Corrosion Behaviors Of Tool Steel In Tannic Acids.

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UNIVERSITI TEKNIKAL MALAYSIA MELAKA

CORROSION BEHAVIORS OF TOOL STEEL IN TANNIC ACIDS

This report is submitted in accordance with requirement of the Universiti Teknikal Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering

(Engineering Materials) with Honours.

YEOH SENG FU

FACULTY OF MANUFACTURING ENGINEERING 2010

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UNIVERSITI TEKNIKAL MALAYSIA MELAKA

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

TAJUK: Corrosion Behaviors of Tool Steel in Tannic Acids

SESI PENGAJIAN: 2009/2010

Saya YEOH SENG FU(B050610153)

mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut: 1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan

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Tarikh: 09th APRIL 2010.

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DECLARATION

I hereby, declared this thesis entitled “Corrosion Behaviors of Tool Steel in Tannic Acids” is the results of my own research except as cited in references.

Signature : ……….

Author’s Name : YEOH SENG FU

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APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial fulfillment of the requirements for the degree of Bachelor of Manufacturing Engineering (Engineering Materials) with Honours. The member of the supervisory committee is as follow:

(Signature of Supervisor) ……… (Official Stamp of Supervisor)

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APPROVAL

(Signature of Principal Supervisor) ………. (Official Stamp of Principal Supervisor)

(Signature of Co-Supervisor) ………. (Official Stamp of Co-Supervisor)

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ABSTRACT

The purpose of this project is to analyze the corrosion behavior of cutting tool material use in the wood industry which cause by tannic acid. According to the wood species and type of metallic materials, the wear of woodcutting tools is very different. The metallic nature of cutting tools, water and water-soluble components in the wood will cause an electrochemical mechanism of corrosion. Both mechanical wear and electrochemical action are responsible of the total wear of metallic tools. Therefore, the objective of this study is to characterize the electrochemical action of the wood medium on the corrosion of the woodcutting tool materials. It identifies the composition element in steel that influence the corrosion behavior. Usually, tannic acid extracts from various plants and will react with the iron to form ferrous-tannates as rust on steel. The method starts with preparing the tannic acids solution in different concentration and immersed the carbon steel blade in tannic solution. The parameter like pH, concentration and temperature changes in experiment to investigate how it affects the corrosion behavior. In order to evaluate composition element affect corrosion behavior, six type specimens (carbon steel and tungsten carbide) need to immerse in tannic acids for certain time. Then, it will apply Gamry Instrument Framework Software to carry out corrosion test for finding its corrosion rate, corrosion resistance and corrosion potential of corroded system. From data obtain, the pH of tannic begin decrease when temperature reaches 60°C and thus increase corrosion rate. Result shows that the material that have highest chromium (>4%) have lowest corrosion rate. Mostly, tungsten carbide has high corrosion resistance than carbon steel. Chemical reaction between tannins and iron produce blue black deposits of iron (III) tannates complexes on surface material. As a result, pitting corrosion occurs as a small hole on that material after several hours.

