Magnesium Technology 2001 E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 662

Veröffentlichungsjahr: 2013

Beschreibung

Papers presented at the Proceedings of the symposium jointly sponsored by the Magnesium Committee and Reactive Metals Committee of the TMS Light Metals Division (LMD), the International Magnesium Association, and the Corrosion and Environmental Effects Committee, a joint committee of the TMS Structural Materials Division (SMD) and the ASM International Materials Science Critical Technology Sector, held during the 2001 TMS Annual Meeting in New Orleans, Louisiana, U.S.A, February 11-15, 2001.

Leseprobe

Contents

Cover

Half Title page

Title page

Copyright page

Preface

Foreword

Session One: Magnesium Reduction - Lloyd M. Pidgeon Memorial Session

Lloyd M. Pidgeon – Magnesium Pioneer

Abstract

Background

Biography

Silicothermic Production

Acknowledgments

References

Addendum

The Pidgeon Process in China and Its Future

Abstract

Introduction

Present Situation

Process Improvement History

Technical Improvements in Pidgeon Process

Prospect of Pidgeon Process In China

Comments and Opinions

Chinese Adaptation of the Pidgeon Process

Abstract

Vertical Larger-Diameter Vacuum Retort Magnesium Reduction Furnace

Abstract

Introduction

Enhancing Reduction Process

Vertical Retort Reduction Furnace

1,200MT/a Demo Plant

Conclusions

References

A Computational Thermodynamic Analysis of Atmospheric Magnesium Production

Abstract

Introduction

Methods

Results and Discussions

Summary

Acknowledgement

References

Producing Magnesium for Use in The Titanium Manufacturing Process

Introduction

Background

Conclusion

References

Modernization at Magcorp-Coming of Age in the 21st Century

Abstract

Session Two: Refining and Recycling

Hydrofluorocarbons as a Replacement for Sulphur Hexafluoride in Magnesium Processing

Abstract

Introduction

Hydrofluorocarbons as a replacement for SF6

HFC-134a as a gas for magnesium melt protection

Other new gas developments

Residual Protection

Environmental implications

Conclusions

Acknowledgements

References

Interfacial Reactions Between SF6 and Molten Magnesium

Abstract

Introduction

Experimental

Results

Discussion

Conclusions

References

U.S. EPA’s SF6 Emission Reduction Partnership for the Magnesium Industry: An Update on Early Success

Introduction

The SF6 Emission Reduction Partnership for the Magnesium Industry

The Pollution Prevention Approach

The MOU—EPA and Partner Responsibilities

History and Growth of the Partnership

Climate Protection Champions

First Year Results

SF6 Emission Reduction Activities

Conclusions and Lessons Learned

Future Steps

References

A New Conti-Process for the Fluxless Recycling of High Purity Magnesium

Abstract

Introduction

Economical Aspects

Recycling Processes

Experimental Procedure

Results

Summary

Acknowledgements

References

Innovative Vacuum Distillation for Magnesium Recycling

Abstract

Introduction

Materials

The Principle of Vacuum Distillation

Vacuum Distillation Experiment

Maximum Recovery

Industrial Demonstration

Further Tasks

Conclusions

Acknowledgement

References

Mathematical Modeling of the Magnesium Refining Furnace

Abstract

Introduction

Refining Principle

The Refining Furnace

Mathematical Modeling

The Numerical Aspects

The Simulations

Conclusions

Acknowledgements

Reference

A New Self-Gravitation Filtering Technique for Rapid Assessing Cleanliness of Magnesium Alloy Melt

Abstract

Introduction

Experimental

Results

Discussion

Conclusions

References

Session Three: Casting and Solidification

Magnesium Alloy Sheet Produced by Twin Roll Casting

Abstract

Introduction

Experimental

Results

Discussion

Conclusions

References

Solidification Behavior of Commercial Magnesium Alloys

Abstract

Introduction

Phase Evolution During Solidification

Solute Segregation

Solidus/Homologous Temperature Profile

Discussion

Conclusions

Acknowledgments

References

The Effect of Aluminium Content and Grain Refinement on Porosity Formation in Mg-Al Alloys

Abstract

Introduction

Experimental Procedure

Results and Discussion

Conclusions

Acknowledgments

References

Effects of Beryllium Content in Thixomolding® AZ91D

Abstract

Introduction

Procedure

Results and Discussion

Fluidity Measurements

Conclusions

References

The Influence of Primary Solid Content on the Tensile Properties of a Thixomolded AZ91D Magnesium Alloy

Abstract

Introduction

Experimental Details

Results and Discussion

Conclusions

References

Session Four: Alloy Development

Magnesium Alloy Development Guided by Thermodynamic Calculations

Abstract

Introduction

Database Development

Alloy Preparation and Creep Resistance Measurements

Conclusions

Acknowledgement

References

Computational Thermodynamics and Experimental Investigation of Mg-Al-Ca Alloys

Abstract

Introduction

Method

Results and Discussions

Summary

Acknowledgements

Reference

Development of Creep Resistant Mg-Al-Sr Alloys

Abstract

Introduction

Theoretical Background

Experimental Procedure

Results and Discussion

Conclusions

Acknowledgments

References

Die Casting Magnesium Alloys for Elevated Temperatures Applications

Abstract

Introduction

Summary

References

Diecastability and Properties of Mg-Al-Sr Based Alloys

Abstract

Introduction

Alloy Preparation and Melt Stability

Casting

Casting Evaluations

Discussion

Conclusions

Future Work

Acknowledgements

References

Tensile and Compressive Creep of Magnesium-Aluminum-Calcium Based Alloys

Abstract

Introduction

Creep in Magnesium Alloys

Experimental Procedure

Results And Discussion

Conclusions

Acknowledgments

References

Creep and Bolt-Load Retention Behavior of a Die Cast MG-Rare Earth Alloy

Abstract

The Mg-Zn-Al Alloys and the Influence of Calcium on their Creep Properties

Abstract

Introduction

Experimental Procedure

Results and Discussion

Conclusions

Acknowledgements

References

Session Five: Physical Metallurgy

Digital Image Analysis Technique for Characterization of Shrinkage and Gas (Air) Porosity in Cast Magnesium Alloys

Abstract

Introduction

Materials

Metallography

Microstructural Parameters of Interest

Summary and Conclusions

Acknowledgements

References

Ductility and the Skin Effect in High Pressure Die Cast Mg-Al Alloys

Abstract

Introduction

Experimental Methods

Results

Discussion

Conclusions

Acknowledgments

References

Microstructure and Microchemistry of Creep Resistant Magnesium Alloys

Abstract

Introduction

Experimental

Results and Discussion

Conclusions

Acknowledgements

References

The Relationship between Microstructure and Creep Behavior in AE42 Magnesium Die Casting Alloy

Abstract

Introduction

Experimental Procedure

Results

Discussion

Summary and Conclusions

Acknowledgements

References

Mg17Al12 Phase Precipitation Kinetics in Die Casting Alloys AZ91D and AM60B

Abstract

1 Introduction

2 Experimental

3 Results

4 Discussion

Summary

Acknowledgements

References

Tem Study of the As-Cast and Aged Microstructures of Mg-Al-Zn Alloys and the Influence of Zn Content On Precipitation

Abstract

Introduction

Experimental Methods

Results

Discussion

Conclusions.

