| Nowadays, the development of nuclear fusion energy in a cleaning and sustainable way has attracted the attentions of all over the world, because of the problems of energy shortage and environmental deterioration being increasingly serious. Wherein, Li2Ti03is considered as one of the most promising candidates among the tritium breeding materials, owing to its excellent tritium release property, higher thermal conductivity and better thermal stability compared with other candidate materials. However, some shortages such as raw materials are expensive or difficult to obtain, technological process is prolonged or high cost are widespread existed in the processes for the preparation of Li2Ti03. Owing to this situation, soft chemistry route was proposed for the synthesis of Li2Ti03in the paper, in which TiCl4, the intermediate product in the metallurgical process of Ti, and LiOH·H2O are used as titanium source and lithium source, respectively. From this, the feasibility of the preparation of Li2TiO3by a soft chemistry route was investigated by thermodynamic theory firstly, and the reliability of the prediction from thermodynamic theory was further confirmed by experiments. The characteristics of TiCl4hydrolysis under soft chemistry conditions and the ability of lithium intercalation of the obtained products from TiCl4hydrolysis were studied, and a two-step process for the preparation of Li2Ti03was proposed. Meanwhile, the in-situ hydrolysis-phase transformation process was optimized on the basis of the results in our previous research. The properties of the obtained Li2Ti03powders were characterized by sintering densification. The conclusions are as follows:l)The potential-pH diagrams of Li-Ti-H2O system at333.15、363.15,393.15and453.15K, and ion activities0.01、0.10and1.00were constructed. As shown in the predominant area diagrams of Li-Ti-H2O system, the stability region of Li2Ti03(hc) occurs under the conditions considered and moves to lower pH area with increasing temperature and ion activity. The predominant area of Li2TiO3(hc) is between pH12.5to13.6at333.15K. It moves to pH ranging from9.9to10.9at453.15K and at0.10activities of all dissolved species. The results indicated that it is feasible to synthesize Li2Ti03under soft chemistry conditions. The results obtained in confirmatory experiments further testified the reliability of the prediction from thermodynamic theory.2) The experimental results of TiCl4hydrolysis demonstrated that the parameter of pH value had a crucial effect on the hydrolysis products under the mild conditions considered. The product prepared at pH1.2-4.1occurs in a poor crystalline and nanosized anatase TiO2polymorph. With increasing pH, the crystallinity and regular shape disappear. When the hydrolysis of TiCl4proceeded at pH>6.0, the products are in amorphous forms. The difference occured in the process of structure transformation of products, prepared by TiCl4hydrolysis, indicated that the products’ property difference. The difference of lithium intercalation abilities of the obtained TiO2in aqueous solution indicated that poor crystalline and nanosized anatase TiO2, obtained by TiCl4hydrolysis at lower pH, are more favorable for lithium intercalation.3) Phase-pure Li2TiO3were synthesized under the conditions of3.0times of the theorical lithium amount, the concentration of LiOH solution1.0mol·L-1and1.5times of the theorical lithium amount, the concentration of LiOH solution2.0mol·L-1by a two-step route. The pellets can be densified by sintering at1100℃for6h, and the relative density and liner shrinkage rate of the obtained sintered bodies is83.6%T.D.(theoretical density based on the Li2Ti03single crystal density of3.43g·cm-3) and9.15%, respectively. The property parameter of powders, obtained by the two-step process, is limited, because of the transformation of nanosized and poor crystalline anatase TiO2into amorphous product under the condition of pH>11.4) The results from optimized in-situ hydrolysis-phase transformation process demonstrated that the lithium used had significantly influenced the properties of the obtained Li2Ti03. Phase-pure and regular-shaped Li2Ti03powders were prepared under the conditions of1.08～1.50times of the theoretical amount of lithium. However, the particle size and its distribution decrease with an increase in the amount of lithium used, which, therefore, strongly affects the sintering densification process and performance parameters of the Li2Ti03ceramic pellets. The smaller the particle size and the narrower the particle size distribution of Li2Ti03powders, the better the degree of densification and the higher the performance parameter values of the pellets. The relative density and liner shrinkage rate of the sintered body increased from80.6%T.D. and7.84%to91.3%T.D. and12.08%, respectively, when the amount of lithium used increased from1.08to1.50times of the theoretical lithium amount. |
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