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Homogeneous Precipitation of Layer Double Hydroxides

机译：双层双氢氧化物的均相沉淀

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Structure of nickel precipitate from decomposition of urea was found to be α-Ni(OH)_2. FTIR analysis revealed the intercalation of cyanate (OCN~-), which is an intermediate product of urea decomposition. This observation implied that the assumption of single step decomposition of urea to carbon dioxide and ammonia was over simplified. For quantitative analysis on the effects of critical system parameters like initial pH and metal ion concentration, a detailed analysis of the possible reactions in urea system was carried out. Numerical solutions to reaction pathways predicted significant accumulation of the intermediate cyanate in the time-temperature range investigated. Further elaboration was possible by considering the effects of hydrolysis products of Ni~(2+) and Ni-amine, Ni-cyanate, and Ni-carbonate complexes in the numerical simulations. Chemical analysis of the precipitate showed a decrease in nitrogen content with increasing reaction times. This was consistent with the predicted decrease in concentration of Ni-cyanate complexes with time. At extended digestion times, formation of Ni-amine complexes limits the complete recovery of the Ni~(2+). From the two phases of Ni(OH)_2, α-phase, with its larger interlayer spacing, offers enhanced electrochemical properties but it transform into thermodynamically stable β-phase. Stabilizing α-phase with Co~(2+) substitution which oxidizes irreversibly to Co~(3+) with electrochemical cycling along with forming layer double hydroxides (LDH's: [M~(2+) _(1-x)M~(3+) _x(OH)_2] ~(x+) [A~(n-)_(x)]~(x-)·mH_2O) were studied. Various compositions of LDH's containing Ni~(2+)/Co~(2+) and Al~(3+) ions were produced by urea and tested with chronopotentiometry to assess their potential utility as rechargeable electrode materials.
机译：发现来自尿素分解的镍沉淀物的结构为α-Ni（OH）_2。 FTIR分析揭示了尿素分解的中间产物氰酸酯（OCN〜-）的嵌入。该观察结果暗示了将尿素一步分解为二氧化碳和氨的假设被简化了。为了定量分析关键系统参数（如初始pH和金属离子浓度）的影响，对尿素系统中可能发生的反应进行了详细分析。反应路径的数值解决方案预测了所研究的时间-温度范围内中间氰酸盐的大量积累。在数值模拟中，考虑到Ni〜（2+）与Ni-胺，Ni-氰酸酯和Ni-碳酸酯配合物的水解产物的影响，可以进行进一步的阐述。沉淀物的化学分析表明，随着反应时间的增加，氮含量降低。这与镍氰酸盐配合物的浓度随时间降低的预期一致。在延长的消化时间，Ni-胺配合物的形成限制了Ni〜（2+）的完全回收。从Ni（OH）_2两相开始，夹层间距较大的α相具有增强的电化学性能，但转变为热力学稳定的β相。具有Co〜（2+）取代作用的稳定α相，通过电化学循环不可逆地氧化为Co〜（3+），并形成双氢氧化物层（LDH's：[M〜（2+）_（1-x）M〜（ 3+）_x（OH）_2]〜（x +）[A〜（n-）_（x / n）]〜（x-）·mH_2O）。尿素产生了含有Ni〜（2 +）/ Co〜（2+）和Al〜（3+）离子的LDH各种成分，并通过计时电位法进行了测试，以评估其作为可再充电电极材料的潜在用途。

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