CHAPTER-3 EXPERIMENTAL-MATERIAL PREPARATION AND TECHNIQUES

Transcription

1 CHAPTER-3 EXPERIMENTAL-MATERIAL PREPARATION AND TECHNIQUES

2 CHAPTER III 3.0 EXPERIMENTAL-MATERIAL PREPARATION AND TECHNIQUES The experimental part contains the synthesis of Barium Titanate powders following the Wet-Chemical processes as follows. Sol-Gel Process Hydrothermal Synthesis 3.1 Synthesis of Barium Titanate using Sol-Gel process Materials Barium Hydroxide Octahydrate Ba(OH) 2.8H 2 O Merck GR grade Titanium tetrachloride LOBA Chemie -LR grade Isopropanol alcohol Merck GR grade Sodium hydroxide Merck GR grade All the chemical reagents were used without any prior purification Procedure Synthesis of Barium Titanate powders was carried out in four necked round bottom flask equipped with mechanical stirrer, water condenser, dropping funnel and nitrogen inlet. The typical set up of the reaction is shown in the Figure 3.1 used during the complete synthesis of barium titanate. The powder was synthesized using the barium precursors as Barium Hydroxide Octahydrate Ba(OH) 2.8H 2 O and titanium precursors as Titanium tetrachloride. The Isopropyl alcohol was used as the reactive solvent and the medium for the reaction. The aqueous solution of the sodium hydroxide was used as the alkaline mineralizer. 65 P age

3 During synthesis the aqueous solution of barium hydroxide octahydrate was prepared by dissolving the weighed amount of solid in water. Simultaneously a solution of titanium tetraisopropoxide was prepared in a four necked round bottom flask as shown in Figure 3.1 by mixing the titanium tetrachloride to isopropanol. Figure 3.1 Typical set up of the reaction The aqueous barium solution was added drop wise in the Ti-isopropoxide solution under continuous stirring and nitrogen atmosphere. The ph of the solution was maintained using the aqueous solution of caustic soda. The 66 P age

4 temperature of the reaction increases from room temperature to elevated temperature. The synthesis of barium titanate ceramic powder was carried out using the Barium hydroxide Ba (OH) 2.8H 2 O and titanium tetrachloride (TiCl 4 ). During synthesis the ratio of the Ba/Ti has been varied and optimized for obtaining the purified product. Several experiments were carried out varying the amounts of Ba and Ti precursors. Thus the Ba/Ti ratio is maintained at 1.02 using, 31.5 g of Ba (OH) 2.8H 2 O and 11.0 ml of TiCl 4. During the synthesis to avoid any immature hydrolysis the alkoxides were prepared using the Titanium tetrachloride and alcohol, alkoxide prepared is reacted further with aqueous solution of barium hydroxide. Titanium (IV) isopropoxide is prepared by diluting 11.0 ml (0.4 M) of Titanium (IV) chloride into (80 ml amount of IPA) Isopropyl alcohol. During the reaction aqueous solution of 0.2M barium hydroxide was prepared by mixing 31.5 g of barium hydroxide octahydrate in the 390 ml of distilled water. The weighed amount of sodium hydroxide was dissolved in 100 ml of water to prepare 12 N alkaline solutions. The addition time of barium solution during the reaction was also optimized. The 12N NaOH solution was added to maintain the ph of the reaction as ph= 8-9. During the reaction the mixture is stirred continuously with high speed to avoid any agglomeration and for preparing the homogenous solution. In order to prevent the generation of barium carbonate (BaCO3) the reaction is carried out 67 P age

