Fabrication of high‐fracture‐strength and gas‐tightness PDC films via PIP process for pressure sensor application

Abstract

High‐fracture‐strength and high‐gas‐tightness thin‐film gas‐pressure sensors were fabricated using a silicon oxycarbonitride polymer‐derived‐ceramic (SiCNO‐PDC) material via a multiple polymer‐infiltration‐pyrolysis (PIP) process. To obtain dense SiCNO ceramic films, two types of liquid polyvinylsilazane (PVSZ) precursors were chosen; a high‐ceramic‐yield precursor with high viscosity (PVSZ‐1) was designed to construct the skeleton of ceramic film, whereas a relatively high‐ceramic‐yield precursor with low viscosity (PVSZ‐2) was designed to infiltrate in ceramic defects. The results confirmed that the PVSZ‐2 can effectively fill both intergranular and intragranular defects of ceramic films pyrolyzed by the PVSZ‐1, and produce the sponge‐like structures with nanosized pores. Although the density of the ceramic films only increased by 2.2%‐5.2% after PIP process, the gas tightness was fundamentally improved, and all ceramic films after PIP process could keep gas‐tight condition without loss of pressure after 72 hours. Similarly, the fracture strengths of the ceramic films after PIP cycles have also been improved, and the value could reach 108 MPa after only three PIP cycles. In addition, because a linear relationship among the load, resonant frequency, and deflection was detected in our ceramic films, the wireless passive gas‐pressure sensors with high‐sensitivity and high‐temperature resistance have been fabricated. It strongly indicates that the ceramic films obtained by our PIP process have real potential to be used as thin‐film gas‐pressure sensing elements in high‐temperature and high‐pressure fields.

Polymer-Derived Si-Based Ceramics: Recent Developments and Perspectives

“…Traditional forming techniques are the earliest and the most conventional techniques, and dry pressing [41,45], isostatic pressing [25,47], and tape casting [65] are more commonly used. The general route for the synthesis of PDCs using traditional forming techniques was to crosslink and solidify the precursor polymers and grind and sieve to obtain crosslinked polymer powders, which were then made into a green body by traditional forming techniques, and finally the green body was pyrolyzed.…”

“…Most of the PDCs prepared by the traditional techniques underwent the powder densification process, and their mechanical strengths were usually higher than those of the emerging forming techniques. Zhang's group [47] used liquid polyvinylsilazane (PVSZ) with different viscosities as precursors, then crosslinked, milled, and isostatic pressing molded them. To reduce the cracks and the porosity in ceramics, PDCs thin-films with high fracture strength and high gas tightness were prepared by polymer infiltration pyrolysis (PIP) process.…”

“…At present, there are two main methods to improve the mechanical properties of PDCs: doping [5,8,17,70,71] and densification [10,47,72]. As mentioned above, doping is a very important method to functionalize PDCs, and the improvement of mechanical properties is also inseparable from doping.…”

“…Polymer-derived Si-based ceramics release small molecular gases during pyrolysis and generate free paths inside the ceramics [47]. It is detrimental to the mechanical properties of ceramics, but this feature can be used to prepare ceramics with hierarchical porous structure and high specific surface area [7,8,12,30,48].…”

“…Wilhelm's group [18] fabricated PDCs-SiOC with high specific surface area (~400 m 2 •g −1 ) by freeze casting and loading with Ni nanoparticles, and it displayed good catalytic activity; in the CO 2 methanation reaction, the maximum conversion rate was 0.49, and the maximum methane selectivity was 0.74. In addition, by functionalizing polymer-derived Si-based ceramics, it can also significantly improve its mechanical [5,15,43,47,61], thermal [41,43,[62][63][64], and electrical properties [6,14,26,40,43], which could be widely used in the preparation of conductive ceramics, sensors, membranes, coatings, and components for usage under harsh environments.…”