How do I calculate activation energy using TGA curves in excel?

By googling "activation energy tga" you can find a lot of information.

The first hit (decomposition kinetics using TGA, TA-075 - TA Instruments) shows which equations to use for both dynamic and isothermal method.

There are several well-known methods (Coats-Redfern method, Freeman-Carroll method etc) ofr isothermal and non-isothermal analysis, but first of all you should know whether your reaction is first order or not. Depending on that you can choose a suitable model.

Hello Arzak,

I am in agreement with Birgit. There are numerous kinetic computation methods that can be used to fit TGA data in order to extract kinetic information. However, you don’t really need to know the reaction order of the process if you’re only interested in extracting the activation energy. For example you can use the isoconversional methods to calculate the activation energy without any prior knowledge of the reaction model.  Also the isoconversional approach allows you to investigate how the activation energy changes as the reaction progresses.

In order to perform the calculations in excel you will need to export the raw data as text files. You will then need to firstly calculate α (which is the degree or conversion or fraction converted) and convert temperature to K (if it is in °C) in excel for the TGA data obtained at each heating rate.

W₀ is the initial sample weight, W_T is the weight at temperature (T) and W_∞ is the weight at the reaction end point.

It is typically a good idea to plot α against Temperature (K) to see how α shifts with heating rate. All you need to do from here is to calculate and plot the left hand side of your chosen isoconversional method against 1/K for a given α.

If you want more information on kinetic computation then read ICTAC Kinetics Committee recommendations for performing kinetic computations on thermal analysis data, 2011.

I hope this helps and good luck

Hello again,

As Samuel already mentioned, the use of the degree of conversion is quite nice. But I still think that one needs to know the reaction that occurs - otherwise it is not possible to accurately describe which reaction is going on during the heating. By that I mean that you still need to know for which reaction you are calculating the activation energy.

The use of the direct Arrhenius method - plotting 1/T (in K^-1) to ln[-{ln(1-α)}/T²] - is also quite elegant - the slope of the plot gives you E/R, assuming the right reaction order n.

In addition, I would suggest an article by Krishnan Rajeshwar in Thermochimica Acta, 45, 1981. It very nicely describes different computational models and also offers several ways for the calculation of the reaction order and also offers some results for their material.

If you have experiments with several different heating rates, you could also use some methods based on them, for example the KAS-method or Carne equation.

To be honest, there are endless ways how to calculate the activation energy (which parameters to plot) and it can be hard to decide which method to choose, but they mostly give results of the same magnitude.

Best of luck!

Is this method suitable for single heating rate? or we have to take it at many heating rates?

I mean that I did TGA for only one heating rate! can I determine the activation energy by the above method?

Thanks

Hi

There is a software, you can calculate the activation energy in a just a few seconds, its name is AKTS (Advanced Kinetic and Technology Solution) all what you need is to load your different heating rates TGA or  DSC curves ( heating rates should be below 8 K/min i.e. 1, 2, 4, 6 ,8 K/min)

However, if you still interesting in calculating the Ea using Excel, please let me know

Hope this helping

Have a very good day

Ahmed 

Hi,

Please share the excel sheet. if you have some books to understand this, please also share.

Regards,

Aroh 

Hi, I also need a spreadsheet on how to calculate activation energy. My main issue is how to compute d(conversion)/dt... 

May i know how to calculate pre-exponential factor (A) from coats redfern method from the intercept graph. I have no idea wht value to use on T.

Dear Ahmed I. Osman, I am unable to import my DSC or TGA file in AKTS (Advanced Kinetic and Technology Solution) can you please help me regarding this. I will be thankful to you.

Thanks

Hey guys!

I know I am coming in very late with a response, but if others are wondering about this, I might have something that could help you.

I have previously calculated the activation energy using the Ozawa/Flynn/Wall Method. This method is described in the ASTM E1641 standard, and once the spreadsheet is set up, it is pretty easy to use.

