|MARIA PREDA, AURELIA MEGHEA,ALINA MELINESCU, ILEANA RĂU||Ceramic pigments based on TiO2 and transitional cations as chromophoric species|
|GAVRIL KOVACS||Ecological glazes obtaining by revaluation of some by - products from the mining industry|
|LIDIA CERCHEZ, MARCELA MUNTEAN||Influence of oxide reagent granulomety on the properties of ceramic fibres|
|ION TEOREANU, ŞTEFANIA STOLERIU
|Cements free of Portland clinkers|
|ANNEMARIE PURI, MARIA GEORGESCU,
|Hardening processes in the Fe2O3-P2O5-H2O system|
|DOREL RADU, CIPRIAN CIUREA, ELENA
|Retention time of the material in the rotary clinkering kiln|
|ZENO GHIZDĂVEŢ, DOREL RADU
|A systemic approach in modeling equipment from the oxide materials industry|
Ceramic pigments based on TiO2 and transitional cations as chromophoric species
In this paper, was studied the diversification possibility of colours of varied shades using as chromophores nickel, cobalt, manganese, iron and chromium oxides and as diluant calcium titanate. It were synthesised five samples, which were firing in the range 1050-13500C. By X-ray diffraction noticed for most pigments the formation of solid solution with perovskit structure. An exception is manganese oxide, which were solubilized in the rutile structure. The colours were been e-xamined by electronic spectra in visible domain and give existence of charge transfer and d-d transitions characterising the used chomophore ions.
Ecological glazes obtaining by revaluation of some by - products from the mining industry
The paper comprises a synthetic, physic-chemical and mineralogical characterization of the main by-products from the mining industry: andesite, basalt, aplite, wollastonite skarn, dolomite-talk, limestone filler, etc. that may be used for obtaining ecological glazes.
For the elaboration of the ecological glazes from the polynary system SiO2-Al2O3-Fe2O3(FeO)-CaO-MgO-Na2O-K2O there have been taken into account the following principles:
-The correlation between composition-synthesis conditions-structure (texture)-properties.
-Establishment of the oxide respectively mineralogic optimum composition of the enamels which to allow under favourable thermal treatment conditions the synthesis of compounds with high crystallization rates, like anortite, wollastonite, diopside and others.
-The ecological glazes produced experimentally are of various colors, opaque, the opaqueness degree being particularly due to the uniformity of the distribution of the calcium silicates crystals (about 70 % crystalline phase) represented by wollastonite and/or anortite as function of the chemical composition and the thermal treatment applied.
- As far as the cost price of the glazes obtained and industrially applied is concerned, this is about 40 to 60 % lower than that of similar, classical glazes, coloured with ceramic pigments.
Influence of oxide reagent granulometry on the properties of ceramic fibres
The present paper has studied the influence of the grain of the oxide reagents on the properties of the ceramic fibres, paying attention on the following aspects:
- Specific obtaining methods for each composition and the influence of the technological parameters.
- Fibres characterization (compositional, physical, structural).
Cements free of Portland clinkers
In the present paper are examined, comparatively binding systems made from mellilite blastfurnace slag and pozzolana materials – fly ash (an industrial by-product) and diatomite (a natural rock). These materials had different specific surface areas. The studied binding systems were characterised by different cementitious materials/pozzolana ratios (1; 0.9; 0.7). As activator was used a mixture of lime and calcium chloride (2%CaCl2 + 6%lime).
The binding systems were subject of mechanical studies and, in some case of chemical studies (chemical bound water).
It was obviously emphasized the cooperative effect – when using the same cementitious material, between the cementitious component/pozzolana ratio and the dispersional characteristics of cementitious material - pozzolana systems (specific surface areas and grain size distribution). So, it is possible to reduce the influence of grain size distribution of binding mixture on its activity, avoiding the need of advanced grinding with high energetic consumption.
Hardening processes in the Fe2O3-P2O5-H2O system
The present paper brings information concerning the influence of some parameters on the hardening and properties of binding materials in Fe2O3-P2O5-H2O system.
The investigated iron phosphate materials harden only very slow at room temperature. A thermal treatment at 300°C determines the development of mechanical strengths, especially for masses with a bigger H3PO4 content. Depending on the composition of the investigated materials, a slowly increase of the mechanical strength up to 800°C (1000°C) can be observed, followed by a steep increase up to 1000-1200°C. The increase of the Fe2O3/P2O5 ratio generally determines the decrease of the mechanical strength values, in a different manner depending on the heat treatment temperature
Retention time of the material in the rotary clinkering kiln
On a worldwide scale, the production of Portland cement is mostly carried out by using the dry pre-calcination process.
In a clinkering installation, the rotary kiln represents the most important thermal and technological unit. It is characterized by a series of constructive and functional parameters (length, diameter, inclination, degree of admission, speed, decarbonation degree of the mixture of raw materials at the entrance). All these parameters can be correlated as to quantity by means of the retention time of the material in the kiln. Thus, a more precise designing of the kiln and a reasonable estimate of the specific output can be achieved.
A systemic approach in modeling equipment from the oxide materials industry
Present paper deals with a series of modern methods used in prediction, optimization and process control of devices and installations used in the oxide materials domain. The reasons for which these techniques are recommended are related to the high level of complexity of equipment and, at the same time, with inherent fluctuations in their functioning, though excepting efficiency associated with an unique and/or deterministic approach. Although the theoretical fundamentals and the computer applications’ development of some of the presented models require special skills in dealing with some mathematical aspects, the working techniques are accessible and, moreover, they are targeting experts coming from both research/development and monitoring/control areas. In order to support this statement, in a future work these theoretical aspects will be exemplified by case studies.
Romanian Journal of Materials