|Krystyna Pietrzak, Natalia Sobczak, Jerzy J. Sobczak, Adam Klasik, Artur Kudyba, Paweł Darłak, Piotr Długosz, Andrzej Wojciechowski, Edmund Sienicki
The sessile drop method was adopted to investigate the effect of multiple re-melting and casting of metal matrix composite on the structural stability of metal-ceramic slurry. Commercial aluminum matrix composite made of the A359Al alloy reinforced with about 20 vol. % Al2O3 particles was produced by DURALCAN and next re-melted and re-cast ten times using two casting methods, i.e. conventional gravity casting and squeeze casting. The samples taken from all composite ingots produced after every cycle of re-melting and re-casting were used for high temperature tests at a temperature of 850°C for 30 min, under vacuum conditions. Both direct observations of the behavior of composite samples placed on alumina substrates during their contact heating and at the test temperature as well as the detailed structural characterization of solidified droplets have shown high structural stability of the metal-ceramic slurry, irrespective of the number of re-melts and type of casting process used afterwards. The high stability of the originally obtained composite microstructure in each subsequent re-melting step in this study also entitles one to question the widely accepted opinion on the difficulties with re-melting of cast composites, and thus their unsuitability for recycling.
Keywords: metal matrix composites, recycling, multiple re-melting, stability of metal-ceramic slurry, sessile drop method,
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Dorota Wilk-Kołodziejczyk, Adam Kowalski, Andrzej Opaliński, Krzysztof Regulski, Barbara Mrzygłód, Grzegorz Gumienny, Krzysztof Jaśkowiec
The study analyzes the effect of Ni and Cu additions on the mechanical properties of ADI cast iron in casts with different wall thickness values. The applied experiment plan included the use of combinations of the Ni addition in the amount of 0.5% and 1.5% and the Cu addition in the amount of 0.5% and 1.0%. The content of the remaining elements equaled: C = 3.3-3.6%, Si = 2.2-2.6%, Mn = 0.10-0.13%, P max. 0.05%, S max. 0.020% (wt. %). Four cast iron melts were performed, by way of casting ingots with a thickness of 25 mm, 50 mm and 75 mm. The cast iron spheroidization was conducted by the flexible conduit method (steel envelope filled with magnesium). In the casting moulds, a special filtering-modifying system was applied. From each melt and each ingot, strength samples were prepared. After isothermal quenching, Rm and A5 were measured. The approximating polynomials (Rm, A5) = f(Ni,Cu) were elaborated. The polynomials make it possible to select the optimal Ni and Cu additions to obtain the required strength or plasticity. Based on the polynomials, three-dimensional diagrams illustrating the above relations were constructed.
Keywords: ADI cast iron, thermal treatment, mechanical properties, structure,
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The aim of the study was to determine the thermophysical characteristics of CuNiMoMn austempered ductile iron (ADI) obtained as a result of standard, one-step heat treatment performed at various temperatures.
Temperature-dependent physical properties of structurally differentiated CuNiMoMn ADI were measured using thermal analysis techniques. Coefficient of thermal expansion, specific heat capacity, density, thermal diffusivity and thermal conductivity can be utilized in designing technological applications, developing databases and computer modeling of austempering heat treatment of ductile cast iron.
Austempering heat treatment causes a significant decrease in thermal diffusivity of ADI as compared to the initial as-cast ductile iron, in the temperature range of stability of ausferritic structure. It was found that as the temperature of isothermal transformation increases, the thermal diffusivity and thermal conductivity decreases despite an increase in the amount of carbon-enriched austenite. This can be explained by the predominant influence of fine acicular ferritic structure on the properties of heat transport in the ADI under study.
Keywords: ADI, ausferrite, thermal analysis, thermophysical properties, thermal conductivity,
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The study attempts to complement the information on the effect of the density of moulding sands with inorganic binders on basic strength parameters, i.e. the tensile and bending strength of moulding sands with hydrated sodium silicate, after the process of fast microwave heating. The tests applied fresh medium quartz sand and three types of commercial non-modified hydrated sodium silicate with a molar module (SiO2/Na2O) ranging from 1.9 to 3.4. The masses made of 0.5 wt. % of water and 1.5 wt. % of binder underwent vibrational densification so as, to obtain different apparent densities (ϱ0) of the moulding sand. The examined strength parameters, after hardening and cooling of the mass samples, were compared to apparent density. The results of the studies of the effect of a diversified density were referred to in the literature data. The occurrence of relations between the apparent density and the tensile and bending strength of the hardened masses was confirmed by means of linear models for advantageous microwave heating, similarly to the previously discussed cases of the use of chemical methods of curing inorganic binders. Also, based on the performed tests, similar strength increases were established, as a result of the changes in the apparent density of the microwave heated masses to those which were observed in the chemically hardened masses. The tests results were used to evaluate the quality of the chemical binders applied in casting according to the strength criteria per 1 wt. % of binder in the mass. In the case of all the tested inorganic binders, an advantageous ratio of strength recalculated to 1 wt. % of binder above the value of 1.20 g/cm3 of the apparent density of the masses based on medium quartz sand, was established.
