186,499 research outputs found
Physical and nanomechanical properties of the synthetic anhydrous crystalline CaCO3 polymorphs: vaterite, aragonite and calcite
No full textThe synthetic anhydrous crystalline CaCO3 polymorphs—vaterite, aragonite and calcite—were tested using dilatometry and nanoindentation. Microstructural changes in the samples before and after measurements were observed under scanning electron microscope and their phase composition quantified with X-ray powder diffraction with the Rietveld method. The thermal expansion coefficients of vaterite and the hardness and elastic modulus of synthetic aragonite are reported for the first time. The physical and nanomechanical properties were measured under similar conditions for each CaCO3 polymorph. Aragonite, calcite and vaterite showed volumetric thermal expansion coefficient at 303 K of 49.2(8), 48.6(2) and 44.1(3) 10−6 K−1, respectively. The elastic modulus increased from 5(4), 16(7) to 31(8) GPa for aragonite, calcite and vaterite, respectively. Average hardness was found lower than values from the literature, ranging from 0.3 to 1.3 GPa. The results are considered of interest for the design of CaCO3-based materials for applications
Influence of additions of synthetic anhydrous calcium carbonate polymorphs on nanolime carbonation
No full textThe influence of synthetic anhydrous calcium carbonate polymorphs, calcite, vaterite and aragonite, on carbonation of nanolime suspension, has been investigated. The higher rates of carbonation observed after 7 days in mixtures containing vaterite and aragonite particles, found explanation in the control exerted by heterogeneous nucleation on the water-mediated reaction mechanism and in the enhanced carbon dioxide diffusivity in the sample volume, both facilitated by the higher specific surface of the powders and the microporous sample fabric. Introduction of synthetic calcium carbonate allowed for exerting control on formed polymorphs, subverting the order of their (meta-)stability. The peculiar microstructure obtained by adding aragonite rod-like particles, mitigates the propagation of desiccation cracks (which impair continuity of the carbonated nanolime film). The mechanism, although still not completely understood, likely involves the regulation of evaporation of liquid fraction and redistribution of the tensional stresses during drying and nanolime crystallization. The obtained results provide new insights into the crystallization of carbonates from nanolime particles and may help in the design of innovative compatible products for consolidation of lime-based materials and carbon dioxide sequestration
Assessment of firing conditions in old fired-clay bricks: The contribution of X-ray powder diffraction with the Rietveld method and small angle neutron scattering
No full textFull characterization of fired-clay bricks is crucial for the improvement of process variables in manufacturing and, in case of old bricks, for restoration/replacement purposes. To this aim, five bricks produced in a plant in Czech Republic in the past have been investigated with a combination of analytical techniques in order to derive information on the firing process. An additional old brick from another brickyard was also used to study the influence of different raw materials on sample microstructure. The potential of X-ray diffraction with the Rietveld method and small angle neutron scattering technique has been exploited to describe the phase transformations taking place during firing and characterize the brick microstructure. Unit-cell parameter of spinel and amount of hematite are proposed as indicators of the maximum firing temperature, although for the latter, limited to bricks produced from the same raw material. The fractal quality of the surface area of pores obtained from small angle neutron scattering is also suggested as a method to distinguish between bricks produced from different raw clays
Aqueous polyacrylate latex nanodispersions used as consolidation agents to improve mechanical properties of Prague sandstone
