chemical processing of ceramics

Despite many recent advances in materials science and engineering, the mance of ceramic components in severe conditions is still far below the ideallimits predicted by theory.. Table of

Chemical Processing

of Ceramics Second Edition

MATERIALS ENGINEERING

1 Modern Ceramic Engineering: Properties, Processing,and Use in Design Second Edition, Revised

and Expanded, David W Richerson

2 Introduction to Engineering Materials: Behavior,Properties, and Selection, G T Murray

3 Rapidly Solidified Alloys: Processes • Structures •Applications, edited by Howard H Liebermann

4 Fiber and Whisker Reinforced Ceramics for StructuralApplications, David Belitskus

5 Thermal Analysis of Ceramics, Robert F Speyer

6 Friction and Wear of Ceramics, edited by

Said Jahanmir

7 Mechanical Properties of Metallic Composites, edited

by Shojiro Ochiai

8 Chemical Processing of Ceramics, edited by

Burtrand I Lee and Edward J A Pope

9 Handbook of Advanced Materials Testing, edited byNicholas P Cheremisinoff and Paul N Cheremisinoff

10 Ceramic Processing and Sintering, M N Rahaman

11 Composites Engineering Handbook, edited by

P K Mallick

12 Porosity of Ceramics, Roy W Rice

13 Intermetallic and Ceramic Coatings, edited by

Narendra B Dahotre and T S Sudarshan

14 Adhesion Promotion Techniques: Technological

Applications, edited by K L Mittal and A Pizzi

15 Impurities in Engineering Materials: Impact, Reliability,and Control, edited by Clyde L Briant

16 Ferroelectric Devices, Kenji Uchino

17 Mechanical Properties of Ceramics and Composites:Grain and Particle Effects, Roy W Rice

18 Solid Lubrication Fundamentals and Applications,Kazuhisa Miyoshi

19 Modeling for Casting and Solidification Processing,edited by Kuang-O (Oscar) Yu

20 Ceramic Fabrication Technology, Roy W Rice

21 Coatings of Polymers and Plastics, edited by

Rose A Ryntz and Philip V Yaneff

and Jayne Giniewicz

23 Ceramic Processing and Sintering, Second Edition,edited by M N Rahaman

24 Handbook of Metallurgical Process Design, edited byGeorge Totten

25 Ceramic Materials for Electronics, Third Edition, Relva Buchanan

26 Physical Metallurgy, William F Hosford

27 Carbon Fibers and Their Composites, Peter Morgan

28 Chemical Processing of Ceramics: Second Edition,Burtrand Lee and Sridhar Komarneni

Chemical Processing

of Ceramics

Second Edition

edited by Burtrand Lee Sridhar Komarneni

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Includes bibliographical references and index.

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on the body’s own regenerative potential? We are also at the threshold of a changefrom an energy-rich society to an energy-declining society How will ceramicshelp industry respond to this need? Can we create recyclable ceramic productsthat are affordable? Can we make products with substantially lower powerrequirements? Again, these questions are difficult, but the creativity of ourresponses may determine the quality of life for the new age.

This new edition of Chemical Processing of Ceramics offers a scientific and

technological framework for achieving creative solutions to the questions posedabove It has been 20 years since the first Ultrastructure and Chemical ProcessingConference proceedings were published Enormous progress has been made inunderstanding the process mechanisms for chemical-based processing of newmaterials The theoretical foundations are now well established and are beingapplied to an expanding range of materials New process methods are beingdiscovered These new developments are all discussed in this new edition Theeditors have made thoughtful selections from the leading researchers in the field.Their success makes this book a must for every serious investigator in the field

of ceramic processing

Larry L Hench

Professor of Ceramic Materials Imperial College, London

Despite many recent advances in materials science and engineering, the mance of ceramic components in severe conditions is still far below the ideallimits predicted by theory The emphasis on the relation between processing,structure, and behavior has been fruitful for ceramic scientists for several decades

perfor-It has been recently realized, however, that major advances in ceramics duringthe next several decades will require an emphasis on molecular-level or nanoscalecontrol Organic chemistry, once abhorred by ceramic engineers trained to defineceramics as “inorganic-nonmetallic materials,” has become a valuable asset indesigning and synthesizing new ceramics It has recently been established that

as the structural scale in ceramics is reduced from macro- to micro- to talline regimes, the basic properties are drastically altered Some brittle ceramicmaterials have been shown to be partially ductile Quantum dot semiconductingceramic particles emit different colors, depending on their size, and this propertycan be useful in various applications

nanocrys-The impetus and the ultimate goal in chemical processing of ceramic materials

is to control physical and chemical variability by the assemblage of uniquelyhomogeneous structures, nanosized second phases, controlled surface composi-tional gradients, and unique combinations of dissimilar materials to achievedesired properties Significant improvements in environmental stability and per-formance should result from such nanoscale or molecular design of materials

A number of books are available that deal with the chemical processing aspect

of ceramic materials, but most of them are conference proceedings This revised

edition of Chemical Processing of Ceramics is written to update, enhance, and

expand the topics in the first edition published in 1994 Many authors who areactively involved in the field of chemical processing of ceramic materials fromall over the world contributed to the first edition The authors in this edition arealso from the international community—Australia, Japan, Germany, Korea,France, Russia, Switzerland, and the U.S.—practicing chemical principles in thefabrication of superior ceramic materials

