Dachamir Hotza

Bio: Dachamir Hotza is an academic researcher from Universidade Federal de Santa Catarina. The author has contributed to research in topics: Ceramic & Tape casting. The author has an hindex of 36, co-authored 402 publications receiving 6577 citations. Previous affiliations of Dachamir Hotza include University of Limoges & University of Hamburg.

Review: aqueous tape casting of ceramic powders

Abstract: Slurry formulations and processing parameters of the water-based tape casting of ceramic powders are reviewed. Additives include binders, like cellulose ethers, vinyl or acrylic-type polymers; plasticizers, like glycols; and dispersants, like ammonium salts of poly(acrylic acids). Mostly alumina powders have been employed. Hydrophobing of ceramic powders permits the aqueous processing even of water-reactive powders, like aluminium nitride. Non-toxicity and non-inflammability of water-based systems represent an alternative to organic solvent-based ones. Aqueous slurries are, on the other hand, complex multiphase systems, very sensitive to process variations. Statistical design of experiments was used for the improvement of the process.

Current developments in reversible solid oxide fuel cells

Abstract: Solid Oxide Fuel Cells (SOFC) and Solid Oxide Electrolyte Cells (SOEC) are often considered precluded mainly by their high cost, even when several technical issues have been continuously tackled over the past decades. Our energetic matrix is essentially based on finite fuel sources, which involve the emission of environmentally hazardous pollutants. Nevertheless, now there are several feasible and profitable benign routes for energy generation through solid oxide cells development, mainly for cells capable to produce energy and store it employing hydrogen as energy carrier. Those cells act reversibly as fuel or electrolyzer systems, which may be integrated in hybrid renewable energy plants and may be referred to as Reversible Solid Oxide Fuel Cells (RSOFC). In this article, the operation principles of SOEC and SOFC and the current state of the electrolyte, fuel and oxygen electrodes has been reviewed and discussed in detail. Each major section is divided into materials families, including manufacturing issues. Novel materials and processing techniques are currently in development and are summarized here. Moreover, key-points are suggested to overcome the known drawbacks and to improve the performance and economic feasibility in order to enhance the commercialization of RSOFC technology.

Effect of nano-SiO2 and nano-TiO2 addition on the rheological behavior and the hardened properties of cement mortars

Abstract: This paper reports on the use of nano-SiO2 (nS) and nano-TiO2 (nT) in cement pastes and mortars. Samples with 0–3 wt.% nS, 0–12 wt.% nT and 0.5 water/binder weight ratio were prepared. Rheological and flow table measurements were carried out. In addition, the design of experiments was applied to validate the results found. The temperature of hydration and compressive strength with 28 days was also determined. In general, mortars exhibited noticeable differences in the rheological behavior, but less evident in temperature of hydration and compressive strength. The values of torque, yield stress and plastic viscosity of mortars with nanoadditives increased significantly, reducing the open testing time in rheology tests. Meanwhile, the flow table values reduced. In addition, spread on table and initial yield stress exhibited a power correlation, while the spread on table and plastic viscosity did not show any special relationship. The results of kinetics of hydration followed the same tendency found by rheology, in which samples with higher amounts of nS and nT showed remarkable changes in relation to the samples without nanoadditives. Mechanical properties were not significantly affected by nanoparticles in the range considered in this work.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

American Society for Testing and Materials

Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

Ultracapacitors: Why, How, and Where is the Technology

Abstract: The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Processing Routes to Macroporous Ceramics: A Review

Abstract: Macroporous ceramics with pore sizes from 400 nm to 4 mm and porosity within the range 20%–97% have been produced for a number of well-established and emerging applications, such as molten metal filtration, catalysis, refractory insulation, and hot gas filtration. These applications take advantage of the unique properties achieved through the incorporation of macropores into solid ceramics. In this article, we review the main processing routes that can be used for the fabrication of macroporous ceramics with tailored microstructure and chemical composition. Emphasis is given to versatile and simple approaches that allow one to control the microstructural features that ultimately determine the properties of the macroporous material. Replica, sacrificial template, and direct foaming techniques are described and compared in terms of microstructures and mechanical properties that can be achieved. Finally, directions to future investigations on the processing of macroporous ceramics are proposed.