Journal of Nuclear Materials 543 (2021) 152580 Contents lists available at ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat Preparation of Li 4 TiO 4 -Li 2 TiO 3 core-shell ceramic pebbles with thick shells and high strength through an improved granulation method Ruichong Chen a,b , Zhijun Liao a,b,∗ , Yanli Shi a,b , Hailiang Wang a,b , Hao Guo a,b , Yuanyuan Zeng a,b , Jianqi Qi a,b , Qiwu Shi c , Tiecheng Lu a,b,∗ a College of Physics, Sichuan University, Chengdu 610064, China b Key Laboratory of Radiation Physics and Technology of the Ministry of Education, Sichuan University, Chengdu 610064, China c College of Materials Science and Engineering, Sichuan University, Chengdu 610064, China a r t i c l e i n f o Article history: Received 3 July 2020 Revised 9 August 2020 Accepted 5 October 2020 Available online 16 October 2020 Key words: Li 4 tio 4 -li 2 tio 3 Core-shell Pvp Thick shell Crush load a b s t r a c t The instability of Li 4 TiO 4 to carbon dioxide (CO 2 ) and moisture (H 2 O) was considered to be the main obstacle to its practical application as a tritium breeding material. Using Li 2 TiO 3 ceramic coating as a physical barrier wrapped on the surface of Li 4 TiO 4 pebbles was still considered to be the optimal so- lution. At present, increasing the thickness and strength of the Li 2 TiO 3 coating to increase the service life of this core-shell pebble has become an urgent problem to be solved. In this study, we success- fully wrapped a thick and uniform Li 2 TiO 3 coating on the Li 4 TiO 4 pebble by an optimized granulation method assisted only by polyvinylpyrrolidone (PVP). The Li 4 TiO 4 -Li 2 TiO 3 core-shell pebbles have high shell thickness (∼370 μm), relatively high wall thickness uniformity (78.86±3.07%) and good sphericity (90.72±1.88%) with a crush load of 47.73±1.49 N. It was demonstrated that PVP not only plays the role of bridge bonding between powders but also serves as a template to induce powder to be assembled layer by layer to form a uniform core-shell structure. © 2020 Elsevier B.V. All rights reserved. 1. Introduction Energy demands and environmental pollution issues urge the increased development of fusion energy [1–3]. To establish the fuel cycle of a deuterium-tritium fusion reactor, sufficient tritium must be produced from the tritium breeder blanket [4,5]. In the blan- ket, lithium-based ceramics are most commonly considered as tri- tium breeder materials due to the large neutron capture cross- section of lithium [6–11]. In recent years, researchers have found that a certain amount of Li or Li-containing compounds in the breeder materials will be evaporated at high temperatures, result- ing in a decrease in overall lithium density [12,13]. It should be noted that lithium density is a key factor in the establishment of a self-sustainable tritium cycle, which will directly affect the final tritium breeding performance. Therefore, the development of tri- tium breeder materials with high lithium density and stable chem- ical properties has become an active research field in recent years [14–17]. Li 4 TiO 4 is thermodynamically stable at temperatures up to at least 950 °C and has a lithium density of 0.51 g/cm 3 , which is ∗ Corresponding author. E-mail addresses: liaozhijun@scu.edu.cn (Z. Liao), lutiecheng@vip.sina.com (T. Lu). higher than most of the tritium breeder materials [18–22]. These characteristics mentioned above may make Li 4 TiO 4 tend to be a promising breeder material. However, Li 4 TiO 4 is very sensitive in ambient air, easily absorbs CO 2 to form Li 2 CO 3 and Li 2 TiO 3 [23,24] , and easy to react with moisture to form LiOH•H 2 O and Li 2 TiO 3 [25]. For tritium breeder materials, it is inevitable to contact with CO 2 and moisture during the operation, storage and handling pro- cess. Thus, the high sensitivity of Li 4 TiO 4 to CO 2 and moisture makes it not a stable breeder material. In order to overcome this issue, our group previously reported a physical coating method to wrap a layer of Li 2 TiO 3 on the surface of Li 4 TiO 4 pebble [26]. However, the Li 2 TiO 3 coating prepared by this method has a low thickness (13 μm) and insufficient coating adhesion, which makes it easy to crack and fall off during sample handling. It should be noted that the Li 2 TiO 3 shell directly affects the overall mechanical properties of Li 4 TiO 4 -Li 2 TiO 3 core-shell pebbles and the stability of Li 4 TiO 4 core. Therefore, increasing the thickness and binding force of the Li 2 TiO 3 coating on Li 4 TiO 4 pebbles has become an urgent problem to be solved. Remarkably, Wang et al. recently proposed a granulation tech- nology for mass production of Li 2 TiO 3 pebbles by using polyvinyl alcohol (PVA) to modify Li 2 TiO 3 precursor powder and sprayed polyvinyl pyrrolidone (PVP) solution during the granulation pro- cess to agglomerate the powder to form spherical pebbles [27]. https://doi.org/10.1016/j.jnucmat.2020.152580 0022-3115/© 2020 Elsevier B.V. All rights reserved.