Thermal Lens Calorimetry - PowerPoint PPT Presentation

1 / 20
About This Presentation
Title:

Thermal Lens Calorimetry

Description:

Distances between components on the optical rail. Laser power. Frequency of the chopper. Aperture diameter ... Prepare a set of standard solutions using ... – PowerPoint PPT presentation

Number of Views:209
Avg rating:3.0/5.0
Slides: 21
Provided by: ashleig1
Category:

less

Transcript and Presenter's Notes

Title: Thermal Lens Calorimetry


1
Thermal Lens Calorimetry
  • Ashleigh Baber
  • Dr. Seidman
  • Karishma Rajani
  • Summer 2004
  • Randolph-Macon Womans College

2
Thermal Lens Phenomena
Higher energy level
photon
Laser Beam
Thermal energy
electron
Ground State
Sample
3
Divergence
4
(No Transcript)
5
Experimental Design
6
Experimental Design without Sample
7
Square Wave
ON
OFF
OFF
8
Experimental Design
9
tc
Ic
10
Cpheat capacity kthermal conductivity tctime
constant Mmolar mass wcconfocal beam
waist rdensity
11
Why Calibrate the Procedure?
  • The appearance of the waveform is affected by
    factors such as
  • Distances between components on the optical rail
  • Laser power
  • Frequency of the chopper
  • Aperture diameter
  • All factors except for the aperture diameter are
    kept constant.

12
Method for Calibrating the Procedure
  • Prepare a set of standard solutions using
    indophenol blue dye and liquids with known heat
    capacities.
  • Measure the bloom diameter and vary the aperture
    of the diaphragm until the correct time constant
    is obtained.
  • Aperture diameter is plotted versus Bloom
    diameter and the result is a straight line. This
    graph may then be used as a calibration curve for
    finding the heat capacity for unknowns.

13
Total Calibration Curve
14
Determining the Cp of Unknowns
  • A solution is made with indophenol blue dye and a
    liquid with an unknown heat capacity.
  • The bloom diameter is measured and using the
    equation for the line, the aperture diameter is
    calculated.
  • Several trials are conducted with the calculated
    aperture diameter to find an average time
    constant which is plugged into the equation to
    find the heat capacity.

15
(No Transcript)
16
Results
  • A range of absorbances fit on one line, reducing
    the time necessary for sample preparation.
  • Error in heat capacities are random, due to the
    precision of the oscilloscope.
  • It seems as though this method could be as
    reliable as solution calorimetry and it has the
    potential to be faster.

17
Experimental Design
18
(No Transcript)
19
(No Transcript)
20
Proposed Procedure
  • Prepare an unknown so that the absorbance falls
    within the range.
  • Measure the sample to diaphragm distance.
  • Calculate the slope and y-intercept from the
    calibration lines.
  • Determine the bloom diameter.
  • Calculate the aperture diameter and run the
    sample.
  • A.D. slope B.D. y-intercept
Write a Comment
User Comments (0)
About PowerShow.com