ABSTRACT

The raw mineral used world-wide in the production of plaster of Paris is gypsum. This is available in Nigeria. Constant importation of plaster of Paris constitutes a drain on national economy and an added cost on ceramic mass production. Its availability has prompted the central direction of this project to analyse, in a comparative way and to see the possibility of local usage which is likely to cut down cost of ceramic production. Gypsum was obtained from three locations, Wurno and Dange in Sokoto State and Weppa in Edo state. The three samples obtained were labelled and transported from sites to the Ceramic Section, Department of Industrial Design, Ahmadu Bello University, Zaria. They were beneficiated and calcined at the Industrial Development Centre (IDC) at the temperature of 1700C. This was done for the three samples from these locations. Various tests were carried out and they included absorbency, shrinkage, compressive and density tests. These tests aided in determining performance of processed plaster of Paris for ceramic mass production. Results showed that the ratio mix of 75-85 plaster/water ratio mix were suitable for ceramic slip casting process. 65 and 70 plaster/water ratio mix were better used for casting models and press moulding process. The processed plaster of Paris from the three locations; Wurno, Dange and Weppa were used in the production of ceramic moulds which were in turn used for production of ceramic wares. The wares were fired and glazed. This showed that gypsum obtained from the three locations can be used for ceramic application. However, Weppa sample was the best of the three locations in performance and colour followed by Wurno. Dange was good but showed early signs of wearing fatique. Wurno and Dange samples were identified as anhydrites CaSO42H2O while Weppa sample was identified as gypsum CaSO4.2H2O.

 

 

TABLE OF CONTENTS

 

Title page – – – – – – – – – – i Declaration – – – – – – – – – – ii Certification – – – – – – – – – – iii Dedication – – – – – – – – – – iv Acknowledgement – – – – – – – – – v Table of contents – – – – – – – – – vii List of tables – – – – – – – – – – ix List of plates – – – – – – – – – – x List of figures – – – – – – – – – – xii Definition of terms – – – – – – – – – xii Abstract – – – – – – – – – – xvii CHAPTER ONE: INTRODUCTION 1.0 Background to the Study – – – – – – – 1 1.1 Statement of the Problem – – – – – – – 4 1.2 Aim of the Study – – – – – – – – 6 1.3 Objectives of the Study – – – – – – – 6 1.4 Research Questions – – – – – – – – 7 1.5 Justification for the Study – – – – – – – 7 1.6 Delimitation – – – – – – – – – 8 1.7 Limitation of the Study – – – – – – – 8 1.8 Significance of the Study – – – – – – – 8 1.9 Scope of the Study – – – – – – – – 9 1.10 Basic Assumption – – – – – – – – 9 CHAPTER TWO: LITERATURE REVIEW 2.0 Introduction – – – – – – – – – 10 2.1 Conceptual Framework – – – – – – – 10 2.2 History and Process of Making Plaster of Paris – – – – 12 2.3 Gypsum Rock, Types, Uses and Theories of Formation – – – 14 2.4 Temperature Options and Heat Treatment in Plaster Processing – – 24 2.5 Information on Various Tests Suitable for this Study – – – 28 2.5.1 X-ray Diffractions (XRD) – – – – – – – 28 2.5.2 X – ray-Fluorescence (XRF) – – – – – – – 29
2.5.3 Compressive Strength – – – – – – – 30
