Densification Of Samples Research Articles

Characterization of composites containing NiAl2O4 spinel phase from Al2O3/NiO and Al2O3/Ni systems

This paper focused on the characterization of the composites containing nickel aluminate spinel from Al2O3/NiO and Al2O3/Ni systems. The composites were prepared by die pressing of powders and subsequent sintering of green bodies in air atmosphere. Composites were characterized by XRD, SEM, EDS and DTA/TG/MS analyses. The physical properties of the composites were measured by Archimedes method. Quantitative description of the composites microstructure was made on the basis of SEM images using computer image analysis. The XRD studies and SEM observations of composites confirmed the presence of two phases Al2O3 and NiAl2O4 in the whole volume of samples from both systems. Spinel phase was evenly distributed throughout the volume of the material. Morphology of NiAl2O4 obtained from both systems was characterized by the presence of voids. The DTA/TG/MS measurements showed the characteristics of organic binder decomposition and type of gases released to the atmosphere during thermal treatment. Moreover, the DTA/TG analysis showed the temperature of spinel-phase formation for both systems. It was found that the spinel-phase NiAl2O4 formation retards the process of densification. Therefore, it can be concluded that densification of samples with spinel phase depends mainly on the volume of spinel phase in composite material and does not depend on the substrates used to prepare spinel phase. The values of the selected properties of Al2O3–Ni- and Al2O3–NiO-based materials confirmed that the physical properties depend on the type of substrates used in the fabrication of composites. The type of powder influences the open porosity of samples. For composites produced using NiO powder, open porosity is lower than for samples formed with nickel powder.

Densification behavior and electrical properties of CuO-doped Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ternary ceramics

CuO modified Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) ternary relaxor based ferroelectrics with the composition near the morphotropic phase boundary were synthesized by two-step columbite precursor method. The introduction of CuO significantly improved the sinterability of PIN–PMN–PT ceramics, resulting in the full densification of samples at lower sintering temperatures. It also profoundly modified the crystal structure and fracture mode of the ceramics. Properly increasing CuO content led to the disappearance of rhombohedral-tetragonal phase transition, remarkably improved the Curie temperature (Tc), and made the ceramics more relaxorlike. The ternary ceramics doped with 0.25wt% CuO possessed optimum piezoelectric properties (d33=584pC/N, d33*=948pC/N, and kp=0.68), high ferroelectric properties (Ec=9.9kV/cm, and Pr=33.1μC/cm2), low dielectric loss (tan δ=0.9%), and wider temperature usage range (Tc=225°C). The obtained properties are much higher than those of previously reported PIN–PMN–PT based ceramics, indicating that CuO doped PIN–PMN–PT is a promising candidate for electromechanical applications with high performance and wide temperature/electric field usage ranges.

Effects of Drying Strategies and Microfibrillated Cellulose Fiber Content on the Properties of Foam-Formed Paper

A novel methodology was used to create a highly porous foam-formed paper that is bonded with highly refined cellulose fiber. In this process, cellulose pulp suspension at various consistencies (0.5, 1.0, 1.5, and 2%) was dispersed in water, followed by foam formation under high shear forces in the presence of a surfactant. Various drying methods were used to achieve foam formation. These included freeze-drying (FD), vacuum-dewatered air-drying (VAD), and dewatered freeze-drying (VFD). Increasing the pulp's consistency and changing the drying techniques from freeze-drying to air-drying resulted in a more compact morphological structure and increased density of foam-formed paper samples. Densification of foam-formed samples was measured using a Dynamic Mechanical Analysis (DMA) machine and a sample with densification at lowest strain value was obtained by a 10 wt% addition of microfibrillated cellulose fiber (MFC). At 10 wt% MFC addition, denser foam-formed paper samples with enhanced microstructure were obtained. Air filtration efficiency and acoustic properties of foam-formed paper were also characterized and optimized by the addition of MFC.

