Solubility Of Zr Research Articles

Mechanism of metamorphic zircon growth in a granulite-facies quartzite, Adirondack Highlands, Grenville Province, New York

Granulite-facies quartzites from the Adirondack Highlands (Grenville Province, New York) contain accessory zircon with ubiquitous metamorphic overgrowths. Detrital zircon cores are resorbed, preserve various internal zoning styles and inclusions, and have ages of 1.3 to 2.7 Ga. These ages constrain the timing of deposition of the protolith sandstone and suggest that the Adirondack Highlands were proximal or part of Laurentia during deposition. Metamorphic overgrowths formed in the quartzites during the Shawinigan orogeny (1.20-1.14 Ga). The average volume of overgrowths in eight samples ranges from 62-87%, with a positive correlation between zircon growth and feldspar content (melt productivity during metamorphism). Melt volumes and Zr solubility were too small to allow the overgrowths to have formed in one dissolution-precipitation event. Crystal-size distributions suggest zircon coarsening by the dissolution of small crystals and Zr transfer via a partial melt, and thus zircon overgrowths date anatexis. These results have implications for provenance studies, as dissolution of small zircon grains and growth of new zircon could bias age spectra of metasedimentary rocks.

Investigation of the Al-Rich Part of the Al-Zr-Hf Phase Diagram for Solid State

Using electrical resistivity measurements, optical microscopy and scanning electron microscopy (SEM) with energy dispersive x-ray analysis (EDX), the Al-rich corner of the Al-Zr-Hf phase diagram was studied. In the investigation the combined solubility of Zr and Hf in solid Al at 600, 500, and 400 °C was determined. Zr and Hf significantly decrease the solubility of each other in solid Al with significant contraction of the Al single phase field with decreasing temperature. Investigation established only two solid phases in equilibrium with Al solid solution, ZrAl3 and HfAl3, with no apparent solubility of either Zr in HfAl3 or Hf in ZrAl3. Taking into account the established extension of the Al single phase field and compositions of the ZrAl3 and HfAl3 compounds in equilibrium with Al solid solution, the partial isothermal sections of the Al-Zr-Hf phase diagram at 600, 500, and 400 °C were constructed.

The phase relationships in the Al–Zr–Ho ternary system at 773 K

The phase relationships in the Al–Zr–Ho ternary system at 773 K have been investigated in the whole compositional range. The existences of 13 binary compounds, i.e. Al 3Zr, Al 2Zr, Al 3Zr 2, AlZr, Al 3Zr 4, Al 2Zr 3, AlZr 2, AlZr 3, AlHo 2, Al 2Ho 3, AlHo, Al 2Ho and Al 3Ho have been confirmed. Al 17Ho 2 was not found at 773 K in this work. In addition, the ternary compound Al 15Ho 4Zr is confirmed. It has AuCu 3 structure and its lattice parameter is a = 0.4201 nm. The results show that the isothermal section consists of 17 single-phase regions, 32 two-phase regions and 16 three-phase regions. The solubility of Zr in Al 2Ho, AlHo and Ho is about 71 at.%, 6 at.% and 12 at.% Zr, respectively. No remarkable solid solubility could be found in the other compounds of the Al–Zr–Ho ternary system at 773 K.

Development of High Strength and High Conductivity Cu-Ag-Zr Alloy

The development trend for diagnostics is reducing the diameter of coaxial signal cables that comprise the probe cable. The thinner super-fine coaxial cable which is offering superior electronic and mechanical properties, such as 75% IACS (International Annealed Copper Standard, electrical conductivity) and 700 ~ 800 MPa in tensile strength has to be developed. Three binary systems, Cu-Ag, Cu-Zr and Ag-Zr were thermodynamically optimized in the present study. Integration of optimized binary phase diagram can give useful information to predict the possible phases for the ternary Cu-Ag-Zr during manufacturing process. The large Cu5Zr particles were found at grain boundaries of as-cast alloys, which results from the strong affinity between Cu and Zr as well as no solubility of Zr in the Cu matrix. This coarse Cu5Zr phase was not dissolved fully during homogenization resides within the microstructure. Therefore, this phase induces decreasing in tensile strength after ageing.

