COMPREHENSIVE INVESTIGATION OF PHASE FORMATION MECHANISM AND PHYSICO-MECHANICAL PROPERTIES OF Ca-Mg-SILICATE

This study aimed to investigate extensively the full phase formation mechanism from the lowest temperature to form the phases to the optimum temperature to crystallize akermanite. The effects of various milling speeds and sintering temperatures on physico-mechanical properties of akermanite prepared using high-energy planetary milling method were also investigated. The minimum formation temperature of akermanite phase (above 800°C) was determined by X-Ray diffraction (XRD) and differential thermal analysis. XRD analysis revealed akermanite had formed through gradual phase development with the increase in temperature. Below 700C, akermanite was structurally unstable while multiple transient compounds (low clinoenstatite, wollastonite, monticellite, and diopside) coexisted, as indicated by low peak intensities. Single phase akermanite was obtained by heat-treating at 1100C. Physical studies suggested the densest akermanite ceramic feature, with tensile strength range of 25.26 ± 1.41 MPa32.10 ± 2.13 MPa and Vickers microhardness range of 1.39 ± 0.04 GPa4.94 ± 0.26 GPa could be obtained at 1250°C.

The Gas-Phase Formation Mechanism of Dibenzofuran (DBF), Dibenzothiophene (DBT), and Carbazole (CA) from Benzofuran (BF), Benzothiophene (BT), and Indole (IN) with Cyclopentadienyl Radical

Benzofuran (BF), benzothiophene (BT), indole (IN), dibenzofuran (DBF), dibenzothiophene (DBT), and carbazole (CA) are typical heterocyclic aromatic compounds (NSO-HETs), which can coexist with polycyclic aromatic hydrocarbons (PAHs) in combustion and pyrolysis conditions. In this work, quantum chemical calculations were carried out to investigate the formation of DBF, DBT, and CA from the reactions of BF, BT, and IN with a cyclopentadienyl radical (CPDyl) by using the hybrid density functional theory (DFT) at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. The rate constants of crucial elementary steps were deduced over 600−1200 K, using canonical variational transition state theory with a small-curvature tunneling contribution (CVT/SCT). This paper showed that the production of DBF, DBT, and CA from the reactions of BF, BT, and IN with CPDyl involved six elementary steps: the addition reaction, ring closure, the first H shift, C–C cleavage, the second H shift, and elimination of CH3 or H. The cleavage of the C–C bond was regarded as the rate-determining step for each pathway due to the extremely high barrier. The 1-methyl substituted products were more easily formed than the 4-methyl substituted products. The main products were DBF and 1-methyl-DBF, DBT and 1-methyl-DBT, and CA and 1-methyl-CA for reactions of BF, BT, and IN with CPDyl, respectively. The ranking of DBF, DBT, and CA formation potential was as follows: DBT and methyl-DBT formation > DBF and methyl-DBF formation > CA, and methyl-CA formation. Comparison with the reaction of naphthalene with CPDyl indicated that the reactions of CPDyl attacking a benzene ring and a furan/thiophene/pyrrole ring could be inferred to be comparable under high temperature conditions.

Polymorphism of nanocrystalline TiO2 prepared in a stagnation flame: formation of the TiO2-II phase

Flame-made TiO2 nanoparticles with tunable polymorphs, including the metastable TiO2-II phase, were prepared and a phase formation mechanism was proposed.