Density functional theory study on the influence of cation ratio on the host layer structure of Zn/Al double hydroxides

A density functional theory （DFT） study has been carried out for [Zn-1AI（OH2）n＋6（OH）2n-2]^3＋ （n=3-6） and [Znn-1AI（OH2）2n-2（OH）2n-2]^3＋ （n = 7） clusters, which include the basic structural information of the brucite-like lattice structure of Zn/Al layered double hydroxides （LDHs） with Zn/AI molar ratio （R） in the range 2-6, in order to understand the effect of the Zn/Al ratio on the structure and stability of binary Zn/Al LDHs. Based on systematic calculations of the geometric parameters and formation energies of the cluster models, it was found that it is possible for Zn^2＋ and Al^3＋ cations to replace Mg^2＋ isomorphously in the brucite-like structure with different R values, resulting in differences in microstructure of the clusters and unit cell parameter a of the Zn/Al LDHs. Analysis of the geometry and bonding around the trivalent Al^3＋ or divalent Zn^2＋ cations reveals that Al^3＋ plays a more significant role than Zn^2＋ in determining the microstructure properties, formation and bonding stability of the corresponding ZnRAl clusters when R〈5, while the influence of Zn^2＋ becomes the dominant factor in the case of R〉 5. These findings are in good agreement with experiments. This work provides a detailed electronic-level understanding of how the composition of cations affects the microstructure and stability of Zn-containing binary LDH layers.

Techniques for quickly changing fuel gas in continuous annealing furnaces

An increasing number of annealing furnaces have recently been using cheaper and cleaner natural gas （NG） instead of liquefied petroleum gas （LPG） as fuel gas.However,the fuel gas of the furnaces often needs to be changed when NG supply is not adequate or when LPG becomes cheaper.Usually,changing the fuel gas involves changing various equipment as well as control parameters for instruments and the control system and hence is time consuming.Therefore,it is important to develop a quick process for changing fuel gas.This study discusses the techniques for quickly changing fuel gas in an annealing furnace.These techniques deal with the design of the pipe,valve and burner,the selection of the flow meter and the flow control valve,the switch of the software and parameters for the control system,as well as the operation,commissioning and hot test of the furnace when the fuel gas is changed.Using these techniques,it is possible to change fuel gas in 6 h.

Temperature of Heavy Fragments in Heavy-Ion Collisions

The heavy fragments in heavy-ion collisions are finally formed after the hot prefragments undergo sequential decay, of whom the temperature should be much lower than that of prefragments. Using the double ratio （DR） method, the isotopic thermometer （Tiso ） for heavy fragment is constructed using the yield of heavy isotopes. Tiso of heavy fragment is obtained by analyzing the measured data in the 1A GeV 124＇136Xe and 140A MeV 48Ca/64Ni reactions. Result shows that Tiso varies from 0.5 MeV to 10 MeV. But most Tiso is around 1 4- 0.5 MeV, which is much lower than temperature of light particles. Result also indicates that the difference between Tiso of heavy fragments in different reactions is very small, and ~o is independent on the size of the reaction system, the incident energy and the neutron-richness of the projectile.