# ASTM E1142-15

Designation E1142 − 15Standard TerminologyRelating to Thermophysical Properties1This standard is issued under the fixed designation E1142; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon ´ indicates an editorial change since the last revision or reapproval.1. Scope1.1 This is a compilation of terms and correspondingdefinitions commonly used in the study of thermophysicalproperties. Terms that are generally understood or definedadequately in other readily available sources are either notincluded or their sources identified.1.2 A definition is a single sentence with additional infor-mation included in a Discussion.1.3 Definitions of terms specific to a particular field such asdynamic mechanical measurements are identified with anitalicized introductory phrase.2. Referenced Documents2.1 ASTM Standards2D4092 Terminology for Plastics Dynamic MechanicalPropertiesE7 Terminology Relating to MetallographyE344 Terminology Relating to Thermometry and Hydrom-etryE2744 Test for Pressure Calibration of ThermalAnalyzers3. Terminology3.1 Definitionsabsolute pressure, npressure measured relative to zeropressure corresponding to empty space.DISCUSSIONAbsolute pressure is atmospheric pressure plus gagepressure.activation energy E, nin chemical kinetics, the energy thatmust be overcome in order for a chemical reaction to occur.DISCUSSIONThe term activation energy was introduced in 1889 bySvante Arrhenius as a mathematical term in the eponymous, empiricalrelationship between temperature and reaction rate constant.admittance, Y, nthe reciprocal of impedance.alpha α loss peak, nin dynamic mechanical measurement,first peak in the damping curve below the melt, in order ofdecreasing temperature or increasing frequency. E7amorphicity, na relative measure of amorphous materialcontent, expressed as a percent of the total material content.angular frequency, ω, nthe number of radians per secondtraversed by a rotating vector that represents any periodicallyvarying quantity.DISCUSSIONAngular frequency, ω, is equal to two π times thefrequency, f.anisotropic, adjhaving different values for a property indifferent directions.anti-thixotropy, nan increase of the apparent viscosity underconstant shear stress or shear rate followed by a gradualrecovery when the stress or shear rate is reduced to zero.arrhenius equation, na mathematical relationship betweenthe specific reaction rate constant and the temperature givenask 5 Ae2E/RT1wherek the reaction rate constant,A the pre-exponential factor,E the energy of activation,R the gas constant, andT the absolute temperature.atmospheric pressure, nthe pressure due to the weight ofthe atmosphere. E2744DISCUSSIONAtmospheric pressure varies with elevation above sealevel, acceleration due to gravity, and weather conditions.barometer, nan instrument for measuring atmospheric pres-sure.beta β loss peak, nin dynamic mechanical measurement,second discrete peak in damping curve below the melt, inorder of decreasing temperature or increasing frequency.D4092boiling pressure, nat a specific temperature, the value of thevapor pressure of the liquid at which it is equal to theexternal pressure.1This terminology is under the jurisdiction of ASTM Committee E37 onThermal Measurements and are the direct responsibility of Subcommittee E37.03 onNomenclature and Definitions.Current edition approved May 1, 2015. Published June 2015. Originallyapproved in 1988. Last previous edition approved in 2014 as E1142 – 14b. DOI10.1520/E1142-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume ination, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1boiling temperature, nat a specific pressure, the tempera-ture at which the vapor pressure of the liquid is equal to theexternal pressure.capacitance, nthat property of a system of conductors anddielectrics that permits the storage of electrical charge whena potential difference exists between the conductors.DISCUSSIONCapacitance is the ratio of a quantity of electric charge,Q, to a potential difference, V. A capacitance value is always positive.The unit of capacitance is the farad, F, which is equivalent to onecoulomb per volt.catalyst, na substance that increases the rate of a chemicalreaction but is not consumed or changed by that reaction.Celsius, ndesignation of the degree on the InternationalPractical Temperature Scale; also used for the name of thescale, as “Celsius Temperature Scale.” erly prior to1948 called “Centigrade.” The Celsius temperature scale isrelated to the International Kelvin Temperature Scale by theequation TcT− 273.16 K.Centigrade, nsee Celsius.coeffıcient of expansion, nsee coefficient of linear thermalexpansion.coefficient of linear thermal expansion, αl, nchange inlength, relative to the length of the