Preparation of a ceramic floor tile body containing sodium carbonate

Preparation of a ceramic floor tile body containing sodium carbonate as strengthening agent, for Lanka Floor Tiles PLC

ISANKA ASHAL PRAMEETH DEIDDENIYA

University of Sri Jayewardenepura, Sri Lanka Bachelor of Science (Honors) degree January 2015

Preparation of a ceramic floor tile body containing sodium carbonate as strengthening agent, for Lanka Floor Tile PLC

A dissertation Submitted to The Department of Physics of the University of Sri Jayewardenepura In partial fulfillment of the requirement for the Bachelor of Science (Honors) degree In Physics

By S. I. A. P. Diddeniya University of Sri Jayewardenepura, Sri Lanka January 2015

DECLARATION The work described in this dissertation was carried out by me in the Department of Physics, University of Sri Jayewardenepura, Sri Lanka under the guidance of Dr. C. L. Ranatunga and has not been submitted elsewhere.

…………………………

24 February 2015

S. I. A. P. Diddeniya

Date of submission

………………………..

………………………………

Dr. C. L. Ranatunga

Mr. S. De Ranasinghe

Internal supervisor

External supervisor

………………………..

………………………………

Dr. P. Geekiyanage

Dr. Pahan Godakumbura

Head/Department of Physics

Coordinator

University of Sri Jayewardenepura

Extended degree program (B.Sc. in Applied Sciences)

My humble effort this dissertation work I dedicate to My loving parents, my sister And my girl friend Who supported me each step of the way.

ACKNOWLEDGEMENTS This research paper is made possible through the help and support from everyone, especially; please allow me to dedicate my acknowledgment of gratitude toward the following significant advisors and contributors. First I would like to gratefully and sincerely thank Dr. C. Lal Ranatunga for his guidance, understanding, patience, and most importantly, his friendship during my graduate studies at University. His mentorship was paramount in providing a well-rounded experience consistent my long-term career goals. He encouraged me to grow as an experimentalist. For everything you’ve done for me, Dr. Ranatunga, I thank you. I would also like to thank all of the members of the Lanka Floor Tiles PLC, especially supervisor Mr. Shelton De Ranasinghe who is the assistant factory manager for giving me the opportunity to act as a mentor. My final thanks go to Dr. Pahan Godakumbura & Dr. D. N. Jayawardane for all the support that was given to make my research a success.

i

LIST OF ABBREVIATIONS XRD

X-ray Diffraction

DTA

Differential thermal analysis

XRF

X-ray fluorescence

DC

Direct current

N. C. B.

Normal ceramic body (without Na2CO3)

LOI

Loss on ignition

ii

TABLE OF CONTENTS ACKNOWLEDGEMENTS .................................................................................................. i LIST OF ABBREVIATIONS ..............................................................................................ii LIST OF FIGURES ............................................................................................................ vi LIST OF TABLES .............................................................................................................vii ABSTRACT ..................................................................................................................... viii CHAPTER 1 ........................................................................................................................ 1 INTRODUCTION ............................................................................................................... 1 1.1 Background ........................................................................................................ 1 1.1.1 Ceramic raw materials ........................................................................ 1 1.1.2 Basic technological parameters in tile production .............................. 3 1.1.3 Ceramic tile ......................................................................................... 4 1.1.4 Ceramic tile body ................................................................................ 4 1.1.5 Mechanical strength of green tile ........................................................ 5 1.1.6 Slip Clay.............................................................................................. 6 1.1.7 Deflocculants ...................................................................................... 6 1.1.8 Spray drying of body slip .................................................................... 9 1.1.9 Fired tile properties ........................................................................... 11 1.2 Literature survey .............................................................................................. 13 1.2.1 Use of sodium carbonate as a binder ................................................ 13 1.2.2 Clay Water suspensions .................................................................... 13 CHAPTER 2 ...................................................................................................................... 19 RESEARCH METHODOLOGY....................................................................................... 19 iii

2.1 Equipment and instruments.............................................................................. 19 2.2 Materials, chemicals, solutions and reagents ................................................... 21 2.3 Viscosity test in laboratory .............................................................................. 22 2.4 Collection of materials ..................................................................................... 22 2.4.1 Body slip preparation ........................................................................ 22 2.5 Comparison of Mechanical strength and other physical properties ................. 23 2.5.1 Collection of materials ...................................................................... 23 2.5.2 Powder preparation (for low viscosity bodies) ................................. 24 2.5.3 Powder pressing and green tile strength test ..................................... 25 2.5.4 Dried tile strength test ....................................................................... 25 2.5.5 Shrinkage, LOI and percentage water absorption tests ..................... 25 2.6 Titration for finding purity of sodium carbonate ............................................. 26 2.6.1 Preparation of a 0.1moldm-3 solution of Sodium Carbonate ............ 26 2.6.2 Preparation of a 0.2moldm-3 solution of hydrochloric acid .............. 26 2.6.3 Titration test ...................................................................................... 26 CHAPTER 3 ...................................................................................................................... 27 RESULTS AND DISCUSSION ........................................................................................ 27 3.1 Effect of Na2CO3 to viscosity .......................................................................... 27 3.2 Effect of Na2CO3togreen tile strength.............................................................. 28 3.3 Effect of Na2CO3 to dried tile strength ............................................................ 28 3.4 Effect on the other physical properties of the fired tile ................................... 30 3.5 Purity of Na2CO3.............................................................................................. 31 3.6 Discussion ........................................................................................................ 32 CHAPTER 4 ...................................................................................................................... 33 iv

