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This paper presents studies on the utilization of aluminosilicate-based mining tailings as raw materials for mullite-based ceramics. Based on the 3:2 stoichiometric composition, mullite was synthesised by reactive sintering with a series of powder mixtures with alumina additions. X-ray diffractometry and scanning electron microscopy analyses revealed that, at the specific mineralogical composition, mullite structure formed surrounded by an amorphous glass phase in reaction-sintered powder mixtures. Results demonstrated that the chemical and mineralogical composition of mining tailings do have an effect on mullite formation possibilities and, only with the particular mineralogical composition, the mullite formation is possible regardless of the correct Al:Si ratio in tailings. Physical and mechanical properties of the formed ceramics were defined, showing comparable values to 3:2 mullite reference. Mullite structure formation enables a better thermal resistance up to above 1450 °C of the formed tailings-based ceramics compared to other aluminosilicates, reflecting their utilization potential for refractory ceramic applications. acceptedVersion

This paper deals with the synthesis and thermal stability of one-part metakaolin geopolymer composites containing high volume of spodumene tailings (Quartz Feldspar Sand; QFS) and glass wool (GW). One of the objectives of the study was to prepare materials encompassing a maximum amount of waste streams with some potential thermal stability. Several compositions were prepared with sodium metasilicate anhydrous (Na2SiO3) wt.% of 0.5, 2.5, 5, 10 and 12,5. The one-part metakaolin geopolymer composites were cured at 60 °C for 24 h and the mechanical properties were assessed at 7 days and after post-heat treatment at 500, 750, 1000, 1100 or 1200 °C. X-ray diffraction, dilatometry, scanning electron microscopy and thermogravimetry analyses were used to study the stability of the prepared geopolymer composites until 1100–1200 °C. The results showed that more than 20 MPa compressive strength could be achieved with metakaolin geopolymer composites containing only 20 wt% of metakaolin. Metakaolin-GW geopolymer composites were stable up to 500 °C. Meanwhile, their counterparts containing QFS were stable up to 1100–1200 °C; samples prepared with higher dosage of sodium (Na2SiO3 > 5 wt%) retained more than 50% of their initial strength after thermal treatment at 1100 °C. Interestingly, for dosages of Na2SiO3 ≤ 5 wt%, more than 300% increase of strength was observed after thermal treatment at 1100–1200 °C. The use of QFS limited the thermal shrinkage at mild temperatures (

A custom-made slurry-type high-speed rubber wheel wear testing system was modified for measuring friction. Friction behaviour of irregularly rough steel against CSM-rubber in water-lubricated contact at a velocity range of 1.7–17 m/s was investigated. A noticeable friction maximum was observed near the midpoint of the range extremities, at 6.7–8.3 m/s, and the resulting wear marks on steel specimens also suggested the highest severity of contact at these medium speeds. Higher end of sliding velocity range returned friction to lower levels and less wear was observed. This was interpreted as a product of reduction in frictional heat due to slight improvement in mixed lubrication. In conclusion, the peculiar friction behaviour was interpreted as a system-specific anomaly, implying that similar problematics could be encountered in other rubber wheel wear test systems as well. acceptedVersion

The effects of a specific laser patterning on friction of silicon nitride bulk ceramic in water against rubber were investigated. A dimple-like patterning was applied to the surfaces of silicon nitride bulk ceramic blocks with pulsed laser drilling. Friction measurements were conducted with a special device designed for high-velocity sliding wear and friction testing of hard materials in wet conditions. Sliding velocities in the water-lubricated test ranged from 3.3 to 33 m/s and the load was 80 N. Anomalies in friction behaviour were observed in 8.3 and 16.7 m/s, which can only partially be explained with test equipment characteristics. submittedVersion

The aim of this study was to investigate phase transformations and glazing of zirconia bulk ceramic as a function of laser processing parameters. Zirconia-based ceramics have good material properties for a variety of applications. The main advantage of zirconia compared to other structural ceramics, like silicon-based ceramics and alumina, is its high fracture toughness (typically over 10MPa√m). This property is largely based on partial stabilization of zirconia, where a portion of the material is in metastable phase, enabling instantaneous phase transformation under mechanical load. This consumes energy otherwise provided to crack propagation. The stable phase of zirconia to exist in room temperature is monoclinic; therefore a rapid cycle of heating and cooling is necessary for achieving metastable tetragonal phase. Pulsed laser processing offers just the right type of thermal cycle for the aforementioned phase transformation to occur. In this study a nanosecond pulsed laser was used for surface processing of zirconia ceramic blocks. During laser processing high energy can be concentrated into small area, causing sudden local heating, which in turn causes material to melt and vaporize instantly. However, heat dissipation remains small due to the short pulse length, leading to the desirable cycle. Temperatures in the process correlate with several parameters: pulse width, peak energy, repetition rate, pulse overlap, material properties and wavelength. Zirconia is a tough material to process in terms of material removal with laser ablation, since it tends to melt rather than evaporate. submittedVersion