Abstract-Due to the sensitivity of their physical properties to selected gases, graphite oxide (GrO) and reduced graphene oxide (RGO) can be used in optical gas sensors. The sensor properties of GrO and RGO depend significantly on the technology used for their production. In this paper the effects of oxidation and reduction processes on graphite physicochemical properties were presented.In many production processes, but also in environmental monitoring, an important problem is the detection of selected gases with adequate selectivity and sensitivity. Recently, much attention has been paid to the development of optical gas sensors, acting both on the basis of optical absorption and the phenomenon of propagation of modes in optical planar structures. It is important that the detection of selected gases should be unambiguous and at a low level of their concentration. Attention should also be paid to the response time of sensors (time of gas detection), which must be as short as possible. The metrological properties of optical gas sensor structures depend mainly on gas sensing layers. In the literature concerning gaseous sensors much attention is devoted to sensors based on graphene, graphite oxide (GrO) and reduced graphene oxide (RGO) [1][2][3]. There are many different methods of production [4-8] graphene based materials, which undoubtedly affects their structural properties. Our earlier studies [9][10] have shown that the sensor properties of graphene based materials significantly depend on the technology used for their production. In the present paper, the effects were investigated of oxidation and reduction processes on graphite physicochemical properties.The research work presented in this paper was designed to describe changes which take place in graphite after its oxidation and reduction. In order to clarify the description, the product obtained in an oxidation process will be referred as graphite oxide and denoted as GrO while the product obtained in a reduction process will be referred as graphite oxide and denoted as RGO. The * E-mail: sabina.drewniak@polsl.pl oxidation process is intended to incorporate the functional groups containing oxygen, e.g. carbonyl, carboxyl, hydroxyl and epoxy between the planes of graphene. The oxidation process was realized using Hummer's method, the reduction process was realized using a temperature of approximately 900 o C and inert conditions [11]. During the reduction process, the number of additional oxygen and hydrogen groups in GrO decreases, giving the RGO structure. The research presented in this paper was conducted using a sample of graphene flakes. Graphite is characterized as an ordered crystallographic structure and has a high content of mineral substance (at 9.7%). Preparation of graphite oxide:Commercial flake graphite powder (90µm), supplied by Signograf was oxidized by a modified Hummer method [12]. Concentrated H 2 SO 4 (95-97%) was used as an acid and KMnO 4 and NaNO 3. A graphite sample (1g) with a particle size <20μm was mixed with the acid and placed in...
BACKGROUND: Zirconia is a commonly used ceramic for fixed full-ceramic restorations. Porcelain-fused-to-metal restorations applied for bruxers are often very quickly destroyed by this group of patients. OBJECTIVE: The aim of this study was to investigate the influence of accelerated aging tests on BruxZir HT 2.0 zirconia. METHODS: Zirconia samples were prepared with ISO 13356:2013 and ISO 14704:2008 protocol recommendations. The ageing conditions were times of 2.5, 5 and 10 hours, and pressure of 0.2 MPa and a temperature of 134°C. RESULTS: The correlation between ageing time and mechanical properties, particularly hardness, was difficult to find, while correlations between hardness and the surface topography and fracturing were clear. CONCLUSION: On the basis of the conducted research, it can be stated that BruxZir HT 2.0 zirconia meets the technical requirements for medical grade zirconia used in dental technology. Future investigations should include phase composition research.
Nitric oxide(NO), nitrogen dioxide (NO2), nitrous oxide (N2O), and their derivatives generally known as nitrogen oxides (NOx) are primary pollutants in the atmosphere originated from natural and anthropogenic sources. The paper presents investigation of electric performance of novel chemiresistor NOx gas sensors. A novel material was utilized for active sensing layer-conductive copolymer and zinc oxide blend. The main advantage of the presented solution is low-cost and environment-friendly production. A series of this type of sensors was manufactured and tested experimentally. During the tests, the gas flow was controlled and signals of sensor responses, temperature, and humidity were computer-acquired using LabVIEW program. Sensor behavior for different thicknesses of the active layer has been investigated and interpreted. The research revealed that the electrical resistance of the sensors has changed in predictable manner depending on the gas concentrations. A recurrent artificial neural network architecture is proposed as a mathematical model to classify sensor responses to gas concentrations variation in a time-dependent regime. In this research, an enhanced method for gas concentration prediction is proposed using non-linear autoregression model with exogenous input (NARX). The performed simulations show good agreement between simulated and experimental data useful for predictions of sensor gas response.
In order for bioceramics to be further used in composites and their applications, it is important to change the surface so that the inert material is ready to interact with another material. Medical grade alumina and zirconia ceramic powders have been chemically etched with three selected acidic mixtures. Powder samples were taken for characterization, which was the key to evaluating a successful surface change. Changes in morphology, together with chemical composition, were studied using scanning electron microscopy, phase composition using X-ray diffraction methods, and nitrogen adsorption/desorption isotherms are used to evaluate specific surface area and porosity. The application of HF negatively affected the morphology of the material and caused agglomeration. The most effective modification of ceramic powders was the application of a piranha solution to obtain a new surface and a satisfactory degree of agglomeration. The prepared micro-roughness of the etched ceramic would provide an improved surface of the material either for its next step of incorporation into the selected matrix or to directly aid in the attachment and proliferation of osteoblast cells.
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