References

Origins of Variability in the Mechanical Properties of AM60 Magnesium Alloy Castings

Abstract

Introduction

Experimental Procedure

Results and Discussion

Summary and Conclusions

Acknowledgements

References

Experimental and Computational Study of Bolt Load Retention Behavior of Magnesium Alloy AM60B

Abstract

Session Six: Forming

Alloy Design and Microstructural Evolution of Thixoformable Magnesium-Nickel Alloys

Abstract

Introduction

Experimental Procedures

Results and Discussion

Conclusion

References

Microstructural Study After Solution Treatments of a Thixocast AZ91

Abstract

Introduction

Experimental procedures

Results and Discussion

Conclusions

Acknowledgements

References

Superplasticity in Coarse Grained Mg-Al Class I Solid Solution of Hcp Structure

Abstract

Introduction

Experimental Procedure

Results

Discussion

Conclusion

Acknowledgements

References

Properties of Fine-Grained Cast Magnesium Alloys for Sheet Manufacture

1 Introduction

2 Objectives

3 Status of the investigations

4 References

Creep and Hot Working of Mg Alloy AZ91

Abstract

Introduction

Experimental Techniques

Results

Microstructural Analysis

Discussion

Conclusions

Acknowledgements

References

Forging of Magnesium Using Squeeze Cast Pre-Form

Abstract

Introduction

Magnesium Forging Stock Supply

Materials and Procedures

Results and Discussion

Conclusions

Acknowledgment

References

Assessment of Equal Channel Angular Extrusion Processing of Magnesium Alloys

Abstract

Introduction

Material

Experimental

Results

Discussion

Summary

Acknowledgments

References

AM70-Magnesium Processed by Semi-Solid Casting

Introduction

Feedstock Material

Heating Operation

Forming and Testing Operation

Results

Summary

References

Session Seven: Corrosion and Future Trends

An Hydrogen Evolution Method for the Estimation of the Corrosion Rate of Magnesium Alloys

Abstract

Introduction

Principle

Experimental Method

Results and Discussion

Conclusions

References

The Interaction Between Microstructure and Corrosion Initiation in Certain Die Cast and Thixomolded® Magnesium Alloys

Abstract

Introduction

Results

Conclusions

References

Acknowledgement

Corrosion Fatigue of High Pressure Die Cast Magnesium Alloys

Abstract

Introduction

Test material and environment

Results and Discussion

Conclusions

References

Magnesium’s Potential for Powertrain Components

Abstract

Addendum

Welding of Magnesium Alloys

Abstract

Surface and Environmental Effects on the Fatigue Behavior of Wrought and Cast Magnesium Alloys

Abstract

Introduction

Experimental

Results and Discussion

Acknowledgements

References

Author Index

Magnesium Technology 2001

Partial funding for this publication was provided by the Seeley W. Mudd Fund.

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PREFACE

PrefaceMagnesium technology is evolving rapidly to meet market demands for this lightest of structural metals, as the success of last year’s inaugural magnesium technology symposium demonstrated. The papers in this volume further document recent advances in magnesium technology. The papers were presented at the Magnesium Technology 2001 Symposium, held at the 2001 TMS Annual Meeting in New Orleans, Louisiana (U.S.A.), February 11 – 15, 2001.

The symposium was divided into seven sessions, to which the seven chapters in this volume correspond:

Magnesium Reduction – Lloyd M. Pidgeon Memorial Session

Refining and Recycling

Casting and Solidification

Alloy Development

Physical Metallurgy

Forming

Corrosion and Future Trends

Of special note was the Lloyd M. Pidgeon Memorial Session on Magnesium Reduction. Dr. Pidgeon was a pioneer in magnesium production technology; his Pidgeon process for producing magnesium metal is still used today, as discussed in a number of papers in the session. The session included a keynote paper describing his career and achievements. His daughter, Ruth Pidgeon Bryson, offers some personal reflections on her father in the Foreword to this volume.

Almost all papers presented here were reviewed for format and technical content. The result, I believe, is a volume of high technical quality. I thank the review committee (composed of the seven session chairs) for their efforts in critically reviewing the papers, and the authors for providing revisions of their papers in time to meet the publication deadline. Thanks also go to the staff at TMS for their efforts to get the volume published prior to the meeting date.

I acknowledge and thank the other members of the organizing committee for their efforts in organizing and promoting this symposium. Joining me on the organizing committee for the Magnesium Technology 2001 Symposium were:

Byron Clow, International Magnesium Association

Gerald Cole, Ford Motor Company

David Creber, Alcan International

Russell Jones, Pacific Northwest National Laboratory

Howard Kaplan, Magcorp

Ramaswami (Neel) Neelameggham, Magcorp

Eric Nyberg, Pacific Northwest National Laboratory

Mihriban Pekguleryuz, Noranda

Nigel Ricketts, CSIRO

Kevin Watson, Noranda

Along with me, these organizers also formed the nucleus of the new Magnesium Committee under the auspices of the Light Metals Division of TMS. The objectives of this committee are to hold an annual symposium on magnesium technology, publish the Magnesium Technology volume, and increase the awareness of magnesium technology worldwide.

Finally, I thank my family, Roberta, Alexander, and David, for being with me in my thoughts wherever I happen to be or whatever I happen to be doing. You make life worth living.

John N. Hryn Argonne National Laboratory Argonne, Illinois, U.S.A

Editor’s Biography

Dr. John N. Hryn is a metallurgical engineer at Argonne National Laboratory and an active member in TMS. He earned his Ph.D. at the University of Toronto in the field of extractive metallurgy and molten salt electrochemistry. As a post-doc at the Massachusetts Institute of Technology, Dr. Hryn designed and performed cell tests with metal anodes in aluminum electrolysis. In 1993, he joined Argonne to work on molten salt battery applications for electric vehicles, and in 1994, he joined the Process Evaluation Section of Argonne’s Energy Systems Division. He has worked on a variety of projects, primarily in light metals technology. Currently, he is the principal investigator on a number of research projects in the light metals area, including recycling aluminum salt cake, reduction of aluminum melt loss, and development of inert anodes for aluminum and magnesium production. Dr. Hryn’s research interest is in developing cost-effective and environmentally sound technologies for metals production, processing, and recycling.

FOREWORD

Lloyd Montgomery Pidgeon, 1903-1999

Lloyd Montgomery Pidgeon died at age 96 on December 9, 1999, his long life almost spanning the twentieth century. His career as a scientist and teacher, which is honoured by the Lloyd M. Pidgeon Memorial Session of The Minerals Metals and Materials Society in New Orleans in 2000, had been a distinguished one.

Eldest son of the Reverend Dr. E. Leslie Pidgeon and Edith Gilker Pidgeon of New Richmond, Gaspé, Quebec, Lloyd was raised in a scholarly household which lived in Ontario and the West, as his father’s calling took him to various congregations across Canada, ending in Montreal. He distinguished himself at school and in university: B.A., University of Manitoba, 1925; M.Sc. Ph.D., McGill, 1929; B.Sc, Oxford 1931 (as a postdoctoral student). He was gold medallist in chemistry at Manitoba, and Ramsay Memorial Fellow from Canada to Oxford in 1929 (his younger brother was to follow as Rhodes Scholar from McGill to Oxford in 1938). Upon his return to Canada, Lloyd became a researcher in the Chemistry department at the National Research Council of Canada in Ottawa, from 1931 to 1943, and was appointed Professor of Metallurgy and Head, Department of Metallurgy and Materials Science at the University of Toronto from 1943 to his retirement in 1968.

