Microstructural evolution and sintering kinetics during spark plasma sintering of Fe and Al blended powder

The reaction diffusion between Fe and Al during spark plasma sintering(SPS)was studied.Microstructural evolution wasinvestigated by X-ray diffraction(XRD)and scanning electron microscopy(SEM)and the sintering kinetics was disclosed.The maininterphase of the SPS sample was Fe2Al5at773-873K.Ball-milling enabled a large number of lattice defects and grain boundariesthus the reaction kinetics was accelerated,although the direct current can also promote those defects.After milling,the phasetransformation kinetics was improved from0.207before mill to4.56×10-3.Besides,this work provided more details for thegeneration of Joule heating.The resistance offered to the electric path was considered to be the source of Joule heating,andparticularly the resistance offered by the different contact interfaces of die,punch,graphite foil and the sample played a leading rolefor the generation of Joule heating during spark plasma sintering.

Densification and Sintering Kinetics of Rare Earth(α′+β′)-Sialon Composites

The sintering processes of Re-(α' + β')-sialon composites (Re=Sm, Dy, Yb) have been investigated by using a specially designed high temperature dilatometer. The initial densification of various samples starts at about 1200℃, and the maximum shrinkage rate of these sialon composites occurs at about 1500℃. The light rare earth sialon has a noticeably tower densification temperature and a higher final shrinkage. The sirtering kinetics of Re-(α' +β')-sialonare much more complex. The Kingery's liquid phase sintering model appears to be applicable,but the mechanism of mass transport in stage two appears to be changeable. The controlling factor shiffs from solution-precipitation to diffusion when densification process proceeds from the earlier part to the later part of this stage.

Sintering Kinetics of Soft-Doped PZT(54/46)Systems

The influence of dopant concentration on PZT (54/46) systems doped with lanthanum and/or niobium is studied. The sintering kinetics is presented for 1 wt% of the dopant used to find the main mechanism which drives this process. The results were compared with a phenomenological model for viscous sintering and solid state sintering. The exponent obtained for viscous sintering in PZTN, PLZT and PLZTN were 0.05, 0.01, and 0.23 respectively, which indicate that the process is reactive liquid in all cases. In the other hand, the exponent obtained for solid state sintering were 6.61, 5.68, and 1.23 respectively, and prevalence Ost-wald ripening and coalescence process together. Both dopants inhibit the grain growth and accelerate the sintering process, which increases with dopant concentration and the combination of both dopants. Shoro-hod-Olevsky model was applied for explain grain growth evolution, but does not coincide strictly with the applied model, which suggest that the process is very complex.

Sintering kinetics involving grain growth and densification of Mg-PSZ nanopowders

Sintering kinetics have been found to be effective in judging the evolution of ceramics.By using magnesium oxide-partially stabilized zirconia(Mg-PSZ)powder prepared by co-precipitation as raw materials,the evolution of densification and grain growth for Mg-PSZ ceramics were investigated.The results indicated that the densification of samples was mainly controlled by grain boundary diffusion in intermediate sintering stage.During the sintering process,the grain growth mechanisms included normal grain growth,abnormal grain growth and solid solution drag-controlled grain growth.Interestingly,the apparent activation energy for grain growth of Mg-PSZ ceramics is lower than that of ZrO_(2)–Y_(2)O_(3)ceramics in the solid solution drag-controlled grain grow process,which will cause grain to grow easily.The sintering kinetics and microstructure of Mg-PSZ ceramics were studied,and the kinetic equation of grain growth at different temperatures was established.The results show that the strength difference between Mg-PSZ and yttrium oxide-stabilized zirconia is closely related to the easy grain growth of Mg-PSZ ceramics.

