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Sensors & Transducers Journal, Vol. 134, Issue 11, November 2011, pp. 107-119The as –prepared samples were characterized by TG/DTA thermal analyzer (SDT Q600 V 20.9 Build20), XRD Philips Analytic X-ray B.V. (PW-3710 Based Model diffraction analysis using Cu-K αradiation), scanning electron microscope (SEM, JEOL JED 2300) coupled with an energy dispersivespectrometer (EDS JEOL 6360 LA), A JEOL JEM–200 CX transmission electron microscopeoperating at 200 kV analysis.2.2. Fabrication and Analysis of Gas SensorsThe sensing performance of the sensors was examined using a “static gas-sensing system. There wereelectrical feeds through the base plate. The heat was fixed on the base plate to heat the sample undertest up to the required operating temperatures. The current passing through the heating element wasmonitored using a relay with adjustable ON and OFF time intervals. A Cr-Al thermocouple was usedto sense the operating temperature of the sensors. The output of the thermocouple was connected todigital temperature indicators. A gas inlet valve was fitted at one port of the base plate. The requiredgas concentration inside the static system was achieved by injecting a known volume of test gas usinga gas-injecting syringe. A constant voltage was applied to the sensors, and current was measured by adigital Pico-ammeter. Air was allowed to pass into the glass dome after every Gases exposure cycle.3. Result and Discussion3.1. Spinel Structure and Formation Analysis2C 2 NH 3 O 2 + (9/2) O 2 → N 2 + CO 2 + 5H 2 OZn (NO 3 ) 3 + Fe (NO 3 ) 3 + 4C 2 H 5 NO 2 → ZnFe 2 O 4 + 8H 2 O + 10H 2 O + 5N 2TG-DTA analysis was performed at a heating rate of 10 K min -1 to investigate the thermal propertiesof. ZnFe 2 O 4. The TG spectrum and its 1 st derivative in Fig. 1 show the thermal decomposition ofZnFe 2 O 4 is the curve indicates that the slight weight loss in ZnFe 2 O 4 powder due to little loss about14.66 at temperature up to 200 0 C in ZnFe 2 O 4 of moisture, carbon dioxide and nitrogen gas. The DTAcurve of ZnFe 2 O 4 recorded in static air and in shown in Fig. 1. The curve shown that ZnFe 2 O 4 did notdecompose, but weight loss was due to dehydrogenation, decarboxylation and denitration. Furtherweight loss of about 16 % between the temperature range 400 0 C and continuous loss in weight about33.33 % up to 550 0 C is attributed to loss of organic materials and yield final product at 600 0 C. Thisweight loss and weight gained was very negligible. This weight change was in the range of 800 0 Cthese indicating that the synthesized powder was almost stable from the begging. The formationtemperature in the present work is found to be comparatively similar than that reported forcorresponding solid state reaction route.The X-ray diffraction pattern of ZnFe 2 O 4 powder is shown in Fig. 2 The observed d values comparedwith standard d values and are in good agreement with standard d value JCPDS data card number82-1042. The structure possesses the cubic may be attributed to the different preparation method whichmay yield different structural defects. The crystalline size was determined from full width of halfmaximum (FWHM) of the most intense peak obtained by shown scanning of X-ray diffraction pattern.The grain size was calculated by using Scherrer’s formula.d = 0.9λ/ βcosθ109
Sensors & Transducers Journal, Vol. 134, Issue 11, November 2011, pp. 107-119Fig. 1. TG-DTA curve of mixed precursor.The crystalline size can be calculated by using Scherrer equation. [21, 22]. Where, d is the crystallinesize, λ is the X-ray wavelength of the Cu K α source (λ=1.54056 A 0 ), β is the FWHM of the mostpredominant peak at 100 % intensity, θ is the Braggs angle at which peak is recorded. In order toobtain pure nanocrystalline ZnFe 2 O 4 particles and understand the thermal characterizations, the asprepared ZnFe 2 O 4 powder is further calcined at 180, 300, 500, 800 and 1000 0 C respectively (thecalcined temperature assigned as T C ). Fig.2 present XRD patterns for ZnFe 2 O 4 oxide nanoparticles.The effects of the calcinations temperature on the crystallite size of ZnFe 2 O 4 particles can bedemonstrated. Traces of ZnFe 2 O 4 crystallites phases (111), (311), (400), (422) and (511) are detectedin the XRD pattern for all calcined temperatures and then their intensities increase abruptly when theT C above 1000 0 C .In general, the sharpness of the XRD peak (i.e. high crystallinity) is increased as theT C increases. According to the (311) diffraction pattern of ZnFe 2 O 4 crystalline, the particle size ofZnFe 2 O 4 can be calculated from the full width at haif-maximum using the Scherrer equation.Obviously, the particle size of ZnFe 2 O 4 changes as the Tc controlled fewer than 180, 300, 500, 800 and1000 0 C, the order is 22.15, 22.90, 25.58, 32.21 and 32.34 nm, respectively. These indicate that thecrystallinity of ZnFe 2 O 4 is accelerated as the Tc above 500 0 C. It illustrates the relationship betweenthe annealing temperature and the average crystal size of the ZnFe 2 O 4 nanoparticles. It is obvious thatthe ZnFe 2 O 4 nanoparticle grows slowly at 300-5000 C and800-1000 0 C, respectively, the nanoparticle grow rapidly at 800 0 C.3.2. Partical Size AnalyzerParticle size distribution studies have been carried out by using dynamic light scattering techniques(DLS) Via Laser input energy of 632nm). It was observed that Zinc Chromium oxide nanoparticleshave narrow size distribution within the range of about 25-30 nm. Fig. 3. which well matches withcalculated from Debye-Scherrer equation.3.3. Morphology and MicrostructureThe microstructure of the sintered samples can be visualized from scanning electron microscope(SEM) tool. Fig. 4 Shown the particle morphology of high resolution, the particles are most irregularin shape with a Nanosize range.110
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