Heat transfer in nitrogen-methane mixtures under pressure with film boiling

Heat transfer from a horizontal cylinder into nitrogen-methane mixtures (0 to 100 molar per cent) was studied in the film boiling range at 0.2 and 2.8 MPa. At constant heat flux density ΔT decreases with increasing methane content.Heat transfer from a horizontal cylinder into nitrogen under pressure was studied in the bubble boiling region, in addition to the film boiling range, to provide a connexion between our experiments made on the horizontal surface, q_max at cylinder ~ 0.7 q_max at horizontal surface. For the relation $\text{q}\text{?}{}_{\mathrm{<mtext>max</mtext>}}\text{/}\text{q}\text{?}{}_{\mathrm{<mtext>min</mtext>}}$ at cylinder a value of ten was obtained at all pressures     

On the determination of the surface free energy of quartz

Studies of water vapor adsorption on quartz by the method analogous to the dynamic gas chromatography step profile method are described. The adsorption was determined by changes in the capacitance of the capacitor (detector) between the coverings of which the quartz powder was placed. Prom the adsorption isotherm the film pressure π of the water film on quartz were determined, obtaining $\text{π}{}_{\max }\text{= 380}\text{erg}\text{cm}{}^2$.An interpretation of the π changes in relation to the film thickness and the kind of wetting process has been proposed. It is concluded that the characteristic film pressure values result from the work of spreading, immersional and adhesional wetting and correspond to thicknesses of about 2, 3 and 4 statistical water monolayers, respectively. The maximum π value, however, probably corresponds to the work of quartz- water adhesion + water cohesion work. On the basis of the thus determined values of π_s, π₁, and π_max, the value of the polar component γ_q^p of the quartz surface free energy was determined, using the value $\text{γ}{}_{\mathrm{q}}{}^{\mathrm{p}}\text{= 76}\text{erg}\text{cm}{}^2$. The calculated average of the γ_q^p value equals 115 $\text{erg}\text{cm}{}^2\text{2}$.     

Analysis of a turbulent boundary layer subjected to a strong adverse pressure gradient

We define two non-dimensional parameters $\text{Λ =}\text{τ}{}_{\mathrm{w}}\text{p}{}_{\mathrm{x}}\text{δ}$ and $\text{R}{}_{\mathrm{p}}\text{=}\text{U}{}_{\mathrm{p}}\text{δ}\text{ν}$ where τ_w is the wall stress, p_x(?0) is the pressure gradient to which the turbulent boundary layer (of thickness δ) is subjected, ν is the kinematic viscosity, $\text{U}{}_{\mathrm{p}}\text{= (}\text{νp}{}_{\mathrm{x}}\text{p}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ is a characteristic velocity and p is the density. The limit corresponding to the strong adverse pressure gradient is formulated as Λ → 0, R_p → ∞, ΛR_p finite. Using appropriate inner and outer asympcotic expansions, both above a wall layer possibly scaling with τ_w and ν, it is found by an application of Millikan's argument that there is an inertial sublayer where the streamwise velocity distribution obeys a half-power law, whose slope depends on Λ, and intercept on ΛR_p. Indeed comparison with available experimental data shows the inner law to be well represented by $\text{u}\text{Up}\text{= (3.5 + 19Λ)(}\text{yU}{}_{\mathrm{p}}\text{ν}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{+ 2.5ΛR}{}_{\mathrm{p}}$. The outer flow obeys a generalized defect law; use of constant eddy viscosity closure yields results in good agreement with experiment.     

Application of the ac potential drop technique to the determination of R curves of tough ferritic steels

The suitability of the AC potential drop (ACPD) technique for detecting crack initiation and monitoring crack extension during slow stable growth has been investigated using side-grooved Charpy size specimens tested in three point bending. For ferritic steels with widely differing initiation and growth characteristics, the potential drop (PD) vs clip gauge opening displacement (CGOD) trace shows consistent behaviour, the most important feature being the occurrence of a minimum around the point of crack initiation. At low current frequency (150 Hz), there is close agreement between $\text{δ}{}_{\min }$, the COD corresponding to the minimum of the PD/CGOD trace and $\text{δ}{}_{\mathrm{i}}$ estimated by the recommended multispecimen technique for $\text{δ}{}_{\mathrm{i}}$ ranging from 0.02 to 0.37mm. In steels with $\text{δ}{}_{\mathrm{i}}$ less than about 0.1 mm, the minimum occurs at the same value of δ for both low (150 Hz) and high (4.7 kHz) frequencies. However, for steels with higher toughness, the minimum shifts to lower δ values as the frequency is increased. It appears that for any steel, there is a maximum frequency below which the minimum corresponds to $\text{δ}{}_{\mathrm{i}}$. It is demonstrated that the ACPD method can be employed to determine $\text{R}$ curves from single specimens.     

