# 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 Standards:2D4092 Terminology for Plastics: Dynamic MechanicalPropertiesE7 Terminology Relating to MetallographyE344 Terminology Relating to Thermometry and Hydrom-etryE2744 Test Method for Pressure Calibration of ThermalAnalyzers3. Terminology3.1 Definitions:absolute pressure, n—pressure measured relative to zeropressure corresponding to empty space.DISCUSSION—Absolute pressure is atmospheric pressure plus gagepressure.activation energy (E), n—in chemical kinetics, the energy thatmust be overcome in order for a chemical reaction to occur.DISCUSSION—The 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, n—the reciprocal of impedance.alpha (α) loss peak, n—in dynamic mechanical measurement,first peak in the damping curve below the melt, in order ofdecreasing temperature or increasing frequency. E7amorphicity, n—a relative measure of amorphous materialcontent, expressed as a percent of the total material content.angular frequency, ω, n—the number of radians per secondtraversed by a rotating vector that represents any periodicallyvarying quantity.DISCUSSION—Angular frequency, ω, is equal to two π times thefrequency, f.anisotropic, adj—having different values for a property indifferent directions.anti-thixotropy, n—an 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, n—a mathematical relationship betweenthe specific reaction rate constant and the temperature givenas:k 5 Ae2E/RT(1)where:k = the reaction rate constant,A = the pre-exponential factor,E = the energy of activation,R = the gas constant, andT = the absolute temperature.atmospheric pressure, n—the pressure due to the weight ofthe atmosphere. E2744DISCUSSION—Atmospheric pressure varies with elevation above sealevel, acceleration due to gravity, and weather conditions.barometer, n—an instrument for measuring atmospheric pres-sure.beta (β) loss peak, n—in dynamic mechanical measurement,second discrete peak in damping curve below the melt, inorder of decreasing temperature or increasing frequency.D4092boiling pressure, n—at 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. DOI:10.1520/E1142-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, 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, n—at a specific pressure, the tempera-ture at which the vapor pressure of the liquid is equal to theexternal pressure.capacitance, n—that property of a system of conductors anddielectrics that permits the storage of electrical charge whena potential difference exists between the conductors.DISCUSSION—Capacitance 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, n—a substance that increases the rate of a chemicalreaction but is not consumed or changed by that reaction.Celsius, n—designation of the degree on the InternationalPractical Temperature Scale; also used for the name of thescale, as “Celsius Temperature Scale.” Formerly (prior to1948) called “Centigrade.” The Celsius temperature scale isrelated to the International Kelvin Temperature Scale by theequation: Tc=T− 273.16 K.Centigrade, n—see Celsius.coeffıcient of expansion, n—see coefficient of linear thermalexpansion.coefficient of linear thermal expansion, αl, n—change inlength, relative to the length of the specimen, accompanyinga unit change of temperature, at a specified temperature.coefficient of viscosity, n—the ratio between an infinitesimallysmall increase in stress and the corresponding increase instrain rate.coefficient of volume thermal expansion αv, n—for a solid orliquid, the change in volume, relative to the volume of thespecimen, accompanying a change of temperature at aspecified temperature.color temperature, n—temperature in degrees Kelvin (K) atwhich a black body must be operated to give a color equal tothat of the source in question.complex modulus, E*, G*, or K*, n—ratio 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“.where:E* = 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*, n—reciprocal of complexshear modulus, where J* = 1/G*. D4092complex tensile compliance, D*, n—reciprocal of complextensile modulus, where D*=1⁄E*. D4092complex viscosity, η*, n—the complex modulus divided by theimposed frequency in rad/s.compliance, J, n—the strain divided by the correspondingstress.DISCUSSION—Compliance is the reciprocal of modulus.composition, n—quantity 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, n—the ratio of thecurrent density (A·cm−2) through a specimen to the potentialgradient (V/cm) in the same direction as the current.DISCUSSION—Conductivity is normally expressed in units(ohm·cm)−1, but the correct SI units are Siemen·m.congruent phases, n—those 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 transformation, n—an 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, n—graphical representation of thecompositions, temperatures, pressures, or combinationsthereof at which the heterogeneous equilibria of a systemoccur.cooling curve, n—graphical representation of specimen tem-perature or temperature change as a function of time ordecreasing environment temperature.cooling rate, n—average slope of the time-temperature curvetaken over a specific time and temperature interval as thetemperature is