|GEORGETA VELCIU, GELA PROROCU, MARIA DIACONESCU
|Ceramic materials for dense oxygen separation membarnes
|Oxide and hybride nanomaterials obtained by sol-gel method
|Special obtaining methods of powders from technical ceramics
MARIA IONESCU, ADRIANA PETRESCU, SANDA ENESCU, MARIA GHEORGHE
|Glassfibre composites substitute for the asbestos cardboard
MARIA GEORGESCU, GEORGETA VOICU, STEFANIA STOLERIU, GEORGE POTERAS
|Reactivity of some andesite aggregates with regard to alkalis in cement
ION TEOREANU, ALICE POP
|Acid corrosion of Portland cement with formation of soluble products
CONSTANTIN AUREL DIMITRESCU, MIHAI BRATU
|Assesing the mill effectiveness in terms of energy
MARIA GHEORGHE, NASTASIA PANAIT, LIDIA RADU, ROMANITA TEODORESCU
|Some consideration regarding Cr and Mo immobilization in hydraulic matrix
VALENTINA CETEAN, NECULAI CIORNEI, AURICA MAFTEI, CONSTANTIN BALUTA, LAURENTIU ARGATU
|The achievement of "hardness stones scale" and the importance for optimization of synthetic diamonds consumption in processing equipments
Ceramic materials for dense oxygen separation membarnes
Oxygen-permeable dense membranes from the ionic and electronic ceramic conductors are used for pure oxygen separation from air at elevated temperatures, in various chemical synthesis processes.
This paper presents a study concerning preparation and characterization of metal oxide compounds having a perovskite type phase structure in the La1-xSrx(Co1-yFey)O3-d system with x= 0.8; 1 and y=0.2; 0.5; 0.8.
The role of the cationic substitution on the phase composition evolution in the synthesis and sintering processes by DTA-TG thermal and X-ray diffraction analysis were studied.
The sintering behavior data as well as electrical conductivity up to 10000C revealed an ionic and electronic conduction mechanism of the studied perovskite compounds and the promising material qualities for the oxygen separation from air at elevated temperatures.
Oxide and hybride nanomaterials obtained by sol-gel method
Sol-gel method is considered as a unique way to process almost all type of amorphous and nanostructured materials with interesting optical, electrical and catalitic properties. In the paper the fundamental aspects of the sol-gel preparation of the oxide and inorganic – organic hibrid materials will be discussed and recent results concerning the obtaining of different types of sol-gel nanomaterial (powders, films and nanocomposites) will be presented.
Special obtaining methods of powders from technical ceramics
This work refers to three advanced methods used for the synthesis of powders with the superior properties followed in the technical ceramics. All these methods have the advantage to be achieved at low temperatures. Due this fact the crystals with small sizes obtain and the properties are improving. The first was presented the synthesis in molten sells, followed in presents for oxide compounds. This method is simple and facile to use. By the combustion synthesis the nitrates as raw materials followed and the combustion materials are urea and hydrazide. The reactions develop at the resulting temperature from the burning of organic substances and have place in the very short time. The third method is the synthesis in the field of microwaves in solutions with water and in solid state respectively. It is showed the influence of lattice defects on microwaves oxide compounds absorbtion.
Glassfibre composites substitute for the asbestos cardboard
The paper presents the results obtained to realize glassfiber cardboard. There were made samples differentiated by :
· fibrous composition :
- discontinuous E glassfibres;
- discontinuous E glassfibres and E glass chopped roving mixture;
- basalt mineral wool waste;
· composition recipe ( binders, fillers, etc.)
· fabrication proceeding :
- continuous proceedings (using the glassfiber paper machine)
- discontinuous proceeding ( pouring into matrix
The physical – mechanical properties of the glassfiber cardboard samples were determined in conformity with european norms. The best results were obtained using the continuous proceeding, with some composition recipes realized from :
a) discontinuous E glassfiber;
b) basalt mineral wool waste
The researches continue to optimize the composition recipes and the realization technology.