CONCLUSION AND FUTURE WORK .......................................................................... 33 4.1 Conclusion ....................................................................................................... 33 4.2 Future Work and Recommendations ............................................................... 33 REFERENCES .................................................................................................................. 34 APPENDICES ................................................................................................................... 37 Appendix A - Calculation methods in factory laboratory...................................... 37 Appendix B - Acid reaction with Na2CO3 ............................................................. 38 Appendix C - Cleaning steps of equipment for titration test ................................. 39 Appendix D - After firing test methods for glazed tile in the laboratory .............. 39

v

LIST OF FIGURES Figure 3.1: Variation of viscosity with Na2CO3 ............................................................... 28

vi

LIST OF TABLES Table 1.1: Inorganic and organic binders............................................................................ 5 Table 1.2: Inorganic and organic deflocculants .................................................................. 7 Table 1.3: Classified particles according to the diameter ................................................. 14 Table 2.1: List of equipment and instruments used .......................................................... 19 Table 2.2: Ceramic body formula ..................................................................................... 22 Table 2.3: Amount of additives for each body slip ........................................................... 23 Table 2.4: Amount of additives for normal ceramic body and selected test bodies ......... 24 Table 3.1: Result of viscosity test of body slip ................................................................. 27 Table 3.2: Result of mechanical strength tests for normal ceramic body ......................... 29 Table 3.3: Result of mechanical strength tests for “test body 1” (Na2CO3 percentage: 0.083%) .............................................................................................................................. 29 Table 3.4: Result of mechanical strength tests for “test body 2” (Na2CO3 percentage: 0.167%) .............................................................................................................................. 30 Table 3.5: Average of mechanical strength ...................................................................... 30 Table 3.6: Result of shrinkage test, LOI test and water absorption test (“Test Body 2”). 31 Table 3.7: Result of water absorption test (“Test Body 2”). ............................................. 31 Table 3.8: Purity results of Na2CO3 samples .................................................................... 31

vii

ABSTRACT Preparation of a ceramic floor tile body containing sodium carbonate as strengthening agent, for Lanka Floor Tile PLC This research work demonstrates the use of a low amount (0.67wt %) of 1:3mixtures of sodium carbonate and sodium silicate as strengthening agent of low plastic ceramic body. It would be highly recommended since it appreciably reduces ruptures of unfired ceramic tiles in their dry state during handling and transporting, and enables the pre-firing steps of the tile factory to be rationalized and productivity to be increased. The general principals of de-flocculation have already been described but it should be remembered that the relative amount of exchangeable ions considerably affects the response to a given deflocculent. For instance, clays usually respond well to a 1:3 mixture of sodium carbonate and sodium silicate, but this ratio may have to be altered if the distribution of exchangeable ions is abnormal. KEY WORDS: ceramic floor tiles, ceramic bodies, unfired bodies, sodium carbonate, sodium silicate, strengthening agent.

viii

CHAPTER 1 INTRODUCTION 1.1 Background A tile is a manufactured piece of durable material such as ceramic, stone, metal, glass or even to cover roofs, floors, walls or other objects to instances tables, countertops. Not only tiles are often made of ceramic, with a hard glaze finish, but other materials are also used as glass, marble, granite and slate tile production. Among them, the tiles are commonly made of ceramic, porcelain and stone because, they are attractive, durable and easy to clean. The raw materials used to form tiles consist of clay minerals extracted from the crust of the earth, natural minerals such as feldspar used to lower the cooking temperature and chemical additives necessary for the forming process.

1.1.1 Ceramic raw materials Raw material is very important in ceramics in various aspects. It is one of the most decisive factors for the quality of a product (LANGE, L.L., 1989). Roughly speaking, half of the quality of a product is determined by the characteristics of raw materials in the current production technology. Use of proper raw material is critical for producing ceramics of high quality at a minimal cost. Technologically, the raw powder sets a fair starting point for industries. Raw materials of high quality are in the market, and are equally available for all users for their disposal. Proper selection of raw powders and their post-treatment is critical for successful competition in the market.

1

Raw materials for ceramic technology can be natural, synthetic, and recycled waste. Chemical composition (X-ray fluorescence analysis), mineralogical composition (quantitative XRD phase analysis and thermal analysis), granulometry (particle size analysis) are main parameters and principal characterization techniques for selecting the ceramic raw material.

1.1.1.1 Plastic raw materials for ceramic technology Kaolin and clay minerals are the main plastic raw materials in ceramic body. Some other ceramic raw materials based on phyllosilicates (talc, pyrophyllite, serpentine) also act as plastic raw material. Function in silicate ceramics as plasticizer during shaping and high-temperature reactions leading to mullite formation. Ball Clay: Ball clays are kaolinitic sedimentary clays that commonly consist of 20-80% kaolinite, 10-25% mica and 6-65% quartz. Localized seams in the same deposit have variations in composition, including the quantity of the major minerals, accessory minerals and carbonaceous materials such as lignite. They are fine-grained and plastic in nature. Ball clays are relatively scarce deposits due to the combination of geological factors needed for their formation and preservation. They are commonly used in the construction of many ceramic articles, where their primary role is to either to impart plasticity or to aid rheological stability during the shaping processes.

1.1.1.2 Non-plastic raw materials for ceramic technology Feldspars (K-rich alkali feldspars), feldspathoids (e.g. nepheline), Silica raw materials (sand, sandstone, quartzite, and massive quartz), Carbonates (calcite CaCO3, magnesite MgCO3 and dolomite CaMg(CO3)2) and Alumina-rich raw materials (bauxite 2

mixture of gibbsite α-Al(OH)3, boehmite γ-AlO(OH) and diaspora α-AlO(OH) with contents of Fe, Ti, Si etc.) are the main non-plastic materials in ceramic body. Other non-plastic raw materials are zircon (ZrSiO4 is a basic raw material for the production of ZrO2), ilmentite (FeTiO3 is a basic raw material for the production of TiO2), wollastonite (CaSiO3), and other some materials including synthetic raw materials (highly pure or mixed oxides with controlled stoichiometry).

1.1.1.3 Important characterization techniques for ceramic raw materials 

Simultaneous thermal analysis (thermogravimetry, dilatometry and DTA) and high-temperature reactions occurring in ceramic raw materials (dehydroxylation and solid state reactions in clay minerals, thermal decomposition of carbonates etc.)



XRD quantitative phase analysis (especially of clay minerals)



Particle size analysis (sedimentation and laser diffraction)



X-ray fluorescence analysis

1.1.2 Basic technological parameters in tile production The final properties and appearance of the product not only depend on the chemical and mineralogical nature of its raw material components but also on the practical as well as the technical requirements demanded by the various processes in the production cycle. 

Grinding



Spray drying 3



Pressing



Drying



Glazing



Glaze firing

1.1.3 Ceramic tile A tile made from clay that has been permanently hardened by heat, often having a decorative glaze (Home depot).

1.1.4 Ceramic tile body A better insight into the composition of a traditional ceramic material can be attained by taking a look at a "standardized" tile body, bearing in mind that with the appropriate modifications, similar observations can be made with regard to other traditional ceramic materials. The base body, then, is generally made up of, CLAYEY MATERIALS, which provide the plasticity needed to obtain a defined form. These include Al, Si and a proportion of Ca, Fe, and Ti. FLUXING MATERIALS such as feldspars, nepheline etc., which, during firing, produce vitreous phases that act as particle-particle adhesives and promote solid-solid reactions; these contribute Na, K, Al and Si. OTHER MATERIALS such as talc, silica, pyrophyllite, CaCO3 etc. used to obtain a certain type of performance: these largely contribute Ca, Mg and Si.