Thus this book presents current developments and concepts in the chemicaltechniques for production and characterization of state-of-the-art ceramic mate-rials in a truly interdisciplinary fashion The 27 chapters are divided into fiveparts reflecting topical groups The first part discusses the starting materials—how

to prepare and modify them in the nanoscale range Powders are the most heavilyused form of starting ceramic materials The synthesis, characterization, andbehavior of ceramic powders are presented in parts I and II In the third part,processing of ceramic films via the sol-gel technique is discussed Fabrication of

nonoxide ceramics is covered in part IV In the last part, several specific examples

of classes of ceramic materials fabricated by chemical processing, including thinfilms, membranes, ferroelectrics, bioceramics, dielectrics, batteries, and super-conductors, are presented These classes of examples are chosen on the basis ofthe current demand and active research The topics on basic principles of the sol-gel technique, sintering, and postsintering processes are not included in thisvolume because there are other excellent books dealing solely with these topics.Although this book is edited, it is organized to reflect the sequence of ceramicsprocessing and the coherent theme of chemical processing for advanced ceramicmaterials Hence this book is suitable as a supplementary textbook for advancedundergraduate and graduate courses in ceramic science and materials chemistry,

as well as an excellent reference book for practicing ceramists, chemists, materialsscientists, and engineers As shown by the data presented in this book, some ofthe interesting results from chemical processing have not yet made their way intoreal applications of ceramic materials We are optimistic that, through furtherresearch, the full potential of chemical processing for high-performance ceramicmaterials can be realized It is hoped that this book, through the authors’ andeditors’ contributions, will bring researchers and engineers in the ceramics andchemical fields closer together to produce superior ceramic materials

Burtrand I Lee Sridhar Komarneni

Burtrand Insung Lee, Ph.D is a professor in

the School of Materials Science & Engineering

at Clemson University, Clemson, South

Caro-lina He obtained his B.S degree in chemistry

from Southern Adventist University,

Tennes-see, and Ph.D degree in materials science and

engineering from the University of Florida,

Gainesville, Florida in 1986 His industrial

working experience includes Biospherics Inc.,

Gel Tech Inc., Kemet Electronics Materials

Corp., Hitachi Ltd., and Samsung Electronics

Dr Lee was a Fulbright Professor at

Nor-wegian Institute of Technology in Norway in

1989 In 1993 he spent a sabbatical year at

Hitachi Research Laboratory as a senior visiting researcher He has publishedover 170 technical papers and other books on ceramic and polymer processing

as well as several U.S patents He has co-organized many national/internationaltechnical symposia on materials and nano-processing Dr Lee received the MRSAward in 1986, Fulbright Scholar Award in 1989, Clemson Board of TrusteeFaculty Excellence Awards in 2001 and 2004, and he was selected as a LadyDavis Fellow in 2004

Dr Lee teaches colloidal and surface science as well as general materialsprocessing at Clemson University He is also director of Nanofabritech® His currentresearch activities are focused on chemical processing of ceramic and polymericmaterials, paying particular attention to surface and interfacial chemistry

Sridhar Komarneni, Ph.D is a professor of

clay mineralogy at The Pennsylvania State

University, University Park, Pennsylvania

He conducts research on synthesis and

pro-cessing of nanophases and nanocomposites

by sol-gel and hydrothermal processing and

on both basic and applied aspects of clay

minerals He has published over 415 refereed

papers and edited or written 13 books during

his career and received numerous awards Dr

Komarneni was elected to The World

Acad-emy of Ceramics, The European AcadAcad-emy of

Sciences and Fellows of The American

Asso-ciation for the Advancement of Science, The

Royal Society of Chemistry, The American Society of Agronomy, The SoilScience Society of America, and The American Ceramic Society He serves as

the editor-in-chief of Journal of Porous Materials.

