INVESTIGATION OF THE PLASTICITY AND REFRACTORY PROPERTIES OF SELECTED CLAY SAMPLES FROM OGUN STATE


Content

ABSTRACT

Nigeria is endowed with vast deposits of clay spread across her various regions. Today, almost all the clay requirement of the country in the form of refractory and bentonite are imported from the Great Britain, China and Japan etc. leading to high cost of procurement and consequently result to high cost of finished products. This work is aimed at investigating the plasticity and refractory properties of locally available clays for possible use in our industries. Ososun, Abule-Oloni, Ile-IseAwo and Osiele clay were collected from Ogun State. The properties investigated include Bulk density, apparent porosity, Linear shrinkage, Thermal shock resistance, Cold crushing strength, and loss on Ignition. The Refractoriness was estimated using Pyrometric Cone Equivalence PCE) while the chemical composition was determined using the Atomic Absorption Spectrophotometer (AAS). Based on the chemical composition analysis, the clays were found to be Aluminosilicate clay and from the result obtained from the physical test, almost all the properties investigated gave results that are acceptable for use as a clay refractory except the compressive strength of all samples fall below the minimum specification which could be attributed to inadequ ate power supply that resulted to inconsistent firing. Findings shows that Ososun and Abule-Oloni Clays can be used for refractory purposes such as firebricks, ramming masses, linings of iron and steel making furnaces and ceramic product such as tiles and furnace crucibles.

 

 


TABLE OF CONTENTS

Contents                                                                                                                    Page No

Title Page ……………………………………………………………………………i

Certification…………………………………………………………………………   ii

Dedication……………………………………………...............................................     iii

Acknowledgement………………………...……...…. ……………………………..   iv

Table of contents…………………………..……………………………………….    v

Abstract……………………………..………………………………………………    vii

 

CHAPTER ONE…………………………………………………………………………  1

1.0         Introduction…………………………………………………………………      1

1.1         Background of the study………………………………………………………   4

1.2         Statement of the problem…………………………………………………………  7

1.2         Aim and Objectives of the study……………………………………………………            7

1.4         Scope and delimitation of the study………………………………………………   8

1.5     Significance of the study …………………………………………………………… 10

Definition of Terms………………………………………………………………………….11

List of Figures……………………………………………………………………………… 12

List of Tables………………………………………………………………………………. 13

 