4

ADDITIVES, largely employed to improve the rheology of aqueous solutions; these may be inorganic or organic and only limited amounts 1%) are introduced into the bodies (SACMI, 2005).

1.1.5 Mechanical strength of green tile One of the most important properties of tiles in ceramic tile manufacture of mechanical strength is the green bodies. Its importance lies in the fact that the materials must withstand the stresses they experience during pre-cooking operations without deterioration. Drying and glass as well as in the successive transmission, storage and heat treatment operations, the tile is subjected to mechanical stresses (bumps, as a result of transport) and thermal stress (expansion and contraction), which can result in material damage. These reasons clearly indicate the importance of green strength for the manufacture of single-fired ceramic floor tiles. However, although studies abound in the literature on the mechanical properties of ceramic fired materials, almost no work has been reported in the green ceramic fracture (R., James S.).

1.1.5.1 Ceramic binders Clay minerals have some binding effect. But it is not enough to production process. Therefore ceramic binders are used as additives to increase the mechanical strength of green tile. There are two types of ceramic binders (See Table1.1). Table 1.1: Inorganic and organic binders Inorganic binder Sodium Silicate

Organic binder Polyvinyl Alcohol 5

Magnesium Aluminum Silicates Bentonite

Starches Carboxymethylcellulose (C. M. C) Dextrin Polyethylene Glycols Wax Emulsions

1.1.6 Slip Clay Modern slip clays are clays as not only could be used for decoration possibly with added dyes as low enamel, for example. Rather, they are a precise formulation of water, clay and a deflocculant which acts to reduce the amount of water required to maintain the liquid state and to maintain pourable clay particles suspended in water and blended. Less water results in less shrinkage, stronger, much faster setup times and less wetting and drying time thus for plaster molds. Plaster is preferred mold material because it offers the best combination of retention of detail, strength and absorbency. The key in the clay slip casting is the dewatering of the sheet once it is in the mold. A deflocculant can be thought of as the prevention of clay particles from "flocking" together or get lumpy. Technically, it is an electrolyte, which is an alkali load changes in molecules or clay particles, causing them to repel each other like magnets in turn make the mixture more fluid (thus less water) (PLANET, Clay).

1.1.7 Deflocculants Deflocculation is very importance part to increase mechanical strength of green tile, because some deflocculation additives act as binders in dried stage. There are two main types of Deflocculant (See Table 1.2). 6

Table 1.2: Inorganic and organic deflocculants Inorganic deflocculants Sodium Carbonate Sodium Silicate Sodium Polyphosphate Sodium Hexametaphosphate Barium Carbonate

organic deflocculants Humic acids Tannins Derivatives of acrylic acids Derivates of oxalic acids

Sodium silicate the most economical and commonly used for clay deflocculant. For many castings, may accumulate in and seal the pores of the plaster mold rendering it useless. Sodium carbonate traditionally used as a secondary deflocculant with Sodium Silicate. It also makes the casting more elastic which may be desirable with elaborate forms that need to stretch in the mold prior to release (PLANET, Clay). Deflocculation is that process in which the solid colloidal particles in the dispersant fluid (e.g. a slip) move away from each other yet remain in suspension because of the repelling electrostatic action that the deflocculant substance induces (by increasing their zeta potential). A fluidizer is a substance capable of making a fluid flow more smoothly (i.e. lowering its viscosity). It is the exact opposite of a thickener, an agent that increases the consistency of a fluid mass. A deflocculant is a substance which, when added in small quantities to a fluid mass, is capable of preventing agglomeration of the colloidal particles and thus their precipitation. Since this effect can be achieved via dispersion (i.e. by addition of the fluid phase) the two can easily be confused: while it is certainly true that a deflocculant also acts as a fluidizer, it is not necessarily true that all fluidizers are also deflocculants. The

7

fundamental mechanisms that explain the deflocculating action may be explained as follows. 1. Shifting of the pH towards basic values by introducing (OH)– ions into the H2O solid system via an addition of monovalent bases or basic electrolytes which by hydrolysis give (OH) - ions (an excess cause’s over-deflocculation). 2. Substitution of other cations constituting the positive side of the diffusers double layer with Na+, K+, Li+, (NH4)+. 3. An increase in the negative charge on the clayey particles by adsorption of certain types of anion (adsorption is preferential for anions of higher valence with a strong electric field). 4. Increase in the total negative charge of the solid-liquid system, assuming a nonionic colloid carrying a negative charge. 5. Addition of a “shielding colloid that shields the suspended particles from the action of flocculants (SACMI, 2005).

1.1.7.1 Sodium carbonate Clay Ca2

Na2CO3

Clay Na

CaCO3

These fundamental reactions make sodium carbonate an excellent deflocculant the more Ca is present the better the effect. The property of precipitating the calcium, while advantageous for the purposes of deflocculation is for example, somewhat less so as regards the life of the plaster casting moulds. Na2CO3, which melts at 850 °C, increases plasticity and the dry bending strength of bodies but reduces the drying rate (SACMI, 2005).

8

1.1.7.2 Sodium silicate Na2 iO3

H2O

iO2

2Na

(OH)

The sodium silicate, which hydrolyses easily with an alkaline reaction (pH >11) gives Na+ and (OH) -by separating the colloidal silica. The silicate is not as aggressive towards the plaster as the carbonate and has binding properties. Where sulphates are present its deflocculating power is reduced (SACMI, 2005).

1.1.7.3 Sodium carbonate with sodium silicate Na2CO3

Na2 iO3

The thus has a higher deflocculating power and results in fewer defects being caused by the aggression of Na2CO3. These are stable solutions that let gelatinous silica separate. Additions usually fall in the 0.2%-0.6% range (by weight) (SACMI, 2005).

1.1.8 Spray drying of body slip The production of granules for the pressing process for the production of tiles is accomplished by spray drying of a ceramic slip. In this process, moisture, particle size distribution, and fluidity or granules are parameters that can be influenced by density and viscosity of slip, pump pressure, and characteristics of the nozzle. In this investigation, these parameters are discussed for two industrial spray dryers (CARTY, William M., 2009).