Reactivity of some andesite aggregates with regard to alkalis in cement
The paper brings data of the authors’ own investigations regarding the alkali reaction capacity of the two andesite aggregates from two different quarries. The methods used for investigations were: petrographic analysis and reactivity testing methods such as: chemical method and mortar bars method – as standardised tests.
The results obtained showed that the andesites have an important potential reactivity, irrespective of their extraction place and of the composition modifications. As consequence, their use in concrete must be done carefully, only after preliminary laboratory tests, showing their compatibility with cements having a low alkali content (Na2O equiv.) or the possibility of their use, considering some preventive measures for diminishing or eliminating the alkali-silica reaction.
Some information regarding the alkali-silica reaction and hydration process and products in the hardened mortars for 12 months, were obtained by electronic microscopy analysis and thermal analysis.
Acid corrosion of Portland cement with formation of soluble products
Understanding the effects of various aggressive mediums on the cement stone offers an opportunity to arrest the aggressive action. The acid corrosion occurs below the pH of 6.5, and may originate from: (i) acid rains, increasingly frequent over the last decades and caused by SO2 and NOx emissions leading to formation of H2SO4 and HNO3; and (ii) the life and service of industrial structures in acid-generating mediums.
The paper aimed at investigating the effect of 4 inorganic and organic acids (HCl, HNO3, HOOCH, and CH3COOH) in 3 different concentrations on a cement type CEM I. The cement samples—pasts and mortars—were kept in water for 28 days and then in acid solutions for 270 days. Determination of strength and mass loss were carried out on cement mortars at terms of 28, 90, 180, and 270 days. The compressive strength underwent decreases, more such for the samples kept in organic acid solutions. The cement pastes underwent chemical analysis and XRD analysis at terms of 28, 90, 180, and 270 days. Significant decreases of CaO concentration with corresponding increasing of the remainder of oxides have been revealed by chemical analysis on the corrosion products. In addition, an increase in acid concentration has led to an increase in the thickness of the layer of corrosion products.
Assesing the mill effectiveness in terms of energy
Effectiveness indices for open- and closed-circuit tube mills are presented together with process calculation relations that can be used both in optimising the operational factors in existing grinding plants and in designing new grinding plants.
Some consideration regarding Cr and Mo immobilization in hydraulic matrix
The paper presents experimental results regarding hardening properties of pastes and leaching properties of hydraulic matrix with Cr(III) and Mo (VI) soluble salts admixture and of the solidification/stabilization (s/s) matrix of two electroplating wastes.
The s/s matrices with different water/binder ratio were studied. Binders contain Portland cement, blastfurnace slag, puzzolans and carbidic sludge.
The release of Mo, Cr, Pb, Zn and Ni as function of some influence parameters as binder and sludge type, binder/sludge ratio, pH of the leachates was studied.
Molibdenum (and less Cromium) releases at a high rate into aqueous solutions with high pH values. It seems that Mo release into basic aqueous solution may be limited of the matrix compactity.
In the paper are presented the experimental methods used to investigate the properties of s/s matrices and their leachates, in order to understand the weak capacity of Mo immobilization.
The achievement of "hardness stones scale" and the importance for optimization of synthetic diamonds consumption in processing equipments
One of the oldest activities of craftsmen worldwide has been processing of natural rocks, for constructive or ornamental uses. During the time, the processing methods developed function by technological and scientific achievements. In the last decades, revolutionary procedures of stone processing have enabled complying with the increasing demand on the world market for ornamental facing in a short time and to high quality standards. Actually, the most used and efficient method for extraction and processing of stones is the use of the diamond equipments. They are machines and tools who include various quantities of diamond granules into a matrix with different compositions. The carried out research had two aims. The first was the achievement of a "hardness stair of stones" by establishing of one quantifiable relation between the processing behavior and stone "hardness" function by physical and mechanical properties measured by destructive and un-destructive tests. The second aim was the achieved of a new Romanian product (diamond segments with optimal synthetic diamonds consumption) for dimension stones processing.
Romanian Journal of Materials