There were characterized from the point of view of the grain-size distribution and the mineralogical composition 8 kaolins (Standard Kaolin, Zettlitz, Arcano DBE, BZ, KOC, Polaris, Bojidar, Popesti). The grain size distribution has been determined using a FRITSCH grain size-meter – “Analysette 22”. The mineralogical composition were established by X-Ray diffraction, using a DRON 3 diffractometer and the quartz content has been ascertained by the extrapolation method. For these frequently used kaolins in the porcelain production there were also determined the technological properties of some casting slips or pastes obtained from the kaolins. The technological properties have been correlated with the grain size distribution and the mineralogical composition obtaining useful information for the optimal shaping recipes – depending on the making process used.
The aim of the present work is the study of the SnO2-CeO2 binary system in the whole concentration range, by classical ceramic method, in the 900-1150°C temperature interval. A small variation of the ceramic characteristics as shrinkage, apparent porosity and archimedic density was observed for all of the studied samples. High values of porosity and, consequently, low values of densities assert the obtaining of porous ceramics. XRD data of the samples thermally treated at 1100°C indicate in the compositional range from 5 to 95 mol% CeO2 the presence of two phasal components (SnO2 and CeO2). No binary compound is formed between the two oxides. The presence of only one phase with tetragonal (rutile), respectively, cubic (fluorite) structure for the compositional domain very close to the end compounds of the SnO2-CeO2 system was noticed. Microstructural parameters obtained by the XRD data confirm this fact.
Study on the synthesis and properies of the ceramic pigments in the CeO2 - PrO2 system
The aim of this paper is to obtain pink-orange-purple colored ceramic pigments in the CeO2-PrO2 system. The pigments were obtained by solid state reactions between cerium salts and proseodimium oxide at 1000-1300ºC. The pigments were examinated for their structures by XRD, color by wavelength measurements and ability to dye ceramic glazes.
Sol-gel nanocomposites based on iron oxides in silica matrices
FexOy - SiO2 sol-gel nanocomposite materials were prepared via alkoxide and aqueous route in order to accomplish a comparative study. As SiO2 source, tetraetho-xysilan (TEOS) and methyltriethoxysilan (MTEOS) in alkoxide route, as well as silica sol Ludox (30%) in the case of aqueous route, were used. As iron source a Fe(III) salt [Fe(NO3)3.9H2O] was chosen. In order to obtain iron oxides with different oxidation states, structures and grain sizes, the gels were annealed at different temperatures. The structural characterization of the obtained materials via the two preparation routes, before and after thermal treatment, was realized by DTA/TG analysis, X-ray diffraction, IR spectro-scopy and transmission electron microscopy (TEM).
Asymmetrical ceramic membranes. Applications for wine clearing and stabilizing
In this work are presented the results obtained with regard to preparing some ceramic membranes with controlled porosity and to the filtering equipment, adequate for the following aim: maintain the stationary flux permeate for a long period of time and assure the quality of filtered wine before bottling. The ceramic membranes have an asymmetric structure, composed from a macroporous ceramic support and a thin layer with a much finer porosity, which ensure the selectivity in the separation processes. The filtering equipment realised at a pilot scale, assures the liquid cross flow through the modules and eliminate in this way the undesirable effect of the polarization concentration. The characteristics and the performances of the ceramic membranes and the parameters of the filtering equipment are presented too.
Hardening and expansion processes in C3S - (CA - CSH2) - H system
Blended expansive cements consisting of Portland cement as a matrix binder and an expansive addition, which is able to form ettringite (C3A.3C.H31*), represent binders having good expansive properties. The composition of the binders and the dosage of the components can control their expansion. The expansive additions consist of an aluminate material (high aluminate cement, sulphoaluminate clinker, Portland high aluminate clincher) and gypsum.
Taking into account that C3S is the main compound of the Portland cement the processes that are going on during their hardening in the presence of sulphate-aluminate additions (CA, C4A3S, C3A) sould be interesting.
The present paper brings information about the hardening and expansive processes in the binding system C3S–(CA+CSH2)–H.