9

1.1.8.1 Viscosity of body slip The viscosity of a ceramic slip is a measure of the internal friction between the molecules of the dispersion. The constant of proportionality of the ratio of the shear stress and the shear rate is the shear viscosity,

γ γ - Viscosity (Pas-1) - Shear stress (Pa) - Shear rate (s-1) External forces, e.g. the shear forces produced on stirring a slip, influence the flow behavior. This leads to variation in the behavior as a function of the strength and duration of the external forces. Viscosity is an important characteristic for ball mill unloading process and spray dryer process. Larger viscosity results in increasing ball mill unloading time and increase the fuel consumption so that the productivity becomes slow and increase the production cost (SCHWARZ, Zschimmer).

1.1.8.2 Thixotropy of body slip When the body slip is left standing, it stiffens and becomes a gel, without separating into two layers. On stirring the original state is regained. The viscosity decreases with increase of both the rate of stirring and time of stirring. Hence are thixotropic liquids. If the shearing stress curve obtained at both increasing and decreasing rate of shear, an anticlockwise hysteresis loop is obtained (on graph shear rate vs. shear 10

stress), showing that the viscosity of the stirred liquid is lower than that of the rested one at any given rate of shear (RANATUNGA, C. L., 2014).

1.1.9 Fired tile properties 1.1.9.1 Shrinkage of ceramic body Moist clay begins to shrink as soon as it is taken out of its plastic storage bag and comes into direct contact with the air. Water is drawn out of the clay until it reaches equilibrium with the moisture content of the surrounding atmosphere. Some potters mistakenly believe if they let the clay air dry for months, it will be thoroughly devoid of water; however, mechanical water (moisture in the studio atmosphere) and chemical water (water tied up on a molecular level within the clay) will still remain in the “bone dry” clay. If the clay is heated too quickly, steam will build up within the piece, causing it to crack or explode in the dryer or kiln. Clay also shrinks during the vitrification, or glass phase, process as it reaches higher temperatures in the kiln. To ensure that water removal and resulting shrinkage occurs slowly, without damaging the ware, the role of the drying and firing processes should be as controlled as possible. Knowing the shrinkage rate of your clay body can help you develop drying and firing cycles that are both efficient and thorough (Digitalfire).

1.1.9.2 Loss-on-ignition (LOI) of ceramic body The LOI summarizes the components within a raw material that burn away or products of decomposition that are lost as gases during firing. Some companies separate the different components of weight lost during firing as C, H2O, SO3, etc. A formula

11

weight of zero should be used in each oxide of this type so there is no impact on fired formula calculations. Note that if a material contains a volatile in its analysis that you would like to enter into the analysis and have it treated like an LOI, and if that item is not contained in the oxides database, you can manually key an 'L' in the status column of the analysis to force foresight to accept it as an LOI type material. A material's formula weight is equal to the sum of the weight of the oxides in its formula divided by (100-LOI) divided by 100(Google search ”what is ceramic tile”).

1.1.9.3 Water absorption A tile’s rate of water absorption: weight of water absorbed as percentage of tile weight. 

Non-vitreous: high absorption (more than 7% water absorbed). Not suitable for outdoor use or for rooms with a lot of moisture, such as bathrooms.



Semi-vitreous: moderate absorption (3% - 7% water absorbed). Not suitable for outdoor use or for wet rooms, such as bathrooms. Vitreous: Low absorption (0.5% - 3% water absorbed). Suitable for outdoor use and for wet rooms, such as bathrooms.



Impervious: lowest absorption (less than 0.5% water absorbed). Suitable for all interior and exterior uses (A.BARCLAY, DPeters, 1976).

12

1.2 Literature survey 1.2.1 Use of sodium carbonate as a binder There is an influence of sodium carbonate content on the behavior of the ceramic tile body composition during the different manufacturing process stages (preparation of the suspension, pressing, and firing), as well as on unfired tile mechanical strength. It has been verified that sodium carbonate can be used as a binder in ceramic tile compositions, since small percentages considerably enhance dry tile mechanical strength. It has furthermore been determined that for each composition there is an optimum addition content, with high increased mechanical strength (up to 70%), without this noticeably affecting the rheological behavior of the suspension to be spray dried (F. QUEREDA, E. Sanchez, J. Garcia-Ten, A. Gozalbo, V. Beltran, J. Sanchez, J. Sales).

1.2.2 Clay Water suspensions 1.2.2.1 Colloidal properties Solid water suspension: shaken-up, left to stand; sedimentation. Larger particles sediment rapidly; smaller particles are slowly. Stoke's law,

V - Rate of sedimentation r - Radius of particles ds - Density of internal phase dl - Density of external phase 13

g - Gravitational constant - Viscosity of medium Stoke's law is only true for particles (D - Diameter of particles) D > 1µm for smaller particles, natural thermal notion (Brownian movement) becomes more important. Brownian movement causes small particles to diffuse upwards against the sedimentation force. If they are sufficiently small they can present complete sedimentation. Such a suspension is said to be colloidal and exhibits some very special properties that are not shown by coarse suspensions.

Since high proportion of clay mineral particles is

considerably smaller than 1µm in diameter they exhibit typical colloidal particles. Table 1.3: Classified particles according to the diameter Type of particles Atoms, Molecules Colloidal particles Emulsions and suspension

Diameter (D) (µm) D < 0.0005 0.001 < D < 1 D>1

Sedimentation law Do not obey Border line Obey

Hence not surprising that colloidal particles behave as they do. Note that colloidal suspension of solid particle in liquids other than water can also be formed (RANATUNGA, C. L., 1989).

1.2.2.2 Properties of colloidal suspension 

Invisible to naked eye.



Just beyond the resolution of optical microscope.



But can be detected indirectly by the light they scatter (Tyndall effect).Brownian motion detected.

14



Electrophoresis; about 200V DC across two Pt electrodes; colloidal clay partials migrate to one of the electrodes; in clay colloidal particles are negatively charged; migrate to anode. Then what are positively charge cations?



Chemical analysis around cathode shows presence of NaOH, KOH, Ca(OH)2, Mg(OH)2



Balancing charge in colloidal suspension is formed by cations (RANATUNGA, C. L., 1989). Na+, K+, Ca2+, Mg2+

1.2.2.3 Charge distribution; Zeta potential ζ Assume a spherical condenser; -ve clay particle at center; cations and water molecules (dipoles) attracted to the negative center -lyosphere; system altogether referred to as colloidal micelle; effective potential of the system now universally accepted as the zeta potential (RANATUNGA, C. L., 1989). 4

d D

- Electrical charge d - Distance negative positive layers D - Dielectric constant In SI units, d kk

15

1.2.2.4 Cation exchange Cations Na+, K+, Ca2+, Mg2+.They can readily be exchanged for others: very rapid reversible reaction (RANATUNGA, C. L., 1989).

