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  • Author: Nicolae Angelescu x
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Abstract

The article presents a comparative analysis on the hydration of cement paste without superplasticizer and water/cement ratio of 0.35 and a cement paste with the same water/cement ratio but has in its composition 2% superplasticizer additive Glenium Sky 526. For characterizing the hydration process of cement paste, both mixtures were subjected to X-ray diffraction and thermogravimetry analysis, at 3, 7, and 28 days passed since the initiation of hydration process.

Abstract

Refractory concretes based on aluminous cements are used with great success in areas where high temperatures are required. The mineralogical composition of the high alumina cement is the main factor which gives the physical and mechanical properties at high temperatures of refractory monolithic materials.

It is therefore desirable to use high alumina cements based on mineralogical compounds with high refractoriness, because in the end those beneficial properties can be found in the final product - refractory concrete.

The aim of this paper is to design, realize and characterize different compositions of high alumina cements based on mineralogical compounds with the highest refractory from the CaO-Al2O3 binary system (i.e. CA, CA2, and CA6), and to find ways of hydraulic activation of calcium hexa aluminate, also.

Abstract

This work is an attempt viewing to emphasize the possibility of using waste - as aggregate - from the demolition of silicoaluminuous refractory linings for manufacturing concrete with aluminuous cement. The article shows further on the possibilities of reducing the cement dosage and of using cheap admixtures.

Abstract

The paper is an attempt to present and evaluate of the some monolithic refractory materials, originating from our research activity, with potential to be used as the thermoprotective linings for the nonferrous metals and ferrous alloys manufacturing installations in foundries and steelworks.

Abstract

The current work is intended to explain the role of some organic admixtures on the hardened structure of refractory concretes with aluminous cement. The influences on the mechanical-structural properties in the normal hardening but in the heating conditions at different temperatures are emphasized, also. These are due to the influence on the hydration process (i.e. the kind of the neoformations and degree of hydration) and implicitly on the size and distribution of structural pores.

Abstract

The development of polymeric materials offers new perspectives of science and technology due to their outstanding properties. These properties are obtained either due to the effect of dispersion polymers and their polymerization either due to their intervention in structure formation. They were prepared epoxy resin polymer concrete, Portland cement, coarse and fine aggregate and to evaluate the influence of resin dosage on microstructures and density of such structures reinforced concrete mixtures. The paper detailing the raw materials used in experimental works and structural properties of concrete studied.

Abstract

In this paper is presented a comparative study regarding the synthesis of hydroxyapatite powders. The chosen method of synthesis of this biomaterial was chemical co-precipitation. The structure, size and morphology of the obtained powders were analyzed by X-ray diffraction, infrared spectroscopy - FTIR, dynamic light diffusion DLS tehnique and scanning electron microscopy-SEM. The results obtained were compared with those obtained on a commercial hydroxyapatite powder. Investigation methods have confirmed the synthesis of a high purity hydroxyapatite with a optimal degree of crystallization and crystallinity for the reconstruction and regeneration of hard tissue.

Abstract

This paper presents the most used processes for the synthesis of hydroxyapatite from aqueous solutions: chemical precipitation, the hydrothermal process and the sol-gel method. The experimental part includes the synthesis of hydroxyapatite by chemical precipitation. The obtained results confirm the obtaining of a ceramic with a high purity and a high degree of crystallization.

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Abstract

Calcium-phosphate cements is one of the most popular types of biomaterials, both due to their specific properties of self - setting and of their superior biocompatibility.

Although in general the phosphocalcic cements, which are the subject of the present paper, have somewhat lower mechanical properties than other biomaterials based on calcium and phosphorus, or even other dental cements of the same nature. The ceramic compositions presented in the present paper constitute a special category of biomaterials due to other notable advantages that characterize them. Thus, this category of materials is defined by a near-perfect adaptation to the surface of the biological tissue, as well as by a convenient resorption rate, processes followed by the generation of optimal bone formation. In this paper are presented principles of realization of the calcium-phosphate cements (raw materials and conditions of production), as well as the properties of these biomaterials, insisting, in particular, on the chemistry of the setting reactions. At the same time, informations regarding the possibilities of clinical use, such as implants are presented.

Abstract

Phosphocalcic glasses, based on ternary system SiO2 - CaO- P2O5 and those doped with copper (SiO2 – CaO - P2O5 - Cu2O) can be obtained by the traditional method of sub-cooling melts or modern methods such as process that uses mechanical energy, neutrons action, deposition in thin layers or by sol-gel technique. This paper shows the experimental results of three compositional phosphocalcic glasses: 50% SiO2 - 43% CaO - 7% P2O5, 50% SiO2 - 38% CaO - 7% P2O5 - 5% Cu2O obtained through sol-gel method and 45% SiO2 - 22.5% CaO - 22.5 Na2O - 5% P2O5 - 5% Cu2O obtained by melting. In order to study their bioactivity, the three compositions were structural analyzed by X-ray diffraction method. In this case the apatite formation was highlighted after soaked in simulated body fluid, but also other compounds (CaCO3 and CuO) resulting from the same process were observed. In case of the melting glass apatite formation has not been highlighted. The functional groups present in the structure of glasses before and after soaking (PO4 3−, CO3 2− and HO) were highlighted by the Fourier Transform Infrared Spectroscopy (FTIR). The elemental chemical composition was confirmed by elemental analysis WD-XRF. The morphology of sol-gel glass powders was revealed by SEM analysis. All glass compositions were tested in terms of antibacterial activity in vitro.