Effect of Zr 4+ doping on the oxygen stoichiometry and phase stability of SrCo 0.8Fe 0.2O 3 − δ oxygen separation membrane

The effect of Zr doping in SrCo 0.8Fe 0.2O 3 − δ (SCF) membranes was investigated. The lattice parameter of SCF increased with the Zr content until 4 at.%, and then leveled off with further increase in the Zr content, revealing that the Zr solubility limit lies at ∼ 4%. The Zr doping resulted in an increase in oxygen stoichiometry (3 − δ) of SCF membranes especially at low oxygen partial pressure. The brownmillerite to perovskite phase transition was investigated by dilatometry in nitrogen (pO 2 = 2 × 10 − 3 atm). The phase transition temperature was lowered by Zr doping: 770 °C for undoped SCF and 710 °C for SCF doped with 4 at.% of Zr. The change in volume associated to the phase transition also became less pronounced for the Zr-doped samples. Compared to the undoped membrane, the Zr-doped SCF exhibited a somewhat lower oxygen permeability, but it remained well-permeable to oxygen at lower operation temperatures due to the stabilization of the perovskite structure.

XAFS measurements on Zr in aqueous fluids at high pressures and temperatures using a modified hydrothermal diamond-anvil cell

Aqueous fluids play a significant role in the transport of heat and matter in the Earth's crust and the upper mantle, and high-field-strength elements such as Zr are important geochemical tracers for these processes. However, the dissolution mechanism and complexation of Zr in the fluids at high pressure and temperature are unknown, in part because very low concentrations present severe experimental challenges. Here, we present an experimental setup for in-situ investigation of the coordination environment of elements at low concentrations in aqueous fluids up to 800 °C and 1.5 GPa using XAFS. Experiments were carried out in a modified hydrothermal diamond-anvil cell optimised for the detection of the fluorescence signal. We have investigated the effects of silicate components dissolved in aqueous fluids on the Zr solubility and complexation at high pressure and temperature. The observed Zr concentrations in fluids containing 7–33 wt% Na2Si2O5 and variable Al contents were between 75 and 720 ppm at 500 to 750°C and ∼300 MPa to ∼700 MPa. Initial XAFS results show clear differences between spectra of Zr in an HCl solution and in an H2O-Na2Si2O5 aqueous fluid, implying considerable differences in the Zr complexation.

Isothermal section of the Ti–Zr–Sn ternary system at 473 K

Ti–Zr–Sn alloys were obtained by melting pure elements in an arc furnace. Mainly by the method of X-ray diffraction (XRD), the character of phase equilibrium at 473 K is studied for the Ti–Zr–Sn system. The isothermal section at 473 K consists of 11 single phase regions, 16 binary phase regions and 6 ternary phase regions. The existence of a binary compound Ti 2Sn 3 was confirmed in the isothermal section. Zr 5Sn 4 was not observed and no ternary compound is found in the ternary system. The solubility of Zr in Ti 3Sn is up to 5 at.% Zr. The solubility of Ti in ZrSn 2 is about 4 at.% Ti. There is continuous solid solubility between Ti 5Sn 3 and Zr 5Sn 3.

Experimental determination and thermodynamic assessment of the phase diagram in the Co–Zr system

The phase diagram in the Co–Zr system was determined using the electron probe microanalyzer (EPMA), differential thermal analysis (DTA) and X-ray diffraction (XRD) technique. The experimental results indicate that (1) the solubility region of the Co 2Zr phase is from 25 to 34 at.% Zr; (2) the CoZr 3 phase exists and the temperature of the peritectoid reaction (CoZr 2 + (βZr) ↔ CoZr 3) is about 981 °C; (3) the solubilities of Zr in the (αCo) phase and Co in the (βZr) phase are about 0.15 and 2.5 at.%, respectively. A thermodynamic assessment of the Co–Zr binary system was carried out by the CALPHAD (calculation of phase diagrams) method. The Gibbs free energies of the solution phases (liquid, fcc, bcc and hcp) were described by the subregular solution model, and those of the intermetallic compounds (Co 11Zr 2, Co 23Zr 6, Co 2Zr, CoZr, CoZr 2 and CoZr 3) were described by the sublattice model. A proper set of the thermodynamic parameters has been derived for describing the Gibbs free energies of each phase in the Co–Zr system. An agreement between the calculated results and experimental data is obtained.

