To better understand and ascertain the mechanisms of flotation reagent interaction with rare earth (RE) minerals, it is necessary to determine the physical and chemical properties of the constituent components. Seven rare earth oxides (CeO2, Er2O3, Nd2O3, Tm2O3, Yb2O3, La2O3, and Tb4O7) that cover the rare earth elements (REEs) from light to heavy REEs have been investigated using Raman spectroscopy. Multiple laser sources (wavelengths of 325 nm, 442 nm, 514 nm, and 632.8 nm) for the Raman shift ranges from 100 cm−1to 5000 cm−1of these excitations were used for each individual rare earth oxide. Raman shifts and fluorescence emission have been identified. Theoretical energy levels for Er, Nd, and Yb were used for the interpretation of fluorescence emission. The experimental results showed good agreement with the theoretical calculation for Er2O3and Nd2O3. Additional fluorescence emission was observed with Yb2O3that did not fit the reported energy level diagram. Tb4O7was observed undergoing laser induced changes during examination.
Polyurethane binder systems based on hydroxyl-terminated polybutadiene (HTPB) possess several superior properties such as superior adhesion, high solid-loading capacity, outstanding mechanical performance, etc. They have been widely used in coatings and adhesives as well as in medical and military industries. The cure reaction between hydroxyl-terminated polybutadiene (HTPB) and diisocyanates plays a key role in the properties of final products as well as the adjustment of process parameters. FT-IR spectroscopy is applied to investigate the kinetics of the curing reaction of HTPB and isophorone diisocyanate (IPDI) in the presence of a low toxic and low viscosity catalyst, stannous isooctoate (TECH). The concentrations of the isocyanate groups (NCO) characterized by FT-IR during the cure reaction with respect to time were recorded at different temperatures and at constant stoichiometric ratio R n[NCO]/n[OH] = 1.0. The kinetic parameters, i.e., activation energy (E a), pre-exponential factor (A), activation enthalpy (∆H) and activation entropy (∆S) were determined. In addition, the curing process and mechanism of the HTPB-IPDI reaction are discussed.
A polyoxometalate‐based ionic liquid‐doped sepiolite (SEP‐PIL) was prepared by electrostatically immobilizing phosphomolybdic acid (PMA) on natural sepiolite embedded with imidazolium cations (SEP‐IL), and its structural properties were fully characterized by various methods. Furthermore, a new intumescent flame‐retardant system (IFR) for high‐density polyethylene (HDPE) was constructed by adding SEP‐PIL into conventional HDPE/IFR composites. The retardant properties and thermal decomposition behaviors were comprehensively investigated. The results showed that the HDPE composite containing 24 wt% IFR and 1 wt% SEP‐PIL passed UL‐94V‐0 rating, and the limiting oxygen index increased from 17.8% (pure HDPE) to 27.6%. In addition, the HDPE/IFR/SEP‐PIL composite had lower peak heat release rate (PHRR) and total heat release (THR) compared to the HDPE/IFR composite. The thermogravimetric analysis demonstrated that the combination of SEP‐PIL with IFR could greatly promote the formation of residual chars. Dynamic rheological measurement further confirmed that the synergistic effect of SEP‐PIL and IFR could greatly improve the flame retardancy of HDPE/IFR/SEP‐PIL composites.
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