As a scientist, Lloyd Pidgeon was known for his development, in the late 1930s and early 1940s, of the ferrosilicon process for the production of high purity magnesium from calcined dolomite, which was quickly transferred to industry in Canada and the United States because of the exigencies of the Second World War. As an academic, his achievement was to modernize and expand the Metallurgy department at the University of Toronto, and, with his colleagues and students, to transform it into a graduate school of international stature, which sent many distinguished graduates to the universities and industries of North America and the world. As a teacher and academic supervisor, his commitment to excellence, his intellectual achievements and strong personality served as an inspiration to his students and challenged them to do their best. For his work, he received recognition and many honours, which were always modestly and gratefully received.

Lloyd’s students and former colleagues said of him in 1969 that he “was known to all of us for his quick wit, his deep intellect, and for his fairness and strong liberal views.” That is a fitting epitaph for the person and scientist whose life and achievements are commemorated by this memorial session.

Ruth Pidgeon Bryson Kingston, Canada December 8, 2000

Session One:Magnesium Reduction - Lloyd M. Pidgeon Memorial Session

Session Chair:R. Neelameggham, Magnesium Corporation of America

LLOYD M. PIDGEON – MAGNESIUM PIONEER

December 2, 1903 – December 9, 1999

Robert E. Brown

Magnesium Assistance Group, Inc226 Deer TracePrattville, Alabama 36067-3806

Abstract

Lloyd Montgomery Pidgeon was an unusual man in an unusual time. His contributions to the development of the magnesium industry have never been appreciated (or even known) by many of today’s magnesium followers. Dr. Pidgeon, working with one technical graduate, achieved commercial development of a process to produce magnesium by reducing calcined dolomite with ferrosilicon, i.e. the silicothermic process. He also received patents for electrolytic magnesium processes. He worked with engineers to design and build six magnesium production plants in a very short period of time. The original plant at Haley, Ontario is still operating. Dr. Pidgeon received many technical honors, but was always quick-witted, with a humorous approach to life.

Background

Much of the content of this keynote address is derived from personal interviews with Dr. Pidgeon and from valuable information supplied by Ruth Pidgeon Bryson, his daughter. I personally had a chance to work briefly with Dr. Pidgeon in 1960 when he was retained as a consultant to a new silicothermic magnesium plant in Selma, Alabama. As plant metallurgist, I was part of a team that was struggling to learn how to operate a Pidgeon Process plant.

In 1994, I had the opportunity to personally spend a full day with Dr. Pidgeon and his wife Frankie, who had accompanied him to Selma in 1960. Neil and Ruth Bryson were hosts and guides during this visit which resulted in a biographical sketch printed in Light Metal Age magazine in April 1995.(1) Much of this paper is directly derived from that work.

Biography

Lloyd Montgomery Pidgeon was born in Markham, Ontario in 1903. In discussing his birth, Dr. Pidgeon said he was reminded of the old joke where the Englishman said he was born in Singapore because his parents happened to be there and he wanted to be close to them. Pidgeon’s father was a Presbyterian clergyman. Dr. Pidgeon said that he does not remember Markham, but does recall living in St. Thomas, which was located near London, Ontario, on the Michigan Central Railroad. The family moved to Vancouver prior to World War I. His father, Dr. E. L. Pidgeon, was somewhat of a freethinker and was not happy in conservative Vancouver. He moved the family to Winnipeg, Manitoba, where he became a leader in the movement for Protestant church union in Canada. Dr. Lloyd Pidgeon received his B.A. at the University of Manitoba in 1925.

The family moved to Montreal in 1925. Dr. Pidgeon’s father moved to a church near the McGill University campus. Lloyd Pidgeon then continued his advanced degree work at McGill University. His doctoral work was on cellulose. He was interested in the paper industry and a Cellulose Institute was planned for McGill. Receiving his Doctorate under the direction of Dr. Otto Maas in 1929, Dr. Pidgeon found that there were very few jobs available.

He sought and won a fellowship grant: The Sir William Ramsay chemical scholarship to Oxford. (Dr. Pidgeon pointed out that Ramsay was the discoverer of the rare gases, helium, xenon, neon, and krypton). At Oxford, Dr. Pidgeon actually worked on and received a B.Sc. Degree under the direction of Sir Alfred Egerton. His work was in the field of anti-knock compounds; investigations were conducted to actually determine just exactly what the “anti knock” mechanism did. This was his first exposure to working on high temperature processes. He joked that he only “professed metallurgy” since his Ph.D. was in chemistry. He left Canada in 1929 just as the Great Depression was beginning and returned in 1931.

Dr. Pidgeon was married to Frances Rundle in Winnipeg in 1928. The Rundle family was one of the pioneer settlers of Winnipeg and Western Canada. The couple lived together for 66 years. (Mrs. Pidgeon passed away in Dec 1994). After completing his studies at Oxford, Dr. Pidgeon returned to Canada and got a job with the National Research Council. His work was centered around experimentation with carbon black and on the utilization of Canadian natural gas (then becoming available in Alberta) to make carbon black for the reinforcement of rubber.

General A.G.L. McNaughton, an ex-military man was the head of the NRC. As war in Europe seemed near, the General felt that magnesium would be needed. He ordered the head of the chemistry department to put someone on magnesium research. Dr. Pidgeon was handed the undefined assignment.

Dr. Pidgeon began to work on the chlorination of brucite and subsequent electrolysis. He went on, “We had an associate committee on metallic magnesium which was set up with representatives from the Research Council, namely me, and a couple of fellows from the Mines Branch (normally responsible for metals) and a couple from the Armed Forces.”

Based on literature research, two basic processes were chosen: the electrolysis of a fused salt and a distillation process that depended on the relative volatility of magnesium. Pidgeon advertised for a high-temperature electrochemist and hired Norman Phillips who immediately started to work on the electrolysis process based on the chlorination of brucite.

Dr. Pidgeon is given full credit in the published literature and technical reference books for developing and commercializing the magnesium production process that used silicon (in the form of ferrosilicon) to reduce calcined dolomite. [Note: Pidgeon reiterated over the years that he did not invent the process or put his name on it. Someone else did that.] It sounds very simple today in the brief encyclopedic descriptions. However, picturing an organic chemist with one assistant struggling with the total literature picture of magnesium production in 1938 is mind boggling. General McNaughton finally said that they were to develop a magnesium process that was energy efficient and would have to use readily available, native Canadian materials. The work with electrolysis was dropped and work was concentrated on the thermal reduction process.

The literature contained some references and patents of the work that was being done in Germany on thermal reduction. However, the process would depend on the ability to produce magnesium vapors and condense them. They would have to be produced by the high temperature reduction of MgO by a suitable reducing agent and the condensation of the evolved magnesium vapor into a dense, solid form.

Only two practical reducing agents were considered: carbon (Hansgirg Process) and silicon. Carbon, by far the cheapest, was ruled out because of its volatile oxide (carbon monoxide). Silicon was readily available as ferrosilicon. The reaction of ferrosilicon and calcined dolomite will produce magnesium vapor, the pressure of which will depend on the temperature of the system. The published vapor pressure over the charge was reported by Doerner of the U.S. Bureau of Mines to be 1.5 to 2.0 mm at 1100°C. This made it unlikely that there could ever be a commercial process developed in a temperature range that would permit alloy steel materials to be used for construction.

