CONTENTS no. 1/2004                                 Romanian Journal of Materials


MARIA PREDA, ALINA MELINESCU, IO TEOREANU, MARIA ZAHARESCU   Hydroxyapatite  synthesis in the microwave field  
GAVRIL KOVACS, CARMEN HUDAC, CALIN BONTA, RADU SUMALAN Porous ceramic granules with destination for hidrocultures  
PETRU BALTA, VASILICA DIMA  Biopersistence of glass fibres  
LUCICA BOROICA, ISIDOR BOROICA, EMIL ROTIU, MIHAI DINULESCU, RARES MEDIANU, DAGMAR HUELSENBERG   Glasses colored with industrial wastes  
MARIA GEORGESCU, ANASTASIA PANAIT   The influence of CaCO3 on hydration and hardening processes in C3S - H2O system   
ADRIANA MOANTA, FLORIN AMZICA   Use the ESP dust as admixture and additional constituent in cement grinding
ANA - MARIA DRAGOMIR, ANAMARIA HAROSA, RAMONA HOTNOG Sustainable development under the use of alternative fuels in the cement industry  
TRAIAN IOVU, ANA-MARIA DRAGOMIR, ANDREEA IONESCU   CO2 emissions in the cement industry and measures to abate
ZENO GHIZDAVET   A stochastic model of the clinkering installation  

Hydroxyapatite  synthesis in the microwave field

The hydroxyapatite contains habitually a low proportion of calcium carbonate which helps their structure stabilisation. In the greater content this later compound transforms at sintering in calcium oxide, which could react with body fluid leadig to HAP formation.  In this work hydroxyapatite was synthesized, at the temperature of water ebullition in the microwave field, using as raw materials CaSO4.2H2O and (NH4)2HPO4. Two samples were synthesised, the first having a hydroxiapatite stoechiometric composition and the second contains 95% stoechiometric mixture of hydroxyapatite and 5% amorphous silica. Samples were mantained at this temperature from 0,5 to 4 hours, in the microwave field. The mineralogical composition of samples was determined by X-ray diffraction. At a plateau shorter than one hour an incipient stage of hydroxyapatite formation is observed. At longer soaking time, a complex mineralogical composition formed by hydroxyapatite, calcium sulphate and calcite in the different proportions was obtained. The obtained samples were also examined by thermal analyses and IR spectroscopy.

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Porous ceramic granules with destination for hidrocultures

There are presented the result of the researches and tests concerning the possibility of obtaining porous ceramic granules from clays and by-products from the sugar and wood processing industries from the Western side of Romania.  The structure of the porous ceramic grains is formed as the result of sintering of the particles of poriferous ingredients at the contact point with the argillaceous binder located around these particles and leaving void spaces between them. In the paper are presented the ecological and economic advantages in the fields of vegetable growing and hidroculture.

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Biopersistence of glass fibres

In the presented work the oxidic vitreous fibers bio-persistence problem is approached and also the manner of in vitro determination of this property. A project was elaborated for a facility for experimental bio-persistence determination taking into account the accumulated by other authors experience in this field. This facility was realized and allows the determination of the chemical interaction intensity by measuring the analyzed glass fiber diameter variation in time. The working conditions are described, allowing the obtainment of reproducible results, comparable with those obtained by means of other methods. The first results concerning the bio-persistence of some oxidic fibers are presented. The method can be used for fiber biopersistence characterization and to study fibers chemical interactions mechanism in different liquid mediums.

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Glasses colored with industrial wastes

The paper presents the results about the colored glasses obtaining by using industrial wastes. By melting at 1450C were obtained different colored glasses that can be used in glass industry. The storage of the waste in the glass matrix is possible up to 40wt%; the obtained materials having a good chemical stability. The glasses were characterized from point of view: -viscosity, hydrolytic stability, transmission and wetting angle on different materials (ceramic or metallic).

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The influence of CaCO3 on hydration and hardening processes in C3S - H2O system

The blended Portland cements containing limestone are interesting from the technical and economical point of view.

For a long time, the ground limestone was consi-dered as un inert material, like ground sand, having a filler effect in the binding systems. In the last years, a more complex effect of the ground limestone has been emphasized: through a filler effect, the fine ground limestone contributes to a densified  hardening structure and through chemical reactions with cement components and water it determines the formation of some calcium carbonate hydrates.

