United States Department of Commerce Technology Administration National Institute of Standards and Technology '0 A111DM 123=131 NIST Special Publication 856 Electroacoustics for Characterization of Particulates and Suspensions Proceedings of Workshop held at the National Institute of Standards and Technology February 3-4, 1993 Gaithersburg, Maryland Subhas G. Malghan, Editor o QC TOO .U57 //856 1993 Jhe National Institute of Standards and Technology was established in 1988 by Congress to "assist industry in the development of technology . needed to improve product quality, to modernize manufacturing processes, to ensure product reliability . and to facilitate rapid commercialization ... of products based on new scientific discoveries." NIST, originally founded as the National Bureau of Standards in 1901, works to strengthen U.S. industry's competitiveness; advance science and engineering; and improve public health, safety, and the environment. 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NIST Special Publication 856 Electroacoustics for Characterization of Particulates and Suspensions Proceedings of Workshop held at the National Institute of Standards and Technology February 3-4, 1993 Gaithersburg, Maryland Subhas G. Malghan, Editor Ceramics Division Materials Science and Engineering Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899 Issued September 1993 U.S. Department of Commerce Ronald H. Brown, Secretary Technology Administration Mary L. Good, Under Secretary for Technology National Institute of Standards and Technology Arati Prabhakar, Director National Institute of Standards U.S. Government Printing Office For sale by the Superintendent and Technology Washington: 1993 of Documents Special Publication 856 U.S. Government Printing Office Natl. Inst. Stand. Technol. Washington, DC 20402 Spec. Publ. 856 308 pages (Sept. 1993) CODEN: NSPUE2 PREFACE Traditionally, interface chemistry of particulates and colloidal stability in liquids has been characterized by techniques based on microelectrophoresis. Since the conception of the zeta potential, colloid scientists have utilized microelectrophoresis and moving boundary electrophoresis extensively for the measurement of electrophoretic mobilities. Significant progress has been made in developing understanding and scientific data on many particulates of commercial and technical interests. Some of the major drawbacks of these methods are the need for use of low concentrations of particulates in the suspensions, the requirement of optical opacity of particulates, and the exclusive restriction to colloidal size particulates. The electroacoustic technique, based on physical effects described by Debye, is relatively new and the laboratory instrumentation has become available only in the last decade. This new instrumentation by Matec Applied Sciences and Pen Kern Inc. is based on the application of either electrical fields or ultrasound as external fields to the particles and measurement of the resulting electrical or ultrasonic response. These instruments, while addressing the primary drawbacks of electrophoresis instruments, allow the determination of signals that are related to the electrokinetic zeta potential for colloidal suspensions in polar and nonpolar media. In recent years, the electroacoustic technique has been extensively utilized for the characterization of a variety of particulates in dense suspensions of polar and nonpolar liquids with great success. As a result of this surge in activity, a number of technical issues have surfaced. In order to discuss these issues and develop a common understanding of the fundamentals of electroacou sties, a workshop was organized at the suggestion of the user community. "Electroacoustics for Characterization of Particulates in Suspensions" is the first workshop on this subject organized by the National Institute of Standards and Technology (NIST). This workshop was held on February 3-4, 1993 at NIST, Gaithersburg, MD. The primary purpose of this workshop was to bring together scientists and engineers working in this field to address relevant scientific and technical issues on the measurement of electroacoustic parameters in the study of particulates. The participants included leading scientists, manufacturers of electroacoustics, and researchers from minerals, ceramics, pharmaceutical, inks, paints, cement and paper industries. The technical content of this workshop included theoretical understanding of electroacoustics, latest developments in equipment, application of electroacoustics to different industrial problems, methods and procedures in the measurement of electroacoustic parameters, interpretation of these measurement parameters, and major issues in the measurements. The participants received a compilation of presentation viewgraphs after the meeting. This proceedings of the workshop has been possible due to the efforts of a number of my colleagues who not only presented their results but also provided their papers. Without their dedication, this would not have been possible. This volume contains all but two papers presented at the workshop. The papers were reviewed by the participants of the workshop. iii In addition, the session chairs prepared the attached notes based on the discussions held under different groups. This report is divided into six sections based on the sessions held at the workshop. The first session constituted papers on theoretical aspects and new data on electroacoustics phenomenon, followed by application of this theory to the development of new instrumentation. Prof. Hunter described the results of verification of electrophoretic mobility and dynamic mobility for mono and polydisperse particles. In addition, data on measurements with the Matec Applied Science's new prototype version of Acoustosizer were presented to illustrate the accuracy of determination of magnitude and phase of the dynamic mobility over a frequency range of 0.3 to 11.1 MHz. Prof. Pendse presented the analysis of high density suspensions by analyzing attenuation coefficient spectra over 1.0 to 100 MHz frequency range to determine particle size distribution. In the area of new instrumentation, both theory and experimental results of Matec Applied Sciences and Pen Kem Inc. were presented by Messrs. D. W. Cannon and P. Goetz, respectively. The second generation of these instruments have the capability to measure both particle size distribution and zeta potential in dense suspensions. In the second session, papers related to applications and procedural aspects of using electroacoustics were presented. Dr. R. O. James discussed the calibration of Electrokinetic Sonic Amplitude instrumentation using lattices and oxide colloids as a function of volume fraction. Excellent precision of the ESA technique in comparison with the classical electrophoresis techniques was demonstrated. The application of ESA technique to concentrated suspensions of carbon black in apolar