Solubility of Zr(IV), Th(IV) and Pu(IV) hydrous oxides in CaCl2solutions and the formation of ternary Ca-M(IV)-OH complexes

AbstractThe solubility of Zr(IV), Th(IV) and Pu(IV) hydrous oxides is investigated at 22±2 °C in alkaline 0.1−4.5 M CaCl2solutions. Further studies are performed with Zr(IV) over the entire pH range in NaCl and CaCl2media, and with Zr(IV) and Th(IV) in alkaline Ca(ClO4)2solutions. The comparison of Zr(IV) data in different ionic media (NaCl, NaClO4, CaCl2and Ca(ClO4)2) of similar ionic strength shows that the solubility in the acidic and neutral pH range is not affected by strong interactions between the aqueous M(IV) species and the medium ions. However, in alkaline CaCl2and Ca(ClO4)2solutions the formation of ternary Ca-M(IV)-OH complexes causes unexpectedly high solubilities of Zr(IV) at pHc=10−12 and [Ca2+]>0.05 M and of Th(IV) at pHc=11−12 and [Ca2+]>0.5 M. The dependence of the Zr(IV) and Th(IV) solubilities on the H+and CaCl2concentrations shows that the complexes Zr(OH)62−and Th(OH)84−with an unusual large number of OH−ligands are stabilized by the formation of associates or ion pairs with Ca2+ions. The SIT is used to derive equilibrium constants at zero ionic strength for the complexes Zr(OH)62−(in calcium-free solutions), Ca2[Zr(OH)6]2+, Ca3[Zr(OH)6]4+and Ca4[Th(OH)8]4+. In analogous studies with Pu(IV) hydrous oxide, the solubility increasing effect of ternary complex formation with Ca2+ions is only observed at CaCl2concentrations above 2 M.

Effect of Al<sub>3</sub>(Sc,Zr) Particles on Tensile Properties of an Al-Zn-Mg-Cu-Sc-Zr Alloy

Small additions of Sc and Zr may considerably improve both strength and ductility of 7000 series aluminum alloys, which is associated with precipitation of fine coherent Al3(Sc,Zr) particles. These particles also increase resistance to recrystallization and promote formation of a stable refined microstructure. Because of very low equilibrium solubility of Sc and Zr in Al alloys, a supersaturated solid solution of these elements in the Al matrix presented after casting is responsible for precipitation of the Al3(Sc,Zr) particles during subsequent heat treatment, while the strengthening effect depends on the particle size and number density. Therefore, it is necessary to optimize precipitation of the Al3(Sc,Zr) particles, in order to achieve superior balance of mechanical properties. In the present work, the effect of heat treatment conditions on microstructure and tensile properties of a developmental 7000 series Al alloy SSA018 modified with Sc and Zr was studied, with special emphasis on the analysis of size and number density of the Al3(Sc,Zr) particles, and their effect on the strength increase.

Phase equilibria of the Zr–Ti–Si ternary system at 773 K

The phase equilibria of the Zr–Ti–Si ternary system at 773 K have been investigated mainly by powder X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive analysis (EDX). The isothermal section consists of 14 single-phase regions, 23 binary-phase regions and 13 ternary-phase regions. The binary compounds Zr 3Si and Zr 5Si 3 are not observed at 773 K. Therefore, there are 10 binary compounds, i.e. Zr 2Si, Zr 3Si 2, Zr 5Si 4, ZrSi, ZrSi 2, Ti 3Si, Ti 5Si 3, Ti 5Si 4, TiSi and TiSi 2 in the Zr–Ti–Si system at 773 K. Ternary compound Si 3Ti 2Zr 3 is found at this isothermal section. The solubilities of Zr in TiSi 2, TiSi, Ti 5Si 4, Ti 5Si 3 and Ti 3Si were determined to be up to 10, 11, 12, 13 and 7 at.% Zr, respectively; the solubilities of Ti in Zr 3Si 2, Zr 5Si 4, ZrSi and ZrSi 2 were about 5.4, 14, 7 and 14 at.% Ti.

