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Standard Operating Procedure for Thermogravimetric Analysis


    Thermogravimetric Analysis is a technique in which the change in mass of a substance is monitored as a function of temperature or time by subjecting a sample in a controlled temperature program in a controlled atmosphere.

      Note: No Corrosive gases can be used.

      Cahn TherMax 500 TGA System

      Introduction

      Thermogravimetric Analyzing (TGA) is commonly employed in research and testing to determine characteristics of materials such as degradation temperatures, absorbed moisture content, the level of inorganic and organic components in a compound, decomposition points of explosives and the presence of solvent residues. It is also often used to estimate the corrosion kinetics in high temperature oxidation.

      The Cahn TherMax 500 TGA system specializes in demanding applications where high temperatures, pressures, and aggressive atmospheres are required.  Pressure can be used to enhance or speed up reactions. The weight changes of a sample is measured over a given temperature and pressure range under specific environmental conditions.

      The furnace temperature follows a temperature profile sequence established by the user in a method in the Thermax software. The software periodically records weight and pressure measurements and stores them on the computer.

      After the measurement cycle or “run” is completed, the data file can be processed in the Analysis mode of the software. Raw or processed data may be plotted on the monitor display or on a graphics plotter, printed in tabular form, or copied on a separate diskette for archiving

      The three parts of the Thermax 500 are the:

      • Mainframe - the instrument hardware which includes: pressure balance, furnace vessel, stand and elevator.
      • Console - which: houses the instrument electronics, displays data and warnings and connects the Thermax with the computer.
      • Pressure/Flow Controller - which: controls pressure in the instrument, controls flow for three (3) gases and indicates pressure in the instrument.
      • The Cahn Thermax 500 instrument measurea weight changes on samples of up to 100 grams,  from room temperature to 1100°C, with a maximum sensitivity of one microgram.
      • The furnace follows a precise temperature profile of ramps and isotherms, established by the user, under constant computer control.
      • Gas flow and pressure is controlled by a pressure/flow controller.
      • Time, weight and temperature data are acquired at defined intervals and the data is stored on the computer's hard disk.
      • Cahn's Thermax software allows you to edit and perform analytical functions on your run data. A permanent record of the raw data or the processed data can be made by printing in tabular form or copying to a diskette.

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      Product Specifications

      BALANCE

      Capacity

       

      Weighing

      100 grams

      Volume

      30 cc

      Weighing Range

      Maximum Weight

      ±10 g

      Sensitivity

      1µg

      Temperature Drift

      10 µg/°C

      Accuracy at ambient temperature

      <0.02%

      Repeatability

      <0.001%


      FURNACE

      Temperature Range

       

      at ambient pressure

      Up to 1100°C

      at 1000 psi

      Up to 1000°C

      Maxiumum Heating Rate

      25°C/min

      Temperature Repeatability

      ±3°C


      PRESSURE LEVEL

      Maximum Pressure at 25°C

      1500 psi

      Maximum Pressure at 1000°C

      1000psi

      Internal Volume

      0.3 liters

      Thermocouple

      1/8" Chromel-Alumel

      Atmospheres

      Static or dynamic gases including H2O, alcohols, aldehydes, ketones, alkanes, dilute acids, H2, CO2.

      Sensitivity

      1µg

      Temperature Drift

      10µg/°C

      Accuracy at Ambient Temperature

      <0.02%

      Repeatability

      <0.001%

       

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      Standard Operating Procedure

      1.0 Log in to ChemFom via the main computer (furthest right computer along the rear wall)

      1.1         Select TGA

      1.2         Click on the time and select the max amount of time that I will be using the TGA

      1.3         Select the “Express Login” button

      2.0         Open all the gas values – should hear a rush indicating the valve is open

      3.0         Move to the TGA computer and open the Thermal Acquisition program

      Locate thermal acquisition program on desktop

      4.0         Make sure the fan is off, if it is not, turn the fan off. You can turn it off through console.

      5.0         Make sure the cage is all the way up before you loosen the bolts to get the sample pan out.

      6.0         Remove clamp near the top of the apparatus and lower the apparatus

      6.1         Loosen all the bolts first . They will need to come all the way or most of the way out

      6.2         Then take the ring off.

      6.3         Ensure that the clamp is no longer in a position to impede the lowering of the apparatus before lowering

      7.0         Clean out the sample tray of any previous sample residue – use qtips/cotton swabs to achieve this – and return the sample tray to the hook

      8.0         Raise the apparatus ensuring everything is correctly aligned and that the inner apparatus slides easily into the outer apparatus

      9.0         Retighten the clamp and ring

      9.1         Ensure the clamp is closed correctly so the ring can fit around it

      9.2         Tighten the six top bolts until finger tight

      9.3         Slide the ring up and around the clamp, aligning the holes and tightening the ring bolt until finger tight

      10.0      Set the gas ratios

      10.1      At present, the desired ratio is the standard ratio of 8:6:6 P:R:F

      11.0      Turn on the fan

      12.0      Moving to the computer software that was previously opened, select the “Tare Balance” button

      'Tare balance' button on top left toolbar

      13.0      Repeat step 5.0

      14.0      Add desired sample to the sample bin

      14.1      Typical samples used are in the 20-50mg range

      15.0      Repeat steps 7.0-8.3

      16.0      Record the initial mass and any other initial conditions of interest shown on the screen

      17.0      Set up the operating method for the test

      'Methods' located on top left menu

      17.1      In the “Method” menu, select the option to edit the current method

      17.2      Save the method under the desired name

      17.3      Change the parameters accordingly

      17.3.1 Keep the Switch States the same

      17.3.2 Select Dynamic or Isothermal (most of my work, if not all of it, will be Isothermal)

      17.3.3 Enter the desired temperature (only one temperature for Isothermal)

      17.3.4 Enter the time duration in seconds

      17.3.5 Set the Max Temperature to the desired temperature

      17.3.6 Set the Min Temperature to 25 degrees C

      17.4      Add operator name and sample name to the parameters list

      17.5      Once all parameters have been entered, save the method and return to the main screen

      'Method settings' pop-up window

      18.0      With everything successfully set up, click the run button to begin running the test

      19.0      Once the test has concluded, record the final mass and other final conditions of interest

      20.0      Save the graph to a flash drive

      21.0      After saving all data, exit the Thermal Acquisition software

      22.0      Turn off the fan

      23.0      Repeat steps 5.0-8.3 to remove remainder of tested sample and clean out the sample bin

      24.0      Turn off the gas valves

      25.0      Returning to the main computer, double the open session and log out to end the session

      A typical TGA graph looks like this. 

      Non-linear graph with wt% decreasing as temperature increases

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      Keywords:standard operating procedure SOP Thermogravimetric Analysis TGA Cahn TherMax 500 microanalysis   Doc ID:98380
      Owner:Beth E.Group:University of Illinois School of Chemical Sciences
      Created:2020-03-02 14:39 CDTUpdated:2021-03-08 13:03 CDT
      Sites:University of Illinois School of Chemical Sciences
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