a non-contact method: optical group connected to a digital camera captures the images of the expanding/contracting specimen as function of the temperature with a resolution of about ±70 micrometre per pixel.[7] As the system allows to heat up the material and measures its longitudinal/vertical movements without any contact between instrument and specimen, it is possible to analyse the most ductile materials, such as the polymers, as well as the most fragile, such as the incoherent ceramic powders for sintering process.

For simpler measurements in a temperature range from 0 to 100 °C, where water is heated up and flow or over the sample. If linear coefficients of expansion of a metal is to be measured, hot water will running through a pipe made from the metal. The pipe warms up to the temperature of the water and the relative expansion can be determined as a function of the water temperature.

For the measurement of the volumetric expansion of liquids one takes a large glass container filled with water. In an expansion tank (glass container with an accurate volume scale) with the sample liquid. If one heats the water up, the sample liquid expands and the volume changes is read. However the expansion of the sample container must also be taken into consideration.

The expansion and retraction coefficient of gases cannot be measured using dilatometer, since the pressure plays a role here. For such measurements a gas thermometer is more suitable.

Dilatometers often include a mechanism for controlling temperature. This may be a furnace for measurements at elevated temperatures (temperatures to 2000 °C), or a cryostat for measurements at temperatures below room temperature. Metallurgical applications often involve sophisticated temperature controls capable of applying precise temperature-time profiles for heating and quenching the sample.[8]

## References

1. ^ Hans Lehmann, refuge Gatzke Dilatometrie and differential thermal analysis for the evaluation of processes ? ? , 1956.
2. ^ Kastle, J. H.; Kelley, W. P. (July 1904). "On the Rate of Crystallization of Plastic Sulphur". American Chemical Journal 32: 483–503.
3. ^ J. J. Neumeier, R. K. Bollinger, G. E. Timmins, C. R. Lane, R. D. Krogstad, and J. Macaluso, "Capacitive-based dilatometer cell constructed of fused quartz for measuring the thermal expansion of solids", Review of Scientific Instruments 79, 033903 (2008).
4. ^ Theta Industries http://www.theta-us.com/dil/dil1.html
5. ^ http://www.usinenouvelle.com/industry/netzsch-geratebau-gmbh-8585/horizontal-pushrod-dilatometer-dil-pc-p72147.html
6. ^ C.Linseis The next step in dilatometry, invention and use of the Linseis Laser Dilatometer , Linseis Messgeraete GmbH, Selb (Germany)
7. ^ M.Paganelli The Non-contact Optical dilatometer designed for the behaviour of Ceramic Raw Materials , Expert System Solutions S.r.l., Modena (Italy).
8. ^ http://www.theta-us.com/quench/QuenchInst.html

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Dilatometer — Please support Wikipedia.
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 Aktuality.sk Doprava pod Strečnom v nedeľu dopoludnia zastane Aktuality.sk Wed, 11 Nov 2015 07:40:17 -0800 Prvý dilatometer budú osádzať medzi 08.00 a 08.45 h, po ňom bude približne hodinová prestávka, aby mohli vodiči odcestovať a uvoľniť komunikáciu. Kým neosadia druhý dilatometer, bude ďalšia 45-minútová odstávka komunikácie. „Časy sú predpokladané ... Azom.com The DIL806 Optical Dilatometer from TA Instruments Azom.com Wed, 15 Aug 2012 03:42:12 -0700 The dilatometer is coupled with a rapid-response DIL 806 furnace, thereby making the tool well-suited for dynamic processes involving dynamic heating rates and multiple temperature steps. The sample is placed in the center of the disc-shaped furnace on ... Autobild.sk V nedeľu zatvoria cestu pod Strečnom Autobild.sk Thu, 19 Nov 2015 02:08:08 -0800 "Bol osadený online dilatometer a budú postupovať ďalšie práce. Stále trváme na tom, aby boli v režime, ktorý čo najmenej obmedzuje premávku. To znamená, v určitých intervaloch cestu uzatvárali a otvárali, aby to bola čo najmenšia záťaž pre obchádzkové ... Azom.com TMA 801 Vertical Dilatometer by TA Instruments Azom.com Wed, 15 Aug 2012 04:04:18 -0700 The TMA 801 operates in a vertical orientation, making it ideal for the analysis of sintering, RCS (rate controlled sintering), viscoelastic behavior and the determination of softening temperatures. The linear motor generates a constant throughout the ... SME.sk Cestu I/18 pod hradom Strečno v nedeľu uzatvoria SME.sk Wed, 18 Nov 2015 01:08:41 -0800 "Bol osadený online dilatometer a budú postupovať ďalšie práce. Stále trváme na tom, aby boli v režime, ktorý čo najmenej obmedzuje premávku. To znamená, v určitých intervaloch cestu uzatvárali a otvárali, aby to bola čo najmenšia záťaž pre obchádzkové ... Orton DIL 2010 B Dilatometer Azom.com Mon, 27 Oct 2008 19:06:17 -0700 Orton dilatometers are designed to measure the dimensional changes of ceramics, glasses, metals, carbon composites, cermets, minerals, and polymers as a function of temperature. The dilatometer records reversible and irreversible changes in length ... Azom.com DIL 805 Quenching Dilatometer from TA Instruments Azom.com Wed, 15 Aug 2012 03:19:48 -0700 Apart from using the principle of the DIL805A, the DIL805D also includes controlled deformation. At a user-defined temperature, a sample is compressed with many deformation programs. With the quenching dilatometer, a cooling process can be carried out ... Azom.com Dilatometer - Unitherm 1000 from Anter Azom.com Mon, 01 Jun 2009 03:30:00 -0700 Unitherm 1000 is a fully computerized dilatometer system designed to measure dimensional changes of a specimen brought about by changes in its thermal environment. Linear thermal expansion coefficient, annealing characteristics and other physical or ...
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