Extractive Metallurgy of Titanium

Conventional and Recent Advances in Extraction and Production of Titanium Metal

Zhigang Zak Fang, Francis Froes, Ying Zhang

• Publisher: Elsevier
• Year: 2019
• Print ISBN:
  9780128172001
• eBook ISBN:
  9780128172018
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Extractive Metallurgy of Titanium: Conventional and Recent Advances in Extraction and Production of Titanium Metal contains information on current and developing processes for the production of titanium. The methods for producing Ti metal are grouped into two categories, including the reduction of TiCl4 and the reduction of TiO2, with their processes classified as either electrochemical or thermochemical. Descriptions of each method or process include both the fundamental principles of the method and the engineering challenges in their practice. In addition, a review of the chemical and physical characteristics of the product produced by each method is included. Sections cover the purity of titanium metal produced based on ASTM and other industry standards, energy consumption, cost and the potential environmental impacts of the processes. - Provides information on new and developing low cost, high integrity methods for titanium metal production - Discusses new markets for titanium due to the decreased cost of newly developed processes - Covers specific information on new methods, including the chemical and physical characteristics produced

Chapter 1

Introduction to the development of processes for primary Ti metal production

Zhigang Zak Fang ¹ , Hyrum D. Lefler ¹ , F.H. Froes ² , and Ying Zhang ^{1 , 3 1} Department of Materials Science & Engineering, University of Utah, Salt Lake City, UT, United States ² Consultant to the Titanium Industry, Tacoma, WA, United States ³ Institute of Process Engineering, Chinese Academy of Sciences (IPE, CAS), China

Abstract

Titanium (Ti) is often referred to as a wonder metal, or the metal of the future, because it has a unique combination of chemical, physical, and mechanical properties. It is a light metal, with a density approximately half that of iron at 4.3 g/cc. Its mechanical strength, ductility, and fracture toughness is in the same realm as that of steel, and in fact, Ti alloys have the highest specific strength among all common industrial metallic alloys. Yet, despite these enviable properties of Ti, the commercial applications of Ti are still very limited, compared to other common structural metals such as steel and aluminum. There are a number of reasons for this, but the number one reason is the cost. When considering possible strategies for significantly reducing the cost of Ti, there is no escaping the fact that as part of this strategy the costs of primary Ti production must come down. This book aims to bring together in one-volume authoritative articles on a variety of primary Ti production processes that have been developed over several decades, with both the fundamentals and the practical aspects of each process being covered. It is our hope that this volume will help to fortify a foundation upon which future research and development and new processes can be built.

Keywords

Deoxygenation; Electrochemical reduction; Thermochemical reduction; Titanium metal production; Kroll Process

Titanium (Ti) is often referred to as a wonder metal, or the metal of the future, because it has a unique combination of chemical, physical, and mechanical properties. It is a light metal, with a density approximately half that of iron at 4.3 g/cc. Its mechanical strength, ductility, and fracture toughness is in the same realm as that of steel, and in fact, Ti alloys have the highest specific strength among all common industrial metallic alloys. This is why Ti alloys are widely used as a structural metal in the aerospace industry. For example, approximately 15% by weight of the Boeing Dreamliner, B-787 is made of Ti [1]. Ti is also known as one of the most corrosion resistant metals owing to the self-protective surface Ti oxide layer. For example, Ti is virtually indestructible in sea water environment, whereas the life of stainless steel is limited in the same environment. For example, one of the largest industrial applications for commercially pure Ti (CP–Ti) is in the chemical processing equipment. Furthermore, Ti is the most biocompatible metal, making it a preferred material for biomedical implants.

Despite the enviable properties of Ti, the commercial applications of Ti are still very limited compared to other common structural metals such as steel and aluminum. In 2017, Ti sponge production worldwide (excluding the United States) was about 170,000 tons, while total sponge production capacity in the United States at the end of 2016 was estimated at around 24,000 tons with the actual US production volumes falling somewhere below that value [2]. These worldwide production volumes are quite small when compared to 1.27 billion tons of pig iron and direct reduced iron [3] and 60 million metric tons of aluminum [4]. In monetary terms, the global market for Ti sponge in 2017 was approximately 1.4 billion US dollars. To put this in perspective, the cost of just the materials required to produce the world's raw steel each year (approximately $250/ton in the first half of 2017 [5]) may be estimated at around 300 billion USD. Meanwhile, the total market value of the primary aluminum market may be estimated at around 130 billion USD annually, if based on the 2017 spot price of 2.17$/kg for aluminum ingot in the United States [4].

Consumption of Ti sponge in the United States increased by about 9% from 2016 to 2017 to about 37,000 tons per annum [6]. Global titanium market growth for 2018 and (predicted) for 2019 have been reported at 5%–6% and 7%–8%, respectively [7]. This is a steady growth, but titanium's rise to ubiquitous application across all market sectors remains limited. There are a number of reasons for this, but the number one reason is the cost. The cost of Ti is simply prohibitive for most industrial and civilian consumer applications. Notably, it is not used in passenger vehicles although it could contribute significantly to the lightweighting of transportation vehicles, which would lead to a quantum leap of the energy efficiency of these vehicles and significant reduction of our dependence on fossil fuels. Table 1.1 compares the cost of primary Ti metal to that of aluminum, stainless steel, and raw steel.

Simple economics dictates that Ti cannot enjoy widespread usage at current prices, when cheaper options are readily available. For this reason, titanium has been used to date only in industries where its properties are essential—no matter what the cost. This has limited titanium to applications in technically demanding sectors such as aerospace and biomedical. Fig. 1.1 shows the breakdown of the industries that currently use Ti.

This high cost of Ti materials begs the question: why? The single most important factor that dictates the cost of Ti is its affinity to oxygen. The chemical stability of Ti dioxide, which is the mineral form of Ti, is surpassed only by Al, Mg, Ca, and some rare-earth metals [9,10]. This fact makes it difficult to extract Ti from its mineral form and also costly to process into desirable alloys (e.g., the vacuum arc remelt process) and their mill products. In fact, it has been estimated that a little over 1/3 of the cost to produce 1″ plate mill product is tied up in the cost to produce the primary Ti metal (i.e., Ti sponge using the current Kroll process), while another 15% is related to vacuum arc remelting and nearly 50% is required for the thermomechanical processing [11]. In order to make Ti significantly more affordable, there is no escaping the fact that the cost for the production of primary Ti must come down.

Table 1.1

Comparison of primary Ti with other primary structura...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Chapter 1. Introduction to the development of processes for primary Ti metal production
• Part 1. Extractive chemical metallurgy processes
• Part 2. Thermochemical reduction of TiCl4
• Part 3. Thermochemical reduction of TiO2
• Part 4. Electrochemical reduction of TiO2 and TiOC
• Index