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ABSTRAK

Tujuan projek ini adalah untuk mengkaji sifat kekasian logam alat pemotong pokok yang diguna dalam kilang kayu disebabkan tannic acids. Dengan merujuk kepada jenis pokok kayu dan bahan logam, kekasian logam alat pemotong pokok adalah berbeza. Kehadiran bahan logam, cecair dan bahan cecair pelarut dalam pokok kayu boleh menyebabkan tindak balas kimia Kedua-dua kakisan logam dan tindak balas kimia adalah penyebab kepada kakisan alat logam. Oleh itu, tujuan projek ini adalah untuk mencari factor-faktor kimia yang menyebabkan tindak balas kakisan logam dalam pokok tannic acids dengan alat logam. Ini akan mengakaji komposisi bahan terkandung dalam logam yang boleh menyebabkan kakisan alat pemotong logam. Biasanya, tannic acids diambil daripada pelbagai jenis pokok dan akan bertindak balas dengan logam untuk membentuk ferrous tannates sebagai kakisan dalam logam. Kaedah project ini dimulakan dengan penyediaan pelbagai kepekatan tannic acids dan rendaman karbon logam ke cecair tannins. Parameter seperti pH, kepekatan dan suhu akan berubah dalam experiment untuk mengkaji bagaimana kakisan logam berlaku. Untuk mencari komposisi bahan yang menpengaruhi kakisan, enam sample karbon logam dan tungsten carbide diperlukan untuk merendam dalam tannic acids untuk beberapa jam. Kemudaian, Gamry Instrument Framework Software akan digunakan untuk mengkaji kakisan logam terutamanya kadar kakisan, rintangan kakisan dan keupayaan kakisan. Keputusan data menunjukan pH tannic akan berkurang apabila suhu mencapai 60°C dan ini akan menyebabkan kadar kakisan meningkat. Hasil experiment menunjukan bahan yang mempunyai komposisi chromium (>4%) tinnggi akan ada yang kadar kakasin yang rendah. Biasanya, tungsten carbide mempunyai ringtangan kakisan yang tinngi berbanding karbon logam. Tindak-balas kimia antara tannic dan ferum menghasilkan mendakan biru hitam ferum(III) tannates pada permukaan bahan tersebut. Ini menyebabkan, pitting kaksian yang ada lubang kecail berlaku pada bahan tersebut selepas beberapa jam.

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DEDICATION

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ACKNOWLEDGEMENT

I would like to extend my warmest gratitude to my supervisor, Dr. Zulkifli bin Mohd Rosli for his excellent supervision, invaluable guidance, advice and assistance towards me throughout this project. Besides, he also gives me some important guidance on how to write a good report.

I would also like to express my deepest appreciation to classmate for their supporting and help me solve the problem along this project. They always give me some theory or information especially in contributing and sharing ideals towards this project. Besides, I also not forget the technician that guide me on how using the apparatus and equipment to process this project. Sometimes, this project also helps by senior of my course. He always shares their previous experience to me especially in this corrosion field study. Without their support and assistance, I cannot carry out this project properly.

Finally, I would like to thanks to my family whose give encouragement and support until I have strength and inspiration to carry out this project with my best ability.

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TABLE OF CONTENT

Abstract i

Abstrack ii

Dedication iii

Acknowledgement iv

Table of Content v

List of Tables ix

List of Figures x

List Abbreviations xii

1.0 CHAPTER 1: INTRODUCTION 1

1.1 Project Overview 1

1.2 Background 2

1.3 Objective 3

1.4 Scope 3

1.5 Problem Statement 3

1.6 Importance of Study 4

2.0 CHAPTER 2: LITERATURE REVIEW 5

2.1 Definition of Tannins 5

2.1.1 Classification of Tannins 6

2.1.2 Chemical Behavior of Tannic Acids 8

2.2 Detection of Tannins 9

2.2.1 Sources of Tannins 9

2.2.2 Tannins in Different Woods 9

2.3 Utilization of Tannins 12

2.4 Wood Cutting Tool Material 13

2.4.1 Tungsten Carbide Steel Alloy 13

2.4.2 Example of Wood Cutting Tool Material 14

2.4.3 Corrosion Behavior from Wood Cutting Industry 15 2.4.4 Alloying Elements for Cutting Tool Material 16

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2.4.5 Microstructure of different Carbon Steel Alloy 17 2.4.6 Relationship between Chromium and Corrosion Rate 18

