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Synthesis of multiphase forsterite–spinel ceramics with improved properties
Nguyen, Martin ; Keršnerová, Lucie (referee) ; Nevřivová, Lenka (referee) ; Vejmelková, Eva (referee) ; Sokolář, Radomír (advisor)
This doctoral thesis is concerned with the synthesis of multiphase forsterite–spinel ceramics with improved properties in comparison with conventional forsterite ceramics. The objective of this work was to optimize the designed raw material mixtures in dependence on the production technology and resulting parameters, particularly in terms of phase composition, microstructure and refractory properties. The results of the research demonstrated an improvement in thermal shock resistance and modulus of rupture as a result of the synergistic effect of the individual phases in terms of the microstructure. In the end, the industrial applicability of the selected mixtures was verified by the corrosion resistance testing against several materials.
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Influence of CaO Content on Specific LCC, ULCC and NCC Properties
Zemánek, David ; Nevřivová, Lenka
Castables are widely used refractory materials with variable applications. Three types of castables (low cement, ultra-low cement and no cement) were tested to compare their specific properties. Also, corrosion resistance test as an important factor influencing castables design was carried out. Potassium carbonate was used as a corrosive medium using static crucible method. The corrosion mechanisms were evaluated by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The results confirmed that the presence of higher amount of calcium oxide from the Calcium Aluminate Cement (CAC) leads to formation of calcite and anorthite. The corrosion resistance was improved with decreasing or replacing the hydraulic bond.
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Corrosion Resistance and Microstructure of Refractory Forsterite-Spinel Ceramics
Nguyen, Martin ; Sokolář, Radomír
This article examines the process for the synthesis of forsterite–spinel refractory ceramics utilizing fly ash and reactive alumina as raw materials. Raw materials were pre-treated, mixed, and sintered at 1 550 °C for 3 h. Sintered samples were characterized by XRD and SEM. Porosity, water absorption, bulk density, refractoriness, refractoriness under load, thermal shock resistance and corrosion resistance by iron and clinker as corrosive media were also investigated. The impact of different raw material mixtures was investigated in accordance with the resulting properties, microstructure, and corrosion resistance of all fired samples. Higher amount of spinel in fired samples led to improved microstructural and mechanical properties and thermal shock resistance.
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Physical properties of ultrafine-grained polycrystals of magnesium based alloys
Vrátná, Jitka
The objective of the thesis is the study of microstructure evolution, mechanical properties, defect structure and corrosion resistance of ultra-fine grained magnesium alloy AZ31 prepared by a combined two-step process: the extrusion and the equal-channel angular pressing (ECAP). The microstructure development was studied using light and transmission electron microscopy and electron backscatter diffraction (EBSD). Mechanical properties were studied by microhardness measurement and tensile tests and the defect structure by positron annihilation spectroscopy (PAS). The results of tensile tests indicates that the characteristic stress σ0.2 increases slightly with increasing number of ECAP passes only to the second pass and then decreases significantly with additional ECAP straining. This behaviour is in accordance with the results of PAS. EBSD measurements show that the microstructure of extruded and ECAPed material has a bimodal distribution of grain sizes. The bimodal distribution becomes homogeneous with increasing number of ECAP passes and no remaining large grains are observed after 8 passes. The average grain size in the specimen after 8 passes is in the submicrometer range and the fraction of high-angle grain boundary (HAGB) is approximately 80%. The extruded specimens after 8 ECAP passes show...
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Vznik korozního makročlánku u rozebíratelných i nerozebíratelných spojů
Daněk, Lukáš
This diploma thesis is focused on corrosion degradation of technical materials used for fire trucks production. It describes what is corrosion, corrosion environment and protection against effects of corrosion. Further, the thesis describes methods of joining materials in the production of fire tank trucks. In the experimental part the thesis deals with the examination of samples during mechanical and corrosion tests with subsequent evaluation. The examined samples are exposed to the effects of salt mist and then subjected to tensile testing. The most suitable method of joining materials for the construction of fire tank trucks is verified here.
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Physical properties of ultrafine-grained polycrystals of magnesium based alloys
Vrátná, Jitka
The objective of the thesis is the study of microstructure evolution, mechanical properties, defect structure and corrosion resistance of ultra-fine grained magnesium alloy AZ31 prepared by a combined two-step process: the extrusion and the equal-channel angular pressing (ECAP). The microstructure development was studied using light and transmission electron microscopy and electron backscatter diffraction (EBSD). Mechanical properties were studied by microhardness measurement and tensile tests and the defect structure by positron annihilation spectroscopy (PAS). The results of tensile tests indicates that the characteristic stress σ0.2 increases slightly with increasing number of ECAP passes only to the second pass and then decreases significantly with additional ECAP straining. This behaviour is in accordance with the results of PAS. EBSD measurements show that the microstructure of extruded and ECAPed material has a bimodal distribution of grain sizes. The bimodal distribution becomes homogeneous with increasing number of ECAP passes and no remaining large grains are observed after 8 passes. The average grain size in the specimen after 8 passes is in the submicrometer range and the fraction of high-angle grain boundary (HAGB) is approximately 80%. The extruded specimens after 8 ECAP passes show...
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Galvanic zinc coating
Půček, František ; Dvořák, Milan (referee) ; Žák, Ladislav (advisor)
This thesis is based on elaboration and full description of galvanic zinc coating, operations and technologies used in them. The thesis is aimed on analysis of corrosion. How is it formed and how is it spreading. The thesis is also aimed on physical-chemical process which takes place on the surface of coated part during technologies used in galvanic zinc coating. The thesis also emphasize on choosing the right method so we can achieve the best results and good economic conditions. In conclusion the thesis analyzes defections in galvanic zinc layer.
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Evaluation of electrochemical characteristics of AZ31 wrought magnesium alloy
Hána, Tomáš ; Tkacz, Jakub (referee) ; Drábiková, Juliána (advisor)
This thesis deals with the issue of electrochemical characterization of AZ31 wrought magnesium alloy, which was exposed to corrosive environment of 0.1 moldm3 solution of sodium chloride. Electrochemical impedance spectroscopy and potentiodynamic tests were used for evaluation of electrochemical characteristics such as corrosion rate, corrosion current density, corrosion potential and polarization resistance. There is a summary of ways of a production of magnesium alloys, influence of alloying element on properties of material and types of corrosion, which leads to degradation of material in the theoretical part. In the experimental part there is characterization of used methods, summary of results and a discussion of obtained data and its comparison.
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Surface treatment of spherical pin
Plášil, Petr ; Kubíček, Jaroslav (referee) ; Žák, Ladislav (advisor)
Diploma thesis is worked-up as a part of master’s studies of engineering technology M2I – K, analyzing the possible methods of surface treatment of spherical pin, that increase its corrosion resistance. Spherical pin is mounted into several types of chassis components such as joints, control arms, etc. The current situation is inconvenient for manufacturers, insufficient corrosion protection increases the number of complaints and this may be reflected in the number of future orders. Via of suitable surface treatment is to achieve a higher corrosion resistance while maintaining the functional properties of pins used.
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