Technologie hmot a dílců AdMaS

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    The role of different high energy ball milling conditions of molybdenum powder on the resulting particles size and morphology
    (Tanger Ltd., 2019-05-24) Dyčková, Lucie; Casas Luna, Mariano; Torres Rodríguez, Jorge Alberto; Dyčka, Martin; Jech, David; Dvořák, Karel; Deák, Andréa; Čelko, Ladislav
    High energy ball milling is a powder processing method in which the powder particle size can be decreased to micrometer size in a relatively short period of time. This method is based on the friction and the high energy kinetic collisions between the balls and the trapped powder particles. The milling process is influenced by many process variables such as mainly the rotational speed, ball to powder weight ratio and processing time. In the present study, high energy ball milling process was performed for molybdenum powder using a high energy ball mill under different milling conditions varying the: (i) rotational speed from 600 to 800 rpm, (ii) ball to powder weight ratio of 100:3 and 100:6, (iii) milling time in the range of 10 to 60 minutes, (iv) process control agent using polyethylene glycol, and (v) milling atmosphere under air or nitrogen. The used initial molybdenum powder was of globular morphology and 100 µm in particle size. The powders after milling were characterized by a scanning electron microscope (SEM) and a laser diffraction size analysis. The particle size of milled powders was decreased down to 1.1 µm. As the most effective ball to powder weight ratio was found 100:6 with the milling speed of 800 rpm. The milling time played a crucial role for the refinement of particles up to 45 min, where the further milling had negligible effect on the overall trend of particle size evolution.
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    Fracture Mechanism of Interpenetrating Iron-Tricalcium Phosphate Composite
    (Trans Tech Publications, 2017-01-01) Horynová, Miroslava; Casas Luna, Mariano; Montufar Jimenez, Edgar Benjamin; Díaz de la Torre, Sebastian; Čelko, Ladislav; Klakurková, Lenka; Diéguez-Trejo, Guillermo; Dvořák, Karel; Zikmund, Tomáš; Kaiser, Jozef
    The usage of iron alloys for bone fractures treatment has been limited due to its high density and elastic modulus, as compared to bone. In contrast, the use of tricalcium phosphate (TCP), a ceramic that promotes bone healing, is mostly limited by its brittle nature. In the present work the fracture mechanism of a novel iron-TCP interpenetrated composite fabricated by spark plasma sintering was studied. Specimens were subjected to a diametral tensile-strength-test. The work of fracture was determined by indirect tensile loading conditions using the diametral tensile strength test. The results revealed that iron has a clear toughening effect on the microstructure of tricalcium phosphate specimens consolidated by spark plasma sintering. This is a promising result to overcome the limited usage of tricalcium phosphate to treat only non-load bearing bone defects.
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    Metal matrix to ceramic matrix transition via feedstock processing of SPS titanium composites alloyed with high silicone content
    (Elsevier, 2018-06-15) Tkachenko, Serhii; Čížek, Jan; Mušálek, Radek; Dvořák, Karel; Spotz, Zdeněk; Montufar Jimenez, Edgar Benjamin; Chráska, Tomáš; Křupka, Ivan; Čelko, Ladislav
    Titanium silicides are promising candidates for use as a reinforcement in advanced light-weight composites due to their excellent mechanical properties and oxidation resistance at high temperatures, sufficient wear resistance, and high chemical stability in various corrosion environments. Direct in-situ synthesis of such composites from titanium-silicon (Ti-Si) powder feedstock by spark plasma sintering (SPS) was used in this study with a particular attention on the effect of the powder processing parameters (blending, co-milling, milling blending) on the microstructure formation and mechanical properties of the sintered composites. As opposed to the previous silicide-reinforced Ti studies, this was done for high silicone content (20 wt%). It was found that, despite the powders initial identical composition, the microstructure and phase content of the compacts varied significantly with the used powder fabrication route. Taking advantage of this, composites ranging from relatively soft metal-matrix (52 vol% metallic Ti; using non-milled Ti and coarse or fine-milled Si) to hard ceramic-matrix (11 vol% metallic Ti, using fine-dispersed joint-milled mixture of Ti and Si) were obtained. Due to in-situ formation of various TiSi2, TiSi, Ti5Si4 and Ti5Si3 silicide reinforcement phases contents with high hardness and stiffness, all the sintered composites showed superior hardness and wear resistance (an increase as much as 44) in comparison to pure Ti. Importantly, hardness and elastic modulus of intermediate compounds TiSi2, TiSi, Ti5Si4 and Ti5Si3 were measured using instrumented indentation technique for the first time and are presented in the paper.
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    The evaluation of the effect of crystallization additives on long term durability of self-compacting concrete
    (IOP Publishing, 2018-07-16) Dufka, Amos; Melichar, Tomáš
    The article deals with the influence of crystallisation additives on the life of self-compacting concrete (so-called SCC concrete) in case of exposure to aggressive gases. The effect of crystallization additives on the properties of such modified composites is generally tested during exposure of liquid media, in this case the attention is focused on influence of selected types of aggressive gases (CO2 and SO2). The impact of individual types of aggressive gases is assessed on the basis of a set of physico-mechanical and physico-chemical analyses.
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    Impact of Aggressive Media on the Properties of Polymeric Coatings with Solidification Products as Fillers
    (MDPI, 2019-11-26) Hodul, Jakub; Mészárosová, Lenka; Žlebek, Tomáš; Drochytka, Rostislav; Dufek, Zdeněk
    Dealing with waste materials, particularly hazardous waste, is a serious problem. Disposal areas keep growing, and the costs incurred are high. Disposing of such waste reduces negative environmental impacts and offers considerable financial savings. This paper focuses on the possibilities of incorporating pollutants found in hazardous wastes as fillers in coatings based on polymers (epoxide and polyurethane). These coatings are intended mainly for concrete and metal bases and offer secondary protection against adverse weather conditions. Important physical and mechanical properties of the newly developed materials were determined; they include surface hardness, impact resistance, tensile properties, and chemical resistance. These properties were also compared to those of the reference filler. At the same time, the influence of aggressive media on the properties of these materials was observed, in particular on flexural characteristics. The microstructures of the developed coatings were tested using a high-resolution optical microscope, before and after exposure to the chemicals. The positive effect of using progressive fillers, such as solidified hazardous waste (a solidification product (SF)), was witnessed by their constructive contribution to the materials’ physical and mechanical properties. The use of solidification products is unambiguously advantageous from technical, ecological, and economical stand points (utilization of hazardous waste as a progressive filler instead of landfilling, improvement of tensile properties, reduction in the price of coating system, and incorporation of the pollutants into the polymer matrix).