Clemson, South Carolina

Dunbar P Birnie, III

Harold Dobberstein

University of CambridgeCambridge, England

Masashi Inoue

Kyoto UniversityKyoto, Japan

Anne Julbe

Universite Montpellier IIMontpellier, France

Pennsylvania State University

University Park, Pennsylvania

Jea Gun Park

Hanyang UniversitySeoul, South Korea

Clemson University

Clemson, South Carolina

Rustum Roy

Pennsylvania State University

University Park, Pennsylvania

Tokyo Institute of Technology and

Teikyo University of Science and

Ying Wang

University of WashingtonSeattle, Washington

Rainer Waser

RWTH Aachen University of Technology

Aachen, Germany

Markus Weinmann

Max-Planck-Institut fur MetallforschungStuttgart, Germany

D.H Yoon

Clemson UniversityClemson, South Carolina

Ki Hyun Yoon

Yonsei UniversitySeoul, Korea

Table of Contents

SECTION I Powder Synthesis and Characterization

Chapter 1 Hydrothermal Synthesis of Ceramic Oxide Powders 3

Shigeyuki Somiya, Rustum Roy, and Sridhar Komarneni

Chapter 2 Solvothermal Synthesis 21

Masashi Inoue

Chapter 3 Mechanochemical Synthesis of Ceramics 65

Aaron C Dodd

Chapter 4 Cryochemical Synthesis of Materials 77

Oleg A Shlyakhtin, Nickolay N Oleynikov, and Yuri D Tretyakov

Chapter 5 Environmentally Benign Approach to Synthesis of

Titanium-Based Oxides by Use of Water-Soluble Titanium Complex 139

Koji Tomita, Deepa Dey, Valery Petrykin, and Masato Kakihana

Chapter 6 Peroxoniobium-Mediated Route toward the

Low-Temperature Synthesis of Alkali Metal Niobates

Free from Organics and Chlorides 161

Deepa Dey and Masato Kakihana

Chapter 7 Synthesis and Modification of Submicron Barium

Titanate Powders 173

Burtrand I Lee, Xinyu Wang, D.H Yoon, Prerak Badheka, Lai Qi,

and Li-Qiong Wang

Chapter 8 Magnetic Particles: Synthesis and Characterization 193

Masataka Ozaki

Lai Qi, Burtrand I Lee, David Morton, and Eric Forsythe

Chapter 10 Characterization of Fine Dry Powders 233

Hendrik K Kammler and Lutz Mädler

SECTION II Powder Processing at Nanoscale

Chapter 11 Theory and Applications of Colloidal Processing 269

Wolfgang Sigmund, Georgios Pyrgiotakis, and Amit Daga

Chapter 12 Nano/microstructure and Property Control of Single and

Multiphase Materials 303

Philippe Colomban

Chapter 13 Nanocomposite Materials 341

Sridhar Komarneni

Chapter 14 Molecular Engineering Route to Two Dimensional

Heterostructural Nanohybrid Materials 369

Jin-Ho Choy and Man Park

Chapter 15 Nanoceramic Particulates for Chemical Mechanical

Planarization in the Ultra Large Scale Integration

Fabrication Process 393

Ungyu Paik, Sang Kyun Kim, Takeo Katoh, and Jea Gun Park

SECTION III Sol-Gel Processing

Chapter 16 Chemical Control of Defect Formation During Spin-Coating

of Sol-Gels 411

Dunbar P Birnie, III

Chapter 17 Preparation and Properties of SiO2 Thin Films by

the Sol-Gel Method Using Photoirradiation and Its

Application to Surface Coating for Display 421

Tomoji Ohishi

SECTION IV Ceramics Via Polymers

Chapter 18 Organosilicon Polymers as Precursors for Ceramics 439

Markus Weinmann

Chapter 19 Polymer Pyrolysis 491

Masaki Narisawa

Chapter 20 Chemical Vapor Deposition of Ceramics 511

Guozhong Cao and Ying Wang

Chapter 21 Ceramic Photonic Crystals: Materials, Synthesis, and

Applications 543

Jeffrey DiMaio and John Ballato

Chapter 22 Tailoring Dielectric Properties of Perovskite Ceramics at

Microwave Frequencies 571

Eung Soo Kim, Ki Hyun Yoon, and Burtrand I Lee

Chapter 23 Synthesis and Processing of High-Temperature

Design and Applications 629

André Ayral, Anne Julbe, and Christian Guizard

Chapter 26 Ceramic Materials for Lithium-Ion Battery Applications 667

Jeffrey P Maranchi, Oleg I Velikokhatnyi, Moni K Datta, Il-Seok Kim, and Prashant N Kumta

Chapter 27 Chemical Solution Deposition of Ferroelectric Thin Films 713

Robert Schwartz, Theodor Schneller, Rainer Waser,

and Harold Dobberstein

Section I

Powder Synthesis and Characterization

of Ceramic Oxide

Powders*

Shigeyuki Somiya, Rustum Roy,

and Sridhar Komarneni

CONTENTS

I Introduction 4

II Hydrothermal Synthesis 5

A Some Results in Different Categories (Hydrothermal Decomposition) 7

1 Ilmenite 7

B Hydrothermal Metal Oxidation 7

1 Zirconium Metal 7

2 Aluminum Metal 8

3 Titanium Metal 8

C Hydrothermal Reactions 8

D Hydrothermal Precipitation or Hydrothermal Hydrolysis 9

1 Alumina 9

2 Zirconia 11

E Hydrothermal Electrochemical Method 11

F Reactive Electrode Submerged Arc 14

G Hydrothermal Mechanochemical Process 14

H Microwave Hydrothermal Process 16

I Hydrothermal Sonochemical Method 18

III Ideal Powders and Real Powders 18

References 19

* Reproduced with permission from the Indian Academy of Sciences This article was originally

published in the Bull Mat Sci., 23, 453–460 and the current version is slightly modified.

4 Chemical Processing of Ceramics, Second Edition

I INTRODUCTION

Inorganic powders play a key role in many fields—ceramics, catalysts, medicines,food, etc.—and many papers and books discuss powder preparation.1–5 Powderpreparation is a very important step in the processing of ceramics Table 1.1presents the methods used for preparing fine ceramic powders.6

g Hot kerosene drying

h Hot petroleum drying

II HYDROTHERMAL SYNTHESIS

The term hydrothermal comes from the earth sciences, where it implies a regime

of high temperatures and water pressures Table 1.2 shows the types of thermal synthesis.7–18 The major differences between hydrothermal processingand other technologies are shown in Table 1.3.4,6,17,19 For typical hydrothermalresearch one needs a high-temperature, high-pressure apparatus called an auto-clave or bomb A great deal of early experimental work was done using the

Hydrothermal hydrolysis—hydrothermal precipitation

Hydrothermal electrochemical reaction

Hydrothermal mechanochemical reaction

1 Powders are formed directly from solution.

2 Powders are anhydrous, crystalline, or amorphous depending on the hydrothermal temperature.

3 Particle size controlled by hydrothermal temperature.

4 Particle shape controlled by starting materials.

5 Ability to control chemical composition, stoichiometry, etc.

6 Powders are highly reactive in sintering.

7 In many cases, powders do not need calcination.

8 In many cases, powders do not need a milling process.

Based on studies mainly by W.J Dawson, D Segal, D.W Johnson, and S Somiya.

