ME4331 – DSC Review APR 29, 2008 Jeung Hwan Choi.

ME4331 – DSC Review

APR 29 , 2008

Jeung Hwan Choi

CALORIMETRY

Calorimetry

- The science of counting the heat of chemical reactions or physical changes.

- In constant-pressure calorimetry, the heat measured represents the enthalpy change.

Differential Scanning Calorimetry

Differential Scanning Calorimetry (DSC) is a thermal analysis method in which the difference in the amount of heat applied (or removed) to increase (or decrease) the temperature of a sample material and a reference material are measured as a function of temperature.

- Höhne et al. (1996) Differential Scanning Calorimetry- Perkin Elmer, Inc. - Wikipedia.org

DIFFERENTIAL SCANNING CALORIMETER

samplefurnace

referencefurnace

- Höhne et al. (1996) Differential Scanning Calorimetry- Perkin Elmer, Inc.

- The DSC will maintain the temperatures of the sample and reference equal during a scan (change of both materials from one temperature to another).

- The Pyris1 Differential Scanning Calorimeter allows the user to change the temperature at a prescribed constant rate (linear temperature control).

DSC – ENDOTHERMIC VS. EXOTHERMIC

- Höhne et al. (1996) Differential Scanning Calorimetry- Perkin Elmer, Inc.

- When the sample undergoes a physical transformation such as phase transitions, more (or less) heat will need to flow to it than the reference to maintain both at the same temperature.

- This noticeable difference results in the appearance of an upper or lower peak, depending on whether the transformation is exothermic or endothermic.

- A solid sample melting to a liquid willrequire more heat flowing to the sampleto increase its temperature at the samerate as the reference, and is an exampleof an endothermic process.

- If a liquid crystallizes into a solid duringa cooling scan, more heat would have tobe removed compared to the referenceand is an example of an exothermicprocess.

DSC outline – latent heat

DSC – MELTING POINT

• Melting point measurement

Reference : Höhne et al. Differential Scanning Calorimetry 1996 Perkin Elmer, Inc.

heating rate = 5 °C/min

- Melting point of a pure substance (i.e. ice) is the onset temperature

- Onset is determined from the intersection of the slopes of the base and the rising curve


DSC - LATENT HEAT

• Latent heat of fusion of ice

Reference : CRC Handbook of Chemistry and Physics 2007


DSC - LATENT HEAT

• Latent heat measurement


2

1

2

1

11T

T

t

t

dTdT

dt

dt

dH

mdt

dt

dH

mh dT

RateingCoolHeat

onCompensatiPower

m

T

T2

1)(

1


Possible errors

- Weight value

- Evolution width

- Baseline error (Instrument based)

- Baseline error (sample based)


DSC - BASELINE

• Selecting a baseline


Standard(linear)

Sigmoidal Horizontal(from right)

Horizontal(from left)

Linear baseline suffices for samples that : - are small in weight / volume - have a small specific transition energy - undergo a slow scanning rate

Otherwise, sigmoidal baseline gives a good result

DSC outline – specific heat

DSC - SPECIFIC HEAT

• Specific heat of ice / water

Reference : CRC Handbook of Chemistry and Physics 2007


DSC - SPECIFIC HEAT

• Specific heat measurement


dT

dt

dt

dH

mdT

dH

mcp

11

RateingCoolHeat

onCompensatiPower

m )(

1


Red :with water

Blue :empty

Green :specific heat


DSC – PHASE DIAGRAM

• System NaCl-H2O Phase Diagram



• 1xNaCl Thermal Analysis



• 23.3%(w/w) NaCl Thermal Analysis



• NaCl+H2O Thermal Analysis

Cryomicroscopy - layout

CRYOMICROSCOPY

• Visualization of freeze-thaw events

Reference : Linkam Scientific Instruments

video text overlay

computer interfaced temperature controller

cooling pump

LN2 dewarmicroscope

cryostage


CRYOMICROSCOPY

• Growth of Primary Ice

Video credits : Bumsoo Han


CRYOMICROSCOPY

• Solidification of the Eutectic

Video credits : Bumsoo Han

ADD: 10xPBS eutectic (photo)

EUTECTIC SOLIDIFICATION

• Phase change behavior in salt solutions (10xPBS)

Photo credits : Adam Grovender

pre-eutectic @ -26°C eutectic @ -26°C(after supercooling)

DSC CAL

• Diamond DSC 5C/min calibrations :

- Baseline Curvature Calibrations

- Baseline Slope Calibrations

- Sample Temperature Calibrations

- Furnace Calibrations

- Heat Flow Calibrations

DSC CAL

• Diamond DSC 5C/min calibrations : Baseline Curvature - minimize amplitude of curve for operating temp. range

Factory default Coarse control : + 1 Fine control : + 3

DSC CAL

• Diamond DSC 5C/min calibrations : Baseline Curvature - minimize amplitude of curve for operating temp. range

Factory default Fine control : + 10 Fine control : + 13

Fine control : + 14 Fine control : + 15 Fine control : + 20

DSC CAL

• Diamond DSC 5C/min calibrations : Baseline Slope - minimize slope of curve for operating temp. range

Factory default Slope : - 5 Slope : - 4

FSlope : - 3 Slope : + 5

DSC CAL

• Diamond DSC 5C/min calibrations : Sample Temp. Cal. - Correctly predict transition temperatures of standards

n-Decane : Expected = -29.66 , Measured = -31.73

Scyclohexane : Expected = -87.06 & 6.54 , Measured = -87.1 & 5.2

DSC CAL

• Diamond DSC 5C/min calibrations : Furnace Calibration - 9-point temperature calibration between upper and lower temp. range - matches platinum resistance thermometer and programmed temp.

-150.04 -125.01 -100.02 -75.02 -50.05 -24.93 -0.002 24.99 49.99 75.01 99.99

DSC CAL

• Diamond DSC 5C/min calibrations : Heat Flow Calibration - match enthalpy values with known reference materials

n-Decane : H = 202.09 vs 201.19 +/- 0.5, -0.45% T = -29.66 vs -29.66 +/- 0.04

DSC CAL

• Diamond DSC 5C/min calibrations : Heat Flow Calibration - match enthalpy values with known reference materials

H2O : H = 333.8 vs 338.6 +/- 0.15, +1.07% T = 0 vs -0.43 +/- 0.01

END OF SLIDES

ME4331 – DSC Review APR 29, 2008 Jeung Hwan Choi.

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