Effect of Sodium Tripolyphosphate and Silica Fume on Hydration of High Alumina Cement

It was found that silica fume can reduce the maximum hydration heat release rate of cement by microcalorimetry,inhibit CAH_(10),promote the generation of C_(3)AH_(6)and strätlingite C_(2)ASH_(8),or promote the conversion of CAH_(10)to C_(3)AH_(6).Sodium tripolyphosphate can retard the early hydration of cement,have a slight effect on 1 d hydration products of cement and inhibit the generation hydration products.Sodium tripolyphosphate and silica fume can promote the early hydration of cement,advance the formation of C_(2)ASH_(8)or the conversion from CAH_(10)to C_(3)AH_(6)at 1 d.

Effects of Dispersive Agent and Alumina Micropowder on Workability of Al_2O_3-MgO Castables for Steel Ladles

This work aims at enhancing the workability of Al2 O3-Mg O castables. Al2 O3-Mg O castables were prepared using tabular alumina particles（ 5-3,3-1,≤1 mm）,tabular alumina fines（ ≤0. 088 mm）,fused magnesia（ ≤1 mm）,reactive alumina micropowder（ PFR40,PBR,and CL） and calcined alumina micropowder（ AC34 B5 and CT） as the main starting materials,calcium aluminate cement（ Secar71） as the binder,and polycarboxylic acid water reducer WS,FS,and AD as the dispersive agent,respectively. Effects of three dispersive agents addition（ 0. 4 mass% WS,0. 2 mass% FS and 1 mass% AD）,two kinds of reactive alumina micropowder addition（ PFR40 and PBR）,composite alumina micropowder addition（ PFR40-AC34 B5 and CL-CT,the mass ratio from 9/0 to 3/6）on the flow value,apparent porosity,bulk density,cold crushing strength and cold modulus of rupture of Al2 O3-MgO castables were investigated. The results show that：（ 1） with PBR or PFR40,the castables with0. 4 mass% WS own better performance than those with0. 2 mass% FS or 1 mass% AD;（ 2） compared with the castables with CL-CT composite powder, the castables with PFR40-AC34 B5 composite powder have slightly higher flow value; with the decreasing ratio of PFR40 and AC34 B5,or the decreasing ratio of CL andCT,the castables have declined flow value and the dried castable specimens have decreased density but the mildly changed strength; in consideration of the high price of reactive alumina,a proper compositing ratio shall be selected.

Influence of synthesis parameters on the properties of LiFePO4/C cathode material

The influence of sintering temperature, carbon content and dispersive agent in bail-milling was investigated on the properties of LiFePO4/C prepared using Fe2O3, NH4H2PO4, Li2CO3 and glucose via solid state reaction. X-ray powder diffraction, scanning electron microscopy and charge-discharge test were applied to the characterization of the LiFePO4/C samples synthesized under different conditions. Sintering temperature affects the crystallite/ particle size and degree ofcrystallinity of LiFePO4, formation of Fe2P and maintenance of carbon in LiFePO4/C. Car- bon maintenance is favored by low sintering temperature, and 700 ℃ is optimum for synthesis of LiFePO4/C with superior electrochemical performance. A higher carbon content in the range of 4.48%-11.03% results in a better rate capability for LiFePO4/C. The dispersive agent used in ball-milling impacts the existent state of carbon in the final product which subsequently determines its charge-discharge behavior. The sample prepared at 700 ℃ by using acetone as the dispersive agent in ball-milling exhibits an excellent rate capability and capacity retention without any fade at 0.1 C, 1C and 2C, with corresponding average discharge capacities of 153.8, 128.3 and 121.0 mA·h·g-1. rest2ectivelv, in the first 50 cvcles.

SiC WHISKER-TOUGHENED ALUMINIUM NITRIDE CERAMICS

Aluminium nitride ceramics containing 15 -30 w/o of SiC whiskers can be sintered to full density (by hot pressing at 1800℃)using 2-3 w/o of Y2O3 additions. The whiskers increase the toughness and strength of the composite, KIC increasing from 2. & to about 5.0 and flexural strength increasing by 30-50%. However, the whiskers must be well dispersed and if the dispersion is not satisfactory, toughness may increase but the strength decreases. The hot-pressing temperature can be reduced by up to 100℃ if Y(NO3)3 . 5H2O is used as the sintering additive instead of Y2O3, but some oxidation of the AIN occurs during heating. Isopropan-2-01 is a better dispersing agent than cyclohexane, but again some oxidation of the AIN does occur.The best sample prepared during this work contained 20 w/o of SiC whiskers and 2 w/o Y2O3 added as Y(NO3)3. 5H2O and mixed in isopropanol. This exhibited a mean strength of 453MPa (maximum 522MPa, measured by disc flexure) and a fracture toughness of5. 5MPam1/2.

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.