Ceramic industry

Ceramic industry

Source of information

1-SHREV’S CHEMICAL PROCESS INDUSTRIES

2-Internet (www. ceramic-research.com)

ceramic

Ceramics include all articles, which are essentially silicates .

Those articles that are made of clay are mainly known as ceramics .

ceramic

Ceramic and anti-melting materials industries represents one of seven major industries in the Egyptian market. It represents 7% of the production value in Egyptian Industrial sectors .

Properties of ceramic

•High corrosion resistance •High resistance to rust

•Low temperature conductivity •Low electrical conductivity

Uses of ceramic •Personal use: glassware, Windows,

pottery, dinnerware, tiles and ceramics, lenses .

•Medical field: compensating devices for bony joints, dental .

•Military industries: materials for vehicle body ground, sea and air sensors

•Computer domain: insulation, transportation and resistors capacitors .

Raw materials

The principal raw materials are sand, feldspar, ball clay, china clay, kaolin, talc and other materials that are used during the manufacturing process, such as soda ash, sodium silicate, calcium carbonate.

Location of raw materials

1-Bentonite

2-Kaolin

3-Whitesand

4-limestone

Function of raw materials1-clay

a)Produces a light colouring during firing b)Gives plasticity and binding characteristics to the mass c)Enhances mechanical characteristic in the fired tiles d)Produces good flow properties e)Gives a good density level during firing due to the individual characteristic of the clays.

Function of raw materials

2-feldspar

a)feldspars play an important role in achieving the vitreous nature of the body and the high mechanical resistance of the product at the end of the firing stage .

b)Acting as a flux, feldspars also facilitate drying and release of gas during firing like other non-plastics.


3-silica

a)facilitate escape of gases during drying and firing .

b)reduces drying shrinkage and increases the whiteness of the fired body


4-talc

used in small quantities (2-6%) in the vitrified tile body composition to enhance the fluxing action of feldspathic materials .

Material testing

1-Chemical Analysis by X-Ray Fluorescence Methodology

2-Thermal Testing

Chemical Analysis by X-Ray Fluorescence Methodology

The basic principle of XRF involves irradiating a sample with incident X-rays and measuring the secondary X-rays emitted.These secondary X-rays which are characteristic of each element in the sample are detected and measured to

give a full analysis of the sample .XRF is a method for measuring elemental contents of raw materials and body formulations but not for identifying the mineralogy .


Conducted for a wide range of purposes for material identification and characterization to quality control monitoring.The types of materials that can be analyzed by XRF include clay, sand feldspar, and limestone.chemical analysis involves the determination of SiO2, Al2O3, Fe2O3, TiO2, MgO, Na2O, K2O, and CaO together with loss on ignition at about 1000°C.


There are 2 sample preparation techniques namely pressed pellet and fused bead.

Pressed pellet

Samples are grinded into powder form and pressed into discs.More suitable for samples with a particular similar mineralogy composition such as limestone.May have identical chemical composition but may differ in terms of mineralogical make-up and particle size.Contamination increases with reduced particle size and an increase in surface area.Preparing the samples using the pressed pellet method is convenient and relatively easy but would not be suitable if a wide range of samples are to be analysed.

Fused beadCarried out by first weighing the ignited sample with a flux such as lithium borate into a platinum dish and subjecting the mixture to high temperatures.

Fused beadThe fusion melt is then casted into a casting mould and cooled.

X-Ray Fluorescence spectrometers

Two types of X-Ray Fluorescence spectrometers namely the sequential spectrometer and simultaneous spectrometer.Simultaneous spectrometers are easier to operate as each channel has its own separate crystal, collimator and detector.The range of elements that can be analysed is limited by the number of pre-determined fixed channels.For the sequential spectrometer, the equipment which is relatively much costlier is able to analyze a very wide range of elements .

Thermal Testing

Yield crucial information that is used to characterise the suitability of new materials, troubleshoot defects and monitor the quality of incoming raw materials.Thermoanalytical methods such as dilatometry and TG-DTA.

Thermal testingDilatometer

method for the determination of dimensional changes versus temperature when the sample undergoes a controlled temperature programme.There are two types of dilatometry analysis namely

irreversible and reversible thermal expansion .

Irreversible thermal expansion

This is expansion of a dry, unfired material as it is subjected to a heating process .

Evaluation of the expansion during firing can provide useful information such as identification of the type of clay be it kaolin, illite...etc

The raw dilatometric curve for Clay 1 is characteristic of an illitic clay, where there is a constant plateau between the temperature ranges of 600-900°C.

The raw dilatometric curve for sample Clay 2 is typical of a kaolinitic clay. Rapid contraction occurs from about 530°C .

Reversible thermal expansion

Performed on fired ware samples such as fired clay, body and glaze samples to measure the coefficient of thermal expansion (COE) .

This parameter determines to a certain extent the compatibility of the ceramic body and glaze.

Incompatibility could lead to crazing of the glaze and also affects its planarity

The sample showed linear coefficient of expansion

Simultaneous Thermal Analysis

Simultaneous Thermal Analyser (TG-DTA) simultaneously carries out DTA (Differential thermal analysis) and TG (Thermal gravimetric analysis).The temperature range is from room temperature to 1080°C .

DTA is used to establish the temperatures at which reactions may occur that involve thermal effects in the material for e.g. emission of gases or vapours, reactions with formation of new crystalline phases...etc .

The temperatures at which the endothermic or exothermic reactions occur are used to identify the material .