6 Chemical Processing of Ceramics, Second Edition

Morey bomb7 and Tuttle-Roy test tube bomb (made by Tem-Press), which areboth as a catalyst and occasionally as a component of solid phases in synthesis

at elevated temperatures (greater than 100°C) and pressures (more than a fewatmospheres) At present, one can get many kinds of autoclaves to coverdifferent pressure–temperature ranges and volumes In the U.S., there are threecompanies:

• Tem-Press—They are the best source for research vessels of all kinds,including test tube bombs and gas intensifiers for specialized gasessuch as argon, hydrogen, oxygen, ammonia, etc

• Autoclave Engineers—They make a complete line of laboratory-scalevalves, tubing, collars, fittings for connections, etc., and they also makevery large autoclaves (1–3 m) for quartz and other chemical processes

• Parr Instrument Co.—They make simple, low-pressure (1000 bars),low-temperature (300°C) laboratory-scale autoclaves (50 ml to 1 L)for low-temperature reactions, including vessels lined with Teflon.For hydrothermal experiments the requirements for starting materials are

an accurately known composition that is as homogeneous, pure, and fine aspossible

FIGURE 1.1 Autoclave with flat plate closure (Morey, G.W., Hydrothermal synthesis, J.

Am Ceram Soc., 36, 279, 1953.)

Casing

Cover Seal disc Shoulder

Liner 1" dia.

Plunger

shown in Figure 1.1 and Figure 1.2 Hydrothermal synthesis involves water

A S OME R ESULTS IN D IFFERENT C ATEGORIES (H YDROTHERMAL

D ECOMPOSITION )

1 Ilmenite

Ilmenite (FeTiO3) is a very stable mineral Extraction of titanium dioxide (TiO2)from such ores has potential Using 10 M KOH or 10 M NaOH mixed withilmenite in a ratio of 5:3 (ilmenite:water) under reaction conditions of 500°C and

300 kg/cm2, ilmenite was decomposed completely after 63 h.20 If the ratio ofilmenite to water is 5:4, under the same conditions, 39 h is needed to decomposethe ilmenite Reactions were as follows, in the case of KOH solution:

3FeTiO3 + H2O → Fe3O4 + 3TiO2 + H2nTiO2 + 2KOH → K2O(TiO2)n + H2O, n = 4 or 6.

B H YDROTHERMAL M ETAL O XIDATION

1 Zirconium Metal

Zirconium metal powder (10–50 g) was reacted with water to form ZrO2:21

Zr + 2H2O (at 300°C) → ZrO2 + ZrHx (400°C) → ZrO2 + 2H2

FIGURE 1.2 Reaction vessel with a cold-cone seat closure (Tem-Press).

Cone seat closure

Pressure tuning

To pump Thermocouple

Thermocouple

Platinum or gold capsule length 1.8 –7.5 cm

Welded or pinched 9''

8 Chemical Processing of Ceramics, Second Edition

At 300°C under 98 MPa, ZrO2 and ZrHx appeared At temperatures above 400°Cunder 98 MPa, ZrHx disappeared and only ZrO2 was formed Figure 1.3 and

2

2 Aluminum Metal

Aluminum metal was reacted with water under 100 MPa at temperatures between

200 and 700°C for up to 6 h.22 AlOOH appeared at 100°C and α-Al2O3 appeared

at between 500 and 700°C

3 Titanium Metal

Titanium metal powder was reacted with water in a ratio of 1:2 in a gold capsuleunder hydrothermal conditions of 100 MPa for 3 h at temperatures of up to700°C.23

H2O

ZrO22–6 µ mFigure 1.5 shows the results

Figure 1.4 show ZrO powders formed by hydrothermal oxidation

distilled water and dried for 48 h at 120°C This starting material was placed into

a platinum or gold tube with various solutions under 100 MPa at 300°C for 24 h(Figure 1.6) The results24,25

D H YDROTHERMAL P RECIPITATION OR H YDROTHERMAL

H YDROLYSIS

1 Alumina

One of the industrial applications of hydrothermal precipitation is ordinary

alu-29 T

FIGURE 1.5 Variation in product amount with temperature in hydrothermal oxidation of

titanium in a closed system under 100 MPa for 3 h.

FIGURE 1.6 TEM of monoclinic zirconia powder using hydrothermal reaction (100 MPa

at 400°C for 24 h) using 8 wt% KF solution

are shown in Table 1.4

mina production The Bayer process is shown in Figure1.7

10 Chemical Processing of Ceramics, Second Edition

TABLE 1.4

Phases Present and Crystallite Size of Products by

Hydrothermal Reaction at 100 MPa for 24 h

Average crystallite size (nm) Mineralizer

Temperature (°C)

Tetragonal ZrO 2 (nm)

Monoclinic ZrO 2 (nm)

Mill

Calcination 1200ºC Wash Classification

Precipitate Al(OH)3

Cool to 55ºC

Settle and filter

solids

2 Zirconia

Hydrothermal homogeneous precipitation is one of the best ways to producezirconia powders The process, properties of the powders, and microstructure of

30,31

E HYDROTHERMAL ELECTROCHEMICAL METHOD

For preparing BaTiO3, titanium and platinum plates are used as anodes andcathodes, respectively A solution of barium nitrate 0.1 N or 0.5 N and temper-atures up to 250°C were used for the experiment The current density was

