CONTENTS no. 4/2002                         Romanian Journal of Materials

AURICA GOLEANU Achieving of some self - glazed porcelain bodies  
MARIA PREDA, ALINA MELINESCU, MARIA ZAHARESCU, ANCA BRAILEANU Hydroxyapatite obtaining by hydrothermal route  
ROXANA DUMITRACHE, ION TEOREANU Fast single-firing of feldspar porcelain: attempts with a view to applying at tableware porcelain 
ELENA DAN, MARCELA MUNTEAN Investigations on the corrossion behaviour of some sulphoaluminate belite cements 
ROXANA FECHET, VASILICA JUNGHEATU Types of clay in the Islaz - Chiscadaga deposit, as usable in cement manufacture
NICOLAE DRAGAN, COSTINEL LEPADATU Modeling, approximations and software for estimation of some structural factors with XRD 
ZENO GHIZDAVET, DOREL RADU Optimal design of complex systems. Applications in oxide materials industry
DANIELA PARASCHIVESCU, FLORENTINA MIHAILESCU, SORIN JINGA Problems of environment protection and conservation in glass fabrication. 1st Part
IOAN FACAOARU, NECULAI CIORNEI, VALENTINA CETEAN Non - destructive method for rapid "in situ" characterization of rocks 

Achieving of some self-glazed porcelain bodies

The present paper is intended to study the s e l f – g l a z i n g   p h e n o m e n o n  in the case of some ceramic bodies within the quaternary system K2O-MgO-Al2O3-SiO2, a phenomenon which illustrates the complexity of the interactions between the components of this system.  In the first part of the paper, the experimental researches are presented, referring to the obtaining of heat resistant self-glazed porcelain bodies.   In order to emphasize some possible reasons of the self-glazing phenomenon, the experimental researches undertaken upon a representative self-glazing composition are presented. Different investigation methods have been used. Thus, in order to characterize the stages of development of its own glaze, reflection measurements have been made. These investigations have proved that in the tested bodies during the firing process, the formation of the glaze by self-glazing starts after the temperature of 1150OC. The optimum development of the glaze layer as a continuos shinny film was achieved around the temperature of  1300OC. Samples of the same body, fired at the temperature of 1300OC, have been analyzed taking into account their chemical composition, by X-ray fluorescence, their mineralogical composition, by X-ray diffraction, as well as their microstructure, by scanning electron microscopy. Taking into account all the results of these investigations, the conclusion is that the ceramic material of the tested samples, consisting mainly of cordierite, is a cordierite ceramic material, which also contains spinel and corundum, as crystalline phases as well as glass phase( amorphous and crypto-crystalline ) and the process of  s e l f – g l a z i n g  is due to the concentration on the sample surface of the components of the body with a low surface tension (potassium oxide, sodium oxide). Here, together with the silicon dioxide and the existing impurities(titanium dioxide, iron trioxide) the above mentioned components develop a siliceous-alkaline melt which becomes stiff during the cooling process, forming a self-glazed layer.



Hydroxyapatite obtaining by hydrothermal route 

Hydroxyapatite  was synthesised by hydrothermal route at 1400C, with two and four hours. By X-ray diffraction it was noticed that obtained powders are mostly composed of hydroxyapatite tricalcium phosphate traces. By thermal analyses it was observed that after a soaking of four hours, two endothermal effects accompanied of weight loss, assigned of water elimination of  free calcium hydroxide and of the water of hydroxyapatite structure.  The calcium hydroxide is not identify  by X-ray diffraction showing its amorphe structure. By IR spectra the presence, in the lattice of synthesised powder of groups as [PO4]3-, [CO3]2- for substituted phosphate ion in hydroxyapatite structure, [HO]- from lattice and the water adsorbed on the surface of  hydroxyapatite grains was established. The grains have a spherical forms and approximate 2mm size determined by electronic microscopy. The results has been interpreted about comparison with a standard sample and based on literature dates.



Fast single-firing of feldspar porcelain: attempts with a view to applying at tableware porcelain 

In the paper is performed an attempt to approach fast single-firing at tableware porcelain products. On this purpose, were used dilatometer analyse for the glaze and porcelain pieces – green and biscuit, with which were associated bulk density measurements for the ceramic pieces used.

The obtained information is suggesting changes for the thermal treatment curve applied at fast single-firing, regarding with those applied for sequential thermal treatment, in two stages (second firing).

