A Chemical and Thermal Characterization Analysis of Kaolin

Abstract

This study evaluates the chemical and thermal characterization of kaolin powder by means of Thermogravimetric Analysis (TGA) and Fourier Transform Infrared (FTIR) Spectroscopy. The TGA study was performed per ASTM E1131 by incrementally heating the sample from 22 °C to 1000 °C and results showed a total weight loss of 5.071 % with 4.354 % occurring between 400 °C and 800 °C as kaolinite dehydroxylated into metakaolin. A high residual mass of 94.930 % left on the basis residue at 1000 °C proved thermal stability and low volatility. Metakaolin being an amorphous aluminosilicate further improved thermal resistance and chemical inertness of the kaolin powder definitions of kaolin that had relevance reindustrial applications.In combination to the TGA study, the FTIR analysis was performed in accordance with ASTM E1252 methodology covering the infrared spectral range of 4000–500 cm?¹ and thus confirmed the mineralogical composition. Firstly, the presence of kaolinite was confirmed by the very sharp Al–OH bending band at 925.87 cm?¹ and additional minor overtone bands at 1984.25 cm?¹ and 2149.94 cm?¹ further confirmed structural composition. Furthermore, there was no significant absorption in the range of 1400–1600 cm?¹ providing evidence for the absence of carbonate or organic impurities and further confirming the purity of the sample.TGA and FTIR evidence shows kaolin has high thermal stability, structural consistency, and mineralogical purity that can serve applications in refractories, insulation bricks, and advanced ceramics.

Introduction

This study focuses on analyzing the chemical composition and thermal behavior of kaolin, a naturally occurring clay mineral (Al?Si?O?(OH)?), using Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR). The aim is to determine kaolin’s suitability for high-temperature applications, such as insulation bricks, ceramics, and refractories.

???? 1. Background and Purpose

• Kaolin is widely used due to properties like:

  • Thermal and structural stability

  • Chemical inertness

  • Low thermal conductivity

• At elevated temperatures, kaolinite transforms into metakaolin, a thermally stable amorphous phase with high pozzolanic activity.

• This transformation and kaolin’s phase purity are crucial for industrial applications requiring durability and energy efficiency.

• The study aims to characterize the thermal decomposition and structural integrity of kaolin using standardized methods (ASTM E1131 and E1252).

???? 2. Methodology

• Sample Preparation: Raw kaolin powder (50g), preheated at 80°C to remove surface moisture.

A. TGA (Thermogravimetric Analysis):

• Instrument: TA Instruments Platinum HT

• Conditions: Heated in nitrogen, 20°C/min, up to 1000°C

• Purpose: Measure weight loss and identify thermal decomposition stages, especially dehydroxylation (conversion to metakaolin)

B. FTIR (Fourier Transform Infrared Spectroscopy):

• Technique: KBr pellet method

• Scan range: 4000 to 400 cm?¹

• Purpose: Identify functional groups, purity, and presence of kaolinite or impurities.

???? 3. Results and Findings

A. TGA Findings:

• Total weight loss: ~5.07% (less than reported in literature ~10–12%)

  • Indicates high purity and low volatile content

• Major mass loss occurred between 400°C–800°C

  • Confirms dehydroxylation of kaolinite to metakaolin

• High residue (~94.93%) supports thermal stability, dimensional integrity, and suitability for insulation applications.

B. FTIR Results:

• Strong absorption band at ~925.87 cm?¹: Al–OH bending, confirming kaolinite structure

• Additional bands at 1984.25 cm?¹ and 2149.94 cm?¹: Combination and overtone modes typical of kaolinite

• Absence of carbonate-related bands (1400–1600 cm?¹): Confirms mineralogical purity, absence of contaminants

???? 4. Interpretation and Application Potential

• High-purity kaolin, with low thermal decomposition and strong structural stability, is ideal for:

  • Thermal insulation bricks

  • Refractory linings

  • High-performance ceramics

• Formation of metakaolin phase further enhances thermal resistance and chemical inertness

• No impurities or reactive phases identified, suggesting excellent potential for advanced thermal and engineering materials

• Also supports composite formation or modification for specific industrial performance goals.

Conclusion

The current research provides significant chemical and thermal analysis of kaolin powder by Thermogravimetric Analysis (TGA) and Fourier Transform Infrared (FTIR) spectroscopy. In accordance with data presented through TGA analysis the sample produced a total weight loss of 5.071%, most weight loss in the temperature range of 400–800 °C because that is when kaolinite fully dehydroxylates to metakaolin. Dehydroxylation is important to enhance the thermal stability as well as significantly enhance the chemical inertness of metakaolin to enable it to be utilized at elevated temperatures. FTIR spectroscopy validated kaolinite phase with a sharp Al–OH bending absorption at 925.87 cm?¹ and validated no detectable impurities of carbonates or organics. This significantly provided the researchers with confidence regarding mineralogical purity and structural integrity of the tested kaolin material. Due to this singular ability to compare to literature, the authors assumed that their low weight loss of the kaolin sample also showed a very pure kaolin sample with very few volatile contents; a positive attribute for greater thermal performance in terms of application as a sustainable insulation and refractory. The overall findings suggest that the kaolin powder investigated possesses good thermal stability, workable chemical composition, and promise for limited industrial uses. It possesses the ability to maintain structural stability upon exposure to thermal cycling, high purity composition, and numerous engineering projects have some structural consideration to be suitable starting material for manufacturing thermal insulation bricks and refractory ceramics, among other inclusion project that are heat-resistant. Continuous study of potential minor alterations to, or necessary combinations of kaolin may be investigated to reflect whether either, mechanical strength or thermal conductivity of kaolin may be altered to suit future industrial needs. Taken in totality, these findings establish the potential of this kaolin powder for sustaining energy efficient and long term industrial processes, and advances environmentally friendly and economical thermal management needs.

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Copyright

Copyright © 2025 Aruna Devi, Anurag Shrivastava, Dr. Rohit Srivastava, Atul Raj. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.