2.5 Corrosion Mechanism in Tannic Acids Solutions 18

2.6 SEM of Cutting Tool Material 22

2.6.1 Carbon Steels in Tannic Acids 22

2.6.2 Tungsten Carbide in Tannic Acids 23

2.7 Pitting Corrosion 23

2.7.1 Determination Extent of Pitting 24

2.7.2 Loss in Mechanical Properties 26

2.8 Planning and Preparation of Corrosion Tests 26

2.8.1 Electrochemical techniques 26

2.8.2 Electrochemical Methods of Corrosion Testing 27

2.8.2.1 Electrochemical Polarization Experiment 28

2.8.3 Immersion Tests 29

2.8.3.1 Total Immersion 29

3.0 CHAPTER 3: METHODOLOGY 30

3.1 Introduction 30

3.2 Process Flow Chart 31

3.3 PH Development of Tannin at Elevated Temperature 32

3.3.1 Preparing Tannic Acid Solution 32

3.3.1.1 Description of Ingredients in Tannic Acid Solution 33

3.3.2 Experimental Procedure 33

3.3.3 Summary 34

3.4 Corrosion Test Analysis 35

3.4.1 Experiment Setup 36

3.4.2 Gamry Framework Software 37

3.4.3 Tafel Technique 37

3.4.3.1 Tafel Technique Analysis 38

3.4.3.2 Calculation of corrosion rate 39

3.4.3.3 Tafel Extrapolation 40

3.4.4 Polarization Resistance Technique 40

3.5 Determination of Extent Pitting 42

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3.6 Microstructure Analysis 43

3.7 Planning of Results and Discussion 44

3.8 Planning of Conclusion and Recommendation 44

4.0 CHAPTER 4: RESULTS AND DISCUSSION 45

4.1 Introduction 45

4.2 PH Development of Tannin at Elevated Temperature 46 4.2.1 PH Development Tannin at 60°C Different Concentration 46 4.2.2 PH Development Tannin at 90°C Different Concentration 47 4.2.3 PH Tannin against Concentration for Different Temperature 48 4.2.4 PH Tannin against Temperature for Different Immersed Time 49

4.3 Corrosion Test Analysis 50

4.3.1 Corrosion Behavior of Carbon Steel 51

4.3.1.1 Corrosion Current Density by Tafel Technique 52 4.3.2 Corrosion Behavior of Tungsten Carbide Alloys 55 4.3.2.1 Corrosion Current Density by Tafel Technique 57

4.3.3 Calculation of Corrosion Rate 60

4.4 Determination of Extent Pitting 64

4.4.1 Mass Loss Measurement 64

4.5 Microstructure Analysis 65

4.6 Corrosion Mechanism in Tannic Acids 68

4.6.1 Corrosion Surface Behavior Carbon Steel Experiment II 68 4.6.2 Corrosion Surface Behavior of Carbon Steel Blade 69

4.7 Corrosion Chemical Reaction 69

5.0 CONCLUSION AND RECOMMENDATIONS 71

5.1 Conclusion 71

5.2 Recommendation and Future Research 73

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APPENDICES

A Carbon Steel A Tafel Graph Data B Carbon Steel B Tafel Graph Data C Carbon Steel C Tafel Graph Data D Tungsten Carbide A Tafel Graph Data E Tungsten Carbide B Tafel Graph Data F Tungsten Carbide C Tafel Graph Data G Material and Equipment

H Gantt Chart PSM I I Gantt Chart PSM II J ASTM G102

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LIST OF TABLES

2.1 Tannin Concentration and PH Value of Different Wood Types 10

2.2 Tannin Content by Wood Type 11

2.3 Woodworker Exposure to Airborne of Tannins 11

2.4 List of Alloying Steel Element 16

2.5 C and Cr Content of the Materials Tested 17

2.6 Microscopically Pit Depth Measurements 25

3.1 Carbon Steel Composition 35

3.2 Tungsten Carbide Alloy Composition and Amount of Binders 35 4.1 Corrosion Potential and Corrosion Current Density of Carbon Steel 54 4.2 Corrosion Potential and Corrosion Current Density of Tungsten Carbide 58

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LIST OF FIGURES

2.1 Gallic acid and Hexahydroxydiphenic Acid 7

2.2 Chemical Structure of the Different Groups of Tannin 7

2.3 Classifications of Tannins 8

2.4 Various Shape of Tungsten Carbide Tool 14

2.5 Pitting Corrosion in Steel Blades in the Wood Cutting Industry 15 2.6 Cemented Tungsten Carbide for Tooling Microstructure 15

