Thermodynamic calculations of Fe-Zr and Fe-Zr-C systems

Thermodynamic calculations of Fe-Zr and Fe-Zr-C systems have been performed using the Thermo-Calc software based on an extensive amount of experimental data, including the thermodynamic measurements and available phase diagram information. The calculated thermodynamic properties and phase diagram in the Fe-Zr system account for the experimental data reasonably, while the calculated solubility of ZrC in γFe in the Fe-Zr-C system is a little smaller than the only experimental data by Narrita; to clear up this discrepancy, further investigations on the Fe-Zr-C as well as the Zr-C systems are needed.     

A 700-GHz SIS antipodal finline mixer fed by a Pickett-Potter horn-reflector antenna

We report the successful operation of a superconductor-insulator-superconductor (SIS) finline mixer operating near the superconducting energy gap of Nb. The mixer employs a new type of Pickett-Potter horn-reflector (PPHR) antenna, which exhibits low sidelobes and low cross-polarization levels, and yet is easy to fabricate. The SIS tunnel junction and all of the integrated superconducting tuning circuits are fabricated from Nb using planar-circuit technology. The mixer employs an antipodal finline section, deposited on one side of a quartz substrate, which transforms the high impedance of the waveguide (/spl ap/300 /spl Omega/) to the low impedance of the microstrip line (/spl ap/20 /spl Omega/). The Nb/Al-oxide/Nb tunnel junction is fabricated at the same time as the finline circuit. In this paper, we describe the design and testing of the mixer, and pay particular attention to the electromagnetic design of the PPHR antenna. We investigate the noise temperature and gain of the mixer over 642-714 GHz, and analyze the experimental results using rigorous theories that were developed specifically for the purpose. Our investigation demonstrates that finline mixers have good performance both below and above the superconducting energy gap.     

Oxidation of Au4Al in un-moulded gold ballbonds after high temperature storage (HTS) in air at 175 °C

BGA devices with 10,000 Å thick Al–1%Si–0.5%Cu pad metallisation were ballbonded with an experimental 4 N gold wire and subjected to HTS (high temperature storage) in air at 175 °C for up to 2000 h. As far as 1000 h pull strengths were normal with failure occurring in the neck but at 1500 and 2000 h all balls lifted away the Si chip. Cross-sections of devices aged to 1000 h showed a relatively thin upper layer of Au₄Al adjacent to the ball and beneath it a thicker layer believed to be another form of Au₄Al that forms by phase transformation of Au₈Al₃. However, in ballbonds subjected to 1500 and 2000 h HTS, cross-sections show that both layers of Au₄Al transformed into new microstructures, the upper Au₄Al layer into an oxide scale and the lower Au₄Al compound into a two-phase microstructure of gold precipitates in a dark oxide matrix. Ball lifts occurred by separation between the scale on the underside of the ball and the two-phase microstructure adhered to the chip. The in situ phase transformation of the lower Au₄Al compound appears consistent with internal oxidation. The Au₈Al₃ compound present at the ballbond periphery under the inner chamber did not appear to appear affected by HTS. It was concluded that the root cause of ball lifts very low adhesion between the new microstructures derived from the upper and lower layers of Au₄Al.     

Critical review of conservation equations for two-phase flow in the U.S. NRC TRACE code

The field equations for two-phase flow in the computer code TRAC/RELAP Advanced Computational Engine or TRACE are examined to determine their validity, their capabilities and limitations in resolving nuclear reactor safety issues. TRACE was developed for the NRC to predict thermohydraulic phenomena in nuclear power plants during operational transients and postulated accidents. TRACE is based on the rigorously derived and well-established two-fluid field equations for 1-D and 3-D two-phase flow.It is shown that:

• (1) 

  The two-fluid field equations for mass conservation as implemented in TRACE are wrong because local mass balances in TRACE are in conflict with mass conservation for the whole reactor system, as shown in Section 3.1.

• (2) 

  Wrong equations of motion are used in TRACE in place of momentum balances, compromising at branch points the prediction of momentum transfer between, and the coupling of, loops in hydraulic networks by impedance (form loss and wall shear) and by inertia and thereby the simulation of reactor component interactions.

• (3) 

  Most seriously, TRACE calculation of heat transfer from fuel elements is incorrect for single and two-phase flows, because Eq. (3-4) of the TRACE Manual is wrong (see Section 5.2).

• (4) 

  Boundary conditions for momentum and energy balances in TRACE are restricted to flow regimes1 with single-phase wall contact because TRACE lacks constitutive relations for solid–fluid exchange of momentum and heat in prevailing flow regimes.

