Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1994 Processing and characterization of zinc sulfide based materials Yong Han Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Materials Science and Engineering Commons Recommended Citation Han, Yong, "Processing and characterization of zinc sulfide asb ed materials " (1994). Retrospective Theses and Dissertations. 10476. https://lib.dr.iastate.edu/rtd/10476 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. 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Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. University Microfilms International A Bell & Howell Information Company 300 North Zeeb Road. Ann Arbor, Ml 48106-1346 USA 313/761-4700 800/521-0600 Order Number 9503561 Processing and characterization of zinc sulfide-based materials Han, Yong, Ph.D. Iowa State University, 1994 UMI 300N.ZeebRA Ann Arbor, MI 48106 Processing and characterization of zinc sulfide based materials by Yong Han A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Department: Materials Science and Engineering Major: Ceramic Engineering Approved: Signature was redacted for privacy. Signature was redacted for privacy. For the Major Department Signature was redacted for privacy. For the Graduate College Iowa State University Ames, Iowa 1994 ii TABLE OF CONTENTS Page GENERAL INTRODUCTION 1 Explanation of Dissertation Organization 6 PAPER I. SYNTHESIS AND CHARACTERIZATION OF ZINC SULFIDE/GALLIUM PHOSPHIDE NANO-COMPOSITE POWDERS 8 ABSTRACT 9 INTRODUCTION 10 EXPERIMENTAL PROCEDURE 13 (1) Zinc Sulfide Precipitation 13 (2) Phosphinogallane Synthesis 13 (3) ZnS/GaP Composite Powder Synthesis 14 (4) Heat Treatment and Characterization 20 RESULTS AND DISCUSSION 21 (1) Characterization of Phosphinogallane 21 (2) Characterization of As-Precipitated and Heat Treated Zinc Sulfide Powders 26 (3) Characterization of As-Prepared and Heat Treated ZnS/GaP Composite Powders 37 CONCLUSION 50 ACKNOWLEDGMENT 51 APPENDIX 52 REFERENCES 55 PAPER II. ZINC SULFIDE/GALLIUM PHOSPHIDE COMPOSITES BY CHEMICAL VAPOR TRANSPORT 60 ABSTRACT 61 INTRODUCTION 62 THEORETICAL CONSIDERATIONS 64 (1) Fundamentals of Chemical Vapor Transport 64 (2) Equilibrium Constants of Transport Reactions in GaP-I^ System 69 (3) Kinetics of Chemical Vapor Transport in GaP-I^ System 73 EXPERIMENTAL PROCEDURE 77 (1) Starting Materials 77 (2) Chemical Vapor Transport and Consolidation 77 (3) Characterization 78 RESULTS AND DISCUSSION 79 (1) Thermocfynamic and Kinetic Calculations 79 (2) Powder Characterization 86 iii (3) Densified Composites 91 CONCLUSION 104 ACKNOWLEDGMENT 105 REFERENCES 106 PAPER III. FABRICATION AND CHARACTERIZATION OF HOT ISOSTATICALLY PRESSED ZnS/GaP NANOCOMPOSITE CERAMICS 111 ABSTRACT 112 INTRODUCTION 113 EXPERIMENTAL PROCEDURE 118 (1) ZnS/GaP Nanocomposite Powder Synthesis 118 (2) Densification of Nanocomposite Powders 118 (3) Characterization 119 RESULTS AND DISCUSSION 120 (1) Powders and Green Compacts 120 (2) Characterization of As-DensifiedNanocomposites 120 (3) Room-Temperature Mechanical Properties 128 SUMMARY 138 ACKNOWLEDGMENT 139 REFERENCES 140 GENERAL CONCLUSIONS 144 REFERENCES 147 ACKNOWLEDGMENT 150 APPENDIX A. MICROSTRUCTURAL DEVELOPMENT IN NANO-CRYSTALLINE ZINC SULFIDE POWDERS 151 APPENDIX B. PHOSPHINOGALLANE SYNTHESIS 176 1 GENERAL INTRODUCTION Future infrared transmitting windows and domes are expected to perform under harsh atmospheric environments. The primary function of these components is to protect the sensing devices aboard the high speed aircraft from the environment. To serve this purpose, the window material is required to be transparent to the IR region of the spectrum, strong, tough, and have high thermal shock resistance. Two factors are considered responsible for determining the range of transparency. The short wavelength cutoff, , is set by the band gap. Eg, and thus is called the optical absorption edge. The relationship