2.7 Microstructures of Analyzed Carbon Steel 17

2.8 Corrosion-Rates of Materials Influence by Cr Content 18

2.9 Tannin Corroded Carbon Steel View by Microscope 19 2.10 Microscopic Image of Carbon Steel Corroded in Tannin for 3 hours 19 2.11 SEM + EDS Grain Boundary Corrosion (X52CrMoV8-1) 20

2.12 SEM + EDS Tannin–Fe Complex (X52CrMoV8-1) 20

2.13 SEM of Carbon Steel before Immersion 22

2.14 SEM of Carbon Steel before and after Immersion 22 2.15 SEM and Metallographic Cross-Section of the Tungsten Carbide after

Immersed in Tannic Acids for 24 hours 23

2.16 Variations in the Cross-Sectional Shape of Pits. 24 2.17 Cross Section of Pit used for Depth Measurements 25 2.18 Schematic Electrochemical Potential-Current Relationships for Corroding

System 27

2.19 Schematic Diagram of Polarization Cell 28

3.1 The Process Flow Chart of Project 31

3.2 Some Ingredient use to form Tannic Acids Solution 32 3.3 PH Meter, Tannic Acid Solution and Carbon Steel blade in Experiment 33

3.4 Process Flow Chart of Experiment I 34

3.5 Specimen of Different Carbon Steel and Tungsten Carbide CuttingTool 35

3.6 Typical Electrochemical Polarization Cell 36

3.7 Apparatus Set-Up for Corrosion Test 36

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3.9 Experimentally Measured Tafel Polarization Plot 40 3.10 Scale and Carbon Steel Blade before Cutting 42 3.11 Cutting Tool Material is Immersed in Closed Equipment for 5 hours 43

3.12 Disc Polishing and Etching Room 43

3.13 Nital Acids use to Etching the Sample and Optical Microscope 44

4.1 _{PH Value Development of Tannin at 60°C} ₄₆

4.2 PH Value Development of Tannin at 90°C 47

4.3 PH Value Development of Tannin Dependent from Start Concentration 48 4.4 pH value decrement of Tannin increases rapidly at Higher Temperatures 49 4.5 Evolution of Rp Value for Carbon Steel during 6 hours in Tannic Acids 51 4.6 Evolution of Ecorr Value for Carbon Steel during 6 hours in Tannic Acids 51

4.7 Tafel Plot Graph for Carbon Steel A 53

4.8 Tafel Plot Graph for Carbon Steel B 53

4.9 Tafel Plot Graph for Carbon Steel C 54

4.10 Evolution of Rp for Tungsten Carbide Alloy at 6 hours in Tannic Acids 55 4.11 Evolution of Ecorr for Tungsten Carbide Alloy 6 hours in Tannic Acid 56 4.12 Comparison Rp Value of Carbon Steel and Tungsten Carbide 56

4.13 Tafel Plot Graph for Alloy A 57

4.14 Tafel Plot Graph for Alloy B 57

4.15 Tafel plot Graph for Alloy C 58

4.16 Comparison of Electrode Potential of Carbon Steel and Tungsten Carbide 59 4.17 Comparison Log Current Density of Carbon Steel and Tungsten Carbide 59 4.18 Comparison between Corrosion Rates of All Specimens 63 4.19 Carbon Steel Microstructure after in Tannins for 1 hour and 5 hour 65 4.20 Tungsten Carbide Microstructure before and after in Tannins for 5 hours 66 4.21 Microstructure of Tannins Corroded Carbon Steel Blade Surface after

5 hours at Magnification of 10x and 100x 66

4.22 Carbon Steel before and after Immersed in Tannic Acids for 5 Hours 68 4.23 Tungsen Carbide Sample before and after Immersed in Tannic Acids for

5 Hours 68

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LIST OF ABBREVIATIONS

%wt Percentages Weight

ASTM American Society for Testing and Materials

C Carbon

Cr Chromium

CR Corrosion Rate

Ecorr Corrosion Potential

EDS Energy Dispersive X-ray Spectroscopy EIS Electrochemical Impedance Spectroscopy

Fe Iron

HRC Rockwell Hardness C-Scale

Icorr Corrosion Current Density

mv mile volt

Rp Polarization Resistance

SEM Scanning Electron Microscopy UV Ultraviolet

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CHAPTER 1 INTRODUCTION

This chapter is to briefly explain the major information of whole project is carrying out. Overall, it summarized the progress of the whole project which describing on how the project has been done.

