Sintering Powder Mixtures Research Articles

Thermal and thermoelectric properties of ceramics based on zinc oxide alloyed with iron

In this work, we study the effect of adding iron oxides FeO and Fe2O3 in a ratio of 1 : 9 on the thermal and thermoelectric characteristics of ceramics based on zinc oxide ZnO. The samples themselves were made in two stages based on the ceramic technology of sintering powder mixtures in an open atmosphere. Thermal conductivity studies point to the dominant contribution of lattice thermal conductivity at room temperature. The decrease in thermal conductivity as a result of alloying is due to an increase in phonon scattering at point defects introduced into the ZnO lattice (due to the replacement of zinc ions by iron ions) and at grain boundaries (due to microstructure refinement), as well as an increase in porosity (a decrease in density) and the formation of particles of an additional ZnFe2O4 ferrite phase. Alloying wit iron and the accompanying change in the structure of ceramics (decrease in grain size, increase in porosity, precipitation of the ferrite phase) leads to an increase in the thermoelectric figure of merit ZT by 2 times (due to a decrease in electricalresistivity and thermal conductivity with a relatively small decrease in the thermoelectric coefficient). The results obtained can be used to fabricate ZnO-based ceramics with optimal thermoelectric characteristics.

Study of the Nanocomposite Mo2C(1-x)-TiC(x)-SWCNTs by Field Actived Sparck Plasma Sintering Process

Nanocomposites are worn resistant materials used in cutting tool applications. The materials are composed of ultrafine powder hard phase grains surrounded by a tough binder phase carbon nanotubes (Mo2C)1-x–(TiC)x (2≤x≤4)//1Wt% SWCNTs. Composite bicarbide Mo2C-TiC was rapidly synthesised and simultaneously consolidated by field activated sintering technique (spark plasma sintering) at which the extensive volume expansion occurred as a function of the volumic fraction from 20 to 40 vol.% of TiC powders and 1 Wt.% of SWCNTs was reinforcement of the NCMC’s. The sintered powder mixture was examined by XRD patterns, the morphology of the obtained phase was observed by SEM and the phase compositions in different regions were analyzed by EDX. The composites were processed using Field Activated Sintering Technique, spark plasma sintering (SPS) at temperatures in the range of 1700-1800°C with addicting of SWCNTs. The effects of SWCNTs addition on phases morphology, microstructure hardness and fracture toughness of the nanocomposite were investigated. The best product contained 1.0 Wt% SWCNTs from (Mo2C)1-x–(TiC)x , x= 0.2 which was sintered at 1700°C, 70 MPa for 10 min, M0.8T0.2/ 1 Wt% SWCNTs exhibit a better density, highest hardness and good ductility. Relative densification was achieved 99.5 % from the theoretical and good mechanical properties like hardness and fracture toughness (KIC=5.6 Mpa m1/2) are improved. The results were confirmed using Raman scattering resonant spectroscopy.

The Influence of Activating Co and Ni Additions on the Mechanisms of Reaction and Diffusion Interaction During Sintering of PV-N55Т45 TiNi-Based Powders

An investigation of the influence of reaction- and diffusion-induced interactions in the system of PV-N55Т45 TiNi-based powders and activating Co and Ni additions during sintering on special characteristics of microstructure and structural-phase compositions of porous TiNi-based alloys are investigated aimed at designing porous-monolithic structures. Using the method of liquid-phase sintering of TiNi-based powder, porous specimens with activating Co and Ni additions are manufactured with the concentrations of the latter being 0.5, 1.0, 1.5 and 2.0 at.%. It is found out that the activating action of Co is more moderate compared to that of Ni. A calculation of the heat released in the course of the chemical reaction as a result of introduction of activating additions demonstrates that the values of –∆H for manufacturing porous alloys with additions of Co and Ni are 28 and 52 kJ/mol, respectively. It is established that all specimens under study contain the following phases: austenitic B2, martensitic B19′, Ti2Ni, 2(О, N, С) and Ti3Ni4. Moreover, in the material with additions of Ni a TiNi3 phase is observed. Due to an introduction of a monolithic plate into the sintered powder mixture it is possible to compensate for the heat sink at the concentration of the activating Co addition 1.5 at.%. This allows manufacturing porous-monolithic structures based on the TiNi alloy with a high quality of fusion between the porous and monolithic parts.

