Microstructure and thermal stability of sintered pure tungsten processed by multiple direction compression

Multiple direction compression(MDC)was conducted on sintered pure tungsten(99.9%,mass fraction)with different reductions at 1423 K.The microstructure,microhardness and thermal stability of the MDC-processed samples were studied by X-ray diffraction(XRD),electron backscattered diffraction(EBSD)and differential scanning calorimetry(DSC)compared with those of the initial sintered tungsten.The results show that the dislocation density increases significantly with the reduction of MDC,ranging from 3.08×1014 m-2 for the initial sintered tungsten to 8.08×1014 m-2 for the tungsten after MDC with the reduction of 50%.The average grain size decreases from 83.8 to 14.7μm and the microhardness value increases from HV0.2 417 to HV0.2 521.The recrystallization temperature for the tungsten samples processed by MDC is approximately constant at around 1600 K.The MDC of sintered tungsten results in a decrease of grain size concurrent with an increase of uniformly distributed nucleation sites,which leads to the improvement of the thermal stability.

Structural Evolution of Graphene Oxide and Its Thermal Stability During High Temperature Sintering

The thermal reduction of graphene oxide(GO)was performed by a tube furnace at different temperatures,and its structure evolution was investigated in detail.The results showed that the oxygen-containing functional groups on the carbon plane surface of GO gradually decomposed as the temperature increase,and the reduced graphene oxide(rGO)powder was obtained at 800℃.Then,rGO powder was sintered under 30 MPa at 1800℃using spark plasma sintering(SPS)and hot-pressing(HP)to evaluate its structural stability at high temperatures.The defect densities of rGO were reduced after high-temperature sintering.The edge flatness and sp^(2) hybrid carbon plane structure were reconstructed effectively.These results demonstrate that the lamellar structure of rGO maintains the structural integrity during high-temperature sintering without obvious deterioration,which provides experimental and theoretical supports for GO reinforced ceramics.

Effect of Na_(2)O on transition and stability of dicalcium silicate based on sintering process

The phase transition,morphology,stability and pulverization performance of dicalcium silicate(C_(2)S)with different Na_(2)O additions during the high-temperature sintering process were studied using XRD,SEM-EDS,FT-IR,and Raman spectra methods.When the CaO to SiO_(2) molar ratio is 2.0 and the Na_(2)O to SiO_(2) molar ratio is below 0.20,the crystalline calcium silicate compounds includeγ-C_(2)S andβ-C_(2)S.As the Na_(2)O addition increases,the proportion,crystallinity and grain size ofβ-C_(2)S in the sintered products increase,those parameters ofγ-C_(2)S decrease,and the content of amorphous phase increases.Na_(2)O mainly forms solid solutions inβ-C_(2)S and inhibits the transition ofβ-C_(2)S toγ-C_(2)S,resulting in the sintered products unpulverized.The stability of sintered products in alkali solution decreases significantly with the increasing Na_(2)O additions,and theβ-C_(2)S solid solution with Na_(2)O is less stable thanγ-C_(2)S.The mechanism that Na_(2)O affects the transition of C_(2)S as well as its stability was also discussed,which can give actual guidance for the treatment of low-grade alumina-containing resources by the sintering process.

Simulation and Prediction of Alkalinity in Sintering Process Based on Grey Least Squares Support Vector Machine

The prediction of the alkalinity is difficult during the sintering process. Whether or not the level of the alkalinity of sintering process is successful is directly related to the quality of sinter. There is no very good method for predicting the alkalinity by now owing to the high complexity, high nonlinearity, strong coupling, high time delay, and etc. Therefore, a new technique, the grey squares support machine, was introduced. The grey support vector machine model of the alkalinity enabled the development of new equation and algorithm to predict the alkalinity. During modelling, the fluctuation of data sequence was weakened by the grey theory and the support vector machine was capable of processing nonlinear adaptable information, and the grey support vector machine has a combination of those advantages. The results revealed that the alkalinity of sinter could be accurately predicted using this model by reference to small sample and information. The experimental results showed that the grey support vector machine model was effective and practical owing to the advantages of high precision, less samples required, and simple calculation.

Influence of Gd_2O_3 and Yb_2O_3 Co-doping on Phase Stability,Thermo-physical Properties and Sintering of 8YSZ

The role of multicomponent rare earth oxides in phase stability, thermophysical properties and sintering for ZrO2-based thermal barrier coatings （TBCs） materials is investigated. 8YSZ codoped with 3 mol% Gd2O3 and 3 mol% Yb2O3 （GYb-YSZ） powders are synthesized by solid state reaction for 24 h at various temperatures. As temperature increases, stabilizers are dissolved into zirconia matrix gradually. Synthesized at 1 500 °C, GYb-YSZ is basically composed of cubic phase. GYb-YSZ exhibits excellent phase stability and sinters lower than 8YSZ by nearly three times. The thermal conductivity of GYb-YSZ is much lower than that of 8YSZ, and the thermal expansion coefficient of GYb-YSZ is comparable to that of 8YSZ. The influence of Gd2O3 and Yb2O3 co-doping on phase stability, thermal conductivity and sintering of 8YSZ is discussed.