Keywords: casting, moulding sand, hydrated sodium silicate, density, microwave,
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The process of bonding by polymerization of methacrylamide was performed in situ on a quartz matrix at 25°C as well as in a microwave field (150°C; 800 W; 2.45 GHz). The composition of the reaction mixture, beside methylacrylamide as the monomer, was: the initiator (ammonium persulfate), the activator (N,N,N’,N’-tetramethylethylenediamine), the fluidizer (sorbit) and the quartz matrix. The structural changes occurring as a result of macromolecular reactions in the reaction mixture during the process of methacrylamide polymerization and then consolidation of the matrix grains, were determined by means of Fourier transform infrared spectroscopy (FTIR). It was found that during the cross-linking, new bonds are formed within the polar groups, of the following types: -OH, >NH, >C=O and silanol (Si-O). Also, a thermoanalysis of the reaction system was performed in the temperature range of 25-500°C with the use of dispersed reflection spectroscopy (FTIR-DRS). These studies aimed at determining the temperature range in which we can observe changes connected with the cross-linking of the system, and not its thermodestruction. For the obtained post-reaction system, SEM microscopic examinations were performed. The obtained knowledge of the bonding process, preceded by methacrylamide polymerization performed in situ on a quartz matrix, will make it possible to conduct further research in the scope of the technology of forming and consolidating polymer-silicate systems with the method of 3D printing.
Keywords: gelcasting, polymerization, cross-linking, hardening, polymethacrylamide, mineral matrix,
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Beata Grabowska, Żaneta Kurleto-Kozioł
This paper presented the spectral study (FTIR, UV-Vis) for samples of non-activated bentonite (calcium) which has in its composition a main mineral resource, montmorillonite (MMT). MMT, as a component which contains calcium ions (Ca-MMT, was modified physically and chemically. The process of physical activations was initiated by an ultrasound field (40 kHz) with the use of a modificator in the form of potassium carbonate with an activation time of 1 h. To measure the efficiency of the modification for modified physically and chemically samples of montmorillonite (K-MMT) in bentonite there was performed a cycle of test including structural (FITR) and spectrofotometric (UV-Vis) analysis. It was stated that the type and method of making the modification including change of time in which physical factors are influencing the non-activated bentonite influences on the change of ion exchange of montmorillonite (CEC). Both modified physically (ultrasound) and chemically (potassium cations) MMT in calcium bentonite exhibits CEC on a slightly lower level than CEC used in the moulding sand technology of sodium bentonite. Modified MMT can be therefore used as an alternative material for green sand.
Keywords: montmorillonite, montmorillonite modification, ion exchange, CEC, ultrasound field,
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Karolina Kaczmarska, Beata Grabowska
Structural (FTIR) and thermo-analytic (DRIFT) studies were conducted on modified starch in the form of sodium salt of carboxymethyl starch (CMS-Na0.6) in the initial state, i.e. a colloidal solution, and in a cross-linked form prepared by physical means (temperature, microwave radiation). Modified starch CMS-Na0.6 was obtained by way of etherification of potato starch. The first part of the article presents the structural analysis of CMS-Na0.6 before and after cross-linking by means of physical factors based on the results of infrared spectroscopy tests (FTIR) obtained with the use of the transmission technique. The second part identifies the structural changes in the etherified starch with the use of Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFT), recording the spectra in the temperature range of 25-500°C. Based on the courses of the obtained IR spectra, it was established that during the operation of physical factors (temperature, microwave radiation), cross-linking of the colloid CMS-Na0.6 was observed as a result of total evaporation of the solvent water and next dehydration and formation of intra- and intermolecular cross-linking hydrogen bonds. The spectroscopic method DRIFT was applied to determine the progress of the thermal decomposition of CMS-Na0.6 during a controlled temperature increase in the range of 25-500°C. It was established that the process of thermal degradation begins already at 280°C. The performed analysis of the obtained structural test results constitutes a complementation of the research conducted in the scope of applying etherified starch as a binder in moulding sand technology.
Keywords: spectroscopic studies, cross-linking, polymer binder, modified starch,
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