A Comparative Study of Different Amorphous and Paracrystalline Silica by NMR and SEM/EDS

This work aimed to research the structure models of amorphous materials. Five amorphous and paracrystalline samples(natural or artificial) were investigated via 29Si/27 Al nuclear magnetic resonance(NMR) and field emission scanning electron microscopy/energy dispersive spectroscopy(FE-SEM/EDS). The results of NMR showed the resonances of different specimens:-93.2 ppm,-101.8 ppm,-111.8 ppm for natural pozzolana opal shale(POS). These peaks were assigned to the Q2(2OH), Q3(OH)/Q4(1Al) and Q4 respectively. The results of 27 Al MAS NMR indicated that Al substituted for Si site in tetrahedral existing in the POS, while the Al/Si atomic ratio in opal was low(around 0.04). For the alkali-silicate-hydrate gel, there were at least three resolved signals assigned to Q0 and Q1, respectively. For the fused silica glass powder, there were the primary signals centered about at the range from-107 to-137 ppm, which were assigned to Q4 units. In addition, the peaks at around-98 and-108 ppm were corresponding to Q3(1OH) and Q4 units existing in aerogel silica structure.

Leaching of iron concentrate separated from kiln slag in zinc hydrometallurgy with hydrochloric acid and its mechanism

It is taken as a novel prospective process to treat iron concentrate from hydrometallurgical zinc kiln slag forcomprehensive utilization of valuable metals by a hydrochloric acid leaching-spray pyrolysis method.The leaching mechanism ofdifferent valuable metals was studied.The results revealed that the leaching rates of Ag,Pb,Cu,Fe,As and Zn were99.91%,99.25%,95.12%,90.15%,87.58%and58.15%,respectively with6mol/L HCl and L/S ratio of10:1at60°C for120min.The actionof SiO2in leaching solution was also studied.The results showed that the precipitation and settlement of SiO2(amorphous)adsorbedpart of metal ions in solution,which greatly inhibited the leaching of Cu,Fe,As and Zn,so it is crucial to control the precipitation ofamorphous SiO2.

Molecule Dynamics Study on Heat Transfer at Gas-Nanoparticle Interface

The molecular dynamics(MD)simulations were used to understand the heat transfer process between the gas phase and the solid skeleton in the nanoporous silica aerogels.The amorphous silica nanoparticles were generated by the MD simulations and the energy accommodation coefficient(EAC)between the gases and the nanoparticles was calculated based on the results of the nonequilibrium molecular dynamics(NEMD)simulations.The apparent thermal conductivity(ATC)of the gases between the heat source and heat sink was also obtained.The effects of the temperature,the particle diameter and the molecule type on the EAC and the ATC were investigated.The results indicate that the EAC decreases with the increase of temperature within the calculating range.When the preset temperature is constant,the EAC increases with the increasing of the particle diameter and eventually approaches a specific value.When the preset temperature is 300 K and the particle size is 4 nm,the obtained EAC for the N2 gas and the O2 gas is close to each other and both are less than that of the Ar gas.The results also indicate that the heat transferred through the gas-nanoparticle interface is far less than that through the neighbouring nanoparticles in silica aerogels.

Heteroclitins R-S: new dibenzocylooctadiene lignans from Kadsura heteroclita

AIM: To study the dibenzocylooctadiene lignans from the stems of Kadsura heteroclita. METHOD: Chromatographic separations of silica gel and semi-preparative HPLC were used. All of the structures were elucidated on the basis of spectroscopic analysis,including 2D-NMR and HR-MS techniques. RESULTS: Four dibenzocylooctadiene lignans were isolated from K. heteroclita. Their structures were identified as heteroclitin R(1), heteroclitin S(2), gonisin O(3), and schisanlignone A(4). CONCLUSION: Heteroclitin R(1) and heteroclitin S(2) are new natural lignans.