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2.5.4 Shrinkage Test – – – – – – – – 30 2.5.5 Density Test – – – – – – – – – 30 2.5.6 Absorbency Test – – – – – – – – 30 2.5.7 Practical Casting and Mould Release Test – – – – – 30 2.6 General Information on Mould Making and Slip Casting – – – 31 CHAPTER THREE: MATERIALS AND METHODS 3.0 Research Design and Procedure – – – – – – 33 3.1 Preparations for Field Trip – – – – – – – 33 3.2 Field Trips and Prospecting of Material – – – – – 35 3.3 Physical Analysis of Gypsum Tests – – – – – – 36 3.3.1 Streak Test – – – – – – – – – 36 3.3.2 Cleavage Test – – – – – – – – – 37 3.3.3 Hardness Test – – – – – – – – – 37 3.3.4 Moh’s Scale of Mineral Hardness: – – – – – – 37 3.3.5 Colour/Optical Properties – – – – – – – 38 3.3.6 Lustre – – – – – – – – – – 39 3.3.7 Habit, Form or Shape – – – – – – – – 39 3.3.8 Specific Gravity – – – – – – – – 40 3.4 Preparation of Gypsum for Calcination (Crushing/Grinding) – – 41 3.5 Calcination of Ground Gypsum into Plaster – – – – – 43 3.5.1 Determining temperature – – – – – – – 44 3.5.2 Plaster production cycle – – – – – – – 44 3.6 Calcination – – – – – – – – – 45 3.6.1 Kiln for Calcination – – – – – – – – 45 3.7 Sieving of Processed Plaster – – – – – – – 48 3.8 General Observations on Calcination Process – – – – 50 3.9 Production of Metal Moulds for Test Tiles – – – – – 51 3.10 Production of Metal and Wooden Moulds for Test Tiles – – – 54 3.11 The Practical Use of Processed Plaster of Paris for Ceramic Productions – 54 3.11.1 Determining Plaster/Water Ratio – – – – – – 55 3.11.2 Preparation and production of models – – – – – 56 3.11.3 Sprig/stamp simple mould – – – – – – – 56 3.11.4 One piece mould – – – – – – – – 56
3.11.5 Two piece moulds – – – – – – – – 57
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3.11.6 Three-piece mould – – – – – – – – 58 3.11.7 Casting Slip – – – – – – – – – 58 3.11.8 Casting with commercial plaster moulds – – – – – 59 3.12 Preparation/Production of Test Cylinders and Tiles – – – – 59 3.13 Absorbency Test – – – – – – – – 62 3.13.1 Experiment: – – – – – – – – – 62 3.13.2 Instrument: – – – – – – – – – 62 3.14 Shrinkage Test and Results – – – – – – – 63 3.14.1 Experiment – – – – – – – – – 64 3.15 Compressive Strength Tests – – – – – – – 64 3.15.1 The Hounsefield Tensometre – – – – – – – 65 3.16 Density Test – — – – – – – – 67 3.16.1 Bulk Density – – – – – – – – – 68 CHAPTER FOUR: RESULT, ANALYSIS AND DISCUSSION 4.0 Introduction – – – – – – – – – 69 4.1 Absorbency Test – – – – – – – – 69 4.1.1 Discussion – – – – – – – – – 70 4.1.2 Comparative analysis of Wurno, Dange and Weppa Absorbency Test – 72 4.2 Shrinkage Test and Results – – – – – – – 73 4.2.1 Discussion – – – – – – – – – 73 4.3 Compressive Strength Tests – – – – – – – 74 4.3.1 Load/Force Reading of Compressive Strength Tests – – – – 74 4.3.2 Comparative Analysis of Wurno, Dange and Weppa Compressive Strength 76 4.3.3 Compressive (stress) Strength Observation – – – – – 77 4.3.4 Discussion of Compressive Strength Test on Wurno, Dange and Weppa Gypsum Plaster – – – – – – – – – – 77 4.4 Density Test – – – – – – – – – 84 4.4.1 Observation of Dry Density Test on Wurno, Dange and Weppa Gypsum/Water ratio mix – – – – – – – – – 87 4.4.2 Discussion on Dry Density Test of Wurno, Dange and Weppa Plaster/Water Ratio Mix – – – – – – – – – 87 4.4.2.1 Density of Wurno Plaster – – – – – – – 87 4.4.2.2 Density of Dange Plaster – – – – – – – 88
4.4.2.3 Density of Weppa Plaster – – – – – – – 88
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4.4.3 Comparative Analysis of Dry Density Tests in Wurno, Dange and Weppa Plaster 88 4.4.4 Discussion on bulk density – – – – – – – 89 4.4.5 Comparative Analysis of Bulk Density of Wurno, Dange and Weppa Processed Plaster. – – – – – – – – – – 91 4.5 XRF (X-Ray Fluorescence Spectrometer) – – – – – 91 4.5.1 Analysis of XRF (X-ray Fluorescence Spectrometer) – – – 97 4.5.2 Discussion on raw gypsum and processed plaster from Wurno – – 98 4.5.3 Discussion on Raw Gypsum and processed plaster from Dange – – 101 4.5.4 Discussion on Raw Gypsum and processed plaster from Weppa – – 105 4.6 X-Ray Diffraction (XRD) – – – – – – – 107 4.6.1 Discussion on XRD Analysis of Gypsum and Plaster from Wurno, Dange and Weppa Areas – – – – – – – – – 110 4.6.2 Discussion on Raw Gypsum from Wurno, Dange and Weppa Gypsum – 110 4.6.3 Discussion on Processed Plaster from Wurno, Dange and Weppa – – 111 CHAPTER FIVE: SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 5.0 Introduction – – – – – – – – – 112 5.1 Summary – – – – – – – – – 112 5.2 Conclusion – – – – – – – – – 115 5.3 General Recommendation – – – – – – – 116 5.4 Recommendation for Further Studies – – – – – – 117 5.5 Contribution to knowledge – – – – – – – 118 References – – – – – – – – – 120 Appendices – – – – – – – – – 125