Effect of Microwave Curing to the Compressive Strength of Fly Ash Based Geopolymer Mortar

With the advancement of technology and the economic crisis in Malaysia, has been promoting the development of infrastructure in the use of new structural materials but overall is unsatisfactory in terms of cost savings. One of the alternatives that can be used is to use fly ash as a cement replacement in manufacturing mortar. Replacement of cement with geopolymerization mortar can reduce manufacturing costs and could reduce global warming arising from the production of cement for the production of Portland cement for the release of CO2 into the atmosphere, where CO2 gas gives the largest contribution to global warming . The study will be focused on the effect of microwave curing with various durations and temperature to the mechanical and physical properties of fly ash based geopolymer mortar. For the conventional heating technique, heat is distributed in the specimen from the exterior to the interior leading to the non-uniform and long heating period to attain the required temperature. Application of microwave to the fresh concrete results in removal of water, collapse of capillary pore and densification of sample. Heat curing has been applied to construction materials especially for the precast concrete to improve the strength development process. This concrete attains sufficient strength in short curing time, so the molds can be reused, and the final products can be rapidly delivered to the site. The effect of curing temperature together with their aging days of the cured product will also be investigated. Mechanical properties of the product will be tested using compressive test, and density of the samples.

Low temperature co-fired Co2Z barium–strontium ferrite materials with BBSC glass

In this paper, we prepared Co2Z barium–strontium ferrite material (Ba1.5Sr1.5Co2Fe24O41) with BBSC (Bi2O3–B2O3–SiO2–CuO) glass by traditional solid state method. Using BBSC glass, the barium–strontium ferrite materials were successful synthesized in low temperature (920 °C). The effects of BBSC upon microstructure and magnetic properties of materials were systematically investigated. BBSC glass promoted the single phase formation of Co2Z ferrite and enhanced the densification of samples. With BBSC glass increased from 1 to 4 wt%, saturation magnetization (MS) increased gradually from 36.5 to 50.3 emu/g, coercivity (HC) decreased first and then increased, and magnetic permeability (μ′) increased first and then decreased. The materials with 3 wt% glass possessed excellent performances, including MS = 49.6 emu/g, HC = 164 Oe, μ′ = 7, and tan δμ was about 0.03.

Coupled Electro-Thermo-Mechanical Finite Element Modeling of the Spark Plasma Sintering Technique

This paper deals with the development of a novel and predictive finite element method (FEM) model coupling electrical, thermal, and mechanical time-dependent contributions for simulating the behavior of a powdery material submitted to a spark plasma sintering (SPS) treatment by using COMSOL Multiphysics® software. The original approach of this work lies in the use of the modified Cam-Clay model to solve the mechanical phenomenon occurring during a SPS sintering treatment. As the powder properties and behaviors are different from the final sintered material and display a nonlinear dependence as a function of temperature and pressure, the model includes the description of the sample densification. In this way, numerical and experimental results obtained on conductive model material (aluminum) such as temperature, stress distributions, and shrinkage, were directly compared. This FEM model demonstrated the ability to predict the powder behavior during temperature-controlled experiments precisely, as they are typically performed in the SPS technique. This approach exhibits a remarkable level of interest because it takes into account the nature of the material and also the specific characteristics of the powder studied.

Microstructure and magnetic properties of low-temperature-fired NiCuZn ferrites with SiO2–CaO–Na2O–K2O glass

The low-temperature-fired NiCuZn ferrites with SiO2–CaO–Na2O–K2O (SCNK) glass additives are prepared by the conventional solid-state reaction method. The effects of SCNK glass additives on sintering behavior, microstructures and magnetic properties of NiCuZn ferrites are also investigated. Results show that SCNK glass additives overtly improve the densification of samples through the formation of liquid phase and grains growth promotion. The appropriate SCNK glass additives not only can noticeably increase the initial permeability (μi) and saturation flux density (Bs), but also can obviously reduce the remanent flux density (Br) and coercive filed strength (Hc). However, too much glass additives will deteriorate the magnetic properties. In summary, 0.2 wt% SCNK glass added in NiCuZn ferrite shows excellent magnetic properties: μi = 648.18 (100 kHz), Bs = 166.21 mT, Br = 83.57 mT and Hc = 39.38 A m−1.

