Zuhair A. Munir

Bio: Zuhair A. Munir is an academic researcher from University of California, Davis. The author has contributed to research in topics: Combustion & Spark plasma sintering. The author has an hindex of 55, co-authored 278 publications receiving 14416 citations. Previous affiliations of Zuhair A. Munir include University of California & Lawrence Livermore National Laboratory.

1000 at 1000: The effect of electric field and pressure on the synthesis and consolidation of materials: a review of the spark plasma sintering method.

Abstract: The use of electric current to activate the consolidation and reaction-sintering of materials is reviewed with special emphasis of the spark plasma sintering method. The method has been used extensively over the past decade with results showing clear benefits over conventional methods. The review critically examines the important features of this method and their individual roles in the observed enhancement of the consolidation process and the properties of the resulting materials.

Self-propagating exothermic reactions: the synthesis of high-temperature materials by combustion

Abstract: A review of the method of self-propagating high-temperature synthesis (SHS) is presented. The review emphasizes the mechanisms of the rapid, non-isothermal reactions associated with this method. Theoretical analyses pertaining to such reactions are presented and examples of experimental observations on solid-solid and solid-gas interactions are discussed.

Electric Current Activation of Sintering: A Review of the Pulsed Electric Current Sintering Process

Abstract: The phenomenal increase during the past decade in research utilizing pulsed electric current to activate sintering is attributed generally to the intrinsic advantages of the method relative to conventional sintering methods and to the observations of the enhanced properties of materials consolidated by this method. This review focuses on the fundamental aspects of the process, discussing the reported observations and simulation studies in terms of the basic aspects of the process and identifying the intrinsic benefits of the use of the parameters of current (and pulsing), pressure, and heating rate.

Fundamental investigations on the spark plasma sintering/synthesis process: II. Modeling of current and temperature distributions

Abstract: Modeling and experimental analyses were carried out to investigate current and temperature distributions under typical spark plasma sintering (SPS) conditions. The simulation utilized two sample materials with widely differing electrical conductivities, alumina and copper. Current and heat generation gradients were evaluated in the radial and axial directions for both cases. Radial gradients result in significant differences in temperature between the surface of the graphite die and its center, in agreement with experimental measurements. Axial gradients are shown to influence the homogeneity of the product.

Combustion and plasma synthesis of high-temperature materials

Abstract: Various papers on combustion and plasmas synthesis of high-temperature materials are presented. Individual topics addressed include: self-propagation high-temperature synthesis, modeling and numerical computation of a nonsteady SHS process, new modes of quasi-periodic burning in combustion synthesis, combustion synthesis of intermetallic compounds, combustion synthesis of nickel aluminides, advanced ceramics via SHS, simultaneous combustion synthesis and densification of AlN, combustion synthesis of oxide-carbide composites. Also discussed are: combustion synthesis in the Ti-C-Ni-Al systems, combustion synthesis dynamics modeling, shock-induced reaction synthesis-assisted processing of ceramics, shock consolidation of combustion-synthesized ceramics, thermal plasma synthesis ceramic powders and coatings, formation of refractory aerosol particles, silica particle formation using the counterflow diffusion flame burner, synthesis of Si, SiC, and Si3N4 powders under high number density conditions.

1000 at 1000: The effect of electric field and pressure on the synthesis and consolidation of materials: a review of the spark plasma sintering method.

Abstract: The use of electric current to activate the consolidation and reaction-sintering of materials is reviewed with special emphasis of the spark plasma sintering method. The method has been used extensively over the past decade with results showing clear benefits over conventional methods. The review critically examines the important features of this method and their individual roles in the observed enhancement of the consolidation process and the properties of the resulting materials.

Refractory Diborides of Zirconium and Hafnium

Abstract: This paper reviews the crystal chemistry, synthesis, densification, microstructure, mechanical properties, and oxidation behavior of zirconium diboride (ZrB2) and hafnium diboride (HfB2) ceramics. The refractory diborides exhibit partial or complete solid solution with other transition metal diborides, which allows compositional tailoring of properties such as thermal expansion coefficient and hardness. Carbothermal reduction is the typical synthesis route, but reactive processes, solution methods, and pre-ceramic polymers can also be used. Typically, diborides are densified by hot pressing, but recently solid state and liquid phase sintering routes have been developed. Fine-grained ZrB2 and HfB2 have strengths of a few hundred MPa, which can increase to over 1 GPa with the addition of SiC. Pure diborides exhibit parabolic oxidation kinetics at temperatures below 1100°C, but B2O3 volatility leads to rapid, linear oxidation kinetics above that temperature. The addition of silica scale formers such as SiC or MoSi2 improves the oxidation behavior above 1100°C. Based on their unique combination of properties, ZrB2 and HfB2 ceramics are candidates for use in the extreme environments associated with hypersonic flight, atmospheric re-entry, and rocket propulsion.