The standard is well described, and to apply it it is pretty easy. You only have to get the degradation curves at 4 different rates, and then with the prescribed calculation, you can get a chart that with its slope will give you the activation energy. The example temperature they give is 1, 2, 5, 10°C, which can be pretty time consuming (as repeatability also should be proven). My undergrad research was based on testing if at different rates the composite would act the similar way. For more info you can look at "Thermal degradation of MWCNT/polypropylene nanocomposites: A comparison of TGA and laser pulse heating" but for my composite using higher rates was okay.

If someone would like to know what the spreadsheet looks like, you can message me.

Hope this will help someone.

Regards,

ASTM or Friedman are good options for Excel. However I would like to know how is possible to solve those models in Matlab, python or Fortran. I have 5,10,20,30, 40 and 50K/min.

Thank you

Ahmed I. Osman

Hello Sir,

kindly share excel sheet to calculate Ea.

Hi @ Mohsina Taj

If you want to calculate it then send me the data and I will calculate it for you using my software

Thanks

Ahmed

helpful

You can calculate Ea* from TGA can be calculated by using H.H. Horowitz and G. Metzger, Anal, Chem., 35 (1963) 1464. Coats and Redfern Nature(London) 201(1964) 68 and DTA by using] H.J. Borchardt and F. Daniels, J. Am. Chem. Soc., 79 (1957) 41. and del H and del S by using R Roy et al J Chem Soc, Dalton trans (1984)1681 .

I want to ask, if we are calculating activation energy in between a range of temperature(T1 and T2), what will be the fraction of mass.

i.e. mo=initial mass( will it be mass taken at starting of TGA or at T1?), m= mass at temperature(will it be mass taken at T2?), m infinity= final mass(will it be mass at the end temperature of TGA of mass at T2). please make it clear

How activation energy is determined using kissinger eqn (in spreadsheet) with the help of temperature and sensitivity column in dsc?

Ashish

I have thé dame. Question as you.

Have you round thé answer jet?

If you round it telle me, ans I will do thé dame

Thanks un advance

Ahmed I. Osman Respected sir,

I want to learn tha analysis of TGA and its analysis basically which mathod you think is a more suitable and also which software you are using it to analysis

Hi Ravi Varasada,

If you are conducting kinetic modelling on biomass feedstock, then the differential isoconversional method is the most accurate and reliable method.

Kind regards

Ahmed

Thanks, Prof. Ahmed

I would like to ask you if I can use AKTS to get the thermodynamic and transport files.dat for reactions such as NH3 decomposition reactions.

Thanks

Mostafa

Hey Ravi Varasada

You can use MS excel to obtain the kinetics of the materials you are working with. Remember to keep your temperatures in Kelvin. Be sure to obtain the conversion rate from the change in mass, then obtain a natural log of the conversion as a function of its temperature at each specific time.

Regards,

Vianney Andrew Yiga Thanks For your valuable reply but i want to learn the thing about the parameter and calculations

Ravi Varasada I have attached an excel file for you to follow. This is based on Coats-Redfern (1 heating rate)

What is the relationship between onset temperature (determined from TGA weight loss curve) and Ea? Are they must be linearly proportional?

The easiest way is to you use the Kissinger method:

This method gives the value of activation energy from a plot of ln(θ/Tm²) against 1,000/Tm (temperature in Kelvin) for a series of measurements recorded at different heating rates (θ), where Tm represents the temperature at which peak differential thermal analysis (DTG) deflection takes place to estimate the Ea and A:

ln(θ/Tm²)= ln(AR/Ea)-Ea/(RT), R=8.4497 J/mol.K.

y= b- ax:

y= ln(θ/Tm²),

R=8.4497 J/mol.K.

a= Ea/R = slope -> from the slope Ea= a*R

b= ln(AR/Ea)= constant --> A= (Ea/R)*exp(b)

P.N: temperature in Kelvin

Also you can use KAS or FWO methods.

Good Luck

Montassar-Ayari@ how can I be in touch with you for more explanation concerning parameters estimations