CONTENTS no. 2/2002                                    Romanian Journal of Materials

GAVRIL KOVACS Masses and glazes for household and decorative vitrus products  
LIDIA CERCHEZ, MARCELA MUNTEAN Influence of the grain size of oxide reagents on the main properties of barium polytitanate - based dielectric ceramics  
RADU PITICESCU, CLAUDE MONTY, MARIJA KOSEC, ADRIAN MOTOC, CATALIN GEORGESCU, BARBARA MALIC Synthesis, processing and characterisation of zirconia based nanoceramics 


Profiled ceramic micropackeges for microwave diodes 


Influence of preparation method on solid solutions structure in MgO - NiO system 


Investigations in view of enhancing the performances of binding and composite masses   


Correlation viscozity - basicity in silicate glasses 
ZENO GHIZDAVET Mathematical modelling of the microwave drying process  
FLORIN ALEXA Etnodesign - contextual materials and princiles a manifesto for the new millenium  

Masses and glazes for household and decorative vitrus products

In this paper there are presented the results of the laboratory experiments concerning the design, the selection and introduction in production of new vitrus masses meeting the following requirements vitrification temperature more than (over) 1000C, maximum firing temperature 12000C, water absorption less than 1 %, and a compact structured relatively fired body (shivering).


Influence of the grain size of oxide reagents on the main properties of barium polytitanate - based dielectric ceramics

This paper presents a study on the influence of the grain of oxide reagents used to obtain barium polyti­tanates - based dielectric ceramics used as dielectric resonators in high frequency fields. The polytitanate dielectric ceramic materials that made the object of this article are BaTi4O9 and Ba2Ti9O20, compounds situated In the maximum Ti02 content area of the BaO-Ti02 system. The physsical properties, especially the electric properties were determined on the obtained samples by measurings in high frequency and structural fields.


Synthesis, processing and characterisation of zirconia based nanoceramics

Yttria - zirconia nanocrystalline powders (YSZ) have been obtained by two different routes: hydrothermal and evaporation—condensation processes. In the hydrothermal route, experiments were developed in a Teflon autoclave with a 2L volume and maximum working temperature 3000C. In the evaporation-condensation process nanophases were prepared in a solar furnace reactor. A glass balloon in which the atmosphere is controlled makes the reactor at a power rate around 2 kW and temperatures up to 3300 C. The powders obtained in both routes have been characterised by chemical analysis, XRD, SEMITEM and BET surface analysis.

The complex thermal analysis and preliminary slnterability studies performed on these powders lead to the conclusion that presence of hydroxyl groups, which are stable at higher temperatures due to the high Interfacial activity of nanopowders, lead to the formation of agglomerated particles. Probably hard agglomerates are also present even if the surface analysis has revealed a very large surface area. The powders obtained in the vaporisation-condensation process were also nanocrystalline, with soft agglomerates. The crystallisation degree for these powders was better, compared to that of hydrothermal powders, but the yield is lower.

Oxygen conductivity of sintered pellets was Investigated by impedance spectrometry in order to calculate the grain boundary contributions. Possibilities offered by these nanomaterials to be used as oxygen sensors and oxygen pumps working at temperatures around 3000C are discussed.


Profiled ceramic micropackeges for microwave diode

The present paper refers to realisation of profiled amic micropackages (Ieadless inverted devices) for mounting of microwave diodes. Using corundum ceramic and electronic purity materials, the ceramic micropackages have been realised by adapting technological processes (deposition of metallic films, hing etc.) and equipment specific to the electronic llponent industry. The utilisation on a large scale of microwave electronics in civil and military communications, reducing the equipment size and increasing the ius of action and reability led to manufacturing of srowave electronic components and implicitly to dern mounting technologies.

To fabricate a profiled micropackages, we used Ce­nic substrates (content of Al203— 99%, excellent pla­sity, surface roughness under 0.15 microns), and me-Ic layouts. The dimensional precision and mechanical properties [1] of profiled ceramic micropackages solve the possibility of electronic component automatic unting on these types of micropackages through the surfaces mounting technique on stripline circuits.


Influence of preparation method on solid solutions structure in MgO - NiO system

One of the most important XRD applications is due to the fact that the distortion of the diffraction line profile can be used to study the evolution of some mi­crostructure parameters, depending on the preparation methods and treatment. The mean size <D> of mosaic blocks, the mean strain <S> and the lattice constants are among the most important parameters which react on the changes of the local structures. The purpose of study was to observe if the mixtures in the MgO-NiO system, obtained by three different routes of prepara­tion, oxides mixtures, nitrites mixture and sol-gel method, followed calcinated at 12000C different times, form solid solutions. We also wanted ascertain if the structural changes can be observed by using the analysis of XR profiles based on the integral breadth method and on the XRAY3.O specialized program.


Investigations in view of enhancing the performances of binding and composite masses

The paper brings information about possibilities of modelling the properties of binding and composites based on Portland cement with fine and ultrafine siliceous additions, either admixed or non-admixed with sulphonated naphthalene-formaldehyde polymer super­ticizer. As reactive siliceous additions, granulated furnace slag, steam power plant fly ash—both ground in advance up to a high fineness—, and silica fume have been used. The paper aimed at finding the in­fluence of the fine and ultrafine additions as well as of superplasticizer on the performances of binding masses of paste and mortar type, respectively. It was emphasised that reducing the water/binder ratio from 0.5 to 0.4 determines increasing of the flexural and compres­strength under conditions of maintaining the same ability of the binding composite masses. Finely ground fly ash may constitute an alternative to silica fume,  subject to shortages in present-day Romania, pro­dvided that a superplasticizer is used in addition.


Correlation viscozity - basicity in silicate glasses

It is known that in the majority of cases, the glass properties are calculated in relation with the oxi­dic composition, the shape of dependence functions differing from author to author and provinding different precisions of calculus.

Considering the oxidic glasses as chemical sys­tems, the importance of their acido-basic characteris emphasised. In this way it is possible to colligate the different properties, especially those concerning the composition (the viscosity, dilatation coefficient, the re­fraction index, etc.), with fundamental of the vitreous systems, the basicity.

The calculated basicity for different types and compositions of glasses has been corelated with their viscosity at different temperatures.


Mathematical modelling of the microwave drying process  

In the paper it was revealed a simple mathematical model of the microwave drying based on the energy conservation law. Further a comparison between the results of both theoretical and experimental approach is performed, regarding thin plates like shaped products. It is to be expected that the model will become a first step in optimizing the microwave drying process.


Etnodesign - contextual materials and princiles a manifesto for the new millenium

Ethnodesign means a strategy to restore the identity of rural areas.

It could be perceived as a school for designers and experts from diverse disciplines (that could work together with the indigenous people of a particular geographic area),who will take into account all the contextual factors that confer local identity.

Due to this new discipline, many design prin­ciples specific for traditional societies, could be suc­cessfully applied to contemporary rural area, pulling an end to the import of urban design.


Romanian Journal of Materials