CONTENTS no. 1/2002                                                                                          Romanian Journal of Materials


ROXANA DUMITRACHE, ION TEOREANU The influence of the sintering degree on the sorption properties of the glazes
MARIA GEORGESCU A well-deserved recognition "Nicolae Teclu" prize awarded by the Romanian Academy to Professor Doctor Engineer ION TEOREANU 
ANA MARIAN, NICOLAE MURESAN New colours for fine ceramics decoration 
ECATERINA ANDRONESCU, ADRIANA ŞOMĂCESCU, LIDIA CERCHEZ, CLAUDIU ŞOMĂCESCU   Synthesis and properties of some dielectric ceramics - resonant to high frequency 
CHRISTU TARDEI, GHEORGHE GAVRILIU, VIRGINIA BURGHELEA Fluorapatite, preparation and properties. A solubility study. 
ADRIAN TOADER, ELENA RADULESCU, ELISABETA NEDELESCU, ADRIANA MEAUTA, LAURENTIU DRAGU Effect of solid fuel use on the heat engineering and operational factors a clinker burning plant 
ALEXANDRA TATCU, ANDREEA IONESCU, ANA MARIA DRAGOMIR Reducing the environmental pollution in cement manufacture 
SABINA BOTEA, ION DOBRIN, CONSTANTIN PETRACHE, CONSTANTIN DRAGAN Technology and new materials used to protect the packed glass sheets 
LIVIU LITERAT, LEVENTE C. BODIZS The influence of humidity on the rheological behaviour of ceramic powders in the pressing process 
HANS HELMUTH REHNER, MIHAI THALER, ZENO GHIZDAVET Considerations on calculation of firing curve for glazed materials  
DANIELA NASTAC, MARCELA MUNTEAN Application of IR spectroscopy to study sulphate phase from the Portland cement 

The influence of the sintering degree on the sorption properties of the glazes

The sintering degree of the ceramic body, and corresponding its density, is considered to be among of its most interesting properties through its significant influence on the behaviour of ceramic body during glazing and on the properties of the fired cera-
mics.

In present communication there are reported the results of correlated determinations of sorption of glaze and corresponding thickness of layered unfired glaze porosity of frit feldspar porcelain.

The unglazed body has been fired at 930°C for 16 hours, using the usual firing regime. It has been found that the technique used to shape the body (isostatic pressing, turning or casting) has a great deal of influence on the body as porosity and, therefore, on the sorption of the glaze and on the thickness of the unfired glaze layer.

Other parameters influencing the processing stages, in correlation with the fired glaze layer thickness on both the isostatically pressed and turning shaped bodies have been equally considered.

Inceput

New colours for fine ceramics decoration

Today some of the most important problems in industry are environment and work protection, problems which concerns also the regulation of toxic substances. In the ceramic industry the major source of toxic substances ( lead, cadmium, zinc ) are ceramic colours used for on glaze decoration, first through the fluxes that take part in a wide range between 70-90%, into ceramic colours composition.

This paper shows the experimental results in achievement of the new ceramic colours with characteristic quality in accordance with European and International Standards.

It has been made new fluxes by joining the actions of fusibility increasing, the brightness, glistening and elasticity assurance, all of these established by the presence of alkaline oxides, earth-alkaline oxides, boric oxide, etc., with that of the increased chemical resistance and the equilibrium of the expansion coefficient guaranteed by the pre-sence of ZrO2, TiO2, SiO2 and Al2O3. The fluxes homogeneity has been established by x-ray diffraction and thermodi-ferential analysis. It has been measured the soften field, at thermal microscope and the expansion coefficient at the Leitz-Wetzler dilatometer.

The fluxes that has been mixed together with the ceramic pigments led us to the new ceramic colours of firing temperatures between 800-850 0C with chemical stability and glistening, without lead, for decorating on glaze of ceramic products.

Inceput

Synthesis and properties of some dielectric ceramics - resonant to high frequency 

The paper presents results obtained in the synthesis of some dielectric ceramics with resonating proprieties at high frequency, adopting the solution of doping the highly titanate compounds of BT4 and B2T9 type with substituents oxides. The nature of the substitution is based on replacing Ti+4 on the crystal lattice with Zr+4 and Sn+4 type isovalent atoms or with heterovalent atoms of Zn+2 type together with Nb+5.

Inceput

Fluorapatite, preparation and properties. A solubility study. 

Due to their good biocompatibility, calcium phosphates (CP) can be used in the human body to repair or to replace skeleton structures affected by diseases or trauma. Consequently, a perfect knowledge of their reactivity in vivo and in vitro, particularly the mechanism of their degradation and the relationships with microstructure are needed. The aim of this work is to synthesize and characterize the single phase material, fluor-
apatite (FAP).

In order to determine the influence of aqueous media the powders (FAP) were immersed in solutions
(1 %), with different compositions (acid, basic, and neutral) for various periods of time. The pH of the solutions was measured.

Inceput 

Effect of solid fuel use on the heat engineering and operational factors a clinker burning plant 

Cement producers are constantly seeking solutions to reduce production costs. To date, one of the ways to reduce production costs is replacing conventional gas or liquid fuels with cheaper fuels. The paper presents the case study of a 3000 tpd clinker burning plant having converted from using conventional fuels to solid fuels (coal, petcoke). The paper reveals the effect of using petcoke on the heat engineering and operational parameters of the clinker burning plant.

Inceput

Reducing the environmental pollution in cement manufacture  

Under conditions of upgrading programmes, Romanian cement plants have allotted much of their investment to reducing polluting emissions to comply with the norms. This paper presents the accomplishments attained regarding the environmental protection in the dry-process cement manufacture.

Inceput

Technology and new materials used to protect the packed glass sheets 

The present paper describes a new technology and material used for electrostatic settlement on the glass sheets surface, of a biodegradable powder, as paper subtitute.

This technology has already been used at GEROM Buzău and it won Gold Medal at Invention Exposition Geneve 2000 the.

The advantages of this technology and material used are:

- a biodegradable powder as paper substitute is used;

- this powder is not harmful, it can be easily removed and it doesn˘ t leave tracks on the glass sheets surface;

- its price is much lower than that of paper;

- wood is saved, paper being no longer used;

- human efforts at work are decreased.

Inceput

The influence of humidity on the rheological behaviour of ceramic powders in the pressing process

One pursuits the effect of the humidity on the shape of the pressing curves. The alterations of the shape particularities are interpreted as rheologic modifications. One also discusses the deviation of the mathematical models and their validity at the pressing phenomena.

Inceput

Considerations on calculation of firing curve for glazed materials 

The paper presents a newly calculation method of the heating / cooling rate, which can be applied for plate shaped, glazed materials. It is a known fact that not only in the case of thermal shock but also in the process of obtaining the product, when the temperature variation is constant, there will occur internal stresses within the material. In order to avoid the object’s destruction, the firing curve can be computed by taking into account the glaze-ceramic mismatch.

 Inceput

Application of IR spectroscopy to study sulphate phase from the Portland cement 

The present paper describes the application of IR spectroscopy to study the sulphate phase from ordinary Portland cement. A detailed discussion on vibration modes of sulphate ion is presented. The spectral bands of alkali sulphates which are present in Portland cement are discussed. It was considered aspects of the variations in relative intensity and frequency of spectral bands.

 Inceput

Romanian Journal of Materials