Influence of nano-sized La2O3 addition on the sintering behavior and mechanical properties of WC–La2O3 composites

This work explores the addition effect of nano-sized La2O3 powder (0–7wt%) on the sintering behavior, microstructure and mechanical properties of WC–La2O3 composites prepared by spark plasma sintering at 1600°C under a uniaxial pressure of 50MPa. The results indicated that when the content of La2O3 increased from 0 to 7wt%, both the onset and termination temperatures for sample densification were delayed. The onset temperature increased from 850 to 975°C and the termination temperature raised from 1400 to 1600°C, respectively. The relative density of the samples raised from 96% (for pure WC) to 97.5% (for the composites with 3–7wt% La2O3). The added La2O3 could suppress the growth of WC grains and inhibit the formation of triangle prism shaped WC grains. However, with more La2O3 (more than 5wt% in this work), the agglomeration of La2O3 became serious. With the increase in La2O3 content, the Vickers hardness and flexural strength of the samples initially increased and then decreased, reaching the maximum of 2100 HV10 with 3wt% La2O3 and 1300MPa with 1wt% La2O3, respectively. However, the Palmqvist indentation fracture toughness gradually decreased from 7.5 to 5.5MPam1/2 when the content of La2O3 increased from 0 to 7wt%.

Pressureless Sintering of ZrB<sub>2</sub> with β-SiC Addition

Zirconium diboride (ZrB2) is a covalent compound that leads the category of ultra high temperature ceramics materials owing to its unique properties. In this work, the effect of addition of beta-silicon carbide (β-SiC) in pressureless sintering of ZrB2 was investigated. Four compositions were prepared with 0, 10, 20 e 30 vol% of SiC. ZrB2 powder and mixtures were prepared in by planetary milling with SiC spheres at 4 h. Two sintering temperatures were used, one at 2050 oC/1h and other at 2150 °C/1h. The addition of SiC has promoted an increasing in densification with the increasing of SiC content. The total densification of sample sintered at 2050 oC was 90% of theoretical density for sample with 30 vol% of SiC, while the maximum densification for temperature of 2150 oC was 91,0 %TD.

Hot Pressing Sintering of ZrB<sub>2</sub> with β-SiC Addition

Zirconium diboride (ZrB2) is a material of particular interest because of the excellent and unique property combination of high melting point, high electrical and thermal conductivity. In this work, the effect of addition of beta-silicon carbide (β-SiC) on hot pressing sintering of ZrB2 was investigated. Four compositions were studied with 0, 10, 20 e 30 vol% of SiC. ZrB2 powder and mixtures were prepared by planetary milling with SiC spheres during 4 h. Samples were sintered at 1850 °C/1h with a pressure of 20 MPa in argon atmosphere. β-SiC has undergone phase transformation to α-SiC during sintering. The addition of SiC increased densification with increasing of SiC content. The total densification of sample was 96.8 % of theoretical density for sample with 30 vol% of SiC and Vickers hardness was 19.9 ± 0.3 GPa.

Effects of Nb2O5–WO3 additive on microstructure and magnetic properties of low-temperature-fired NiCuZn ferrites

The low-temperature-fired NiCuZn ferrites with different amount of Nb2O5 and WO3 additives were prepared by solid-state reaction method. The effects of Nb2O5 and WO3 additives on sintering behavior, microstructures and magnetic properties of NiCuZn ferrites were investigated. It is found that Nb2O5 and WO3 additives overtly improve the densification of samples through grains uniformity and grains growth promotion. The appropriate Nb2O5 and WO3 additives not only can noticeably increase the initial permeability (μ i ) and saturation flux density (B s ), but also can obviously reduce the remanent flux density (B r ) and coercive field strength (H c ). However, too much additive will deteriorate the magnetic properties. By contrast, 0.2 wt% Nb2O5 and 0.5 wt% WO3 added in NiCuZn ferrites shows excellent magnetic properties: μ i = 674.81 at 100 kHz, B s = 142.48 mT, B r = 63.32 mT and H c = 31.39 A m−1.

Synthesis and characterization of Y2O3 doped Na–β″-Al2O3 solid electrolyte by double zeta process

Y2O3 doped Na–β″–Al2O3 was firstly synthesized by double zeta process with Al2O3, Na2CO3, Li2CO3 and Y2O3 as the starting materials. Effects of the Y2O3 content on the microstructure and mechanical and electrical properties of the Na–β″-Al2O3 were studied. Both the density and the bending strength of the samples can be effectively improved by doping Y2O3. Only a part of Y3+ can be diffused into the Na–β″-Al2O3 crystal lattice, and the rest of Y3+ form the solid solution with Al2O3 in the grain boundaries, which restrains the grain growth and accelerates the densification of samples during the sintering process. The optimal amount of doping is 0.5wt%, the bending strength and conductivity are approximately 16% and 52% higher compared to the un-doped samples, respectively.

