|VIRGINIA BURGHELEA, MIHAELA ALINA MELINESCU, GEANINA DUMITRASCU, IOANA VLAICU, IOAN MIRCEA POPESCU||Chromatic characterisation of Cucuteni ceramics - Scanteia A2|
|CRISTINA VASILE, LASZLO SZELL, VALERIA MURESAN, ELISABETA NAGY||Influence of the nature of raw materials on the specific features of the electro-techncal porcelains|
|MARIA SPATARU, MARCELA MUNTEAN, ADINA MIHAIL||Ceramic wall from alumina-zircon slip casting|
|LIVIU LITERAT, ALEXANDRU ORBAN||The behaviour of some superaluminous ceramic powders atomised in the process of isostatic pressing|
|DOREL RADU, CLAUDIU MAZILU, BOGDAN GRIGORAS||Basicity percentage utiliyation for the lithium coordination number determination in the lithium disilcate glass|
|ION TEOREANU, GRAZIELA GUSLICOV||Effects of the surfactants, industrial by-products on the behaviour of the Portland cement at grinding|
|PEDRO VALDEZ-TAMEZ, ALEJANDRO DURAN-HERRERA, CEZAR JUAREZ-ALVARADO||Hydration development evaluation of natural pozzolan - calcium hydroxide systems|
|ALINA BADANOIU, DORINEL VOINITCHI||The influence of organic polymer additions and of the cement grain size used for the preparation of carbon fibres composites|
|LUCRETIA BREZEANU, VALENTINA CETEAN||Considerations on the building technique of the dacians in the 1st millenium B.C.|
Chromatic characterisation of Cucuteni ceramics - Scanteia A2
Seven ceramic fragments from the archaeological site at Scanteia-Iassy were examined thouroughly. They come from semivitrified ceramic pottery, decorated with many geometric motifs in white, black and red applied on the outside and/or the inside.
The crystalline mineralogical constituents of the ceramic support as well as the pigments were identified by Roentgen diffraction. Also, the texture of the ceramic fragments was examined by optical microscopy. The colour of the ceramic support and the pigments was determined objectively through spectrocolorimetric measurements in the visible domain of the spectrum.
Influence of the nature of raw materials on the specific features of the electro-technical porcelains
The porcelain has multiple use functions, due to some basic properties, such as resistance to atmosphere agents and mechanical resistance. Primordial for the isolating ceramics are the high electric resistance, chemical inertia and thermal stability.
Experimental works aimed at making the synthesis of some aluminium ceramic masses with optimal characteristics for obtaining the medium and high tension ceramic insulators, starting from raw materials of different origins (native and imported), used in a mixture or individually, in variable proportions.
Ceramic wall from alumina-zircon slip casting
Aqueous suspensions from alumina-zirconium silicate, two raw materials nonplastics were obtained as to able for Wet-forming method in plaster moulds by addition of Arabic gum, sodium carboxymethylcellulose and polyvinyl alcohol.
Some specific rheological properties and technical data of slip casting such as: pH, viscosity, volume weight, medium particle size were carried out.
Wall thickness, time of shaping ceramic wall, green density, is shown.
The behaviour of some superaluminous ceramic powders atomised in the process of isostatic pressing
The results of an experimental study regarding the isostatic pressing of some superaluminous ceramic powders, meant to help in the production of ceramic insulators for sparking plugs, are analyzed. The influence of the pressing upon the structure, the porosity and the density of the green bodies, estimated on different areas (length, diameter) and the contraction at sintering was followed. Correlations between these parameters and mathematic models for the processes were searched.
Basicity percentage utiliyation for the lithium coordination number determination in the lithium disilcate glass
The structure of the oxide vitreous systems is characterized at a first structural level, by the type and the proportions of the constitutive ions, by the coordination number of the cations in relation with the oxygen, by the internuclear distances and the angles between the formed chemical bonds. Concrete structural information can be gathered by utilizing different experimental techniques (x-rays or neutrons diffraction, XPS, MAS-NRM, 3Q-MAS NRM, etc.). For the alkali-silicate glasses generally exists a series of data reported in literature, but in fact there are fewer results referring to the Li+ ion coordination in glasses from the Li2O-SiO2 system.
In this work, an attempt of determining the coordination number of the Li+ ion in the lithium disilicate glass (LS2) is presented by using a globalizing structural characteristic - the basicity percentage (pB). This is experimentally determined from spectroscopic measurements. The experimental data processing shows a coordination number for Li+ in LS2 glass equal to 2, value found in other literature reports too.
Effects of the surfactants, industrial by-products on the behaviour of the Portland cement at grinding
The paper describes the use of three categories of industrial by-product surfactants such as (i) in which prevails phthalic groups or similar functionally mixed groups, (ii) mixes containing phthalic, phenolic and/or glycolic groups, and (iii) poly glycol compound mixes. Additive ratios, were used for two characteristic types of Portland cement, ranging from 0.05% to 0.50%, depending on the case. The grindability, the particle size distribution and the flowability of the Portland cement were monitored under conditions of grinding with surfactants. The results have been analysed in comparison with reference samples (i.e., without surfactant) and in relation to the grinding surfactant category. In all cases, the positive effect of the grinding surfactants has been pointed out in terms of their action in the comminution process, the particle size distribution and flowing characteristics of the obtained cements.
Hydration development evaluation of natural pozzolan - calcium hydroxide systems
This research covers the characterization of four natural pozzolan materials with igneous origin. The pozzolanic activity index of natural pozzolan-calcium hydroxide systems was determined using the compressive strength of mortar cubes. The rate of the pozzolanic reaction was determined in pastes with the same mix design that was used to make the mortars, this was achieved measuring the changes in time in the Calcium Hydroxide concentration. This information can be used as a preliminary selection tool, to evaluate the pozzolanic potential of natural pozzolan quarries.
The influence of organic polymer additions and of the cement grain size used for the preparation of carbon fibres composites
The influence of the grain size of the cement used for the preparation of cementitious matrices based on Portland cement with polymer additions is presented in this paper. These matrices are one of the components of the cementitious carbon fibres composites, presently studied at Royal Institute of Technology, Stockholm, Sweden. The main advantage of this type of matrices, is their lower toxicity and higher durability compared with the classic organic matrix based on epoxy resins. The main disadvantage of this type of compo-sites is the lower bond strengths between carbon fibres and the cementitious matrices. In order to improve this bond strength, new compositions of the cementitious matrix (based on very fine cement and organic polymer additions) were designed and tested. This paper presents the influence of polymer addition (30%) and the cement grain size on some properties of the binding matrix in fresh state (workability) and hardened state (flexural and compressive strengths and bond strengths to the carbon fibres).
Considerations on the building technique of the dacians in the 1st millenium B.C.
Romanian Journal of Materials