02-11-2016, 11:27 AM
Preparation of Calcium Titanate and Calcium Zirconate Nano Powders by Molten Salt Synthesis Method
1463479965-PREPARATIONOFPEROVSKITEOXIDETITANATESBYMOLTENSALTTECHNIQUE (1).docx (Size: 1.31 MB / Downloads: 7)
Abstract
The perovskite ceramics, such as the alkaline earth titanates and zirconates and their binary systems are of interest for their temperature insensitive dielectric properties. The calcium titanate and calcium zirconate find applications in pulse discharge capacitors and energy storage capacitors and these dielectric materials could impact in microwave capacitors, electric hybrid and fuel cell vehicles. In the present work, calcium titanate and calcium zirconate nano powders were prepared by molten salt synthesis route. Calcium oxide and zirconium oxide and titanium dioxide were used as precursors obtain respective nano powders. The prepared nano powders were characterized by XRD, FTIR, TGA/ DTA, SEM technique. Two line about the results
1. INTRODUCTION:
Calcium titanate (CaTiO3) is one of the alkaline earth titanates compound similar to barium titanate (BaTiO3), magnesium titanium oxide (MgTiO3) and strontium titanate (SrTiO3). These titanates have recently attracted attention of many researchers because they find applications as ferroelectric, semi-conductive, photorefractive materials and catalysts [1]. calcium titanate is widely usedas dielectric in different fields of electronics applications [2–4]. CaTiO3 is recommended as a prospective ceramic material for microwave applications because it possesses relative permittivity and low dielectric losses [5]. Dielectric ceramics are used to produce a variety of components such as oscillators, filters and resonators for microwave systems
Calcium titanate is also find application for the treatment of radioactive wastes since it forms a number of solid solutions with rare earth metals [6-9]. based materials are used as catalysts for partial oxidation of light hydrocarbons [10]. calcium titanate has been tried as quantum paraelectrics like SrTiO3 and KTaO3 [15]. Moreover, According to Chandra et al [17], the (Ca1-xPbx)TiO3 system exhibits a ferroelectric behavior of CaTiO3 at very low temperature (TC ~ 105 K).[16] and an antiferroelectric phase transition in the temperature range 140-170 K, similar to that observed in (Ca1-xSrx)TiO3 system by Ranjan et al
Calcium titanate particles in the nanometer size regime have been successfully synthesized by mechanochemical method and used for photodegradation of methylene blue dye with respect to various dye concentrations and catalyst amount. CaTiO3 treatment exhibited 93 % degradation. The dye Antimicrobial activity shows that CaTiO3 photocatalyst was found to be non toxic to the environment[21].
[21] A green chemistry approach for synthesis of CaTiO3 Photocatalyst: its effects on degradation of methylene blue, phytotoxicity and microbial Study.
Sharad S. Gaikwad, Ashok V. Borhade and Vishwas B. Gaikwad,
Der Pharma Chemica, 2012, 4 (1):184-193
Calciumtitanate (CaTiO3) possesses excellent corrosion resistance, biocompatibility and good bioactivity properties due to its physical–chemical properties [22,23]. CaTiO3 ceramic coatings on titanium alloys by micro-arc oxidation, can significantly improve the corrosion resistance and osteointegration [24].
[22] HuangP,XuKW,HanY.MaterLett2005;59:185–9.
[23] WeiDQ,ZhouY,JiaDC,WangYMJ.BiomedMaterResB2008;84:444–51.
[24] SongWH,JunYK,HanY,HongSH.Biomaterials2004;25:3341–9.
The biocompatibility and electrical conductivity properties of HA-40 wt%BaTiO3 (25.9 vol% BaTiO3) and HA-40 wt% CaTiO3 (35.3 wt% CaTiO3) composites were investigated to verify its suitability as hard tissue replacement materials and found that are biocompatible and show good dielectric behavior comparable to dry human bone[25].
[25]Multifunctionality of Perovskites BaTiO3 and CaTiO3 in a Composite with Hydroxyapatite as Orthopedic Implant Materials.
A. K. DUBEY, B. BASU, K. BALANI, R. GUO AND A. S. BHALLA,
Integrated Ferroelectrics, 131:119–126, 2011
CALCIUM ZIRCONATE
The synthesis and characterization and photoluminescence of Eu3+doped CaZrO3 nano phosphors. The has been reported and found that the emission spectraof prepared phosphor shows good PLspectra in orange-red region so that the prepared phosphor is useful for display devices application[26].
[26] Optical studies of Eu3+doped CaZrO3phosphor for display device applications.
Neha Tiwari, R.K. Kuraria, S.R. Kuraria,
Optik 126 (2015) 3488–3491.
