Al2O3-Al2TiO5-TiO2 composites can be obtained by the infiltration of molecular titanium precursors into presintered α-Al2O3 (corundum) cylinders. Two titanium tetraalkoxides, and two dialkoxy titanium bis(acetylacetonates) serve as precursors for TiO2 (rutile) and Al2TiO5 (tialite). The precursors were infiltrated as ethanolic solutions. After sintering at 1550, 1600, and 1650°C, the prepared ceramics’ properties were investigated by SEM, in-situ HT-XRD, and conventional XRD. Titanium tetraisopropoxide leads to the highest content of Al2TiO5 in the composite. The more reactive the precursor, considering the Al2O3/precursor interface, the lower and more anisotropic the grain growth, the more homogeneous is the TiO2 contribution and the higher is the content of Al2TiO5. Raising the sintering temperature causes an increase of the crystalline Al2TiO5 content as well as of the grain growth. Moreover, the reactivity of the precursor molecule influences the Ti/(Al + Ti) ratio in the obtained tialite phase.
Metallic foams are materials of which the research is still on-going, with the broad applicability in many different areas (e.g. automotive industry, building industry, medicine, etc.). These metallic materials have specific properties, such as large rigidity at low density, high thermal conductivity, capability to absorb energy, etc. The work is focused on the preparation of these materials using conventional casting technology (infiltration method), which ensures rapid and economically feasible method for production of shaped components. In the experimental part we studied conditions of casting of metallic foams with open pores and irregular cell structure made of ferrous and nonferrous alloys by use of various types of filler material (precursors).
The present article describes selected aspects of investment casting technology for manufacturing of open-cell aluminium. The main focus is, among others, on the precursor thickening. Two groups of total 30 samples were produced, basing on open-cell polyurethane foam used as the precursor. Each of the two sample groups was thickened with a different type of suspension consisting of carbonaceous substances and organic binders. The influence of the coating mixture type was compared, leading to conclusions regarding the desired composition and fluidity of the suspensions. Both sample groups of the obtained open-cell aluminium had stochastic cell distributions, the average pore diameter was 5.2 mm and the PPI index was 8. The apparent densities were respectively: 0.485 g/cm3 and 0.312 g/cm3, which reflected the impact of the precursor coating. Additionally, samples from both groups differed in quality.
Internal structure of metal foams is one of the most important factors that determine its mechanical properties. There exists a number of methods for studying the nature of the inner porous structure. Unfortunately most of these processes is destructive and therefore it is not possible to reuse the sample. From this point of view, as a suitable method seems to be the ability of using the so-called X-ray microtomography (also micro-CT). This is a non-destructive methodology used in a number of fields (industry, science, archaeology, medicine) for a description of the material distribution in the space (e.g. pores, fillers, defects, etc.). In principle, this technology works on different absorption of X-ray radiation by materials with changing proton number. The contribution was worked out in collaboration with experts from the Faculty of Electrical Engineering and Computer Science of the VŠB-Technical University of Ostrava and it is focused on the analysis of internal structure of the metal foam casting with irregular arrangement of internal pores by using micro-CT. The obtained data were evaluated in the commercial software VGStudio MAX 2.2 and in the FOTOMNG system. For the evaluation of these data a new specialized module was introduced in this system. Several methods of pre-processing the image was prepared for the measurement. This preliminary processing consists, for example, from a binary image thresholding for better diversity between the internal porosity and the material itself or functions for colour inversion.