A Low Cost Tester of Glaze Melt Fluidity
A One-speed Lab or Studio Slurry Mixer
A Textbook Cone 6 Matte Glaze With Problems
Adjusting Glaze Expansion by Calculation to Solve Shivering
Alberta Slip, 20 Years of Substitution for Albany Slip
An Overview of Ceramic Stains
Are You in Control of Your Production Process?
Are Your Glazes Food Safe or are They Leachable?
Attack on Glass: Corrosion Attack Mechanisms
Ball Milling Glazes, Bodies, Engobes
Binders for Ceramic Bodies
Bringing Out the Big Guns in Craze Control: MgO (G1215U)
Ceramic Glazes Today
Ceramic Material Nomenclature

Changing Our View of Glazes
Chemistry vs. Matrix Blending to Create Glazes from Native Materials
Concentrate on One Good Glaze
Cone 6 Floating Blue Glaze Recipe
Copper Red Glazes
Crazing and Bacteria: Is There a Hazard?
Crazing in Stoneware Glazes: Treating the Causes, Not the Symptoms
Creating a Non-Glaze Ceramic Slip or Engobe
Creating Your Own Budget Glaze
Crystal Glazes: Understanding the Process and Materials
Deflocculants: A Detailed Overview
Demonstrating Glaze Fit Issues to Students
Diagnosing a Casting Problem at a Sanitaryware Plant
Drying Ceramics Without Cracks
Duplicating Albany Slip
Duplicating AP Green Fireclay
Electric Hobby Kilns: What You Need to Know
Fighting the Glaze Dragon
Firing Clay Test Bars
Firing: What Happens to Ceramic Ware in a Firing Kiln
First You See It Then You Don't: Raku Glaze Stability
Fixing a glaze that does not stay in suspension
Formulating a Clear Glaze Compatible with Chrome-Tin Stains
Formulating a Porcelain
Formulating Ash and Native-Material Glazes
Formulating Your Own Clay Body
G1214M Cone 5-7 20x5 Glossy Base Glaze
G1214W Cone 6 Transparent Base Glaze
G1214Z Cone 6 Matte Base Glaze
G1916M Cone 06-04 Base Glaze
G1947U/G2571A Cone 10/10R Base Matte/Glossy Glazes
Getting the Glaze Color You Want: Working With Stains
Glaze and Body Pigments and Stains in the Ceramic Tile Industry
Glaze Chemistry Basics - Formula, Analysis, Mole%, Unity, LOI
Glaze chemistry using a frit of approximate analysis
Glaze Recipes: Formulate Your Own Instead
Glaze Types, Formulation and Application in the Tile Industry
Having Your Glaze Tested for Toxic Metal Release
High Gloss Glazes
How a Material Chemical Analysis is Done
How desktop INSIGHT Deals With Unity, LOI and Formula Weight
How to Find and Test Your Own Native Clays
How to Liner-Glaze a Mug
I've Always Done It This Way!
Inkjet Decoration of Ceramic Tiles
Interpreting Orton Cones
Is Your Fired Ware Safe?
Leaching Cone 6 Glaze Case Study
Limit Formulas and Target Formulas
Low Budget Testing of the Raw and Fired Properties of a Glaze
Low Fire White Talc Casting Body Recipe
Make Your Own Ball Mill Stand
Making Glaze Testing Cones
Monoporosa or Single Fired Wall Tiles
Organic Matter in Clays: Detailed Overview
Outdoor Weather Resistant Ceramics
Overview of Paper Clay
Painting Glazes Rather Than Dipping or Spraying
Particle Size Distribution of Ceramic Powders
Porcelain Tile, Vitrified or Granito Tile
Rationalizing Conflicting Opinions About Plasticity
Ravenscrag Slip is Born
Recylcing Scrap Clay
Reducing the Firing Temperature of a Glaze From Cone 10 to 6
Single Fire Glazing
Soluble Salts in Minerals: Detailed Overview
Some Keys to Dealing With Firing Cracks
Stoneware Casting Body Recipes
Substituting Cornwall Stone
Super-Refined Terra Sigillata
The Chemistry, Physics and Manufacturing of Glaze Frits
The Effect of Glaze Fit on Fired Ware Strength
The Four Levels on Which to View Ceramic Glazes
The Majolica Earthenware Process
The Physics of Clay Bodies
The Potter's Prayer
The Right Chemistry for a Cone 6 MgO Matte
The Trials of Being the Only Technical Person in the Club
The Whining Stops Here: A Realistic Look at Clay Bodies
Those Unlabelled Bags and Buckets
Tiles and Mosaics for Potters
Toxicity of Firebricks Used in Ovens
Trafficking in Glaze Recipes
Understanding Ceramic Materials
Understanding Ceramic Oxides
Understanding Glaze Slurry Properties
Understanding the Deflocculation Process in Slip Casting
Understanding the Terra Cotta Slip Casting Recipes In North America
Understanding Thermal Expansion in Ceramic Glazes
Unwanted Crystallization in a Cone 6 Glaze
Variegating Glazes
Volcanic Ash
What Determines a Glaze's Firing Temperature?
What is a Mole, Checking Out the Mole
What is the Glaze Dragon?
Where Do I Start?
Why Textbook Glazes Are So Difficult

