Thermal Exposition Research Articles

Microscopic analysis of the stainless steel weld metal after long-term thermal exposition in the primary circuit of the nuclear power plant

Microscopic analysis of the stainless steel weld metal after long-term thermal exposition in the primary circuit of the nuclear power plant

Effect of high temperature and accelerated aging in high density micro-concrete

The design of concrete often requires numerous mix proportions and tentative mixings, which translates into a great number of specimens and tests. The process may be optimized by using small-scale specimens, which results in the saving of material, equipment and time, offering advantages such as better handling, easy kneading or smaller curing spaces. Nevertheless, the ability of small-scale specimens to reproduce the experimental properties determined through conventional samples is an open issue. The hypothesis of this study is that the differences between standard and small-scale specimens may be mitigated by applying a change of scale to the aggregates. The durability of high-density concrete for radiation shielding, in terms of weathering resistance and behaviour against heating cycles, has been determined by means of conventional and small-scale specimens (including scaled aggregates). The effects of various aggressive external agents (heating cycles, seawater and water with K2SO4) and the correlation between the results from scaled and standard specimens were determined. The analysis of the results enabled to establish the suitability of the use of micro-concretes to characterize concretes. In this study, the correlations between scaled and non-scaled models have been obtained in properties such as compressive strength, mass variation and ultrasonic pulse velocity after undergoing durability and thermal exposition tests.

Melt milling as manufacturing method for solid crystalline suspensions

Production of submicron particles (0.1–1 μm) has been identified by the pharmaceutical industry as a key technology to enhance the bioavailability of poorly water-soluble drugs. However, nanosuspensions derived from commonly applied wet milling suffer from long-term stability issues, making further downstream processing necessary. In previous works, the formulation as a long–term stable solid crystalline suspension (SCS) was introduced, for which the crystalline drug is ground in a (molten) hydrophilic carrier matrix. The model formulation of the antimycotic Griseofulvin and the sugar alcohol Xylitol was reused for comparative purposes. Due to process limitations regarding the degree of comminution, the present work demonstrates the application of fine grinding in the framework of SCS manufacturing. A custom-built mill with annular gap geometry successfully yielded particles in the targeted submicron range. A process optimization study lead to improved energy utilization during grinding, which reduced the necessary grinding time and, thereby, the thermal exposition of the drug. Investigation of solid-state properties of the SCS, via differential scanning calorimetry and x-ray powder diffraction, showed no alteration even for extended grinding times. In dissolution experiments, the melt-milled SCS outperformed its predecessors, although mostly agglomerates were found by SEM imaging in the solidified product. In conclusion, melt milling is a valuable tool to overcome low aqueous solubility.

Enhanced adhesion resistance of an 8YSZ thermal barrier coating trough the formation of zircon and mullite as self-healing reaction products under cyclic oxidation conditions

The formation of ZrSiO4 (zircon), 3Al2O3·2SiO2 (mullite), and amorphous SiO2 as healing products from the oxidation reaction of the SiC (silicon carbide) self-healing agent, occurred after 250 h of thermal exposition (ten thermal cycles of 25 h at 1100 °C). By SEM and TEM analysis of adhesion fracture surfaces, both zircon and mullite complex oxides were identified mainly along micro-cracks adjacent to theTGO-TC interface and forming bridges-like bonds with the ZrO2-TC and Al2O3-TGO compounds. Then adherence resistance seems to be enhanced by the formation of these bonds and by the mere presence of self-healing products retarding or blocking crack propagation.

A Middle Palaeolithic wooden digging stick from Aranbaltza III, Spain.

