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Dai L.,Hebei United University | Dai L.,Hebei Province Key Laboratory of Inorganic and Non Metal Materials | Wang X.,Hebei United University | Zhou H.,Hebei United University | And 5 more authors.
Ceramics International | Year: 2015

ZrC was successfully synthesized by direct electrolysis of non-sintering ZrO2/C mixture in molten CaCl2 electrolyte. The process of the electrochemical solid state reduction was investigated by characterizing the composition and microstructure of the products under different experimental conditions, in conjunction with analyzing the voltammetric features of initial powders in molten CaCl2. The results showed that the pure ZrC powder could be obtained by direct electrolysis of non-sintering ZrO2/C mixture in 1123 K CaCl2 melt at 3.1 V for 7 h when carbon content in mixture was over stoichiometric ratio of ZrC. Besides the role of carbon source, carbon also promoted the electrochemical reduction of ZrO2. The reaction process involved the electrochemical reduction of ZrO2 in the presence of carbon to form ZrC with CaZrO3 as intermediate. © 2014 Elsevier Ltd and Techna Group S.r.l.


Dai L.,Hebei United University | Dai L.,Hebei Province Key Laboratory of Inorganic and Non Metal Materials | Lu Y.,Hebei United University | Wang X.,Hebei United University | And 4 more authors.
International Journal of Refractory Metals and Hard Materials | Year: 2015

Abstract Chromium carbides were synthesized by direct electrolysis of non-sintering Cr2O3/C precursors in CaCl2 molten at 1123 K. A series of electrolysis experiments were conducted with different Cr2O3/C molar ratios, cell voltages and electrolysis time. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) techniques, respectively. The results showed that the single-phase Cr7C3 powders with a mean diameter of < 200 nm were prepared after electrolysis at 2.8 V for 5 h in 1123 K CaCl2 melt. By prolonging the electrolysis time to 10 h, the product was converted into a Cr7C3 and Cr3C2 composite. Carbon was not only used as a raw material, but could also accelerate the rate of electrochemical reduction of Cr2O3. The reaction procedure forming the chromium carbides involved the electro-deoxidation of Cr2O3 and combined with carbon simultaneously. © 2015 Elsevier Ltd. All rights reserved.


Meng W.,University of Science and Technology of China | Dai L.,University of Science and Technology of China | Dai L.,Hebei Province Key Laboratory of Inorganic and Non Metal Materials | Zhu J.,University of Science and Technology of China | And 4 more authors.
Electrochimica Acta | Year: 2016

The TiO2@WO3 core-shell composite with mass ratio of core and shell4:1 was prepared by a hydrothermal synthesis method using sodium tungstate dehydrate, nitric acid and commercial TiO2 powder as raw materials. A novel mixed potential NH3 sensor was fabricated by using above-mentioned TiO2@WO3 as sensing electrode and La10Si5.5Al0.5O27 as solid electrolyte. X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology and structure of the samples. The sensor response to NH3 was examined at 400∼550 °C. The experimental results indicated that the sensor based on TiO2@WO3 sensing electrode possessed greatly enhanced NH3 sensing properties including higher and more stable response value and faster response rate compared to the sensor using TiO2, WO3 or TiO2-WO3 mixture sensing electrode under the same conditions. The responding potential values of the sensor with TiO2@WO3 sensing electrode exhibited a linear dependence on the logarithm of the NH3 concentrations. The highest NH3 sensitivity of 74.8 mV/decade was achieved at 450 °C. In the meantime, the sensors also showed well anti-interference capability to CH4, CO2 and H2, but noticeable cross sensitivity toward NO2 was observed. O2 effect on responding signal could be calibrated by predetermining O2 content. © 2016 Elsevier Ltd. All rights reserved.


Dai L.,University of Science and Technology of China | Dai L.,Hebei Province Key Laboratory of Inorganic and Non Metal Materials | Zhou H.,University of Science and Technology of China | Yang G.,University of Science and Technology of China | And 4 more authors.
Journal of Alloys and Compounds | Year: 2016

An amperometric type NH3 sensor based on La10Si5MgO26 electrolyte is reported in this paper. The design of this type sensor is significantly simplified due to the in-situ preparation of the nano-structured CoWO4 sensing electrode in the pre-sintered porous La10Si5MgO26 layer by impregnation method. The XRD and SEM investigations show that the CoWO4 particles with the diameters about 50-100 nm are obtained after calcined at 800°C for 3 h. The performance of the sensor is investigated with respect to the sensitivity at different temperatures, influence of the CoWO4 loading and calcination temperatures, reproducibility and selectivity. The complex-impedance measurements are performed to analyze the mechanism of the sensor. The results show that the sensor exhibits good amperometric response-recovery characteristics to NH3 in the temperature range of 500-650°C at a constant bias voltage of 400 mV. Good linear correlations between the response currents and the NH3 concentrations for 30-300 ppm are obtained. The influences of the loading and calcination temperature of the CoWO4 sensing electrode on the sensing performance of the sensor suggest that the enhanced triple phase boundary is in favor of the improvement of the sensing performances. The present sensor also displays good reproducibility and low cross-sensitivities to various co-existing gases. © 2015 Elsevier B.V. All rights reserved.


Dai L.,University of Science and Technology of China | Dai L.,Hebei Province Key Laboratory of Inorganic and Non Metal Materials | Liu Y.,University of Science and Technology of China | Meng W.,University of Science and Technology of China | And 6 more authors.
Sensors and Actuators, B: Chemical | Year: 2016

In2O3 with different morphologies are prepared by the hydrothermal method and examined as the sensing electrodes (SE) of the mixed potential type NH3 sensors with La10Si5MgO26 as electrolyte. Compared with In2O3 micro/nano spheres and micron rods, the sensor using In2O3 nanospheres-SE exhibits higher sensitivity (-58.94 mV/decade) to NH3 at 550°C. The sensor is also found to be insensitive to the coexistant gases (H2, CH4 and CO2), while the notable cross-interference of NO2 is observed. In order to improve the anti-interference of the sensor to NO2, CuO is used as the reference electrode (RE) instead of Pt electrode. As a result, the response potential difference (ΔV) of the sensor to 100 ppm NH3 is lowered from 44% (for Pt-RE) to 15.6% (for CuO-RE) in the presence of 100 ppm NO2. The sensor using In2O3 nanospheres-SE and CuO-RE also shows well response-recovery characteristics to NH3 at 400-600°C. The response ΔV values of the sensor linearly depend on the logarithm of the NH3 concentrations in the range of 25-500 ppm. The mixed-potential-model of the sensor is identified by the polarization curves in different atmospheres. © 2016 Elsevier B.V. All rights reserved.

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