Stability of the perovskite phase LaBO3 (B = V,Cr, Mn,Fe, Co,Ni) in reducing atmosphere I. Experimental results

The chemical stability of perovskites LaBO₃ where B = V, Cr, Mn, Fe, Co, Ni was studied by thermogravimetry at 1000°C in gas mixtures of $\text{CO}{}_2\text{H}{}_2$, $\text{O}{}_2\text{CO}{}_2$ and $\text{O}{}_2\text{Ar}$ at 1 bar.The stability limits of the perovskite phases expressed in terms of -log Po₂★ (Po₂★ = critical oxygen partial pressure in bar) were for LaCrO₃ and LaVO₃ (greater than 21.1), LaFeO₃ (16.95), LaMnO₃ (15.05), LaCoO₃ (7.0) and for LaNiO₃ (～0.6). The changes in standard enthalpy ΔH° and entropy ΔS° of the following reactions were obtained.$\text{LaVO}{}_4\text{=}\text{LaVO}{}_3\text{+}\text{1}\text{20}{}_2\text{δ=328}\text{kJ}\text{mol}\text{°=135}\text{J}\text{mol·deg.}$,$\text{LaMnO}{}_3\text{=}\text{1}\text{2}\text{La}{}_2\text{O}{}_3\text{+}\text{MnO}$     

Dependence of the crystallization rate of vacuum-deposited amorphous antimony films on the film thickness

The crystallization rate of vacuum-deposited amorphous antimony (a-Sb) films was investigated as a function of the film thickness d. Experimental plots of the observed growth rate v against d^-1 for systems such as Sb/glass and Sb/Ge show that the relationship between v and d^-1 are convex towards the origin. Such a feature is well interpreted by a model in which

$\text{v=}\text{1}\text{d}\text{∫}\text{d}\text{0}\text{u}\text{d}\text{z}$

where u is the actual growth rate of the crystallite in the a-Sb film and z the distance from the film surface adjacent to the substrate. The quantity u is assumed to vary as follows: u = αzⁿ + u_s when 0 ? z ? d_s0, u = u_i when d_s0 ? z ? d ? d_v0 and u = β(d ? z)ⁿ + u_v, when d ? d_v0 ? z ? d where $\text{α =}\text{(u}{}_{\mathrm{i}}\text{? u}{}_{\mathrm{<mtext>s</mtext>}}\text{)}\text{d}{}_{\mathrm{<mtext>s</mtext><mtext>0</mtext>}}{}^{\mathrm{n}}$, $\text{β =}\text{(u}{}_{\mathrm{i}}\text{? u}{}_{\mathrm{<mtext>v</mtext>}}\text{)}\text{d}{}_{\mathrm{<mtext>v</mtext><mtext>0</mtext>}}{}^{\mathrm{n}}$, d_s0 and d_v0 are thickness of surface regions near the substrate and the vacuum respectively, u_i is the growth rate inside the film, u_s and u_v are the rates at surfaces adjacent to the substrate and the vacuum respectively and n an adjustable numerical parameter. As a typical example, for the Sb/Ge system at 30°C, u_i, u_s and u_v are estimated to be 139 μm s^-1, 25.4 μm s^-1 and 0.2 μm s^-1 respectively and d_s0 and d_v0 to be 133 Å and 143 Å respectively with n = 3.     

Temperature characteristics and thermal instability in composite ac superconductors

The evolution of thermal instability in a superconducting system which is operating in a normal state can lead to severe damage (burnout) of the system.On the basis of numerical calculations, the temperature characteristics of a uniform, helium-cooled, ac superconductor operating in a normal state were analyzed. The system is thermally stable as long as the current is lower than the maximum equilibrium current $\text{i}{}_{\mathrm{～}}{}^1$, or its frequency is higher than the minimum equilibrium frequency Ω¹. Near the limiting values $\text{i}{}_{\mathrm{～}}{}^1$ and Ω¹, a narrow region of parameters has been found where the conductor characteristics change drastically. According to the specific changes in the temperature characteristics in this region, the approach of dangerous values $\text{i}{}_{\mathrm{～}}{}^1$ and Ω¹ can be detected beforehand.Peculiarities of the conductor's behaviour in this region are explained and the limiting equilibrium ac cycles described. The onset of thermal instability as the superconductor overheats is also studied.The findings are well supported by experimental evidence.     

