氢还原重量法测定硝酸铑产品中铑含量

根据冶金工艺中铑的精炼原理,建立了氢还原重量法测定硝酸铑产品中铑含量的方法。研究并优化了测定条件,考察了杂质元素对铑分析结果的影响。结果表明:在0.3～0.9 mol/L硝酸介质中,硝酸铑与氯化铵形成一种(NH₄)₃ RhCl₆红色络合物晶体,该晶体经过在约100 ℃烘干水分、350 ℃分解铵盐、750 ℃氢还原为海绵铑和105 ℃干燥后可以采用重量法测定其中的铑。用该方法测定硝酸铑产品中质量分数为6.55%、7.36%、8.05% 、9.99%和20.05%铑的极差(R)为±0.01%,标准偏差(SD)为0.004 1%,相对标准偏差(RSD,n=22)在0.02%～0.06%范围。本法测定结果较YS/T 594-2006标准配套分析方法的准确度和精密度高。     

硫酸亚铁电位滴定法测定金、钯合金中金的不确定度评定

通过硫酸亚铁电位滴定法测定AuBe1、AuNi9、AuAgCu35-5、PdAgCuAuPtZn30-14-10-10-1合金中Au的实践,分析了测定不同Au含量过程中的不确定度来源,建立了数学模型,计算了各标准不确定度分量、合成标准不确定度和扩展不确定度。结果表明：测定合金样品中9.99%、60.16%、90.85%、98.93%的Au含量,扩展不确定度分别为0.02%、0.14%、0.22%、0.24%。     

EDTA差减滴定法测定钼精矿和钼焙砂中钼含量

用盐酸羟胺还原钼(Ⅵ)至钼(Ⅴ),EDTA络合钼(Ⅴ)及共存离子,锌盐滴定过量EDTA求得合量。于等量试液中不加盐酸羟胺,EDTA络合共存离子,滴定至近终点用酒石酸钾钠掩蔽钼(Ⅵ),锌盐滴定过量EDTA求得分量。二者之差即为钼量。2%～5%钨(Ⅵ)、铬(Ⅵ)或钒(Ⅴ)等共存离子不干扰测定。测定10.00～15.00 mg钼,相对误差-0.20%～+0.20%,测定37%～57%的钼含量,相对标准偏差0.10%～0.15%,样品加标准回收率99.60%～100.80%。方法结果准确度与钼酸铅重量法的一致,但本法选择性好、分析快速。     

Toward high stability single crystal material by structural regulation with high and low temperature mixing sinter

Single-crystal cathode materials are a potential research focus for high-nickel ternary cathode materials owing to their high compaction density and good electrochemical stability. However, in the traditional sintering process, lithium is lost because of the long-time and higher-temperature sintering, which reduces the migration energy barrier of Ni²⁺ and increases the degree of mixing of Li⁺ and Ni²⁺. Herein, for the first time, a method for short-time high-temperature sintering combined with low-temperature heat preservation is proposed to prepare LiNi_0.6Co_0.6Mn_0.2O₂ (NCM622) single crystal materials in a mixed molten salt system of LiOH and Li₂CO₃. In analyses of morphology, structure and electrochemical properties, the prepared NCM622 exhibits excellent cycling stability owing to an ordered layered structure and low cation mixing degree. The single-crystal material shows an excellent capacity retention of 93.19% (150.49–140.24mAh·g^?1) after 100 cycles at 1 C in the voltage range of 2.8–4.3 V. The single crystal particles exhibit reliable stability after long cycling without microcracks in the cycled particles. Furthermore, the preparation cost could be significantly reduced with a closed loop of the flux salt. The short-time high-temperature combined with the low-temperature holding sintering method may provide an effective strategy for the synthesis of other single-crystal materials with excellent electrochemical properties.