At this point, Dr. Pidgeon of the National Research Council in Canada and Glenn Bagley of Union Carbide in the U.S. conducted experiments which were designed to verify the vapor pressure of magnesium over the dolomite charge at 1100°C. They worked separately and independently with no knowledge of the other’s existence. They both came up with the determination that the pressure over the charge was actually more in the order of 30 mm. This would make it possible to design steel reactors to produce magnesium. Pidgeon went with the horizontal tubular retort and Bagley went with very large vertical retorts (2).

Laboratory experimentation was conducted on a simple retort process by the NRC. Experiments concluded that it was possible to use silicon to reduce calcined dolomite and produce commercial magnesium at temperatures where an alloyed steel retort would have a reasonable life. After the pilot plant was built with 2-4″ retorts, the first indications that alkali metals could become a problem were seen. These metals, mainly sodium and potassium, would not condense easily and would sometimes run out of the retorts. Special design modifications had to be made as the process developed to handle the sodium and potassium contents.

One of the big secrets of the Pidgeon Process success was the fact that the process was designed to be operated continuously at the reduction temperature. This prevented the large grain growth in the retorts that was so evident in the other processes such as the Bagley process that involved heating and cooling. Dr. Pidgeon also proved that it was also true that the condensing had to be done at a high temperature to get good crystalline deposits with no powder.

At this point, because the NRC did not go beyond the laboratory experimental stage, outside help was sought to continue process development. Two Canadian gold miners, Walter Segsworth (Mich. Tech ‘06) and Robert Jowsey, were looking for ways to help the Canadian war effort. They searched for a suitable source of dolomite and eventually found a very pure deposit in the Ottawa valley near Haley, Ontario. The promoters also included Thayer Lindsley (Falconbridge Nickel). They built a 5,000-tpy silicothermic plant at Haley, Ontario, adjacent to a very pure dolomite deposit. The company was called Dominion Magnesium and continues to operate today as Timminco. Dr. Pidgeon was appointed to be Director of Research at Dominion Magnesium in 1941.

Major C.J.P. Ball, the British magnesium pioneer said, “This successful translation of the Pidgeon Process from pilot plant to commercial production in such a relatively short period of time was a remarkable achievement, of great value to Canada and the USA, where five similar plants were built.”(3)

During this time, Dr. Pidgeon was immersed in the rapid development of magnesium that was taking place throughout North America. He was contacted by many industrialists, including Henry Kaiser, for advice and consulting for silicothermic magnesium plant design. He worked with a large engineering firm, Singmaster and Breyer, to design and construct several of the plants built by the US Defense Plant Corporation. One of these plants was located at Luckey, Ohio and was run by National Lead. This plant was the most efficient of all the Pidgeon Process plants. (The plant manager was Edward Rowley, later Chairman of NL Industries and a leading proponent of the Great Salt Lake Magnesium project. The Luckey plant engineer was Robert Couch, later President of Amax Specialty Metals, who purchased the GSL Magnesium plant from NL Industries.}

Dr. Pidgeon was appointed Professor and head of the Department of Metallurgical Engineering at the University of Toronto in 1943. He was very successful in building a strong graduate school in Metallurgy and his department was one of the best in Canada. Many of his graduate students went on to leading positions in industry and academia. His appreciation of the physics of metals led to the growth of physical metallurgy. The department also expanded to include Material Science in 1965. He retired and was made Professor Emeritus in 1969.

Dr. Pidgeon was awarded major honors including the MBE (Member of the British Empire, awarded by King George VI), Officer of the Order of Canada, INCO Medal for contributions to Extractive Metallurgy, The Monel Medal of Columbia University for distinguished achievements in Mineral Technology, the Alcan Medal for contribution to the field of Metallurgy, the Falconbridge Innovation Award (with Timminco Metals).

He also received honors from many of the major metals organizations including The International Magnesium Association, The Canadian Institute of Mining and Metallurgy, The American Institute of Mining and Metallurgical Engineers. He is listed in Who’s Who in Science, Who’s Who in Canadian Science, Canadian Men of Science, and several other publications.

Silicothermic Production

The total amount of magnesium produced by the Pidgeon (horizontal retort) Process from the first plant at Haley, Ontario, Canada, through to about 1980 was an estimated 600,000 long tons of magnesium (4). This does not count production from the Italian process, the Brazilian process, the Magnetherm process, nor the Bagley vertical retorts in Spokane. These are technically silicothermic processes, but they use other furnace arrangements.

It appears from the production numbers available, that China has equaled this total magnesium production by the Pidgeon Process. Expansion in the number and capacity of the Pidgeon process plants in China is continuing.

Acknowledgments

The author is deeply indebted to Light Metal Age magazine for permission to use much of this material which was printed there first. Deepest thanks to Neil and Ruth Bryson for their warm hospitality and help in developing the original profile of Dr. Pidgeon. Special thanks to Ruth for her co-authorship of the original biographical sketch of Dr. Pidgeon. (1)

References

1. R.E. Brown and Ruth Bryson, “Magnesium Industry Legend”, Light Metal Age, Volume 53, No.3 & 4, April 1995, pp. 44–45

2. L.M. Pidgeon and W.A. Alexander, “Thermal Production of Magnesium”, Transactions of AIMME, Volume 159, 1944 pp. 315–352

3. C. J.P. Ball, “The History of Magnesium”, Presidential Address to British Institute of Metals. 1956

4. Klagsbrunn, H.A., “Wartime Aluminum and Magnesium Production”, Industrial and Engineering Chemistry, Vol. 37, No. 7, July 1945

Addendum

List of Canadian Patents by Dr. L.M. Pidgeon

1.

463416

Production of Calcium

2.

424665

Magnesium Producing Apparatus

3.

424664

Volatilizable Metal Recovery Apparatus

4.

424663

Volatilizable Metal Recovery Apparatus

5.

424662

Magnesium Producing Apparatus

6.

420245

Magnesium Production Apparatus

7.

420244

Magnesium Producing Apparatus

8.

420243

Magnesium Producing Apparatus

9.

420242

Ductile Magnesium Production

10.

420421

Volatilizable Metal Recovery Apparatus

11.

420240

Thermal Magnesium Production

12.

420239

Thermal Magnesium Production

13.

415765

Magnesium Producing Apparatus

14.

415764

Volatilizable Metal Recovering Apparatus

15.

412169

Anhydrous Magnesium Chloride

16.

361606

Aromatic Liquid and Carbon Black Production

Author Note

Dr. Pidgeon also has many U.S. Patents that followed the same line as the Canadian patents.

THE PIDGEON PROCESS IN CHINA AND ITS FUTURE

Jing Chun Zang

Gold River Magnesium Plant Ningxia Huayuan Magnesium Group No. 50 Wenhuadong Street, Yinchuan, China 750004

Weinan Ding

Sinomag 1204 Floor 1 Landmark Tower, 8 Dongsanhuan Bei Lu, Beijing, China 100004

Abstract

Magnesium production in China has been growing steadily over the past 10 years. Most of the metal has been produced by the Pidgeon process. This process uses horizontal steel tubes called retorts, in furnaces and under vacuum. In the retorts mixtures of finely ground calcined dolomite and ferrosilicon formed into briquettes react to form magnesium vapors which are condensed and later remelted into ingots. The Pidgeon process was long thought to be uneconomic and obsolete. The Chinese have used the advantages of excellent raw material, location, large skilled labor supply, and low capital costs to produce magnesium by this process. The Chinese magnesium is being sold at the lowest prices in the world and lower than aluminum on a pound for pound basis.