Aranbaltza is an archaeological complex formed by at least three open-air sites. Between 2014 and 2015 a test excavation carried out in Aranbaltza III revealed the presence of a sand and clay sedimentary sequence formed in floodplain environments, within which six sedimentary units have been identified. This sequence was formed between 137–50 ka, and includes several archaeological horizons, attesting to the long-term presence of Neanderthal communities in this area. One of these horizons, corresponding with Unit 4, yielded two wooden tools. One of these tools is a beveled pointed tool that was shaped through a complex operational sequence involving branch shaping, bark peeling, twig removal, shaping, polishing, thermal exposition and chopping. A use-wear analysis of the tool shows it to have traces related with digging soil so it has been interpreted as representing a digging stick. This is the first time such a tool has been identified in a European Late Middle Palaeolithic context; it also represents one of the first well-preserved Middle Palaeolithic wooden tool found in southern Europe. This artefact represents one of the few examples available of wooden tool preservation for the European Palaeolithic, allowing us to further explore the role wooden technologies played in Neanderthal communities.

Failure Mechanism of Yttria Stabilized Zirconia Atmospheric Plasma Sprayed Thermal Barrier Coatings Subjected to Calcia-Magnesia-Alumino-Silicate Environmental Attack

The contribution focuses on the description of failure mechanism of atmospheric plasma sprayed multilayer thermal barrier coatings subjected to calcia-magnesia-alumino-silicate (CMAS) environmental attack. To identify exothermic and endothermic reactions which occurred during heating/cooling by means of calorimetry was also utilized initial yttria stabilized zirconia (YSZ) powder subsequently used for thermal spraying of multilayer thermal barrier coating system (TBCs), CMAS powder later on utilized for thin layer deposition and its mixture. Atmospheric plasma spray technique was used to produce the TBCs on a grit blasted nickel-based superalloy substrates, where CoNiCrAlY powder was used for deposition of a bond coat and YSZ powder was sprayed as a top coat. In accordance to the aerospace standard the thin layer of CMAS was deposited on as sprayed TBCs samples surface from its colloidal solution by paint brush method. Burner-rig test, utilizing direct propane-oxygen flame, was used for thermal cyclic exposition of the multilayer coated samples at the temperature of 1150 °C. Samples after thermal cyclic exposure test were investigated by means of materialographic analysis approaches. The significant reduction in life-time of CMAS coated YSZ top coat was observed due to lower melting point phase formation and molten silicate crystallization within the pores providing the spallation identified as a major mechanism of TBCs failure.

The Effect of Thermal Exposition on the Relaxation of Residual Stresses in a Reinforced Cylindrical Sample in Creep

The Effect of Thermal Exposition on the Relaxation of Residual Stresses in a Reinforced Cylindrical Sample in Creep

Structure of Nanocrystalline Nickel Prepared by Powder Metallurgy

Nanocrystaline nickel was prepared by selective leaching technology. Consequently, the powder was compacted by spark plasma sintering method. This process is suitable due to its high heating rates, which leads to relatively low thermal exposition of compacted material. The dependence of structure of compacted material on preparation conditions is described in this paper.

The Influence of Colour Solution of the ETICS Surface on its Thermal Exposition

The colour solution of the surface of the façade is one of the basic factors for reaching the requested aesthetic and architectonic expression of the building. This target is sometimes reached by using very saturated tones of colours or changing dark and light tones on one façade. Such solution is often risky as one of the characteristics of dark colour tones is high absorption of solar and scattered radiation. Its thermal compound causes warming of the outer layers of the façade proportionally to the surface colour saturation. This consequence is very serious especially for thin-layer plaster of external thermal insulation composite systems (ETICS) immediately exposed to dynamic effect of external environment temperature changes, which can be even increased by inappropriate colour solution of the ETICS surface. This paper focuses on evaluation of the influence of ETICS surface colouring on the thermal load.

Polyurethane Foams with Pyrimidine Rings

Abstract Oligoetherols based on pyrimidine ring were obtained upon reaction of barbituric acid with glycidol and alkylene carbonates. These oligoetherols were then used to obtain polyurethane foams in the reaction of oligoetherols with isocyanates and water. The protocol of foam synthesis was optimized by the choice of proper kind of oligoetherol and synthetic composition. The thermal resistance was studied by dynamic and static methods with concomitant monitoring of compressive strength. The polyurethane foams have similar physical properties as the classic ones except their enhanced thermal resistance. They stand long-time heating even at 200°C. Moreover thermal exposition of foams results generally in increase of their compressive strength.