Preparation of Mullite–TiC–TiN Materials by a Spark Plasma Method with High Compaction Loading and Their Properties

The phase composition of synthesized TiC and TiN materials and also the properties of mullite–TiC–TiN specimens with a different ratio of TiC and TiN, sintered by a spark plasma method in the range 1200 – 1600°C with a compaction load of 75 MPa are studied. Specimens with a different ratio of TiC and TiN are characterized by intense mullitization in the range from 1200 to 1600°C. an increase in TiC concentration, and correspondingly a reduction in TiN concentration in sintered powder mixtures facilitates formation at 1500°C of a densely sintered crystallized structure consisting of numerous mullite crystals, TiC and partly TiN, formed from melts. In the range 1400 – 1600°C the relative density and linear shrinkage of specimens gradually increases with a reduction in open porosity, but specimen elasticity modulus, Vickers hardness, and ultimate strength in compression increase.

Sintering temperature-microstructure-property relationships of alumina matrix composites with silicon carbide and silica additives

AbstractAlumina-based composites were fabricated by reaction sintering from two different sintering powder mixtures: alumina with silica (SiO2) and alumina with silicon carbide (SiC; to allow oxidation to form SiO2). After sintering, SiO2 underwent complete reaction to form alumina/mullite composites. In terms of microstructure, the density and grain size of ceramic samples were investigated. The density of the composites prepared by alumina and SiC was lower than those of alumina and the composites prepared by alumina and SiO2. The grain size increased as the sintering temperature increased. In terms of mechanical properties, fracture surfaces, hardness, and fracture toughness were investigated. It was found that the fracture surface of alumina was rather intergranular, whereas the fracture surface of the composites was more transgranular. The hardness of the composites was higher than that of alumina at the same sintering temperature. However, the fracture toughness of the composites was not significantly different compared to that of alumina.

Effect of Single Walled Carbon Nanotubes (SWCNTs) Addition during Field Activated Sparck Plasma Sinter (FASPS) in the Ceramics Matrix Nanocomposites (Mo<sub>2</sub>C)<sub>1-x</sub>(TiC) <sub>x</sub> (2≤x≤4): Physical, Mechanical Properties and Sintering B

Nanocomposites are wear resistant materials used in cutting toAbstract Nanocomposites are wear resistant materials used in cutting tool applications. The materials are composed of ultrafine powder hard phase grains surrounded by a tough binder phase carbon nanotubes (Mo2C)1-x(TiC)x (2≤x≤4)//1Wt% SWCNTs. Composite bicarbide Mo2C-TiC was rapidly synthesised and simultaneously consolidated by Field activated sintering technique (spark plasma sintering) at which the extensive volume expansion occurred as a function of the volumic fraction from 20 to 40 vol.% of TiC powders and 1 Wt.% of SWCNTs as reinforcement of the CMNC’s. The sintered powder mixture was examined by XRD patterns, the morphology of the obtained phase was observed by SEM and the phase compositions in different regions were analyzed by EDX. The composites were processed using Field Activated Sintering Technique, spark plasma sintering (SPS) at temperatures in the range of 1700-1800&#8451 with addicting of SWCNTs. The effects of SWCNTs addition on phases morphology, microstructure hardness and fracture toughness of the nanocomposite were investigated. The best product contained 1.0 Wt.% SWCNTs from (Mo2</subC) 1-x</sub(TiC)x</sub, x= 0.2 which was sintered at 1700 &#8451, 70 MPa for 10 min, M0.8T0.2/ 1 Wt% SWCNTs exhibit a better density, highest hardness and a good ductility. Relative densification was achieved 99.5 % from the theoretical and a good mechanical properties like hardness and fracture toughness (KIC =5.6 Mpa m1/2) are enhanced. The results were confirmed using Raman spectroscopy.ol applications. The materials are composed of ultrafine powder hard phase grains surrounded by a tough binder phase carbon nanotubes (Mo2C)1_x–(TiC)x (2≤x≤4)//1Wt% SWCNTs. Composite bicarbide Mo2C-TiC was rapidly synthesised and simultaneously consolidated by Field activated sintering technique (spark plasma sintering) at which the extensive volume expansion occurred as a function of the volumic fraction from 20 to 40 vol.% of TiC powders and 1 Wt% of SWCNTs as reinforcement of the NCMC's. The sintered powder mixture was examined by XRD patterns, the morphology of the obtained phase was observed by SEM and the phase compositions in different regions were analyzed by EDX. The composites were processed using Field Activated Sintering Technique, spark plasma sintering (SPS) at temperatures in the range of 1700-1800℃ with addicting of SWCNTs. The effects of SWCNTs addition on phases morphology, microstructure hardness and fracture toughness of the nanocomposite were investigated. The best product contained 1.0 Wt% SWCNTs from (Mo2C)1_x–(TiC)x, x= 0.2 which was sintered at 1700 ℃ , 70 MPa for 10 min, M0.8T0.2/ 1 Wt% SWCNTs exhibit a better density, highest hardness and a good ductility. Relative densification was achieved 99.5 % from the theoretical and a good mechanical properties like hardness and fracture toughness (KIC=5.6 Mpa m1/2) are enhanced. The results were confirmed using Raman spectroscopy.

