Structure and Crystallization of High-Calcium, CMAS Glass Ceramics Synthesized with a High Content of Slag

In this work, more than 70 wt % of ferromanganese slag (containing 40 wt % CaO) was used to synthesize high-calcium, CaO-MgO-Al2O3-SiO2 (CMAS) glass ceramics. The effect of SiO2/CaO on the structure, crystallization behavior and microstructure of high-calcium, CMAS, slag glass ceramics was studied by IR, NMR, DSC, XRD and SEM. The results showed that in the high-calcium, CMAS glass ceramics, the main existing forms of silicon–oxygen tetrahedra (Qn) were Q0 and Q1. With the increase in the SiO2/CaO, Qn changed from Q0 and Q1 (main units) to Q1 (main units) and Q2, and then to Q1 and Q2 (main units). The polymerization degree of Qn changed from low to high, making the glass more stable, which led to the increase in crystallization temperature and the decrease in crystallization kinetic constant (k) and frequency factor (υ). At the same time, the change in the Qn structure resulted in a gradual change to the main crystal, from akermanite to diopside–wollastonite.

DETERMINATION OF THE COMPRESSION STRENGTH RP OF MULTILAYER PLATES MADE OF SLAGOSITALS

The methodology of creating multifunctional acoustic automated devices has been further developed, it is based on the construction of simple algorithms for transforming and processing signals of measuring instruments. A differential acoustic method for controlling the physical and mechanical parameters of multilayer plates made of slag glass-ceramics has been investigated. A structural diagram of an automated device for measuring acoustic control of the ultimate compressive strength Rр of a controlled slag glass-ceramics plate is proposed. The option of automation of the measurement process considered in the article makes it possible to carry out measuring control of the strength characteristics for a relatively short period of time and by averaging the results of measurements of the physical and mechanical parameters of slag glass-ceramic plates, leads to a decrease in the values of random measurement errors and thereby contributes to an increase in the accuracy of measurements of physical and mechanical parameters of slag glass-ceramics products. The values of the relative increments of the attenuation coefficient ∆ƞ23/ƞ4were obtained, while the ranges of the values of the attenuation coefficient of a transmission of various waveforms of the piezoelectric transducer correspond to the ranges of the compressive strength Rр of the test sample. At the same time, the control of the strength of the material Rр at multiple frequencies is due to the fact that even a slight change in the geometric parameters of the slag glass-ceramics slab leads to a change in the generalized parameters of the universal transformation functions of the measuring differential acoustic devices, which are associated with the physical and mechanical characteristics of the controlled material of the sample The proposed two-parameter differential acoustic control method allows to keep in mind the linkage between temperature and mechanical parameters: the unequal distribution of the temperature along the length of the sample and the uneven distribution deformation of temperature with the localization of this plastic component in the middle part of the slag glass-ceramics plate, which is most significantly affected by temperature and, as a consequence, is subject to gradual destruction.

Research Progress of Slag Structure and Hydration Activity

Slag is widely used as mineral admixtures in cement-based materials by its potential hydration activity. It has the advantage of saving resources and energy, reducing carbon emission, improving the performance of concrete, and plays an increasingly important role in the building materials industry. But the early strength of slag is low, and the industrialization of useful hydration products also need to be activated, so the utilization rate of slag in high grade cement is restricted. The hydration activity of slag depends not only on the content of vitreous in slag, but also on the structure of vitreous slag. To explore slag glass micro composition and structure of its active role, The slag micro-structure was analyzed from the structure levels, and then the factors affecting the activity of slag was evaluated. The potential advantages and disadvantages of some different methods to active slag were discussed such as physical ways, chemical activation method and compound activation way. The existing problems and development direction of improving the activity of slag were summarized , which could provide a valuable reference for the efficient use of slag.