CHAPTER TWO…………………………………………………………………………. 14

2.0         Literature Review……………………………………………………………………14

2.1         Nature of Refractory Clay…………………………………………………………  15

2.1.1     Classes of Refractory Clay………………………………………………………… 16

2.2         Properties of Clay……………………………………………………………………20

2.2.1     Thermal properties of clay…………………………………………………………  22

2.2.2     Physical Properties of Clay………………………………………………………… 25

2.2.3     Mechanical properties of Clay………………………………………………………28       

CHAPTER THREE

3.0         Experimental Procedure……………………………………………………………  30

3.1         Sourcing of materials for preparation……………………………………………… 30

3.2         Tools and equipment used for the production processes……………………………31

3.3         Experimental Procedure for the Research Work……………………………………32

3.4         Characterization Procedure………………………………………………………….33

3.4.1     Determination of Plasticity Index………………………………………………      33

3.4.2     Bulk density………………………………………………………………………    34

3.4.3     Moisture content……………………………………………………………………34

3.4.4     Fired linear shrinkage  ………………………………………………………………34

3.4.5     Compressive Strength ………………………………………………………………35

3.4.6    Determination of Thermal Shock Resistance……………………………………...36

3.4.7    Determination of refractoriness (PCE) ……………………………………………  36       

CHAPTER FOUR…………………………………………………………………………            37

4.0 Results and Discussion………………………………………………………………… 37

4.1         Compositional Analysis of clay Samples from Ogun State……………………….   37

4.2         Atterberg Limits…………………………………………………………………..   38

4.3         Sieving Results (Particle Size Distribution) ………………………………………   42

4.4         Physico-mechanical Properties……………………………………………………    43       

CHAPTER 5 …………………..………………………………………………………..    49

5.0         Conclusion………………………………………………………………………..    49             References…………………………………………………………………………  51      

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHAPTER ONE

1.0       Introduction

Clay is a common name for a number of fine-grained, earthy materials that become plastic when wet. Chemically, clays are hydrous aluminum silicates, ordinarily containing impurities, e.g., potassium, sodium, calcium, magnesium, or iron, in small amounts Grimshaw (1959). They are divided into two classes: residual clay, found in the place of origin, and transported clay, also known as sedimentary clay, removed from the place of origin by an agent of erosion and deposited in a new and possibly distant position. Residual clays are most commonly formed by surface weathering, which gives rise to clay in three ways—by the chemical decomposition of rocks, such as granite, containing silica and alumina; by the solution of rocks, such as limestone, containing clayey impurities, which, being insoluble, are deposited as clay; and by the disintegration and solution of shale (Ryan,1978). One of the commonest processes of clay formation is the chemical decomposition of feldspar. Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks, usually silicate-bearing, by low concentrations of carbonic acid and other diluted solvents. These solvents, usually acidic, migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed by hydrothermal activity Guggenheim et al., (1995). Clay deposits may be formed in place as residual deposits in soil, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy depositional environments such as large

lakes and marine basins. Primary clays, also known as kaolins, are located at the site of formation. Secondary clay deposits have been moved by erosion and water from their primary location. Depending on the academic source, there are three or four main groups of clays: kaolinite, montmorillonite-smectite, illite, and chlorite. Chlorites are not always considered to be clay, sometimes being classified as a separate group within the phyllosilicates. There are approximately 30 different types of "pure" clays in these categories, but most "natural" clays are mixtures of these different types, along with other weathered minerals. Ehlers et al.,(1982)..

Clays exhibit plasticity when mixed with water in certain proportions. When dry, clay becomes firm and when fired in a kiln, permanent physical and chemical changes occur. These reactions, among other changes, cause the clay to be converted into a ceramic material. Because of these properties, clay is used for making pottery items, both utilitarian and decorative. Different types of clay, when used with different minerals and firing conditions, are used to produce earthenware, stoneware, and porcelain. Clay, being relatively impermeable to water, is also used where natural seals are needed, such as in the cores of dams, or as a barrier in landfills against toxic seepage (lining the landfill, preferably in combination with geotextiles). Hillier (2003) Clay is one of the oldest building materials on Earth, among other ancient, naturally-occurring geologic materials such as stone and organic materials like wood. Between one-half and two-thirds of the world's population, in traditional societies as well as developed countries, still live or work in a building made with clay as an essential part of its load-bearing structure.

Properties of the clays include plasticity, shrinkage under firing and under air drying, fineness of grain, color after firing, hardness, cohesion, and capacity of the surface to take decoration. On the basis of such qualities clays are variously divided into classes or groups; products are generally made from mixtures of clays and other substances. The purest clays are the china clays A refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures or as components of systems, that are exposed to environments above 1,000 °F (811 K; 538 °C)". Guggenheim et al., (1995).

Refractory materials are used in linings for furnaces, kilns, incinerators, reactors and crucibles. Refractory materials must be chemically and physically stable at high temperatures. Depending on the operating environment, they need to be resistant to thermal shock, be chemically inert, and/or have specific ranges of thermal conductivity and of the coefficient of thermal expansion. The oxides of aluminum (alumina), silicon (silica) and magnesium (magnesia) are the most important materials used in the manufacturing of refractories. Another oxide usually found in refractories is the oxide of calcium (lime). Fire clays are also widely used in the manufacture of refractories. Refractories must be chosen according to the conditions they will face. Some applications require special refractory materials. Zirconia is used when the material must withstand extremely high temperatures. Silicon carbide and carbon (graphite) are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with oxygen, as they will oxidize and burn.