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CHAPTER ONE

NTRODUCTION 1.0 Background to the Study The normal production processes involved in ceramic design and practice is often times tedious and demanding. The necessities for faster mode of production such as the use of plaster of Paris mould have become imperative for ceramic production process in recent times. The production and use of moulds in their various forms seem to bring relief and solution to initial production methods that seem more strenuous at accomplishing mass production. Although there are various types of moulds, the plaster of Paris mould appears to be the type common with most ceramic mass productions. Ceramic moulds are made from plaster of Paris produced from gypsum. It was first developed in Montmartre, France around 1770, which gave rise to its name plaster of Paris and the discovery revolutionised mass production by slip casting. Gypsum is a rock or natural mineral that is mined from the earth, usually referred to as hydrous calcium sulphate, or (CaSO₄.2H₂O). When gypsum is exposed to heat treatment, 75% of water loss is recorded. This changes it to hemihydrates (CaSO₄.½H₂O). In other words, gypsum + heat = plaster (and ¾ water which evaporates). The making of plaster is done by grinding gypsum, and then heating it until the chemically-bonded water partially evaporates from 1000C to about 180⁰C.
It is evident from past studies that gypsum is available in Nigeria. Researchers and writers alike have tried to establish this fact from their findings. Examples of such reports can be found with the Ministry of Solid minerals Development 2000, and Mohammed-Sani, 2002. According to Akpakip, (1993), moulds may come in various forms but the medium which can best be adapted for ceramic production is gypsum plaster. This is so because moulds made from plaster have the ability or tendency to absorb large quantity of water from casting slip,
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thus making it a cheap and reliable medium for ceramic production that cannot for now, be substituted with other media. Generally, moulds may be produced using other media such as metal, cement, wood, earthenware, silicone gel, polyvinyl and so on, (Sullayman, 2006, Akomolafe, 1991). Moulds of different types are often used to execute both small and large projects. These could work well for non-clay processes and allied disciplines but not with ceramic mass production due to the peculiarity of its production. This may be due to the fact that most ceramic productions use clay in wet state (plastic or slurry) or such materials (ceramic bodies) that form or dry on plaster moulds. An exception is when other mechanical processes like dust / granular pressing, isostatic pressing, tape casting, and rain pressing, and so on are involved. However, the fact remains that whether mould is made in a single one piece, two-piece, three-piece or multiple-piece form, its production helps in replicating art, craft or other industrial products exactly, either in relief or in-the-round. In other words, to attain accuracy, uniformity in weight, size and finishing, mould-making and its usage are desirable. Akpakip, (1996) worked on using gypsum in the area of plaster of Paris production. The major thrust of this study is to analyse the composite nature of gypsum which can be used as guide toward producing ceramic plaster.