First experience with MR-guided focused ultrasound in the treatment of Parkinson's disease.

BackgroundRadiofrequency (RF) subthalamotomies have been proposed since the 1960s to treat patients suffering from Parkinson's disease (PD). Recently, the magnetic resonance (MR)-guided focused ultrasound technology (MRgFUS) offers the possibility to perform subthalamic thermocoagulations with reduced risks and optimized accuracy. We describe here the initial results of the MRgFUS pallidothalamic tractotomy (PTT), an anatomical and physiological update of the earlier subthalamotomies.MethodsThirteen consecutive patients suffering from chronic (mean disease duration 9.7 years) and therapy-resistant PD were treated unilaterally with an MRgFUS PTT. Primary relief assessment indicators were the score reduction of the Unified Parkinson Disease Rating Scale (UPDRS) and the patient estimation of global symptom relief (GSR) taken at 3 months follow-up. Final temperatures at target were between 52°C and 59°C. The MR examinations were performed before the treatment, 2 days and 3 months after it. The accuracy of the targeting was calculated on 2 days post-treatment MR pictures for each PTT lesion.ResultsThe first four patients received a PTT using the lesional parameters applied for thalamotomies. They experienced clear-cut recurrences at 3 months (mean UPDRS relief 7.6%, mean GSR 22.5%), and their MR showed no sign of thermal lesion in T2-weighted (T2w) images. As a consequence, the treatment protocol was adapted for the following nine patients by applying repetition of the final temperatures 4 to 5 times. That produced thermocoagulations of larger volumes (172 mm3 against 83 mm3 for the first four patients), which remained visible at 3 months on T2w images. These nine patients enjoyed a mean UPDRS reduction of 60.9% and a GSR of 56.7%, very close to the results obtained with radiofrequency lesioning. The targeting accuracy for the whole patient group was 0.5, 0.5, and 0.6 mm for the anteroposterior (AP), mediolateral (ML), and dorsoventral (DV) dimensions, respectively.ConclusionsThis study demonstrated the feasibility, safety, and accuracy of the MRgFUS PTT. To obtain similar results as the ones of RF PTT, it was necessary to integrate the fact that white matter, in this case, the pallidothalamic tract, requires repeated thermal exposition to achieve full lesioning and thus full therapeutic effect.

Coating of Cr-V Ledeburitic Steel with CrN Containing 7% of Ag

Abstract Samples made from Vanadis 6 PM ledeburitic tool steel were surface machined, ground and mirror polished. Prior the deposition, they were heat treated to a hardness of 60 HRC. CrAg7N-coatings were deposited by magnetron sputtering technique, using pure Cr and Ag targets, in a composite low pressure nitrogen/argon atmosphere and at a temperature of 500 °C. The coatings have an average thickness of 4.3 μm. They grew in a very well visible columnar manner, but, individual silver agglomerates were visible along the columnar crystals, also. The average size of silver agglomerates lies well below 50 nm, e.g. one can suggest that they are capable to be solved and release the Ag atoms to be migrated to the free surface during thermal exposition. The coatings had a good adhesion on the surface - the first critical loads, established by scratch-testing method, ranged between 30 and 39 N.