1.1 Project Overview

Generally, the main purpose of project is to investigate corrosion behavior of tool steel in tannic acid from the plant. The whole project is emphasis on composition of the cutting tool blade in tannic acids and how it affected by temperature, pH and concentration. The aim of this research is to characterize the corrosion behavior of different steels in various wood processing environments. To carry out this project, the understanding of characteristic of tannic acid and composition element in material are significant aspect.

Moreover, the estimation method of corrosion data from Gamry Instrument Framework Software using Tafel Technique and Polarization Resistance method is very crucial. Before starting up with experiment, concentration of tannic acid and composition of sample require verify because different concentration of tannins will give different corrosion behavior.

The experimental procedure of this project is divided into three main categories which are sample preparation, corrosion test and data analysis. This project was carry out via Tafel Technique and Polarization Resistance method by immerse the sample in different concentration and temperature of tannic acid. After sample preparation,

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justified. Tafel graph will be used to represent result and microstructure of sample

will view in optical microscope. Mass loss measurement will be measure to obtain degradation rate of carbon steel blade in tannins solution.

Finally, Tafel and Polarization Resistance graph are interpreted and several justifications will make base on result obtain. Moreover, discussion on requirement of composition element material is included in order to produce a good cutting tool for wood industry. Recommendation and future research are discussed in this work.

1.2 Background

Basically, tannic acid is a class of natural, non-toxic and biodegradable organic compound which is extracted from plant sources. However, this tannic acids will cause the corrosion appear at wood cutting tools when use to sawing the plant. According to wood species and type of metallic materials, the wear of wood cutting tools is very different. The metallic nature of cutting tools, water and water-soluble components in wood will cause an electrochemical mechanism of corrosion. Both mechanical wear and electrochemical action are responsible of the total wear of metallic tools. Therefore, objective of this study is to characterize electrochemical corrosion action of wood medium with wood cutting tool materials.

Usually, both mechanical and corrosive mechanisms are responsible for corrosion of wood cutting tools. The determination of each relative magnitude mechanism is a challenge for wood industry attempting to improve and to adapt the quality of cutting tools. For example, machining of a wood known as “acid” like oak generally generates a tool wear greater than machining of a wood which having a pH nearly 7. The wood moisture and multi component nature of cutting tools also play an important role in kinetics of tools degradation. The aim of this study is to characterize the electrochemical degradation part of the tools in contact with a wood medium which prepared from plant.

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1.3 Objective

i. To analyze the corrosion behavior of cutting tool material (carbon steel and tungsten carbide) in tannic acid by electrochemical method

ii. To determine corrosion rate of tool steel by using Polarization Resistance and Tafel Technique under Gamry Instrument Framework Software

iii. To evaluate the effect of pH, concentration and temperatures of tannin acids to the corrosion behavior of cutting tool material

iv. To identify composition element in cutting tool material that influence its corrosion behavior

1.4 Scope

The scope of this project is study about the corrosion mechanism of the cutting tool in the wood industry which cause by tannic acids. The sample uses are three different types of carbon steel and tungsten carbide. The tannic acids will be prepared in different type solution. This sample will be immersed in tannic acids for different temperature. The corroded samples were viewed by optical microscope. The all corrosion test is control under Gamry Instrument Framework Software with Tafel Technique and Polarization Resistance Method. Through Tafel graph, the data can interpret from the Tafel plot such as corrosion current density and corrosion potential of corroded system. Analysis on corroded microstructure will include in this project.

1.5 Problem Statement

Obviously, the cutting tools in the wood industry often suffer from corrosion. These is due to wood industry are poor knowledge on degradation phenomenon of tools in contact with wood. It shows that different woods have a different corrosive impact. It is very difficult to know which type of cutting tool to use for sawing the various type of wood which contain different concentration tannic acid. So, it is important to learn more about the corrosive agent of different woods.