There are some undeniable facts about the importance of mould in ceramic production that should be addressed and discussed at this stage. The first is that moulds are good for precision and replication for the production either in general art/craft works (in the form of household utensils or decorative wares), or in the minute scientific ceramic productions such as dentures and other medical body part replacement. Secondly, availability of mould and its use reduces time spent on the job and conserves energy which can be directed toward production of more ceramic wares. Lastly, the introduction and use of moulds in ceramic
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production process must be acknowledged as it has made an otherwise unaffordable ceramics available and affordable to everyone. These facts, among others, are the reasons why production and use of plaster, ipso facto moulds should be encouraged and sustained. The constant requirement and demand for gypsum for production as raw material by cement and other allied industries in Nigeria served as a parameter for investigation of the availability and location of gypsum within the nation. However in 1995, during the reign of General Sani Abacha, the military Head of State from 1993 to 1998, placed a ban on the importation of gypsum into the country. This was due to the fact that some geological surveys revealed that Nigeria is rich in gypsum mineral (Mohammed-Sani, 2002). The availability of gypsum in commercial quantity made it imperative for industrialists to harness the information to the advantage of cement manufacturing, classroom board chalks and plaster of Paris. Holding this thought in mind, it is pertinent to state that one of the focal points of this study is to locally source and mine gypsum. The three locations namely; Wurno and Dange in Wurno and Dange Local Government Areas of Sokoto State, and Weppa in Agenebode Local Government Area of Edo State have provided the sites. There is need to further investigate the samples collected, ascertain their properties such as their chemical and mineralogical constituents and then process them into plaster of Paris that can be suitable for ceramic purposes. A comparative analysis of the various types of gypsum obtained and plaster of Paris processed will be assessed to determine their comparative strengths in the making of mould formed with selected ratio mixes in line with the existing acceptable standards (USG, 2002; British Geological Survey, 2006; Guler and Cigdem 2012 and Singh, 2013).
The study is expected to contribute towards broadening the scope for creative interest and knowledge of material exploration, processing and analyses. It is also evident from available
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literature that there are ample amount of gypsum deposits at Dange and Wurno areas of Sokoto State, and Weppa in Agenebode of Edo State as contained in Mohammed-Sani (2002), Ojo, (1995), and Ministry of Solid Minerals Development, (2000). According to Sullayman, (1991), Arayela, (2006) in the factories and industries where various ceramic wares are produced, moulds are used as convenient mode of production, whether slip casting, jiggering, jolleying or dry pressing. It answers the question of standardisation, uniformity, time and material management in factories. Although the studio potter and the traditional practitioners of pottery may be sufficient with throwing and their making standards, industrial mass production can only suffice with moulds. It is also production from factory or industrially-produced wares that may facilitate exportation of indigenous ceramics, thereby improving Nigeria’s foreign exchange capacity and giving the country a chance to compete favourably with other countries of the world in production and exports of ceramic goods. Therefore mould making is important in the mass production process of ceramics for profitability, cost effectiveness and time management. 1.1 Statement of the Problem Ceramic ware production at traditional level within local communities in Nigeria are both historical and immemorial. Contemporary concept of production in Nigeria started from the early twentieth century to the mid-20th century when Mr. Micheal Cardew introduced the contemporary concept of ceramic practice along with an already existing traditional method at Suleja near Abuja. Ahuwan, (2003) and Fawowe, (2004) posit that coupled with introduction of ceramics into school curriculum, eventually, industries emerged amidst the very favourable production environment such as access to importation of raw material, functional infrastructural facilities and strong monetary base (Naira) that could be used for importation of goods and services.
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With the political dispensation of the civilian administration in the 1980s there emerged an upsurge in the economic stability of the country which had a significant negative implication on Nigeria’s economy and industrial growth. The outcome of all these are, inflation, unstable exchange rates, difficulty in importation, power instability and collapse of infrastructures. All these affected industrial developments including ceramic manufacturing. It is true that imported ceramics have purchase advantage over locally made ones, which might have been due to method of production. The methods of production overseas are through mass production which encourages industrial production and growth. The consistency in design with perfect use of gypsum plaster (plaster of Paris) arising from emphasis put on product design of pro-to-types before working moulds are produced fro models. This aspect of ceramic production is a shortcoming to local ceramic production in Nigeria which invariably translates to higher cost of overhead in production cost.
