This thesis deals with the detection of gases. Based on the research, the theoretical part is devoted to the principles and construction of chemical gas sensors, especially the chemoresistive gas sensors, mainly with the active layer consisting of metal oxides and carbon nanotubes. In the second half of the theoretical part the carbon nanostructures, their properties and the methodology of preparation are reviewed. The experimental part deals with the type of support structure, preparation of the active layer and the method of its deposition and he principle of detection. In the results and discussion, the thesis focuses on the detailed processing of the results and the evaluation of the response ammonia, the impact of the modifications and procedures. In the end, the results obtained are compared, both with each other and with the relevant literature.

The aim of this thesis was to assess the degree of conformity between the mechanical properties evaluated by numerical simulation in software MAGMA5 and the measured values of hardness and ultimate tensile strength of lamellar graphite iron castings. The theoretical part of this thesis deals with the classification of cast iron, structural components of lamellar graphite iron, and the factors defining the resulting mechanical properties of the material. The practical part presents an attempt to find empirical dependencies between input parameters and results evaluated by simulation software. At the end, an analysis of the correlation between reality and simulation software is performed.

Master’s thesis focuses on the history and current progress in research of molten salt reactors around the world, with an emphasis placed on the properties of molten salts and the problems associated with their use. In relation to the practical part, one chapter is devoted to the creation of input file in the MCNP software. The practical part deals with neutron activation analysis of graphite prism experiment, which is filled with powder NaCl salt. This experiment is focused on the effect of salt on neutron flux with different energy levels. The whole problem was also simulated in the MCNP environment along with the experiment. At the end of the thesis, the individual methods are compared and evaluated.

Tato práce je zaměřena na zlepšení tepelného managementu mikroelektroniky implementací materiálů na bázi uhlíku, přesněji grafitových fólií, do tepelné architektury mikroelektroniky. Práce začíná vysvětlením současných metod chlazení a výzev v oblasti mikroelektroniky. Poté přechází k běžně používaným materiálům - hliníku a mědi a přidává do výběru i uhlíkové alotropie. Ve druhé části tato práce obsahuje několik příkladů použití pyrolytické grafitové fólie v tepelném managementu mikroelektroniky, prokazuje jeho použitelnost a analyzuje přínosy pro šíření tepla, tepelnou vodivost při dodržení elektrické izolace a možné využití ve flexibilní elektronice.

Diploma thesis in the first part deals with the production, properties and application of compacted graphite iron. After then calculation model which is used in ProCAST software for the predicting mechanical and structural properties of compacted graphite iron is presented and differences between versions 2010 and 2011 are shown. The last part of the thesis deals with simulation of mechanical and structural properties on the test specimen and real casting, which is poured in Heunisch foundry Ltd. and results of the simulation and measured values are compared.

The Pebble Bed Modular Reactor (PBMR) is a high temperature graphite-moderated nuclear reactor that uses helium as a coolant. The triple coated (TRISO) particles contain enriched uranium oxide fuel which is coated with layers of various forms of pyrolytic carbon and silicon carbide. The TRISO particles are further embedded in the matrix of spherical graphite pebbles. The graphite matrix is a composite moulded from a compound containing natural flake graphite (64 wt.%), synthetic graphite (16 wt.%) and a phenolic resin binder (20 wt.%) heated to 1800 °C in inert atmosphere. The graphitic composite provides structural integrity, encasement and act as a moderator material. In this work, low density model graphite composites similar to those used in nuclear applications as encasement material in fuel pebbles were made by uniaxial cold compression moulding. The graphitic composites contained various ratios of natural flake graphite and synthetic graphite at fixed phenolic novolac resin binder content of 20 wt.% (green state). The fabrication process employed entails mixing the graphite powders, followed by addition of methanol phenolic resin solution to the graphite powder mix, drying, grinding, milling and sieving; and finally compression moulding in a stainless steel die at 13 MPa using a hydraulic press. The green moulded disc specimens were then carbonized at 900 °C in nitrogen atmosphere to remove volatiles followed by annealing at 1800 °C in helium atmosphere. The annealing step diminishes structural defects and result in densification of the composites. The microstructure of fabricated graphitic composites was characterized using various techniques. Particle Size Distributions determined using Laser diffraction showed that the inclusion of the binder leads to agglomeration. The composite powders had larger mean particle sizes than the raw graphite powders showing the binding effect of the novolac phenolic resin. X-ray diffraction studies showed that the graphitic composites had a hexagonal crystal structure after annealing. Raman spectroscopy revealed the presence of the structurally disordered phase derived from the resin carbon (indicated by the pronounced D-band in the Raman spectra). XRD and Raman observations were consistent with literature and gave results supporting existing knowledge base. Optical microscopy revealed a flake-like microstructure for composites containing natural graphite and needle-coke like particles for composites containing mainly synthetic graphite. Optical microscopy confirmed that the effect of the manufacturing route employed here was to align the particles in the direction perpendicular to the compression moulding direction. As a result, the graphitic composites exhibited anisotropic property behavior. The bulk density of the composites increased with the increase in the natural graphite content due to compactability of natural flakes in the manufacturing route. Thermogravimetric analysis studies on the composites showed that they were stable in air to 650 °C. Composites containing mainly synthetic graphite were thermally more stable in air compared to their natural graphite counterparts. The linear coefficients of thermal expansion of the composites were measured using thermomechanical analysis (20-600 °C). In the moulding direction, the average CTE (αP) values were in the range (5-9) × 10-6 K-1 and increased with increment in the natural graphite content in the composite. In the direction perpendicular to moulding direction, the average CTE (αN) values were in the range (1.7-2.1) × 10-6 K-1 showing that the expansion was similar or constant in this direction. Therefore an anisotropic expansion ratio, i.e. αP:αN, of about 3 was observed in the composites. This anisotropy is attributable to the alignment of the filler particles in the manufacturing route. The thermal conductivity of the annealed composites were measured in the pressing direction from 100 to 1000 °C and the values ranged from 19 to 30 W m-1 K-1. Anisotropy was also observed as far as strength was concerned. A composite containing 64:16:20 wt.% ratio had the best mechanical properties, high thermal conductivity and slightly high expansion coefficient. This work demonstrates the complimentary properties of the graphite fillers in the composites. It also reports for the first time, data on the effect of variation of the filler graphites on microstructure and properties of model low density compression moulded graphitic composites. / Thesis (PhD)--University of Pretoria, 2013. / gm2014 / Chemistry / unrestricted

