Ferenc Kristály

Detailed clay mineralogy of the Triassic-Jurassic boundary section at Kendlbachgraben (Northern Calcareous Alps, Austria)

Abstract The Triassic-Jurassic boundary (TJB) is marked by one of the five largest Phanerozoic mass extinctions. To constrain existing models for TJB events, we obtained a stratigraphically highly resolved dataset from a marine section at Kendlbachgraben, Austria. The topmost Triassic Kössen Formation contains low to medium-charged smectite and vermiculite as alteration products of mafic-ultramafic minerals. The clay minerals in the boundary mudstone are kaolinite ≥ illite + muscovite >> smectite > chlorite. Predominant kaolinite suggests humid climate and abundant terrigenous input. In the lowermost Jurassic, the clay mineral pattern changes to illite + muscovite >> kaolinite >> smectite, which reflects change to less humid and more moderate climate. The topmost Kössen Formation also contains clay spherules. Their composition, shape and size indicate that they are alteration products of airborne volcanic glass droplets solidified in the air, settled in the sea and altered rapidly with negligible transport in terrestrial or marine environments. Our data are consistent with sudden climatic change at the TJB, as a result of large-scale volcanic activity of the Central Atlantic Magmatic Province which produced distal airfall volcanic ash.

Synthesis and 1-butene hydrogenation activity of platinum decorated bamboo-shaped multiwall carbon nanotubes

Bamboo-shaped carbon nanotubes (BCNT) were prepared from three different amines on supported iron (Fe) and nickel (Ni) catalysts by catalytic chemical vapor deposition. The main factors governing product morphology and defect site density were identified. Post-synthetic oxidative functionalization was used to add carboxyl groups to the nanotubes, and then platinum (Pt) nanoparticles were deposited on the surface by the in situ reduction of a platinum salt. The average Pt nanoparticle diameter was found to be affected by the extent of surface functionalization. The catalytic performance of the synthesized Pt/BCNT samples were examined in the hydrogenation of 1-butene, in order to show that the catalytic activity of the bamboo like carbon nanotube supported Pt catalyst is similar to the conventional Pt catalysts in heterogeneous catalytic hydrogenation. The best overall performance was achieved when the bamboo-shaped nanotube support was synthesized on 5 wt% Fe/Al(OH)3 catalyst from triethylamine and decorated with 5 wt% platinum nanoparticles.

The Transformation of Added Vegetal Waste Materials during Clay Brick Firing

Vegetal materials are generated in high amounts and are applied as additives in clay bricks since ancient times. They have a certain heat contribution to the firing process. As revealed by X-ray Powder Diffraction, main component of vegetal waste materials is cellulose. Thermal and Evolved Gas Analysis revealed the combustion process in its details. Mixtures of clay and vegetal additives prepare for test bodies were analyzed by Thermal Analysis. The thermal effects were quantified by Differential Thermal Analysis and correlated with Thermogravimetry and Derivative Thermogravimetry.

Correlations between Combustion Type Additives and Expansion after Extrusion of Clay Bricks

Experimental work was conducted on illite-chlorite and kaolinite-carbonate rich clays to investigate effects of pore forming additive materials. Three types of additives were applied: vegetal materials like sawdust, sunflower seeds hull and rice husks; lignite, as high organic content mineral material; fuel-grade coke, as synthetic additive. Raw materials were characterized regarding their composition, thermal behavior, microstructure and chemical composition. Expansion of extruded samples was detected after pressing release. Correlations were determined between the type and cellulose content of vegetal materials and expansion caused. The mineral and synthetic additive does not produce expansion, but lowers the working moisture needed.

Phase Transformation and Morphology Evolution of Ti50Cu25Ni20Sn5 during Mechanical Milling

Nanocrystalline/amorphous powder was produced by ball milling of Ti50Cu25Ni20Sn5 (at.%) master alloy. Both laser diffraction particle size analyzer and scanning electron microscope (SEM) were used to monitor the changes in the particle size as well as in the shape of particles as a function of milling time. During ball milling, the average particle size decreased with milling time from >320 µm to ~38 µm after 180 min of milling. The deformation-induced hardening and phase transformation caused the hardness value to increase from 506 to 779 HV. X-ray diffraction (XRD) analysis was used to observe the changes in the phases/amorphous content as a function of milling time. The amount of amorphous fraction increased continuously until 120 min milling (36 wt % amorphous content). The interval of crystallite size was between 1 and 10 nm after 180 min of milling with 25 wt % amorphous fractions. Cubic Cu(Ni,Cu)Ti2 structure was transformed into the orthorhombic structure owing to the shear/stress, dislocations, and Cu substitution during the milling process.

