Supplementary information files for Hot ceramic lithography of silica-based ceramic cores: The effect of process temperature on vat-photopolymierisation

Supplementary files for article Hot ceramic lithography of silica-based ceramic cores: The effect of process temperature on vat-photopolymierisation
An enhanced-temperature vat photo-polymerisation of ceramic-loaded mixtures, or so called hot ceramic lithography, has been presented in this paper, for 3D printing silica-based ceramic cores used in the investment casting of hot section parts in aero and industrial turbines. The pre and post-sintering properties of the 3D printed ceramic parts highly depend on the polymerisation degree of the base resin binders and the rheological behaviour of ceramic slurry, and hot lithography can play a significant role both. First, the paper aimed to better understand how different printing temperatures (25,35,45 and 55 °C) would affect the properties of the base binder mixtures before loading ceramic particles, by conducting tensile, DMA and FTIR analysis on binder-only prints. The impact of elevated printing temperature on the mechanical properties of ceramic loaded binder mixtures was further investigated. The highest mechanical properties for the base binder and the ceramic loaded mixtures were achieved when the process temperature was set closer to the binder mixtures' initial glass transition temperature (when the binder is cured at room-temperature). This printing temperature is yet lower than the level causing heat-induced cross-linking yet high to enhance the mobility of monomers and active species, when compared with conventional room-temperature vat photopolymerisation printing. The results indicate that printing temperature, if set as described, can significantly impact the mechanical property of parts and conversion rate of the base binders for a successful print process. The second part of this study investigates the impact of temperature on the rheological behaviour and peeling forces of highly loaded ceramic-loaded mixtures (61.2 vol.% of SiO2-ZrSiO4). The suspension showed shear thickening behaviour at 25 °C, hindering the replenishment of the slurry during printing, while a high transition from shear-thickening to shear-thinning behaviour, ideal for flawless ceramic 3D printing, was observed at an optimum process temperature of 35 °C. When print temperature increases to 45 °C and then 55 °C, the viscosity of the mixture at very low shear rate (when the material is static during printing) increases, hence affecting peeling forces. Comparing peeling force measurements and FTIR results showed the higher cross-linking density, and the reactivity of the base binder, leads to a stronger adhesion between the cured layers and the printer's transparent film, hence higher separation/peeling forces. To sum up, hot ceramic lithography at the right printing temperature can resolve many print and post print issues, such as deformation and cracking, leading to a stronger and more dimensionally-accurate ceramic components.

本文所附补充文件针对《基于二氧化硅陶瓷芯的热陶瓷立体光刻：工艺温度对池式光聚合的影响》一文的阐述。文中提出了一种增强温度下的陶瓷颗粒混合物池式光聚合技术，亦即所谓的热陶瓷立体光刻，该技术适用于3D打印用于航空和工业涡轮机热部件投资铸造的二氧化硅陶瓷芯。3D打印陶瓷部件的预烧结和后烧结性能高度依赖于基础树脂粘结剂的聚合度和陶瓷浆料的流变行为，而热立体光刻在此过程中发挥着至关重要的作用。首先，本研究旨在深入探究不同打印温度（25°C、35°C、45°C和55°C）对未加载陶瓷颗粒的基础粘结剂混合物性能的影响，通过在仅粘结剂打印件上执行拉伸、DMA和FTIR分析来实现。进一步研究了提高打印温度对陶瓷加载粘结剂混合物机械性能的影响。当工艺温度设定接近粘结剂混合物的初始玻璃化转变温度（粘结剂在室温下固化时）时，基础粘结剂和陶瓷加载混合物实现了最高的机械性能。此打印温度低于引起热诱导交联的水平，但高于传统室温池式光聚合打印，从而增强单体和活性物种的流动性。结果表明，若将打印温度设定如上所述，将显著影响部件的机械性能和基础粘结剂的转换率，从而保证打印过程的成功。本研究第二部分探讨了温度对高含量陶瓷加载混合物（61.2体积百分比的SiO2-ZrSiO4）的流变行为和剥离力的 影响。悬浮液在25°C时表现出剪切增稠行为，阻碍了打印过程中的浆料补充，而在最佳工艺温度35°C时，观察到从剪切增稠到剪切减薄的过渡，这对于实现完美的陶瓷3D打印非常理想。当打印温度升高至45°C和55°C时，在极低剪切速率（打印过程中材料处于静态时）下，混合物的粘度增加，从而影响剥离力。剥离力测量和FTIR结果比较显示，较高的交联密度和基础粘结剂的活性导致了固化层与打印机透明薄膜之间更强的粘附，因此产生了更高的分离/剥离力。总之，在适当的打印温度下进行热陶瓷立体光刻可以解决许多打印和后打印问题，如变形和开裂，从而实现更强、尺寸精度更高的陶瓷组件。