# Compositional Properties and Colorimetric Characterization of Calcined Clays from the Central-West Region of Paraná and Their Application as Sustainable Pigment in Paints

## TL;DR

This study explores how calcining clays from Brazil at different temperatures affects their properties and potential use as sustainable pigments in paints.

## Contribution

The novel contribution is identifying a clay sample with high iron content that shows significant color variation and structural changes suitable for pigment use.

## Key findings

- Clay sample BC showed significant structural and color changes due to iron compound phase changes during calcination.
- Clay sample GC retained structural stability even after calcination at 1000°C.
- BC demonstrated greater potential as a pigment due to pronounced color variation.

## Abstract

This study investigated
two clays from the Guarapuava region, Paraná,
Brazil, which were calcined at different temperatures. Their compositional
and structural properties were evaluated using diverse characterization
techniques, and their colorimetric analysis was performed using the
CIELab* system. Significant changes in the structural and granulometric
properties of the clays were observed, as well as colorimetric changes
in the samples that occurred due to calcination at temperatures of
200, 400, 600, 800, and 1000 °C. The clays were tested as pigments
in colorless and white acrylic paints and applied to plaster blocks.
Among the two clay samples, one (designated GC) exhibited a high quartz
content and showed no significant structural changes even after calcination
at 1000 °C, as confirmed by XRD analysis. In contrast, the sample
designated BC, which presented the highest iron content via EDXRF
analysis, demonstrated the most significant structural alterations
and phase changes in XRD, TGA, and particle size tests. Furthermore,
BC yielded more pronounced color variations due to changes in the
phases of its iron compounds, indicating its greater potential for
use as a pigment.