Blends of fly ash and natural calcite, mechanically activated for 0–400 s in a planetary mill, were used to synthesize geopolymers at ambient temperature. The calcite content in the blends was 0–10 wt.%. Sodium hydroxide solution was used as an alkaline agent. Mechanical activation of the raw material considerably enhanced its reactivity with respect to the alkaline agent, as was observed using Fourier-transform infrared spectroscopy, isothermal conduction calorimetry, thermogravimetry coupled with mass spectrometry analysis of the evolved gas, and SEM/EDS. The addition of calcite to the fly ash improved the compressive strength of the geopolymers, especially during the early age of curing. For 7 d aged geopolymers based on the 90% fly ash + 10% calcite blend, the strength was 8.0-, 3.5- and 2.9-fold higher than that for the geopolymers based on the unblended fly ash for 30 s, 180 s and 400 s mechanical activation time, respectively. Using Mössbauer spectroscopy, it was revealed that iron present in the fly ash did not play a significant part in the geopolymerization process. The dominant reaction product was sodium containing aluminosilicate hydrogel (N-A-S-H gel). Calcite was found to transform, to a small extent, to vaterite and Ca(OH)₂ in the course of the geopolymerization.

Dimensionality and orientation of hexagonal boron nitride (h-BN) nanosheets are promising to create and control their unique properties for diverse applications. However, low-temperature deposition of vertically oriented h-BN nanosheets is a significant challenge. Here we report on the low-temperature plasma synthesis of maze-like h-BN nanowalls (BNNWs) from a mixture of triethylamine borane (TEAB) and ammonia at temperatures as low as 400 °C. The maze-like BNNWs contained vertically aligned stacks of h-BN nanosheets. Wavy h-BN nanowalls with randomly oriented nanocrystalline structure are also fabricated. Simple and effective control of morphological type of BNNWs by the deposition temperature is demonstrated. Despite the lower synthesis temperature, thermal stability and oxidation resistivity of the maze-like BNNWs are higher than for the wavy nanowalls. The structure and oxidation of the nanowalls was found to be the critical factor for their thermal stability and controlled luminescence properties. Cytotoxic study demonstrated significant antibacterial effect of both maze-like and wavy h-BN nanowalls against E. coli. The reported results reveal a significant potential of h-BN nanowalls for a broad range of applications from electronics to biomedicine.

The effect of modifiers on the hydration of cements was studied by isothermal calorimetry. Thermochemical experiments were carried out using a TAM III isothermal calorimeter (TA Instruments). For the TAM III calorimeter, a method was developed for conducting experiments on monitoring the thermal activity of solid-phase samples with the possibility of repeated use of steel ampoules with a volume of 20 ml. The processes of hydration of Portland cement grade CEM I 42.5B D0 LLC "Holcim Rus" without a modifier and with modifiers polycarboxylate type S (POLYPLAST LLC and «Glass Powder) were studied. Heat release thermograms were recorded, which showed good reproducibility of the results and their similarity with those available in the literature for similar studies carried out according to standard methods using a TAM AIR isothermal calorimeter (TA Instruments). This indicates the reliability of the obtained data and the possibility of using the method proposed in this article to study the processes of hydration of cements. The maximum heat release on the thermograms of samples with a polycarboxylate modifier is observed approximately 20 h after the start of heat release monitoring. Samples without the modifier and with the glass powder modifier show the maximum heat release approximately 10 h after the start of the experiment. Analysis of the results showed that the presence of modifiers leads to increased heat release during cement hydration in relation to its initial composition. Accordingly, it takes less time to complete hydration. However, it is also necessary to take into account the possible risks of violation of the technological modes of operation of the corresponding equipment due to excessive heat release during the hydration of modified cements. For citation: Usacheva T.R., Krainova A.A., Vinogradova L.A., Oganyan V.V., Kokurina G.N., Myshenkov M.S., Anufrikov Yu.A., Shasherina A.Yu., Adamtsevich A.O. Study of the influence of modifiers on the hydration of cement by the method of isothermal calorimetry. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 6. P. 88-93. DOI: 10.6060/ivkkt.20246706.6979.