Improvement of coercivity and thermal stability of Nd-Fe-B sintered magnets by intergranular addition of Tb80Fe20 alloy

To improve the coercivity and temperature stability of Nd-Fe-B sintered magnets for high-temperature applications,the eutectic Tb_(80)Fe_(20)(wt%)alloy powders were added into the Nd-Fe-B sintered magnets by intergranular method to enhance the coercivity(H_(cj))and thermal stability.The micro structure,magnetic properties and thermal stability of the Nd-Fe-B magnets with different Tb_(80)Fe_(20)contents were studied.The experimental results demonstrate that the coercivity(H_(cj))of the sintered Nd-Fe-B magnet is significantly enhanced from 14.12 to 27.78 kOe,and the remanence(Br)decreases not obviously by introducing 4 wt%Tb_(80)Fe_(20)alloy.Meanwhile,the reversible tempe rature coefficients of coercivity(β)and remanence(α)of the Nd-Fe-B magnets are increased from-0.5634%/℃to-0.4506%/℃and-0.1276%/℃to-0.1199%/℃at 20-170℃,respectively.The Curie temperature(TC)of the Nd-Fe-B magnet is slightly enhanced with the increase of Tb_(80)Fe_(20)content.Moreover,the irreversible flux magnetic loss(hirr)is obviously reduced as Tb80Fe20addition increases.Further analysis of the microstructure reveals that a modified microstructure,i.e.clear and continuous RE-rich grain boundary layer,is acquired in the sintered magnets by introducing Tb_(80)Fe_(20)alloy.The associated mechanisms on improved coercivity and thermal stability were comprehensively researched.

Magnetic Properties and Thermal Stability of Sintered Nd-Fe-B Magnet with Dy-Ni Additive

A sintered（Nd_（0.8）Pr_（0.2））_（30.7）FebalB_（0.98）Cu_（0.2） magnet with 3% intergranular Dy_（85）Ni_（15） additive is prepared to study the magnetic properties and thermal stability of the Nd-Fe-B magnet. The results show that the magnet with or without additive obtains its optimum comprehensive magnetic properties at the sintering temperature of 1 030 ℃ and 1 040 ℃, respectively. The maximum coercivity of the magnet with additive reaches 15.16 k Oe, while that of the magnet without additive is just 11.88 k Oe. Further investigation on microstructure indicates that the grains of the magnet with additive form a modified ＂core shell＂ structure. Adding Dy_（85）Ni_（15） can significantly enhance the coercivity of Nd-Fe-B magnet and thus decrease its coercivity temperature coefficient.

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.

Effect of alloying elements on thermal stability of nanocrystalline Al alloys

The effect of incorporating limited-diffusivity elements such as Fe and Ti on thermal stability of the nanocrystalline Al alloy was investigated.Al−10wt.%Fe and Al−10wt.%Fe−5wt.%Ti alloys were fabricated.The initial mixtures of powders were milled for 100 h in vacuum.The bulk samples were fabricated from the milled powders in a high frequency induction heat sintering(HFIHS)system.The milled powders and the bulk sintered samples were characterized by X-ray diffraction(XRD),Vickers microhardness,field emission scanning electron microscopy(FESEM-EDS)and transmission electron microscopy(TEM).The observations indicated that Fe and Ti were completely dispersed in the matrix to form a supersaturated solid solution(SSSS)with Al.Additionally,the inclusion of alloying elements led to an increase in hardness and yield strength of the alloy by 127%and 152%,respectively.The elevated temperature compression tests were carried out to evaluate the thermal stability of the alloys.The Al−10wt.%Fe−5wt.%Ti alloy revealed the optimum thermally stable behavior of the three alloys studied.The incorporation of Fe and Ti improved the thermal stability of the developed alloys through inhibiting the grain growth,hindering dissolution and growth of second phases(such as Al13Fe4 and Al13Ti),and forming a stable solid solution.

Research on sintering process of YSZ electrolyte

Yttria stabilized zirconia (YSZ) has widely been used as electrolyte in solid oxide fuel cell (SOFC). The microstructure of YSZ related to the fabrication process was discussed in the paper. With YSZ nano-powders about 40-100 nm as raw material, the YSZ adobe was manufactured by tape calendering process. The named three-step sintering process was performed at 1000 ℃ for 2 h, then raised the temperature with normal rate and as soon as up to 1400 ℃, the furnace was controlled at 1250-1300 ℃ for 10-20 h. The high dense YSZs with the relative density of 96%-99% were obtained; the grain size of YSZ could be reduced to 0.5-3 μm. The above result is benefited to co-fired in the electrode-supported SOFCs.

