Ion Teoreanu

Mechanisms and effects of additives from the dihydroxy-compound class on Portland cement grinding

Abstract The present paper investigates the action and effects of wet surface active additives from the dihydroxy-compound class (ethylene glycol, propylene glycol, and polypropylene glycol) on Portland cement grinding, starting from the present knowledge of surface chemistry, with application to the solids and particularly the size reduction process. The investigations were performed using the comparative kinetic measurements of the size reduction process, aiming at the evolution in time of the specific surface of the solid; the grinding aptitude measurements, considered as specific power consumption, under comparable conditions; size distribution and flow capacity determinations of the ground cements. Within the homologous series of surfactants, the regularity of the additive’s effect on the process, which is dependent on the composition of the additives, is noted. The action mechanisms of the additives are discussed. The results obtained have obvious useful implications.

Microwave processing of Ba2Ti9O20 ceramic

Abstract Microwave synthesis of Ba 2 Ti 9 O 20 was realized. The dependence between microwave characteristics, the duration of treatment and the degree of transformation of initial reacting powder was examined. At the same time, features of samples sintered by microwaves were compared to those sintered by conventional methods (in electric furnaces).

Expansive sulphate aluminate cements

Abstract The possibility to prepare expensive sulphate aluminate masses from certain wastes (phosphogypsum and belitic waste) and usual raw materials (limestone, bauxite) has been investigated. The chemical and minerological composition of these synthetic clinkers as well as the nature of their hydration products has been determined by current methods. The mechanism of cement expansion and the factors affecting the correlation between mechanical strength and expansion have been also studied.

Sintered Hydroxyapatite with Additives

In present paper the sintering behaviour of HAP in the presence of 5 and 10wt% NC2P was studied. Relative density of 67-72% were obtained for samples sintered at temperatures ranged between 1000-1150°C. The shrinkage data revealed the formation of a liquid phase at 1100°C. This process was accompanied by the density increase and the porosity diminution respectively. The phase composition was investigated by X-ray diffraction. Even the major phase identified was 3CaO . P2O5, however small amounts of HAP were also detected until 1150°C. The IR spectra confirmed the presence of a HO ions in the HAP lattice at temperatures lower than 1150 0 C. Introduction Hydroxyapatite (HAP) is an inorganic compound of human bone, beside other phosphates, calcium carbonate, etc. It has two very important properties for the medical applications namely high bioactivity and good biocompatibility. The biocompatibility consists in the development of a strong chemical bond between the human bone and the HAP-based ceramics. Due to this characteristic HAP is especially used in reparatory orthopaedic and dental surgery. HAP can be obtained on synthetic way by various methods: chemical precipitation, sol-gel and hydrothermal route, etc. HAP contains one water molecule in its formulae, which can be released at temperatures between 600 and 850°C. However, due the reversibility of the reaction in the humid environment, HAP remains hydrated even at higher temperature [1]. Different additives are often used in order to improve the HAP properties. Santos and all [2] have studied the influence of glasses with compositions which belong to the P2O5-CaO-Na2O-SiO2 and P2O5-CaO-Na2O-Al2O3 systems, on the sintering behaviour of HAP fired at 1350 0 C with a soaking time of one hour. They have noticed an important increase of fracture toughness. The content of used glass was of 2 to 4% and the samples were fired in the range of 1200 to 1300°C for one hour at maximum temperature and cooled in the furnace. It was confirmed that there is only one crystalline phase, 3CaO . P2O5 at 1350°C there, the dissociation of HAP being total. Several substitutions of the host ions in the HAP lattice, such as CO3 2which can replace HO and PO4 3, F on the PO4 3sites, as well as Mg 2+ and Na + incorporated on the Ca 2+ sites were earlier reported [3]. The influence of other additives such as CaF2, Li2O, Na2O, NaPO3 and NaPO4 was also studied [4]. The calcium fluoride was found to be improper because it can react with HAP leading to the formation of free calcium oxide, which determines flaws appearance of products. Lithium oxide has a good influence on sintering of samples at high temperature when an eutectic melt is formed between 3CaO . P2O5 and Li3PO4. The NaPO3 and Na3PO4 compounds do not exhibit a significant effect concerning the density increase, because the lack of the liquid phase at the grains boundary. The aim of the work is to study the sintering behaviour of some HAP-based ceramics with sodium oxide used as additive. The compositions considered are located on the tie line HAPNa2O . 2CaO . P2O5 of the quathernary Na2O-CaO-P2O5-H2O system. Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 2091-2094 doi:10.4028/www.scientific.net/KEM.264-268.2091