1.2.2.5 Cation exchange capacity 

Units; milli-equivalent of exchangeable ion per 100g of clay.



For pure kaolinite, from 2 to 12 m.e. per 100 g.



For montmorillonite about 100 m.e. per 100 g.



For disordered kaolinites (ball clays and fire clays) 30 m.e. per 100 g.



Suppose we have natural clay with chief exchangeable ion Ca2+ then initially suspension is flocculated.



If we wish to deflocculate it, we must add a salt of Na or K o If we add deflocculant NaCl Ca Clay

NaCI

Na Clay

CaCl2

Since it is reversible, before the completion of the conversion, the reverse reaction initiates. Complete conversion never achieved. o If we add deflocculant Na2CO3 Ca Clay

Na2CO3

Na Clay

CaCO3

Complete reaction achieved. 

Choice of dellocculant depends on the exchangeable cation. Many detlocculants precipitate undesirable cation; e.g. sodium carbonate, sodium oxalate.

16



More complex ones like sodium silicate act in a slightly different way (RANATUNGA, C. L., 1989).

1.2.2.6 Dry strength For the reason given above, flocculated clays are, on the whole, easier to dry than deflocculated clays. The strength of dry unfired clays, however, depends principally on the area of contact between adjacent particles. Deflocculated system always has a greater area or contact. Deflocculated clays have higher dry strength than flocculated clays (RANATUNGA, C. L., 1989).

1.2.2.7 Plasticity Cohesive moldable to any shape and retains its shape. Clay + water mixture develops plasticity. One common feature is their particles are very small; in colloidal dimensions (RANATUNGA, C. L., 1989).

1.2.2.8 Dry strength of ball clay Ball clays are noted for their high dry strength, which is why they are used in pottery body and to small extent china. The dry strength of ball clay depends, 

On the proportion or “clay substance”.



On its fineness.



The exchangeable cations.



On the amount or organic matter present.

17

Generally, Na+, K+, clays have higher dry strength than H+, Ca2+, Mg2+clays. Ball clays with high organic matter content gives strongest dry strength (suggest black ball clays) (RANATUNGA, C. L., 1989).

1.2.2.9 Cation exchange and deflocculation 

Ball clays have high cation exchange capacity ranging from 5 to 20 m.e.l00 mg.



So many of them require a considerable amount of electrolyte for deflocculation.



Particularly ball clays with a high percentage of organic matter; these are, moreover, not readily overflocculated.



The chief exchangeable ions are H+, Ca2+, Mg2+, Na+ and K+.

The general principles of deflocculation have already been described but it should be remembered that the relative amounts of exchangeable ions considerably affect the response to a given deflocculant instance, clays usually respond well to a 1:1 mixture of sodium carbonate and sodium silicate but this ratio may have to be altered if the distribution of exchangeable ions is abnormal (RANATUNGA, C. L., 1989).

18

CHAPTER 2 RESEARCH METHODOLOGY When it comes to research methodology initially basic tasks in laboratory work was followed such as collection of glassware and necessary equipment, cleaning of glassware, distillation of required solvents etc. All the instrumental conditions, experimental procedures and sampling strategies are included in this chapter.

2.1 Equipment and instruments Equipment and instruments used for experiments are listed in the Table 2.1. Table 2.1: List of equipment and instruments used Equipment

Specifications Can be weigh two decimal point gram accuracy(least count 0.01g) Can mill maximum 600g dried weight of material with 40% water at a stretch Pressing machine is 320bar, can press 83g of moistened powder at a stretch, Temperature of dryer is 150oC Unit of reading: Nmm-2 Instrument for the determination of max load and flexing modulus of rupture on, agglomerated materials and natural stones. Semiautomatic instrument, consisting and adjustable supports to the sample. The upper knife (with electronic adjustable speed as requested to the standards), shall come down to press the sample till breakage. The instrument is produced according to the ISO 10545-4 standard, other standards on request with accessories. Test pieces: from 100×50mm up to 650×650mm. Capacity: 100cc, This Density Cup is

Electronic balance Pot mill machine Laboratory press machine Laboratory dryer

Strength testing machine

Density cups 19

precision engineered of stainless steel and shaped in a cylinder form with a stainless steel lid. A tiny hole in the center of the lid allows removing excess paint and air bubbles for highest accuracy. The tolerance of Density Cups is 0.1% and a specific gravity test is carried out in accordance with ISO at a temperature of 23+2oC. This range of precision ISO Flow Cups is made of Anodized Aluminum and shows a nice highly polished finishing offering high accuracy combined with a user-friendly operation. Combined with the precision drilled orifice at the bottom of the ISO flow cup this ISO flow cup is the ideal instrument for your laboratory and research. Digital stop watch and clock with 6-digit LCD and 3 operation buttons 1000 microns sieve 600 microns sieve 300 microns sieve 150 microns sieve 63 microns sieve 44 microns sieve Maximum design temperature 1300ºC. Pressed steel free standing cabinet with stove enamel paint finish. High quality insulation brick linings. Fully compliant electro mechanical door safety interlocks. Over temperature kiln lining protection. A choice of control systems. A two-level finishing dryer. It rapidly removes the moisture contained in material being fed from the press, glazing machine or storage area. Extremely effective drying is provided by an innovative high-efficiency system based on small high speed burners and a system of stainless steel pipes that transfer heat mainly by radiation. The products of combustion seep out through small holes in the ducts and thus add convection heating to the radiation effect. Instead of the traditional recirculation fans, the ceramic rollers

Viscosity flow cups

Stop watch

Sieves

Laboratory kiln

Production kiln

20

feature an exhaust air extraction fan only. Combustion air is drawn from the system that already exists on the kiln. Using ceramic and stainless steel components eliminates the risk of contaminating products with metallic particles. The two levels are managed automatically and independently of each other. 2×500ml beakers, 1×250ml conical flask, 1×25ml burette, 1×20ml pipette, 1×10ml pipette, a burette stand, awashbottle

Titration equipment

2.2 Materials, chemicals, solutions and reagents Ball clay (Al2O3.2SiO2.2H2O) Potassium Feldspar (K2O.Al2O3.6SiO2) Dolomite (MgCO3.CaCO3) Silica sand (SiO2) FG8104A (ceramic diluting agent) Sodium silicate (Na2SiO3) Sodium carbonate (Na2CO3) Concentrated (w/w: 36%) hydro choric acid (HCl) Water Distilled water 0.1 moldm-3 Na2CO3 solution 0.2 moldm-3 HCl solution Methyl orange

21

2.3 Viscosity test in laboratory First low viscosity level was found by sodium carbonate content of ceramic body slip. The following steps were followed for this test. First normal ceramic body (NCB) slip was prepared.