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Usually, the cutting process in industry will cause high temperature because the friction occurs between the cutting blade and wood. As a result, the corrosion rate

will increase. Therefore, it is needed to evaluate on how the corrosiveness of tannins

changes relative to temperature. It also require investigating how improve the understanding of material composition and parameter that affect corrosion to enhance the corrosion resistance against tannin.

The large number of parameters related to machining with different wood materials hinders the evolution in wear of tools. The determination of the relative magnitude of each mechanism is a challenge for wood industry attempting to improve and to adapt the quality of cutting tools. For example, the machining of a wood known as “acid” like oak generally generates a tool wear greater than the machining of a wood that having a pH close to 7. Therefore, wood moisture and multi-component nature of cutting tools also play an important role in the kinetics of tools degradation. So both mechanical and corrosive mechanisms are responsible of wear of wood cutting tools

Besides, the high cost of the high alloy steel also cause the industry wood to use tool steel although high alloy steel have higher corrosion resistance properties. So, the selection type of tool steel is very important to give maximum protection against tannic acids. In order to solve this problem, the study about the composition in tool steel use and their function in each element in composition is very significant because it will affect corrosion behavior.

1.6 Importance of Study

This project is significant for the wood industry in order to increase their lifetime of cutting tool. Based on the problem, the parameter that affects corrosion behavior of cutting tool needs to be identified. The selection type of cutting tool is very important in order to obtain maximum protection. Therefore, the study of composition and its element in wood cutting tool material is very significant.

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CHAPTER 2 LITERATURE REVIEW

This chapter consists of information which related to the study such as the theory and method that had been used by the others in order to investigate the corrosion behavior of tool steel in tannic acids. This information is important because it will lead to this study applicability until complete. In this research, it also the best way to guide and face the problem encountered during the completion of this study.

2.1 Definition of Tannins

The term “tannins” is no longer strange in chemistry field. It is comes from the ancient Celtic word for oak which is a typical source of tannins for leather making (Bisanda et al., 2003). According to Khanbabaee and Van Ree (2001), the name “tannin” is derived from the French word „Tanin‟ which means a tanning substance that used for a range of natural polyphenols. The ancient society had been using tannins to convert animal skin to form leather which are able to interact and precipitate proteins including the protein found in animal skin (Hagerman, 2002). In nature, the tannins are found worldwide in many different families of the higher plants such as in chestnut, pine and oak wood.

Tannins are secondary metabolites that widely found in plant kingdom and it produce by condensation of simple phenolics (Chavan et al., 2001). Although tannins themselves are secondary phenolic metabolites, their chemical reactivities and biological activities have distinguished them from other plant of secondary phenolics (Hagerman, 2002).

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Many researchers have tried to define tannins based on their structures, chemical reactivity and biological activities. However, the complexity of tannins has hindered their efforts to provide an appropriate definition for tannins. Batesmith and Swain (1962) have defined tannins as water soluble phenolics with molecular weights between 300 and 3000 Daltons (Da) which can exhibit usual phenolic reactions and showing the ability to precipitate alkaloids, gelatins and other proteins. However, this definition does not include all tannins since tannins with higher molecular weight of up to 20000 Da have been isolated. Griffith (1991) described tannins as “macromolecular phenolic substances” and divided them into two main group which are hydrolysable tannins and condensed tannins. Haslam (1989) is tried to emphasize the multiplicity of phenolic group characteristic of tannins for substitute the term “polyphenol” for “tannin”. He noted that tannins with molecular weight up to 20000 Da have been reported and tannins complex not only with proteins and alkaloids but with certain polysaccharides as well.

Tannins acid which is a class of natural, non-toxic and biodegradable organic compound is extracted from plant sources (Rahim et al., 2005). It have been suggested as a suitable replacement as corrosion inhibitor in aqueous media, component of rust converters, pigment in paint coating, corrosion inhibitor of reinforcing steel in concrete, chemical cleaning agents for removing iron-based deposited and oxygen scavenger for boiler water treatment system.

