Formation Temperature Of Liquid Phase Research Articles

Experimental investigation and thermodynamic modelling of WC-Fe-Ni-Co-Cr cemented carbides

This work investigates the effect of Cr addition into the FeCoNi binder phase of the cemented carbides (WC-FeCoNi) using experimental and computational techniques. Liquid phase formation temperatures and C contents of WC-Fe-Ni-Co-Cr alloys were used as experimental results. Based on this, a thermodynamic modelling was conducted on the W-C-Fe-Ni-Co-Cr system using the CALPHAD (CALculation of PHAse Diagrams) approach. Taking into account the experimental and theoretical results, it was shown that the error in the solidus and liquidus temperatures were lower in the database generated in this work in comparison to the commercial thermodynamic databases for steels and cemented carbides. Using the database developed in the present work, the experimental data can be well reproduced.In addition, the maximum solubility of Cr to avoid the formation of Cr-rich carbides was also deduced from this study.

Effect of Borax On Sintering Kinetics, Microstructure and Mechanical Properties of Porous Glass-Ceramics From Coal Fly Ash by Direct Overfiring

The direct sintering process of coal fly ash for the preparation of glass-ceramics is the liquid-phase sintering process, from non-densification to densification. When the temperature exceeds the densification temperature point, the porosity of glass-ceramics on the contrary increases and the pore diameter increases. This provides a basis to prepare porous glass-ceramics by direct overfiring. Adding borax to coal fly ash can reduce the temperature of liquid phase formation, reduce the preparing temperature of porous glass-ceramics, achieve the purpose of energy saving. The effects of borax on the structure, properties and sintering kinetics of porous glass-ceramics prepared from coal fly ash by overfiring were investigated. It is found that the introduction of B-O bond can change the network structure of non-crystalline vitreous in coal fly ash, reduce the melting temperature, promote the formation of liquid phase, and thus increase the porosity of porous glass-ceramics. This paper provides a certain experimental basis for the preparation of porous glass-ceramics by direct overfiring of coal fly ash at low temperature without adding pore-forming agent, and provides a new possibility for the high-value resource utilization of coal fly ash.

Effect of MgO/Al<sub>2</sub>O<sub>3</sub> on Fluidity of SFCA-Based Binder Phase

The fluidity of sinter binder phase is one of the main properties that determine the quality of sinter, and it is also an important index to characterize the quality of sinter. So far, iron and steel enterprises mainly produce high alkalinity sinter, and its binder phase is mainly composite calcium ferrite based binder phase. Therefore, the research object of this paper is the composite calcium ferrite based binder phase of high alkalinity sinter. The effect of MgO/Al₂O₃ on the fluidity of high calcium composite calcium ferrite based binder phase was investigated from three aspects: fluidity index, liquid phase formation temperature and melting time by using chemical pure reagent and melting point velocimeter. The results show that in the range of MgO/Al₂O₃ from 0.46 to 0.68, with the increase of the ratio of MgO to Al₂O₃, the fluidity index first increases and then decreases, and the maximum value is obtained at MgO/Al₂O₃=0.65; The melting time decreases first and then increases. At the same time, the minimum value is obtained at MgO/Al₂O₃=0.65, and the influence on the melting time becomes more and more obvious with the increase of MgO/Al₂O₃ ratio; the characteristic temperature of liquid phase formation increases briefly and then decreases.

Analysis of Rational Proportion of Raw Materials Based on Biomass

Most of the air pollutants in the steel industry come from the sintering process, and the air pollutants produced by the sintering process mainly come from the sinter fuel (coke breeze). The S and N content of biomass fuel is low; therefore, biomass fuel is used instead of coke breeze for sintering to reduce the emission of the sinter flue gas pollutants. However, the use of biomass fuel reduces the sintering layer temperature, which results in the deterioration of the sinter properties. In order to ensure the quality of sintering base on biomass fuel, the thermodynamic calculation and related experiments were carried out, the effects of different basicity, MgO and Al2O3 content on the formation of low melting point minerals in sintered mixture were studied, and the suitable composition of sintered mixture was determined in this paper, so as to reduce the liquid phase formation temperature of sinter and increase in biomass fuel addition, which provided theoretical support for the application of biomass fuel in sintering. Experimental results indicate that the suitable conditions for the low-temperature sintering were a basicity of 2.0, and MgO and Al2O3 contents of 1.0% and 1.8%, respectively. Under this condition, more biomass fuel can be used to replace coke breeze, and the emission of flue gas pollutants can be greatly reduced.

