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Effect of oxidation on the wetting of coal surfaces by water: experimental and molecular dynamics simulation studies

Li E., Lu Y., Cheng F., Wang X., Miller J. D.

Physicochemical Problems of Mineral Processing

2018

Vol. 54, iss. 4

1039--1051

The wettability of coal surfaces by water continues to be one of the key factors which determines the success of coal flotation. Consequently, oxidation of coal surfaces is a fundamental issue of interest. In this work, the effect of oxidation on the wetting of coal surfaces and the interaction between water molecules and oxygen-containing sites at the coal surface was investigated based on advancing/receding contact angle measurements and molecular dynamics simulations. For the simulation studies, a flat coal surface was constructed with the assistance of the molecular repulsion between graphite surfaces and the assembly of Wiser coal molecules. Our results indicated that the simulated advancing and receding contact angles were very similar, and both of them decreased, as expected, with an increase of hydroxyl sites at the coal surface. The good agreement between the simulated advancing/receding contact angles and the experimental receding contact angle values suggested that the configuration of the systems and the set of parameters for the simulation were appropriate. The spreading of water is mainly due to the hydrogen bonds formed between the interfacial water molecules and the hydroxyl sites at the coal surface. The hydroxyl groups show stronger hydration capacity than other oxygen-containing groups according to the calculated hydrogen bonds and interaction energies.

Preparation and properties of low temperature sintered CaO-B2O3-SiO2 microwave dielectric ceramics using the solid-state reaction

Zhou X., Li E., Yang S., Li B., Tang B., Yuan Y., Zhang S.

Materials Science Poland

2013

Vol. 31, No. 3

404--409

The LTCC CaO–B2O3–SiO2 (CBS) ceramics were synthesized via solid-state reaction process without any sintering aid. The effects of different sintering temperatures and B2O3 content on the microwave and mechanical properties were investigated. The results show that the best sintering temperature is around 950 °C and increasing amount of B2O3 promotes the crystallization of CaB2O4 enhancing the flexure strength of the CBS ceramics. However, the dielectric and mechanical properties deteriorated rapidly while the amount of B2O3 exceeded 25 wt.%. The sample with 20.5 wt.% B2O3 sintered at 950 °C had the best properties with er = 6.06; tand = 0.0015 (1 MHz) and a high flexure strength qf > 180 MPa.