Introduction

The first magnesium meal was produced by Fushun Aluminium Plant by the electrolytic process in 1958. The first metal produced by the Pidgeon process was in Nanjing in 1978, but the costs of production were much higher than the electrolytic process. In 1988, Shenyang Al and Mg Engineering & Research Institute completed the design and installation of the first Magnesium plant using the Pidgeon Process. It was located in Tongshan, Hubei Province with a design capacity of 500 metric tons per year.

After this plant was started, two Pidgeon plants were set up in Ningxia with a total capacity of 2000 metric tons per year. Additional Pidgeon plants were built in Shanxi and Henan provinces. The number of magnesium production plants using the Pidgeon Process was over 200 by 1997. The plant sizes varied from 100 metric tons per year to 3000 metric tons per year. The total Chinese capacity was more than 200,000 metric tons per year in 1999, while the actual production reached 160,000 metric tons. There were 3 special features that assisted in the development of the magnesium industry,: 1) Good raw material and large labor supply (no high technology, small investment); 2) Private and family businesses (not the normal state-owned plant); 3) World market oriented.

Magnesium produced in China has had a big impact on the world market. It is available in large quantities for an extremely low price compared with other magnesium. The quantity and price of Chinese magnesium has helped to increase the interest of many industries, particularly automotive. Rapid reduction in selling prices also caused many of the smaller Chinese magnesium plants to close. These closures were also due to the anti-dumping duties and the decrease in the prices in Europe and North America.

Chinese producers are consolidating their process knowledge and working with research and engineering institutions to further improve the process, improve productivity and quality with better service, to reduce costs, and to increase the production capacity.

The development of the Chinese magnesium industry has changed the structure of world supply and demand, facilitated and encouraged the technical development and new applications in many new fabrication and industry areas.

Present Situation

The Pidgeon Process is used in China to produce over 95% of all primary magnesium. About 40% of the world production is by the Pidgeon Process. Other countries that use the Pidgeon process are Canada, India, and North Korea. Today, there are about 130 plants running with Pidgeon process in China. Average capacity is over 1000 metric tons per year. There are 10 plants with over 4000 metric tons per year capacity and four plants with a capacity of over 10,000 metric tons per year. In the past several years, many of the small magnesium producers have merged together to become larger enterprises.

There are about 10 joint ventures for producing magnesium. The largest foreign investment in these ventures is from Japan and then North America. Participation from Europe has been small. Norsk Hydro is talking about alloy production in Xi’an, Ningxia with a capacity of 5000 mt per year.

In 2000, owing to the weak magnesium market price in the world and new anti-dumping charges in Europe, many small magnesium production in China are expected to close. However, Ningxia Huayuan Magnesium Group plans to increase its magnesium output capacity by 12,000 mt in 2001. Wenxi Yinguang will also add 10,000 mt within 2001, Taiyuan Tongxiang Magnesium will add 7,000 mt at end of 2000. The total magnesium production capacity is expected to be about 260,000 mt in 2001 and 300,000 mt in 2002, including alloys, anodes and powder/granules.

The Pidgeon Process has developed rapidly in China for several reasons:

1. There is a rapidly increasing demand for magnesium on the world market

2. There are convenient circumstances in China, flexible structure, global oriented production and marketing.

3. Excellent raw material. For example, Ningxia has 5 to 100 million tons of dolomite resources; 200,000 tons of locally produced ferrosilicon; 30 to 200 billion tons of high quality Anthracite coal; 2.2 million KW at US$0.03/Kwh; suitable dry climate, annual precipitation of 200-700 mm.

4. Qualified and experienced operating workers; reasonable labor costs; more mechanical/automatic equipment.

5. Plants require small initial investment and have a very short payback period.

Process Improvement History

In the past ten years of operating the Pidgeon process in China, the theory remains the same. However, some technical advantages have developed that have improved quality and reduced the cost of operation.

Technical Improvements in Pidgeon Process

A summary of the improvements that have been made and are being made include the following:

1. Heating of reduction furnace is improved with anthracite or coal powder instead of coal gas. Cost reduction of more than 10 million RMB (about $1.2 million) for one plant with capacity of about 6000 mt per year. It means that the cost of one metric ton of pure Mg metal shall be lowered by $450.

2. Vacuum for the process to be supplied by steam jet ejectors instead of mechanical pumps. The new process is more effective and faster (30 min instead of 2 hours to lower pressure to 10 Pa or under). It requires lower maintenance and no vacuum oil. Steam comes from surplus energy of reduction furnaces in a waste heat recovery boiler. More than US$150,000 shall be reduced in the installation of a 6,000 mtpy plant and 932 KW of electric capacity eliminated. The production costs per ton of pure magnesium shall be reduced by US$80 (for electricity and vacuum oil).

3. Coating the surface of the reduction tubes with special paint would extend the lifetime of the tube from 4 months to 8 months. That will cut costs by US$85-150 per ton of pure magnesium.

4. Weighing and making up the charges will be computer rather than manual, which will increase precision and uniformity of the charges, ending waste, especially of FeSi.

5. Casting ingots in a continuous conveyor by pumping reduces oxidation and burning loss, improved internal cleanliness and surface appearance.

6. Double quality inspections: Chemical and Spectrometer, raw materials & semi / end products.

Prospect of Pidgeon Process In China

Overview

As can be seen from the prior discussions, the development of the Chinese magnesium industry is very young. The production of magnesium metal by the Pidgeon Process is expected to have some impact on the world market.

The total Chinese magnesium production capacity will increase to 300,000 metric tons per year in the next 2-3 years. China’s magnesium producers need to improve quality control and service. They need to work to eliminate any anti-dumping charges from other countries, and to help develop the domestic automobile market. Also, if the demand for magnesium in the European and North American markets increases, it will provide a bright opportunity for the Chinese magnesium sector.

Investors from Western Europe, North America, Japan and Taiwan are welcome to work together to develop the Mg sector using the Pidgeon process. The development would be under the fair participation and technology exchange. With the abundance of raw materials in China, the foundation for the magnesium industry is very solid.

Summary

In the last part of 2000, the magnesium price for Chinese magnesium dropped to US$1400 / mt, FOB Chinese port, because of the weakness of the Euro and purchasing panic on the announcement of increased anti-dumping duties in EC. Because there are a large number of small Chinese magnesium producers, independent and speculative traders, a defense against the challenger is very difficult. It can be seen that Chinese magnesium is too dependent on the international free market.

Fig. 1 List of Pidgeon Process Plants with Capacities of over 3000 metric tons per year.

Fig. 2 Technical and Economic Comparison between Chinese and Japanese Pidgeon Process.