No full textThis investigation aims at assessing the potential of polyacrylate latex nanodispersions as consolidation agents for sandstones. Four different latex types, implementing polymer fluorination and chemical crosslinking, have been synthesized at the scope and fully characterized. The Prague sandstone employed in this study has been selected as an example of highly porous stones used as building materials for many historical monuments. Two different concentration levels of nanodispersions have been adopted. The consolidated stone samples have been tested using a combination of physical-mechanical tests and microscopic observations. Compared to the non-treated samples, significant increments of mechanical properties (e.g. up to 3.3 times higher bending strength) have been detected after the consolidation treatment with concentrated products. Moreover, when 10 times diluted latex nanodispersions have been applied, the improvement of mechanical properties has still been significant, while moisture transport properties, such as water absorption, have been found to be comparable with those of the untreated sample. Fluorinated polymers imparted better hydrophobic properties with a contact angle above 100°. Observations using a scanning electron microscope revealed the good filling and bridging capacity of the applied consolidation agents. As demonstrated, by acting on the polymer structure, that is, by tuning the degree of crosslinking, polymer fluorination and gel content, the properties of these novel polyacrylate latex nanodispersions can be tailored to the specific stone and type of decay in order to improve the effectiveness of the treatments and obtain the desired final properties. The flexibility of their chemistry offers new opportunities for preserving objects of cultural heritage that are also at risk due to the ongoing climate change
Influence of linseed oil on the microstructure and composition of lime and lime-metakaolin pastes after a long curing time
No full textThis study investigates the effect of linseed oil on the microstructure of lime and lime-metakaolin pastes after 68 months of curing under controlled conditions. The hydrophobicity imparted by linseed oil to the pastes’ bulk was confirmed by measuring water drops’ contact angle. The results of thermal analysis, X-ray powder diffraction, and Fourier transform infrared spectroscopy showed that linseed oil significantly hindered the carbonation reaction in both lime and lime-metakaolin pastes and promoted the development of amorphous phases. The obtained results also indicated that linseed oil could foster the pozzolanic reaction in the lime-metakaolin system by stabilizing and/or promoting the development of hydration products resulting in reduced shrinkage in comparison with the reference
Mechanism of magnesium phosphate cement retardation by citric acid
No full textCitric acid modulates the release of heat and the rates of reaction in magnesium phosphate cements, chemically-bonded ceramics employed in biomaterials, for the encapsulation of nuclear wastes and in civil engineering. To gain knowledge on the mechanism of action of citric acid and, therefore, help in the effective material design, the reaction was studied in-situ to address molecular issues. The results indicated that citric acid enhances dissolution of MgO by promoting surface ligand-exchange reaction which leads to a net acceleration of the first reaction step. The Mg2+ ions released in solution are complexed by citrates. The degree of supersaturation is therefore reduced, delaying the nucleation of phosphates. The growth of stable nuclei, the crystal growth, and the amorphous-to-crystalline transformation are hindered due to citrate adsorption. The formed surface complexes are prevalently inner-sphere complexes exhibiting the combined coordination of hydroxyl and carboxylate groups. The mutating chemical environment dictates the coordination modes of citrate, the competition with phosphates, and the stable forms of phosphate products
The use of mineralogical indicators for the assessment of firing temperature in fired-clay bodies
No full textFired-clay bricks are frequently object of conservative actions aimed at the preservation of cultural heritage. Information on firing conditions is relevant for the production of custom made replacement bricks, since, as a widely accepted principle, they should be close match to the pre-existing ones. In this work, the mineralogical and microstructural evolution of fired-clay bodies is described using a combination of analytical techniques, and an approach for the assessment of firing temperature using calibration curves built from the results of X-ray powder diffraction quantitative phase analysis with the Rietveld method, is presented. The weight fractions of hematite, mullite and the amorphous fraction, from two raw clays fired in the laboratory at different temperatures, have been used to assess the firing temperature of two industrially produced bricks. The values derived applying these three methods were in good agreement with the nominal temperatures of the industrial cycles. This approach might be of interest for the assessment of the firing conditions of a broader range of historical/archaeological fired-clay materials
