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Concretes, depending on their application, may be exposed to elevated temperatures during their lifetime, especially when placed near or in a furnace or during an accidental fire. The thermal stability of alkali-activated mortars and hydrated mortars prepared using ladle slag and two different aggregates was studied. A commercial calcium aluminate cement was used as a comparison for the properties after exposure to temperatures up to 1000°C. All samples were characterised and analysed through a strength test, dilatometric analysis, thermogravimetric analysis, ultrasonic pulse velocity and scanning electron microscopy. The hydrated ladle slag mortars exhibited properties similar to or better than the commercial calcium aluminate cement, while the alkali-activated ladle slag's thermal properties were inferior to the hydrated ladle slag mortars. The tests also showed that the use of ferrochrome slag aggregates in hydrated ladle slag mortars exhibited similar properties to those using sand aggregate mortars. The damage behaviours of the mortars were dependent on the temperature-induced dehydration, dehydroxylation and thermal incompatibility between the paste and aggregates. The results from this study specify the possibilities of using 100% industrial by-product-based mortar and near-zero carbon dioxide emissions as a fire-resistant material in furnaces, buildings and fireplaces.

This paper deals with the valorization of quartz and felspar rich lithium mine tailings (QFS) in the development of construction materials. Ladle slag was used as green strength increasing agent. Sodium hydroxide and carbonate were used as fluxing agents to allow sintering at 700–900 °C. Of these, sodium hydroxide was found to be the more efficient. The sintered ceramics were characterized by X-ray diffraction, scanning electron microscopy, compressive test, water absorption, apparent density and dilatometry; the results were found to comply with ASTM C62-99 specifications for building brick, and interesting for a sustainable use of resources.

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

Customized square grid arrangements of different groove depths (1.0, 1.5 and 3.0 µm) and separations (10 and 30 µm) were successfully laser patterned, using a nanosecond pulsed fibre laser, on the surface of 10 mol% ceria-stabilized zirconia and alumina (10CeTZP-AlO) nanocomposite discs (diameter: 10 mm; thickness: 1.5 mm). The patterned surfaces and the in vitro biological response of osteoblasts (SAOS-2) towards them were thoroughly analysed. In terms of composition, the laser treatment was found to cause superficial monoclinic-tetragonal zirconia phase transformation and alumina evaporation. In vitro, the most effective grid configuration for osseous differentiation was found to be 1.5 µm groove depth and 10 µm groove separation, and confocal microscopy revealed that the cells show a tendency to be sorted as groove depth increases. It is thought that custom-made patterns could be produced to guide cell attachment in vivo, which could favour implant integration and reduce healing time., This research has been supported by the Spanish Ministry of Science and Innovation (MICINN) under the Project MAT2012-38645 and by the Principality of Asturias under the Project GRUPIN 14-109. Additionally, Lidia Goyos-Ball acknowledges financial support from the JAE-PREDOC (2011) program (CSIC).

Mine tailings account for most of the environmental incidents related to the extractive industry, with risks increasing due to steadily rising tonnage of low-grade ore and extreme weather events. Recycling of tailings in raw-material-intensive applications presents an interesting alternative to costly tailings management with associated restoration efforts. Chemically bonded ceramics may offer a route to upgrading mine tailings into raw materials for ceramics. In this review such chemically bonded ceramic methods that may be used to recycle mine tailings as raw materials, are reviewed while focusing in particular on two methods: 1) geopolymerization/alkali activation and 2) chemically bonded phosphate ceramics. The aim of the review is not to give exhaustive review on the wide topic, but to scope the required boundary conditions that need to be met for such utilization. According to the findings, alkali activation has been studied for 28 separate silicate minerals in the scientific literature, and presents a viable method, which is already in commercial use in calcium-rich cement-like binder applications. Phosphate bonding literature is more focused on phosphate containing minerals and waste encapsulation. Very little work has been done on low-calcium tailings utilization with either technology, and more knowledge is needed on the effect of different pre-treatment methods to increase reactivity of mine tailings in chemically bonded ceramics.

The present study valorized Finnish mining tailings waste to identify opportunities for the use of ceramics technologies. On the basis of their mineralogical and chemical contents, the five selected tailings wastes represented felsic mining tailings (FMT) rich in quartz and alkali feldspars, mining tailings dominated by Mg- and Fe-bearing minerals (MgFeMT), and mining tailings rich in carbonate minerals (CMT). Preliminary pilot studies indicated that the FMT materials are potential secondary raw materials for mullite-type ceramics. An Al additive was needed, since the Al₂O₃ content of the studied tailings was too low for mullitization. In addition, carbonate-bearing tailings with Ca silicates can be applicable for chemically bonded phosphate ceramic (CBPC) synthesis. Based on a literature review, FMT are viable source materials for the production of geopolymers, but a high initial Si:Al ratio (in quartz-rich FMT) may lead to partial geopolymerization. Preliminary results from the geopolymerization of pre-heated phlogopite mica mixed with metakaolin gave promising findings, with the formation of a geopolymer having good compressive strength. The findings support the viability of MgFeMT materials rich in phlogopite mica for the production of alkali-activated ceramics

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 use of industrial by-products as substitute to conventional natural resources in ceramic production is of interest from an environment preservation and solid wastes management. This paper deals with the recycling of tailings from spodumene concentration during lithium production (Quartz Feldspar Sand; QFS), for the production of porcelain and structural materials. The QFS obtained from spodumene processing consisted mainly of quartz, albite, microcline with traces of muscovite. Mixtures of QFS and standard porcelain ingredients were sintered at 1050–1200 °C at 50 °C intervals and their properties were compared with a conventional porcelain composition prepared under the same conditions. Phase composition was assessed by XRD analysis using Rietveld refinement. Tests such as water absorption, apparent density, sintering shrinkage, compressive and flexural strength were used for physical comparison. The results showed that higher densification was achieved at 1200 °C, with a drastic reduction of water absorption below 1%. A compressive strength of 40 MPa was obtained at 1050 °C in the composition made of 50 wt% QFS and 50 wt% kaolin, increasing to 85 MPa at 1100 °C. The strength increase was attributed to better glassy phase formation and mullite growth. The QFS was found to contain no hazardous elements and showed promising sintering results, indicating its high suitability to substitute conventional resources in the production of ceramic materials.

Due to increased production speeds in modern process environments, the loading conditions in sliding contact applications have become more challenging. Therefore it is important to have good understanding of wear mechanisms in high-speed sliding conditions. A wear testing device was manufactured for the purpose of cost-efficient simulation of water-containing high-speed sliding conditions. Sliding speeds up to 40 meters per second can be achieved while abrasive-containing slurry is fed into the contact interface of material samples and a rubber coated drum. High-speed wear tests were run with three ceramic materials: silicon nitride, silicon carbide and partially stabilized zirconia. Wear behavior of these ceramics was analyzed as a function of sliding speed and slurry composition. Results indicate that in mild wear region increase in sliding speed reduced overall wear, whereas in severe wear conditions increasing speed accelerated wear. A transition from mild to severe wear was observed for silicon carbide when tested in alumina-containing slurry. For the materials that had high enough hardness, wear rates were dictated by the respective order of fracture toughness. Visual inspection of the worn samples supported the interpretation of wear mode transition.

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