Table 1.Magnesium Process Comparisons World Electrolytic vs. Pidgeon Process in Ningxia

Comments and Opinions

1. The capacity of Chinese magnesium industry shall be increased to meet the world demand. The price will be going down further to where the supply and demand of domestic supply shall be changed slightly. Under this assumption, the Mg supply and demand gap will be widened in the world market in 2000-2001. However, after this period, the outlet for this demand will increase.

2. The low price and large capacity will make it difficult for new projects already running or just being planned. But it will encourage new applications in different areas. If China can enter the WTO smoothly in 2001, we believe that western enterprises will participate in the magnesium industry in China.

3. Because of unreasonable anti-dumping duties, the export of Chinese magnesium shall be prevented from reaching many markets.

4. Use of magnesium in the domestic market by automotive, electronic, and metallurgical industries is an important factor. But it is presently a secondary role as they need qualified manpower, machinery, money and markets.

5. The price of alloys is directly affected by the price of pure magnesium. The price will continue to stay low for the next few months. Further effort to improve the quality and service is needed. Aluminum and magnesium prices are related. Magnesium is used in many aluminum alloys. A magnesium price of US$1,900 to 2,100/mt would be very good both for the users and the producers.

CHINESE ADAPTATION OF THE PIDGEON PROCESS

Gerald S. Cole

Ford Motor Company, Dearborn, MI 48121, U.S.A.

Abstract

The author recently participated in the first Chinese Magnesium conference in Beijing and visited 5 plants, 4 of which were primary producers and 1 which was only a recycler. He will discuss the Chinese method for producing ultra low-cost Mg and will examine the potential impact of this low cost metal on the West. He will support his observations through video analysis of the modified Chinese Pidgeon process.

VERTICAL LARGER-DIAMETER VACUUM RETORT MAGNESIUM REDUCTION FURNACE

Xiaoming Mei, Alfred Yu, Shixian Shang and Tianbai Zhu

Nanjing Welbow Metals Co., Ltd. 1 Yunhai Road, Jingqiao Lishui, Nanjing, Jiangsu 211224, China

Abstract

A new magnesium reduction technique has been developed to improve the Pidgeon reduction process. A demo-plant of 1000t magnesium per year succeeds in applying this new technique. Firstly, a new furnace is developed and a larger-diameter vertical settled vacuum retort is used instead of traditional horizontal retort. So the furnace can be designed with more compact structure to raise the magnesium output per furnace volume. Secondly, calcined dolomites and ferrosilicon is compressed into given unitary shape for enhancing heat and mass transfer during the reduction and shorten remarkably the reduction time. The shape is designed with reference to the numerical simulation result. Demo operation shows that, with application of the technology, significantly production capacity increases in the same furnace, reduction period decreases (only two thirds of the traditional reduction period), energy consumption decreases too, retort’s life extends, operation becomes easy and the total production cost reduces.

Introduction

Among the techniques of magnesium production, Pidgeon reduction process is one of those that have been widely applied. The advantage of Pidgeon process is that it produces high purity magnesium that especially meets the requirement of automotive industry. Its shortage is that in the commonly used horizontal reduction furnace (Figure 1), heat and mass transfer conditions in the retort is very poor, so that its energy consumption is high, productivity is low, operating condition is intensive, unit investment is high, facility needs more area and it is not suited for large scale production and management.

Figure 1: Typical horizontal retort reduction furnace

Based on the situation of China resources, Pidgeon process will still be the main technique for producing magnesium in future. This paper will introduce a Vertical Larger-diameter Vacuum Retort Magnesium Reduction Furnace and its demo-plant of 1000t that has overcome the shortage of horizontal magnesium reduction furnace, and that will make larger-scale production by using Pidgeon process possible.

Enhancing Reduction Process

Horizontal retort

In the horizontal reduction furnace, calcined dolomite and ferrosilicon (>75%Si) are finely ground, mixed, and compressed into briquettes, then packed in paper bags and thrown into the retort. At a temperature of 1150°C~1200°C and 5-20 Pa vacuum, after 12-14 hrs chemical reaction, magnesium is reduced. Figure 2 shows a section draft of a typical horizontal retort.

Figure 2: Typical horizontal retort

1—Retort, 2—briquettes, 3—Baffle, 4– Cooling jacket, 5– Vaccum pipe, 6– Crystal magnesium

In the process, due to its structure, heat can only transfer in one direction, meanwhile the heat conductivity of retort contents is very low, so it warms up very slowly, thus cause the long reduction time cycle and vast energy consumption. Since the retort diameter is short, the material loading is little, so the productivity is not high.

Vertical retort

To overcome the shortages of horizontal magnesium reduction furnace, and make large-scale production by using Pidgeon process possible, heat and mass transfer of material in the retort must be enhanced. In view of the shortages of horizontal retort, vertical retort is introduced to shorten reduction time, reduce energy consumption and increase loading of unit retort through enhancing reaction process.

It is shown in Figure 3 that calcined dolomite and ferrosilicon are mixed, crushed and compressed into circularity with slots. All circular stuff are overlapped on a suspender, and then put into furnace by using a lift. Due to slots in the circular stuff, the retort can heat the metal suspender through radiation quickly, and make the suspender become another heat source, thus change the heat transfer from one way to two directions, heat transfer in the stuff is thus enhanced. Meanwhile, slots in the stuff, spaces between suspender, stuff and retort also improve the mass transfer condition. So the stuff can be heated up quickly, and the reaction speed is faster.

Figure 3: Section draft of vertical retort

Numerical optimization

A numerical model of heat and mass transfer in the vertical retort was set up. Figure 4 shows the two-dimensional model structure. There is radiation heat exchange between retort and stuff outer surface, between retort and suspender, between suspender and stuff inner surface, and between retort, suspender and slot sections. In the stuff, there is conduction heat transfer from surface to center, and also convection heat transfer and mass transfer while magnesium is reduced and magnesium vapor moves out. The model is to optimize the process, the dimensions of retort and circular stuff, and reaction cycle. Calculation was validated by experimental and operation data.

Figure 4: Model structure

Example of calculation results

Under the conditions of same/different thickness, loading and retort temperature, reaction processes of circular stuff with and without slots were all simulated. Table 1 is one of the results.

Table I Comparison for different shapes with same loading

Vertical Retort Reduction Furnace

Based on the above analysis and study, a new reduction furnace was designed. The retort is set vertically in the new furnace, instead of horizontally, thus the structure of the furnace is entirely different from the old one. Figure 3 is a section draft of the new vertical retort reduction furnace. It is composed of retort (vertical), furnace and combustion chamber. It can burn gas, diesel, heavy oil or coal. Reduction stuff is first pressed into pellets, and then compressed into circularity with slots as shown in figure 2. Stuff is set on the suspender and then put into furnace for reduction. In designing the new furnace, numerical optimization was used for making the furnace flow field and temperature field even and reasonable, the furnace itself is more compact, thus compared with horizontal retort furnace, the new furnace has the following advantages: low Investment for same capacity, high productivity, low energy consumption, long retort’s life-span is extended. Figure 5 is Section draft of vertical retort furnace.

Figure 5: Section draft of vertical retort furnace

1,200MT/a Demo Plant

After careful study, a 1200mt/a demo magnesium plant was built in Nanjing Welbow Metals Co., Ltd. to validate its practicability of this new technique. Table 2 shows the investment, capacity comparisons between vertical retort furnace and horizontal retort furnace at same area location.

