This research aims to study the antibacterial coatings of invasive surgical medical devices, including dental implants, to reduce superficial and deep local infections over the long term. To obtain the coating without altering the initial properties of the substrate (dental implant made of TiZr bioalloy), simple, cost-effective, and efficient methods were employed, such as chemical deposition of silver (Ag). The deposition characteristics were analyzed using scanning electron microscopy (SEM), EDX analysis, and FT-IR infrared analysis. The in vitro testing of antimicrobial activity was conducted using the diffusion method by cultivating the bacterial strains Escherichia coli (E. coli) ATCC25922 and Staphylococcus aureus (S. aureus) ATCC25923 and measuring the diameter of the bacterial inhibition zone. Investigations and biocompatibility evaluations were performed on both uncoated and silver-coated (Ag) samples by analyzing cell viability and morphology in the presence of human fetal osteoblasts (hFOB cell line) and human gingival fibroblasts (HFIB-G cells) after 8 days of incubation. The research results confirm the biocompatibility of the coating, demonstrated by the lack of significant differences in cell density between the Ag-coated samples and the control group, as well as by the fact that the silver-coated surface effectively supports actin cytoskeleton organization, adhesion, and migration of both human osteoblasts and gingival fibroblasts. The results regarding the antibacterial efficiency of the silver implant coating indicated that the E. coli bacterial strain is more resistant than S. aureus. The resistance difference between the two bacterial strains was attributed to differences in the structure of their cell envelopes.

This paper presents an analysis of standards applied in tribology, especially concerning materials, test methods and failures of machine components, related to exploitation under load and motion. By the help of their own research and based on open literature, the authors justify the use of standards in tribology, but also the researchers’ initiative to develop new and more particular test methods and materials with application in tribology, starting from the already standardized ones. The market asks for products that could be rapidly and efficiently assessed by standards, but laboratory work ask for standards in order to compare old and new, original solutions. Thus, using standards does not block the researchers’ work, but helps to point out the new solution and even to develop new materials and test methods that accelerates the introduction of these new solution in actual applications. There are given examples of applying standards in tribology laboratories and how they are used or extend in order to point out a beneficial aspect of the tribological behavior.

This paper presents an analysis based on experimental data for pointing out the behavior of rapeseed oil when it is additivated with a modifier of friction and wear, the nano hexagonal Boron nitride. All tests are done on a four-ball machine, in mild regime. Test parameters were sliding velocity (0.38 m/s, 0.53 m/s, 0.69 m/s, corresponding to the spindle rotational speed of the four-ball machine of 1000 rpm, 1400 rpm, 1800 rpm (±10 rpm),), force (100 N – 300 N), test duration 1 h. There were calculated the average friction coefficient during the test and the average wear scar diameter (WSD) for each test. The same test parameters were done twice and the values in this paper are the average of these two tests. Wear was discussed for the same velocity range, in terms of WSD, but for comparing tests with different sliding velocity (implicitly, different sliding distances), there was used the wear rate of the wear scar diameter. The results on wear parameters, using additivated rapeseed oil, do not show spectacular results for the parameters tested in this study, but underline the “insensitivity” of the lubricants to the variation of the test regime (especially with respect to sliding speed), which is desirable for certain applications.

This paper presents characteristics of severe regime, tested on four ball machines for rapeseed oil and new formulated lubricant based on rapeseed oil and additivated with nano ZnO (average particle size 14 nm), in different concentrations (0.25% wt, 0.50 %wt and 1.0 %wt, respectively). Tests were done taking into account the procedure in SR EN ISO 20623:2018 Petroleum and related products - Determination of the extreme pressure and anti-wear properties of lubricants - Four-ball method (European conditions): starting from 500 N and increasing load in step of 50 N, at 1400 rpm, for 1 minute. There were recorded the wear scar diameter (WSD), the friction coefficient and the temperature of the oil bath, at the end of each test. Except for the concentration of 0.25% nano additive, the other two additivated lubricants have the wear-load curve lower meaning that, under higher loads, the nano additive prevents the severe wear of the ball surface.

