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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[edit]

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[edit]

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]

See also[edit]

References[edit]

  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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79 news items

 
Azom.com
Wed, 15 Aug 2012 03:42:12 -0700

TA Instruments' DIL 806 optical dilatometer is an advanced and versatile tool designed for thermal expansion and contraction measurements. It is perfectly suited for measuring thin, irregularly-shaped soft sample lengths without contact. The DIL 806 is ...
 
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 ...
 
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
Wed, 15 Aug 2012 02:34:33 -0700

Suitable for the widest range of routine thermal expansion measurements, the DIL 801 and DIL801L are horizontally configured single-sample dilatometers. The DIL 801 is designed for measurements under vacuum or inert gas while the DIL 801L is designed ...
 
Azom.com
Wed, 15 Aug 2012 03:19:48 -0700

TA Instruments' DIL805A/D is a unique dilatometer designed for determining the deformation parameter and for creating continuous cooling, TTT-, and DTTT- diagrams. The DIL805A (quenching) has high heating rates of up to 4000°C/s and cooling rates of ...
 
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 ...

Azom.com

Azom.com
Mon, 04 May 2015 06:41:15 -0700

The new dilatometer DIL 402 Expedis Select and Supreme offer state-of-the-art dilatometer technology and are desiged for a wide range of sophisticated applications. All instruments of the DIL Expedis series feature the revolutionary NanoEye measuring ...
 
Marketwired (press release)
Thu, 26 Feb 2015 06:26:15 -0800

The plastic properties of the clean coal samples were measured by the Gieseler Fluidity test and Ruhr Dilatometer test. The tests were conducted on Seam 2 samples only. The small mass available from Seam 1 and Seam 2 samples deemed testing irrelevant ...
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