Jirasak Tharajak

Biocompatibility of transition metal-substituted cobalt ferrite nanoparticles

Transition metals of copper, zinc, manganese, and nickel were substituted into cobalt ferrite nanoparticles via a sol–gel route using citric acid as a chelating agent. The microstructure and elemental compositions of the nanoparticles were characterized using scanning electron microscopy combined with energy dispersive X-ray spectroscopy. The particle size of the nanoparticles was investigated using particle size analyzer, and the zeta potentials were measured using zeta potential analyzer. The phase components of the synthesized transition metal-substituted cobalt ferrite nanoparticles were studied using Raman spectroscopy. The biocompatibility of the nanoparticles was assessed using osteoblast-like cells. Results indicated that the substitution of transition metals strongly influences the physical, chemical properties, and biocompatibility of the cobalt ferrite nanoparticles.

Friction Coefficient and Worn Surface of Ferromagnetic Materials under Magnetic Fields

Several machine components including a part of electrical circuit box, an electrical motor and an automotive part were common ferromagnetic materials used under the magnetic fields. In the general, their friction had occurred in the magnetized materials during operation. The friction coefficient of the sample under magnetic fields was different from the sample without magnetic field treatment. Its friction coefficient had correlation with wear behavior of specimens. The wear protection procedures for the ferromagnetic parts during operation are recognized different from others without magnetization. Its friction coefficient was thus used to measure the wear characteristics with a ball on disc friction tester. The microstructure of wear trace and debris was investigated by scanning electron microscope. From the results, the magnetic fields affected the change of friction coefficient. The friction coefficient was decreased with an increasing magnetic intensity. This was because the wear debris was induced and thus decreased the adhesive wear mode during friction test.

Development of Thermal Spray Map for Liquid Feeding Thermal Spray System

This research work exhibits a procedure to classify and reorder thermal spray data point so that relationships and correlations between competing processes and materials can be identified. The broad range data mining of published experimental work was performed to create thermal spray map (TS map). A single TS map displayed the correlation between standoff distance (SOD) and feeding particle size is mainly focused. The discussion and evaluation of TS map was taken place. These data mining could be useful to use and/or adapt as reference points for the thermal spray experiment set up in the future.

Antimicrobial Property of Cold-Sprayed Transition Metals-Substituted Hydroxyapatite/PEEK Coating

The antibacterial property of several types of transition metals such as silver, nickel, zinc, and copper substituted hydroxyapatite (HA) composite coatings was investigated against staphylococcus aureus (S. aureus). Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX). Transition metals-substituted hydroxyapatite/PEEK coatings were successfully deposited using cold spraying parameters of 10-14 bars at preheated air temperature between 150 and 160 °C. The results indicated that copper substituted hydroxyapatite showed the best antimicrobial property against S. aureus.

Antimicrobial Property of Hydroxyapatite Derivative Nanoparticles

Recently, the antimicrobial activity of ceramic nanoparticles has been highlighted and much attention is now directed toward using them as a new substitute over conventional organic agents, which tend to contain noxious materials harmful to humans. The use of these ceramics has the advantage of containing mineral elements that are essential to the human body as well as a strong antibacterial activity, even when present in small concentrations. In this work, the antimicrobial ceramics based on hydroxyapatite (HA) were successfully prepared in a wet chemical process with additions of several types of transition metal salts. Eventually, we presented methods for the synthesis of modified HA and their antimicrobial efficiency against S. aureus. The incorporation of transition ions into HA backbone structure can be used as effective bioactive delivery systems for the slow release of antibiotics.

Influence of Lubricating Ceramic Content on Oxidation and Water Contact Angle of Carbon Steel

Hexagonal boron nitride (hBN) has wide variety of possible applications in different fields as from the metallurgy to the cosmetic products. This hBN microstructure provided excellent lubricating properties and then had potential to apply on metal surface in order to improve friction and prevented the metal substrate from oxidation. In this study, the several concentrations of hBN were added into epoxy resin and coated on the carbon steel substrate. The results indicated that the optimum concentration of used hBN increased water contact angle and prevented carbon steel substrate from oxidation. This useful knowledge can be further used to support industrial work especially in preventive corrosion/oxidation field.

Influence of Feedstock Feed Rate on the Properties of SPPS-Deposited Cobalt Ferrite Splats

Cobalt ferrite sol-gel solution was deposited onto mild steel substrates to form single splats using a solution precursor plasma spray (SPPS) process. It was revealed that the thermal oxidation of cobalt and iron salts occurred mainly into six different formations of deposited splats. These formulations were cobalt monoxide (CoO), maghemite (γ-Fe2O3), cobalt oxide (Co3O4), cobalt oxyhydroxide (CoOOH), goethite (α-FeOOH), hematite (α-Fe2O3), magnetite (Fe3O4), and cobalt ferrite (CoFe2O4). The surface topographies of the splats exhibited burned, unmolten, partially molten, and completely molten splats. The feed rates of SPPS process played the important role on several properties of the splat such as splat morphologies and percentage of the obtained composite splat phases.

A Potential Application of the Mechanical Tensile Strength Test for Indicating Paper Biodegradation

Tensile strength test for paper has been regularly used in measurement of paper quality in the industry. In this study, changes in properties of paper during biodegradation were compared by measurement of the tensile strength cellulose activity. Samples of filter paper and polyethylene coated paper were digested with cellulose degrading Bacillus isolates. Treatment with water was used as a negative control. The paper samples were cut into precise shape according to the standard protocol of mechanical tensile strength test to measure the maximum tensile force. After removing bacterial biomass, reducing sugars were measured as a surrogate for callulase activity in the spent fermentation broth and the paper samples were subjected to the mechanical strength, breaking load and stretch tests. The results showed the amount of stretch in paper was critically reduced over longer contact time in bacterial culture. Changes in the mechanical strength were apparent within 3-7 days of contact time, whereas changes in reducing sugars were observed only after 7-10 days of incubation depending on the paper type. In filter paper samples, more reducing sugars and less mechanical strength indicated increased biodegradation of the cellulose matrix. Overall, the mechanical tensile strength test was deemed an early indicator for paper biodegradation that may have commercial application.

Antimicrobial Properties of Transition Metals Substituted Chitosan against Cobetia Marina

This research work offers the new organic compound which has potential to replace the use of tributylin (TBT) in antifouling application. All modified chitosan powders were synthesized using in-house powder processing techniques. Pure and modified chitosan were evaluated for fouling properties via antimicrobial activity test against Cobetia Marina (C. Marina). The results indicated that copper substituted chitosan (CS-Cu) showed the highest inhibition zone and lowest number of C. Marina survival. It can be implied that CS-Cu showed the best antimicrobial ability against C. Marina.

Cold Spray Modification of ZnO-Cu Coatings for Bacterial Attachment Inhibition

This research work describes the processing of antibacterial and hydrophobic feedstock suitable for marine antifouling coatings. A composition of agglomerated ZnO-Cu powder and respective produced coatings were evaluated for fouling properties via antimicrobial activity test. Wettability of coating was also determined by contact angle measurements. These new antifouling coatings aim to prevent the growth of biofilm, reduce biofouling and improve both maintenance cost and fuel efficiency of the maritime structures and vessels. It should be able to extend dry docking cycle by providing an alternative environmentally compliant coating that is long lasting compared to conventional paint coatings. The results showed that ZnO and copper composites inhibit the C. marina attachment on the coating surfaces.