Binary compounds such as tungsten carbide or boron nitride can be very refractory. Hafnium carbide is the most refractory binary compound known, with a melting point of 3890 °C. Hugh (1992) the ternary compound tantalum hafnium carbide has one of the highest melting points of all known compounds (4215 °C). McGraw-Hill (1977).

1.1             Background of the study

Interest in clays has increased in recent years due to their physic-chemical and plastic properties, which make them some of the most widely used materials in industry for making traditional ceramics. Since Atterberg (1911) much work has been done in soils and sediments in an attempt to evaluate the influence of the various factors involved in the plasticity of clay samples, such as their mineralogical composition, shape, size distribution of particles, interaction among clays or with water or dissolved salts, the effect of cementing, clay genesis, etc. Casagrande published his well-known soil chart in 1948, and Dumbleton and West (1966) studied the relationships between clay contents and the plastic and liquid limits of natural soils from around the world, in an attempt to define the contribution of clay component to the engineering properties of soil as a whole. More specifically, Bain (1971) focussed on industrial clays (halloysite, kaolinite, illite, mixed layers, several kinds of smectites, sepiolite and paylygorskite), Decleer et al,. (1983) correlated mineral composition, chemistry and granulometry with plastic and liquid limits in Belgian clays, and Hawkins et al., (1986) did similar analysis in the UK, while Al-Homoud et al., (1996) focussed on clay beds causing landslides and Ohtsubo et al. (2002) on marine clays.

Perhaps the most recent and conclusive contribution is by Schmitzet al., (2004) who introduced equivalent basal spacing (EBS), a parameter obtained by multiplying the relative amount of a clay with its basal spacing (Å) known from the literature.

Most of the traditional ceramic mixtures show plastic type behaviour, due to the presence of the plate-like morphology of the particles of the clay-based raw materials that are able to slide over each other due to the water retained in the interstitial spaces that acts as lubricant. When necessary, commercial plasticizers might be added, such as methylcellulose or hydroxypropyl methylcellulose. The measurement and control of the plasticity is essential to achieve good fabrication conditions (correct shapes and low processing times). However, the common practice is somewhat empirical, due to the large number of influent parameters and the lack of sensitive quantification means for the evaluation of the complex relationship between the flow characteristics and processed components’ properties.

Raw materials used in the traditional ceramics industry can be classified as clay (plastic) and non-clay (non-plastic) minerals. Clays are the chief raw material for many commercial structural ceramic products such as wall tiles, roofing tiles, building bricks, and white wares. Chemically, clay minerals are phyllo- silicates with ions arranged in parallel planes forming layers (Graw-Hill, 1977). Clays occur in deposits of greatly varying nature. No two deposits have exactly the same clay and frequently different samples of clay from the same deposit differ.

Clay products such as wall tiles, ceramic wares, burnt bricks, roofing, and floor tiles are cheaper and durable building materials than cement especially under tropical conditions. An optimum combination of various clays is the essential ingredient in ceramic wall tile composition, which provides plasticity and green strength during forming stages and contributes substantially to the color of the fired products depending upon the impurity of oxides present.

The formation, structure, mineralogical and other physico-chemical properties of various types of clay minerals are widely being studied. Two factors are helping the development of good refractories using the local raw materials. The first one is the growing number of metallurgical industries that are in dire need of these refractories, while the other factor is the difficulty in sourcing for foreign exchange market, a situation that has led to higher and unaffordable cost of procuring the refractory materials needed by these industries. Some of the refractory materials usually employed are fireclay, quartz sand, magnesite, sillimanite, berylia, alumina, chromite, zirconia, boron, nitride, graphite and carbide.

