Witold Szymanski

Single and Multilayer Growth of Graphene from the Liquid Phase

The preparation of poly crystalline graphene from the liquid phase has been discussed.The mechanism of graphene growth from the liquid phaseon the Cu-Ni alloy and the type of atmosphere, used inthe graphene fabrication-acetylene, ethylene, hydrogen has been presented. Stages of nucleation and poly crystalline growth of graphene were identified. The paper presents theresults of a single-and multi-layered graphene growth phase.It is assumed the final result will mean the optimization of the industrial-scale production of low-cost poly crystalline graphene.

Bacterial colonisation of bioceramic surfaces

Abstract Hydroxyapatite (HAp – Ca10(PO4)6(OH)2) and tricalcium phosphate (TCP – Ca3(PO4)2) are bioceramic materials of special interest with regards to bone surgery, in particular the repair of bone tissue defects. These materials are highly biocompatible with bone and soft tissue; they are bioactive, osteoconductive and resistant to sterilisation processes. In comparison with other biomaterials, particularly metallic materials, bioceramic surfaces exhibit high resistance to bacterial colonisation. This is currently considered to be one of the most important issues concerning materials used in medicine, due to the fact that bacterial biofilm is difficult to combat or remove and can be responsible for recurrent infections. The aim of the present study was to evaluate bacterial colonisation on the surface of different calcium phosphate based materials.

A Fully Transparent Flexible Sensor for Cryogenic Temperatures Based on High Strength Metallurgical Graphene

Low-temperature electronics operating in below zero temperatures or even below the lower limit of the common −65 to 125 °C temperature range are essential in medical diagnostics, in space exploration and aviation, in processing and storage of food and mainly in scientific research, like superconducting materials engineering and their applications—superconducting magnets, superconducting energy storage, and magnetic levitation systems. Such electronic devices demand special approach to the materials used in passive elements and sensors. The main goal of this work was the implementation of a fully transparent, flexible cryogenic temperature sensor with graphene structures as sensing element. Electrodes were made of transparent ITO (Indium Tin Oxide) or ITO/Ag/ITO conductive layers by laser ablation and finally encapsulated in a polymer coating. A helium closed-cycle cryostat has been used in measurements of the electrical properties of these graphene-based temperature sensors under cryogenic conditions. The sensors were repeatedly cooled from room temperature to cryogenic temperature. Graphene structures were characterized using Raman spectroscopy. The observation of the resistance changes as a function of temperature indicates the potential use of graphene layers in the construction of temperature sensors. The temperature characteristics of the analyzed graphene sensors exhibit no clear anomalies or strong non-linearity in the entire studied temperature range (as compared to the typical carbon sensor).

Mechanical and tribological properties of gradient a-C:H/Ti coatings

The unusual combination of high hardness and very low friction coefficient are the most attractive tribological parameters of DLC (diamond-like carbon) layers. However, their usability is strongly restricted by the limited thickness due to high residual stress. The main goal of the presented work was to obtain thick, wear resistant and well adherent DLC layers while keeping their perfect friction parameters. As a proposed solution a Ti-TixCy gradient layer was manufactured as the adhesion improving interlayer followed by a thick diamond-like carbon film. This kind of combination seems to be very promising for many applications, where dry friction conditions for highly loaded elements can be observed. Both layers were obtained in one process using a hybrid deposition system combining PVD and CVD techniques in one reaction chamber. The investigation was performed on nitrided samples made from X53CrMnNiN21-9 valve steel. Structural features, surface topography, tribological and mechanical properties of manufactured layers were evaluated. The results of the investigation confirmed that the presented deposition technique makes it possible to manufacture thick and well adherent carbon layers with high hardness and very good tribological parameters. Preliminary investigation results prove the possibility of application of presented technology in automotive industry.

Frictional Behavior of Polyurethane Modified by Carbon Coatings Synthesized in Dual-Frequency Plasma

ABSTRACT A method for changing the surface properties of polymeric materials is by plasma treatment and, in particular, the modification by carbon coatings synthesized using plasma techniques. This article presents the tribological properties of carbon coatings produced on polyurethane substrates by a dual-frequency plasma technique. The analyses were made in terms of placement of the samples in the reactor and the number of modification steps. The samples were characterized by atomic force microscopy and friction tests, which were performed using a ball-on-disc tribometer. The chemical structure of the produced coatings was analyzed with the use of Raman spectroscopy. The obtained results show that the best tribological properties were characteristic of carbon coatings produced on samples placed onto the water-cooled electrode without preliminary ion etching in an argon atmosphere. The modifications decreased the coefficient of friction from 1.2, characteristic of unmodified polyurethane, to a value of about 0.38. The wear rate was reduced from 16.8 × 10−5 to a value of 4 × 10−9 mm3/Nm. Based on analysis of the wear tracks it was determined that for the proposed combination of a ZrO2 ball versus a polyurethane disc modified with a diamond-like carbon (DLC) layer the dominant mechanism of wear is friction; however, in extreme cases, when the DLC coating is worn out, characteristic debris can be observed.