Microstructural and mechanical characteristics of in situ metal matrix composites

Abstract: During the past decade, considerable research effort has been directed towards the development of in situ metal matrix composites (MMCs), in which the reinforcements are formed in situ by exothermal reactions between elements or between elements and compounds. Using this approach, MMCs with a wide range of matrix materials (including aluminum, titanium, copper, nickel and iron), and second-phase particles (including borides, carbides, nitrides, oxides and their mixtures) have been produced. Because of the formation of ultrafine and stable ceramic reinforcements, the in situ MMCs are found to exhibit excellent mechanical properties. In this review article, current development on the fabrication, microstructure and mechanical properties of the composites reinforced with in situ ceramic phases will be addressed. Particular attention is paid to the mechanisms responsible for the formation of in situ reinforcements, and for creep failure of the aluminum-based matrix composites.

Advances in thermoelectric materials research: Looking back and moving forward

Abstract: BACKGROUND Heat and electricity are two forms of energy that are at opposite ends of a spectrum Heat is ubiquitous, but with low quality, whereas electricity is versatile, but its production is demanding Thermoelectrics offers a simple and environmentally friendly solution for direct heat-to-electricity conversion A thermoelectric (TE) device can directly convert heat emanating from the Sun, radioisotopes, automobiles, industrial sectors, or even the human body to electricity Electricity also can drive a TE device to work as a solid-state heat pump for distributed spot-size refrigeration TE devices are free of moving parts and feasible for miniaturization, run quietly, and do not emit greenhouse gasses The full potential of TE devices may be unleashed by working in tandem with other energy-conversion technologies Thermoelectrics found niche applications in the 20th century, especially where efficiency was of a lower priority than energy availability and reliability Broader (beyond niche) application of thermoelectrics in the 21st century requires developing higher-performance materials The figure of merit, ZT, is the primary measure of material performance Enhancing the ZT requires optimizing the adversely interdependent electrical resistivity, Seebeck coefficient, and thermal conductivity, as a group On the microscopic level, high material performance stems from a delicate concert among trade-offs between phase stability and instability, structural order and disorder, bond covalency and ionicity, band convergence and splitting, itinerant and localized electronic states, and carrier mobility and effective mass ADVANCES Innovative transport mechanisms are the fountain of youth of TE materials research In the past two decades, many potentially paradigm-changing mechanisms were identified, eg, resonant levels, modulation doping, band convergence, classical and quantum size effects, anharmonicity, the Rashba effect, the spin Seebeck effect, and topological states These mechanisms embody the current states of understanding and manipulating the interplay among the charge, lattice, orbital, and spin degrees of freedom in TE materials Many strategies were successfully implemented in a wide range of materials, eg, V2VI3 compounds, VVI compounds, filled skutterudites and clathrates, half-Heusler alloys, diamond-like structured compounds, Zintl phases, oxides and mixed-anion oxides, silicides, transition metal chalcogenides, and organic materials In addition, advanced material synthesis and processing techniques, for example, melt spinning, self-sustaining heating synthesis, and field-assisted sintering, helped reach a much broader phase space where traditional metallurgy and melt-growth recipes fell short Given the ubiquity of heat and the modular aspects of TE devices, these advances ensure that thermoelectrics plays an important role as part of a solutions package to address our global energy needs OUTLOOK The emerging roles of spin and orbital states, new breakthroughs in multiscale defect engineering, and controlled anharmonicity may hold the key to developing next generation TE materials To accelerate exploring the broad phase space of higher multinary compounds, we need a synergy of theory, machine learning, three-dimensional printing, and fast experimental characterizations We expect this synergy to help refine current materials selection and make TE materials research more data driven We also expect increasing efforts to develop high-performance materials out of nontoxic and earth-abundant elements The desire to move away from Freon and other refrigerant-based cooling should shift TE materials research from power generation to solid-state refrigeration International round-robin measurements to cross-check the high ZT values of emerging materials will help identify those that hold the most promise We hope the renewable energy landscape will be reshaped if the recent trend of progress continues into the foreseeable future

Consolidation/synthesis of materials by electric current activated/assisted sintering

Abstract: This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.