5 under nitrogen atmosphere with continuous stirring. After complete addition of reagents in the required amount the temperature of the reaction is increased from 40 C to 100 C temperature. Thus during the course of work different reaction parameters were studied. The reaction parameters such as reaction time, reaction temperature were varied for the optimization of the reaction to obtain pure and high yield. The optimization of the process parameters is required to obtain the highest value of the dielectric constant. The reaction time was varied from 10 minutes to 80 minutes. The reaction temperature is varied from 40 ºC to 100 ºC. The prepared barium hydroxide solution is added in the Titanium solution at constant rate at elevated temperature under nitrogen atmosphere. After appropriate aging, BaTiO 3 suspension is filtered and washed using soxhlet extractor for 24 hrs to remove the remaining sodium ions from the filtered cake. This filtered cake is then kept in oven for overnight at 110 ⁰C. A detailed flow chart of the synthesis process is presented in Figure 3.2. Subsequently the powder so synthesized is used for preparation of pellets for characterizations. The electrical measurements were carried out on the pellet, thus the pellets were prepared using the synthesized BaTiO 3 powder by applying a load of five ton for one minutes. The prepared pellets were than sintered before characterization and measurement. The optimization of sintering time and temperature is required for best possible results from the product. The sintering time is varied from 1 hrs to 3 hrs and sintering temperature was varied 1000 ⁰C to 1200 ⁰C. 68 P age

6 Figure 3.2 Flow chart for Sol-Gel process 69 P age

7 3.2 Synthesis of Barium Titanate using Hydrothermal process Materials Barium Hydroxide Octahydrate Ba(OH) 2.8H 2 O Merck GR grade Titanium tetraisopropoxide 97 % solution Aldrich Chemicals -GR grade Isopropanol alcohol Merck GR grade Tetra methyl ammonium hydroxide (TMAH) Merck GR grade All the chemical reagents were used without any prior purification Procedure The barium titanate powders were synthesized using the barium precursors as barium hydroxide octahydrate Ba(OH) 2.8H 2 O, Titanium isopropoxide as titanium precursors (Ti(i-OPr) 4, TITP. Isopropyl alcohol was used as the diluting solvent for the reaction. The typical set up of the reaction is shown in the Figure 3.1 used during the complete synthesis of barium titanate. Tetra methyl ammonium hydroxide (TMAH, Merck) is used as an alkaline mineralizer. During synthesis the aqueous solution of barium hydroxide octahydrate was prepared by dissolving the weighed amount of solid in water. Simultaneously titanium tetraisopropoxide was diluted using isopropanol in a four necked round bottom flask as shown in Figure 3.1. The aqueous barium solution was added drop wise in the Ti-isopropoxide solution under continuous stirring and nitrogen atmosphere. The ph of the 70 P age

8 solution was maintained by TMAH. The temperature of the reaction increases from room temperature to elevated temperature. During this experiment, gm of barium hydroxide octahydrate was dissolved in 390 ml of hot water in an air tight round bottom flask fitted with agitator in the presence of nitrogen and at an atmospheric pressure under agitation. The solid dissolution us carried out in the hot water under inert atmosphere to avoid the unwanted formation of barium carbonate (BaCO 3 ). After complete dissolution the concentrated solution is filtered through wattmann paper to remove the unwanted impurities. Simultaneously diluted 40 ml of titanium tetraisoproxide by dissolving in 100 ml isopropanol under agitation in different reaction vessel. The diluted solution of TITP is dropped slowly into the clear solution of Barium Hydroxide under vigorous stirring. The solution resulted in white colloidal sol after addition of 10 ml of TMAH as weak base to neutralize the weak acid generated in reaction. The required amount of barium hydroxide Octahydrate and Titanium isopropoxide is used during the synthesis for maintaining Ba/Ti ratio about one. The reaction mixture is than transferred to the autoclave sealed vessel under nitrogen atmosphere. The hydrothermal synthesis is carried out to study the effect of high temperature and pressure on the particle size of the ceramic powder. The effect of different reaction parameters were also studied during the course of work. 71 P age

9 The sealed vessel is heated at varied temperature 130, 150, and 170 ºC varying the reaction time as 1 3 hr. The resultant precipitate is then cooled to room temperature and washed with water several times and finally dried at room temperature. Yield of barium titanate powder was %. The samples synthesized varying the reaction time and temperature are used for further characterization and studied the dielectric properties. Thus the particles size obtained from the different reactions are correlated with the dielectric properties by converting the powder in to pellet form. The particles were compacted or consolidated into pellets by pressing hydrostatically with a force of 4816 kg/cm 2 for about one minute. The effect of sintering during the course of the studies was carried out. The sintering time was varied from ⁰C varying the sintering time from hr. %. A detailed flow chart of the synthesis process is presented in Figure P age