2.1.1 Classification of Tannins

Tannins are classified into two broad groups which is

i. Hydrolysable ( Gallic Tannins and Ellagic Tannins) ii. Condensed tannins (Proanthocyanidine)

Figure 2.1 (a) represent the chemical structure of Gallic acid and (b) represent the structure of Ellagic acids. Hydrolysable tannins are presented in oak tree and chestnut (5-10%). Condensed tannins are derived from Catechine and are present in the bark of oak tree (6-17%) or spruce (10-18%).

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(a) (b)

Figure 2.1: (a) Gallic acid and (b) Hexahydroxydiphenic acid Source: Winkelmann et al. (2006).

Based on the molecular structures, Khanbabae and Van Ree (2001) suggested that tannins can be divided into four major groups which are Gallotannins, Ellagitannins, complex tannins and condensed tannins as show in the Figure 2.3. Their chemical structures are described as follow:

i. Gallotannins are tannins in which galloyl units or their metadepsidic derivatives are bound to diverse polyol, catechin and ortriterpenoid units. ii. Ellagitannins are tannins in which at least two galloyl units are C-C

coupled to each other and not contain a glycosidically link catechin unit. iii. Complex tannins are tannins in which a catechin unit is bound

glycosidically to a gallotannin or an ellagitannin unit.

iv. Condensed tannins are all oligomeric and polymeric proanthocyanidins formed by linkage of C-4 of one catechin with C-8 or C-6 of the next monomeric catechin (Khanbabaee and Van Ree, 2001).

Figure 2.2: Chemical Structure of the different groups of Tannin: (a) Condensed Tannin, (b) Hydrolyzable Tannin. Source: Winkelmann et al. (2006).

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the sample surface was analyzed by optical microscopy. It was to identify the surface behavior of the sample before corrosion and after corrosion. The comparison between corrosion current density and corrosion resistance sample needs to be justified. Tafel graph will be used to represent result and microstructure of sample will view in optical microscope. Mass loss measurement will be measure to obtain degradation rate of carbon steel blade in tannins solution.

1.2 Background

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1.3 Objective

i. To analyze the corrosion behavior of cutting tool material (carbon steel and tungsten carbide) in tannic acid by electrochemical method

ii. To determine corrosion rate of tool steel by using Polarization Resistance and Tafel Technique under Gamry Instrument Framework Software

iii. To evaluate the effect of pH, concentration and temperatures of tannin acids to the corrosion behavior of cutting tool material

iv. To identify composition element in cutting tool material that influence its corrosion behavior

1.4 Scope

1.5 Problem Statement

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Usually, the cutting process in industry will cause high temperature because the friction occurs between the cutting blade and wood. As a result, the corrosion rate will increase. Therefore, it is needed to evaluate on how the corrosiveness of tannins changes relative to temperature. It also require investigating how improve the understanding of material composition and parameter that affect corrosion to enhance the corrosion resistance against tannin.

1.6 Importance of Study

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CHAPTER 2

LITERATURE REVIEW

2.1 Definition of Tannins

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2.1.1 Classification of Tannins

Tannins are classified into two broad groups which is

i. Hydrolysable ( Gallic Tannins and Ellagic Tannins) ii. Condensed tannins (Proanthocyanidine)

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(a) (b)

Figure 2.1: (a) Gallic acid and (b) Hexahydroxydiphenic acid Source: Winkelmann et al. (2006).

coupled to each other and not contain a glycosidically link catechin unit. iii. Complex tannins are tannins in which a catechin unit is bound

glycosidically to a gallotannin or an ellagitannin unit.

iv. Condensed tannins are all oligomeric and polymeric proanthocyanidins formed by linkage of C-4 of one catechin with C-8 or C-6 of the next monomeric catechin (Khanbabaee and Van Ree, 2001).

Figure 2.2: Chemical Structure of the different groups of Tannin: (a) Condensed Tannin, (b) Hydrolyzable Tannin. Source: Winkelmann et al. (2006).

Corrosion Behaviors Of Tool Steel In Tannic Acids.

UNIVERSITI TEKNIKAL MALAYSIA MELAKA