CONTENTS no. 1/2003                                   Romanian Journal of Materials

IOAN LAZAU, DOREL COR, CLAUDIA APETRII, RADU I. LAZAU, CORNELIA PACURARIU Thermoresistant pigments with perowskit structure
LUCIA GAGEA, CRINA SUCIU, ANIKO TOTH Synthesis and characterization of some alumina micropowders 
CAMELIA CAPATANA, PETRU BALTA Copper ruby glass - new data and interpretations   
ANCA TOSUN, ADRIANA PETRESCU, ALEXANDRINA ENESCU, MARIA IONESCU Light thermoinsulating products obtained by recycling glass fibre wastes  
LUCICA BOROICA, ISIDOR BOROICA, MIHAI DINULESCU, EMIL RO'IU, DAGMAR HULSENBERG Ecological solution for polluted wastes neutralization   
ALINA BADANOIU, MARIA GEORGESCU, ANNEMARIE PURI High performance binding system with silica fume content 
MARIA GHEORGHE, ROMANITA TEODORESCU Experimental model regarding to the leaching of the heavy metals immobilised in cement pastes 
FIAMETTA KORMOS, RODICA  MORAR, VALERIA FARCAS, DOINA PRODAN, IOSIF CHEREJI Studies on minor components determination in coal fly ash from Romanian thermoelectric power plants 

Thermoresistant pigmenst with perowskit structure

The perowskit structure is intensely studied due to the fact that it represents the basis of some materials that develop very interesting electrical properties as piezolelectricity, ferroelectricity and high – temperature superconductivity. Recently, the perowskit crystalline network has been considered as a starting point in obtaining thermoresistant pigments, being noticed red pigments derived from YAlO3 by substituing Al3+ with Cr3+.

The present paper shows the results obtained concerning some reddish – pink pigments with perowskit structure, ABO3, in which: A3+=Y3+, La3+, Nd3+, Gd3+, Dy3+, and B3+=Al3+, Cr3+


Synthesis and characterization of some alumina micropowders

The present study focused on finding methods to obtain alumina precursors with polymorphic forms at low temperatures that can be used as raw materials for preparing thin porous layers.

The method used to prepare thin porous layers was that of mixing two liquids. The reagents were soluble aluminum salts (aluminum chloride and aluminum nitrate), nitric acid and organic compounds (ethylene glycol and glycerin).  Synthesized gels were roasted at different temperatures and were examined to determine the structure and morphology of the resulting crystals.  By using different methods to prepare gels it was intended to find out the influence of organic components on the characteristic temperature of alumina transition phase as well as on the morphology and size of Al2O3 crystals.



Copper ruby glass - new data and interpretations

The results of a research work of some less understood redox mechanisms and processes of copper ruby obtainment are presented. The copper ruby formation conditions in a borate glass and in silicate and phosphate glasses were studied, using organic reducer and Sn.

Without reducer the cuprous oxide cannot form the colloidal aggregates, which determine the red ruby color apparition. The use of an organic reducer (saccharose) for copper reducing to Cuo is not advantageous the obtained ruby being of a poor quality. Using a Cu-Sn alloy results in a high quality ruby having a pure color and a high transparence.

The accumulated knowledge on redox process mechanisms and on ruby formation allows taking into consideration the possibility of copper ruby producing on an industrial line. In this way the eventual replacement of the cadmium sulfo-selenide ruby would became possible, cadmium being toxic and pollutant.


Light thermoinsulating products obtained by recycling glass fibre wastes

The glass fibre waste represent a big  problem for the environment;they are nondegradable and for this reason they are no more axccepted in the echological litter hollows.the glass fiber waste include raw materials and energy and should be revaluated in a superior way.

The paper presents the researches made to obtain  thermoinsulating products starting  from the coarse glass fibre waste produced in the glass fibre plant FIROS S.A.

The glass fiber waste are first processed, breaking them up to the appropriate granulometry , then  they are melted in a minioven and precessed by flamme attenuation technology  in glass microfibers whose diameters ranged between 4 – 8 microns.In a next stage there are realized light  thermoinsulating products – boards –using short glass fibres ( the matrix), reinforcing fibres, mineral fillers,organic or anorganic binders.