This paper presents the influence of BN as additive in refined rapeseed oil in a mass concentration of 1%wt on the tribological parameters. Tests are done on a four-ball machine. The test parameters were load: 100 N...300 N and the the sliding speeds of 0.38 m/s, 0.53 m/s and 0.69 m/s, respectively. Particles of hexagonal BN have 500 ± 100 nm. The rapeseed oil was supplied by Expur SA Bucharest. For the tested ranges of the parameters, the additivation of rapeseed oil with BN does not improve the friction coefficient, but the wear rate of WSD seems to be less sensitive for the more severe regimes when the vegetal oil is additivated. The additivation of rapeseed oil with BN is still efficient for the tested ranges of load and speed as compared to the neat rapeseed oil, but there is visible that friction coefficient and analysed wear parameter are less influenced by the regime for the concentration of 1% BN in rapeseed oil.

Graphene oxide and graphite filled polyester composites were prepared by using conventional melt-mixing methods in order to improve tribological performance of polyester. It was investigated friction stability, microhardness, friction coefficient, and specific wear rate of the composites in details. It was found that the presence of graphite and graphene oxide influenced friction coefficient and wear rate of the composites. Graphene oxide decreased wear rate with increasing of test speed and graphite decreased wear rate for composite for all speeds. Tribological performance of the polyester/graphene composites is mainly attributed to bigger thermal conductivity for graphene, which can easily dissipate the heat which appears during the friction process at bigger forces. The positive influence of graphite on coefficient of friction (COF) of the composites is the result of the clivage of graphite layers during the loadings due to van der Waals weak bonds between the graphite layers.

A new class of polyester nanocomposites with graphene oxide and graphite has been obtained through a specific chemical method. Aiming to assess the tribological performance of this type of material, a basic experimental plan has been conceived which includes block-on-ring test, wear rate measurement, Vickers micro hardness test and scanning electron microscopy. Accordingly, the influence of graphene oxide and graphite on coefficient of friction and friction stability were investigated through wear test of nanocomposite blocks against steel rings. At the same time, specific wear rate was inferred in order to examine the mass loss which is strongly dependent on surface micro hardness. After wear test, SEM analysis allowed identification of the transfer film between nanocomposite surface and steel counterpart, and the occurrence of the third body. A careful examination of the friction coefficient recordings has highlighted the effect of the contact condition during the dry sliding test.

Vegetable oil-based lubricants have several disadvantages as compared to mineral and synthetic ones, including low viscosity that not encourage the generation of a continuous film when the tribosystem runs, consequently, implying a mixt or boundary. This is why the additivation of such oils is of great interests for researchers, producers and users. This paper presents results of testing the soybean oil additivated with nano graphite (0.25%wt, 0.50%wt and 1%wt) on a four ball machine. The friction coefficient is slightly increased for the additivated lubricants, but no evident dependency on concentration and test conditions was noticed. Supplementary tests will give the opportunity of a statistical approach of this parameter. Any concentration of nano graphite makes the wear parameter (wear scar diameter) to slightly increase as compared to the values obtained for the non-additivated soybean oil. The increase of the nano graphite concentration in this vegetable oil does not influence significantly the wear parameter, meaning that, at least for the tested regime, this is not an efficient anti-wear additive.

It is well-known the fact that carbon nanotubes (CNTs) contain carbon atoms in different hybridization states (sp 3 and sp 2 ), that generates complex structures (diamond and graphite respectively). These multiple connections generate strong interaction of forces between particular CNTs, that means Van der Waals forces and also π-π type those immediate result in the agglomerates obtaining and, singularizing the composite materials, the first effect is clusters generation process. The physical-chemical properties of nanocomposite materials are influenced by the appropriate CNTs dispersion obtaining in the matrix. This fact is efficiently obtained when the interactions energy between CNTs themselves is lower than the dispersion energy cumulated with the interactions energy between CNTs and the matrix. The dispersion energy considers CNTs blending techniques inside the matrix and the interactions energy between CNTs and the matrix supposes the chemical bond obtaining and physical-chemical interactions between CNTs and the matrix. The aim of this paper is to present some techniques of oxidative chemical treatment in order to obtain a CNTs functionalized surface as well as some techniques of coating with ceramic materials molecular layers in order to increase the chemical bond energy and the physical-chemical interactions between CNTs and the matrix. We used simple treatment methods of CNTs in acidic solutions (HNO 3 – H 2 SO 4 ) and basic solutions (NH 3 ) having hydrogen peroxide as the oxidant agent (H 2 O 2 30%). CNTs coating process with ceramic materials was made by using the precipitation method of their components (Fe 2 O 3 ) from the supersaturated aqueous solutions.