Impregnation of olive mill wastewater on dry biomasses: Impact on chemical properties and combustion performances

Mediterranean countries generate large amounts of olive oil byproducts mainly OMWW (olive mill wastewater) and EOSW (exhausted olive solid waste). Although solid residues have various valorization strategies, there is no economically viable solution for the OMWW disposal. This study aims to recover the OMWW organic contents through solid biofuels production. Hence sawdust and EOSW were used for the OMWW impregnation. The potential of the obtained samples, namely: IS (impregnated sawdust) and IEOSW (impregnated exhausted olive solid waste) were evaluated. Therefore, the physicochemical characterizations and thermogravimetric analyses of the samples were first performed. Secondly, the samples densification into pellets and their combustion in a domestic combustor were carried out. Combustion efficiencies, gaseous and PM (particulate matter) emissions as well as ash contents were evaluated.The analysis finding shows that addition of OMWW leads to an increase of energy content through the heating values increase. An increase of the impregnated samples reactivity was observed and assigned to the potassium catalytic effect. Combustion performances show that the OMWW addition has not a negative effect on their firing quality. Moreover, a beneficial effect on the pollutant emissions is observed with IEOSW pellets. The developed strategy constitutes a promising issue for the OMWW disposal and recovery.

Application of Microwave Treatment for the Plasticisation of Beech Wood (Fagus sylvatica L.) and its Densification for Flooring System Purposes

In this study, the application of microwave treatment for wood plasticisation and its densification for flooring system purposes is presented. Microwave plasticisation was carried out using a continuous laboratory device at a frequency of 2.45 GHz, and the testing samples made from European beech (Fagus sylvatica L.) wood were plasticised at different power modes (2 kW, 3.5 kW, and 5 kW). Afterwards, the densification (ratio 50%) of pre-treated samples was performed. The surface temperature (Ts) and average moisture content (MC) of the samples were measured after plasticisation. The results showed the influence of the chosen mode on MC decrease and rapid Ts increase. Thus, the densification of testing samples is affected by different initial conditions that occur during the plasticisation process (MC and Ts). The Brinell hardness (HB) of the densified samples increased by about 57% (2 kW), 103% (3.5 kW), and 83% (5 kW), compared with control samples. These results provide a better understanding of microwave plasticisation usability and its potential optimisation and application in the wood flooring industry.

Characterization of severely deformed new composites fabricated by powder metallurgy including a stage of mechanical alloying

Mechanical properties of new composites having a binary matrix of Al–4Cu reinforced with TiO2 nano particles were investigated. The composites which consisted of 2wt% and 8wt% of TiO2 reinforcement particles, were fabricated using mechanical alloying and a powder metallurgy route. Morphology, phases and compounds formed during ball milling and densification of samples were studied. With increasing percentages of the reinforcement particles, mechanical properties of the composites were enhanced. Microstructural evolution and mechanical properties changes of the composites after application of twist extrusion (TE), as a severe plastic deformation (SPD) process, were also investigated. It was revealed that the more TE passes the higher hardness and yield strength obtained. In addition, increasing TE passes, led to occurrence of a more homogeneous distribution of the reinforcement particles within the structure, and development of an ultrafine-grained nano-structure. The maximum allowable number of TE passes was found to be four, above which the materials failed.

Thermoelectric properties of indium doped PbTe1-ySey alloys

Lead telluride and its alloys are well known for their thermoelectric applications. Here, a systematic study of PbTe1-ySey alloys doped with indium has been done. The powder X-Ray diffraction combined with Rietveld analysis confirmed the polycrystalline single phase nature of the samples, while microstructural analysis with scanning electron microscope results showed densification of samples and presence of micrometer sized particles. The temperature dependent transport properties showed that in these alloys, indium neither pinned the Fermi level as it does in PbTe, nor acted as a resonant dopant as in SnTe. At high temperatures, bipolar effect was observed which restricted the zT to 0.66 at 800 K for the sample with 30% Se content.