Sintering kinetics of YAG ceramics

Solid state reactive （SSR） sintering kinetics was observed for YAG ceramics. There were two densification stages in sin- tering process due to its reaction. After the first stage, samples began to expand, then, the second densification stage began. At a heat- ing rate of 10 ℃/min, the sample warped down and warped back to straight. The apparent activation energy of the first densification process was about 522 kJ/mol for the initial shrinkage of A1203 and Y203 mixed powder green-body, which increased in the follow- ing process due to the solid state reaction. In the second densification stage, synthesis reaction of YAG still worked. Green-bodies processed with higher heating rate got more shrinkage at the same temperature than lower heating rate green bodies. And its kinetic field diagram was abnormal, compared with that of other reported ceramics, such as Al203. It was found that the reaction of YAG provided positive effect to the sintering driving force. The apparent activation energy for densification of SSR YAG sintered in ArH5 atmosphere was 855 kJ/mol at temperature holding sintering. And the apparent activation energy for grain growth was 1053 kJ/mol.

Isothermal reduction kinetics and mineral phase of chromium-bearing vanadium–titanium sinter reduced with CO gas at 873–1273 K

Reduction of chromium-bearing vanadium–titanium sinter（CVTS） was studied under simulated conditions of a blast furnace, and thermodynamics and kinetics were theoretically analyzed. Reduction kinetics of CVTS at different temperatures was evaluated using a shrinking unreacted core model. The microstructure, mineral phase, and variation of the sinter during reduction were observed by X-ray diffraction, scanning electron microscopy, and metallographic microscopy. Results indicate that porosity of CVTS increased with temperature. Meanwhile, the reduction degree of the sinter improved with the reduction rate. Reduction of the sinter was controlled by a chemical reaction at the initial stage and inner diffusion at the final stage. Activation energies measured 29.22–99.69 k J/mol. Phase transformations in CVTS reduction are as follows： Fe_2O_3→Fe_3O_4→FeO→Fe; Fe_2TiO_5→Fe_2TiO_4→FeTiO_3; FeO·V_2O_3→V_2O_3; FeO·Cr_2O_3→Cr_2O_3.

One step sintering of homogenized bauxite raw material and kinetic study

A one-step sintering process of bauxite raw material from direct mining was completed, and the kinetics of this process was analyzed thoroughly. The results show that the sintering kinetics of bauxite raw material exhibits the liquid-phase sintering behavior. A small portion of impurities existed in the raw material act as a liquid phase. After X-ray diffraction analyses, scanning electron microscopy observations, and kinetics calculations, sintering temperature and heating duration were determined as the two major factors contributing to the sintering process and densification of bauxite ore. An elevated heating temperature and longer duration favor the densification process. The major obstacle for the densification of bauxite material is attributed to the formation of the enclosed blowhole during liquid-phase sintering.

A Study on the Thermal Stability of La_2O_3-TiO_2 Supports

In this paper,various techniques including BET,XRD,SEM and XPS were used to study the sintering of pure and La_2O_3-doped titania.The experimental results show that sintering of titania proceeds via volume diffu- sion.Adding of lanthanum oxide decreases the rate of sintering and hinders the phase transition from anatase to rutile crystal by strong surface interaction between the mixed crystals(La_4Ti_9O_(24),La_(0.66)TiO_(2.99))and TiO_2.

High performance of La-doped Y2O3 transparent ceramics

As an optical material,Y2O3 transparent ceramics are desirable for application as laser host materials.However,it is difficult to sinter and dense of Y2O3 hinders the preparation of high-quality optical ceramics via traditional processes.In this work,we use La2O3 as a sintering aid for fabricating high-transparency Y2O3 ceramics using a vacuum sintering process.It is demonstrated that the in-line optical transmittance of 15.0 at%La-doped Y2O3 at a wavelength of 1100 nm achieves a transmittance of 81.2%.A sintering kinetics analysis reveals that a grain-boundary-diffusion-controlled mechanism dominates the faster densification at high La3+concentrations.It is also shown that both the mechanical and thermal properties of Y2O3 transparent ceramics are significantly improved upon the increase of La2O3 sintering additives.The results indicate that a La-doped Y2O3 transparent ceramic is a promising candidate for a laser host material.