100 mA/cm2 Under these conditions we were able to produce BaTiO3 powder

Fe2O3 0.005 0.005 0.005

Na2O 0.001 0.001 0.001

Cl – <0.01 <0.01 <0.01 Ignition loss 1.5 1.5 8.0 Crystallite size (nm) 22 22 20 Average particle size ( µ m) a 0.5 0.5 1.5 Specific surface area (m 2 /g) b 20 25 95 Sintered specimens 1400ºC × 2 h 1500ºC × 2 h

Bulk density (g/cm 3 ) 6.05 5.85

Bending strength (Mpa) c 1000 300

Fracture toughness (Mpam 1/2 ) d 6.0 2.5

Vicker’s hardness (GPa) 12.5 11

Figure 1.11 shows an apparatus used in the hydrothermal electrochemical method

The BaTiO powder produced by this process is shown in Figure 1.12 ZrO was

12 Chemical Processing of Ceramics, Second Edition

FIGURE 1.8 ZrO2 produced by the hydrothermal homogeneous precipitation process.

FIGURE 1.9 TEM of different grades of zirconia powder using hydrothermal

homoge-Urea, CO(NH2)2Zirconium oxychloride

FIGURE 1.10 TEM of zirconia sintered at 1400°C for 2 h.

FIGURE 1.11 Schematic of the electrochemical cell and circuit arrangements for anodic

oxidation of a titanium metal plate under hydrothermal conditions (A) Counter electrode (platinum plate), cathode; (B) thermocouple; (C) stirrer; (D) reference electrode (platinum plate); (E) working electrode (titanium plate), anode.

10 µ m

stat Ammeter

14 Chemical Processing of Ceramics, Second Edition

F REACTIVE ELECTRODE SUBMERGED ARC

Reactive electrode submerged arc (RESA) is a totally new process for making ders.34,35 RESA produces extremely high temperatures (approximately 10,000 K) with

pow-a pressure of 1 pow-atm H2O (possibly more in the nanoenvironment) It allows one tochange liquids very easily Figure 1.13 shows the apparatus to produce powders

G HYDROTHERMAL MECHANOCHEMICAL PROCESS

Ba(OH)2 and FeCl3 were used as starting materials The precipitate was

crystal-FIGURE 1.12 TEM of BaTiO3 powders prepared by the hydrothermal electrochemical method (250°C, 0.5 N Ba(NO3)2, titanium plate).

FIGURE 1.13 Schematic of microprocessor-controlled RESA apparatus for fine powder

preparation (A Kumar and R Roy).

Linear

actuator

AC power

225 A

Printer

Computer interface

Power load

Power load Dielectric fluid

Gas inlet

electrodes Metal

Current sensor

lized hydrothermally in an apparatus (Figure 1.14) combined with an attritor and

ambient water pressure The starting solutions with the precipitate and stainlesssteel balls (5 mm diameter) were placed in Teflon beakers A Teflon propellerwas rotated in the beaker under 200°C and 2 MPa The speed of the propellerwas from 0 to 107 rpm The number of stainless steel balls was 200, 500, and

700 X-ray diffraction profiles are shown in Figure 1.15.36

FIGURE 1.14 Experimental apparatus for hydrothermal mechanochemical reactions.

FIGURE 1.15 X-ray diffraction profiles of (a) starting materials, (b) material fabricated

at 200°C under 2 MPa for 4 h without rotation, and (c) material fabricated at 200°C for

(a) (b) (c)

BaO 6Fe2O3BaO Fe2O3

20 Cuka

16 Chemical Processing of Ceramics, Second Edition

H M ICROWAVE H YDROTHERMAL P ROCESS

Microwave-assisted hydrothermal synthesis is a novel powder processing nology for the production of a variety of ceramic oxides and metal powders underclosed-system conditions Komarneni et al developed this hydrothermal processinto which microwaves are introduced.37–48 This closed-system technology not

tech-FIGURE 1.16 Microwave-assisted reaction system (MARS 5).

FIGURE 1.17 Components of reaction vessel used in the MARS-5 unit.

Cover

Cover Locking nut

Locking nut

Thermowell Thermowell

only prevents pollution during the synthesis of lead-based materials, but alsosaves energy, and thus could substantially reduce the cost of producing manyceramic powders Hydrothermal microwave treatment of 0.5 M TiCl4 was done

250°C The parameters used are temperature, pressure, time, concentration of themetal solution, pH, etc The key result is crystallization reactions, which lead tofaster kinetics by one or two orders of magnitude compared to conventionalhydrothermal processing The use of microwaves in both solid and liquid states

is gaining in popularity for many reasons, but especially because of the potentialenergy savings The use of microwaves under hydrothermal conditions can accel-erate the synthesis of anhydrous ceramic oxides such as titania, hematite, bariumtitanate, lead zirconate titanate, lead titanate, potassium niobate, and metal pow-ders such as nickel, cobalt, platinum, palladium, gold, silver, etc., and this isexpected to lead to energy savings The term “microwave-hydrothermal” process-ing was first coined by us for reactions taking place in solutions that are heated

to temperatures greater than 100°C in the presence of microwaves The value ofthis technique has been demonstrated in rapid heating to the temperature oftreatment, which can save energy; increasing the reaction kinetics by one to twoorders of magnitude; forming novel phases; and eliminating metastable phases.Figure 1.18 shows a nanophase powder of hematite

FIGURE 1.18 Hematite synthesized from 0.02 M ferric nitrate at 100°C under

micro-wave-hydrothermal conditions.

in 1 M HCl to form rutile The system (Figure 1.16) operated at a 2.45 GHz Thevessel is lined with Teflon (Figure 1.17) and the system is able to operate up to