Simultaneously, are required modifications of glaze mixture behavior at thermal treatment and, in consequences, modifications in glaze compositions.

With these mentioned conclusions were made preliminary trials – attempts, for design and realize a glaze, which applied on a green piece – with subsequent fast single-firing leaded to obtain a correspondently quality for the fired glazed piece.

Further on, will be extend investigations for profound thoroughgoing study of formation processes in ceramic piece and glaze, with single-firing implications to tableware feldspar porcelain products.



Investigations on the corrosion behaviour of some sulphoaluminate belite cements 

The corrosion behavior of concrete significantly depends on the cement matrix resistance against the  aggressive environmental conditions.

The aim of the contribution is the study on corrosion resistance of a sulphoaluminate belite cement (SAB), based on fly ash, as raw material, exposed to the aggressive solutions 90 and 180 days. For comparison,  test specimens made from ordinary Portland cement (OPC), and slag blended Portland cement (SPC), with well known corrosion resistance were used. The results, obtained after 90 and 180 days provided that the SAB cement , made from fly ash based raw materials show a decreased acidic resistance and a good resistance of  sulphate and chloride attack, in comparison with OPC and SPC.



Technological solutions to obtain road cement  

The paper presents the operating conditions to develop the road cement sort CD 40 (special cement for roads, with characteristics according to STAS 10092/78) in two compositional formulas of the raw mix: that is, with ordinary raw materials and with silica modulus corrective addition. The paper brings information regarding both the evolution of the operational factors while manufacturing the two-variant road cement and the quality of the resulting road cement.


Types of clay in the Islaz - Chiscadaga deposit, as usable in cement manufacture  

The paper brings information regarding the types of clayly rocks in the Islaz–Chiscadaga clay deposit, as usable in the cement manufacture. Carrying out of detailed geological and laboratory works has led to obtaining new geological and qualitative reconnaissance data from the deposit. It has been highlighted that the types of clayly material are appropriate for use as an aluminosiliceous component, alongside limestone, in the cement manufacture.


Modeling, approximations and software for estimation of some structural factors with XRD   

The target of program XRAY3.0 was the rapid determination of microstructure parameters, crystallite mean size <D>, lattice mean strain <S> and lattice constants for crystallised powders from the X-ray recorded diffraction spectra. The diffraction peaks and the Ka doublets separation have been simulated through Pearson-VII analytic functions. There are described the main models and approximations that are the basis of analytic estimate of structural factors <D> and <S> in connection with the method of integral breadth. There were discussed the principles with which the observed data can be corrected by instrumental aberrations when a proper standard exists. The practical procedures of simulation and mathematical estimate of structural factors from digitalized XRD spectra were established from these principles and then they were included in the program. The main menu and some instruments provided by the program were also discussed in this work. Quantitative and qualitative  estimates that are based on procedures included in XRAY3.0 will be discussed in a subsequent paper.



Optimal design of complex systems.  Applications in 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.



Problems of environment protection and conservation in glass fabrication. 1st Part


The prolonged pollution of the environment has caused a huge extension of the contemporary ecological problems worldwide. In the actual economic context, the industrial manufacturers have learned to comply to the rules imposed by governments but mainly to the demands of the consumers related to the quality of the environment.

The glass manufacturers can not allow themselves to be an exception to these rules and thus have to adapt themselves to the major changes by improving the manufacturing technologies meaning, "clean" ones. The field of protection and preservation of environment is well covered by the romanian legislation adopted after 1990. But enouncing the environmental problems is not enough. A strong support to industry in general and to Glass Industry in particular, in the effort of solving the problems is also necessary.



Non-destructive method for rapid "in situ" characterization of rocks   

The effective determination of the field and place of application of the products resulting from stone working is a compulsory requirement in the building activity and is solved by laboratory analyses. This article presents details on the determination, by non-destructive method, of the compression strength of the rocks, both “in situ” (in the deposit) and in a   laboratory. The originality of the method consists in simplifying the determination process of this parameter, a method that is in agreement with the systems proposed to apply in the European Community. The method has the advantage of being applicable in quarries, where knowledge of this parameter leads to a rationalizing of the working, and more especially to a selection, by quality criteria, of the blocks. The method is applicable to all categories of natural consolidated hard rocks, being a viable alternative for deposits with an inhomogeneous composition as to quality and structure.


Romanian Journal of Materials