Interactions of Cr2+ with the F− ligands in CdF2:Cr2+

Superhyperfine structure s.h.f.s. resulting from the Cr²⁺ - F^? interaction was studied in Cr²⁺ doped CdF₂ crystals. The s.h.f.s. observed can be described with by the following spin-Hamiltonian

$\text{H}\text{=}\text{g}{}_{\mathrm{eff}}\text{β}\text{HS}{}_{\mathrm{z}}\text{+ST}{}_{\mathrm{i}}\text{I+ST}{}_{\mathrm{j}}\text{I}$

The constants calculated are $\text{T}{}_{\mathrm{i\perp }}\text{≈}\text{T}{}_{\mathrm{i}}\text{= 50}\text{MHz}$$\text{T}{}_{\mathrm{j\perp }}\text{≈}\text{T}{}_{\mathrm{j}}\text{= 5}\text{MHz}$. The measurements were made with an ESR spectrometer at X band at 4.2 OK.     

Thermal expansion — An empirical correlation

The average thermal expansion coefficient (α_L) of a large variety of cubic and close-packed materials is shown to depend upon the coincidence of preferred orbital extension and site symmetry as well as melting point (Mp in °C). The product $\text{α}{}_{\mathrm{<mtext>L</mtext>}}\text{M}{}_{\mathrm{<mtext>p</mtext>}}\text{? 0.016}$ tends to hold for close-packed structures and $\text{α}{}_{\mathrm{<mtext>L</mtext>}}\text{M}{}_{\mathrm{<mtext>p</mtext>}}\text{? 0.027}$ for rectilinear arrays. Deviations occur when orbital extension tends to sp³ symmetry for an ion in an octahedral site or the site symmetry is reduced to tetrahedral or planar.     

A new method of sulfur vapor pressure control and its application to the V-S system

A new apparatus for obtaining partial pressure of sulfur was devised by using liquid sulfur and carrier gas of nitrogen. This successfully works in the range of ～10^?4 to ～1 atm of Ps₂ at any temperature higher than about 400°C up to about 1000°C. As an application of it, the equilibrium study of V-S system was done at 800°C. Two phases V₃S₄ and V₅S₈, each having homogeneity range, were found while no existence of the V₂S₃ phase could be detected thermodynamically and X-ray crystallogrpahically at this temperature. The standard free energy of following reaction, $\text{VS}{}_{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}\text{+}\text{2}\text{15}$$\text{S}{}_2\text{=}\text{VS}\text{8}\text{5}$, was calculated by considering the transition-Ps₂ and the activities and · ΔG° (1073K) = ?1150 cal·mole^?1was obtained with an estimated uncertainty of ± 100 cal to the above reaction.     

Crack initiation from a sharp notch and stretched zone

The “crack tip COD” at the fracture initiation mainly consists of the stretched zone, the new surface which appeared due to the slip deformation at the notch tip. Therefore, the COD or the stretched zone width at the fracture initiation is a very important parameter which reflects the notch tip behavior until fracture initiation.In the case of fibrous crack initiation, the stretched zone width ($\text{S}{}_{\mathrm{i}}$) and COD ($\text{δ}{}_{\mathrm{i}}$), where $\text{δ}{}_{\mathrm{i}}$ ≈ √2 $\text{S}{}_{\mathrm{i}}$, take almost constant values regardless of temperature, specimen geometry, preloading (if the total $\text{δ}{}_{\mathrm{i}}$ is taken), slit angle (in the case of mixed mode condition) and so on, while, in the case of cleavage fracture initiation, COD and the stretched zone width take various values between the value at the fibrous crack initiation ($\text{δ}{}_{\mathrm{i}}$ or $\text{S}{}_{\mathrm{i}}$) and almost zero, depending on temperature and plastic constraint.     

A simple model of stress intensity range threshold and crack closure stress

The cyclic stress intensity threshold (Δ$\text{K}{}_{\mathrm{TH}}$) below which cracks will not propagate varies with length for short cracks. A model is proposed which relates Δ$\text{K}{}_{\mathrm{TH}}$ to the crack closure stress arising from fracture surface roughness. This is used to predict a variation in Δ$\text{K}{}_{\mathrm{TH}}$ with crack length for surface cracks in Ti 6Al-2Sn-4Zn-6Mo alloy, based upon measured values of crack opening displacement arising from roughness. The predicted variation in Δ$\text{K}{}_{\mathrm{TH}}$ with crack length is found to be similar to that obtained from the empirical model of Δ$\text{K}{}_{\mathrm{TH}}$ proposed by El Haddad et al.[5]. The application of the new model to estimate the value of crack closure stress arising from crack tip plasticity for short surface cracks is also discussed.     