The present paper brings information concerning the influence of the presence of CaCO3 additions (10-40%) upon the C3S hydration and hardening for a period of 90 days.

In the presence of 10% CaCO3, the hydration rate of C3S is increased and the hydrates which are formed, determine the development of the greater mechanical strengths. Hihger proportions than 10% CaCO3 determine a favorable influence upon the early hydration and har-dening stages only. For longer periods of time, CaCO3 delays these processes. After 14-90 days, there were registered decreases of the mechanical strengths more significant for the higher proportions of CaCO3.

The additions of CaCO3 did not cause changes in the nature of the hydrates. No carbonate silicate hydrate was identified.    

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Use the ESP dust as admixture and additional constituent in cement grinding

The paper brings information regarding the possibilities to use the ESP dust by-product resulted from the cement manufacturing procces as minor addition, besides slag and tuff in cement clinker grinding, under two conditions: in a ratio of 5%, as per SR EN 197/1 2002 and in a ratio of 10%.

Investigations carried out to establish the effect of the ratio of ESP dust addition on the physical and chemical characteristics of blended cements have revealed an optimal ESP dust ratio of 5% both for slag cements and for tuff cements.

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Sustainable development under the use of alternative fuels in the cement industry

With fossil fuel reserves being short in Romania and energy issues gaining a forefront spot within economic development and environmental protection, recent years have found alternative fuel use in the cement industry to be a viable solution as far as both non-replenishing fossil fuel resource preservation and waste management are concerned.

Recently, in order to reduce production costs (of which as much as 25% goes to electric energy) cement plants in Europe are considering the utilization of alternative fuels as heat engineering replacement for fossil fuels (particularly natural gas and fuel oil).

The types of waste able to be employed as fuel in the cement industry are liquid energetic fuels: used oils, pigments, dyes, organic compounds from the drugs industry, etc.; pasty energetic fuels: slams, sludge, tars from the petroleum industry, steel industry, water treatment, etc; solid energetic fuels: used tyres, wood waste, paper waste, plastic waste, etc.; and non-energetic fuels: pyrite cinder, fly ash, slag, etc.

As far as ecology is concerned, the benefits brought about by using alternative fuels in the cement industry include: preservation of natural resources by using alternative fuels and raw materials, abatement of CO2 emissions per tonne of cement, recovery and use of the energy of alternative fuels in clinker manufacture, dimini-shing of the environmental impact (non-regulated landfill disposal, water and soil pollution, etc.) as well as quality improvement of the environment, and assurance of full disposal under conditions of safety for the environment and a fully closed product life cycle.

 

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CO2 emissions in the cement industry and measures to abate  

Cement manufacture releases significant emissions of CO2 resulting from fuel combustion and limestone decarbonation, as well as from electric power use with the process equipment. In industrialized countries in Europe, subsequently to the restricted emissions laid down in the enforced legislation, the cement industry has been motivated on a sustained basis to strive to reduce fuel and power consumption, with corresponding benefits to abating CO2 emissions.

The foremost strategies to reduce CO2 emissions aim at enhancing energy efficiency, substituting alternative fuels (waste fuel) for fossil fuels, replacing raw materials by waste, and using waste as addition in cement grinding.

The Kyoto Protocol, sanctioned in December 1997 at the UN Framework Convention on Climate Change and ratified by Romania in January 2001, imposes lining up of our cement industry to commitments regarding setting limits for and abating emissions of carbon dioxide - a gas responsible for the greenhouse effect.

The paper reveals the items in the balance of CO2 emissions as well as measures to abate CO2 emissions in a cement plant.

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A stochastic model of the clinkering installation

Clinkering installations represent systems that have not been well described, yet, by an overall, analytical mathematical model, due to the large number of parameters involved, their probabilistic features along with the given complexity of the whole plant (from the point of view of both constructive and its functionality reasons, as well). A possible investigation method used in the present paper makes use of stochastic modeling, for which, on the basis of a set of testing values the trajectory of the granular material and the consecutive changes of its states were simulated.

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Romanian Journal of Materials