Influence of the powder characteristics on the properties of the Bi-based superconductors

Abstract Bi-based ceramic materials with superconducting properties were prepared using the solid state reaction technique, starting with reactive powders obtained via oxalate coprecipitation, as well as by the traditional powders route. The powder characteristics were evaluated using BET method and transmission electron microscopy (TEM). The stages of the high T c supeconducting phases formation process were investigated by TG, DTA, XRD and IR methods. The dependence of the electric resistance versus temperature was recorded. The densities of the obtained samples have been also determined. The results emphasised high reactivity and shorter reaction times of the ceramic bodies obtained by the coprecipitation method.

Defining Properties of Fly Ashes for their Usage in Silicate Binder Industry

Present paper deals with investigation regarding the most important characteristics of fly ashes (especially, Romanian fly ashes) for use in cement fabrication. These characteristics can be classified as: (i) morphological and surface characteristics; (ii) physical properties; (iii) compositional characteristics. It is pointed out the interdependence between these characteristics, reflected in mechanical (at grinding) and chemical (at Portland clinkers and Portland blended cements fabrication) behaviour of fly ashes. Introduction Fly ashes are industrial by-products, obtained in large quantities, and if not used they can become a dangerous environmental factor, with both ecological and economical consequences. Due to their composition and chemical activity, fly ashes exhibit an intrinsic potential for a wide use, including building materials industry (especially cements) [1-3]. The use of fly ashes in cement industry concerns three important aspects: (i) obtaining of unitary Portland cements, as raw material when replacing the clay component in the raw mixture preparation [1-4]; (ii) obtaining of blended Portland cements with pozzolana admixtures (especially fly ashes) [2,3]; (iii) obtaining of blended silicate cements free of Portland clinker – cementitious material (slag) – pozzolana (fly ashes) – activator binding systems [3]. The most important characteristics of fly ashes for use in silicate cements fabrication can be classified: (a) morphological and surface characteristics; (b) physical properties; (c) chemical properties. Experimental Considering previous aspects, the morphology of fly ash grains and their surface shape were studied. Specific surface area, grain size distribution of fly ashes, bulk density mass and grinding aptitude were determined as well as their oxide and phase composition. For a better understanding of the important influence of the fly ashes upon the studied properties, correlations between characteristics and behaviour of such cements made with fly ashes were established. Results and Discussion The microscopic evaluation of fly ashes points out their morphologic heterogeneity (an Hitachi electronic microscope was used). Most of researchers [1-5] define fly ashes as a mixture of grains having different shapes and colours. In this mixture one can distinguish full round spherical particles or with grooves having different depths or particles with holes and open shells. The surface of particles is, generally, smooth and shiny. The empty spherical grains (resulted from expanding the melt drops) were named cenospheres. The spherical particles with open cavities filled with smaller grains were named plerospheres. Figure 1. Fly ash spherical open particle containing smaller grains and surrounded by cenospheres and irregular shape grains [4] Figure 1 shows the fly ash morphology [4]. Beside spherical smooth particles can also appear coarse particles of Fe2O3 or Fe3O4, containing quartz particles, porous spherical or irregular grains and unburned coal particles. For a better grindability and a good behaviour in cement fabrication and use, fly ashes must contain a high proportion of cenosphere grains free of quartz and other crystalline minerals (i.e. mullite) with a low proportion of compact irregular grains and spherical course grains of Fe2O3 or Fe3O4 microcrystals. The grain size parameters, as measurable quantities, are important characteristics for fly ashes reactivity in solid-state reactions (at Portland cement fabrication) and for pozzolana activity of fly ashes (at hardening of Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 2149-2152 doi:10.4028/www.scientific.net/KEM.264-268.2149

Thermal studies on the hardening behaviour of cements ground with additives

A study was carried out on the effects on the hardening of Portland cements of thesurfactants (dihydroxy alcohols and ethers and aminoalcohols) used as grinding additives. The effects were found to depend on the molecular mass of the surfactants and to correlate with the surface forces in the given reactant systems.