Diao Quan,Zhang Xiaomei,Li Jie,Yin Yuna,Jiao Mingli,Cao Jian,Su Chaohua,Yang Kai
The phenol-formaldehyde (PF) resin microspheres were firstly used as the template in the sensing electrode (SE) preparation process of sensors based on Y 2 O 3 stabilized ZrO 2 (YSZ). The PF resin microspheres were synthesized by a facile hydrothermal method. The high char yield and the few morphological changes of PF resin microspheres before and after sintering at 900 °C indicated the perfect thermal stability at high temperature. The sensors using MnCr 2 O 4 admixed with various contents PF microspheres (0 wt%, 5 wt%, 10 wt%, and 20 wt%) were fabricated and their sensing performances on NO 2 gas were also investigated. The sensor with sensing electrode prepared by MnCr 2 O 4 with 10 wt% PF showed the best NO 2 sensing performance with a response of 110.8 mV to 100 ppm NO 2 as well as the higher sensitivity (87.4 mV/decade) with the NO 2 concentration ranging from 10 to 500 ppm at 550 °C. According to the mixed-potential mechanism, the porous electrode is good for gas penetration, so the gas can easily reach the MnCr 2 O 4 /YSZ/gas triple phase boundary (TPB) to participate in the electrochemical reactions. Additionally, the sensor exhibited excellent selectivity and repeatability, which indicated its potential application in the NO 2 detection.
Luo Shuxuan,Ma Xingyue,Chen Ziwei,Zhang Lei,Wang Wanlin,Sun Yongqi
Chromium, broadly present in metallurgical systems such as stainless steel slags and vanadium-bearing slags, tends to be in a trivalent form bound in spinel phases due to their ultrahigh stability. To explore the stability of chromium bearing spinels with different divalent cations, herein ACr 2 O 4 (A=Mg, Zn, Mn) spinels were synthesized and stability-tested under both alkaline and acidic environments. X-ray diffraction (XRD) and refinement results reveal that MnCr 2 O 4 exhibited the largest lattice parameters. X-ray photoelectron spectroscopy (XPS) results show that MnCr 2 O 4 had the highest oxygen vacancy concentration, potentially triggering structural instability, consistent with the Fourier-transform infrared (FTIR) and Raman analyses. To further investigate the stability of ACr 2 O 4 spinels in alkaline and acidic environments, we introduced CaO and SiO 2 , respectively, for high temperature calcinations. XRD analyses reveal that ACr 2 O 4 spinels exhibited a high instability under an alkaline condition, with an increasing degree of instability for MgCr 2 O 4 , ZnCr 2 O 4 , and MnCr 2 O 4 successively. We further quantified the relationship between the oxygen vacancy concentrations and the divalent cations containing in spinels as well as the spinel stabilities under an alkaline environment. Under an acidic condition, all ACr 2 O 4 spinels demonstrated a relatively strong structural stability. The understanding of formation and stability of chromium bearing spinels under different conditions could contribute to potential modifications and applications of spinels especially with regard to resource recycling in metallurgy.
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