Experimental and theoretical study of WC-40Fe-20Co-40Ni

The liquid phase formation temperatures of the quinary system W-C-Co-Fe-Ni with a ratio of Fe:Co:Ni = 40:20:40 were determined by means of DSC analysis. Besides, the experimental C-window of this system with a binder content of 14.3 ± 2 wt% is accurately defined. Based on the experimental results, a thermodynamic modelling is carried out using the CALPHAD approach. Temperature-composition sections of the W-C-Co-Fe-Ni system with different binder contents are calculated to verify the rationality of the present modelling. There is a good correlation between the experimental and calculated results showing that the experimental data can be well reproduced by the present modelling.

Comparative study on utilization of different types of municipal solid waste incineration bottom ash for clinker sintering

In this study, two types of municipal solid waste incineration (MSWI) bottom ash (BA) (MSWI-BA-A, water quenched, MSWI-BA-B, natural cooling), are utilized as alternative materials for clinker sintering. Fixed clinker modulus (lime saturation ratio = 0.90 ± 0.01, silica modulus = 2.6 ± 0.1 and alumina modulus = 1.5 ± 0.1), designed gradient addition ratio of MSWIBA (0, 3%, 6%, 9% and 12%) and same sintering temperature (1723.15 K) are adopted to conduct the experiments. Raw materials are characterized by XRF, X-ray diffraction and differential thermal analysis. Clinkers are analyzed and evaluated by XRF, X-ray diffraction, petrographic analysis, compressive and flexural strength tests and toxicity characteristic leaching procedure. The major difference of the two types of MSWIBA is LOI value which is supposed to be the most probable reason for huge difference between liquid phase formation temperature variation and incremental introduction of MSWI. MSWI-BA-A increases liquid phase formation temperature. Liquid phase formation temperatures and MSWI-BA-B samples addition ratios nearly present negative linear correlation. All clinkers sintered with addition of MSWIBA slightly reduce water demand for normal consistency. MSWIBA addition poses relatively obvious influence on initial setting time and little effect on final setting time. There is an increase in initial strength and a decrease in 28-day strength of clinkers sintered with MSWIBA, 28-day compressive strength decreases with the incremental introduction of MSWIBA. Distinct characteristics, such as free lime, periclase, orthorhombic tricalcium aluminate (C3A) crystal and secondary Belite crystal, are observed by petrographic analysis. MSWIBA is significant source of free lime and periclase in clinkers. Incremental input of alkali introduced by MSWIBA influences clinker sintering and mineral crystallinzation, further results in orthorhombic C3A crystal and indistinct Alite edge caused by corrosion. Leaching concentration of heavy metals from mortars prepared with the sintering clinkers is lower than corresponding concentration of the Chinese National Standard GB 30760-2014.

Structural and morphological characterization of iron-doped sol-gel derived mullite powders

The structural and morphological properties of iron-doped mullite powders are the subject of the present study. The powders of undoped and iron-doped mullite in the composition range of 3–15 wt% Fe2O3 were synthesized by a combination of sol-gel and combustion methods. The excess of water and urea were introduced in reaction solutions to enhance the copolymerization of aluminum and silicon species. The results of structural characterization revealed that the synthesized mullite powders were amorphous of a hybrid type. The specific surface area of the undoped mullite powder was 262 m2 g-1 with a maximum pore radius (dp) of 2 nm classifying it into mesoporous materials. The addition of iron has reduced the specific surface area, while the pore size value remained the same except for the sample with 3 wt% Fe2O3 (SBET = 278 m2 g-1; dp = 3 nm). The presence of iron caused lowering the temperature of liquid phase formation, while present urea combusted providing the increase of the temperature locally that caused the sintering and formation of agglomerates of smaller particles. However, the results of the particle size analysis are not straightforward. The values of mean volume diameter (D[3,4]) indicated that the particle size increased to 6 wt% Fe2O3 (123.6 μm), and then decreased and for the sample with 12 wt% Fe2O3, it was equal to 96.6 μm. Thus, the added iron contributed to the more uniform particle size distribution. The SEM analysis has also shown the coarse powder particles consisted of the coalesced smaller particles.