Effect of ZnO addition on the structure, microstructure and dielectric and piezoelectric properties of K0.5Na0.5NbO3 ceramics

Microstructure, structure and electrical and dielectric properties of ZnO-doped K0.5Na0.5NbO3 (KNN) ceramics were investigated. Powders were obtained by the conventional solid-state method. Samples doped with 0 to 1 mol% of ZnO were sintered at 1125 °C for 2 h. Through XRD spectra, the perovskite structure was detected, in addition to small peaks corresponding to secondary phases. It was also observed that zinc changed the microstructure and grain size of KNN ceramics. The addition of 0.5 mol% of Zn2+ produced a softening effect in the ferroelectric properties of the material, and increased its final density. Conversely, the addition of 1 mol% of Zn2+ reduced the sample densification.

Surface methods for monitoring the densification of parts in the selective laser sintering process

Purpose – The purpose of this paper is to characterize polyamide parts prepared by the SLS process using techniques that are dependent on surface properties and compare the results to density measurements in order to assess which technique better reflects the degree of densification achieved using different laser power levels. Design/methodology/approach – Fabrication of Nylon 12 (Duraform PA) samples and their characterization by apparent density measurements, perfilometry, Raman spectroscopy, scanning electron microscopy, specific surface area and contact angle measurements. Findings – Methods dependent on surface analysis are not suitable indicators of the degree of sample densification. Among the surface methods, the results from Raman spectroscopy are the ones with the best performance. Incipient sintering of the superficial layers and raw material powder on the surface, inherent to the parts made by the SLS process, strongly interfere with the characterization. Originality/value – Quantitative comparison of a number of surface probing methods for monitoring densification of SLS parts. Characterization of sample surfaces with and without raw material powder.

Effects of various fillers on sintering, microstructures and properties of Ca-Ba-Al-B-Si-O glass/ceramic composites

Low-temperature sintering and properties of LTCC (low temperature co-fired ceramics) materials based on CaO-BaO-Al2O3-B2O3-SiO2 glass and various fillers such as Al2O3, silica glass, christobalite, AlN, ZrO2, MgO·SiO2, TiO2 were investigated. The results show that densification, crystallization, microstructures and dielectric properties of the composites are found to strongly depend on the type of filler. The densification process of glass/ceramic composites with various fillers is mainly from 600 °C to 925 °C, and the initial compacting temperature of samples is 600 °C. The initial rapid densification of samples starts at its glass softening temperature. LTCC compositions containing Al2O3, silica glass, AlN and MgO·SiO2 fillers start to have the crystallization peaks at 890, 903, 869 and 844 °C, respectively. The crystallization peaks are believed as correlated to the crystallization of CaAl2SiO8, β-SiO2, Ca2Al2SiO7 and β-SiO2. The composite ceramic with Al2O3, silica glass and TiO2 ceramic have a better dense structure and better smooth fracture surface. Sample for Al2O3 has the lowest dielectric loss tanδ value of 0.00091, whereas the sample for MgO·SiO2 has the highest dielectric loss tanδ value of 0.02576. The sample for TiO2 has the highest dielectric constant value of 14.46, whereas the sample for AlN has the lowest dielectric constant value of 4.61.

Microstructure and Electrical Properties of Y<sub>2</sub>O<sub>3</sub> and Sb<sub>2</sub>O<sub>3</sub> Co-Doped ZnO-Based Varistors

Through a conventional ceramic process, Y2O3 and Sb2O3 co-doped ZnO-based varistors were prepared. The microstructure and electrical properties of the as-prepared varistors were investigated. Y2O3 could act as an inhibitor to the growth of ZnO grains when working with Sb2O3. The mean size of ZnO grains in the Sb2O3 and Y2O3 co-doped samples was smaller than those of the samples only added with Y2O3 or Sb2O3. And with appropriately increased ratio of Y:Sb, it would result in increased sample densification. When the doping level of Y2O3 was small, the nonlinear coefficientand breakdown voltage of the varistors would increase with increasing doping amounts of Y2O3, and the leakage current would decrease. However, when Y2O3 was doped without Sb2O3, both the nonlinear coefficientand breakdown voltage of the varistors would decrease sharply, thus the leakage current increase dramatically. The electrical properties of the Sb2O3 and Y2O3 co-doped varistors would be better than those of the samples only added with Y2O3 or Sb2O3, and when the Y:Sb atom ratio was 5, the nonlinear coefficients, breakdown voltages and leakage current of the varistors reached their optimum values of 777 V/mm, 23 and 0.17 mA/cm2, respectively.