10 Figure 3.3 Flow chart for Hydrothermal process 73 P age

11 3.3 Preparation of Pellets The powder synthesized using wet chemical process was used further for preparation of pellet by applying pressure of 4816 kg/cm 2 for about one minute. The effect of sintering was studied on the prepared pellets by varying the sintering time and temperature. The conducting silver paste was applied on both the surfaces of sintered pellets for measurement purpose. These silver pasted sintered pellets were used measuring dielectric properties. The microstructure of the sintered barium titanate is characterized by Scanning Electron Microscopy on polished and thermally etched samples. Energy Dispersive Spectroscopy (EDS) analysis is also conducted on the samples using INCA X-Sight, Model 7583, Oxford make EDS attachment on the SEM. The crystallite size is measured using line-broadening of X-ray diffraction signature from the alloys. X-ray Diffraction work is performed on a Bruker AXS D8 Advance X-Ray diffractometer using Ni filtered Cu-Kα radiation. Normal XRD scans with step resolution of 0.02 with time step of 0.5 sec is used. To ensure stability of the measurements with respect to change in resolution in angular coordinates and time, measurements are repeated with angular step size (in 2θ) of 0.05 with time step of 2 sec. The Cu - K α2 diffraction signal is removed by a standard stripping procedure to obtain the correct lattice parameters and grain size. The relative dielectric constant (ε r ) and the dielectric loss (tanδ) are measured at room temperature using Genrad 1658, RLC Digibridge. All measurements are made at 50 Hz, by applying 1 V potential difference across the test capacitor. 74 Page

12 The dielectric measurements for each sample synthesized varying the reaction time and temperature of the materials is listed in Chapter V Results and discussion. Thus, on detail studies and optimizing the reaction parameters the best synthesized materials was used further for dopant studies and polymer ceramic composite studies. 3.4 Doping of Barium Titanate with Rare Earth Elements The barium titanate powder synthesized using optimized hydrothermal process is further used for studying the effect of rare earth elements Lanthanum and Magnesium as Dopants for the ceramic powder Materials Hydrothermally synthesized BaTiO 3 powder Lanthanum chloride - Merck GR grade Magnesium chloride - Merck GR grade Procedure Barium Titanate powder was doped with the rare earth elements using the wet chemical process. During the process hydrothermally synthesized barium titanate is used for the dopant studies. The ceramic rare earth dopants were added to Barium Titanate using the chemical route synthesis, to study the doping effect on Barium Titanate for improving its dielectric properties. The Barium Titanate was synthesized via hydrothermal process as mentioned above. The solution of Lanthanum chloride LaCl3 was prepared by dissolving a 75 P age

13 required amount of LaCl 3 in distilled water. The resultant solution was added drop wise in the main solution of Barium Titanate under continuous stirring. The whole solution was fitted in the autoclave under the inert atmosphere. The reaction was continued at optimized reaction temperature and time for 150 C and 2 hr. The temperature and the pressure of the reaction have to be maintained during the course of the reaction. The material was cooled to room temperature, filtered washed and dried. Different sets of reactions were carried out varying the concentration from 0.1 to 1 wt % with respect to Barium Titanate. The resulting powder was used further for different characterization studies including its dielectric properties. Similarly, the effect of magnesium doping (MgCl 2.2H 2 O) with Barium Titanate was also studied using hydrothermal process by varying concentration from 0.1 to 1 wt% and studying its dielectric properties. The Magnesium chloride was dissolved in water and was added to the reaction mixture of barium titanate solution dropwise and allowed the reaction to continued for 2 hours at 150 ºC. The materials was filtered, washed and dried. The doped powders were dried and were used for further characterization and studied the dielectric properties. 76 P age