18 Chemical Processing of Ceramics, Second Edition

I HYDROTHERMAL SONOCHEMICAL METHOD

Ultrasonic waves are often used in analytical chemistry for dissolving powderinto solution.49 The hydrothermal sonochemical method is a new method forsynthesizing materials.50

III IDEAL POWDERS AND REAL POWDERS

The characteristics of ideal powders and real powders produced by hydrothermalprocessing are shown in Table 1.6 and Table 1.7 Hydrothermal powders are close

to ideal powders

TABLE 1.6 Characteristics of an Ideal Powder

Fine powder less than 1 µm Soft or no agglomeration Narrow particle size distribution Morphology: sphere

Chemical composition controllable Microstructure controllable Uniformity

Free flowing Fewer defects, dense particle Less stress

Reactivity, sinterability Crystallinity

Reproducibility Process controllable

TABLE 1.7

Characteristics of Hydrothermal Powders

Fine powder less than 1 µm

No or weak agglomeration

Single crystal in general; depends on preparation temperature

Flow ability: forming is good

Good homogeneity

Good sinterability

No pores in grain

Narrow particle size distribution

Ability to synthesize low-temperature form and/or metastable form

Ability to make composites such as organic and inorganic mixtures

Ability to make a material that has a very high vapor pressure

3 Vincenzini, P., Ed., Ceramic Powders, Elsevier Scientific, Amsterdam, 1025, 1983.

4 Segal, D., Chemical Synthesis of Advanced Ceramic Materials, Cambridge

Uni-versity Press, Cambridge, 182, 1989.

5 Ganguli, D., and Chatterjee, M., Ceramic Powder Preparation: A Handbook,

Kluwer Academic, Dordrecht, The Netherlands, 1997, 221.

6 Somiya, S., and Akiba, T., Trans MRS-J, 24, 531, 1999.

7 Morey, G.W., Hydrothermal synthesis, J Am Ceram Soc., 36, 279, 1953.

8 Walker, A.C., J Am Ceram Soc., 36, 250, 1953.

9 Eitel, W., Silicate Science, vol IV, Academic Press, New York, 149, 1966.

10 Laudise, R.A., Hydrothermal Growth: The Growth of Single Crystals, Prentice

Hall, Englewood Cliffs, NJ, 275, 1970.

11 Lobachev, A.N., Ed., Hydrothermal Synthesis of Crystals, Consultant Bureau, New

York, 1971, 152.

12 Somiya, S., Ed., Proceedings of the First International Symposium on

Hydrother-mal Reactions, Gakujutsu Bunken Fukyu Kai, Tokyo, 965, 1983.

13 Somiya, S., Ed., Hydrothermal Reactions for Material Science and Engineering:

An Overview of Research in Japan, Elsevier Applied Science, London, 505, 1989.

14 Somiya, S., Advanced Materials: Frontiers in Materials Science and Engineering,

vol 19B, Elsevier Science, Amsterdam, 1105, 1993

15 Rabenau, A.A., Chem Int Ed Engl., 24, 1026, 1985.

16 Brice, L.C., Hydrothermal Growth, Crystal Growth Processes, Blackie Halsted

Press, Glasgow, 194, 1986.

17 Dawson, W.J., Hydrothermal synthesis of advanced ceramic powders, Am Ceram.

Soc Bull., 67, 1673, 1988.

18 Byrappa, K., Ed., Hydrothermal Growth of Crystals, Progress in Crystal Growth

and Characterization of Materials, Pergamon Press, Oxford, 1991.

19 Johnson, D.W., Jr., Advances in Ceramics, vol 21, Innovations in Ceramic Powder

Preparation, G.L Messing et al., Eds., American Ceramic Society, Westerville,

OH, 3, 1987.

20 Ismail, M.G.M.U., and Somiya, S., Proceedings of the International Symposium

on Hydrothermal Reactions, Gakujutsu Bunken Fukyu Kai, Tokyo, 669, 1983.

21 Yoshimura, M., and Somiya, S., Rep Res Lab Eng Mat Tokyo Inst Technol.,

9, 53, 1984.

22 Toraya, H et al., Advances in Ceramics, vol 12, Science and Technology of

Zirconia II, American Ceramic Society, Westerville, OH, 806, 1984.

23 Yoshimura, M et al., Rep Res Lab Eng Mat Tokyo Inst Technol., 12, 59, 1987.

24 Tani, E., Yoshimura, M., and Somiya, S., Hydrothermal preparation of ultrafine monoclinic ZrO2 powder, J Am Ceram Soc., 64, C181, 1981.

25 Nishizawa, H et al., J Am Ceram Soc., 65, 343, 1982.

26 Komarneni, S et al., Advanced Ceramic Materials, 1, 87, 1986.

27 Haberko, K et al., J Am Ceram Soc., 74, 2622, 1991.

28 Haberko, K et al., J Am Ceram Soc., 78, 3397, 1995.

20 Chemical Processing of Ceramics, Second Edition

29 Riman, R., The Textbook of Ceramic Powder Technologies, American Ceramic

Society, Westerville, OH, 1999.

30 Hishinuma, K et al., Advances in Ceramics, vol 24, Science and Technology of

Zirconia III, Somiya, S., Yamamoto, N., and Hanagida, H., Eds., American

Ceramic Society, Westerville, OH, 201, 1988.

31 Somiya, S et al., Hydrothermal Growth of Crystals, vol 21, Progress in Crystal

Growth and Characterization of Materials, Byrappa, K., Ed., Pergamon Press,

Oxford, 195, 1991.