Table II Investment, capacity comparisons

Items

Vertical furnace

Horizontal furnace

Number of retorts

36

9

Area located (m*m)

8*6m

8*4m

Diameter of retort

400mm

300mm

Length of retort

1800mm

2700mm

Total investment (US$)

14,457

9,638

Construction period

same

same

Capacity (t/d)

2.16

0.43

Investment/capacity (US$/t)

22.31

74.71

It is obviously that, for same capacity, investment of vertical reduction furnace is only 1/3.3 of horizontal furnace.

Table 3 shows the operation economy comparison between this demo plant and a same capacity plant using horizontal retort furnace.

Table III Economy for producing It magnesium

Conclusions

1. By using vertical large diameter retort furnace in Pidgeon magnesium reduction process, compared with horizontal retort furnace, it makes the furnace more compact, the output of same volume furnace increases.

2. Enhancement of heat and mass transfer makes the retort contents warm up quickly and shorten the reduction period.

3. Productivity increases remarkably, meanwhile, energy consumption and production cost decrease.

4. Operation becomes easy, it is fit for large scale production.

References

1. Emley, E.F. Principles of magnesium technology. Pergamon Press. 1966

2. G.V. Raynor, The physical metallurgy of magnesium and its alloys. Pergamon press, P13-14. 1959.

3. Riyao Xu, Magnesium, China Metallurgy Press, 1986

A COMPUTATIONAL THERMODYNAMIC ANALYSIS OF ATMOSPHERIC MAGNESIUM PRODUCTION

Melissa Marshall and Zi-Kui Liu

Department of Materials Science and Engineering The Pennsylvania State University University Park, PA 16802

Roy Christini

ALCOA Technical Center 100 Technical Drive ALCOA Center, PA 15069

Abstract

The Magnetherm process is the most widely used thermal reduction process for commercial magnesium production. This process requires a vacuum atmosphere, ferrosilicon reductant, and dolomite ore. The vacuum atmosphere is typically 0.1 atm. However, the vacuum atmosphere creates two major problems: air leakage and batch operation to tap excess slag. The air leakage contaminates the magnesium vapor and the batch operation lowers productivity. Atmospheric production of magnesium could eliminate the vacuum requirement. By increasing the pressure inside the furnace to atmospheric pressure, a pressure difference would not exist between the outside and the inside of the furnace. Air would not leak into the furnace and excess slag could be tapped without stopping the production. However, the atmospheric magnesium process will require a different reaction temperature and slag composition since under current operating parameters, magnesium cannot be produced when the pressure is over 0.63 atm. A computational thermodynamic analysis was completed on a variety of slag compositions and reaction temperatures. The data collected was used to determine three key factors: (1) purity of the magnesium vapor; (2) aggressiveness of the slag; and (3) fraction of solids in the bulk slag.

Introduction

Currently, the two basic processes for producing magnesium are the electrolysis of fused anhydrous MgCl2 and the thermal reduction of MgO by ferrosilicon[1]. The thermal production uses dolomite as the ore and ferrosilicon as the reductant. The Magnetherm process is the most employed thermal reduction process. It is a batch operation that requires a vacuum atmosphere to produce magnesium[2]. The vacuum atmosphere is crucial because the magnesium producing reactions are slowed as pressure increases due to the decrease of thermodynamic driving force of the magnesium formation.

Although the Magnetherm process has been successful, the vacuum atmosphere creates two major problems. First, air leaks lead to contamination problems. Cracks and broken seals in the furnace allow air to enter and oxidize the magnesium because of the pressure differential between the outside atmosphere and the vacuum inside[2, 3]. The second problem is that batch operation causes production rates to fall. Any time the excess slag needs to be tapped or the magnesium condenser needs to be removed, the production process must be stopped and the furnace be brought to atmospheric pressure with an inert gas such as argon[2].

There have been several efforts to develop technologies to produce magnesium at atmospheric pressure[2, 4-6]. Based on thermodynamic calculations using current operating temperature and slag composition, the formation of magnesium ceases to occur under pressures higher than 0.63atm[2]. To increase the pressure to 1atm, different operating temperatures and slag compositions have to be defined for the process to be thermodynamically possible. In the present work, computational thermodynamics approach will be used to design a new set of operating temperature and slag compositions for the atmospheric magnesium production. Fig. 1 shows schematically the Magnetherm process of magnesium production.

Figure 1: Schematic diagram of the Magnetherm process of magnesium production.

Methods

Computational thermodynamics is commonly referred as CALPHAD (CALculation of PHAse Diagram). It has been under development since 1970’s[7] and, its development in the past three decades was discussed by Saunders and Miodownik[8]. In this approach, the Gibbs energy of individual phases is modeled as a function of composition, temperature, magnetic critical temperature, and sometimes pressure, and collected in a thermodynamic database, which can be used to make various types of stable and metastable phase equilibrium and thermodynamic driving force calculations[9] through minimization of the Gibbs energy under given conditions. This approach also forms the foundation of the emerging concept of system materials design[10, 11].

Thermodynamic modeling begins with the evaluation of thermodynamic descriptions of unary and binary systems. By combining thermodynamic descriptions of constitutive binary systems and ternary experimental data, thermodynamic descriptions of ternary systems are developed, and so forth. These descriptions cover the whole composition and temperature ranges, including experimentally uninvestigated regions. A common thermodynamic database for pure elements, i.e. the so-called SGTE database, has been compiled by Dinsdale[12]. This provides a basis for international collaboration in developing multicomponent thermodynamic databases because a common pure element database makes it possible to combine various databases together.

In the Magnetherm process, the main feed raw materials are dolomite, ferrosilicon, and alumina or aluminum[13]. The design objective is to find the relative amounts of CaO, MgO, SiO2, and A12O3 in the system and operating temperature under one atmospheric pressure under certain criteria of the purity of magnesium vapor, the fraction of solid phases in the slag, and the silicon content in the residual ferrosilicon. The relative amounts of these oxides can then be used to calculate the ratio of feed raw materials depending on their chemistry. The purity of magnesium vapor determines the quality of the final product, the fraction of solid phases in the slag is critical so that the slag can be tapped out, and the silicon content in the residual ferrosilicon is extremely important to the safety of the whole operation because a too low Si content will dissolve the carbon hearth.

Based on the above analysis, a design flow chart is shown in Fig. 2. The primary elements that contaminate the magnesium vapor are calcium and silicon, which are calculated from the equilibrium between the slag phase and the gas phase, as are the fraction of the solid phases in the slag and the Si content in the residual ferrosilicon. The design targets in the present work are the following:

Figure 2: Atmospheric magnesium production as a system

The Si and Ca contents in the magnesium vapor are less than 0.25wt% and 3.0wt%, respectively.

The fraction of solid phases in the slag is less than 55%.

The Si content in the residual ferrosilicon is higher than 22%.

The first target is from the quality requirement. The second target is from the past experimental observation. The third target is calculated from the Fe-Si-C ternary phase equilibrium with the typical C content in the residual ferrosilicon being between 0.5 and 1wt%, as to be discussed in more details later. By considering all three targets simultaneously, the proper slag compositions can be calculated. The ratio of feed raw materials may then be evaluated from the mass balance.