Measuring with high precision the electrical resistance of highly ordered natural graphite samples from a Brazil mine, we have identified a transition at ∼350 K with ∼40 K transition width. The steplike change in temperature of the resistance, its magnetic irreversibility and time dependence after a field change, consistent with trapped flux and flux creep, and the partial magnetic flux expulsion obtained by magnetization measurements, suggest the existence of granular superconductivity below 350 K. The zero-field virgin state can only be reached again after zero field cooling the sample from above the transition. Paradoxically, the extraordinarily high transition temperature we found for this and several other graphite samples is the reason why this transition remained undetected so far. The existence of well ordered rhombohedral graphite phase in all measured samples has been proved by x-rays diffraction measurements, suggesting its interfaces with the Bernal phase as a possible origin for the high-temperature superconductivity, as theoretical studies predicted. The localization of the granular superconductivity at these two dimensional interfaces prevents the observation of a zero resistance state or of a full Meissner state.

Raman spectroscopy is an irreplaceable method for chemical and structural characterization of many substances. This is especially true for carbonaceous matter. It is non-destructive and capable of determining the crystallinity of the studied carbonaceous phase, and subsequently, with the aid of empirical relations, also the temperature of formation of the rock under study. Until very recently, the most of the Raman spectroscopy measurements was conducted only single point-wise on grains chosen on purpose, e.g., in an optical microscope. Alongside with the evolution and affordability of the Raman spectroscopic technique it is now very appealing to utilize the possibility of Raman mapping coupled to the automated analysis of large quantities of acquired spectra. The aim of this study was to critically evaluate the pros and cons of such an approach on selected rocks with varying carbon content and crystallinity of the carbonaceous phase. The samples range from graphite, Karelian shungite, elemental carbon-rich carbonates, alpine schist to eclogite. In general, we can rate the large area mapping as suitable in many cases, however, there are certain issues associated with the method, especially concerning the sample preparation and automated analysis. Several actions are proposed to limit the pitfalls...

>Magister Scientiae - MSc / This work reports the use of a pencil graphite electrode (PGE) as inexpensive and sensitive electrochemical sensing platform fabricated by using electrochemically reduced graphene oxide (ERGO) in conjunction with an in-situ plated thin mercury film. For the first time the ERGOHgF-PGE sensor is proposed for simultaneous detection of cadmium (Cd2+), copper (Cu2+), lead (Pb2+) and zinc (Zn2+) using N-Nitroso-N-phenylhydroxylamine (cupferron) as complexing agent by square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV). The technique is based on the adsorption of cupferron- metal ion complexes onto the surface of the ERGO-HgFPGE at 0.1 V for 60 s carried out in 0.1 M acetate buffer solution (pH 4.6). The synthesized graphene oxide (GO) and graphene nanosheets (GNs) were characterized using different analytical techniques such as FT-IR which confirms the presence of oxygen moieties embedded in the graphitic structure and further demonstrated by UV-Vis, validating the synthesis of GO / 2023