Ecological solution for polluted wastes neutralization 

In Romania exist wastes from metallurgical and machine building industries. Some wastes contained toxic metals that are dangerous for people and environment.

The investigated waste is like suspension and must be dried. It contents Cr6+ ion, about 10wt%, which can cause diseases of the digestive and breathing systems.

The paper presents the researches of the National Glass Institute team and co-workers from UPB and TUI Germany to obtain a composite with a soda-lime matrix.

The glass is from chemical point of view, a relative stable material against acids, water and alkali. That is way it can be used to obtain some composites which are able to incorporate different other materials with a lower chemical stability [1].

There were obtained, by sintering at 800-1000°C, co-lored composite having different shapes and a lower price. They can be used as decorative and building materials. By melting at 1450°C were obtained black glasses that can be used in making decorative objects. The storage of the waste in the glass matrix is possible up to 40wt%, the obtained materials having a good chemical stability (no chromium ions dissolve in water).



High performance binding system with silica fume content

 In this paper some of the properties (mechanical strength and durability) of DSP composites based on Portland cement (clinker) with 5 up to 15% silica fume admixtures and Romanian plasticizers (LSC, DISAN) are presented. For optimum dosages of the silica fume admixtures and plasticizer additions, correlated with the reduction of water to binder ratio used for the composites preparation, strengths increases of 40-80%, compared with the composites base on normal Portland cement, were obtained after 28 days of hardening. The studied composites have good sulphate resistance and freezing-thawing stability. The improvement of these properties are due to the reduction of the Ca(OH)2 content in the hardened composites and also due to their less permeable structure.



Road cements 

The European Standard ENV 13282–2000, “Hydraulic road binders. Composition, specifications and conformity criteria,” deals with the hydraulic road binders designed for use in road bases, sub-bases and capping layers in road construction and for soil improvement and stabilisation. Within the action of affiliating Romania to European Standards, adopting the fore mentioned European Standard is auspicious in both economic and environmental protection terms for cement manufacturers and complex road works constructors as well. The paper approaches the research and development of road cement sorts type ENV 13282–2000, and presents the results obtained in the laboratory, at industrial scale, and at placing the investigated cements according to the requirements in the effective regulations for developing road base and sub-base courses.


Experimental model regarding to the leaching of the heavy metals immobilised in cement pastes 

The compatibility of electroplating sludge with stabilisation/solidification (s/s) cementitious matrix is based on to high pH value of the matrix pores aqueous solution and on the matrix phase and mineralogical composition which allows micro encapsulation, adsorption, precipitation, and ionic substitution of heavy metals.

 Two types of electroplating sludge (from two industrial companies) with Cr, Cu, Mo Pb and Zn content, have been solidified/stabilized into cementitious matrix. The heavy metals release has been evaluated by a cumulated 180 days - leaching static test, at liquid (distilled water): solid surface ratio of 10:1.

 The role of the diffusion on-the heavy metals leaching rate, from s/s cementitious matrix, has been investigated. The experimental leaching procedure has been relied on the tank tests described by the Netherlands Norm NEN 7345, and American National Standard 16.1 - ANS 16.1.


Studies on minor components determination in coal fly ash from Romanian thermoelectric power plants 

The great amounts of coal fly ash formed in the last 30-40 years in Romania represent a dangerous waste for human health and environment as well. The attempts for this waste utilization as additives in building materials leaded to the necessity of studying the chemical composition, especially the content in secondary components and to radioactivity measurements. The chemical composition and properties of coal fly ashes vary with the source and type of the coal used in thermos-electric power plant. The paper reports experimental results concerning secondary components (TiO2, P2O5, Mn2O3) concentration in coal fly ash obtained by molecular and atomic absorption spectrophotometry measurements as well as radioactivity concentration due to the following natural radionuclides: K-40, Ra-226 and Th-232. According to the experiments it was established that Romanian coal fly ash through its nature (adequate chemical composition and relatively low radioactivity level) could be used in building materials industry.



Romanian Journal of Materials