The leaching of sulfuric acid converted product of scheelite in NH_(3)·H_(2)O−NH_(4)HCO_(3)solution was systemically studied to improve sulfuric acid conversion−ammonium salts leaching technology route for ammoni...The leaching of sulfuric acid converted product of scheelite in NH_(3)·H_(2)O−NH_(4)HCO_(3)solution was systemically studied to improve sulfuric acid conversion−ammonium salts leaching technology route for ammonium paratungstate production.The results showed that the WO_(3)leaching efficiency was about 99%under optimal conditions of 350 r/min,liquid-to-solid ratio of 3 mL/g,1 mol/L NH_(4)HCO_(3),4 mol/L NH_(3)·H_(2)O,25℃,and 15 min.During the leaching,CaSO_(4)almost had no change and was still in a banding or rod-like shape in short leaching time,while conglobate CaCO_(3)was gradually formed on the CaSO_(4)surface.A secondary reaction might occur between CaSO_(4)and WO_(4)^(2−),which could be restrained by a certain amount of CO_(3)^(2−)in the solution.There was no CaCO_(3)phase determined by XRD in leaching residue of converted product for scheelite concentrate under optimal conditions,which was different from that for synthetic scheelite.The leaching process could be explained by neutralization reaction of H_(2)WO_(4)and solid transformation of CaSO_(4)in NH_(3)·H_(2)O−NH_(4)HCO_(3)solution.展开更多
难熔高熵合金(refractory high entropy alloys,RHEAs)因具备高的服役温度和优异的热稳定性在航空航天等超高温领域有广阔的应用前景。然而,难熔高熵合金目前面临综合力学性能不足等问题,限制了其进一步应用。针对此,本文在WMoTaV基础...难熔高熵合金(refractory high entropy alloys,RHEAs)因具备高的服役温度和优异的热稳定性在航空航天等超高温领域有广阔的应用前景。然而,难熔高熵合金目前面临综合力学性能不足等问题,限制了其进一步应用。针对此,本文在WMoTaV基础上进一步引入Ti元素,制备一种WMoTaVTi难熔高熵合金,重点研究烧结温度对合金烧结致密化、显微组织和力学性能的影响。研究结果表明:随着烧结温度的升高,合金的晶粒尺寸逐渐增加,屈服强度呈现先增加后降低的趋势。当烧结温度为1500℃时,合金具有最佳的综合性能,此时其相对密度超过99%,室温压缩屈服强度为1672 MPa,断裂应变为16.6%,断口形貌主要为沿晶断裂;相比于WMoTaV难熔高熵合金,合金的屈服强度提高了18%。由于粉末冶金过程中引入少量O元素,该合金主要由BCC基体相和少量FCC结构的TiO析出相组成,随着烧结温度的升高,基体的固溶度增加,TiO相的体积分数逐渐减少。合金强度的提高主要归因于固溶强化和析出强化两种强化机制。展开更多
文摘The leaching of sulfuric acid converted product of scheelite in NH_(3)·H_(2)O−NH_(4)HCO_(3)solution was systemically studied to improve sulfuric acid conversion−ammonium salts leaching technology route for ammonium paratungstate production.The results showed that the WO_(3)leaching efficiency was about 99%under optimal conditions of 350 r/min,liquid-to-solid ratio of 3 mL/g,1 mol/L NH_(4)HCO_(3),4 mol/L NH_(3)·H_(2)O,25℃,and 15 min.During the leaching,CaSO_(4)almost had no change and was still in a banding or rod-like shape in short leaching time,while conglobate CaCO_(3)was gradually formed on the CaSO_(4)surface.A secondary reaction might occur between CaSO_(4)and WO_(4)^(2−),which could be restrained by a certain amount of CO_(3)^(2−)in the solution.There was no CaCO_(3)phase determined by XRD in leaching residue of converted product for scheelite concentrate under optimal conditions,which was different from that for synthetic scheelite.The leaching process could be explained by neutralization reaction of H_(2)WO_(4)and solid transformation of CaSO_(4)in NH_(3)·H_(2)O−NH_(4)HCO_(3)solution.
文摘难熔高熵合金(refractory high entropy alloys,RHEAs)因具备高的服役温度和优异的热稳定性在航空航天等超高温领域有广阔的应用前景。然而,难熔高熵合金目前面临综合力学性能不足等问题,限制了其进一步应用。针对此,本文在WMoTaV基础上进一步引入Ti元素,制备一种WMoTaVTi难熔高熵合金,重点研究烧结温度对合金烧结致密化、显微组织和力学性能的影响。研究结果表明:随着烧结温度的升高,合金的晶粒尺寸逐渐增加,屈服强度呈现先增加后降低的趋势。当烧结温度为1500℃时,合金具有最佳的综合性能,此时其相对密度超过99%,室温压缩屈服强度为1672 MPa,断裂应变为16.6%,断口形貌主要为沿晶断裂;相比于WMoTaV难熔高熵合金,合金的屈服强度提高了18%。由于粉末冶金过程中引入少量O元素,该合金主要由BCC基体相和少量FCC结构的TiO析出相组成,随着烧结温度的升高,基体的固溶度增加,TiO相的体积分数逐渐减少。合金强度的提高主要归因于固溶强化和析出强化两种强化机制。