Effect of substrate amendment on alkaline minerals and aggregate stability in bauxite residue

Bauxite residue is an alkaline waste material in the process of alumina production due to its characteristics of higher salinity and alkalinity,which results in environmental issues and extremely restricts the sustainable development of alumina industries.In this work,we conduct a column experiment to study the effects of two amendments on aggregate stability and variations in alkaline minerals of bauxite residue.The two amendments are phosphogypsum(PG)and phosphogypsum and vermicompost(PVC).The dominant fraction in aggregate is 1–0.25 mm in diameter on the surface,which takes up 39.34%,39.38%,and 44.51%for CK,PG,and PVC,respectively.Additions of PG and PVC decreased pH,EC,ESP,exchangeable Na^+concentration and the percentage of alkaline minerals,and then increased exchangeable Ca^2+concentration in bauxite residue.There was significant positive correlation between pH and exchangeable Na^+concentration,the percentage of cancrinite,tricalcium aluminate and calcite;while negative correlation was found in pH value versus exchangeable Ca^2+concentration.Theses findings confirmed that additions of phosphogypsum and vermicompost have a stimulative effect on aggregate stability in bauxite residue.In particular,amendment neutralization(phosphogypsum+vermicompost)in column represents an advantage for large-scale simulation of vegetation rehabilitate in bauxite residue disposal areas.

Highly active and sintering-resistant heteroepitaxy of Au nanoparticles on ZnO nanowires for CO oxidation

Gold was supported on commercial ZnO powders(P) and homemade ZnO nanowires(NWs) by a modified deposition–precipitation method. X-ray diffraction and transmission electron microscopy investigation indicated that the size of the Au nanoparticles(NPs) depended strongly on the calcination temperature.The Au NPs were highly dispersed(< 5 nm) on both supports with calcination temperatures < 400 °C.However, after calcination at 600 °C the Au NPs aggregated much more severely on ZnO P than on ZnO NWs. Gold NPs epitaxially grew into the {10–10} facets of the ZnO NWs after calcination at temperatures > 400 °C. Such unique anchoring mechanism accounts for the much better experimentally observed sintering resistance. X-ray photoelectron spectra showed that Au existed as both metallic Au0 and Auδ+species in all the synthesized catalysts with or without calcination treatment; the ratios of Auδ+/Au0,however, varied, depending on the treatment conditions. Catalytic tests showed that the activity for CO oxidation strongly depended on the size of the Au NPs. After calcination at 600 °C, the specific rate for CO oxidation at room temperature decreased about 30 times on Au/ZnO P but only about 4 times on Au/ZnO NW. Stability tests demonstrated that the Au/ZnO NW catalysts had better stability for CO oxidation.

Acting mechanism of F,K,and Na in the solid phase sintering reaction of the Baiyunebo iron ore

The effect of F,K,and Na on the solid phase reaction of the Baiyunebo iron ore was investigated by differential thermal analysis （DTA） and X-ray diffraction（XRD）.It has been identified that alkaline elements K and Na in the Baiyunebo ore instigate the formation of low melting point compounds Na2SiO3 and Na2O·Fe2O3 and the generation of molten state in the solid phase sintering.Element F in the Baiyunebo ore facilitates the formation of cuspidine compound 3CaO·2SiO2·CaF2 in the solid phase reaction.The cuspidine compound is kept in solid as one of the final products through the entire sintering process due to its high melting point.In the sintering process,CaF2and SiO2 react with CaO first and form 3CaO·2SiO2·CaF2 and 3CaO·2SiO2,so the formation of ferrites,Na2O·Fe2O3,and 2CaO·Fe2O3 is inhibited.

Boosting selectivity and stability on Pt/BN catalysts for propane dehydrogenation via calcination & reduction-mediated strong metal-support interaction

Propane dehydrogenation(PDH) provides an alternative route for producing propylene. Herein, we demonstrates that h-BN is a promising support of Pt-based catalysts for PDH. The Pt catalysts supported on h-BN were prepared by an impregnation method using Pt(NH_(3))_(4)(NO_(3))_(2) as metal precursors. It has been found that the Pt/BN catalyst undergoing calcination and reduction is highly stable in both PDH reaction and coke-burning regeneration, together with low coke deposition and outstanding propylene selectivity(99%). Detailed characterizations reveal that the high coke resistance and high propylene selectivity of the Pt/BN catalyst are derived not only from the absence of acidity on BN support, but also from the calcination-induced and reduction-adjusted strong metal-support interaction(SMSI) between Pt and BN, which causes the partial encapsulation of Pt particles by BO_(x) overlayers. The BO_(x) overlayers can block the low-coordinated Pt sites and constrain Pt particles into smaller ensembles, suppressing side reactions such as cracking and deep dehydrogenation. Moreover, the BO_(x) overlayers can effectively inhibit Pt sintering by the spatial isolation of Pt during periodic reaction-regeneration cycles. In this work, the catalyst support for PDH is expanded to nonoxide BN, and the understanding of SMSI between Pt and BN will provide rational design strategy for BN-based catalysts.