decreased.critical curve, n—in a binary, or higher order, phase diagram,a locus of points along which two or more phases exist instable thermodynamic equilibrium.critical point, n—in a binary phase diagram, that specific valueof composition, temperature, pressure, or combinationsthereof at which the phases of a heterogeneous equilibriumbecome identical.critical pressure, n—that pressure at the critical point.critical surface, n—in a ternary or higher order phase diagram,the area upon which the phases in equilibrium becomeidentical. E7critical temperature, n—that temperature at the critical point.crystal, n—solid composed of atoms, ions, or molecules,arranged in a pattern which is periodic in three dimensions.E7E1142 − 152crystallinity, n—regular arrangement of the atoms of a solid inspace.DISCUSSION—In 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, n—crystalline grain not bounded by habit planes.E7crystallization, n—arrangement of previously disordered ma-terial segments of repeating patterns into geometric symme-try.crystallization temperature, n—that temperature at which aspecimen undergoes crystallization upon cooling.Curie point, n—see Curie temperature.Curie temperature, n—temperature above which a ferromag-netic or ferroelectric material becomes paramagnetic, orparaelectric, respectively.DISCUSSION—There may be more than one if there are multiplematerials.damping, n—loss in energy, dissipated as heat, that resultswhen a material or material system is subjected to anoscillatory load or displacement. D4092devitrification, n—crystallization of an amorphous substance.E7dielectric constant, n—see permittivity, relative.dielectric dissipation factor, D, n—the ratio of the loss factor,ε“, to the absolute permittivity, ε , or:D 5 ε“/ε (2)DISCUSSION—The 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, n—the angle whose tangent is thedissipation factor or arctan ε“/ε .DISCUSSION—It is also the difference between 90 degrees and thephase angle.differential thermocouple, n—see differential thermopile.differential thermopile, n—a 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, n—the increase in volume caused by shear.dipole relaxation time, γ, n—the 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.DISCUSSION—Under 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, n—see tangent delta.dissociation, n—as applied to heterogeneous equilibria, thetransformation of one phase into two or more new phases, allof different composition. E7dynamic modulus, n—see complex modulus.elasticity, n—that property of materials that causes them toreturn to their original form or condition after the appliedforce is removed. D4092elastic limit, n—the greatest stress that can be applied to amaterial without permanent deformation.elastic modulus, n—the ratio of stress to corresponding strainwithin the elastic limit of the stress-strain curve.DISCUSSION—The elastic modulus may also be measured in tension(E´), compression (K´), flexure (E´), or shear (G´). (See also complexmodulus.)enthalpy, n—a 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.DISCUSSION—At constant pressure the change in enthalpy measuresthe quantity of heat exchanged by the system and its surrounding.equilibrium diagram, n—see constitutional diagram.eutectic point, n—see eutectic.eutectic, adj—mixture of two or more substances whichsolidifies as a whole when cooled from the liquid state,without change in composition.DISCUSSION—The 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, n—the change in dimension resulting from aninfinitesimal change in an independent variable (such astemperature or humidity).failure, n—the point beyond which a material ceases to befunctionally capable of its intended use.failure criterion, n—specification of the chemical, physical,mechanical, electrical, or other condition under which amaterial ceases to be functionally capable of its intended use.failure temperature (Tf), n—the temperature at which amaterial fails.Fahrenheit, n—designation of a degree on the Fahrenheittemperature scale that is related to the International PracticalTemperature Scale by means of the equation:TF5 1.8 TC132 (3)where:TF= the temperature in degree Fahrenheit, andTC= the temperature in degrees Celsius.freezing temperature, n—see crystallization temperature.frequency, f, n—the number of cycles per unit time of periodicprocess.DISCUSSION—The unit is Hertz (Hz) which is equal to 1 cycle per/s.E1142 − 153frequency profile, n—in dynamic mechanical measurement,plot of the dynamic properties of a material, at a constanttemperature, as a function of test frequency. D4092gage pressure, n—pressure measured relative to atmosphericpressure.DISCUSSION—Gage pressure is the difference between absolute pres-sure and atmospheric pressure.gamma (γ) loss peak, n—in dynamic mechanicalmeasurement, third peak in the damping curve below themelt, in the order of decreasing temperature or increasingfrequency. D4092Gibbs Phase Rule, n—maximum 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): P+F=C+2. E7glass transition, n—reversible 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.DISCUSSION—The 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