Studies on crack growth rate under high temperature creep,fatigue and creep-fatigue interaction—I: On the experimental studies on crack growth rate as affected by aσg,σg and temperature

Many experimental studies have been reported on the measurements of crack growth rate and the observation of crack growth behaviour under high temperature creep, fatigue and creep-fatigue interaction in literatures. However, many of them have been done in air atmosphere. Furthermore, in many of them the measurements of the crack growth rate have been carried out by interrupting intermittently the running of the testing machine. In such experiments the complex effects due to the atmosphere, the interruption period and the corresponding unloading operation for the crack length measurement might have been involved.In the present paper in order to eliminate such effects, series of experimental studies on the crack growth behaviour under creep, fatigue and creep-fatigue interaction conditions on 304 stainless steel have been carried out by using high temperature microscope and observing the crack length continuously during running the test without interruption in vacuum of 10^?5mm Hg.Among the results, it was found that crack growth rates on a time basis, $\text{da/dt}$, under high temperature creep and creep-fatigue interaction conditions can not be described in terms of solely elastic stress intensity factor $\text{k}{}_{\mathrm{i}}$ or only net section stress σ_net, both independent of gross section stress σ_g. The relation between crack growth rate and stress intensity factor under high temperature fatigue condition changes with some trend according to gross section stress at lower $\text{K}{}_{\mathrm{I}}$ level and it can be approximately described in terms of stress intensity factor $\text{K}{}_{\mathrm{I}}$ only, at higher $\text{K}{}_{\mathrm{I}}$ level. The threshold stress intensity factor and the threshold net section stress under high temperature creep, fatigue and creep-fatigue interaction conditions appears to be almost independent of temperature.     

Crystal chemistry of lithium in octahedrally coordinated structures III. A new structure-type in the system K2O:Li2O:TiO2 (KxLixTi4−x2O8)

A new compound in the system K₂O:Li₂O:TiO₂ corresponding to the formula $\text{K}{}_{\mathrm{<mtext>x</mtext>}}\text{Li}{}_{\mathrm{<mtext>x</mtext>}}\text{Ti}{}_{\mathrm{<mtext>4?</mtext><mtext>x</mtext><mtext>2</mtext>}}\text{O}{}_8$ was found to be orthorhombic with a=3.821, b=15.921, c=2.973A space group Cmcm. The similarity between this unit cell and those of Rb_xMn_xTi_2?xO₄ and FeO(OH) has been used to predict the structure of this new phase. From the composition of this phase and that of the hollandite and ramsdellite phases in this system, it can be deduced that some of the Li⁺ ions occur in the tunnels as well as in octahedral coordination substituting for titanium.     

On the cofactors of zero-sum matrices of higher nullity

A generalization of the equicofactor property of zero-sum matrices is considered. Let Y be a square matrix of order m · n. Consider partitioning of Y to into m² square submatrices Y(i,j); ij = 1,2,3.,m resulting from partitioning of the sets of rows and columns of into m equal subsets, each of which contains n successive rows or columns. Subbpose that each of these submatrices has the zero-sum property and choose an arbitrary element y_{ji, ki} in each of the diagonal submatrices Y(i,i); i = 1,2,3.,m. It is shown in the paper that all the cofactors of the products

in the expansion of the determinant |Y| are equal     

Flux-pinning by superconductor-normal boundaries

It is shown that flux-pinning by Nb₃Sn-Cu interfaces in in-situ superconducting composites can lead to a pinning function of the form $\text{F}{}_{\mathrm{p}}\text{∝ b}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1 ? b)}{}^2$, as is found experimentally.     

Fatigue crack growth rate under full yielding condition for 15CDV6 steel

Strain fatigue crack growth rate was studied using center cracked specimens for 15CDV6 steel tempered at 200°C after quenching by means of the method which deflections were controlled to a sloping load vs deflection line. Cyclic $\text{J-}\text{integral}$ values estimated from load vs deflection hysteresis loops are correlated with the growth rate. The relationship between them can be expressed by a simple power function $\text{da/dN = 2.5 × 10}{}^{\mathrm{?4}}\text{(ΔJ)}{}^{1.38}$ The plastic portion Δ$\text{J}{}_{\mathrm{p}}$ in $\text{J-}\text{integral}$ is exponentially increased as the deflection increases, while the peak value of the elastic portion Δ$\text{J}{}_{\mathrm{e}}$ appears as the deflection varies. These relations may provide a convenient way to use $\text{J-}\text{integral}$ in engineering practice. A concept is proposed that “high strain rate induces cleavage”. The critical value of the strain rate for the steel tested is 10^?4/sec. If the strain rate is higher than this value, cleavage predominates on the fracture surface. On the other hand, if it is lower than this value, dimples will prevail.     