14 3.5 Surface Modification of Barium Titanate The hydrothermally synthesized barium titanate powder using the optimized reaction process having highest dielectric constant is used for preparation of polymer ceramic nanocomposites. The surface modification of powder was required to increase the compatibility of the powder with polymer matrix Materials Hydrothermally synthesized Barium titanate 3-Glycidoxypropyl (trimethoxy) silane Aldrich Acetic acid-merck Procedure Hydrothermally prepared nano Barium Titanate was organically modified using 3-Glycidoxypropyl (trimethoxy) silane. The different aqueous solutions of 0.1, 0.3 and 0.5 wt% of silane (with respect to Barium Titanate) were prepared. During addition of silane to the acidified water, the system was stirred for about 15 min before it hydrolyzed and formed a clear and homogeneous solution. The weighed amount of powder was mixed with the aqueous silane solution. The silane was applied on ceramic nanoparticles as diluted in order to improve processability and to increase filler wetting and dispersion. Aqueous solution was prepared, adjusting the ph of the water to 3.5 with acetic acid and then introducing the silane. The fillers were mixed with the silane for several minutes without additional solvent. After applying the silane, the powder of BaTiO 3 was dried at 110 C to avoid condensation of silanol groups at the surface. Silane treated 77 P age

15 Barium Titanate was crushed in motor pastel. The crushed powder was sieved and it was used to prepare nanocomposites. 3.6 Preparation of Polymer-Ceramic composites Materials Silane modified Barium titanate Epoxy- Diglycidyl ether of Bisphenol-A (DEGBA) Kuver Chemicals Poly (vinylidene fluoride) (PVDF) - Aldrich Chemicals Polyvinylbutyral (PVB) - National Chemicals Di-n-octyl phthalate-sulab chemicals Dimethyl formamide (DMF) LR grade Procedure Hydrothermally synthesized Barium Titanate using optimized process was used for preparation of polymer ceramic nanocomposites. Glycidoxytrimethoxy silane was applied onto ceramic particles as diluted aqueous solutions of 0.1, 0.3 and 0.5 wt% (with respect to Barium Titanate) of silane in order to improve processability and increase filler wet-out and dispersion. Aqueous solution was prepared, adjusting the ph of the water to 3.5 with acetic acid and then introducing the silane. After the silane was added to the acidified water, the system was stirred for about 15 min before it hydrolyzed and formed a clear and homogeneous solution. The fillers were mixed with the silane for several minutes without additional solvent. After applying the silane, the BaTiO 3 was dried at Page

16 C to avoid condensation of silanol groups at the surface. The detection of small quantities of silane in the products after the silanization process was achieved by Fourier Transform Infrared Spectrometry (FTIR) Epoxy-Ceramic Composite Weighed amount of silane modified Barium Titanate powder and epoxy resin were mixed efficiently using mechanical stirrer for 5 min at speed of 1000 RPM. The mixture was stirred and a weighed amount of commercially available curing agent was added in the reaction mixture and stirred for five more seconds. The whole reaction mixture was subsequently poured in the mould. The material was cured at room temperature for two hours followed by post curing at 60 C for one hour. The composite so prepared was released out of mould. The different composites were prepared by varying the percentage of barium titanate loading from 60 to 90 wt%. The composites were evaluated for the dielectric properties PVDF-Ceramic Composite The granule of PVDF was dissolved in Dimethyl formamide (DMF). The silane modified hydrothermally synthesized barium titanate powder was mixed in parts under continuous stirring. The calculated amount of di-n-octyl phthalate was added and mixed well and allowed to cure at room temperature. The different composites were prepared by varying the percentage of barium titanate loading from 60 to 90 wt%. The composites were evaluated for the dielectric properties. 79 P age

17 PVB-Ceramic Composite The powder of PVB was dissolved in Dimethyl formamide (DMF). The silane modified hydrothermally synthesized barium titanate powder was mixed in parts under continuous stirring. The calculated amount of di-n-octyl phthalate was added and mixed well and allowed to cure at room temperature. The different composites were prepared by varying the percentage of barium titanate loading from 60 to 90 wt%. The composites were evaluated for the dielectric properties. All these above mentioned samples, powders, modified BT powder, doped BT powder and polymer composites were characterized using different analytical techniques. These samples were also tested for dielectric measurements. 80 P age