2.4 Collection of materials The tile body was made up of natural minerals that are always used by the company. Ball clay, feldspar, silica sand and dolomite were mixed in the usual recipe.

2.4.1 Body slip preparation Materials were dried in laboratory dryer. Then they were weighed according to the below body formula for a total of 600g. (See Table 2.2) Table 2.2: Ceramic body formula Raw material Ball clay Feldspar Silica sand Dolomite Total

Percentage (%) 31 46 19 4

For 600g 186 276 114 24

100

600

The weighted materials were loaded to the pot mill jug. Water was added 40%. Sodium silicate, FG8104A and sodium carbonate were added to the pot mill jug (the details of the amounts added shown in the Table 2.3 below).

22

Table 2.3: Amount of additives for each body slip Additives FG8104A For Percentage Percentage For 600g (g) 600g (%) (%) (g) Sodium silicate

Body slip

Normal ceramic body slip Test 1 body slip Test 2 body slip Test 3 body slip Test 4 body slip Test 5 body slip Test 6 body slip

Sodium carbonate For Percentage 600g (%) (g)

0.5

3.0

0.267

1.6

0

0

0.5 0.5 0.5 0.5 0.5 0.5

3.0 3.0 3.0 3.0 3.0 3.0

0.267 0.267 0.267 0.267 0.267 0.267

1.6 1.6 1.6 1.6 1.6 1.6

0.083 0.167 0.25 0.333 0.417 0.5

0.5 1.0 1.5 2.0 2.5 3.0

The mixture was milled in the pot mill machine for 30 min and ceramic body slip was prepared for each ceramic bodies: Normal ceramic body slip, Test 1 body slip, Test 2 body slip, Test 3 body slip, Test 4 body slip, Test 5 body slip and Test 6 body slip. That slip was put to the plastic bucket and viscosity and density were measured.

2.5 Comparison of Mechanical strength and other physical properties First test bodies of low viscosity (viscosity near to normal ceramic body) were selected. Sample tiles were made regarding normal ceramic body formula and selected test body formulas according to following steps and green mechanical strength, dried mechanical strength and other importance properties were tested in the laboratory by using sample tile.

2.5.1 Collection of materials The tile body was made up of natural minerals that are always used by the company. Ball clay, feldspar, silica sand and dolomite were mixed in the usual manner. 23

2.5.2 Powder preparation (for low viscosity bodies) Materials were dried in laboratory dryer. Then they were weighed according to the following body formula for a total of 600g. (See above Table 2.2) The weighted materials were loaded to the pot mill jug. Water was added 40%. Sodium silicate, sodium carbonate and FG8104A were added to the pot mill jug (the details of the amounts added shown in the Table 2.4below). Table 2.4: Amount of additives for normal ceramic body and selected test bodies

Additives

FG8104A Sodium silicate Sodium carbonate

Normal ceramic body(without sodium carbonate) For Percentage 600g (%) (g) 0.267 1.6 0.5 3.0 0

0

Test ceramic body (Test 1)

0.267 0.5

For 600g (g) 1.6 3.0

0.083

0.5

Percentage (%)

Test ceramic body (Test 2)

0.267 0.5

For 600g (g) 1.6 3.0

0.167

1.0

Percentage (%)

The mixture was milled in the pot mill machine for 30 min. Three slips were obtained as the output. Density, viscosity and residue of each slip were measured. Slip was kept in the tray and dried in the laboratory dryer in 150oC. After that the slip was ground by using a mortar. Then the ground powder was sieved by using 1000 microns sieve. Added 5.5% water to the powder and mixed well. After that moisture powder was sieved again by using 1000 microns sieve. The moistened powder was kept in for 30 min.

24

2.5.3 Powder pressing and green tile strength test 83g of moistened powder was separated. Then it was pressed using press machine.15 green tiles (sample tiles) were prepared in the size of 100mm×50mm per test. The tiles were separated into three groups each having 5 tiles. Green tile strength was checked for 5 sample tiles by using strength testing machine.

2.5.4 Dried tile strength test 5 sample tiles were dried in laboratory drier (150oC) for one hour per test. After that dried tile strength was tested for them by using strength testing machine.

2.5.5 Shrinkage, LOI and percentage water absorption tests 5 sample tiles were dried in the laboratory dryer (150oC) for two hours per test. After that dried size (length) and dried tile weight were measured. Those values were recorded. After that those tiles were kept on the 400mm×400mm half fired (till 800oC) tile and were fired in the production kiln for 58 min. Fired tiles size (length) and fired tile weight were measured. After that 5 fired tiles were put to the water bath and were kept 2 hours in boiling water. Also those tiles were kept in the water bath till cool to room temperature. Those tiles were taken from water bath and were wiped by using pure clout. Finally weight and size (length) were measured.

25

2.6 Titration for finding purity of sodium carbonate 2.6.1 Preparation of a 0.1moldm-3 solution of Sodium Carbonate 2.65g sodium carbonate powder was weighed by using electronic balance. Weighed sodium carbonate powder was put to the 500 ml beaker and distilled water was added till 250ml level of beaker. Finally solution was mixed well.

2.6.2 Preparation of a 0.2moldm-3 solution of hydrochloric acid 10.13g concentrated hydro choleric acid was weighed by using electronic balance. Weighed concentrated hydro choleric acid was put to the 500ml beaker and distilled water was added till 500ml level of beaker. Finally solution was mixed well.

2.6.3 Titration test First titration equipment was prepared. Washed burette was mounted vertically on the burette stand and 0.2moldm-3HCl solution was filled to burette till 25ml level of burette. Also 0.1moldm-3 Na2CO3solutionswere filled to the 20ml pipette. After that measured 20ml Na2CO3 solution in the pipette was put to the 250ml washed conical flask and 2 drops of methyl orange was added to the conical flask. Also conical flask was mounted on burette sand vertically below to burette. After burette valve was opened very slowly. Final titration point was identified by methyl orange indicator.