Simultaneous Thermal Analysis

TG quantitatively evaluates increases or losses in weight of the material caused by the corresponding oxidation reactions, vapour or gas reactions.Uses

Determine the amount of weight loss due to gaseous decomposition of organic or carbonate content...etc and their temperature ranges.Monitor the changes of incoming raw materials (such as clay deposits, raw material lots or different suppliers) to predict the effect on the firing process and production batches .

The TG-DTA analysis for limestone sample showed an endothermic peak at 912°C with a total weight loss of 43.7% due to the decomposition of CaCO3 to CaO and CO2

The TG-DTA analysis for Clay 3 is typical of well-ordered kaolin with total weight loss of about 12.8% .

The TG-DTA analysis for Clay 4 is typical of disordered kaolin with total weight loss of about 11.0% .

Physical Properties Testing

1-Particle Size Analysis

2-Fired Properties a)Fired shrinkage b)Water absorption c)Fired Colour

1-Particle Size Analysis

Measurement range of 0.1 to 1000μm .measure the quantities of particles in each size class in a sample such as clay, limestone powder, ceramic body formulation...etc .

Size distribution of the clay particles is important because the spread of the distribution affects many properties of the ceramic body slips, plastic forming bodies as well as many dry and fired ceramic body properties .

2-Fired Properties

Fired shrinkage

Determine the size of the finished product .If the shrinkage is too large or it is allowed to occur too rapidly, cracking or distortion of the product.The fired shrinkage of the clay provides information on the variations in the composition of the clay.

2-Fired Properties Water absorption

The water absorption is determined using the "boiling technique ."

The fired specimen was first weighed (Fired Weight).

The specimen was then immersed in boiling water for 2 hours after which they are left to soak in cool water.

Excess moisture is wiped away from the surface of the specimen and then weighed (Soaked Weight).

2-Fired Properties Fired Colour

For fired colour, the values of L, a and b are determined. Scale L is a measure of lightness, a is a measure of redness or greenness and b is a measure of yellowness or blueness .Hunterlab Colourimeter

Production Process of Ceramic Tiles


Batching

The batching or proportioning may be done by volume or by mass.

Grinding

The purpose of grinding is to obtain smaller particles out of coarser size ones. Besides that, it also increases reactivity of materials.

There are essentially two methods of grinding namely the wet and dry grinding method.


Spray drying the process that converts the body slip obtained from the mill to a granulate with a size distribution and moisture content suitable for pressing.

The two most important properties to be controlled are the moisture content and the size distribution of the granulate

Production Process of Ceramic Tiles Pressing


Drying of the ceramic tile is carried out between the pressing stage and the firing process.Drying is performed automatically and continuously in vertical or horizontal fast dryers .

Glazes are considered as one of the important materials in the ceramic industry. They are glasses specially designed to have thermal expansion to match the ceramic substrate.


Firing

The requirements for successful firing process are :

Proper firing temperature, 750 to 1200°C

Uniform heating and cooling of the ware

An atmosphere free from dust

Sorting

At the sorting stage the products are classified according to the quality .

Finished Product Testing 1-Microscopy Analysis

2-Ceramic Tiles Technical Properties

a) Dimension

b) Water Absorption

c) Modulus of Rupture & Bending Strength

d) Surface Abrasion Test

e) Crazing Resistance

f) Chemical and Stain resistance

g) Slip Resistance

1-Microscopy AnalysisThe Stereo and Polarizing Microscope are very useful tools for microscopy analysis .

In the investigation of product failure or defects such as spot-holes, contaminants, surface dirt, black/ green speck...etc, microscopy analysis provides clues to the cause of defects so that action may be taken to solve the problem .

Microstructure analysis of the ceramic body provides important information in assessing the compactness and sintering of bodies after firing.

1-Microscopy Analysis

Examples of the cross section of several types of defects


a) Dimension

A planarity tester is used to measure the key dimensional characteristics of the ceramic tile.

b) Water Absorption

Water absorption is the amount of water that a ceramic tile can absorb under certain experimental conditions expressed in terms of the percentage by weight of the dry tile.

c) Modulus of Rupture & Bending Strength

Determines whether the tile is capable of bearing the static or dynamic loads to which the floor or wall may be subjected to during use.

d) Surface Abrasion Test

The resistance of the surface of the tile to the movements of other materials such as wheels, soles of shoes worn by people walking across the tile surface or mud, sand...etc that come into contact with it.

e) Crazing Resistance

Refers to hairline cracks on the surface of the glazed tile; the pattern formed by these fine fissures may be either circular or irregular .


f) Chemical and Stain resistance

The behavior of a ceramic surface when it comes into contact with aggressive chemicals that may react with the surface itself.g) Slip Resistance

Slip resistance is the measure of tiled surface slipperiness .


Pollution 1-Air emissions

2-Effluents

3-Solid wastes

4-Workplace

5-Hazardous waste

Impacts and effects1-Impact of air emissions

a) Particulate matters

b) Sulfur Oxides

c) Nitrogen Oxides

d) Carbon dioxide

e) Dust

f) Silicon dioxide

g) Kaolin Clay

h) Bentonite Clay

i) Soda ash

2-Impact of Effluents

3-Impact of Solid Wastes

4-Impact on Workplace

Special thanks

DR. Shehata Ali Shehata

Thanks for your attention

Mohammed Mahmoud saad

2015Chemistry &Geology

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Ceramic industry