Formation of Intermetallic Structures by Spark Plasma Sintering of Titanium and Aluminum Powders

Sintered compacts fabricated by spark plasma sintering (SPS) at 1050оС were investigated. Titanium and aluminum powders in a ratio of 25 % (at.) and 75 % (at.) respectively were chosen as starting materials. Powder mixture heating up to elevated temperatures led to a partial loss of an aluminum component and to the formation of a multiphase structure consisting of Al3Ti, Al2Ti, AlTi and AlTi3. The density of sintered powder mixtures was 3.7 g/cm3; an average microhardness value was about 470 HV.

Effects of processing parameters on properties of selective laser melting Mg–9%Al powder mixture

In the present study, selective laser melting (SLM) was used to sinter a powder mixture of Mg–9%Al. Both densification mechanism and microstructure evolution of laser sintered powder mixture were established. The effect of laser processing parameter on Mg–9%Al powder using SLM was also investigated. It can be found that a maximum relative density was 82% with preferable process parameters of v = 0.02 m/s, P = 15 W. An overlapped structure can be obtained when decreasing the laser energy density due to an incomplete melt. On the other hand, a severe particulate agglomeration appeared as the increase of the laser energy due to a balling effect. A critical scanning speed of 0.02 m/s can ensure that the particulates were well melted and not evaporated during the experiment. Moreover, the Mg and Al elements were dispersed uniformly in the samples. The microstructure and composition phase were studied through scanning electron microscopy (SEM) and X-ray elemental mapping (XRD) respectively.

Reaction sintering fabrication of (AlN, TiN)–Al2O3 composite

Abstract The (AlN, TiN)–Al2O3 composites were fabricated by reaction sintering powder mixtures containing 10–30 wt.% (Al, Ti)–Al2O3 at 1420–1520°C in nitrogen. It was found that the densification and mechanical properties of the sintered composites depended strongly on the Al, Ti contents of the starting powder and hot pressing parameters. Reaction sintering 20 wt.% (Al, Ti)–Al2O3 powder in nitrogen in 1520°C for 30 min yields (AlN, TiN)–Al2O3 composites with the best mechanical properties, with a hardness HRA of 94.1, bending strength of 687 MPa, and fracture toughness of 6.5 MPa m1/2. Microstructure analysis indicated that TiN is present as well dispersed particulates within a matrix of Al2O3. The AlN identified by XRD was not directly observed, but probably resides at the Al2O3 grain boundary. The fracture mode of these composites was observed to be transgranular.

Reactions between Calcium- and Strontium-Substituted Lanthanum Cobaltite Ceramic Membranes and Calcium Silicate Sealing Materials

The reaction between Ca- and Sr-substituted LaCoO3 and CaSiO3/Ca2SiO4 has been studied by electron microscopy (SEM and TEM) and X-ray diffraction. The aim was to investigate the chemical stability of these materials as a model system for, respectively, a membrane and a sealing material in dense oxygen-permeable membrane systems. Sintered powder mixtures of the two materials were analyzed to gain information about coexistent phases in the CaO/SrO−La2O3-CoO−SiO2 system. The estimated phase composition along the CaSiO3-LaCoO3 line has been worked out. The chemical aspects of glass−ceramic sealing of dense perovskite membranes were studied by making diffusion couples. LaCoO3 was found to be kinetically more stable to calcium silicate than Ca- and Sr-substituted LaCoO3. The results also revealed that Ca2SiO4 is a more suitable sealing material than CaSiO3, due to lower reactivity. Thus, the stability of the membrane/sealant interface was observed to be quite sensitive to the O:Si ratio of the calcium silicate: 3 < O:Si < 4 will give rise to good sealing properties and moderate reactivity to the membrane material. A suitable material is a two-phase material with O:Si close to four, e.g. an orthosilicate glass−ceramic material with small amounts of metasilicate or disilicate glass.

Averaged expression for the bulk-density vector of the capillary force in a sintered powder mixture

An expression for the surface force in a medium with developed boundary surface that is convenient for practice is obtained by an additional space averaging of the known expression for the bulk density of this force in the form of surface-energy doubled density tensor divergence.

