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Ceramics & Clays

Introduction

  • One of the largest groups of materials with the properties of non-metals and all are made  by firing or burning, often including silicates and metal oxides.

Raw Materials used in Ceramics

  • The traditional ceramics industry is largely based on various combinations of clay minerals, feldspar and silica.
  • The mineral raw materials used in the ceramic industry are mainly inorganic, non-metallic, crystalline solids formed by complex geologic processes.
  • Oxygen, silicon, and aluminium together account for90% of the elements in the earth’s crust, these, together with other minerals compounds of oxygen, constitute the greatest bulk of naturally occurring ceramic raw materials.
  • Clay Minerals
  • Talc and related Minerals
  • Silica  and Silicate Minerals
  • Feldspars and related Minerals.
  • Refractory Raw Materials

Types of Clay

  • Kaolin or China Clay
  • Ball Clays
  • Fire Clays
  • Flint Clays
  • Pottery Clays
  • Shale
  • Vitrifying Clays
  • Brick Clays
  • Slip Clays

Characteristics of Ceramics

  • Clays have  the ability to form clay-water composition and to maintain their shape and strength during drying and firing.
  • They fuse over a temperature range depending on their composition in such a way as to become dense and strong without losing their shape.

Traditional Ceramic Processes

1. Preparation of Raw Materials

  • Crushing
  • Grinding

2. Shaping Processes

  • Slip Casting
  • Plastic Casting

3. Semi-dry Process

4. Dry Process

New Ceramic Processes

1. Preparation of Raw Materials

  • Freeze Drying
  • Precipitation from solution

2. Shaping

  • Hot pressing
  • Isostatic pressing
  • Doctor-blade process
  • Injection moulding

3. Sintering

  • To bond individual grains into a solid mass
  • To increase density
  • To reduce or eliminate porosity

4. Finishing

  • To increase dimensional accuracy
  • To improve surface finish
  • To make minor changes in part geometry

Why Ceramic materials are more better than others??

  • Cheap in terms of its starting materials.
  • Compared to metals, lightweight and retain their strength up to 1000oC where metals tends to fail.
  • They have electrical, optical, and magnetic properties of value in the computer and electronic industries.

Common Factors which Effects the Process

  • Oxidation
  • Decomposition reactions
  • Phase transformations
  • Trapped gases
  • Non uniform mixing
  • Over firing
  • Hot pressing

Uses

  • Structural clay products
  • Whitewares
  • Refractories
  • Glasses
  • Abrasives
  • Cements
  • Advanced ceramics

Clay

  • Clay is  formed by the decomposition of rock through the action of weathering.
  • Impurities, such as sticks and leaves are taken out and the clay is then packaged for our use.

Type of Clay

1. Attaching Clay

  • Scoring
  • Slip

2. Hand Building

  • Pinch Pots
  • Coiling
  • Slab Rolling

Scoring

  • Scoring is the best way of attaching one piece of clay to another.
  • If clay is not properly scored, it will fall apart either when drying or during the firing process.

Slip

  • Slip is liquefied clay.
  • Slip is applied to scored surfaces and acts as a sort of “glue” onto attach one piece of clay to another.

Pinch Pots

  • They are formed by quickly pinching and turning a kneaded ball of clay. One of the most simple hand building techniques.

Coiling

  • Coiling is an ancient hand building method in which walls are constructed with and rolled, rope-like pieces of clay. The joints are then smoothed over to create one solid piece.

Slab Rolling

  • Slab construction is another rand building technique, in which the clay is rolled out onto flat pieces. The slabs are usually an even, consistent thickness and are then cut, scored, slipped and joined together.

Stages of Clay

  • Slip
  • Plastic
  • Leather-Hard
  • Greenware
  • Glazeware
  • Kiln

Important Points

  • Clay can be no thicker then your thumb.
  • Wedge clay to remove air bubbles, achieve uniform consistency, and to line up the particles of clay.
  • Don’t glaze the bottom of a piece.
  • Clay dust can be harmful if you are exposed to it for long periods of time, so keep your area clean, clay scraps off the floor and clean with water and a sponge.
  • Trapped air can cause clay to explode. So hollow out sculptural forms and put needle holes from the bottom of a piece.

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