 The refractories need of Nigeria which is a developing industrial nation is potentially enormous. It was estimated that the Ajaokuta Steel Company and Delta Steel Company will, at full capacity, respectively require 43,503 and 25,000 tonnes/year of fireclay refractories for their activities; and these products are sourced from abroad (Hassan et al., 1993). Ijagbemi (2002) noted that small-scale industries in Nnewi and elsewhere in the country have recently embarked on the fabrication of spare parts. These spare parts are fabricated using high temperature furnaces [foundry melting furnaces and heat-treatment furnaces] that require refractories as linings. Most of the refractories consumed in this country are sourced from abroad whereas there are many clay deposits in Nigeria that could be used as refractories. Ijagbemi (2002) reported that in 1987 alone, Nigeria imported 27 million metric tonnes of refractories. The country expends a lot of foreign exchange importing refractories. Yet, a lot of clay deposits abound in the country, which can be developed to meet our local needs. Earlier works on various Nigerian clay deposits have shown many of them to be rather high in silica content and low in alumina (NMDC, 1999; Hassan, 2001). However, a number of deposits were found suitable for use as refractory raw materials; that is, if properly processed. Therefore, the development of our local materials for the production of refractories to meet our industrial and technological requirements is not only justified but imperative.

1.2       Statement of the problem

Nigeria is endowed with vast deposits of clay spread across her various regions. Today, almost all the clay requirement of the country in the form of refractory and bentonite are imported leading to high cost of procurement and consequently result to high cost of finished products.

The limit in the application of local ceramic deposits (clay)  is as a result of inadequate study to examine the relevant mineralogical parameters affecting the plasticity and refractoriness of samples, in order to easily distinguish and select those suited for certain technological applications.

 

1.3     Aim and Objectives of the study

The aim of this project is to investigate the plasticity and refractory properties of clay        samples of the selected area with the following objectives:

 

(i)                To investigate the plasticity of clay samples of Ososun, Abule-Oloni, Ile-IseAwo and Osiele clays, all from Ogun State;

(ii)             To investigate the refractory properties of clay samples of Ososun and Abule-Oloni, all from Ogun State;

(iii)           To determine the effect of water content on the workability of the sampled clay.

 

1.4       Scope and de-limitation of the study

This work is designed to investigate the chemical composition, plasticity and refractory properties of samples clay selected from Ososoun, Abule-Oloni, Ile-IseAwo and Osiele in Ogun State.

The beneficiation of the clay sample is done by filtration and sieving to a fine particles size of 100μm. The prepared samples clay is pressed in a circular disc of 3cm by 7cm before firing at different temperature ranges.

 

The scope of this study is limited to the chemical composition, plasticity, shrinkage, bulk density, strength and refractory test carried out in the laboratory and the firing temperature of the furnace which could not exceed 1400oC.


 

Figure 1.1: Map of Nigeria Showing Ogun State map at Latitude6.9098ON and Longitude 3.2584OE Showing the location for the Clay deposits (Source: Ogun State Bureau of Land and Survey).

 

1.5     Significance  of the study

The development and production of ceramic material from many clay deposits in Nigeria for modern usage has been very slow. This research study therefore traces the success and failure of using local ceramic deposits (clay) to produce modern table wares with particular reference to the stone ware pottery. This research work would also cite the study and analysis of physical properties of ceramic deposits to research on local materials for modern production of ceramic wares.

The demand for ceramic wares particularly table wares architectural ceramic in Nigeria has been on the increase for some time. The study would enable us to put into process the use of local ceramic deposits for the production of ceramic wares such as sanitary ware and table ware which would be easily available, cost effective and create job opportunities for people to earn a living. More so, the research provides adequate study to find local substitute for the imported raw materials for the production of ceramic wares.

The industries which are directly working in the areas related to this study will immensely benefit from this study whenever they have access to its findings. It would be easy for prospective investors to know the physical and chemical properties of these clay minerals. The knowledge will guide their decision on whether the properties required for their products can be found in any of these clay deposits.

In conclusion, the result of this study will be of help to other researchers who may be seeking for related information while carrying out a similar research work in future if the result is made available to them in their education resource centers.

Definition of Terms

Beneficiation: process of winning valuable minerals from gangue (impurities)

Ceramic: A non-organic and non-metallic substance, often an oxide or carbide.

Ceramic ware: an article made of ceramic.

Plasticity:  a basic clay property that permits this material to form a plastic body

Refractory: materials which are capable of withstanding very high temperature condition without losing their chemical and mechanical integrity.

 


 

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