Hydrogen Solubility in Pd/V2O5 Composites Formed by Internal Oxidization and Hydrogen Isotherms in Un-oxidized Pd-V Alloys

Pd-V alloys were internally oxidized (IOed) resulting in composites of nano-particle V₂O₅ precipitates within Pd matrices. These composites were found to interact with H₂ to form hydrogen bronzes, H _x V₂O₅, within the Pd matrix where x can vary between 1.65 and 2.20. Relative partial molar enthalpies for H intercalation into the H-bronze within the Pd/V₂O₅ composite were measured calorimetrically as a function of the H content of the bronze, and these molar enthalpies decrease in magnitude from about ?75 to ?20 kJ/mol H as the H content increases. H₂ isotherms have also been measured in disordered, fcc Pd_0.96V_0.04, Pd_0.945V_0.055, and Pd_0.93V_0.07 alloys from 273 K to 343 K (0 °C to 70 °C). Thermodynamic data have been derived from these isotherms. The relative partial molar enthalpies at infinite dilution of H, $\Updelta H_{\hbox{H}}^\circ,$ increase with atom fraction V, X $_{\hbox{V}},$ while the corresponding standard partial molar entropies, $\Updelta \hbox{S}_{\hbox{H}}^\circ,$ decrease with $\hbox{X}_{\hbox{V}}.$ The first-order term, g₁, in a polynomial expansion of the excess or non-ideal chemical potential of H in r = H-to-metal, mol ratio, decreases in magnitude with $\hbox{X}_{\hbox{V}}$ at a given temperature.     

Effect of Tungsten on Primary Creep Deformation and Minimum Creep Rate of Reduced Activation Ferritic-Martensitic Steel

Effect of tungsten on transient creep deformation and minimum creep rate of reduced activation ferritic-martensitic (RAFM) steel has been assessed. Tungsten content in the 9Cr-RAFM steel has been varied between 1 and 2 wt pct, and creep tests were carried out over the stress range of 180 and 260 MPa at 823 K (550 °C). The tempered martensitic steel exhibited primary creep followed by tertiary stage of creep deformation with a minimum in creep deformation rate. The primary creep behavior has been assessed based on the Garofalo relationship, \( \varepsilon = \varepsilon_{\text{o}} + \varepsilon_{\text{T}} [1-\exp (-r^{\prime} \cdot t)] + \dot{\varepsilon }_{\text{m}} \cdot t \) , considering minimum creep rate \( \dot{\varepsilon }_{\text{m}} \) instead of steady-state creep rate \( \dot{\varepsilon }_{\text{s}} \) . The relationships between (i) rate of exhaustion of transient creep r′ with minimum creep rate, (ii) rate of exhaustion of transient creep r′ with time to reach minimum creep rate, and (iii) initial creep rate \( \dot{\varepsilon }_{\text{i}} \) with minimum creep rate revealed that the first-order reaction-rate theory has prevailed throughout the transient region of the RAFM steel having different tungsten contents. The rate of exhaustion of transient creep r′ and minimum creep rate \( \dot{\varepsilon }_{\text{m}} \) decreased, whereas the transient strain ? _T increased with increase in tungsten content. A master transient creep curve of the steels has been developed considering the variation of \( \frac{{\left( {\varepsilon - \varepsilon_{\text{o}} } \right)}}{{\varepsilon_{\text{T}} }} \) with \( \frac{{\dot{\varepsilon }_{\text{m}} \cdot t}}{{\varepsilon_{\text{T}} }} \) . The effect of tungsten on the variation of minimum creep rate with applied stress has been rationalized by invoking the back-stress concept.     