The Magmatic and Fluid Evolution of the Motzfeldt Intrusion in South Greenland: Insights into the Formation of Agpaitic and Miaskitic Rocks

The 1� 275 Ga Motzfeldt intrusive complex in the Gardar failed-rift Province in South Greenland formed from six successively intruding melt batches (SM1^SM6) interpreted to be derived from a common magma source at depth. Five units (SM1^SM5) crystallized an alkaline to peralkaline, miaskitic mineral assemblage of amphibole, clinopyroxene, feldspar, nepheline, Fe^Ti oxides, zircon, apatite, fluorite and rarely olivine.The last magmatic batch (SM6) is characterized by an agpaitic mineral assemblage of aegirine, nepheline, alkali-feldspar, eudialyte and rare fluorite or sodalite. Coexisting mafic minerals constrain the crystallization conditions of the miaskitic rocks to about 850^6008C, whereas solidus temperatures below 5008C are indicated by coexisting alkali feldspars in the agpaitic rocks. Oxygen fugacities during the orthomagmatic stage are below the FMQ (fayalite^ magnetite^quartz) buffer (FMQ ^0 � 5t o ^2� 0) whereas late hematite provides evidence of a higher relative oxygen fugacity during late-stage alteration. The Nd and oxygen isotope compositions of amphiboles and pyroxenes are homogeneous throughout the complex and suggest a common, mantle-derived magma source for all six units which is comparable with other Gardar intrusions.The hydrogen isotopic composition of amphiboles (dD^99 to ^132%) indicates lowtemperature fluid^rock interaction with low fluid^rock ratios. Fluid inclusion studies indicate that H2O^NaCl fluids present during the magmatic stages in the miaskitic units had salinities of510 wt % NaCl eq. Calcite crystals in fluid inclusions within these rocks suggest that CO2 or HCO3 ^ was an important component of the original fluid phase. In contrast, the agpaitic unit is characterized by a CH4^H2O^ NaClfluid.The C^O^H isotope compositionsofthefluid inclusions in all units are consistent with mixing between a small volume of magmatic fluid and a large volume of meteoric water. The chemical evolution of the Motzfeldt complex is a type example of the connection of the transition from miaskitic to agpaitic mineral assemblages with redox-dependent fluid^solid equilibria.Thetransitionfromarelatively oxidized to a relatively reduced fluid is correlated with a change from a more reduced, Fe 2þ -bearing miaskitic (taramite^arfvedsonite, zircon, SM1^SM5) to a more oxidized, Fe 3þ -bearing agpaitic assemblage (aegirine, eudialyte, SM6).We suggest that coupled fluid^solid redox equilibria involving Fe 2þ ,F e 3þ ,C O2 and CH4 in this case were simply driven by temperature decrease and an overall increase in Na (þ K) in the melt.This observation sheds light on the heavily debated miaskite^ agpaite transition.The combined temperature and compositional effect stabilized Fe 3þ ,C H 4 and enhanced the solubility of Zr (possibly as Na^Zr^Si^O complexes) in the latest stage melt (SM6) resulting in the crystallization ofan agpaitic mineral assemblage. In terms of redox conditions during crystallization, the Motzfeldt rocks represent an intermediate case in the Gardar Province between more oxidized, CO2dominated intrusions such as the syenite^carbonatite complex of

The phase equilibria of the La-Ti-Si ternary system at 773 K

Abstract The phase equilibria of the Zr–Ti–Si ternary system at 773 K have been investigated mainly by powder X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive analysis (EDX). The isothermal section consists of 14 single-phase regions, 23 binary-phase regions and 13 ternary-phase regions. The binary compounds Zr3Si and Zr5Si3 are not observed at 773 K. Therefore, there are 10 binary compounds, i.e. Zr2Si, Zr3Si2, Zr5Si4, ZrSi, ZrSi2, Ti3Si, Ti5Si3, Ti5Si4, TiSi and TiSi2 in the Zr–Ti–Si system at 773 K. Ternary compound Si3Ti2Zr3 is found at this isothermal section. The solubilities of Zr in TiSi2, TiSi, Ti5Si4, Ti5Si3 and Ti3Si were determined to be up to 10, 11, 12, 13 and 7 at.% Zr, respectively; the solubilities of Ti in Zr3Si2, Zr5Si4, ZrSi and ZrSi2 were about 5.4, 14, 7 and 14 at.% Ti.