Oxygen dissociation pressure of ndmno3

Measurement of oxygen partial pressures at the lower phase boundaries in neodymium manganite have been made in the temperature range 1173–1473 K. The electrical conductivity method was used to detect the decomposition reaction with flowing H₂- CO₂ mixtures in order to fix the oxygen potential. The oxygen partial pressure of dissociation over the compound NdMnO₃: NdMnO₃ (s) = $\text{1}\text{2}$ Nd₂O₃ (s) + MnO (s) + $\text{1}\text{4}$ O₂ (g) is given by the equation:

$\text{log (P}{}_{\mathrm{O2}}\text{/atm) = ?}\text{(2.762 ± 0.019) · 10}{}^4\text{T}\text{+ (9.02 ± 0.14)}$

The molal enthalpy and entropy of the reaction for the abovementioned reaction were determined as ΔH^O_R,1323 = 132.2 KJ mol^?1 and ΔS^O_R,1323 = 43.2 J mol ^?1K^?1, respectively.     

Thermodynamic investigations of ternary lithium-transition metal-oxygen cathode materials

The reaction of lithium with three transition metal oxides (MnO, LiFeO₂, and LiCoO₂) has been investigated by an equilibrium electrochemical technique in cells of the type:

$\text{(?) Al, Li}{}_{0.9}\text{Al/LiClKcl}{}_{\mathrm{(l)}}\text{/[Li}{}_{\mathrm{x}}\text{MO}{}_{\mathrm{y}}\text{] (+)}$

Each system exhibits long constant voltage plateaus characterized by three-phase equilibria. The compositional range of reaction of lithium with MnO is 2.0 equivalents, whereas 3.0 equivalents may be reacted with the compounds LiFeO₂ and LiCoO₂. The ternary iron and cobalt oxide systems have been found to be kinetically fast (10–15 mA/cm²) and reversible at 400°C. The free energies of formation ΔG_f^o of Li₅FeO₄, LiFeO₂, and LiCoO₂ were calculated and found to be ?399.88, ?154.18, and ?131.62 kcal/mole, respectively. Replacement of sulfide with oxide cathode materials might reduce the high temperature lithium battery corrosion problems currently associated with sulfur-containing cells.     

Mechanics of fatigue crack propagation by crack-tip plastic blunting

The power relation between the fatigue crack propagation rate $\text{d}\text{a/}\text{d}\text{N}$ and the $\text{J}$ integral range $\text{ΔJ}$ was obtained for OFHC copper, 0.04%C steel and stainless steel (Type 304). The physical meaning of the relation was investigated based on the observation of the crack opening behavior and fractography. The striations, whose spacing was equal to $\text{d}\text{a/}\text{d}\text{N}$, confirm crack-tip blunting as being an operating mechanism for crack growth. $\text{d}\text{a/}\text{d}\text{N}$ was expressed as a power function of the crack-tip opening displacement (Δ CTOD), $\text{d}\text{a/}\text{d}\text{N = A(Δ}\text{CTOD}\text{)}{}^{\mathrm{p}}$, where $\text{p}$ was larger than one. The major portion of Δ CTOD contributes to crack growth at high rates, while a considerable fraction of Δ CTOD occurs behind the crack tip at low rates. Δ CTOD is correlated to $\text{ΔJ}$ divided by the yield strength σ'_Y through the equation,$\text{Δ}\text{CTOD}\text{= B(ΔJ/σ}{}_{\mathrm{Y}}\text{′)}{}^{\mathrm{q}}$, where $\text{q}$ is nearly equal to one for 0.04%C steel and is larger than one for copper. The variation of $\text{q}$ with material was explained based on the observed distribution of the crack opening displacement. The final equation for fatigue crack growth is given as $\text{d}\text{a/}\text{d}$N = A · B^p(ΔJ/σ_Y′)^pq. When the shape of the crack tip opening is geometrically similar, both $\text{p}$ and $\text{q}$ are one. For a general case, both are larger than one, yielding the exponent of the $\text{d}\text{a/}\text{d}\text{N-ΔJ}$ relation deviating from 1 up to 2.3.