In order to obtain better homogenous composite material, different carbon nanotubes (CNTs) dispersion techniques in the polymeric matrix are very well known. Due to the strong interactions between CNTs, the efficiency of these dispersion techniques is highly limited. The aim of this paper is to present improvement techniques considered as new step in the global dispersion process before the composite material final shape finalization. At this moment, it is very difficult to carry out a classical dispersion from technological point of view. In this paper, more than the acknowledged mechanical and ultrasonic dispersion method, the introduction of a genuine dispersion technique is proposed; it refers to an external vibrant magnetic field able to determine a vibration movement of CNTs covered by a molecular Fe (III) oxide. This external vibrant magnetic field is made by using a permanent magnet involved in a rotational movement around its own axis and also interacts with the individual CNTs own magnetic fields. The maintenance of a tensioned vibrating state at the individual CNT level contributes to a good dispersion state preservation and increases the connections and physical-chemical interactions hindering. The dispersion efficiency in a vibrant magnetic field was studied using the comparative methods, correlating the electronic microscopy analysis with the mechanical strength tests. With respect to the composite material obtained under these conditions, a significant quality improvement as well as a mechanical strength increase was observed.

In order for the implant to exert its antibacterial function in optimal conditions its surface has to be covered with uniformity chemical deposition which confers antibacterial properties. The experiments demonstrated that the most effective forms of the silver which determine the microbial joining are the silver salts and therefore a more uniform coverage of the implant. The paper presents the research results on the chemical deposition conditions of the metallic silver on the Ti10Zr oral implant so as to obtain its optimal behaviour during operation.

This paper presents the influence of adding nano graphene particles in soybean oil in different massic concentration (0.25%, 0.50% and 1%) on the tribological parameters: friction coefficient, wear scar diameter. Tests are done on a four-ball machine from the lubricant laboratory LubriTest, at “Dunarea de Jos” University of Galati. The test parameters were load: 100 N, 200 N and 300 N and the speed 1800 rpm. The additive was supplied by PlasmaChem and the dry graphene nanoplatelets have a thickness: 1-4 nm; particles size: up to 2 μm, purity: 91 at.%. The soybean oil was supplied by Prutul Galati. The test balls are lime polished, made of chrome alloyed steel balls, having 12.7±0.0005 mm in diameter, with 64-66 HRC hardness, as delivered by SKF. The sample oil volume required for each test was 8 ml ±1 ml. The test method for investigating the lubricating capacity was EN ISO 20623:2003 Petroleum and related products Determination of the extreme-pressure and anti-wear properties of fluids four ball method.

This paper analyses the influence of carbon filler content over the mechanical properties of vinyl ester nanocomposite. The carbon fillers used in this study were graphite and graphene nano sized particles in the following weight percentage: 0.10, 0.15 and 0.20. The mechanical properties such as modulus of elasticity, flexural stress and flexural strain were determined using three point bending tests. A significant enhancement of overall mechanical properties were achieved for some of the nanocomposite materials studied.

In this article it is presented the influence of nanocellulose and microcellulose to mechanical and thermal properties of their composite with polyester. It used DMA method to determine the elastic and plastic behavior of polyester/nanocellulose and polyester/microcellulose composite. It is determined storage modulus, loss modulus, damping factor and glass transition temperature for polyester/microcellulose and polyester/nanocellulose composite. For all composite can be observed a good improvement of mechanical and thermal properties. Polyester/nanocellulose composites showed better properties than polyester/microcellulose composite due to strongest chemical bonds between nanocellulose and polyester matrix.