Results and Discussions

Let us first consider the Si content in the residual ferrosilicon. It is known that if silicon levels become too low, the carbon hearth will dissolve into the residual ferrosilicon. The carbon dissolution could cause a serious safety problem if the residual slag eats a hole in the hearth and slag flows out of the furnace. Also, the furnace would require maintenance more frequently if the carbon hearth were attacked. Therefore, a thermodynamic equilibrium must be established between the residual ferrosilicon and the carbon hearth. Fig. 3 shows the isothermal section of the Fe-Si-C ternary system at 1650°C with the thermodynamic description taken from the literature[14] using Thermo-Calc[15]. The phase boundary between the liquid single-phase region, i.e. the residual ferrosilicon, and the two-phase regions determines the critical Si content in the residual ferrosilicon. This Si content increases with the decrease of the C content as shown in Fig. 3. It is also noted that the liquid is in equilibrium with the SiC phase at the carbon content less than 1.5wt%, which is the carbon content at the three-phase equilibrium point of liquid, graphite, and SiC. This indicates that SiC will form between the residual ferrosilicon and the carbon hearth. If the residual ferrosilicon is in equilibrium with the SiC phase, further dissolution of the carbon hearth can be prevented. Given the low limit of the C content in the residual ferrosilicon being 0.5wt%, the Si content on the two-phase boundary is calculated for different temperatures and plotted in Fig. 4. It is used to determine the minimum Si content in the residual ferrosilicon for the carbon hearth safety.

Figure 3: The calculated isothermal section of the Fe-Si-C system at 1650°C.

Figure 4: The liquid/SiC phase boundary as a function of temperature with 0.5wt% C in the Fe-Si-C system.

The base system in the slag is the CaO-MgO-SiO2. The calculated liquidus projection of the ternary system using Thermo-Calc is shown in Fig. 5 from the work by Huang et al.[16]. The addition of Al2O3 lowers the liquidus temperature as shown in Fig. 6 for 10wt% Al2O3 (see e.g. ref. [6]). The thermodynamic calculations between the gas, slag and ferrosilicon phases were carried out using the FACT program and its solution database[17] for various temperatures and compositions in the system. The relative amount of each phase and their compositions are obtained directly from the calculations and are compared with the design targets. However, due to the incompleteness of the current database on various solid phases in this multicomponent system, the fraction of solid phases in the slag phase could not be calculated directly. It has been estimated based on the previously established empirical relationships at ALCOA between the fraction of the solid phases in the slag phase and the composition of the slag phase.

Figure 5: The calculated liquidus projection on the composition triangle in weight percent of the CaO-MgO-SiO2 system. The dotted lines are isotherms calculated with 100K intervals with the temperature in °C.

Figure 6: The liquidus projection of the CaO-MgO-SiO2 with 10wt% Al2O3.

With above analysis, the operating temperature and the relative amounts of the component CaO, MgO, SiO2, and Al2O3 in the system are determined according to the designed targets. The operating temperature is suggested to be 1650°C and the ratio is 59:6:27-30:5-8. Under these conditions, the Ca and Si contents in the magnesium vapor are between 0.1 to 1.3wt% and 0.05 to 0.07wt%, respectively. The fraction of the solid phases in the slag is between 40 to 45%, and the Si content in the residual ferrosilicon is over 25%. All design targets have been fulfilled. From the production point of view, the relative amounts of CaO, MgO, SiO2, and Al2O3 in the system can also be used to calculated the ratio of the feeding raw materials provided the compositions of the raw materials are known.

Summary

The atmospheric production of magnesium has been investigated through computational thermodynamics aiming to improve the current vacuum production in the Magnetherm process. The slag chemistry and the operating temperature are determined with the designed targets on the purity of magnesium vapor, the fraction of solid phases in the slag, and the Si content in the residual ferrosilicon. The present work contributes to the development of the atmospheric production of magnesium with the optimized processing parameters, which reduces the amount of experimental work and shortens the development time.

Acknowledgement

The computer program, Thermo-Calc, is licensed to the Pennsylvania State University from The Foundation of Computational Thermodynamics through ThermCalc AB in Sweden. The computer program, FACT, is licensed to ALCOA from École Polytechnique de Montréal, Montréal, Canade. This program is supported by ALCOA and The National Science Foundation CAREER Award under DMR-9983532 managed by Dr. Bruce MacDonald.

References

1 I. J. Polmear, Mater. Sci. Technol., 10, (1994) 1–16.

2. R. A. Christini and M. D. Ballain, Magnetherm Atmospheric Pressure Operation: Aluminum Reactivity in a Silicate Slag, Conference Light Metals 1991, New Orleans, Louisiana, USA (1991), pp. 1189–1196.

3. A. M. Cameron, A. van Hattem and V. G. Aurich, Extractive Metallurgy of Magnesium, Conference Magnesium Technology, London, UK (1987), pp. pp. 7–17.

4. A. M. Cameron, Magnesium Production, Patent US5090996, 1992

5. A. M. Cameron, L. A. Lewis and C. F. Drumm, The thermodynamic and economic modeling of a novel magnesium production process, Conference Proceedings of the Third International Magnesium Conference, Manchester, UK (1997), pp. 7–18.

6. R. A. Christini, Method of producing magnesium vapor at atmospheric pressure, Patent US5383953, 1995

7. L. Kaufman and H. Bernstein, Computer Calculation of Phase Diagrams with Special Reference to Refractory Metals (Academic Press, New York, 1970).

8. N. Saunders and A. P. Miodownik, CALPHAD (Calculation of Phase Diagrams): A Comprehensive Guide (Pergamon, Oxford ; New York, 1998).

9. Z. K. Liu, Design magnesium alloys: how computational thermodynamics can help, Magnesium Technology 2000 (USA), Nashville, TN, USA (Minerals, Metals and Materials Society, Warrendale, PA, 2000), pp. 191–198.

10. G. B. Olson, Science, 277, (1997) 1237–1242.

11. P. J. Spencer, MRS Bull., 24, (1999) 18–19.

12. A. T. Dinsdale, CALPHAD, 15, (1991) 317–425.

13. R. A. Christini and M. D. Ballain, Aluminothermic Magnetherm: Development of Aluminum Skim and Aluminum Shot as Reductants, Conference The Reinhardt Schuhmann International Symposium on Innovative Technology and Reactor Design in Extraction Metallurgy, Colorado Springs, Colorado (1986), pp. 965–986.

14. J. Miettinen, Calphad, 22, (1998) 231–256.

15. B. Jansson, B. Jonsson, B. Sundman and J. Agren, Thermochim. Acta, 214, (1993) 93–96.

16. W. M. Huang, M, Hillert and X. Z. Wang, Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science, 26, (1995) 2293–2310.

17. C. W. Bale, Facility for the Analysis of Chemical Thermodynamics (FACT), École Polytechnique de Montréal, Montreal, Canada, 1999

PRODUCING MAGNESIUM FOR USE IN THE TITANIUM MANUFACTURING PROCESS

Laura K. Simpson, Matthew R. Earlam

Titanium Metals Corporation P.O. Box 2128 Henderson, Nevada 89009

Introduction

Titanium Metals Corporation (TIMET) has been producing titanium metal for aerospace applications since 1950. TIMET is a fully integrated titanium manufacturer; we convert rutile ore into sponge; melt and refine ingot and slab; manufacture mill products and castings; and distribute our products globally. TIMET also sells intermediate products such as raw titanium sponge, alloyed ingot and titanium tetrachloride.