26

CHAPTER 3 RESULTS AND DISCUSSION 3.1 Effect of Na2CO3 to viscosity Viscosity is an important characteristic for ball mill unloading process and spray drying process. Larger viscosity results in increasing ball mill unloading time and increases the fuel consumption so that the productivity becomes slow and increase the production cost. The company has a viscosity of 1.200+/-0.1 Eo for the density of 1.770+/-0.01gml-1currently as the lab standard.0.083% and 0.167% of Na2CO3resulted in the above viscosity. Test result shown below Table: 3.1. Table 3.1: Result of viscosity test of body slip Body slip Normal ceramic body slip Test body 1 Test body 2 Test body 3 Test body 4 Test body 5 Test body 6

Viscosity (E0) 1.249 1.221 1.251 1.346 1.360 1.469 1.717

Density (gml-1) 1.773 1.761 1.771 1.766 1.771 1.774 1.755

Variations of viscosity of body slip with Na2CO3 content shown below Figure 1.

27

Figure 3.1: Variation of viscosity with Na2CO3

3.2 Effect of Na2CO3togreen tile strength Both bodies “Test 1” and “Test 2” (0.083% and 0.167% of Na2CO3) increased the green tile strength. 0.083% increased the strength to the value of 8.48kgcm-2 which is 20.97% higher than the existing value. 0.167% increased the strength to the value of 12.92kgcm-2which is 25.92% higher than the existing value. Full test results are shown below Table 3.2, Table 3.3, Table 3.4, and Table 3.5.

3.3 Effect of Na2CO3 to dried tile strength Both bodies “Test 1” and “Test 2” (which has 0.083% and 0.167% of Na2CO3respectively) increased the dried tile strength. Body “Test 1” (0.083%) increased the strength to the value of 10.67kgcm-2 which is 52.21% higher than the existing value. Body “Test 2” (0.167%) increased the strength to the value of 15.22kgcm-2 which is

28

47.34% higher than the existing value. Full test results are shown below Table 3.2, Table 3.3, Table 3.4, and Table 3.5. Table 3.2: Result of mechanical strength tests for normal ceramic body

Green tile

1 2 3 4 5

Weight (g) 81.6 81.9 81.8 82.1 82.3

Thickness (mm) 8.09 8.10 8.12 8.11 8.17

Strength (Nmm-2) 0.62 0.83 0.58 0.76 0.65

Strength (kgcm-2) 6.32 8.46 5.91 7.74 6.62

Dried tile

6 7 8 9 10

77.1 77.4 77.3 77.3 77.6

8.20 8.14 8.16 8.12 8.19

1.02 1.01 1.02 1.06 0.96

10.39 10.29 10.39 10.80 9.78

N.C.B.

Tile No.

Table 3.3: Result of mechanical strength tests for “test body 1” (Na2CO3 percentage: 0.083%) Test body 1

Tile No.

Green tile

1 2 3 4 5

Weight (g) 81.4 81.2 81.4 81.7 81.3

Thickness (mm) 8.12 8.14 8.15 8.08 8.16

Strength (Nmm-2) 0.79 0.85 0.88 0.82 0.84

Strength (kgcm-2) 8.05 8.66 8.79 8.36 8.56

Dried tile

6 7 8 9 10

77.3 77.5 77.2 77.1 77.0

8.13 8.13 8.11 8.15 8.12

1.24 1.27 1.31 1.28 1.24

12.64 12.94 13.35 13.05 12.64

29

Table 3.4: Result of mechanical strength tests for “test body 2” (Na2CO3 percentage: 0.167%) Test body 2

Tile No.

Green tile

1 2 3 4 5

Weight (g) 81.6 81.8 81.8 82.0 81.7

Thickness (mm) 8.02 7.99 8.01 7.99 8.01

Strength (Nmm-2) 1.13 1.18 0.93 1.00 1.00

Strength (kgcm-2) 11.51 12.00 9.48 10.19 10.19

Dried tile

6 7 8 9 10

77.4 77.2 77.4 77.3 77.5

7.98 8.02 8.00 7.98 8.04

1.59 1.37 1.63 1.40 1.48

16.20 13.98 16.61 14.28 15.08

Table 3.5: Average of mechanical strength

N. C. B. Average of green tile strength (kgcm-2) Average of dried tile strength (kgcm-2)



7.01 10.33

Test body 1 8.48 12.92

Test body 2 10.67 15.22

The increment of strength of body of “test body 2” is greater than that of “test body1.” Hence all further tests performed only for the “test body 2.”

3.4 Effect on the other physical properties of the fired tile An increment of the shrinkage from value 24.83% in the finished tile could be seen. LOI value didn’t change. Water absorption percentage decreased by 28.44%. Full test results are shown below Table 3.6 and Table 3.7.

30

Table 3.6: Result of shrinkage test, LOI test and water absorption test (“Test Body 2”).

Tile No 11 12 13 14

N .C. B. 5.95 6.03 6.04 6.07

Average

6.02

LOI (%) Test body 2 5.99 5.92 6.05 6.06

Shrinkage (%) N .C. B. Test body 2 3.07 3.08 3.05 3.80 2.97 3.76 2.97 3.74

6.00

3.02

3.77

Table 3.7: Result of water absorption test (“Test Body 2”). Water Absorption (%) N .C. B. Test body 2 8.39 5.95 8.74 6.30 8.62 6.17

Tile No 11 12 13

8.58

Average

6.14

3.5 Purity of Na2CO3 The purity of the Na2CO3 in the source is important to measure the actual amount of Na2CO3 added into the mixture. The following Table 3.7 shows the purity of the Na2CO3 in source. Table 3.8: Purity results of Na2CO3 samples

Sample No.

HCl (×10-3mol)

Na2CO3 (×10-3mol)

1 2 3 4

3.87 3.67 3.65 3.64

1.935 1.835 1.825 1.820

Purity of Na2CO3 (%) 96.75 91.75 91.25 91.00

Average

3.70

1.853

92.69

31

3.6 Discussion The results of the test successfully propose a standard that is practical to run in the production process. Pressure of the press machine could be reduced from 430 bars to 390 bars. The new tile was able to show positive advantages to the production line. The temperature of the firing zone of the production kiln could be reduced from 1212oC to 1190oC due to the decrement of shrinkage. These caused to reduce the production cost of the process and increase the productivity in the factory.