In this article we are going to study the influence graphene oxide and graphite have on thermal characteristics of polyester composites with the previously mentioned additives. By using the TMA method we managed to determine the coefficient of linear thermal expansion (CLTE) as well as the Tg of polyester composites with graphene oxide and graphite. We also calculated the average value of CLTE for the entire temperature interval studied, for temperatures below Tg in the 30-50 0 C interval and temperatures higher than Tg, in 70-190 0 C interval. For each of these values it has been noticed a significant decrease of CLET. The influence of the additives on Tg of the polyester composites additivated with graphene oxide and graphite has resulted in its increase

The influences of oxide grapheme and grapheme in thermosetting polymer composites are complex and they very much depend on the chemical bonds formed between the additives and the polymer matrix. This study has used polyester as polymeric matrix and oxide grapheme and graphite as additives. Determination of glass transition temperature (Tg) is important for practical uses of polyester composites due to the changes of characteristics triggered by transition, thus the polymer passes from elastic to plastic state. In order to determine the Tg we used TMA, DSC, DMA tests. The differences in determined Tg values for the same composite are due to different measurements as resulted from each test.

This article presents a description of mechanical properties for composites materials obtained by polyester resin and two types of reinforcements nanocellulose and microcellulose. Mechanical properties and an analysis of the results obtained by laboratory testing specimens, according to standards requirements in force, speed loading for three points bendings. Finally, conclusions and recomandations are based on the results. Mechanical test methods for reinforced polymer composites have to be appropriate to the type of composite analyzed as the structure of the product to be carried out starting from such material with their real working conditions. For any polymer composite material is appreciated the need for a minimum of trials on which it can be satisfactorily characterize material, for three bending points test 5 specimens.

The paper presents a synthesis of the laboratory research on the conditions of achieving chemical deposition of silver on oral implants made of Ti base alloy (bioalloy Ti10Zr). There were used several chemical deposition regimes in which were modified deposition parameters (temperature, stirring time) for two types of implants (different screw thread geometry). Study of the influence of deposition conditions was performed through analysis at scanning electron microscope (SEM) with EDX analyzer. The results revealed the presence of silver, microdispersed particles with morphologies and degrees of dispersion dependent on the factors and technological conditions of obtaining the chemical deposition.

Friction coefficient and linear wear rate of polyester-carbon nanotubes composites were investigated through ball-on-flat reciprocating test, under dry sliding contact. Three types of nanoscopic fillers were used: multiwall carbon nanotubes (MWCNT), functionalized multiwall carbon nanotubes (MWCNT-COOH) and singlewall carbon nanotubes (SWCNT), with three values of weight content 0.1, 0.15 and 0.2 wt%. Comparative analysis was done for polyester and its composites tested over 14 m sliding distance, under three values of load, 30 N, 40 N and 50 N. Composites containing MWCNT underwent a decrease in friction coefficient and linear wear rate only in case of 50N loading. An improvement of wear behavior under 50N loading was obtained for the composite with 0.10 wt% functionalized carbon nanotubes. Generally, better values of wear rate at 50 N loading were recorded in case of composites with 0.15 wt% and 0.20 wt% MWCNT and SWCNT, respectively. Optical and electronic investigation of the worn surfaces revealed the occurrence of abrasive, adhesive and fatigue wear. Abrasive wear is due to the hard particles detached from the counterpart which produce scratches and furrows on sliding track. Adhesive wear results when soft particle of polymer are caught and blocked among the asperities of counterpart, and it develops over a local area, being influenced by temperature rise. Fatigue and abrasive wear are responsible for the formation of the 3rd body between contacting parts which affects the friction and wear behavior. Morphological analysis of worn surface showed the rise of transfer film that induces instability of wear parameters.

Graphenes have aroused great interest among the scientists lately, due to their special physical properties which are supposed to be transferred to composite materials [1,2,3,6]. Some polymers show low mechanical properties which can be improved by adding various types of materials [9,13]. Using nanoparticles, an enhancement of mechanical, thermal and electrical properties can be obtained, even for small contents of additives [10,11,12,14,15,16]. The evaluation of mechanical properties of polymer composites with graphene can be achieved relying on the three-point bending tests [4]. This work presents a few conclusions resulting from the three points bending tests of the polyester composites with graphene and graphite [7,8].