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Sintering of a nano-crystalline metastable alumina

Influence of the firing parameters on the phase development and microstructural evolution

Journal of Thermal Analysis and Calorimetry
Authors:
Paola Palmero
and
M. Lombardi

Abstract  

The influence of the heating rate on phase transformation and microstructural evolution during sintering of a de-agglomerated nanocrystalline, transition alumina was investigated. A low heating rate treatment allowed to decrease the α-Al2O3 crystallization temperature as well as to displace densification at lower temperatures, also implying a refinement of the fired microstructures. In addition, the set-up of sintering cycles in which the heating rate changed in the range 0.5–20°C min−1 starting from intermediate, selected temperatures resulted in a further retention of a very fine and homogeneous grain size in final materials.

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Journal of Thermal Analysis and Calorimetry
Authors:
I. Shishkovsky
,
V. Scherbakov
,
Y. Morozov
,
M. Kuznetsov
, and
I. Parkin

Abstract  

This work reports the temperature behavior associated with formation of new metal-polymer, intermetallic, and ceramic materials by Selective Laser Sintering. Here, experimental data produced from temperature measurements for inert as well as reaction powder compositions and the combustion wave front is reported. Analysis using an analog-digital-analog computer converter allowed some control of laser movement and hence some control of the exothermal reaction — in so doing it provided near optimum conditions for forming layered 3D articles.

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Abstract  

Sintering of polymeric powders is a peculiar characteristic of many processing technologies, including rotational moulding and selective laser sintering (SLS). During polymer sintering, viscosity reduction in the melt state promotes densification of polymer powders, through a double stage mechanism, involving powder coalescence and bubble removal. In particular, sintering of semi-crystalline polymers is strongly influenced by the melting behaviour. Nevertheless, melting itself in absence of pressure is not necessarily accompanied by powder sintering, unless low viscosities are achieved. In this work, the melting and sintering behaviour of recycled high density polyethylene (rHDPE) have been analysed through differential scanning calorimetry (DSC) and Thermomechanical Analysis (TMA). Efficient models capable of describing the melting temperature distribution and rate of sintering of rHDPE powders have been developed, highlighting the inherent differences between the two distinct processes.

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Abstract  

The sintering behavior of gadolinia-doped ceria powders was studied by the master sintering curve (MSC). Dilatometric analyses of powders produced by a soft chemical method were performed to provide the experimental data set for the construction of the MSC. The assumed model provided good fittings of the MSC and the activation energy for the sintering of Ce1−x Gd x O3−δ, with x = 0, 0.05, 0.1, and 0.2 were found to be in the 218–325 KJ/mol range, depending on the dopant content. The results supported that both the nanometric size of the particles and the difference in ionic radii between Gd3+ and Ce4+ affects the sintering of Gd-doped CeO2.

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Abstract  

Aiming the use of the sewage sludge produced in one of the largest Brazilian wastewater treatment stations as a raw material for the ceramic industry, the sintering process of the ashes produced from its calcination was evaluated by heating microscopy thermal analysis (HMTA). From the microprocessed images, a method was developed to obtain HMTA dimensional change curves as a function of temperature, equivalent to those usually obtained from dilatometers or by thermomechanical analysis (TMA). The final product after sintering at 1050°C, characterized by X-ray fluorescence spectrometry, scanning electron microscopy and X-ray dispersive energy, indicates the presence of a vitreous phase containing phosphorus, which explains the good sintering properties of the studied calcined sludge, as shown from its HMTA dimensional change curve.

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Journal of Thermal Analysis and Calorimetry
Authors:
M Yasuoka
,
Y Nishimura
,
T Nagaoka
, and
K Watari

Abstract  

The ceramic industry uses enormous amounts of energy to produce products at high temperatures. Energy-saving measures based on sintering process improvements are examined. Oxide ceramics were irradiated by two different methods during microwave sintering: intermittent use of the same high power levels (time-control method) and continuous use of lower, increasing levels of power (power-control method). We found that: 1) the power consumption and efficiency of the time-control method were lower than those of the power-control method; 2) the power-control method gave more precise control of temperature under our experimental conditions; 3) sample densification did not differ greatly between the two methods; and 4) grain growth did not differ greatly between the two methods.

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Journal of Thermal Analysis and Calorimetry
Authors:
Alessandra Bianco
,
Ilaria Cacciotti
,
Mariangela Lombardi
,
Laura Montanaro
, and
G. Gusmano

Abstract  

Hydroxyapatite (HA) nanopowders were synthesised following two different precipitation routes: (a) from calcium nitrate and diammonium hydrogen phosphate solutions and (b) from calcium hydroxide suspension and phosphoric acid solution. The influence of precipitation process, concentration, and synthesis temperature on HA particle size and morphology, phase composition, thermal stability, and sintering behaviour was investigated by means of: thermogravimetry and differential thermal analysis (TG-DTA), induced coupled plasma–atomic emission spectroscopy (ICP-AES), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), electron microscopy (TEM, SEM) and dilatometry.

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During the sintering of multicomponent disperse systems prepared from mixtures of the components, a variety of solid-state reactions, phase formation or dissolution, and the occurrence of a liquid phase determine the densification and the final microstructure of the material.

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1 Introduction Due to its success with the production of complicated parts, 3D printing techniques like selective laser melting (SLM) and selective laser sintering are being used with different materials and in various areas [ 1 , 2 ]. In the

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Abstract  

The YBCO-PbS superconductors have some interesting features, like better normal state and superconducting properties and enhanced shielding action towards magnetic fields. Present paper reports on the thermoanalytical and X-ray diffraction studies on these materials. The studies indicate that PbS addition enhances the synthesis of Y-123 Phase and lowers the temperature of partial melting of this phase which helps in reducing the voids. The metallurgical reaction occuring in sintering of PbS doped YBCO superconductors has been investigated and in light of the findings an explanation is given for the improved properties of these materials.

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