Study of dehydration and rehydration processes of portlandite in mature and young cement pastes

The hydration process of the cements induces the formation of different kinds of hydration products. The main products of hydration are C-S-H gel and portlandite (Ca(OH)2). The C-S-H gel is an amorphous compound that is discomposed progressivity with the temperature until approximately 1,000 � C, while the portlandite is discom- posed between 450 and 550 � C. Also, calcium carbonate can be formed as a consequence of the portlandite carbonation. All of these processes can be analysed and quantified by simultaneous differential thermal analysis and thermo- gravimetric analysis. And by X-ray diffraction it is possible to identify the crystalline phases. Some authors have cor- roborated that the portlandite can be rehydrated, after dehydration processes due to thermal exposition of the cement paste. But all of these experiments have been made with young cement pastes or at temperatures lower than 650 � C. In this work the behaviour of young and mature cement pastes have been studied in relation with the port- landite decomposition and the possibility of the rehydration of it in water presence. We found that young pastes and old pastes, stored at laboratory conditions, and later burned, show a certain grade of rehydration, specially the pastes burned at 650 � C (with&80% of reformation of portlandite) with respect to the pastes burned at 1,000 � C (between 20 and 40%). It is corroborate that the rehydration process is directly related to the formation of CaO during the burning. Also, a formation of unstable portlandite is detected in young pastes burned at 650 � C, which can be rehydrated easily. Although, the mature pastes that have been burned initially and stored under laboratory conditions cannot be rehydrated, due to the formation of stable products during the storage.

Synthesis, biological activity and HPLC validation of 1,2,3,4-tetrahydroacridine derivatives as acetylcholinesterase inhibitors

The synthesis and biochemical evaluation of new hybrids of tacrine (THA) and 4-fluorobenzoic acid (4-FBA) possessing activity towards acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibition are presented. The compounds of interest were obtained from the reaction of activated 4-FBA and diamino derivatives of 1,2,3,4-tetrahydroacridine. The compounds C6-2KW/HCl, C6-4KW/HCl and C6-3KW/HCl have four-fold higher antiacetylcholinesterase activity than THA. All of the acquired compounds present higher selectivity towards AChE than THA and lower selectivity towards BuChE. In addition, a rapid, selective and stability-indicating HPLC method was developed and validated for the determination of C6-2KW/HCl, C6-3KW/HCl and C6-4KW/HCl. THA and 4-FBA were found to be the main impurities. Chromatographic separation was achieved isocratically on a Waters Symmetry C18 150 × 3.9 mm, 4 μm column with a mobile phase of acetonitrile/buffer (17 mM sodium dodecyl sulphate and 8.3 mM sodium dihydrogen phosphate, 50:50 v/v) (overall pH 4). A 1.5 ml/min flow rate and a 247 nm wavelength were chosen for this method. C6-2KW/HCl, C6-3KW/HCl and C6-4KW/HCl were subjected to acidic and basic hydrolysis, chemical oxidation, thermal exposition at 60 °C and intense UV light. The limits of detection (LOD) and quantification (LOQ) were less than 2 μg/ml and 6 μg/ml for C6-2KW/HCl, C6-3KW/HCl and C6-4KW/HCl, 0.04 μg/ml and 0.12 μg/ml for THA, 0.42 μg/ml and 1.41 μg/ml for 4-FBA, respectively.

Polyurethane foams with pyrimidine rings in polymer molecules

New polyurethane foams were obtained by reaction of oligoetherols synthesized from hydroxymethyl derivative of barbituric acid (HMBA) and propylene oxide (PO) with methylenediphenyl 4,4'-diisocyanate (MDI) and water. Thermal stability of the polyurethane foams containing pyrimidine rings in polymer molecules were investigated. They are stable at 150-200 °C for long time. The influence of oligoetherol chain length and composition on properties of foams were studied in details. The studies of mechanical properties before and after thermal exposition were studied in order to optimize the compositions of polyurethane foams to ensure good thermal stability.