The Properties of YSZ Electrolyte Sintering at 1300 ℃

The properties of yttria stabilized zirconia（YSZ） related to the sintering process were discussed.YSZ nano-powders about 40-100 nm as raw material,the sub-micrometer grain sizes such as 0.4-3 μm in YSZ were gotten by sintering process at 1300 ℃,which was performed at 1000 ℃ for 2 h,then raised the temperature at the rate of 50 ℃ / h to 1400 ℃,then decreased directly to 1300 ℃ in 30 minutes,finally at 1300 ℃ for 5-20 hours.The ratio of bigger grain size becomes larger as the holding time increasing at 1300 ℃.The grains less than 1 μm are about 50%,eg,43.2%,52.2% and 51.1% related to 1300 ℃ holding 5 hours,8 hours and 10 hours,respectively.As YSZ grain size became small,the electrical conductivities did not decrease,even increased,about 0.20 s/cm at 1000 ℃.The reduced sintering temperature and time were benefited to co-fire with the electrodes in electrode-supported SOFCs.

A METHOD TO IMPROVE DIMENSIONAL STABILITY OF PF PARTICLEBOARD

A method of alkaline pretreatment of particles was designed to produce three types of chips. The pretreatmentet of particles in 1% water solution of NaOH for 30 minutes offered a possibility of producing PF bonded particleboards with minimal irrecoverable swell and a reduction in thickness swelling. The method used in this work could be used to produce more stable PF particeboard.

Sintering and Phase Transformation of 7wt% Calcia-stabilized Zirconia Ceramics

Calcia stabilized zirconia（CSZ） ceramics were prepared with 7wt% calcia-stabilized zirconia powder by pressureless sintering technology. The crystal phases of the sintered samples were studied by X-ray diffraction（XRD） and Raman spectroscopy techniques, and the microstructures of the fracture surfaces were observed by scanning electron spectroscopy（SEM）. The phase compositions and the lattice parameters of cubic calcia-stabilized zirconia were calculated by XRD patterns. As the sintering temperature increasing from 1400℃ to 1600℃, the monoclinic zirconia content decreases gradually, finally all monoclinic phase transforms to cubic calcia-stabilized zirconia, which is deter- mined to be Ca0.134Zr0.866O1.866. It is revealed that monoclinic zirconia is the main factor causing minute cracks on the surface of sintered samples, and the combination of the XRD patterns and Raman spectra is an effective way to research the phase transformations of zirconia.

Processing and Sintering of Agglomerate-free CaO-ZrO2 Powder

Coprecipitation supercritical fluid drying technology has been employed to synthesize calcia-stabilized zirconia ultrafine powder with low-cost inorganic salts as the starting materials. The sintering behaviors of these powders were also investigated. The results showed that supercritical fluid drying could effectively alleviate the hard agglomeration of grains during the gel drying process, and the morphology of the powder retained the network texture of the original gel. The resulting particles were characterized by small particle size (5-20 nm), better monodispersity and high surface area, which gave rise to high activity and sinterability. Consequently, these powders could readily be compacted into the desired shape and their densification could be carried out in shorter time and at lower temperatures. For instance, nanometer-sized powder calcined at 600癈 for 2 h could be cold-pressed into a green body and sintered at 1100?for 0.5 h to attain a dense body with bulk density of 5.9718 g/cm3 and specific pore volume of 0.0008 cm3/g.

Distinct Electrical and Mechanical Responses of a Cu-10Fe Composite Prepared by Hot-Pressed Sintering and Post Treatment

A Cu-10wt%Fe composite was prepared through hot-pressed sintering,and the material was subsequently solution treated.The hot-pressed sintered and solution treated materials were rolled and aged.The precipitation behavior and performance changes were systematically studied by using scanning electron microscopy and transmission electron microscopy.In contrast to the hot-pressed sintered specimen,the solution treatment significantly affects the thermal stability and properties of the Cu-10wt%Fe composite.The Cu-10wt%Fe composite was prepared after solid solution,cold rolling and aging at 773 K for 1 h,and it obtained excellent tensile strength of 494 MPa,uniform elongation of 16.3%,electrical conductivity of 51.1%IACS and softening temperature of 838 K.Mechanisms for the distinct difference in thermal stability and properties between hot-pressed sintered and solution treated specimens were analyzed.These findings provide a theoretical basis for designing high-performance Cu-based in-situ composites by post treatment.