Effect of Al2O3/SiO2 on the structure and properties of blast furnace slag glass-ceramics

Different Al2O3/SiO2 glass-ceramics were prepared from blast furnace slag by traditional sintering method. The structure and properties of glasses or glass-ceramics were investigated by DSC, XRD, SEM, FTIR, 27Al MAS NMR. The DSC results showed that with the increase of Al2O3/SiO2, the glass transition temperature (Tg) first increased and then decreased, reached the minimum when Al2O3/SiO2 was 0.34. The volume density, bending strength and microhardness of glass-ceramics also showed the same variation rule. The FTIR and 27Al MAS NMR spectra results revealed this phenomenon. When Al2O3/SiO2 was 0.19, a large amount of Si4+ was added to the glass network to make the structure dense. With Al2O3/SiO2 increased from 0.24 to 0.34, the amount of [AlO6] in the glass increased while [AlO4] decreased, and the degree of network polymerization of the glass decreased; as Al2O3/SiO2 further increased from 0.34 to 0.39, [AlO4] increased and [AlO6] decreased in the glass, and the degree of network polymerization of the glass increased. The XRD results showed that the crystal phase of the glass-ceramics was composed of gehlenite, diopside and hyalophane. Moreover, with the increase of Al2O3/SiO2, the gehlenite content in the glass-ceramics increased, while the content of diopside and hyalophane decreased.

Effect of curing conditions on the compressive strength of sodium carbonate activated slag-glass powder mortar

This study presents the experimental investigation of the effect of curing media on the properties of mortar mixtures made with sodium carbonate activated slag-glass powder as a binder. Slag and glass powder were used at an equal percentage as the aluminosilicate precursor and the binary blend was activated with sodium carbonate. The compressive strength and ultrasonic pulse velocity of the mixtures cured in different conditions were investigated. The curing conditions used in this study are dry, moist, and submerged curing. Microstructural investigations were also carried out to understand the microstructural properties of the mixtures exposed to these curing conditions. Results from this study showed that moist curing is the most effective curing method for mortar made with sodium carbonate alkali-activated slag-glass powder as a binder. Microstructural evaluations further confirm the strength results as mortar samples cured in a moist condition exhibited a denser microstructure.

Wildfire-driven release of metal(loid)s from topsoils in a smelter-polluted semi-arid area: an experimental approach

<p>Wildfires contribute to global emissions of trace elements. This study focuses on highly polluted areas near an operating copper smelter and old mine-tailing disposal sites in Tsumeb (semi-arid north of Namibia), where wildfires frequently occur. Capturing of particulates windblown from the ore processing and smelting areas by vegetation (trees, grass) leads to the topsoil enrichment with metal(loid) contaminants (up to 7090 mg/kg Cu, 2070 mg/kg As, 4820 mg/kg Pb, 3480 mg/kg Zn, 75 mg/kg Cd, 7.66 mg/kg Hg). Experimental samples corresponding to representative biomass-rich topsoils (bushland with acacia and marula trees, grassland) were investigated using a combination of mineralogical and geochemical methods. Wildfires were simulated using a thermodesorption (TD) technique (75-670 °C; Hg) and an experimental setup composed of a temperature-controlled furnace (250-850 °C), an aerosol-filtering unit and a gas-trapping device (As, Cd, Cu, Pb, Zn). The obtained ashes were investigated to depict any mineralogical and chemical transformations in order to understand temperature-dependent release of metal(loid) contaminants during the simulated wildfire.</p><p>Thermodesorption experiments indicated that more than 90% of Hg was released at ~340 °C, which corresponded to predominant grassland-fire conditions. A comparison with the TD curves of the Hg reference compounds confirmed that the Hg in the biomass-rich topsoils occurs as a mixture of Hg bound to the organic matter and metacinnabar (black HgS), which exhibited similarities with the TD pattern of smelter flue dust residue. Temperature-dependent release of other metal(loid)s (As, Cd, Cu, Pb, Zn) is dependent on their solid-state speciation. Cadmium is released at ~750 °C, corresponding to the thermal decomposition of carbonates, in which Cd is mainly bound. Arsenic exhibits first remobilization step at <350 °C (decomposition of arsenolite, As<sub>2</sub>O<sub>3</sub>) and the second step at >650 °C corresponding to the instability of arsenates and As-rich slag glass. Other contaminants (Cu, Pb, Zn) were mainly bound in carbonates, slag particles and sulfides/sulfosalts. During the simulated wildfire, they were mainly retained in the ash and were remobilized to a lesser degree at >650 °C. Calculations indicated that at 850 °C (worse-case wildfire scenario) 2-17 % of total As, Cu, Pb and Zn, 27-79 % of total Cd and 100 % of Hg can be volatilized from these biomass-rich contaminated topsoils.</p><p>This study was supported by the Czech Science Foundation (GACR project no. 19-18513S) and a student grant from the Grant Agency of Charles University (GAUK no. 1598218).</p>