Rapporten behandlar och utvärderar tre olika isolermaterial, Polyisocyanurat (PIR), grafitcellplast och mineralull, vid tilläggsisolering av miljonprogrammets byggnationer.  Stora delar av miljonprogrammet är nu i behov av upprustning. Samhällets skärpta krav gällande energiförbrukning gör att nya rationella metoder och material krävs för att tillgodose ställda krav. Att tilläggsisolera är en del i denna upprustning, och eftersom valet av isolermaterial ofta faller på gamla beprövade metoder och materialval, såsom mineralull, syftar denna rapport till att öka kunskapen om alternativa, mer högpresterande isolermaterial. Isolermaterialens egenskaper tas först upp och behandlas i en generell jämförelse där ekonomiska och tekniska aspekter beaktas. För att konkretisera och påvisa utfallet i ett specifikt fall genomförs en studie för ett referensprojekt, kvarteret Hundlokan, som ägs och förvaltas av Fastighets AB Förvaltaren. I studien undersöks tre olika alternativ för vart och ett av materialen vid tilläggsisolering utvändigt av Hundlokans fasader. Samtliga alternativ ställs sedan mot varandra och utvärderas med hjälp av: fukt-, U-värdes-, energi-, kostnads- och LCC-beräkningar (livscykelkostnad). Enklare fuktberäkningar som påvisar relativ fuktighet (RF), ånghalt och temperatur i väggens olika skikt genomförs. Resultatet visar att alla alternativ anses vara möjliga att tillämpa utan att fuktproblem ska behöva uppstå. Mer avancerade beräkningar bör genomföras vid projektering. Energiberäkningarna för de olika alternativen och även ursprungsfallet görs i ”VIP-energy” för att möjliggöra en realistisk jämförelse där skillnaderna i transmissionsförluster ställs mot varandra. I kostnadsberäkningarna påvisas skillnaderna i produktionskostnaderna för de olika alternativen. Dessa tillsammans med energibesparingen i form av minskade transmissionsförluster ligger sedan till grund för LCC-beräkningarna. Då stora ytor av fasaden i kv. Hundlokan upptas av fönster och indragna balkonger som skapar köldbryggor görs med ökad isolertjocklek ingen stor energibesparing i form av minskade transmissionsförluster. Initialkostnaderna för de tjockare isoleralternativen blir för höga för att möjliggöra återbetalning inom rimlig tidsram. Slutsatsen blir att tilläggsisolering med alternativa material till mineralull kan vara lönsamt och bör alltid undersökas i ombyggnadsprojekt. I det specifika fallet kvarteret Hundlokan är tilläggsisolering med 10 cm PIR det mest lönsamma alternativet. / This report treats and evaluates three different types of insulation materials: Polyisocyanurate (PIR), graphite foam and mineral wool, at additional insulation of houses from the Swedish “millionprogram”. Large parts of the houses from the millionprogram are now in need of restoration. The stricter rules laid down by the society regarding the use of energy, demands new, rational methods and materials to satisfy the regulations. Additional insulation is a step in meeting the energy regulatory requirements, and since the choice of insulation often is limited to traditional out tried methods and choices of materials, such as mineral wool, this report will explore the alternative, high-performance insulation materials. The insulation material’s qualities will be treated in a general comparisment where economical and technical aspects will be covered. In order to concretize and demonstrate the outcome in a specific case, a case study will be executed for the neighborhood Hundlokan owned and managed by Fastighets AB Förvaltaren. In the case study, three different alternatives will be examined, for each and every material at the additional insulation, outwardly at Hundlokan’s facades. All these alternatives are compared with each other and evaluated with regards to moister, u-value, energy, costs and LCC- calculations (Life cycle analysis). Simpler moisture calculations are implemented demonstrating the relative humidity (RF), steam level and temperature in the walls different layers. The results of the moisture calculations demonstrate that all alternatives seem possible to apply without the risk of the occurrence of any moisture problems. But more advanced moisture calculations are recommended to be carried out for restoration projects. Energy calculations regarding the different alternatives and the current state will be performed with “VIP-energy” in order to enable a realistic comparisment between the differences at transmission losses. Differences are shown within the cost’s calculations in production costs for the different alternatives. These along together with the energy savings in terms of less transmission losses are bases for the LCC-calculations. A large surface of the facade is covered by windows and recessed balconies which create thermal bridges, increased thickness of the isolation results in no larger energy savings in terms of decreased transmission losses.  The initial costs for the thicker isolation alternatives will be high in order to enable repayment within a reasonable time frame. The conclusion is that adding insulation with alternative materials than mineral wool can be profitable and should always be examined in reconstruction projects. For the specific case, Hundlokan additional insulation with 10 cm PIR is the most profitable option.