CONTENTS no. 4/2004                                                                                        Romanian Journal of Materials


ION TEOREANU, PAULA CARLAN, ION CHICINAS Al2O3Cermets 

JRG TPFER, JULIA MRBE, STEFAN BARTH, EDDA MLLER, FRANZ BECHTOLD

Ni-Cu-Zn ferrites for multilayer inductors 

ALEXANDRU ORBAN, MARIA TUROS, LIVIU LITERAT

Considerations regarding the axial pressing moulding method for grinding parts

HORATIU NICIU, BOGDAN GRIGORAS, DANIELA NICIU, NICOLETA STOIAN, VIRGINIA MADUTA  

The use of synthetic special quartz glasses in the spectrophotometer cells manufacturing
ION TEOREANU, ADRIANA MOANTA Effects of intergrinding surface - active additives on the grinding and hardening performance of composite cements with low ratios of Portland cement 
DOREL RADU, CORINA IBRIS Uniformity degree - a generalised statistical indicator for estimating the dispersion of polygranular mixtures 
MARIA GHORGHE, SILVIANA MARICA Environment management in mineral resources exploitation from ceramic building industry  
ENIKO FAZACAS, MARCELA MUNTEAN, JOSEF FAZACAS Terra-cotta stoves  

Al2O3Cermets

Following conventional pressing-sintering procedures, there were prepared compositions of the cermet type Al2O3-Cr with maximum 30vol % metal content. There were used, as basic materials, chrome-metal powder obtained by the electrolytic method and alumina powder obtained by the gel precipitation method. There were also prepared cermet samples of  type Al2O3-Cr with metallic admixtures of the type Ni, Mo, W. The resulted samples were analyzed from the point of view of the morphological, physical and mechanical properties hardness, bending strength and fracture toughness. The bending strength is up to 490 MPa and the fracture toughness up to 4.40 Pa.m0.5. The SEM analysis indicates an intra and inter-grain breaking, both for the ceramic component and for the metallic component. The other properties studied show, function of the cermet content, values adequate to the performing structural materials.

 

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Ni-Cu-Zn ferrites for multilayer inductors

Ni-Cu-Zn ferrites are soft magnetic materials for multilayer inductors with a low sintering temperature of 900C and good performance at intermediate frequencies. Multilayer devices are  produced by co-firing ferrite layers with internal Ag conductors.

Sub-micron ferrite powders and sintering additives are required to obtain a microstructure with maximum permeability. Ferrite tapes prepared by tape casting were screen printed with Au or Ag conductors, laminated and sintered. The LTCC process for the fabrication of multilayer inductors is outlined. Different types of multilayer inductors have been prepared and the inductance varies between 2 H to 2 mH.

Correlations between the ferrite permeability and the inductor design are  discussed.

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Considerations regarding the axial pressing moulding method for grinding parts

         This study is focusing on the behavior of a super aluminous ceramic powder (specially destined for shaping by axial pressing) in the process of compaction under the action of the axial pressing forces. We were interested to establishing relations between the action force, porosity and density of the green body,  and also the sintering shrinkage.

         For the experiment we used cylindrical moulds which had different surfaces and heights of the filling room. The process of compaction was accomplished by bilateral axial pressing.

         The evolution with pressure of the compaction, porosity and deformation of the granules and of the green body of pressing, as well as the sintering shrinkage, were observed on samples of powder which had an already established composition, morphology and granulometry.

         From the data of the experiment we established (graphically and analytically) pressing functions and also correlations between the pressure and the physical and mechanical parameters that have already been mentioned.

         The mathematic molding suggest some information on the phenomenology of the process of compaction (rheology, deformation and fragmentation of the granules) as well as some data regarding the most propitious domain for the pressing forces and for the conditions at sintering.

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The use of synthetic special quartz glasses in the spectrophotometer cells manufacturing

This paper presents experimental works made  for quartz synthesis optical glass used at a production with a high value by example the spectrophotometry cells. Synthesis quartz glass made by gaseous faze hydrolysis of silica halogenated compounds in flame, has a superior transmission by comparing with common optical glasses in the UV-VIS range and this is the reasons why its recommended for UV -VIS spectrophotometry applications. The characteristics of the quartz glass corresponds to the cells high quality parameters, for spectrophotometry, assuring a characterization domain in a larger UV range and a better resistance at the chemical attack. The basis technological parameters of the obtaining process for the UV-VIS spectrophotometry cells made of synthesis optical quartz glass are presented.

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Effects of intergrinding surface - active additives on the grinding and hardening performance of composite cements with low ratios of Portland cement

Investigations were carried out to explore the effect of intergrinding surface-active additives (ISAAs) on the specific power consumption and the physical and mechanical properties of ordinary Portland cement (OPC) and Portland composite cements (PCCs) with high ratios of blast furnace slag (GBFS). Cements ground without ISAAs were taken as reference cements (RCs). As intergrinding surface-active additive the experiments involved triethanolamine (TEA) in three distinct ratios (0.01%, 0.03% and 0.05%) related to the weight of the cement to grind. All cements were ground up to a specific surface area of about 4500 cm2/g. Grinding GBFS and PCCs each without ISAAs was found to involve much less specific power consumption than grinding OPC. The effect of ISAAs on the specific power consumption at grinding was notably higher for OPC than for PCCs. In all of the cases, the 0.03% ratio of ISAAs was optimal with respect to the specific power consumption at grinding. In addition, PCCs interground with TEA were found to feature strength increases at hardening over the corresponding RCs at all curing terms.

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Uniformity degree - a generalised statistical indicator for estimating the dispersion of polygranular mixtures

One of the most important characteristics of polygranular mixtures is the particle distribution on various distributrion classes. That is the reason for establishing along the time of analytical expressions for describing from mathematical point of view of various types of granulometric distribution. On tha basis of statistical anal;ysis of a large number of experimental data or from theoretical considerations (rarely) have ben developed expressions representing distribution laws [1-5]. These laws may be used for characterising granulometric distribution of polygranular mixtures from oxide materials area in general or from the cement technology in particular (Annex 1).

In powder technology, dimensional characterization of polygranular mixtures can be made on the basis of granulometric distribution data (discrete or continue) and it consist in calculating different diameters and specific surface.

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Environment management in mineral resources exploitation from ceramic building industry

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Terra-cotta stoves

For immemorial years the heat and the fire fascinated the men. The fire was the main ways of survive, even in the oldest time. The fire transforms the chemical energy of the wood in the thermal energy, which assures the necessary heating.  The glassed tile stove (terra-cotta stove) as heating way was used, even in exclusivity, in Nord and East of Europe the fire place, which today are frequently in many new buildings are Mediterranean provenience.

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Romanian Journal of Materials