KAOLIN

KAOLIN

1. General Introduction

Kaolin is a white, refractory clay formed through the weathering of aluminosilicate minerals, typically feldspar. Its primary mineralogical component is Kaolinite, with the theoretical chemical formula:

Al₂O₃ · 2SiO₂ · 2H₂O

Kaolin is a fundamental and indispensable raw material in the ceramic industry, directly involved in :

• Ceramic body – shaping and structural formation
• Ceramic glaze – stabilization, smoothing, and surface finishing

High-quality kaolin is usually refined to remove impurities such as Fe₂O₃ and TiO₂, achieving high whiteness and purity, which is essential for whiteware and premium ceramic products.

2. Composition and Classification

2.1. Chemical Composition (Theoretical)

Component	Formula	Content (%)
Aluminum Oxide	Al₂O₃	~30 – 39.5
Silicon Dioxide	SiO₂	~42 – 56
Structural Water	H₂O	~12 – 13.9

Note: Industrial kaolin always contains small amounts of impurities (Fe₂O₃, TiO₂).
Lower Fe₂O₃ and TiO₂ contents result in higher fired whiteness, which is especially critical for white porcelain and high-grade glazes.

2.2. Classification by Ceramic Application

• Refined (Washed) Kaolin
  • High whiteness (typically ≥ 75–85%)
  • Low Fe and Ti content
  • Used for: premium porcelain, sanitary ware, ceramic glazes
• Industrial (Crude) Kaolin
  • Medium whiteness
  • Used for: ceramic tiles, wall & floor tiles, products not requiring high whiteness

3. Typical Technical Properties (Ceramic Grade)

Parameter	Characteristics
Mineral formula	Al₂O₃ · 2SiO₂ · 2H₂O
Plasticity	Medium – good workability
Refractoriness	Stable and easy to control
Fired whiteness	High (depends on Fe₂O₃, TiO₂ content)

4. Applications in Ceramics

4.1. Ceramic Body Applications

Kaolin is a key component in body formulations for tableware, sanitary ware, electrical porcelain, and ceramic tiles:

• Improves plasticity and formability
  Facilitates mixing, pressing, rolling, or slip casting due to fine particle size and suitable water absorption.
• Enhances mechanical strength after firing
  Al₂O₃ from kaolin contributes to the formation of mullite (3Al₂O₃·2SiO₂) at high temperatures, a critical crystalline phase that improves strength, hardness, and thermal resistance.
• Improves product whiteness
  Refined kaolin ensures bright, clean whiteness, especially for high-end ceramic products.
• Reduces cracking and deformation
  Helps control drying and firing shrinkage.

4.2. Glaze Applications

Kaolin is an essential component in glaze formulations:

• Source of Al₂O₃ and SiO₂
  Al₂O₃ stabilizes the glaze, increases viscosity, and reduces excessive glaze flow, peeling, or crawling.
• Suspending agent – anti-settling
  Maintains uniform dispersion of glaze particles, preventing hard settling during storage.
• Improves surface smoothness and gloss
  Fine kaolin particles contribute to smooth, glossy fired surfaces with consistent color.
• Adjusts glaze melting behavior
  Helps balance glaze vitrification to match the firing temperature of the ceramic body.