32 Yoo, S.E., Yoshimura, M., and Somiya, S., Preparation of BaTiO3 and LiNbO3powders by hydrothermal anodic oxidation, in Sintering ’87, vol l, 4th Interna- tional Symposium on the Science and Technology of Sintering, Nov 4–6, Somiya

S et al., Eds., Elsevier, New York, 108, 1988.

33 Yoshimura, M et al., Rep Res Lab Eng Mat Tokyo Inst Technol., 14, 21, 1989.

34 Kumar, A., and Roy, R., J Mater Res., 3, 1373, 1988.

35 Kumar, A., and Roy, R., J Am Ceram Soc., 72, 354, 1989.

36 Yoshimura, M et al., J Ceram Soc Jap Int Ed., 97, 14, 1989.

37 Komarneni, S., Roy, R., and Li Q.H., Mater Res Bull., 27, 1393, 1992.

38 Komarneni, S., Li, Q.H., Stefasson, K.M and Roy, R., J Mater Res., 8, 3176,

1993.

39 Komarneni, S., and Li, Q.H., J Mater Chem., 4, 1903, 1994.

40 Komarneni, S., Pidugu, R., Li, and Roy, R., J Mater Res., 10, 1687, 1995.

41 Komarneni, S., Hussen, M.Z., Liu, C., Breval, E., and Malla, P.B., Eur J Solid

State Inorg Chem., 32, 837, 1995.

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ceramic and metal powders, in Novel Techniques in Synthesis and Processing of

Advanced Materials, Singh, J., and Copley, S.M., Eds., Minerals, Metals, and

Materials Society, Warrendale, PA, 103, 1995.

43 Komarneni, S., and Menon, V.C., Mater Letts., 27, 313, 1996.

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45 Komarneni, S., Rajha, P.K., and Katsuki, H., Mater Chem Phys., 61, 50, 1999.

46 Katsuki, H., Furuta, S., and Komarneni, S., J Porous Mater., 8, 5, 2001.

47 Katsuki, H., and Komarneni, S., J Am Ceram Soc., 84, 2313, 2001.

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Microwave-polyol process for Pt and Ag nanoparticles, Langmuir, 18, 5959, 2002.

49 Milia, A.M., Sonochemistry and Cavitation, Gordon and Breach Publishers,

Lux-embourg, 543, 1995.

50 Meskin, P.E., Barantchikov, A.Y., Ivanov, V.K., Kisterev, E.V., Burukhin, A.A.,

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Chem., 389, 207, 2003.

9 Other Nitrogen-Containing Compounds 30

10 Dipolar Aprotic Solvents 30III Solvothermal Synthesis of Metal Oxides 31

A Solvothermal Dehydration 31

1 Solvothermal Dehydration of Aluminum Hydroxide

in Alcohols 32

2 Alcohothermal Dehydration of Hydroxides of Metals

Other Than Aluminum 34

3 Solvothermal Dehydration of Aluminum Hydroxide

in Glycols and Related Solvents 35

4 Glycothermal Synthesis of α-Alumina 36

B Solvothermal Decomposition of Metal Alkoxides 37

1 Metal Alkoxide in Inert Organic Solvents 37

2 Metal Alkoxides in Inert Organic Solvent: Synthesis

of Mixed Oxides 40

3 Metal Acetylacetonate in Inert Organic Solvent 41

4 Metal Carboxylates 41

5 Cupferron Complexes 42

22 Chemical Processing of Ceramics, Second Edition

6 Solvothermal Decomposition of Alkoxide Followed

by Removal of Organic Media in a Supercritical

or Subcritical State 42

7 Metal Alkoxide in Alcohols 43

8 Reaction of Alkoxide in Secondary Alcohols 44

9 Reaction of Alkoxide in Glycols 45

C Glycothermal Synthesis of Mixed Metal Oxides 46

1 Rare Earth Aluminum Garnets 46

2 Rare-Earth (Nd-Lu) Gallium Garnets 47

3 Metastable Hexagonal REFeO3 48

4 Other Mixed Oxides 48

5 Reaction in Ethylene Glycol 50

D Crystallization of Amorphous Starting Materials 50

E Hydrothermal Crystallization in Organic Media 53

F Solvothermal Ion Exchange and Intercalation 54

G Solvothermal Oxidation of Metals 55

H Solvothermal Reduction 56References 56

I INTRODUCTION

Metal oxides are usually prepared by calcinations of suitable precursors such ashydroxides, nitrates, carbonates, carboxylates, etc This process usually givesoxides with pseudomorphs of the starting materials When large amounts ofthermal energy are applied for the decomposition of the precursors, it facilitiessintering of the product particles and therefore aggregated particles are obtained.When mixed oxides such as spinel, perovskite, and pyrochlore are the desiredproducts, heat treatment at higher temperatures is required

For the preparation of inorganic materials with well-defined morphologies,liquid phase syntheses are preferred These synthetic reactions proceed at rela-tively lower temperatures and therefore require lower energies The sol-gel (alkox-ide) method is one of these methods;1,2 however, this method usually givesamorphous products, and calcination of the products is required to obtain crys-tallized products In this chapter, solvothermal methods are dealt with, which areconvenient for the synthesis of a variety of inorganic materials General consid-erations for solvothermal reactions are discussed first and then the solvothermalsynthesis of metal oxides is reviewed

Recently, use of organic media for inorganic synthesis has garnered muchattention Since 1984, we have been exploring the synthesis of inorganic materials

in organic media at elevated temperatures (200 to 300°C) under autogenouspressure of the organics.3 This technique is now generally called the “solvother-mal” method.4 The term “solvothermal” means reactions in liquid or supercriticalmedia at temperatures higher than the boiling point of the medium Hydrothermalreactions are one type of solvothermal reaction To carry out reactions at temper-atures higher than the boiling point of the reaction medium, pressure vessels

(autoclaves) are usually required Some researchers favor the use of sealedampoules of glass or silica, but these experiments should be carried out with greatcare because the ampoules are easily broken by the internal pressure of thereaction medium To avoid explosion of the ampoules, they may be placed in anautoclave together with a suitable medium to create a vapor pressure to balancethe internal pressure of the ampoule.

