The composition of the steel sample used is as follows (wt. %): 9.98 Cr, 2.68 Mo, 1.45 Mn, 0.58 Si, 0.54 Ti, 0.49 Cu, 0.32 Co, 0.24 V and remaining 83.72 Fe. Steel samples having size 50 cm X 30 cm X 3 mm were polished by the reported methods before titania film deposition [25].
The morphology and thickness coated samples were studied by Field Emission Scanning Electron Microscopy (FE-SEM) using a Carl Zeiss EVO18 microscope. The roughness of coating determined by atomic force microscopic (AFM) analysis, performed on Bruker Multimode 8HR microscope. Vibration and noise damping experiments were carried out on custom made Brüel & Kjaer :- Impact hammer type 8206-001 having sensitivity 11.4mV/N, piezoelectric charge accelerometer type 4384, data acquisition module LAN-XI type 3050- A-060 with 6 channel inputs, PULSE Lab Shop’s 7700, Modal exciter (Type 4824) with a force rating of 100 N, Microphone Type: 4189-A-02.
2.1. Synthesis and characterization of titania sol
The oxime-modified titanium(IV) isopropoxide was synthesized by the reported method. [29] Titanium(IV) isopropoxide (2.000g) was added to the anhydrous benzene solution containg acetoxime (1.028 g). Reaction is maintained for 4 hours under refluxing (85°C) conditions. The acetoxime-modified titanium(IV) isopropoxide isolated after vaporization of solvent under vacuum conditions.
2.2. Deposition of titania coatings over Steel alloy
TiO2 sol was prepared by acid hydrolysis of acetoxime-modified titanium(IV) isopropoxide using nitric acid and maintain the pH 3.5 [29]. Prior to coating, the samples were mechanically ground down upto 800, grit with silicon carbide (SiC) paper and then washed in ethonal to remove impurities. The TiO2 spray coating over the steel samples were performed by gun spray machine with following parameters: 04 cycles; spray distance: 15 cm; nozzle size: 0.7mm and sample position: 90°.
2.3. Vibration and noise measurement
Under controlled laboratory environment, modal testing of two different plates (i) bare steel plate (ii) Tio2 coated steel plate was carried. The process is explained subsequently -
The setup shown above depicts rowing hammer test, conducted over the plates. Each plate (of size 50 cm X 30 cm X 3 mm) was marked according to the mesh of 10 x 20 so that each block measures 2 cm x 2 cm. The nodes (excluding the edges) were numbered from 1 to 171 in such a matter that 86th node became the center of the plate. The accelerometer was fixed at a strategic location inside the plate (Point No. 71) to be able to capture the initial five modes of vibration. The plate was excited using the hammer at every other node on the plate (rowing hammer test) as shown in figure 1. For each excitation given, response function was obtained from the accelerometer readings. For indicative purpose, we have shown one of the frequency response function and the corresponding coherence function in figure 2. The peaks obtained in the Frequency Response Function (FRF) indicate modes of free vibration of the plate [15, 30]. Further, the coherence function attaining value of one (for almost the entire range of excitation) indicates the response function is reliable and good.
To verify the modal frequencies obtained from rowing hammer test, another test was conducted in which natural frequency of first mode of vibration was obtained using the modal shaker. In this setup, an additional modal exciter (shaker) was used to provide excitation at the center of the plate to excite first mode of vibration.
In this shaker test, to measure the the force of excitation provided by shaker, force transducer was installed in between the shaker and the plate. Further, accelerometer was strategically located very close to the shaker excitation since this region which have maximum acceleration in the first mode. The shaker was excited using the signal from the set of function generator and power amplifier. Force and acceleration was measured for various frequencies of excitation. Different frequency inputs were given to the setup in the vicinity of the first natural frequency obtained from impact hammer test. This helped in hunting down the first forced natural frequency of the plate. For each of the frequency input, the output of accelerometer and force transducer is noted in the form of the response ratio (ratio of acceleration and force).