Gábor Dobos

Catalytic performance of carbon nanotubes in H2O2 decomposition: Experimental and quantum chemical study

The catalytic performance of multi-walled carbon nanotubes (MWCNTs) with different surface chemistry was studied in the decomposition reaction of H2O2 at various values of pH and temperature. A comparative analysis of experimental and quantum chemical calculation results is given. It has been shown that both the lowest calculated activation energy (∼18.9 kJ/mol) and the highest rate constant correspond to the N-containing CNT. The calculated chemisorption energy values correlate with the operation stability of MWCNTs. Based on the proposed quantum chemical model it was found that the catalytic activity of carbon materials in electron transfer reactions is controlled by their electron donor capability.

[Carbon/carbon implants in oral and maxillofacial surgery--Part 2].

In their previous report, the authors presented observations regarding the long-term application of carbon/carbon implants. After evaluating the good functional and aesthetic results, the effect of the human body on the structure and morphology of the implants was investigated with state of the art methods. An implant retrieved from the body after eight years was compared to implants which were sterilized but not implanted (reference). Carbon and oxygen were the main components of both implants, however, as a result of the interaction with the human body the amount of oxygen increased 3-4 times and phosphorus, sulphur, calcium and iron were detectable as trace elements on the surface. The width of the carbon fibres (5-7 µm) building up the implants was not changed during the interaction with the human body. The surface of the implant retrieved from the human body was covered with a 15-17 µm thick layer, not present on the reference implant, having a similar composition to that of the carbon fibres (high amount of calcium that is typical to bone tissue was not detected). According to these results, the structure and the morphology of the implants were not altered notably by the human body.

Development of analytically capable time-of-flight mass spectrometer with continuous ion introduction.

The present article describes the results and findings explored in the course of the development of the analytically capable prototype of continuous time-of-flight (CTOF) mass spectrometer. Currently marketed pulsed TOF (PTOF) instruments use ion introduction with a 10 ns or so pulse width, followed by a waiting period roughly 100 micros. Accordingly, the sample is under excitation in 10(-4) part of the total measuring time. This very low duty cycle severely limits the sensitivity of the PTOF method. A possible approach to deal with this problem is to use linear sinusoidal dual modulation technique (CTOF) as described in this article. This way the sensitivity of the method is increased, due to the 50% duty cycle of the excitation. All other types of TOF spectrometer use secondary electron multiplier (SEM) for detection, which unfortunately discriminates in amplification in favor of the lighter ions. This discrimination effect is especially undesirable in a mass spectrometric method, which targets high mass range. In CTOF method, SEM is replaced with Faraday cup detector, thus eliminating the mass discrimination effect. Omitting SEM is made possible by the high ion intensity and the very slow ion detection with some hundred hertz detection bandwidth. The electrometer electronics of the Faraday cup detector operates with amplification 10(10) V/A. The primary ion beam is highly monoenergetic due to the construction of the ion gun, which made possible to omit any electrostatic mirror configuration for bunching the ions. The measurement is controlled by a personal computer and the intelligent signal generator Type Tabor WW 2571, which uses the direct digital synthesis technique for making arbitrary wave forms. The data are collected by a Labjack interface board, and the fast Fourier transformation is performed by the software. Noble gas mixture has been used to test the analytical capabilities of the prototype setup. Measurement presented proves the results of the mathematical calculations as well as the future potentiality for use in chemical analysis of gaseous mixtures.

Evaluation of voltage dip severity (a proposal)

The paper gives a novel approach to decide if a voltage dip was severe or the equipment attended should operate continuously during the dip. The method gives the possibility to create simple but characteristic general indices like the well known SAIDI. Results of long term measurements will be evaluated with the proposed method and compared with the norm-like classification.

Examination of the Surface Phosphorus Content of Anodized Medical Grade Titanium Samples

In case of titanium dental implants, the main goal is to create a surface where the bone cells can attach well, therefore osseointegration can occur. The chemical composition of the surface has an important role, because the surface has a direct contact with the living tissue and induces different reactions for example peri implantitis or osseointegration. In our work titanium sample made from the most commonly used dental implant material (Ti Grade 5) were investigated. The samples were treated by chemical etching in hydrogen-chloride and in phosphoric acid to remove the cut generated burr. After that the samples were anodized in phosphoric acid solution at 10 V, 20 V, 30 V or 40 V. As a result of these treatments, titanium-dioxide layers were created on the surfaces. Phosphorus (originating from the phosphoric acid bath) may also be found on the surfaces. This may promote osseointegration. The surface compositions were investigated with the aid of Secondary Ion Mass Spectrometry (SIMS). Based on these results we can conclude that anodization in phosphoric acid solution increases the phosphorus content of the surface. Approximately to the middle of the titanium-dioxide layer the phosphorus content is constant but lower with one order of magnitude than on the surface. In the deeper layers the phosphorus content continues to decrease until the base material where it significantly reduce.

AES investigation of inhomogenous metal-insulator samples.

In this article, the secondary electron-emission properties of both vertically and laterally inhomogeneous samples are discussed. To study the effect of surface coverage, the total electron-emission yield of tungsten and niobium samples was measured as a function of primary electron energy and oxide thickness. A method is suggested to avoid charging difficulties during AES measurements of samples that consist of both metal and various insulator parts.

Formation and characterization of electric contacts on CVD diamond films prepared by ion implantation

Diamond layers have a potential application as the highest band-gap semiconductor for electronic devices. One of the major problems is to form electric contact on the diamond surface useful for an electronic device. This paper shows the properties of the contacts formed by the very promising ion implantation technique. The diamond layers were deposited with Microwave Assisted Chemical Vapor Deposition (MW-CVD) equipped with special extra features like High Voltage Bias and Heated Substrate Holder [1]. Phosphoruos ion implantation and gold deposition were used for the contact formation. This technique resulted graphitization the top of the diamond film and intermixing of gold with the graphite or diamond surface. The properties of the contacts were tested with surface conduction characterization methods, and the properties of the contact to diamond interface was investigated with SIMS (Secondary Ion Mass Spectroscopy ) and XPS (X-ray Photoelectron Spectroscopy).