Ceramic Tile Clay Body Formulation

Description

An overview of the technical challenges a technician in the tile industry faces in making good tiles from the least expensive materials and process possible.

Article

The ceramic tile industry is by far the largest user of clay bodies in ceramics. If you are a technician from another sector of ceramic industry the dust pressing process of compacting 8% moisture powder at 500 kg/cm2 seems foreign. You may wonder what types of body formulations are used in tile. Not surprisingly, the familiar principles apply. Tiles need to develop high fired strength in the kiln like many other kinds of ceramic ware. Dry tiles must of course have strength so they can be handled and survive glazing operations. Generally bodies are needed that fire strong at the lowest possible temperatures. Surfaces absolutely must be durable and defect free. That being said, R&D often faces constant pressure from management to lower costs, this generally means finding ways to use lesser quality materials, firing lower or making the tiles thinner. Of course this means some compromises in quality.

Of course, body formulation depends on the quality of tiles a company wants to produce: Irrespective of color, tiles fall into two broad categories. Porous after firing (wall tiles, single and double firing) and zero porosity (floor tiles). Porous bodies contain calcium or magnesium compounds so they develop new crystal phases during firing and those crystals are responsible for mechanical strength. Usually shrinkage is very low or zero but porosity is higher than 10%. For vitrified bodies mechanical strength is a product of a glassy phase developing during firing (from feldspars). These bodies contain negligible amounts of calcium compounds. Shrinkage is usually higher than 5%. Red and white bodies can be of either type.

R&D are always looking for ways to produce the best tiles possible from the most economical materials possible, so formulation is strongly affected by locally available raw materials or by materials having a low freight cost (trading is well organized in the tile supply chain). Thus, it is no surprise that each body is tailor-made. There are also contract factors at play. A machinery supplier (e.g. Italian) usually provides the complete know-how to attain a quality and quantity stated in a contract (that contract specifies the body formulation). In other cases, these machinery suppliers do allow customers in whom they have confidence leeway to formulate their own bodies (e.g. Chinese companies).

As expected, white burning tile bodies need less clay than is customary in other types of ceramic industry since they are not plastic formed (30-40% clays and/or kaolins are typical). This makes more room for feldspar (40-60%) and even other fluxing materials (e.g. dolomite or calcium carbonate or talc 0-5%, calcium carbonate can be 10 or more in case of wall tiles bodies). Finally 0-10% quartz is employed as a thermal expansion regulator (less than typical stonewares).