It must be noted that the liquid structure of the solvent is essentiallyunchanged at above or below the boiling point because the compressibility of theliquid is quite small (Note that near the critical point, the structure of the solvent

is drastically altered by changes in the solvent density.) Higher pressure mayincrease or decrease the reaction rate; it depends on the relative volume of theactivated complex at the transition state to the volume of the starting molecule(s).However, it is known that to measure the effect of reaction pressure, GPa-scalepressure is required This means that the autogenous pressure created by the vaporpressure of the solvent has only a minor effect on the reaction rate Thereforethere is no need to differentiate the reactions at the temperatures above and belowthe boiling point Consequently “solvothermal” reaction should be defined moreloosely as the reaction in a liquid (or supercritical) medium at high temperatures.Reactions in a closed system using autoclaves or sealed ampoules and in an opensystem using a flask equipped with a reflux condenser sometimes give completelydifferent results, especially when a low boiling point byproduct such as water isformed

Various compounds have been prepared by solvothermal reactions: metals,5,6metal oxides,7,8 chalcogenides,9,10 nitrides,4,9,11 phosphides,12 open-frameworkstructures,13,14 oxometalate clusters,15,16 organic-inorganic hybrid materials,14,17,18and even carbon nanotubes.19,20 Most of the solvothermal products are nano- ormicroparticles with well-defined morphologies The distribution of the particlesize of the product is usually quite narrow, and formation of monodispersedparticles is frequently reported.21,22 When the solvent molecules or additives arepreferentially adsorbed on (or have a specific interaction with) a certain surface

of the products, growth of the surface is prohibited and therefore products withunique morphologies may be formed by the solvothermal reaction.9,23,24 Thusnanorods,24 wires,25 tubes,26 and sheets27 of various types of products have beenobtained solvothermally

II CHOICE OF THE REACTION MEDIUM

A INORGANIC MEDIUM

1 Water

Water (boiling point [bp], 100°C; critical temperature [Tc], 374°C; critical sure [Pc], 218 atm) is the most widely examined reaction medium for solvother-mal reactions Geochemists first applied this technique to explore the formationmechanism of minerals and thus quite long reaction periods were applied to

pres-24 Chemical Processing of Ceramics, Second Editionexamine the equilibrium conversion of minerals Today researchers seek morerapid conversion to synthesize materials, and therefore adequate synthesis of theprecursors by, for example, the coprecipitation method and the sol-gel methodbecome more important Addition of salt, acid, or base may facilitate the reaction

or alter the morphology of the products These materials are called mineralizers.Fluoride ions sometimes have a drastic effect on the hydrothermal synthesis ofmaterials Besides the excellent article by Somiya, Roy, and Komarneni in thisbook, many review articles have appeared on hydrothermal synthesis;28–32 there-fore this technique will not be discussed further in this chapter

2 Ammonia

Besides water for hydrothermal reactions, liquid ammonia (bp, 78°C; Tc, 132°C;

Pc, 113 atm) is also used for the solvothermal synthesis of nitrides Metastable

or otherwise unobtainable nitride materials were reported to be formed by thismethod.33–35 Ammonium and amide (NH2) ions are the strongest acid and base,respectively, for the liquid ammonia system, and therefore ammonium salt acts

as the acid mineralizer,36 while amide ion can be prepared by addition of alkalimetals to the solvent Since ammonia has a low boiling point, the reaction pressure

is usually quite high

3 Other Inorganics

Sulfur dioxide (bp, −10°C; Tc, 157.5°C; Pc, 78 atm) is another interesting

inor-ganic solvent This compound has a high dielectric constant and low basicity(actually, it acts as an acid) To the best of my knowledge, there have been noarticles that apply this solvent for the solvothermal synthesis of inorganic mate-rials However, the highly corrosive nature of this solvent may limit its use inautoclaves

Hydrofluoric acid (bp, 19.5°C; Tc, 188°C; Pc, 64 atm), nitrogen dioxide (bp,21°C; Tc, 158.2°C; Pc, 100 atm; in equilibrium with N2O4), sulfuric acid (decom-position at 280°C), and polyphosphoric acid are candidates for solvents in sol-vothermal reactions, and the reactions of these solvents will produce a variety ofproducts that cannot be prepared by any other methods For example, Bialowons

et al.37 reported that solvothermal treatment of (O2)2Ti7F30 in anhydrous HF at300°C yielded single crystals of TiF4 Solvothermal reactions in these solventsmay produce fruitful results and a new field seems to be awaiting many research-ers

B ORGANIC MEDIUM

1 General Considerations

Various organic solvents have been applied for the synthesis of inorganic rials Because most of inorganic synthesis researchers are not familiar withorganic solvents, some important features are summarized here