This paper presents the effects of different process parameters in producing Al-STi-1B grain refiner,i.e.various sequences and reaction time,on grain refinement efficiency of aluminum castings.It was found that differ...This paper presents the effects of different process parameters in producing Al-STi-1B grain refiner,i.e.various sequences and reaction time,on grain refinement efficiency of aluminum castings.It was found that different process parameters resulted in different morphology and size distribution of TiAl-3 and TiB-2 in grain refiner. The experiment was carried out by adding KBF-4 and K-2TiF-6 to molten aluminum.The melting temperature was controlled at 800℃in an electric resistance furnace.Three different sequences of KBF-4 and K-2TiF-6 additions were applied,i.e.,adding KBF-4 before K-2TiF-6,adding K-2TiF-4 before KBF-4 and mixing both KBF-4 and K-2TiF-6 before adding to molten aluminum.Three different holding time at 1 min,30 min and 60 min were applied.The results showed that no significant difference of morphology and size distribution was found by varying three different sequences.Whereas,the different holding time provided major differences in both morphology and size distribution,which are technically expectable from diffusion and agglomeration between particles resulting in larger particle size and wider range of size distribution of TiAI3 and TiB2.If the reaction time was longer than 30 rain,morphology of both TiAl-3 and TiB-2 became too large.If the reaction time was too short,less reaction between TiAl-3 and TiB2 to form would be obtained.For grain refinement efficiency, it was found that mixing KBF-4 and K-2TiF-6 before adding to molten aluminum with a holding time of 30 min resulted in best grain refinement efficiency.展开更多
The exploration of the appropriate red phosphor with good luminescence properties is an important issue in the development of current white light-emitting diode(WLED) devices. Transition metal Mn-doped compounds are f...The exploration of the appropriate red phosphor with good luminescence properties is an important issue in the development of current white light-emitting diode(WLED) devices. Transition metal Mn-doped compounds are fascinating luminescent materials. Herein, we performed a systematic theoretical study of the microstructure and optical properties of K_2TiF_6:Mn^(4+) using the CALYPSO structure search method in combination with first-principles calculations. We uncovered a novel structure of K_2TiF_6:Mn^(4+) with space group P-3m1 symmetry, where the impurity Mn_(4+) ions are accurately located at the center of the MnF_6 octahedra. Based on our developed complete energy matrix diagonalization(CEMD)method, we calculated transition lines for ~2E_g →~4A_2,~4A_2→~4T_2, and^4A_2→T2at 642 nm, 471 nm, and 352 nm,respectively, which are in good agreement with the available experimental data. More remarkably, we also found another transition(~4A_2→~2T_2) that lies at 380 nm, which should be a promising candidate for laser action.展开更多
文摘This paper presents the effects of different process parameters in producing Al-STi-1B grain refiner,i.e.various sequences and reaction time,on grain refinement efficiency of aluminum castings.It was found that different process parameters resulted in different morphology and size distribution of TiAl-3 and TiB-2 in grain refiner. The experiment was carried out by adding KBF-4 and K-2TiF-6 to molten aluminum.The melting temperature was controlled at 800℃in an electric resistance furnace.Three different sequences of KBF-4 and K-2TiF-6 additions were applied,i.e.,adding KBF-4 before K-2TiF-6,adding K-2TiF-4 before KBF-4 and mixing both KBF-4 and K-2TiF-6 before adding to molten aluminum.Three different holding time at 1 min,30 min and 60 min were applied.The results showed that no significant difference of morphology and size distribution was found by varying three different sequences.Whereas,the different holding time provided major differences in both morphology and size distribution,which are technically expectable from diffusion and agglomeration between particles resulting in larger particle size and wider range of size distribution of TiAI3 and TiB2.If the reaction time was longer than 30 rain,morphology of both TiAl-3 and TiB-2 became too large.If the reaction time was too short,less reaction between TiAl-3 and TiB2 to form would be obtained.For grain refinement efficiency, it was found that mixing KBF-4 and K-2TiF-6 before adding to molten aluminum with a holding time of 30 min resulted in best grain refinement efficiency.
基金Project supported by the National Natural Science Foundation of China(Grant No.11574220)Fundamental Research Funds for the Central Universities,China(Grant No.SWU118055)+1 种基金the Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund(the second phase)China
文摘The exploration of the appropriate red phosphor with good luminescence properties is an important issue in the development of current white light-emitting diode(WLED) devices. Transition metal Mn-doped compounds are fascinating luminescent materials. Herein, we performed a systematic theoretical study of the microstructure and optical properties of K_2TiF_6:Mn^(4+) using the CALYPSO structure search method in combination with first-principles calculations. We uncovered a novel structure of K_2TiF_6:Mn^(4+) with space group P-3m1 symmetry, where the impurity Mn_(4+) ions are accurately located at the center of the MnF_6 octahedra. Based on our developed complete energy matrix diagonalization(CEMD)method, we calculated transition lines for ~2E_g →~4A_2,~4A_2→~4T_2, and^4A_2→T2at 642 nm, 471 nm, and 352 nm,respectively, which are in good agreement with the available experimental data. More remarkably, we also found another transition(~4A_2→~2T_2) that lies at 380 nm, which should be a promising candidate for laser action.
