Roles of polyacrylate dispersant in the synthesis of well-dispersed BaSO_4 nanoparticles by simple precipitation

Well-dispersed BaSO4 nanoparticles were synthesized in the presence of sodium polyacrylate （PAAS） by a simple precipitation method, with BaCl2 and （NH4）2SO4 as reactants. The different roles performed by PAAS in the synthesis of BaSO4 nanoparticles were investigated using X-ray diffractometry, Fourier transform infrared spectroscopy, and transmission electron microscopy. The results indicate that the assynthesized BaSO4 nanoparticles were spheres with an average diameter of 30 nm and that their surfaces were affected by the PAAS. Under a typical procedure employed, PAAS reacted with BaCl2 to yield an intermediate, serving as a control releasing agent and separating the nucleation and crystal growth processes of the BaSO4 nuclei. During formation of the BaSO4 nanospheres, the intermediate slowly dissolved and released barium and polyacrylate ions, inhibiting the growth and aggregation of newly formed BaSO4 seeds and resulting in particles of narrow diameter distribution and improved dispersibility. Moreover, these polyacrylate ions further modified the surfaces of the BaSO4 nanoparticles.

Effects of samarium addition on as-cast microstructure, grain refinement and mechanical properties of Mg-6Zn-0.4Zr magnesium alloy

In this paper, the microstructural evolution, grain refinement and mechanical properties of as-cast Mg-6Zn-0.4Zr alloys with varying Sm contents（0, 2 wt.%, 4 wt.% and 6 wt.%） were investigated by using an optical microscope（OM）, a scanning electron microscope（SEM） equipped with energy dispersive spectroscope（EDS）, an X-ray diffractometer（XRD） and mechanical tests at room temperature, respectively. The experimental results indicated that the addition of Sm could obviously refine the as-cast grains, modify the eutectic morphology and affect the mechanical properties of the alloys. The main phases in Mg-6Zn-xSm-0.4Zr alloys included matrix α-Mg, Mg2Zn3, Mg（41）Sm5 and MgZ nS m. With Sm content increasing to 4%, the MgZ nS m phase was created, meanwhile, the morphology of some eutectic phases revealed apparently lamellar structure, which had a bad effect on the mechanical properties. In addition, the maximum values of ultimate tensile strength（UTS, 214 MPa） and elongation（EL, 7.42%） were simultaneously obtained from the alloy with 2% Sm. However, Sm addition had no obvious effects on the fracture behavior of the alloys, namely, the fracture pattern of Mg-6Zn-0.4Zr alloy belonged to inter-granular and brittle modes while the fracture regimes of all the Sm-containing alloys were dominated by the mixture of inter-granular and trans-granular modes.

Effect of Alloying Method on Microstructure and Wear Resistance of Fe-Cr-V-B Based Alloy

The microstructure and wear behavior of Fe-Cr-V-B based alloy was investigated.Each of the specimens was characterized by metallographic techniques and hardness test.Phase analysis of alloy was performed by X-ray diffraction（XRD）,scanning electron microscopy（SEM）and energy dispersive spectroscopy（EDS）.The results showed that the microstructure of Fe-Cr-V-B based as-cast alloy containing 8.6mass% V was composed ofα-（Fe,Cr）solid solution,VC carbides,and V_3B_4 borides,whereas the as-cast alloy containing 24.8mass% Cr was composed ofα-（Fe,Cr）solid solution and V_3B_4borides;the eutectic V_3B_4 borides mainly comprise M2B-type borides（M presents Fe and Cr）.The existence of a large amount of V atoms affects the growth pattern of eutectic borides,which mainly display rod-like and grainy structure.The wear behavior of the experimental alloy has been investigated using pin-on-disk type friction and wear apparatus.The comparison of experimental results indicated that the relative wear resistance of the alloy containing 8.6mass% V after destabilization heat treatment in a conventional furnace at 1 373 K for 2hwas about six times higher than that of the high chromium（19mass%）cast iron.