Effects of Cooling Rate and Solute Content on the Grain Refinement of Mg-Gd-Y Alloys by Aluminum

The effect of Al additions on grain refinement of Mg-Gd-Y alloys with different solute contents at different cooling rates has been investigated. For all alloys, significant grain refinement was due to the formation of Al₂(Gd _x Y_1?x ) nucleant particles. The number density and size distribution of Al₂(Gd _x Y_1?x ) were affected by both solute content and the cooling rate. Grain sizes (d _gs) of Mg-Gd-Y base alloys and of Mg-Gd-Y-Al alloys were related to solute content (defined by the growth restriction factor, Q), cooling rate ( \( \dot{T} \) ), and area number density (ρ _ns) and size (d _p) of nucleant particles that can be activated. It is found that grain sizes of Mg-Gd-Y base alloys follow the relationship \( d_{\text{gs}} = a + \frac{b}{{Q\sqrt {\dot{T}} }} \) , while grain sizes of Al-refined samples follow the relationship \( d_{\text{gs}} = \frac{a'}{{\sqrt {\rho {}_{\text{ns}}} }} + \frac{b'}{{\sqrt {\dot{T}} Qd_{\text{p}} }} \) , where a, b, a′, and b′ were constants. In addition, the grain refinement effect of Al additions was more susceptible to solute content and the cooling rate than that of Zr which is regarded as the most efficient grain refiner for Mg alloys.     

Free energies of formation of WC and W2C,and the thermodynamic properties of carbon in solid tungsten

The activity of carbon in the two-phase regions W + WC and W + W₂C has been obtained from the carbon content of iron rods equilibrated with mixtures of metal plus carbide powders. From this activity data the standard free energies of formation of WC and W₂C have been calculated to be ΔG _f ⁰(WC) = -10,100 + 1.19T ± 100 cal/mole (-42,300 + 4.98T ± 400 J/mole) (1150 to 1575 K) ΔG _f ⁰(W₂C) = - 7300 - 0.56T ± 100 cal/mole (- 30,500 - 2.34T ± 400 J/mole). (1575 to 1660 K) The temperature of the eutectoid reaction W₂C = W + WC was fixed at 1575 ± 5K. Using available data for the solubility of C in solid W, the relative partial molar free energy of C in the dilute solid solution was calculated to be $$\Delta \bar G_C^\alpha {\text{ = 23,000 }} - {\text{ }}[{\text{0}}{\text{.68 }} - R\ln X_C^\alpha ]{\text{ }}T \pm 3000 cal/mole (96,200 - [2.85 - R\ln X_C^\alpha ]{\text{ }}T \pm 12,600 J$$ The heat solution of C in W obtained was \(\Delta \bar H_C^\alpha {\text{ = 23,000 }} \pm {\text{ 5000 cal/mole (96,200 }} \pm {\text{ 20,000 J/mole)}}\) and the excess entropy for the interstitial solid solution, assuming that the carbon atoms are in the octahedral sites, \(\Delta \bar S_C^\alpha {\text{ = (}}xs,i{\text{) }} = - {\text{1}}{\text{.5 }} \pm {\text{ 2 cal/deg - mole (}} - {\text{6}}{\text{.3 }} \pm {\text{ 8 J/deg - mole)}}\) .     

Stress dependence of high-temperature creep in Fe−Mo and Fe−Co alloys

The stress dependence of high-temperature creep and the alloying effects on it were investigated both in the ferromagnetic and the paramagnetic temperature regions of alpha iron and Fe?Mo and Fe?Co alloys. The steady-state creep rate, \(\dot \varepsilon _s \) , of alpha iron was found to obey a power law relationship, \(\dot \varepsilon _s \propto \sigma ^n \) (n: constant) in the temperature range above 0.5T _m (T _m : the melting temperature). The stress exponent,n, was 4.6 at all the temperatures examined. By addition of molybdenumn decreased to 3, while it remained unchanged by addition of cobalt. It seems that the change inn due to alloying is mainly attributed to the change in activation area for creep,A ^*, which results in the change in stress dependence of dislocation velocity. The magnetic transformation was found not to influence the stress dependence of \(\dot \varepsilon _s \) .     