specimen, accompanyinga unit change of temperature, at a specified temperature.coefficient of viscosity, nthe ratio between an infinitesimallysmall increase in stress and the corresponding increase instrain rate.coefficient of volume thermal expansion αv, nfor a solid orliquid, the change in volume, relative to the volume of thespecimen, accompanying a change of temperature at aspecified temperature.color temperature, ntemperature in degrees Kelvin K atwhich a black body must be operated to give a color equal tothat of the source in plex modulus, E*, G*, or K*, nratio of the stress tostrain where each is a factor that may be represented by acomplex number as follows E*E iE“,G*G iG“,and K*K iK“.whereE* complex modulus, measured in tension or flexure,E storage modulus, measured in tension or flexure,E9 loss modulus, measured in tension or flexure,G* complex modulus, measured in shear,G storage modulus, measured in shear,G9 loss modulus, measured in shear,K* complex modulus, measured in compression,K storage modulus, measured in compressionK9 loss modulus, measured in compression, andi 5œ21 , measured in compression.The complex modulus may be measured in tension orflexure, E*, compression, K*, or in shear, G*. D4092complex shear compliance, J*, nreciprocal of complexshear modulus, where J* 1/G*. D4092complex tensile compliance, D*, nreciprocal of complextensile modulus, where D*1⁄E*. D4092complex viscosity, η*, nthe complex modulus divided by theimposed frequency in rad/pliance, J, nthe strain divided by the correspondingstress.DISCUSSIONCompliance is the reciprocal of position, nquantity of the components of a mixture;usually expressed in terms of the weight percentage, or theatomic percentage of each of the components in the mixture.E7conductivity, electrical volume, σ, nthe ratio of thecurrent density A·cm−2 through a specimen to the potentialgradient V/cm in the same direction as the current.DISCUSSIONConductivity is normally expressed in unitsohm·cm−1, but the correct SI units are Siemen·m.congruent phases, nthose states of matter of unique com-position that co-exist at equilibrium at a single point intemperature and pressure; for example, the two coexistingphases of a two-phase equilibrium. E7congruent transation, nan isothermal, or isobaric,phase change in which both of the phases concerned have thesame composition throughout the process; the order of asystem becomes unary at a composition of congruency. E7constitutional diagram, ngraphical representation of thecompositions, temperatures, pressures, or combinationsthereof at which the heterogeneous equilibria of a systemoccur.cooling curve, ngraphical representation of specimen tem-perature or temperature change as a function of time ordecreasing environment temperature.cooling rate, naverage slope of the time-temperature curvetaken over a specific time and temperature interval as thetemperature is decreased.critical curve, nin a binary, or higher order, phase diagram,a locus of points along which two or more phases exist instable thermodynamic equilibrium.critical point, nin a binary phase diagram, that specific valueof composition, temperature, pressure, or combinationsthereof at which the phases of a heterogeneous equilibriumbecome identical.critical pressure, nthat pressure at the critical point.critical surface, nin a ternary or higher order phase diagram,the area upon which the phases in equilibrium becomeidentical. E7critical temperature, nthat temperature at the critical point.crystal, nsolid composed of atoms, ions, or molecules,arranged in a pattern which is periodic in three dimensions.E7E1142 − 152crystallinity, nregular arrangement of the atoms of a solid inspace.DISCUSSIONIn most materials, this state is usually imperfectlyachieved. The crystalline regions ordered regions are submicroscopicvolumes in which there is more or less regularity of arrangement of thecomponent molecules.crystallite, ncrystalline grain not bounded by habit planes.E7crystallization, narrangement of previously disordered ma-terial segments of repeating patterns into geometric symme-try.crystallization temperature, nthat temperature at which aspecimen undergoes crystallization upon cooling.Curie point, nsee Curie temperature.Curie temperature, ntemperature above which a ferromag-netic or ferroelectric material becomes paramagnetic, orparaelectric, respectively.DISCUSSIONThere may be more than one if there are multiplematerials.damping, nloss in energy, dissipated as heat, that resultswhen a material or material system is subjected to anoscillatory load or displacement. D4092devitrification, ncrystallization of an amorphous substance.E7dielectric constant, nsee permittivity, relative.dielectric dissipation factor, D, nthe ratio of the loss factor,ε“, to the