ION TEOREANU, PAULA CARLAN, ION CHICINAS
|Influence of chrome powder obtaining processes on the defining properties of Al2O3-Cr cermets|
MARIA PREDA, ALINA MELINESCU, ION TEOREANU, ROXANA TRUSCA, GHEORGHE COTIGA
|Alternating routes for hydroxyapatite synthesis|
ROBERT IANOS, IOAN LAZAU, CORNELIA PACURARIU
|The synthesis of various oxides using the combustion method. Study of the reactivity of different metal nitrates-fuels mixtures|
MARIA IOAN, LILIANA RADU, CONSTANTA MANDOIU
|A rapid method for assessing the standard strength of cement|
PETRU BALTA, MIHAI DINULESCU
|Silicate melts nanostructure influence on viscosity|
|NELU SPIRATOS, CARMEL JOLICOEUR||Concrete chemical admixtures: perspective and challenges|
|VALENTINA CETEAN||New applied knowledge, eco-innovation and intelligent manufacturing in natural stone processing|
Influence of chrome powder obtaining processes on the defining properties of Al2O3-Cr cermets
Defining proprieties of Al2O3-Cr cermets were comparatively examined in the compositional field in which the ceramic component is preponderant. The chrome powder was obtained by two different chemical ways. In preparing the cermets, there were used, as the case required, besides their main components, metallic Ni, Mo, and W admixtures, obtained by oxide reduction. The research works carried out took into consideration the determining and comprehensive correlations between composition-processing-structure-proprieties. With this end in view, relevant physico-mechanical proprieties of the cermets under study were examined, namely, density, hardness, bending strength, toughness.
Alternating routes for hydroxyapatite synthesis
In this research two routes of stoichiometric hydroxyapatite (HAp) synthesis were examined the first by thermal treatment in hydrothermal conditions and the second by microwave heating. For the hydrothermal method at 140°C and a plateau of 4 hours, a mixture of Ca(OH)2 and H3PO4 was used. In this case by X-ray diffraction and FTIR spectroscopy, calcite specific peaks were identified beside hydroxyapatite that shows an incomplete reaction. By microwave heating two types of samples were synthesised as a function of raw materials used. One sample was synthesised from CaSO4.2H2O, Ca(OH)2 and (NH4)2HPO4 and other from Ca(NO3)2, Ca(OH)2 and (NH4)2HPO4. In the first case three hours of thermal treatment were required to obtain pure hydroxyapatite. In the second case when Ca(NO3)2.4H2O was used the reaction was fulfilled after only one hour. By scanning electron microscopy (SEM), it was found that in all cases grain agglomerates were obtained. These are irregular for hydrothermal synthesis and for the synthesis by microwave heating starting from calcium nitrate. The agglomerates present prismatic shape when CaSO4.2H2O was used as main raw materials.
The synthesis of various oxides using the combustion method. Study of the reactivity of different metal nitrates-fuels mixtures
The paper deals with a systematic and in the same time original approach of some great importance problems, concerning the synthesis of high reactivity powders using the combustion method, ensuring the prerequisites for the rational elaboration of the recipes in order to obtain the desired compound. In order to justify the more or less different behavior of some metal nitrates in respect to various fuels, within the paper there has been studied the interaction between a great number of metal nitrates M(NO3)x (Mx+ = Na+, K+, Mg2+, Ca2+, Sr2+, Al3+, Cr3+, Fe3+, Co2+) and a variety of fuels, frequently used in the combustion synthesis method: urea, glycine and β-alanine. Moreover, there has also been studied the heating interaction between the three fuels and HNO3. The experimental results suggest that, on one hand, there is a predilection of metal nitrates in respect to certain fuels, and on the other hand, the formation of some complex combinations between the metal cation and the used fuel does not represent the decisive element in the initiation and the subsequent development of the combustion reactions.
A rapid method for assessing the standard strength of cement
Investigations carried out in the testing laboratory at CEPROCIM SA have led to devising an experimental model designed to quantify the thermal amount released during early hydration of cement up to reaching the maximum temperature in relation to the strength of the respective cement. The paper presents the results obtained using this experimental model within the testing laboratory in Fieni Cement plant, CARPATCEMENT HOLDING SA for cement CEM I from current cement production. Application of the correspondence relation y = f(x), where y is the 28-day compressive strength and x is the early heat of hydration (QhM), has led to a rapid assessment of the cement standard strength with a precision of ±2.5 MPa.
Silicate melts nanostructure influence on viscosity
Estimating by calculus the nature and the amount of the nano aggregates that are forming in simple silicate melts as a result of the chemical structural equilibrium established during the melting time the deduction of a new equation for viscosity calculation was possible, considering the mean weight molecular mass and temperature. For a constant temperature, the viscosity logarithm is direct proportional to the logarithm of the mean weight molecular mass, the respective straight lines having decreasing slopes at the temperature increase and inflexions at certain dimensions of the structural aggregates. These peculiarities are interpreted in relation with the nature and dimensions of the flow units, which modify at the temperature increase. Thus are evidenced, in this way too, the complexity of the temperature influence on viscosity.
Concrete chemical admixtures: perspective and challenges
The recent developments in specification of concrete performance, in cement composition and in concrete placing technologies have jointly created important new challenges for chemical admixtures. Early applications of chemical admixtures in Portland cement concrete aimed improvements in setting time, workability, strength, or frost resistance. In current concrete applications, chemical admixtures are often expected to perform a range of other functions, for example, compensate for changes resulting from variations in binder composition (blended cements), provide highly fluid, yet cohesive mixes (self-consolidating), control setting times and rate of strength development, maintain dimensional stability (shrinkage), prevent corrosion of reinforcing bar and, ultimately, contribute to increasing durability and service life of concrete infrastructure. This paper provides an overview of the application context and evolution of several important chemical admixtures and offers comments on the likely challenges facing future admixture development.
New applied knowledge, eco-innovation and intelligent manufacturing in natural stone processing
The I-STONE project – RE-ENGINEERING OF NATURAL STONE PRODUCTION CHAIN BY KNOWLEDGE BASED PROCESSES, ECO-INNOVATION AND NEW ORGANISATIONAL PARADIGMS, Contract no. 515762, is carried out within the European Research Programme FP6 between 2005 and 2009. The consortium comprises 36 companies from 24 countries and the coordinator is PEDRINI SPA AD UNICO SOCIO, Italy. Romania is represented by PROCEMA GEOLOGI Ltd – with geological research and design profile, an institute for macromolecular chemistry (“PETRU PONI” Iasi) and a SME for impregnation materials (Connex Group Ltd Iasi). The specialists from PROCEMA GEOLOGI take part in Task 5.1 workgroup of I-STONE. Within the testing programme of the behaviour of natural stone finished products, 17 rocks from the following categories were included: limestone, marbles, travertine, granites, gabbros, shale, of which three are from Romania: Ruschita marble, Geoagiu travertine and Baschioi sandstone. This represents a first stage in including some national products in the informative guidebook on stones used in construction, a long-term instrument for the unified European market.
Romanian Journal of Materials