Determination of Isothermal Section of Fe-Ni-Zr Ternary System at 1198K

Phase relations in the Fe-Ti-Zr ternary system at 1 173 K were investigated by means of diffusion-triple approach together with electron probe microanalysis(EPMA) technique. A series of tie lines and tie-triangles were determined and the isothermal section at 1 173 K was established, which consists of four three-phase fields: β(Ti, Zr)+FeZr2+FeTi, FeZr2+FeTi+Fe2Zr, FeTi +Fe2Zr +Fe2Ti and Fe2Zr +Fe2Ti +Fe. The results show that the largest solubility of Ti in Fe2Zr is about 11.3%(mole fraction) and the solid solubility of Ti in FeZr2 is about 26.9%, the solid solubility of Zr in Fe2Ti is about 8.1% and the solid solubility of Zr in FeTi is 7.2%. The binary compound FeZr2 is nearly a linear compound. No ternary compound is found.

Determination of isothermal section of Fe-Ti-Zr ternary system at 1173 K

Phase relations in the Fe-Ti-Zr ternary system at 1173 K were investigated by means of diffusion-triple approach together with electron probe microanalysis(EPMA) technique. A series of tie lines and tie-triangles were determined and the isothermal section at 1173 K was established, which consists of four three-phase fields: β(Ti, Zr) + FeZr 2 + FeTi, FeZr 2 + FeTi + Fe 2Zr, FeTi + Fe 2Zr + Fe 2Ti and Fe 2Zr + Fe 2Ti + Fe. The results show that the largest solubility of Ti in Fe 2Zr is about 11.3%(mole fraction) and the solid solubility of Ti in FeZr 2 is about 26.9%, the solid solubility of Zr in Fe 2Ti is about 8.1% and the solid solubility of Zr in FeTi is 7.2%. The binary compound FeZr 2 is nearly a linear compound. No ternary compound is found.

Micro‐Raman study of Zr‐substituted Bi4Ti3O12 ceramics

AbstractWe have studied the lattice vibrational modes of Zr‐substituted Bi4Ti3O12 ceramics using micro‐Raman spectroscopy. Replacement of Zr at the Ti site in the perovskite block is found from the increase in the lattice parameters as a function of Zr contents. Combined X‐ray diffraction patterns and Raman analysis suggested less than 40 mole% Zr solubility in Bi4Ti3O12. At 40 mole% of Zr substitution or above, the unreacted monoclinic‐phase ZrO2 is observed in the X‐ray diffraction patterns and the Raman spectra. The incorporation of Zr in Bi4Ti3O12 reduces the soft mode wavenumber and the transition temperature. Moreover, temperature dependent studies confirmed the ferroelectric to paraelectric transition in Bi4Ti3O12 at about 675 °C. On increasing the Zr content up to 40% on the Ti sites of Bi4Ti3O12, a systematic decrease in the phase transition temperature from 675 to 630 °C was observed. Copyright © 2007 John Wiley & Sons, Ltd.

Investigation of polynuclear Zr(IV) hydroxide complexes by nanoelectrospray mass-spectrometry combined with XAFS

Polynuclear species of zirconium in acidic aqueous solution are investigated by combining X-ray absorption spectroscopy (XAFS) and nanoelectrospray mass spectrometry (ESI-MS). Species distributions are measured between pHC 0 and pHC 3 for [Zr]=1.5-10 mM. While the monomer remains a minor species, with increasing pH the degree of polymerization increases and the formation of tetramers, pentamers, octamers, and larger polymers is observed. The high resolution of the mass spectrometer permits the unambiguous determination of polynuclear zirconium hydroxide complexes by means of their isotopic patterns. The relative abundances of mononuclear and polynuclear species present simultaneously in solution are measured, even if one of the species contributes only 0.1% of the Zr concentration. For the first time it has been directly observed that the hydrolysis of polynuclear Zr species is a continuous process which leads to charge compensation through the sequential substitution of water molecules by hydroxide ligands until doubly charged polymers dominate at conditions (H+ and Zr concentrations) close to the solubility of Zr(OH)4(am). The invasiveness of the electrospray process was minimized by using very mild declustering conditions, leaving the polynuclear species within a solvent shell of approximately 20 water molecules.