Phase components of the sintered Mg– x wt% LaNi 5 ( x=20–50) composites and their hydrogenation properties

Mg– x wt% LaNi 5 ( x=20–50) composite materials were prepared by sintering powder mixtures of magnesium and LaNi 5 at 973 K for 1 h. The microstructures were studied using optical microscopy, X-ray diffraction and scanning electron microscopy. After sintering, the samples with x=20 and 30 consisted of Mg, Mg 2Ni and LaMg 12. As x increased to 40, the La 2Mg 17 phase started to form. With further increase in x to 50, Mg and LaMg 12 vanished, and Mg 2Ni and La 2Mg 17 were the major phases. The phase abundance as a function of composition was determined by Rietveld analysis. It is also found that LaMg 12 is not a well-defined stoichiometric compound but exists within a composition range. Compared with pure magnesium, all samples were more easily activated under hydrogen pressure of 5 MPa at 623 K. From the viewpoint of pressure–composition isotherms ( P– C isotherms) of hydrogenation, the sintered Mg– x wt% LaNi 5 ( x=20–50) composites work as a mixture of pure magnesium and Mg 2Ni.

Mechanical Properties of Spinel/Mica Composites.

Mechanical properties of dense spinel/mica composites were investigated. The composites were fabricated by sintering powder mixtures containing spinel as a matrix and 5, 10 and 20mass% Fph-glass or Tm-glass. Fph-glass has the composition of fluorophlogopite. Tm-glass has the composition of tetrasilicic mica enriched in K2O and SiO2 components. The microstructures of the composites obtained by sintering powder mixtures containing 5, 10 and 20% Tm-glass (Tm-composites: Tm-5, Tm-10 and Tm-20) were fine and the intergranular phase among the spinel grains consisted of mica crystallites embedded in glass. The microstructures of the sintered composites obtained by sintering powder mixtures containing 5, 10 and 20% Fph-glass (Fph-composites: Fph-5, Fph-10 and Fph-20) were coarser and the intergranular phase among the spinel grains was crystalline. Strength values were in the range of 293-199MPa. In Fph-5 and Tm-5, crack propagation occurred in a brittle fashion through the spinel-spinel grain boundaries. High strength values were obtained only because Fph-5 and Tm-5 composites had smaller critical defect size. In Tm-10 and Tm-20, cracks also propagated mainly in the intergranular glassy region and brittle fracture occurred. In Fph-10 and Fph-20, deviation and branching of the cracks occurred along large-grown mica and spinel grains and led to toughening of the composites. Furthermore, the results of Hertz indentation tests showed that in Fph-10 and Fph-20, quasi-plastic deformation occurred and the post-indentation strength values of these specimens were higher than those of Tm-composites, which showed cone-like cracking.

Various Types of Bubble-Containing Silica Glasses Fabricated by Sintering Powder Mixtures of Silica with Silicon Nitride.

Bubble-containing silica glasses were fabricated by sintering amorphous silica powders with small amount of silicon nitride powders. Sintering was performed at 1800°C in N2 gas atmosphere. It was found that the addition of Si3N4 is effective for forming bubbles. By controlling the Si3N4 content, various types of bubble-containing silica glasses, such as the so-called the opaque silica glass and the foamed silica glass, could be obtained. Addition of 0.004mol% Si3N4 produced highly opaque silica glasses containing a large number of small bubbles, while 0.431mol% Si3N4 resulted in low-density foamed silica glasses containing large 1mm-sized bubbles. Wide variations of bubble size and density were observed on these glasses. Thermal conductivities were estimated and compared with several literature values. The relation between thermal conductivity and bubble density was discussed based on a model simulation.

Microstructural and microchemical characterization of the interface between La 0.85Sr 0.15MnO 3 and Y 2O 3-stabilized ZrO 2

La 0.85Sr 0.15MnO 3 and Y 2O 3-stabilized ZrO 2 may be used as cathode and electrolyte materials, respectively, in solid oxide fuel cells. One of the requirements of the cathode-electrolyte interface is that high impedance phases are not formed at the interface during manufacture or operation of the SOFC. The interfaces of interest were prepared as a diffusion couple and by sintered powder mixtures of La 0.85Sr 0.15MnO 3 and Y 2O 3-stabilized ZrO 2. The structures at the interfaces were examined by transmission electron microscopy. Chemical analyses were made by energy dispersive X-ray spectroscopy. A Zr, La-based pyrochlore-type crystalline phase has been observed at some of the interfaces between La 0.85Sr 0.15MnO 3 and Y 2O 3-stabilized ZrO 2. In the present paper, changes in element ratios are used to obtain knowledge on how the elements diffuse with respect to each other at the interface. It was found that the formation of pyrochlore depends on the content of Mn in the La 0.85Sr 0.15MnO 3 and on the ratio between La 0.85Sr 0.15MnO 3 and Y 2O 3-stabilized ZrO 2.

