Synthesis of ZnAl2O4 and Evaluation of the Response in Propane Atmospheres of Pellets and Thick Films Manufactured with Powders of the Oxide

Abstract

ZnAl2O4 nanoparticles were synthesized employing a colloidal method. The oxide powders were obtained at 300 °C, and their crystalline phase was corroborated by X-ray diffraction. The composition and chemical structure of the ZnAl2O4 was carried out by X-ray and photoelectron spectroscopy (XPS). The optical properties were studied by UV-vis spectroscopy, confirming that the ZnAl2O4 nanoparticles had a direct transition with bandgap energy of 3.2 eV. The oxide’s microstructures were microbars of ~18.2 nm in size (on average), as analyzed by scanning (SEM) and transmission (TEM) electron microscopies. Dynamic and stationary gas detection tests were performed in controlled propane atmospheres, obtaining variations concerning the concentration of the test gas and the operating temperature. The optimum temperatures for detecting propane concentrations were 200 and 300 °C. In the static test results, the ZnAl2O4 showed increases in propane response since changes in the material’s electrical conductance were recorded (conductance = 1/electrical resistance, Ω). The increases were ~2.8 at 200 °C and ~7.8 at 300 °C. The yield shown by the ZnAl2O4 nanoparticles for detecting propane concentrations was optimal compared to other similar oxides categorized as potential gas sensors.

Electrical Response of the Spinel ZnAl2O4 and Its Application in the Detection of Propane Gas

“…For some years now, the literature has reported that spinel-type transition metal oxides conform to the general formula XM 2 O 4 [1,2], where X can be the divalent cations Fe 2+ , Appl. Sci.…”

“…These compounds show interesting physical (such as magnetic and refractory) and chemical properties that make them suitable for several technological applications [3][4][5]. Moreover, they possess high resistance to acids, high melting points, relatively high surface areas, and good catalytic properties [1]. The good properties of these materials are due mainly to the nanometric size of their particles [6].…”

“…The ZnAl 2 O 4 is a spinel-type ternary compound [1,2,8], a ceramic semiconductor material with a bandgap of 3.5-3.9 eV [9,10]. According to the literature, ZnAl 2 O 4 can be adjusted to the aluminates' formula XAl 2 O 4 [5,11], where X is replaced by the divalent cation Zn 2+ [3,5].…”

“…It has been intensively studied due to its attractive properties, such as high thermal stability, low-temperature sinterability, low surface acidity, good diffusion, and high quantum yields [13], which have promoted its technological application in different fields. These applications include optical coatings, photo-electronic devices, display technologies, ceramics, and sensors [1,9,14]. Some reports have stated that the ZnAl 2 O 4 possesses high sensitivity, good linearity, small hysteresis, and short response and recovery times in humid [9] and propane [1] atmospheres, which is attributed to the porosity and the nanostructures (such as nanorods) obtained during the compound's synthesis [9].…”

“…These applications include optical coatings, photo-electronic devices, display technologies, ceramics, and sensors [1,9,14]. Some reports have stated that the ZnAl 2 O 4 possesses high sensitivity, good linearity, small hysteresis, and short response and recovery times in humid [9] and propane [1] atmospheres, which is attributed to the porosity and the nanostructures (such as nanorods) obtained during the compound's synthesis [9]. The goal now is to apply new materials (such as the semiconductors) to toxic gas detection systems [15][16][17].…”