Thermodynamics of the system NaF-AlF3. Part IV: The cryolite liquidus curve

The theory of the variation of activity of a binary compoundAXB with composition in a $$a_{A_x B} = {\text{ }}K \cdot a_A^x \cdot a_B $$ the activity coefficient should be defined as $$\gamma _{A_x B} {\text{ = }}K \cdot \gamma _A^x {\text{ }} \cdot {\text{ }}\gamma _B {\text{ = }}a_{A_x B} {\text{/(}}n_A^x {\text{ }} \cdot {\text{ }}n_B {\text{)}}$$ K is chosen so that^aA_xb is unity in the stoichiometric liquid (or, if preferred, so that γA_XB is unity). Such an activity coefficient possesses the property of approaching a limiting value at the stoichiometric composition, and the analog of Raoult’s law is^aA_xB∝ n_A ^x nB From this it follows that a plot of log (n_A ^x nB) against 1/T should show the same limiting tangent for points on both sides of the liquidus curve. Data for Na₃AlF₆ do not pass this test. With the aid of previously measured activities the discrepancy can be resolved if it be assumed that the solid material separating has a composition (2.824 ±0.005)NaF A1F₃; the calculated enthalpy of fusion of this material is 24,270 cal/gfw, and the standard deviation of the liquidus points from the least-squares line is ±2.3 deg.     

Solubility product of aluminum nitride in 3 percent silicon iron

The solubility product of aluminum nitride in 3 pct silicon iron was determined experimentally from 1273 to 1473 K with results described by the equation $$\begin{gathered} \log [pct \underline {Al} _{\alpha (3Si) } pct \underline N _{\alpha (3Si)} ] \hfill \\ = {\text{--11,900/}}T + 3.56 \hfill \\ \end{gathered} $$ whereT is in kelvins and concentrations are in weight percent. In the experiments the equilibrium distribution of nitrogen between purified gamma iron (fcc) and 3 pct silicon alpha iron (bcc) was determined between 1273 and 1523 K.     

The Solubility and Diffusivity of Fluorine in Solid Copper from Electrochemical Measurements

The solubility and diffusivity of fluorine in solid copper were determined electrochemically using the double solid-state cell $$Ni + NiF_2 \left| {CaF_2 } \right|Cu\left| {CaF_2 } \right|Ni + NiF_2 .$$ In the temperature range 757 to 920°C, the diffusivity of fluorine in solid copper was found to be $$D_F \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 9.32 \times 10^{ - 2} \exp \left( {\frac{{ - 98,910 {J \mathord{\left/ {\vphantom {J {mole}}} \right. \kern-\nulldelimiterspace} {mole}}}} {{RT}}} \right).$$ . The results obtained for the dissolution of fluorine as atoms in solid copper showed large scatter. However, the equilibrium dissolution of fluorine follows Sieverts’ law. Above the melting point (770°C) of CuF₂, the mean solubility of fluorine in solid copper, for the equilibrium Cu(s)+ CuF ₂(l), follows the relationship $$N_F^s (atom fraction) = 0.98 \exp \left( {\frac{{ - 79,500 {J \mathord{\left/ {\vphantom {J {mole}}} \right. \kern-\nulldelimiterspace} {mole}}}} {{RT}}} \right).$$      

An Insight into Slag Structure from Sulphide Capacities

The molar sulphide capacities $ C_{\text{S}}^{'} $ ?=?(mol?pct?S) ( $ P_{{{\text{O}}_{2} }} /P_{{{\text{S}}_{2} }} $ )^1/2 on four binary systems, MgO-SiO₂, CaO-SiO₂, MnO-SiO₂ and FeO-SiO₂ are elucidated so as to compare the magnitudes of the basicities of four metallic oxides and to estimate the temperature dependencies of the basicities of metallic oxides. The enthalpy changes of the reaction?2O^??=?O?+?O^2?, viz. the silicate polymerization reaction (denoted as $ \Updelta H_{(8)}^{^\circ } $ ) have been calculated from the slopes of the log $ C_{\text{S}}^{'} $ vs 1/T curves for four binary silicates. The $ \Updelta H_{(8)}^{^\circ } $ value is considered in the present work to be an index of the basicity of silicate melts. The basicities obtained on the basis of the $ \Updelta H_{(8)}^{^\circ } $ values are in the order MgO?<?CaO?<?MnO?<?FeO, which are determined by two effects; (i) ionicity of chemical bonds between metallic and oxygen ions and (ii) clustering of metallic oxides in silicates. It is also found that the basicity of the FeO-SiO₂ system is larger at higher temperatures.