While white burning high temperature fired tiles are of course ideal, practicality, especially material and transportation costs, normally determines the type of body actually employed. Often the pressure to use less expensive local materials is great because materials can represent 50% of total production cost. For example, a small production unit with 10,000 sqm/calendar day output needs about 200 tons/day of materials for the body (about $15,000 US day). Sometimes a geological survey and opening of new mines and processing units are part of a tile project. Practicality works the other way around also, tile plants are built near the mines of material suppliers and agents to minimize transportation costs (USA production of tiles is close to Texas or Tennessee mines). Excluding red clays, some materials have a very wide market in tile. For instance, in the case of vitrified bodies, clays from Ukraine are used in all European countries, Russia, Middle East and even in India. Turkish feldspar is widely used in all Mediterranean countries and Russia.

If you look at the backside of a typical glazed floor tile you will find at many tile stores, most are made from brown and red burning clays fired to varying states of vitrification. Many technicians are not fully aware at how much lower temperatures these bodies can fire and yet still be strong and hard and even vitrified. However it can be difficult for R&D to adapt white engobes (reguired for a glaze base) that have dry and fired fit and adherence. Also, redder burning clays can have very narrow and volatile vitrifying ranges and properties of locally available clays can vary alot, QC must be alert and capable to adjust. Part of the secret of firing these bodies is doing it quickly. Some companies are blessed with quite remarkable local materials and abilities to process them internally (eg Turkey), others have much poorer materials and resources (eg India, Pakistan) and others can rely on a nearby well developed supplier channel (eg. Spain).

In many cases binders are employed to improve mechanical strength (of green tiles after pressing) where clays of sufficient plasticity are not available. Examples of binders are lignin sulfonate, polyacrylates, polyvinyl alcohol, starch, carboxymethyl cellulose, sodium silicate, bentonite, etc. Organic binders can pose a significant problem: these generate a black core in tiles during firing if organic matter content of clays is high. In the opinion of xxxx the best binder is sodium silicate, also used as deflocculant, and it can improve mechanical strength 2-4 bar without black coring and it is inexpensive.

As noted, one thing cannot be compromised in tile: Companies must have body materials with no particulate contaminants. Some go to the incredible effort of wet processing materials, filter pressing and dry pelletizing their own materials. However, for others who process their own materials, there is pressure from management to minimize processing to cut equipment and material costs, this can put R&D in a difficult position. Of course, like any body, many properties must be monitored. If you are going to be involved in tile you are going to need to know about monitoring material properties both to maintain product consistency and quality but also to weigh these against cost. For example:

As with any ceramic manufacture, there is a need to be practical in the lab. It makes little sense to be testing chemistry and mineralogy on fancy machines when there are particulate and plasticity issues with the body, for example. A page full of lab numbers are no substitute for understanding properties like plasticity and devitrification and the relationships between chemistry, mineralogy and physical properties. But most important are the physical properties, often only simple tests flag key changes and rationalize what to do.

Related Information

Low expansion glazes craze less, but they can shiver

Example of serious glaze shivering using G1215U low expansion glaze on a high silica body at cone 6. Be careful to do a thermal stress test before using a transparent glaze on functional ware.

A classic Albany glaze that often shivers

These mugs have experienced very serious shivering. This is an Albany Slip glaze with 10% lithium carbonate, it is known to have a very low thermal expansion. This problem can be solved by reducing the amount of lithium or adding high-expansion sodium or potassium. However these fixes will likely affect the appearance.

A batch of fired clay test bars in the Plainsman Clays lab

A batch of fired test bars that have just been boiled and weighed, from these we get dry shrinkage, fired shrinkage and porosity. Each pile is a different mix, fired to various temperatures. Test runs are on the left, production runs on the right. Each bar is stamped with an ID and specimen number (the different specimens are the different temperatures) and the measurements have all be entered into our group account at insight-live.com. Now I have to take each pile and assess the results to make decisions on what to do next (documenting these in insight-live).

Links

Articles Glaze Types, Formulation and Application in the Tile Industry
An technical overview of various glaze type used in the tile industry along with consideration of the materials, processes and firing.

By Tony Hansen


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