Adhesion of E. coli Bacteria Cells to Prosthodontic Alloys Surfaces Modified by TiO2 Sol-Gel Coatings

The evaluation of the degree of bacteria E. coli adhesion to modified surfaces of the chosen prosthodontic alloys was presented. The study was carried out on Co-Cr (Wironit), Ni-Cr (Fantocer), and Fe-Cr-Ni (Magnum AN) alloys. Bare substrate as a control and titanium dioxide coated samples were used. The samples were placed for 24 hours in bacterial culture medium. After incubation period, a number of bacterial cells were evaluated by scanning electron microscope. The study revealed that modification of the alloy surfaces by titanium dioxide coating significantly decreases the amount of bacteria adhering to the surfaces and that additionally bare metal alloy substrates have a different degree of susceptibility to bacterial adhesion.

Effect of double-phase segregations formed due to two-stage aging on the strength properties of alloy PN-EN 2024

Commercial alloy PN-EN 2024 of the Al – Cu – Mg system is studied after one-stage and two-stage heat treatment. The strength properties, the hardness, the modulus of elasticity and the friction factor of the alloy are determined. The microstructure of the alloy is studied by the method of atomic force microscopy. The two-stage heat treatment is shown to be effective for simultaneous increase in the strength and ductility of the alloy.

Physicochemical and Biological Investigation of Different Structures of Carbon Coatings Deposited onto Polyurethane

The aim of this study was to examine the thrombogenic properties of polyurethane that was surface modified with carbon coatings. Physicochemical properties of manufactured coatings were investigated using transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy and contact angle measurement methods. Samples were examined by the Impact-R method evaluating the level of platelets activation and adhesion of particular blood cell elements. The analysis of antimicrobial resistance against E. coli colonization and viability of endothelial cells showed that polyurethane modified with use of carbon layers constituted an interesting solution for biomedical application.

Evaluation of the Erosive Potential of Selected Isotonic Drinks: In Vitro Studies

BACKGROUND Isotonic drinks are an important component of the diet of athletes. Sports drinks cause the body to maintain proper hydration and supplement minerals which are lost in sweat during excessive exercising. Aside from the benefits of isotonic drinks, it is important to be aware of the harmful effects of citric acid within the products, which could cause enamel erosion. OBJECTIVES The aim of the study was to evaluate the erosive potential of sports drinks using confocal scanning laser microscopy (CLSM). MATERIAL AND METHODS The studies measured the change of surface roughness of the dental enamel after etching using Isostar, Powerade and Gatorade drinks, and Fortuna orange juice. Measurements were repeated after 1, 2 and 3 h of exposure to the selected liquid. The evaluation of calcium compound contents was carried out using the complexonometric method. RESULTS The surface roughness measurements of dental enamel showed that the lowest values of the parameters Ra and Rz were obtained for Isostar and orange juice. The research of the calcium content in the selected beverages showed the highest value in Isostar (320.0 mg/L) and the lowest in Powerade (40.0 mg/L) and Gatorade (21.0 mg/L). CONCLUSIONS Our study confirms that Isostar is the safest sports drink, among the analyzed beverages, for athletes, because it causes the least erosive changes in dental enamel. It is recommended to supplement beverages to reduce their potential for erosion using calcium compounds.

Resistance-temperature characteristics of CVD and high strength metallurgical graphene

Gas sorption conditions on the graphene surface, as well as their influence on graphene properties, play a significant role when applications are considered. The influence of temperature and pressure on electric properties of graphene were investigated and discussed within this work, which was conducted in order to determine the border values for the sorption and desorption process of hydrogen on the graphene surface. The temperature was changed within the range of 243-373 K. Two types of graphene were used for comparison: one of graphene synthesised by our own method using chemical vapour deposition (CVD) and one of high strength metallurgical graphene (HSMG) in both conducting (cHSMG) and semiconducting (scHSMG) varieties. The characteristics were determined under hydrogen atmosphere in a fitted apparatus under pressure. The overall target material relies on the hydrogen storage of a designed graphene-based composite.