It is obvious that Nigeria has large geological deposits of Gypsum which could be used to produce plaster of Paris but this has been undermined significantly when compared to other countries like Canada, United States of America and Mauritania. These countries have developed their gypsum for the production of plaster of Paris. The importation of this commodity into Nigeria as a country has become very expernsive for cottage level utilization hence the need for local research like this to boost local use of Nigerian gypsum for industrial use. This study there is to inquire into the chemical and mineralogical properties of gypsum deposits obtained from Wurno, Dange and Weppa as raw materials and their comparative suitability for the production of ceramic plaster. The study will also endeavour to establish the characteristics of plaster made from the gypsum obtained, determining the water plaster ratio suitable for ceramic mould making and carrying out the comprehensive comparative
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analyses required from the three deposits, using approved or acceptable parameters for the analysis. 1.2 Aim of the Study The aim of this study is to process and assess the suitability of local gypsum deposits from Wurno, Dange, and Weppa areas with a view to apply them in ceramic mould-making. This will be done through the processing of the gypsum into plaster and undertaking comparative analyses of gypsum samples from the three sites mentioned above. 1.3 Objectives of the Study The objectives of the study are to: 1. sample and assess the chemical properties of gypsum obtained from Wurno, Dange and Weppa areas by means of x-ray fluorescence spectrophotometer (XRF). 2. assess the mineralogical properties of Wurno, Dange and Weppa plaster by means of x-ray diffraction (XRD) 3. process Wurno, Dange and Weppa gypsum into plaster of Paris for ceramic mould making, using available standard process, 4. produce test bars of various plaster / water ratio from samples of processed plaster for expected tensile strength and absorbency tests 5. carry out physical performance tests such as; shrinkage test, absorbency test, compressive strength test, density test and mould release test. 6. produce moulds from the best water / plaster ratio mix from test bars, and make comparative analysis of the behaviour of plasters obtained from the three sites along the path of slip casting, press moulding and so on to ascertained and establish their performance variations.
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1.4 Research Questions 1. Using X-ray Fluorescence Spectrophotometer (XRF), what are the chemical properties differentia among gypsum obtained from Wurno, Dange and Weppa? 2. Using X-ray Diffraction (XRD), what are the mineralogical properties of plasters obtained from Wurno, Dange and Weppa gypsum samples? 3. What is the casting performance of Wurno, Dange and Weppa plaster when standard water/plaster ratio is applied? 4. How responsive is the plaster/water ratio mixes in relation to total water absorbency of the processed plaster from the above mentioned three locations? 5. How effective are the shrinkage, absorbency and compressive strength capacity of the plaster performance to mould release? 6. Are there any significant differences in the outcome of the final cast wares from the mould produced using plaster of Paris processed from the three study areas for this study? 1.5 Justification for the Study The absence of locally processed plaster has resulted in high cost of ceramic production in Nigeria because of high cost of purchasing imported plaster of Paris. This study seeks to harness the locally available gypsum for manufacturing of indigenous plaster of Paris such that the dependence on importation could be drastically reduced and subsequently impact positively on the cost of ceramic mass production in Nigeria. It is also to provide a good data base for all findings such as information on gypsum locations, chemical composition of gypsum and procedure to produce plaster with the material from the varied locations.
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1.6 Delimitation The study is delimited to gypsum obtained around Wurno, Dange and Weppa in Sokoto and Edo States of Nigeria, for ceramic plaster processing. 1.7 Limitation of the Study There are materials in terms of literature on this study area but detailed information on the processing of local gypsum for the three sites in this project are non-existent. Availability and accessibility of places for analyses of mineral or material are limited, thereby time consuming. The present security situation in Nigeria posed a big challenge, especially in selecting the locations of gypsum to access within Nigeria, especially in the North Eastern Nigeria. 1.8 Significance of the Study The significant of the study is to provide a comprehensive data base for practical information on all tests and analyses carried out within the study. It expanded the horizon of indigenous technology into development of locally processed plaster of Paris for pottery and ceramic purposes. The study revealed the potentials of the local gypsum mined in Nigeria with potentials in contributing to the economic development of the nation. It would provide local substitutes for plaster which could be made by indigenous industries and investors who may want to turn the results of the research into wealth and useable products. 1.9 Scope of the Study The study covers the identification of the different properties of gypsum, process of plaster production technology and comparative analyses of the various gypsums obtained and eventual utilization of processed plaster of Paris for mould-making for ceramic manufacture.
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1.10 Basic Assumption This study assumes that the raw gypsum rock obtained from these locations would display sufficient characteristics that will make them suitable for all the processing into plaster moulds and also pass the intended tests suitable to accomplish this study. It is also assumed that sufficient electricity supply would be available during the cause of plaster processing.
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