Effects of Extruder Head’s Geometry on the Properties of Extruded Ceramic Products

A plastic brick clay with high clay mineral content was selected and the effects of different extruder heads on the main physical properties of the extruded products were investigated. The raw material was processed by a laboratory extruder after homogenization and wetting. Extruder heads with conical and special (spherical and torus) inner shape were applied to form and produce the green products which were examined after drying and firing. The rotation of the extruder screw was also varied between 15-55 1/min. Applying optical microscopy and SEM, the structure of the green products was analyzed. In addition to the physical properties of the products, the pressure caused by the extruder heads was determined by theoretical calculation and measurement. The results revealed that the physical properties of the products could be changed only by changing the shaping die geometry when the product size and production method remained unchanged. Maximal compressive strength of fired brick products (35.45 MPa) was obtained in case of the spherical head while the use of torus head caused some 5% decrease in the power consumption of the extruder. The density of fired products decreased and water adsorption increased when the rotation speed of the extruder screw was increased. The measurements confirmed the theoretical order of the applied extruder heads in terms of capability of pressure generation.

Development and Application of Carbon-Layer-Stabilized, Nitrogen-Doped, Bamboo-Like Carbon Nanotube Catalysts in CO2 Hydrogenation

Abstract Nitrogen‐doped, bamboo‐like carbon nanotubes (BCNTs) were synthesized from butylamine by catalytic chemical vapor deposition (CCVD method). The nanotubes were oxidized by H2SO4/HNO3 treatment and used to prepare calcium alginate gelled BCNT spheres. These beads were first carbonized and then Pd, Rh and Ni nanoparticles were anchored on the surface of the spheres. These systems were then applied as catalysts in CO2 hydrogenation. The BCNT support was examined by Raman spectroscopy, dynamic light scattering (DLS) and X‐ray photoelectron spectroscopy (XPS). The prepared catalysts were characterized by HRTEM and SEM. The oxidation pretreatment of BCNTs was successful, with the electrokinetic potential of the water‐based dispersion of BCNTs measuring −59.9 mV, meaning the nanotube dispersion is stable. Pyridinic and graphitic types of incorporated nitrogen centers were identified in the structure of the nanotubes, according to the XPS measurements. The Pd‐containing BCNT sphere catalyst was the most efficient in the catalytic studies. The highest conversion was reached on the Pd catalyst at 723 K, as well as at 873 K. The difference in the formation rate of CO was much less at 873 K between the Pd and Rh compared to the 723 K values. Accordingly, the application of Pd‐containing BCNT/carbon‐supported catalyst favored the generation of CO. However, the Ni‐BCNT/carbon catalyst leads to the formation of CH4 as the major product.

Low temperature rehydration of thermally dehydroxylated Bayer–gibbsite, evolution and transformation of phases

Rehydration processes in water vapor medium of thermally decomposed Bayer precipitated aluminum hydroxides were investigated. Three different thermal treatment methods were applied with variant temperatures and retention times resulting different composition (amount of remaining gibbsite, evolved boehmite, amount and character of amorphous phase), and surface properties. Rehydrated products were analyzed by X-ray diffractometry, thermal analysis, N2 sorption analysis and scanning electron microscopy. Sample underwent the highest mass loss during thermal treatment has shown the highest water uptake. Significant transformation was shown by oxide-like amorphous phases, yielding hydrated amorphous phase, from which crystalline hydroxide phases emerged, under the given circumstances bayerite and nordstrandite. Partial amorphisation of remaining gibbsite was experienced in early stage of rehydration, which suggests the dissolution of gibbsite by adsorbed water and subsequent recrystallization of it. Initial boehmite content of samples did not transform into other phases.

Összehasonlító archeometriai téglavizsgálatok a Dél-Alföldön@@@Comparative archaeometric study of bricks from the Southern Alföld

The study focuses on the comparative archaeometric (petrographic, geochemical and archaeobotanical) analysis of the brick samples from the excavation of twenty-four rural churches of the Arpadian Age and the Late Middle Ages (11th–16th centuries), two kindred monasteries and three Arpadian Age settlements in Counties Bekes and Csongrad. One of the main goals of the analysis was to determine the composition and the firing temperature of the bricks.

Effect of Organic Additives on Friction Properties of Clay Based Compounds

In the traditional heavy-clay industry, compounds are usually prepared by the addition of organic waste material. These additives originate mainly from the wood, food or paper industries. The purpose of this study is to present the results of the examination of friction contact between the wall of the forming die and the clay compounds containing organic additives. Saw dust and ground sunflower seed shell were mixed to clay in 0 wt%, 3 wt% and 5 wt%. The water content of compounds was also varied. The clay and the additives were described by morphology, XRD, bulk density and equivalent diameter. Friction tests were carried out on a special tribometer up to plastic deformation of the sample. The coefficient of friction decreased when normal stress was increased for all the ten compounds. Average results showed that the tendency of change in the value of the coefficient of friction could be divided into three sections: a decreasing, a quasi constant and a shearing section. It follows from this that the coefficient of friction can be characterized with a number only inside the quasi constant section, i.e. between two definable normal stress values. Averaged coefficient of friction was between 0.17 and 0.21 for saw dust and between 0.19 and 0.21 for the compounds with ground sunflower seed shell.