Effect of Alumina on Liquid Phase Formation in Sintering Process of Iron Ore Fines

The formation of liquid phase is of great significance for improving the quality of high basicity sinter which is widely used as raw materials in blast furnace ironmaking. As an important component of gangue in iron ore, alumina affects the amount of liquid phase by influencing the formation of calcium ferrites‐bonding phase. In this work, the hematite solid solution with aluminum (Hss) was prepared and sintered with CaO to investigate the effect of alumina on liquid phase formation in sintering process of iron ore fines. Three homogeneous phases of CaFe2O4 (CF), Ca2Fe15.57O25.56 (CF3.9), and Ca3.18Fe15.48Al1.34O28 (CFA) are prepared to determine the melting temperature by using DSC method. XRD, SEM‐EDS, and optical microscope are used to characterize the change of mineral and microstructure of sintered samples. The results show that an Fe‐rich calcium ferrite CF3.9 is produced above 1200 °C in Fe2O3‐CaO binary system. The liquid phase formation temperature can be reduced to 1206 °C when CF3.9 and CF coexist. The ternary calcium ferrite CFA, which has a eutectic temperature of 1201 °C with CF, is generated above 990 °C in Fe2O3‐CaO‐Al2O3 ternary system. The formation of liquid phase is promoted by adding alumina in moderation through changing the mass ratio of CF to CFA, and the largest amount of liquid phase is produced when the ratio is 8:2.

Characterisation and Performance Optimisation of WC-MC/M(C,N)-Co Hardmetals

WC-MC/M(C,N)-Co hardmetals with 10 wt% Co were prepared in undoped, as well as in either Cr- or V-doped form. The starting formulations contained 5 wt% TiC or 5% (TiC+TiN), the latter with two different TiC/TiN ratios, and 10 wt% (Ta,Nb)C. For each composition, a low-C grade (Ms ≈ 75%) and a high-C grade (Ms ≈ 88%) was adjusted by C or W addition, to end up with 18 different hardmetal formulations, prepared in an industrial process. Model alloys, MC and M(C,N) phases with a composition reflecting the composition of these phases in the hardmetal were prepared, too. A variety of data was collected: binder phase and hard phase compositions of model alloys by wavelength-dispersive electron-probe microanalysis (WDS-EPMA), liquid phase formation temperatures in model alloys with free C and eta by differential thermal analysis (DTA), respectively, thermal conductivities of MC and M(C,N) phases and hardmetals by laser-flash temperature conductivity and heat capacity measurements up to 950 °C, crystallite-size distribution by electron backscatter diffraction EBSD, hardness HV30, Palmqvist-Shetty fracture toughness KIC, Weibull evaluation of the transverse rupture strength (TRS), oxidation resistance in air as well as milling tests on coated hardmetals with Ti(C,N)/Al2O3 and (Ti,Al)N layers.

Effect of size on phase transformation temperatures in Ge/Bi/Ge films

Despite numerous studies the nature of phase transformations of nanomaterials in confinement remains among grand scientific challenges of nanoscience and nanotechnology. We address this issue in a comprehensive experimental study of melting and crystallization of 3–100 nm thick bismuth films confined between germanium layers. Layered Ge/Bi/Ge films modeled a “nanosized object – matrix” system and were formed by successive deposition of the components in a high vacuum. Two experimental approaches were used to trace the phase state of the system. The first one is based on studying crystalline structure during in situ heating and cooling of the samples in a transmission electron microscope. The second one is a differential method based on the registration of an abrupt change in the morphology of the films during their melting. It has been shown that the eutectic temperature is not a monotonic function of size. It decreases gradually as the size of the Ge/Bi/Ge system reduces and reaches its lowest value ≈ 190 °C for a ≈5 nm thick Bi film. For a thinner Bi film, the liquid phase formation temperature quickly rises in the system. The data on the metal-induced crystallization of amorphous germanium films in contact with bismuth, as well as the data on the crystallization of a liquid phase confined between Ge layers are presented. The processes of interphase interaction in the studied system are discussed.

