Research Background
Piezoelectric ceramics can achieve the conversion between mechanical energy and electrical energy, making them key materials in important fields such as information communication, biomedical, defense industry, and consumer electronics. Since the discovery of lead zirconate titanate (PZT) in 1955, its excellent piezoelectric properties have led to its rapid application in sensors, actuators, and transducers, and it still dominates the market today. However, the high lead content (about 60 wt%) in PZT raises serious lead pollution issues during production, use, and recycling. With the ongoing global focus on environmental sustainability, governments around the world have implemented strict regulations to restrict the use of lead. The development of environmentally friendly lead-free piezoelectric materials has become an important scientific frontier and competitive focus in the field of functional materials internationally. Currently, lead-free piezoelectric systems represented by barium titanate (BT), potassium sodium niobate (KNN), and sodium bismuth titanate (BNT) have demonstrated excellent electrical properties, with some specific applications even surpassing those of lead-containing piezoelectric ceramics.
Although the above systems do not contain toxic lead elements, they still pose potential pressure on human health and the ecological environment during production, use, and disposal. Taking KNN ceramics as an example, niobium is the most abundant element in this system (accounting for about 54% by mass), its low abundance in the earth’s crust and the complexity of its extraction and purification processes can also cause environmental stress. Therefore, it is crucial to conduct a comprehensive environmental impact assessment of lead-free piezoelectric ceramics in a broader context.
Work Overview
The School of Materials Science and Engineering at Tsinghua University collaborated with Wuzhen Laboratory, Tongxiang Qingfeng Technology Co., Ltd., and the Central Party School (National Academy of Governance) to publish a research paper in Ecomat. This study conducted a full life cycle assessment (Life Cycle Assessment, LCA) comparing the ecological and energy sustainability impacts of lead-free KNN and lead-containing PZT ceramics from the acquisition of raw materials, production, use, to disposal (Figure 1a). The study found that the toxicity impact of PZT ceramics mainly comes from the extraction and processing of lead oxide as a raw material. In comparison, while the main toxicity impact of KNN ceramics comes from niobium oxide, its impact is significantly lower, with the overall impact on ecology and human health being only 20% of that of PZT (Figure 1b).
By comparing three key environmental impact indicators (acidification factor, eutrophication factor, and global warming factor) between KNN and PZT, it was found that the acidification impact of PZT ceramics is 1.25 times that of KNN ceramics, while the eutrophication impact is more than twice that of KNN ceramics. Resource consumption analysis indicates that PZT and KNN ceramics impact resource indicators through the non-biotic resource consumption potential of lead oxide and niobium oxide, respectively, but KNN ceramics only have 11% of the resource impact of PZT ceramics. From these three aspects, PZT ceramics exhibit greater negative impacts, with pressure on ecological and energy sustainability exceeding that of KNN ceramics by 3.5 times (Figure 1c). This also means that KNN ceramics pose lower risks to human health and are more conducive to the sustainable development of the ecological environment.
Figure 1 (a) The entire life cycle process of piezoelectric ceramics from raw material acquisition, production, use to final disposal; (b) Comparison of toxicity impacts of unit volume PZT and KNN piezoelectric ceramics over their life cycles; (c) Comparison of toxicity, environmental pressure, resource pressure, and waste emissions of unit volume PZT and KNN piezoelectric ceramics over their life cycles.
Work Highlights
1. Through a full life cycle assessment, the impacts of PZT and KNN ceramics on human health and ecological sustainability were quantified. The life cycle assessment indicated that PZT ceramics exhibit higher negative impacts compared to KNN ceramics, mainly due to the extraction, processing, and pollutant emissions associated with lead oxide as a raw material.
2. Compared to PZT ceramics, KNN ceramics pose lower risks to human health and have greater environmental sustainability. Nevertheless, there is an urgent need to develop more environmentally friendly extraction methods for niobium oxide raw materials to minimize energy consumption and waste emissions, thereby further reducing the negative impacts of KNN ceramics during production.
The related research findings titled “Life Cycle Assessment of Lead-Free Potassium Sodium Niobate versus Lead Zirconate Titanate: Energy and Environmental Impacts” were recently published in the internationally renowned journal EcoMat. Researcher Wang Ke’s team from Tsinghua University’s School of Materials Science and Engineering, Wu Yanqi, and Pak-Sheng Soon (who graduated with a master’s degree in 2022) are co-first authors of the paper. Dr. Liu Yixuan from Tsinghua University and Professors Guo Zhaohui from the Central Party School (National Academy of Governance) and Dr. Gong Wen from Tongxiang Qingfeng Technology Co., Ltd. are the corresponding authors of the paper. This research was supported by the National Natural Science Foundation, the Key Research and Development Program of Zhejiang Province, and the Leading Team Project of Innovation and Entrepreneurship in Jiaxing City.
Paper link: https://doi.org/10.1002/eom2.12450
References:
Wuzhen Laboratory: https://www.wuzhenlab.com/
Tongxiang Qingfeng Technology Co., Ltd.: http://www.tsingfeng-tech.com/
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