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Determination of the enthalpy

The reaction enthalpy is the enthalpy change of a sample during a chemical reaction. Reactions that release energy in the form of heat are called exothermic. Reactions in which energy must be supplied as endothermic.

Melt enthalpies are a simple example of endothermic processes, since one usually has to give heat work in a system in order to break up its solid crystal structure and convert it into a liquid phase with molecules that move freely relative to one another. An example of an exothermic reaction is a simple combustion process in which a substance reacts with oxygen to release energy.

Enthalpy determination with a calorimeter

If one measures a reaction on a calorimeter, one looks at the sample temperature comparatively with an ideally unreactive reference, which is in the same sample space and thus the same atmosphere. Both experience the same temperature environment. If the temperature of the sample to be measured rises or falls in comparison to the reference, a reaction takes place here.

Bestimmung Enthalpie mit Kalorimeter von Linseis

Sample holder of a calorimeter (Chip-DSC 10) on the upper side, reference measurement integrated on the underside of the sensor

Applications to determine enthalpy

Application: Asphalt

Measuring curve: Asphalt Enthalpy

Introduction and application: Asphalt is a sticky, black and highly viscous liquid or semisolid substance and consists of bitumen and aggregate. The primary use of asphalt is in road construction, where it is used as the glue or binder forthe aggregate particles.

Analysis using DSC: DSC is useful in studying the thermal behaviour of asphalts. It gives important parameters such as glass transition temperature, range of melting temperature of crystallites, and enthalpy of melting. Immediately following the Tg transition a small exothermic effect has been seen for most of the asphalts. This is believed to be the result of crystallization which occurs during the heating process. Following this exothermic effect are two or three endothermic peaks. The third one usually appears as a shoulder on the second peak. DSC testing of fractions based on their different chemical nature indicates that naphthene aromatics make a great contribution to the endothermic effect of the parent asphalt. Polar aromatics are presumed to be mainly responsible for the shoulder peak since they show a small endothermic effect at about the same temperature range. Asphaltene, due to its chemical nature, shows no endothermic effect.

Application: Melting and crystallization

Linseis DSC Polymer application - Melting and crystallization

Melting and Crystallization: Melting and crystallization are phase changes from organized solid to amorphous phases and vice-versa. Melting is a one-step process while crystallization involves nucleation and crystal growth. The enthalpy of melting can be used to measure crystallinity. Any process that makes it easier for molecules to be organized will raise the melting temperature. The crystallinity can also be calculated. For this sample must be pure material, not copolymer or fille. It must know enthalpy of melting for 100 % crystalline material (DHlit) and it can use a standard DHlit for relative crystallnity. The Crystallization is a two step process: Nucleation and Growth. The onset temperature is the nucleation TN. The peak maximum is the crystallization temperature Tc.

 

LINSEIS devices for determining the enthalpy

DTA PT 1600

DTA-PT1600
  • High temperature DTA
  • Modular instrument design (sample robot, gas dosing systems, muliple furnaces on a turntable, etc.)
  • Qualitative analysis of endothermic and exothermic reactions
  • Temperature range: -150°C up to 1000/1600/1750/2400°C
Details

Chip-DSC 10

Chip-DSC-10
  • The perfect DSC for Quality control and Education
  • Cost effective, space saving and highly innivative Chip DSC
  • -180 up to 600°C (LN2 Quench cooling)
Details

Chip-DSC 100

Chip-DSC-100
  • Unique Chip Technology – The next step in DSC
  • Modular expandable design (Sample Robot, Cooling options etc.)
  • Temperature range -180 up to 600°C (Peltier cooling, Closed-loop Intracooler or LN2 cooling)
Details

DSC PT 1000

DSC-PT1000
  • State of the Art DSC with user exchangable Metal Sensors
  • Temperature range -180 to 750°C
Details

DSC PT 1600

TGA-PT1600
  • Modular high temperature DSC
  • Determination of specific heat (Cp) and enthalpy from high temperature metals and ceramics
  • Temperature range -150 to 2400°C
Details

STA PT 1000

STA-PT1000
  • (TGA) Thermogravimety and (DSC) Differential Scanning Calorimetry
  • True top loading TG-DSC heat flux sensors
  • Numerous user excheangable TG, TG-DSC and TG-DTA sensors for any kind of application
  • Temperature range: RT up to 1000°C
Details

STA PT 1600

STA-PT1600
  • (TGA) Thermogravimety and (DSC) Differential Scanning Calorimetry
  • True top loading TG-DSC heat flux sensors
  • Numerous user excheangable TG, TG-DSC and TG-DTA sensors for any kind of application
  • Modular design: sample robot, turntable for up to two furnaces, vacuum tight design, different gas dosing systems, high pressure (up to 5 bar) option, vapor dosing system etc.
  • Temperature range: -150 up to 1600/1750/2000/2400°C
Details

STA MSB PT 1

  • Magnetic Levitation Balance (MSB)
  • Separation of balance and reactor for most demanding applications
  • -196 up to 2400°C
  • From Vacuum to 150 bar
  • For corrosive and toxic gases
Details

STA HP High Pressure

STA-HP2
  • Worlds only pressure TG-DSC (STA)
  • Combined (TGA) Thermogravimetry – (DSC) Differential Scanning Calorimetry
  • Different Gas and Vapor Dosing accessories
  • RT up to 1000/1400/ 1600/ 1800°C
  • From Vacuum up to 150 bar
Details