Fluxing Agents on Ceramification of Composites of MgO-Al2O3-SiO2/Boron Phenolic Resin

Fluxing agents of zinc borate, antimony oxide, galss frit A and glass frit B, with different melting or softening point temperatures, were added into MgO-Al2O3-SiO2/boron phenol formaldehyde resin (MAS/BPF) composites to lower the formation temperature of eutectic liquid phase and promote the ceramification of ceramifiable composites. The effects of fluxing agents on the thermogravimetric properties, phase evolution, and microstructure evolution of MAS / BPF composites were characterized by TG-DSC, XRD and SEM analyses. The results reveal that the addition of a fluxing agent highly reduces the decomposition rate of MAS / BPF composites. Fluxing agents lower the formation temperatures of liquid phases of ceramifiable MAS / BPF composites obviously, and then promote the ceramification and densification process. The final residues of composites are ceramic surrounded by large amount of glass phases.

The role of CaO additive on sintering of aluminum nitride ceramics

AlN with 0.5–8wt% CaO was pressureless sintered between 1100°C and 1800°C. The results of density, second-phases, microstructure, and weight loss were used to identify the possible mechanisms that may cause a significant delay on the densification of AlN with CaO additive. It was observed that the additive content is the main parameter controlling the densification behavior during liquid phase sintering (LPS) of AlN with CaO. The positive effects of increasing the CaO content were associated with the decrease in the temperature of liquid-phase formation and the increase of the liquid-phase fraction during sintering. The negative effects were associated with the high viscosity of the liquid-phase below 1600°C, the formation of large pores, and the gas entrapment in closed pores. The balance between positive and negative effects results in an intermediate additive content (around 2wt% CaO), which is best to promote densification of AlN at a temperature as low as 1650°C.

Melting behavior of the Nowotny phase Mo4.8Si3C0.6

Mixtures of the Mo5Si3 silicide with 1.1–2.4 wt % carbon were melted after reaction sintering and the formation of the Nowotny phase (Mo4.8Si3C0.6), and the effect of various heat treatments on the phase composition of the samples was studied. The crystallization of the melted samples leads to a reduction of the volume fraction of the Nowotny phase relative to that after reaction sintering, but subsequent annealing below the liquid phase formation temperature allows the volume fraction of Mo4.8Si3C0.6 to be again raised. We discuss possible causes of the observed phase transformations.

Effect of sintering additive composition on microstructure and mechanical properties of silicon nitride

Silicon nitride ceramics doped with four different composition of sintering additives were prepared by hot pressing (HP) sintering. The effect of CeO2 addition and Yb2O3 addition on the formation temperature of liquid phase, the densification, the microstructure and the mechanical properties of Si3N4 ceramics were investigated. The results show that their effects are independent of each other. Furthermore, in comparison to Si3N4 ceramics sintered with sole lanthanide oxides, the samples sintered with both CeO2 and Yb2O3 additions exhibited superior mechanical properties even with a lower sintering temperature.

Experimental investigation and thermodynamic assessment of the C–Co–Fe–Ni–W system

The liquid phase formation temperatures of WC–(Co,Fe,Ni) alloys with free carbon and M6C phase, respectively, were determined by means of Differential Scanning Calorimetry (DSC) analysis. Based on the experimental results, a thermodynamic modelling is conducted on the C–Co–Fe–Ni–W quinary system using the CALPHAD (CALculation of PHAse Diagram) technique. Temperature-composition sections and projections concerning the sintering areas of the WC–(Co,Fe,Ni) hardmetals are calculated to verify the rationality of the present modelling. Comprehensive comparisons between the experimental and calculated results show that all the experiments can be well reproduced by the present modelling.

Metallurgy and thermochemistry of cermet/hardmetal laminates

Laminates of Ti(C,N)–WC–(Ta,Nb)C–Co/Ni cermets with WC–Co hardmetals were studied with respect to liquid-phase formation, bulk microstructure and microstructure evolution at the various interfaces. To adapt the cermet to the sintering behaviour of the hardmetal, investigations on mass change, influence of nitrogen pressure, as well as Cr and C doping on liquid-phase formation temperatures were performed. In addition, shrinkage and CO and N2 outgasing were studied.The bonding of cermets (CMs) to hardmetals (HMs) and that of 1:1, 1:2 and 2:1 mixtures of cermet/hardmetal (CM/HM) is tight, i.e. no pores occur. No major distortion or bending was observed although the shrinkage of each of the alloys was quite different. At the interfaces an intermixing occurred because of diffusion. At the CM/HM 2:1/1:2 interface a graded diffusion zone with more than 100μm thickness formed.In a bi-layer cermet/hardmetal laminate the interface microstructure was dependent on the nitrogen pressure in the sintering chamber. Enrichment of Co and nitrides occurred at lower than equilibrium pressure, whereas WC precipitated in the cermet at high nitrogen pressure.