between and Eg is given by' = Ac/Eg (1) where h is Planck's constant and c is the velocity of light. The long wavelength cutoff of semiconductors and insulators are determined by lattice vibrations thus is called the phonon edge or the vibrational edge. A mathematical representation of the fundamental absorption frequency of a real material is too complicated and beyond the scope of this dissertation. However, the absorption fi-equency can be calculated for a linear diatomic molecule^ by (2) 2 where C is the force constant and m is the atomic mass. This relationship indicates that a material with a weaker bonding, i.e. smaller C, and a larger reduced mass will result in a small absorption frequency and hence the long wavelength cutoff will extend further into the far infrared. The IR window and dome materials are divided into two groups based mainly on the wavelength range of interest. The 3-5 |im transmitting materials are mainly used to protect the detectors of IR-guided missiles. The 8-12 |im transmitting windows and domes are primarily employed in high speed thermal imaging systems. A variety of strong oxide ceramics such as magnesium aluminate spinel, yttria, aluminum oxynitride, sapphire, and fluoride glasses are infrared transparent in the 3-5 |im regime.' However, only a limited number of materials are known to show a tolerable combination of thermomechanical properties and transparency in the 8-12 |im region."* This is because the weak chemical bonding in these materials which allows the long wavelenth tranparency, in turn, results in poor mechanical strength as expressed earlier. Zinc sulfide is currently being used as a compromise material for 8-12 ^m transmitting window and dome applications. The optical ceramic components are produced in many ways. Single ciystalline parts can be fabricated by cutting ingots grown from melt. However, it is very expensive and difficult to grow large single crystals of ceramics. Therefore, they are inadequate for bulk window and dome applicaions. Most of the commercial ZnS windows are CVD grown using zinc vapor and HjS gas.^ Although these windows exhibit excellent optical properties, nonuniform microstructures and large grain sizes (2-60 |im) result in poor mechanical 3 properties. For example, Knoop hardness values ranging from 160 to 250 kg/mm" were reported.®'Fully dense, fine grained, and microstucturally uniform polycrystalline ceramics, on the other hand, may yield an optimum combination of optical and mechanical properties. It is well known that the random packing of particles with a wide size distribution resuhs in higer densities in green compacts than that of monodisperse particles. However, it is believed that monosize particles will result in a more uniform microstructure after densification. Celikkaya and Akinc demonstrated this by hot pressing spherical, submicron, monodisperse ZnS powders that were homogeneously precipitated using thermal decomposition of thioacetamide.®'Mechanical properties of ZnS can be further improved by incorporating reinforcing phases. Solid solution strengthening of ZnS by Ga2S3 was demonstrated by Zhang et Significant improvement in fracture toughness can also be achieved by imbedding submicrometer size diamond particles in the matrix of ZnS. Table I presents a summary of physical properties of some existing 8-12 |im transmitting ceramic materials.' ' " " The main goal of this study was to improve the mechanical properties of ZnS. It involved the preparation, processing, and characterization of ZnS/GaP composite materials. Gallium phosphide was chosen because it has higher hardness and strength than ZnS. It also has better thermal shock resistance due to low thermal expansion and high thermal conductivity. In addition, GaP has the same crystal structure as ZnS. Traditional composite processing is mainly based on either mechanical mixing or precipitation of a secondary