Eu3+-doped perovskite type CaZrO3-based phosphors were synthesized and, two different cations weres co-doped; with Sr2+ and Mg2+. the 6mol%Mg2+-doped sample exhibited the highest emission peak intensity[27].
[27]Synthesis andcharacterizationofEu3+ doped CaZrO3-based perovskite type phosphors.partIILpropertiesrelatedtothetwodifferent dominant Eu3+ substitution sites.
YoheiShimokawa, SatoshiSakaida, ShinyaIwata, KojiInoue, SawaoHonda, YujiIwamoto,
Journal ofLuminescence157(2015)113–118.
It is reported that the dielectric properties of CaZrO3 with glass frit addition are strongly dependent on the densification[28].
[28] Decreasing of CaZrO3 sintering temperature with glass frit addition.
Woo-Jin Leea, Akihiro Wakahara, Bok-Hee Kim,
Ceramics International 31 (2005) 521–524
CaZrO3, material, was deposited through plasma spraying on stainless steel (316L) substrates at arc currents of 400, 500 and 600A. Plasma sprayed CaZrO3 coating not only enhanced the wear resistance of the stainless steel but also showed the potential to furnish a bioactive surface[29].
[29]Effect of arc current on microstructure, texturing and wear behavior of plasma sprayed CaZrO3 coatings
M. Khalid, M.Mujahid, A.NusairKhan, R.S.Rawat, K.Mehmood,
Ceramics International 39 (2013) 2293–2302.
The electrical conductivities of Ca1 − xZrO3 − δ (0 ≤ x ≤ 0.10) ceramics were measured as a function of nonstoichiometry (x) and oxygen partial pressure (Po2) using impedance spectroscopy between 700 °C and 1100 °C. The stoichiometric CaZrO3 was a mixed ionic and electronic (hole) conductor in a high Po2 region. The analysis of impedance spectra revealed that the contributions of the grain and the grain boundary to the total conductivity were nearly constant independent of Po2 at 700 °C[30].
[30]The mixed ionic and electronic conductivity of CaZrO3 with cation nonstoichiometry and oxygen partial pressure
Soon Cheol Hwang, Gyeong Man Choi,
Solid State Ionics 179 (2008) 1042–1045
The microstructure of CaZrO3 flame sprayed coatings which confirms the potentiality of CaZrO3 coatings in thermal barrier applications[31].
CaZrO3 powders were synthesized by a chemical method The humidity sensing properties were evaluated by using an inductance, capacitance and resistance analyzer. The results revealed that all samples responded to the humidity by showing a change in resistance values. Complex impedance measurements indicated that the improved sample sensitivities can be attributed to their mesoporous structure along with hetero-junctions formed by second phases
. EXPERIMENTAL WORKS
Preparation Procedure:
The present investigation focusses on the preparation of calcium titanate (CaTiO3) and calcium zirconate (CaZrO3) prevoskite compounds by molten salt synthesis route (MSS). The MSS method is one of the simplest, most versatile, and cost-effective approaches for obtaining crystalline, chemically-purified, single-phase powders, at lower temperatures with shorter duration. The final product has little impurities as compared with conventional solid-state reactions. This technique uses salts as the reaction medium. The successes of the technique lies on (i) the identity as well as the size of the anion associated with the salt, (ii) the solubilities/dissolution rates of the constituent components within the molten salt, (iii) the precise melting point of either the salt or complex salt mixture, (iv) heating temperature and duration, (v) the unique morphological (e.g., shape) and chemical composition of the precursors,
The method of preparation of fine crystalline CaTiO3 and CaZrO3 powders is shown in Fig. 4.1. Calcium oxide (CaO) and Titanium dioxide (TiO2) and zirconium dioxide (ZrO2) were used as the starting materials. A eutectic mixture of sodium chloride (NaCl) and potassium chloride (KCl) is used as the flux. All these reagents were weighed according to the stoichiometric proportion, thoroughly mixed and used for the reaction. The homogeneous mixture of the reactants were transferred to an alumina crucible and heated in a electrical resistance furnace. The contents were heated at 8500C for 5 hours. During the decomposition and dissociation reaction, the diffusion of reacting species took place in the molten medium. The resulting product was then finely ground and washed with hot distilled water followed by 1% hydrochloric acid the final product is fine calcium titanate CaTiO3 and calcium zirconate CaZrO3 powders. Then the powders were repeatedly washed with hot distilled water and acetone.
Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) of the precursor powder were carried out using STA 1500 PL thermal sciences, version V4.30 analyzer. XRD analysis was carried out using X-ray powder diffractometer (Philips 8030X-ray Diffractor) with CuKα radiation (λ=1.5406 Å). The XRD patterns were compared with the standard JCPDS files. The elemental analysis of the powders was determined using the energy dispersive X-ray analysis (EDS) technique. This analytical tool was an attachment to the SEM (scanning electron microscope) unit. FT-IR analysis was performed with a Perklin Elmer UK paragon - 500 spectroscope in the mid infrared region (4000–400 cm−1). For each sample preparation, approximately 2 mg of sample was dispersed in 300 mg of KBr powder and pressed into a pellet. The pellets were used for the spectral analysis.
3. RESULTS AND DISCUSSION
In order to understand the thermal decomposition and dissociation reactions that occur during the precursor transformation into the final product, differentional thermal analysis and thermo gravimetric analysis were performed.Figure 2(a,b) shows the corresponding DTA-TGA curve for different precursor The possible reactions are recorded in the temperature range of 35 to 800 C The curve exhibits discrete regions of weight loss on the final product CaTiO3 and CaZrO3. There is a gradual decrease in weight loss noticed between room temperature to 260.88 C. Beyond this temperature, there is an abnormal loss in weight has been noticed upto 272.28 C. The major weight loss in this region is attributed to the dissociation of chemical compounds especially moisture and oxygen from the precursor. After this temperature, the loss in weight is meagre indicating the phase transformation of amorphous powder into crystalline CaTiO3 and CaZrO3. The DTA curve reflects the same information where an exothermic peak appeared at 217.90 C is responsible for the chemical dissociation of inbound water molecules. Another exothermic peak appears at 262.66 C which is attributed to the decomposition of the reactants. The gradual decrease in the DTA curve upto 800 C exhibits the transformation of the reactants into the final product CaTiO3 and CaZrO3.
The composition and the phase purity of the products were examined by XRD pattern. Figure 3 (a) and (b) show strong diffraction peaks indicating good crystallinity of the sample. The hkl values are in good agreement with the literature data corresponding to the perovskite structures of calcium titanate CaTiO3 (JCPDS No 89-8033), Calcium zirconate (JCPDS No. 35-0790) compounds
Figure 4(a) and (b) show the morphological features of the powders it is seen that the crystals exhibit diamond shaped structure in the size range of micrometers. SEM images of the CaTiO3 and CaZrO3 compounds are show in the fig. The SEM images reveal that the particles are homogenous in nature with thick agglomeration. As can be seen from the micrographs, the grain size of the crystals are in micron scale range. This may be possible due to the presence of molten flux during the synthesis process.
The SEM image in Fig.5.9 shows that the morphology of CaTiO3 powders exhibiting shows agglomerated particles.
The SEM image in Fig.5.10 shows that the morphology of CaZrO3 powders reveal agglomerated particles with porous microstructure ranging between 0.79μm to1.19 μm.
EDAX analysis provides data on chemical composition across the interface by tracing characteristic X-rays generated as a result of transitions between inner atomic electron energy levels of a specific element. EDAX spectra has shown in Figure 5 (a) and (b) reveal that the CaTiO3 and CaZrO3 is mainly composed of Ca, Ti/Zr and O. The EDAX profiles exemplifies that the constituent elements are in appropriate stoicheiometry in the synthesized compounds. The elemental analysis data is presented in Table 5.1.
Figure 6 (a) and (b) show the FT-IR spectrum of CaTiO3 and CaZrO3.The bands appeared spectrum around 458.79 and 612.73 are assigned to the stretching vibration due to the interaction between the oxygen and the metal bonds. The bands located around 1044.55 and 1634.72 cm-1 are responsible to the unantisymmetric and symmetric stretching vibration modes of metal- oxygen bonds. This observation is good agreement with the reported literature.
[A green chemistry approach for synthesis of CaTiO3 Photocatalyst: its effects
on degradation of methylene blue, phytotoxicity and microbial Study, Sharad S. Gaikwad, Ashok V. Borhade† and Vishwas B. Gaikwad, Der Pharma Chemica, 2012, 4 (1):184-193] There is a peak in the region around 3625.70 cm-1 which clearly indicates the presence of moisture in the prepared oxide powders.
4. CONCLUSION
CaTiO3 and CaZrO3 fine particles are successfully prepared by a single step, comprehensive molten salt technique. The TGA-DTA study discloses that the compound is formed at around 600 C and the formation involves several exothermic reactions. XRD patterns and SEM micrographs divulge the formation of desired orthorhombic phase of pervoskite type structure with the grain size in the range of nanometers. The EDS spectrum declares that the obtained product does not contain any impurities. The FTIR spectrum shows the characteristic vibration modes of CaTiO3 and CaZrO3.