Influences of the preparation methods of WC–Co powders on the sintering and microstructure of coarse grained WC–8Co hardmetals

WC–8Co slurry powder, ball milling powder and composite powder were prepared and WC–8Co hardmetals were produced via vacuum sintering at 1450°C. The morphologies, the lattice distortion and the thermal expansion test of WC–8Co powders were investigated using scanning electron microscope, X-ray diffraction and dilatometer, respectively. The results show that the lattice distortion can decrease the liquid phase formation temperature and influence the shrinkage of WC–8Co. The strains of ball milling powder, slurry powder, composite powder (4.09μm) and composite powder (2.08μm) are 0.185%, 0.029%, 0.028% and 0.05%, whose corresponding liquid phase formation temperatures are 1356°C, 1331°C, 1350°C, and 1345°C respectively. The solid phase shrinkage proportions of slurry powder, composite powder (4.09μm) and composite powder (2.08μm) are 45.50%, 45.73% and 53.00%, respectively. However, the solid phase shrinkage proportion of WC–8Co ball milling powder is up to 75.23% due to the highest strain. Furthermore, the comparison of microstructures between WC–8Co alloy (from ball milling powder) and WC–8Co alloy (from 4.09μm composite powder) confirms that decreasing the degree of lattice distortion can increase the liquid phase formation temperature and inhibit the growth of WC grain.

Influencing Factors and Effects of Assimilation Characteristic of Iron Ores in Sintering Process

Iron ore’s assimilation characteristic reflecting the beginning formation temperature of liquid phase in sintering process plays very important role on the fluidity of liquid phase and bonding strength of sinter body. Experimental study of assimilation characteristics of 12 kinds of iron ores were conducted using micro-sinter equipment, and pure reagent simulating tests of assimilation characteristic were also carried out for the purpose of achieving the influence of chemical composition on the assimilation characteristic. In addition, effects of assimilation characteristic of iron ore on the fluidity and bonding capacity of bonding phase were also researched. This study showed that SiO2 and LOI promoted the assimilation of iron ore, low Al2O3 (<1.5 mass%) was good to the assimilation, but high Al2O3 (≥1.5 mass%) was bad, MgO was adverse to assimilation of magnetite concentrate. In addition, lower assimilation temperature of iron ore led to higher superheat degree of liquid phase at a certain sintering temperature, then higher liquid fluidity and bonding strength.

Calculation of mineral phase and liquid phase formation temperature during roasting of vanadium-bearing stone coal using FactSage software

For vanadium extraction from stone coal, roasting is usually a necessary procedure to liberate vanadium from crystal structure. In the roasting process, the characterizations of phase transformation and temperature of onset of sintering are very important. A new method for calculating the mineral phase and liquid phase formation temperature (LPFT) using FactSage software is described in this study. The mineral phases of roasted stone coal with different chemical components calculated by FactSage were consistent with those analyzed by XRD. The change trends of the LPFTs calculated by FactSage also agreed well with those of the temperatures of onset of sintering measured by apparent density method. This new method is less labor-intensive and less costly compared with XRD and apparent density method. Moreover, it also can provide prediction of roasting temperature range, additive species and dosage for vanadium extraction from stone coal.

Reduction of liquid phase formation temperature of TiC–Ni composite by sintering activator addition

Abstract In this work sintering activators (phosphorus: P, copper: Cu and tin: Sn) were added to the TiC–Ni powder mixes. The mixed powders were compacted and then sintered at relatively low sintering temperatures (1200–1300 °C). From differential thermal analysis (DTA) results, it was found that addition of the activators could reduce sintering temperatures needed for densification of the TiC–Ni powder mixes. Reduction of the liquid phase forming temperatures was caused either by melting of eutectic or solid solution materials formed from Ni and the activators powders. Amongst the investigated activators, phosphorous addition showed an effect on increase of mechanical properties of the TiC–Ni composites. In contrast, the addition of other sintering activators showed no evidences of microstructure and mechanical property enhancement.