The content of the expansive additions (CA+CSH2) in the binding mixes was of 10-30%. CA and CH2 were dosed corresponding to an Al2O3/SO3 molar ratio of 1/3. The content of the expansive addition in correlation with the humidity of the curing environment exerted a significant influence on the ettringite formation and on the expansion. This was as greater as the amount of the expansive addition and the humidity of the environment were higher. In the case of the binder with 30% (CA+CSH2), in humid atmosphere, the expansion was so great that the hardening structure formation was hindered (the samples disintegrated).
The best binding behaviour presented the composition that had a content of 10% expansive addition. This composition has developed good mechanical strengths and a relative low expansion, compensating the shrinkage. A relative good correlation between the ettringite formation and the expansion has been pointed out.
The activator influence at hardening process of cementitious - pozzolana binding system
The paper aim is to study the influence of activator mixture, depending on its nature, on the hardening process of cementitious – pozzolana binding systems.
The cementitious material was a melilite blastfurnace slag. Thermal power fly ash and volcanic tuff as pozzolana materials were used. As activators, mixtures of lime and calcium chloride and natrium sulphate were used. The po-zzolana / (cementitious material + pozzolana) weight ratio were: 0, 0.1, 0.3 and, 0.5. The specific surface area of the components was 4000 cm2/g.
Chemical bond water content, calcium ions concentrations, and pH analysis were made on binding pastes or suspensions, as well as mechanical strength determinations on mortars. The obtained data were used to correlate the hardening binding systems behaviour and the activator nature.
Influence of minor oxides upon the brownmilletrite hydraulic properties
Brownmillerite, C4AF, is an important phase of high iron-oxide hydraulic cements, particularly of low e-nergy cements as, sulfoaluminate belite type. Often, in the clinker raw mixture MgO and SO3 can exist as minor components. Different minor oxides present in its structure as solid solution can influence the kinetics of solid state reaction in the oxide mixtures corresponding to the C4AF composition and the hydraulic activity of the brownmillerit.
A comparison between hydraulic properties of brownmilerite obtained with or without minor oxides is presented in the paper.
The fragility of silicate melts - correlation with basicity
The fragile or strong character of melts constitutes one of the recent manners of glass forming liquids description. It is known that only for a few melts the viscosity has an almost Arrhenius variation along the all the usual temperatures domain. These are the so called strong melts, one example being molten SiO2. For the majority of melts the viscosity dependence on temperature is described better by the T-V-F equation. These are the fragile melts. One presents shortly the main ideas and theories elaborated for understanding these structural peculiarities and the proposed methods for fragility identification and characterization. In this work the existence of a clear correlation between the fragility and basicity is demonstrated. One observe that the strong melts have a greater tendency to undercool in vitreous state as the fragile ones which tend to pass towards the field of melts with a greater tendency to devitrification. A series of ideas and data contributing to more deep understanding of structural aspects concerning the melts fragility are discussed and an explanation of this phenomenon for oxide glasses is proposed.
Dependence of properties on oxidecomposition for glasses (35 - x) Na2O.xAl2O3.65B2O3
Glasses within the system Na2O – Al2O3 – B2O3 present both practical and theoretical interest. The theoretical one is motivated by the possible alteration of the coordination number for boron and aluminium as a function of actual chemical composition. Therefore, is expected that compositional and structural changes to modify some of glass properties.
First part of our work was devoted to preparation of glasses defined by the molar formula (35-x) .Na2O.xAl2O3.65B2O3 (x = 0; 5; 10; 12.5; 15; 17.5% mol.). On the prepared glasses there were determined several properties: Tg, Tsoftening, linear thermal expansion coefficient, refractive index, density.
For certain properties, the dependence on chemical composition of glasses was expressed in several ways. The experimental results were compared and validated with similar literature data.
Binding materials for the conservation and restoration of mural painting support
Diagnosing and arresting the causes as well as the effects of degradation on historic monuments, correlated with the development of products in tune with the basic principles of conservation and restoration of historic monuments, are under a constant concern at a national and international level. To this end, the development of binding materials designed for the conservation and restoration of historic monuments is given special consideration. The present paper addresses the development, application and performance in situ of certain binding materials, featuring compressive strength, resistance to salt crystallisation, adherence to support, and SO3 and alkali content, and designed for luting gaps in mural painting supports. In addition, a case study is presented: the Doamnei Church of Bucharest, 17th century.