Experimental zircon/melt and zircon/garnet trace element partitioning and implications for the geochronology of crustal rocks

Garnet is the most commonly used mineral in thermobarometry, whereas zircon is the most robust chronometer to date high-grade metamorphic rocks. To provide a basis for correlation of zircon and garnet growth, we determined experimentally the trace element partitioning between zircon, a hydrous granitic melt and garnet at 20 kbar and 800–1000 °C for P, Y, rare earth elements (REE), Zr, Hf, Th and U. In respect to melt, zircon preferentially incorporates all investigated elements apart from REE with atomic number lower than Sm. At this pressure and in the chosen composition, the distribution coefficient between zircon and melt ( D Zrn/Melt) for REE increases with increasing atomic number of the REE and with decreasing temperature. D Yb Zrn/Melt is ∼ 20 at 1000 °C, but more than an order of magnitude higher at 800 °C. The solubility of Zr in hydrous granitic melts buffered by zircon is about a factor of two lower at 20 kbar than what has been previously established for mid-crustal pressures. Large garnet produced in the experiments allowed determination of garnet/melt trace element partitioning ( D Grt/Melt) at temperatures of 800–1000 °C, conditions relevant for partial melting of crustal rocks. There is a systematic increase in D REE Grt/Melt with decreasing temperature. Zircon contains significantly more heavy-REE than garnet at temperatures of 800–850 °C. Zircon/garnet partition coefficients of heavy-REE decrease with increasing temperature from D Lu Zrn/Melt of 12 at 800 °C to 1.4 at 1000 °C. Middle-REE partitioning is close to unity for the whole investigated temperature range. Different empirically determined zircon/garnet partition coefficients from granulites and ultra-high temperature granulites can potentially be explained by the experimentally determined change of partitioning as a function of temperature. These data can assist in establishing equilibrium between garnet and zircon zones in natural rocks, and in the construction of detailed pressure–temperature–time paths in high-grade metamorphic rocks.

Phase relationships and transport in Ti-, Ce- and Zr-substituted lanthanum silicate systems

The solubility of Ti 4+ in the lattice of apatite-type La 9.83Si 6− x Ti x O 26.75 corresponds to approximately 28% of the Si-site density. The conductivity of La 9.83Si 6− x Ti x O 26.75 ( x = 1–2) is predominantly oxygen-ionic and independent of the oxygen partial pressure in the p(O 2) range from 10 −20 to 0.3 atm. The electron transference numbers determined by the modified faradaic efficiency technique are lower than 0.006 at 900–950 °C in air. The open-circuit voltage of oxygen concentration cells with Ti-doped silicate electrolytes is close to the theoretical Nernst value both under oxygen/air and air/10%H 2–90%N 2 gradients at 700–950 °C, suggesting the stabilization of Ti 4+ in the apatite structure. Titanium addition in La 9.83Si 6− x Ti x O 26.75 ( x = 1–2) leads to decreasing ionic conductivity and increasing activation energies from 93 to 137 kJ/mol, and enhanced degradation in reducing atmospheres due to SiO volatilization. At p(O 2) = 10 −20 atm and 1223 K, the conductivity decrease after 100 h was about 5% for x = 1 and 17% for x = 2. The solubility of Zr 4+ in the La 9.83Si 6− x Zr x O 26.75 system was found to be negligible, while the maximum concentration of Ce 4+ in La 9.4− x Ce x Si 6O 27− δ is approximately 5% with respect to the number of lanthanum sites.

Thermodynamic evaluation of the C−Co−W−Hf−Zr system for cemented carbides applications

Cemented carbides consist of hard carbide particles of hexagonal WC and often also of cubic carbides cemented together in a binder consisting of mainly cobalt (Co). A thermodynamic evaluation of the cubic carbide formers hafnium (Hf) and zirconium (Zr) in cemented carbides has been done. Both thermodynamic evaluations of lower-order systems and experimental investigations have been performed. The new experimental information was necessary for a satisfactory thermodynamic description because there is a lack of earlier experiments of this alloy system. The assessment work with the C-Co-W-Hf-Zr system has resulted in a satisfactory description of the thermodynamic properties compared with the experimental values. This work has been done by combining a new assessment of the CoHf and CoZr systems with already assessed investigations of the Hf-C and Zr-C systems. New experimental information in higher-order systems has been used to improve the thermodynamic descriptions and to verify the reliability of the assessments. The main results of the experimental work are measurements of the composition of the cubic carbide in selected equilibria; measurements of the temperatures of the L+fcc+WC+graphite and L+fcc+WC+M6C equilibria in the C-Co-Hf, C-Co-Zr, and C-Co-W-X (X=Hf and Zr) systems; and measurements of the solubility of Hf and Zr in liquid cobalt. Detailed comparisons between calculated and experimental data are presented.