32

CHAPTER 4 CONCLUSION AND FUTURE WORK 4.1 Conclusion The use of sodium carbonate with sodium silicate in 1:3 ratios in ceramic tile body compositions increases the mechanical strength of the pressed bodies. It has been observed that there is a 0.167% percentage of the sodium carbonate addition for each composition at which dry mechanical strength increases without impairing deflocculation behavior. Additions larger than 0.167% percentage, which depends on the composition, lead to greater increases in mechanical strength but they hinder deflocculation owing to the rise in the ionic force of the medium. It is also considered to be of great usefulness for porcelain tile compositions with which spray-dried powders intended for dry coloring are obtained. The possibility of reducing consumption of resources (raw materials, and energy) with the ensuing reduction in costs associated with raw materials, energy, and transport, as well as greater productivity of the factory.

4.2 Future Work and Recommendations 

Testing this method for other types of tile bodies.



Testing with other types of raw materials

33

REFERENCES A.BARCLAY, DPeters. 1976. New Sources of Alumina. Min. Cong. J. ARBUCKLE. Clays and Clay Bodies. [online]. [Accessed 22 Aug 2014]. Available from World Wide Web: CARTY, William M. 2009. Whitewares and Materials: Ceramic Engineering and Science Proceedings. Ceramic Industry. [online]. [Accessed 22 Aug 2014]. Available from World Wide Web: CHOU, Kevin Ying. 2014. Stabilizers for ceramic body extrusion. US20090143219. Digitalfire. [online]. [Accessed 20 Jan 2015]. Available from World Wide Web: F. QUEREDA, E. Sanchez, J. Garcia-Ten, A. Gozalbo, V. Beltran, J. Sanchez, J. Sales. USE OF SODIUM CARBONATE AS A BINDER IN CERAMIC TILE COMPOSITIONS. [online]. [Accessed 12 Dec 2014]. Available from World Wide Web: Google search ”what is ceramic tile”. [online]. [Accessed 20 Jan 2015]. Available from World Wide Web: Home depot. [online]. [Accessed 12 Dec 2014]. Available from World Wide Web: 34

J.L. AMORO S, E. Sa nchez, V. Cantavella, J.C. Jarque. 2003. Evolution of the mechanical strength of industrially dried ceramic tiles during storage. Journal of the European Ceramic Society. 23, pp.1839–1845. LANGE, L.L. 1989. Journal of the American Ceramic Society. 72, pp.3-15 25. MANFREDINI, A. P. Novaes de Oliveira , T. A MODEL TO PREDICT THE MECHANICAL STRENGTH OF A GREEN CERAMIC BODY. [online]. [Accessed 22 Aug 2014]. Available from World Wide Web: N. DEMIRKOL, A. Capoglu. 2007. Rheological and Green Strength Behaviour of Lowclay Translucent Whiteware Slurries with an Acrylic Type Emulsion Binder Addition. ECerS Conf. 10, pp.434-438. PLANET, Clay. Clay Planet. [online]. [Accessed 12 Dec 2014]. Available from World Wide Web: R., James S. Qualicer. [online]. [Accessed 22 Aug 2014]. Available from World Wide Web: RANATUNGA, C. L. 1989. Formulation of ceramic body mixtures with enhanced characteristics. Unpublished. RANATUNGA, C. L. 2014. Physics of Ceramics and Glass. SACMI. 2005. Applied Ceramic Technology. SCHWARZ, Zschimmer. Mechanisms of action of deflocculants and dispersants in ceramic bodies. [online]. [Accessed 20 Jan 2015]. Available from World Wide Web:

35

SIDNEI JOSE GOMES SOUSA, Jose Nilson Franca de Holanda. 2005. Sintering Behavior of Porous Wall Tile Bodies During Fast Single-Firing Process. Materials Research. 8(2), pp.197-200. T. MANFREDINI, G. C. PELLACANI, P. POZZI. 1991. Preparation of a ceramic floor tile body containing pure bentonite as strengthening agent. [online]. [Accessed 22 Aug 2014]. Available from World Wide Web:

36

APPENDICES Appendix A - Calculation methods in factory laboratory Viscosity calculation formula, t k

iscosity t

-

Time to flow in viscosity flow cup

k

-

Constant (8.62)

Density calculation formula, w v

Density w

-

Mass of liquid in the density cup

v

-

Volume of density cup

Calculation formula of mechanical strength of green tile, R

OR

g

MR

-

Meter reading

g

-

Gravitational acceleration

Shrinkage Percentage, hrinkage L0

-

Length of dried tile

L1

-

Length of fired tile

L

L1 L

37

1

%

LOI Percentage, W W1 W W0

-

mass of dried tile

W1

-

mass of fired tile

1

%

Water absorption percentage, 1

1

%

M0

-

mass of fried

M1

-

mass of wet tile (After testing water bath)

Appendix B - Acid reaction with Na2CO3 Na2CO3 1

:

2HCL

2NaCl

CO2

H2O

2

Ratio of molar between reaction of Na2CO3 and HCL is 1:2.Methyl orange can use identifying point of titration. Methyl orange is a pH indicator frequently used in titrations because of its clear and distinct color change. Because it changes color at the pH of a mid-strength acid, it is usually used in titrations for acids. Unlike a universal indicator, methyl orange does not have a full spectrum of color change, but has a sharper end point. In a solution becoming less acidic, methyl orange moves from red to orange and finally to yellow with the reverse occurring for a solution increasing in acidity. The entire color change occurs in acidic conditions. 38

Appendix C - Cleaning steps of equipment for titration test Burette

- Wash with distilled water and then with the solution going into it.

Conical flask - Wash with distilled water only. Pipette

- Wash with distilled water and then with the solution going into it.

Appendix D - After firing test methods for glazed tile in the laboratory 

Fired strength - fired tile cut to pieces (50mm × length of fired tile) and test strength by using freed tile strength testing machine(MOR machine).Calculate strength using below formula, OR



3

B 2

R

g

2

T

B

-

Distance between bars of MOR machine

MR

-

Meter reading

T

-

Thickness of tile

S

-

Size of tile (50mm)

g

-

Gravitational acceleration

Water absorption - Group (as EN) but also measurement of porosities (this is carried out under vacuum)



Thermal shock - Test with and without immersion in water, heating temp. Changed to 145 °C.



Crazing resistance - 1 hour to reach 5atm and 2 hours holding.

39



Chemical resistance - Harshness of attack depends on utilization and degree of resistance offered by material.



Abrasion resistance (glazed) - Classes from 1 to 5 with stain test compulsory for class 5.



Stain resistance - Potassium permanganate and methylene blue for 24 hours on glazed products: cleaning with water and neutral detergent

40