absolute permittivity, ε , orD 5 ε“/ε 2DISCUSSIONThe dielectric dissipation factor is numerically equal tothe tangent of the dielectric loss angle and may be referred to as the losstangent, tan δ, or the cotangent of the phase angle, θ.dielectric loss angle, nthe angle whose tangent is thedissipation factor or arctan ε“/ε .DISCUSSIONIt is also the difference between 90 degrees and thephase angle.differential thermocouple, nsee differential thermopile.differential thermopile, na number of temperature sensorsconnected in series-opposing and arranged so that there is anincrease in output signal for a given temperature differencebetween alternate junctions maintained at a reference tem-perature and the measured temperature.dilatancy, nthe increase in volume caused by shear.dipole relaxation time, γ, nthe exponential decay timerequired for the electric polarization of any point of asuitably charged dielectric to fall from its original value to1/e of that value, due to the loss of dipole orientation.DISCUSSIONUnder conditions of an alternating applied field and insystems with a single dipole relaxation time, it is equal to 1/ω at the lossfactor peak in cases where the peak is caused by a dipole mechanism.dissipation factor, nsee tangent delta.dissociation, nas applied to heterogeneous equilibria, thetransation of one phase into two or more new phases, allof different composition. E7dynamic modulus, nsee complex modulus.elasticity, nthat property of materials that causes them toreturn to their original or condition after the appliedforce is removed. D4092elastic limit, nthe greatest stress that can be applied to amaterial without permanent deation.elastic modulus, nthe ratio of stress to corresponding strainwithin the elastic limit of the stress-strain curve.DISCUSSIONThe elastic modulus may also be measured in tensionE´, compression K´, flexure E´, or shear G´. See also complexmodulus.enthalpy, na thermodynamic function defined by the equa-tion H U PV where H is the enthalpy, U is the internalenergy, P is the pressure, and V the volume of the system.DISCUSSIONAt constant pressure the change in enthalpy measuresthe quantity of heat exchanged by the system and its surrounding.equilibrium diagram, nsee constitutional diagram.eutectic point, nsee eutectic.eutectic, adjmixture of two or more substances whichsolidifies as a whole when cooled from the liquid state,without change in composition.DISCUSSIONThe temperature at which the eutectic mixture solidifiesis called the eutectic point. This temperature is constant for a givencomposition, and represents the lowest melting point of the system.expansivity, nthe change in dimension resulting from aninfinitesimal change in an independent variable such astemperature or humidity.failure, nthe point beyond which a material ceases to befunctionally capable of its intended use.failure criterion, nspecification of the chemical, physical,mechanical, electrical, or other condition under which amaterial ceases to be functionally capable of its intended use.failure temperature Tf, nthe temperature at which amaterial fails.Fahrenheit, ndesignation of a degree on the Fahrenheittemperature scale that is related to the International PracticalTemperature Scale by means of the equationTF5 1.8 TC132 3whereTF the temperature in degree Fahrenheit, andTC the temperature in degrees Celsius.freezing temperature, nsee crystallization temperature.frequency, f, nthe number of cycles per unit time of periodicprocess.DISCUSSIONThe unit is Hertz Hz which is equal to 1 cycle per/s.E1142 − 153frequency profile, nin dynamic mechanical measurement,plot of the dynamic properties of a material, at a constanttemperature, as a function of test frequency. D4092gage pressure, npressure measured relative to atmosphericpressure.DISCUSSIONGage pressure is the difference between absolute pres-sure and atmospheric pressure.gamma γ loss peak, nin dynamic mechanicalmeasurement, third peak in the damping curve below themelt, in the order of decreasing temperature or increasingfrequency. D4092Gibbs Phase Rule, nmaximum number of phases P thatmay coexist at equilibrium is equal to two, plus the numberof components C in the mixture, minus the number ofdegrees of freedom F PFC2. E7glass transition, nreversible change in an amorphous mate-rial or in amorphous regions of a partially crystallinematerial, from or to a viscous or rubbery condition to orfrom a hard and relatively brittle one.DISCUSSIONThe glass transition generally occurs over a relativelynarrow temperature region and is similar to the solidification of a liquidto a glassy state. Not only do hardness and brittleness undergo rapidchanges in this temperature region, but other properties, such ascoefficient of thermal expansion and specific