Characterisation of historical fired clay bricks with small angle neutron scattering
No full textMechanical properties and performance of fired-clay bricks are strictly related to their microstructure and mineralogical composition. The need for meeting the requirements of a nondestructive or low impact approach aimed at the conservation of cultural heritage objects, is prompting for the search of new analytical methods for their characterisation. Small angle neutron scattering (SANS) is a powerful technique for evaluating and quantifying a statistically representative microstructure of heterogeneous materials. Five historical fired-clay bricks, produced in a manufacturing plant of the Czech Republic, have been investigated. SANS-derived parameters allowed to retrieve the shape of the pore size distribution, characterise the fractal surface of pores, and suggest an empirical relationship between surface area per unit volume of pores and firing temperature
Keman Eğitiminde Konum Geçişlerine Yönelik Otakar Sevcik op 8 Alıştırmalarına İlişkin Uzman Görüşleri
No full textBu araştırma, yükseköğretim kurumlarından Devlet Konservatuvarları veEğitim Fakültelerinin Müzik Öğretmenliği Bölümlerinde görev yapan ve yapmış olankeman eğitimcileri ve keman eğitimci- sanatçılarının görüşleri doğrultusunda, kemaneğitiminde konum geçişlerinde dikkat edilmesi ve uygulanması gereken davranışlarıortaya koymak amacıyla yapılmıştır.Araştırmada verilere ulaşmak için kaynak tarama yöntemi ve görüşmeyöntemi kullanılmıştır. Konuyla ilgili yerli ve yabancı kaynaklar taranmıştır. Yapılangörüşmelerde keman eğitimcilerine Sevcik alıştırmaları, Sevcik op.8 ve konumgeçişleri hakkında sorular sorulup görüşleri alınmıştır. Yapılan görüşmelerde eldeedilen veriler yüzde- frekans değerleri ile tablo halinde verilmiştir.Araştırmada, konum geçişlerinin doğru ve iyi olabilmesi için öncelikle rahatbir duruş ve tutuşun gerektiği; sol elin keman sapında doğru konumlandırılmasıgerektiği; başparmağın inici ve çıkıcı konum geçişlerinde önemli bir işlevi olduğu; solelin esnekliği ve yumuşaklığının sağlanması gerektiği tespit edilmiştir. Yapılankonum değiştirmelerin glissando tekniği kullanılarak yapılması gerektiği, ancakyapılan glissandonun özellikle hissettirilmesi gereken durumlar dışındahissettirilmemesi gerektiği uzmanlarca vurgulanmıştır. Sevcik op. 8’in konumçalıştırması yönünden çok faydalı bir kaynak olduğu; parmakların kuvvetlenmesi,konum geçişlerine hakimiyet ve entonasyon sorunlarının giderilmesi açısındançalıştırılmasının faydalı olacağı; ancak konum geçişlerinin sadece Sevcik op.8 ilesınırlandırılamayacağı ve farklı kaynaklar ile desteklenmesi gerektiği sonucunaulaşılmıştır. The aim of this study is to indicate behaviours which should be consideredand applied in changing position in violin education in accordance with theopinions ofviolin trainers and violin artists who have served and still serving in StateConservatory and Department of Music Teaching in Faculty of Education.In this study, source scanning method and interview method have been used inorder to reach data. In source scanning which has done, domestic and foreign datawere gathered. In interviews which have been had, experts have been asked questionsabout Sevcik exercises, Sevcik op. 8 and changing position; and their opinions havebeen taken. Data obtained in these interviews have been tabulated with their percentfrequency values.In this study, it was concluded that, in order to correct changing position, firstof all, a comfortable stance and grip are necessary; the left hand should be positionedcorrectly in the violin fingerboard; the thumb has an important function in changingpositions moving up and down; the left hand should be flexible and soft. It can beconcluded that changing position should be done using glissando but glisando shouldnot be made feel.In conclusion, this thesis argues that Sevcik op. 8 is a very important sourceabout study of changing position; it is helpful for strengthening the fingers, forproviding control of changing position and for solving intonation problems; butchanging position cannot be limited only to Sevcik op. 8 and it should be supportedwith the help of different textbooks. </p
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