Studies on phase distribution in (O′ + β′)-sialon composites

By pressureless sintering powder mixtures of silicon nitride, silica and alumina, using Y 2 O 3 as a densifying additive, O′-sialon (O′) formation begins at about 1400°C and increases with increasing temperature up to 1600°C. β-Sialon (β′) formation then increases rapidly at the expense of unreacted α-Si 3 N 4 and O′. The ratio of O ′ β′ at higher temperatures (above 1700°C) depends on the aluminium concentration. The more alumina which is present in the starting materials, the less O′ remains in (O′ + β′)-ceramics. The stability of O′ in composite (O′ + β′)-sialon has been studied, and the results show that the reduction of O′at temperatures above 1700°C may be attributed to the formation of a liquid phase which dissolves O′ and produces β′ while cooling down. The stability of synthesized Si 2 N 2 O with and without Al 2 O 3 has also been determined and the results indicate that Si 2 N 2 O and O′ decompose significantly into Si 3 N 4 and β′ respectively only at temperatures above 1800°C. Pulvermischungen von Siliziumnitrid, Silika und Aluminiumoxid mit Y 2 O 3 als Sinterhilfsmittel wurden drucklos gesintert. Dabei wird ab c. 1400°C O′-Sialon gebildet. Ab dieser Temperatur steigt die β-Sialonbildung schnell auf Kosten von noch nicht abreagiertem α-Si 3 N 4 und O′ an. Das Verhältnis O ′ β′ bei Temperaturen oberhalb 1700°C hängt von der Al 2 O 3 -Konzentration ab. Je mehr Al 2 O 3 im Ausgangspulver vorhanden ist, desto weniger O′ verbleibt in (O′ + β′)-Keramiken. Die Stabilität von O′ in O′ + β′-Sialon-Komposites wurde untersucht und die Ergebnisse zeigen, daß die Reduktion von O′ bei Temperaturen oberhalb 1700°C auf die Bildung einer Flüssigphase zurückzuführen ist, die O′ löst und beim abkühlen β′ bildet. Die Stabilität von syntetisiertem Si 2 N 4 O mit und ohne Al 2 O 3 wurde ebenfalls bestimmt und die Ergebnisse zeigen, daß Si 2 N 2 O und O′ sich nur oberhalb von 1800°C deutlich in Si 3 N 4 und β′ zersetzen. Lors du frittage naturel à l'aide d'Y 2 O 3 de mélanges de poudres de nitrure de silicium, de silice et d'alumine, la formation du sialon O′ commence vers 1400°C et se poursuit lors du chauffage jusqu'à 1600°C. Dès lors, il se forme rapidement du sialon β′ à partir du Si 3 N 4 α en excès et de la phase O′. Le taux O ′ β′ à haute température (supérieure à 1700°C) dépend de la concentration en aluminium: plus il y a d'aluminium présent au départ et moins il reste de phase O′ dans les céramiques (O′ + β′). La stabilité du O′ dans le sialon composite (O′ + β′) a été étudiée, et les résultats montrent que la réduction de O′ à des températures supérieus à 1700°C peut être attribuée à la formation d'une phase liquide qui dissout le O′ et produit le β′ au refroidissement. La stabilité du Si 2 N 2 O synthétisé avec et sans Al 2 O 3 a également été déterminée et les résultats montrent que la décomposition de Si 2 N 2 O et O′ respectivement en Si 3 N 4 et β′ ne devient significative qu'à des températures supérieures à 1800°C.

Choice of the optimum thickness of heat insulation in the hot compaction of porous materials

Calculations are made of the thickness of the heat-protective shell of a system for sintering powder mixtures which will ensure a quasiuniform temperature distribution over a given period of time.

Some techniques for obtaining iron-manganese cermet compounds

1. Some methods for obtaining carbon-free iron-manganese alloys were described. 2. The iron-manganese alloys obtained by sintering powder mixtures contain oxides which cannot be reduced by sintering in a very dry hydrogen atmosphere. 3. It is shown that the method of thermodiffusion infiltration produces porous iron-manganese alloys containing no oxides; these powders can be used for producing poreless compounds. 4. The relationship has been established between the degree of infiltration of iron pressings and iron powder by manganese and the process temperature, porosity, time, and the thickness of the powder layer.