Zhanhong Yang

The effect of Zn-Al-hydrotalcites composited with calcium stearate and β-diketone on the thermal stability of PVC.

A clean-route synthesis of Zn-Al-hydrotalcites (Zn-Al-LDHs) using zinc oxide and sodium aluminate solution has been developed. The as-obtained materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The effects of metal ions at different molar ratios on the performance of hydrotalcites were discussed. The results showed that the Zn-Al-hydrotalcites can be successfully synthesized at three different Zn/Al ratios of 3:1, 2:1 and 1:1. Thermal aging tests of polyvinyl chloride (PVC) mixed with Zn-Al-LDHs, calcium stearate (CaSt2) and β-diketone were carried out in a thermal aging test box by observing the color change. The results showed that Zn-Al-LDHs can not only enhance the stability of PVC significantly due to the improved capacity of HCl-adsorption but also increase the initial stability and ensure good-initial coloring due to the presence of the Zn element. The effects of various amounts of Zn-Al-LDHs, CaSt2 and β-diketone on the thermal stability of PVC were discussed. The optimum composition was determined to be 0.1 g Zn-Al-LDHs, 0.15 g CaSt2 and 0.25 g β-diketone in 5 g PVC.

Zn-Al-La hydrotalcite-like compounds as heating stabilizer in PVC resin

Abstract ZnAlLa-CO3 layered double hydroxides (LDHs) with different Zn/Al/La molar ratios were prepared by the constant pH coprecipitation method. The synthetic materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller method (BET) and particle analysis. The results showed that the hydrotalcite-like materials had a layered structure. The ZnAlLa-CO3-LDHs as stabilizers were mixed with PVC resin. The tests of thermal aging, mass loss test and Congo red for the PVC composites were carried out at 180±1 °C, respectively. The results showed that ZnAlLa-CO3- LDHs used as single thermal stabilizers could enhance both the long-term thermal stability and initial thermal stability of PVC, and 2.4 phr (parts per hundred PVC resin) ZnAlLa-CO3-LDHs with Zn/Al/La (molar ratio)=20/8/2 had a better stabilizing effect on PVC than others. Compared with single thermal stabilizers, the composite thermal stabilizers including 0.3 phr calcium stearate (CaSt2), 0.4 phr β-diketone and 2.4 phr ZnAlLa-CO3-LDHs significantly enhanced the thermal stability of PVC sample. And rare earth ion could optimize the conformation of PVC and refrain the initiation of the thermal stability and the thermal stable time was over 220 min. The main reason could be concluded to the special structure of rare earth ion, which had longer atom radius and more coordination numbers. So the rare earth ion (REδ+) could react with the labile chlorine atoms (Clr−) to form a stable coordinate complex.

Electrochemical Behavior of Graphite in KF – AlF3-Based Melt with Low Cryolite Ratio

The electrochemical behavior of graphite in KF-AlF 3 -based melt with a cryolite ratio (molar ratio of KF to AlF 3 ) of 1.3 as well as a low oxygen content at 750°C was investigated by cyclic voltammetry, potentiostatic electrolysis, sampled-current voltammetry, and chronopotentiometry. Aluminum deposited on graphite at a potential of ca. 0.25 V (vs Al) and the electrochemical intercalation of potassium into graphite occurred at ca. -0.1 V (vs Al). The intercalation of potassium into graphite enhanced the formation of Al 4 C 3 . The deposition of aluminum on graphite was a linear diffusion-controlled process, while its reverse reaction involved kinetic limitations. Sampled-current voltammetry results indicated that the aluminum deposition on graphite was depressed in the potential region extending from about 0.1 to 0.03 V (vs Al). Chronopotentiometry results revealed that the critical cathodic current density for potassium intercalation was about 400 mA cm -2 .

Electrochemical Investigation on Kinetics of Potassium Intercalating into Graphite in KF Melt

The kinetics of potassium intercalating into graphite in molten KF at 1163 K was investigated by means of cyclic voltammetry and chronoamperometry. Cyclic voltammetry results indicate that intercalaltion/deintercalation of potassium into/from graphite involve kinetic limitations. The intercalation process of potassium was further confirmed to be governed by both the diffusion of potassium ion in graphite bulk and the phase transition kinetics through the analyses of current-time transient curves with reversible and quasi-reversible equations. The transfer coefficient of the intercalation reaction was calculated to be 0.364 according to the parameters resulting from nonlinear fitting of the current-time transient curves with a quasi-reversible equation. Analysis with scanning electron microscope shows that graphite matrix was severely eroded by intercalation of potassium.