Structure of miniature components from steel produced by forming in semi-solid state

To obtain new unconventional structures with specific mechanical and physical properties is possible not only by the development of new types of materials but also by treatment of conventional materials using unconventional innovative technological procedures. One of these technologies is the forming in semi-solid state involving rapid solidification of miniature components from steels. Production of such components is complicated by a number of technical problems. To explain phenomena of the process and structure development, the production of miniature components from the tool steel X210Cr12 difficult to form was experimentally tested. The structure of this originally ledeburite steel consisted of 95 % of metastable austenite after the treatment. Metastable austenite was located particularly in globular and polygonal grains while the remaining interspaces were filled by lamellar network. The detected high stability of extremely high fraction of metastable austenite was tested under different conditions of thermal exposition and mechanical loading.

Synthesis and Properties of Hyperbranched Polyimides Combined with Silica

AbstractSummary: The novel hyperbranched polyimide ‐ silica hybrid materials containing theoretically 16 wt% of an inorganic phase were prepared via a sol‐gel process. An amine terminated polyimide precursor (hyperbranched polyamic acid) was prepared from commercially available monomers 4,4′,4″‐triaminotriphenylmethane and 4,4′‐oxydiphthalic anhydride in molar ratio 1:1. Tetramethoxysilane and/or 3‐glycidoxypropyltrimethoxysilane (also used as a coupling agent) were used as silica precursors. During thermal exposition the polyimide precursor was transformed to hyperbranched polyimide and hydrolyzed alkoxy groups reacted mutually to form silica. The final products were self‐standing films, whose structure was characterized by using IR and 13C and 29Si solid state NMR spectroscopy. The influence of the amount of silica and/or coupling agent on their structure and thermal properties was described.

Stability of Microstructure of Ultrafine-Grained Copper Under Fatigue and Thermal Exposition

Abstract: Effect of cyclic loading and thermal exposition on microstructure of bulk ultrafine-grained Cu prepared by equal channel angular pressing was experimentally investigated by means of electron backscattering diffraction and by transmission electron microscopy. Stability of the microstructure under stress-controlled cyclic loading with a tensile mean stress of 200 MPa was shown to be high. Neither dynamic grain coarsening nor development of bimodal microstructure was observed. However, annealing at 250 °C for 30 min resulted in formation of bimodal microstructure. Consequently, fatigue strength of annealed specimens was low.

Imaging by Photoelectrochemical Techniques of Laves-Phases γ Zr(Fe,Cr)<sub>2 </sub> Thermally Oxidized on Zircaloy-4

The oxidation of γ-Zr(Fe,Cr)2 intermetallic particles during the thermal exposition of Zircaloy-4 at 470°C in oxygen was investigated with PhotoElectroChemical techniques (PEC). Via the measurement of bandgap, haematite Fe2O3 (2.2 eV), rhomboedric solid solution (FexCr1-x)2O3 (2.6 eV) and chromia Cr2O3 (3.0 eV) phases were identified as components of oxidised particles. Evolution of size, lateral distribution and density of these particles was studied in function of zirconia scale thickness. During the first stage of oxidation, the density of oxidised particles increased with thickness but decreased during a second stage, highlighting in an innovative way the phenomenon of haematite and chromia dissolution in the zirconia matrix. It is concluded that PEC techniques represent a sensitive and powerful way to locally analyse the various semiconductor phases in an oxide scale at the micron scale.

Microstructural changes in long-time thermally exposed Ni-base superalloy studied by SANS

The SANS experiment was a crucial part of a broader investigation of the long-time structural stability of the polycrystalline Ni-base superalloy and its effect on the subsequent creep characteristics. The results of the creep tests have shown that a long isothermal exposure at temperatures of 430 °C and 650 °C up to 25000 h changed the deformation ability and creep life of the exposed specimens. While structure analyses (TEM) showed no evidence of a morphological and/or dimensional γ′ change, the SANS technique was able to reveal significant changes of the morphology of γ′ precipitates already after the shortest applied thermal exposition, 2000 h. The resulting size distributions, distance distributions, mean sizes and mean distances between the precipitates made evident that both the size and the distance increase in the bulk of the alloy with increasing thermal exposure even at such relatively low temperatures.