Without a quantified assessment of consequences from (3) to (4), predictions of phasic fluid velocities, fuel temperatures and important safety parameters, e.g., peak clad temperature, are questionable.Moreover, TRACE cannot predict 3-D single- or two-phase flows because:

• (5) 

  incorrectly averaged equations are used for 3-D predictions,

• (6) 

  fluid shear is ignored but needed to predict counter-current flows with the two-fluid model, and

• (7) 

  fictitious body forces and fictitious distributed mass and heat sources are used to replace contact forces at the wall, mass injection and wall heat fluxes in 3-D mass, momentum and energy equations for both phases. No modeling error estimates are given in the TRACE Manual.

• (8) 

  Imposed perfect mixing in every control volume causes artificial damping and disables TRACE to track reliably propagation of thermal and kinematic disturbances, thereby adversely affecting the prediction of nuclear fuel temperature.

• (9) 

  According to its manual, TRACE relies on numerical diffusion far greater than physical dissipation by turbulence, to solve TRACE's ill-posed field equations and to compensate for missing fluid shear. TRACE with scale-sensitive numerical diffusion is tuned to match data from small-scale experiments. TRACE is therefore not reliable for analyzing full-size power plants. Numerical diffusion could also reduce the ability of TRACE to predict the onset of instability for reactors or test facilities entering large power and flow oscillations.

Agreements of TRACE code results with experimental data from test facilities with isolated full-size components or with data from reduced-size integral-effect tests may be achieved by adjusting numerous coefficients, some of them scale-dependent (i.e., by tuning with documented non-physical coefficients in momentum balances, by spurious time-averaging (through time step adjustment) of algebraic boundary conditions, by built-in, non-physical space grid tuning in momentum balances and in mixture level predictions). Such results may not be applied reliably to full-size systems with realistic interactions between reactor components. TRACE may not be applicable to predict the outcome of postulated accidents for which validations are not possible (e.g., Anticipated Transients without Scram).New experimental techniques are needed first for closure of the two-fluid model. A new approach to TRACE modeling is needed. Recommendations are given for improved code documentation.     

Deposition of thin titanium–copper films with antimicrobial effect by advanced magnetron sputtering methods

The antibacterial effect of thin titanium–copper (Ti–Cu) films combined with sufficient growth of human osteoblastic cells is reported in the paper. Thin Ti–Cu films were prepared by three different plasma-assisted magnetron sputtering methods: direct current magnetron sputtering (dc-MS), dual magnetron sputtering (dual-MS) as well as dual high power impulse magnetron sputtering (dual-HiPIMS). The antimicrobial effect is caused by copper released from the metallic Ti–Cu films, which was measured by atomic absorption spectroscopy (AAS). The copper release is influenced by the chemical and physical properties of the deposited films and was investigated by X-ray diffractometry and X-ray reflectometry (GIXD and XR) techniques. It was found that, within the first 24 h the amount of Cu released from dual-HiPIMS films (about 250 μg) was much higher than from dc-MS and dual-MS films. In vitro planktonic growth tests on Ti–Cu surfaces for Staphylococcus epidermidis and S. aureus demonstrated the killing of both bacteria using the Ti–Cu films prepared using the dual-HiPIMS technique. The killing effects on biofilm bacteria were less obvious. After the total release of copper from the Ti–Cu film the vitality of exposed human osteoblast MG-63 cells increased significantly. An initial cytotoxic effect followed by the growth of osteoblastic cells was demonstrated. The cytotoxic effect combined with growth of osteoblastic cells could be used in joint replacement surgery to reduce the possibility of infection and to increase adoption of the implants.     

A transmission electron microscopy study of the mechanisms of strengthening in heat-treated Co-Cr-Mo-C alloys

Microstructures produced in the Co-Cr-Mo-C alloy H.S.21 were observed by transmission electron microscopy in cast specimens following solutionizing at 1230°C and aging at 650°C and in low-carbon wrought specimens following solutionizing and aging at 650°C and 750°C. In all cases, aging was found to promote the formation of fcc stacking faults and to cause an initial martensitic transformation from the fcc phase to a heavily faulted hep structure. Precipitate formation was observed in hcp areas of the cast material after 20 h at 650°C and in hcp areas of wrought material after 20 h at 750°C. Prolonged aging at 750°C produced a transformation in the hcp structure of wrought specimens, with a relatively fault-free structure replacing the heavily faulted martensitic form. Interruption of fcc slip by both fcc stacking faults and bands of hcp phase was found to be the principal strengthening mechanism activated by aging. Precipitate formation in the hcp plays an increasingly significant role as aging time is increased. This microstructural information is used to explain the observed tensile properties of these alloys after the heat treatments mentioned.     

The static contact angle hysteresis obtained by different experiments for the system PTFE/water

Different experimental methods have been used to determine the static contact angle hysteresis of the system polytetrafluoroethylene/water and the results compared. While the Wilhelmy plate method is not influenced by methodical variations, contact angles determined by the sessile drop and the pendant bubble methods vary with the drop or bubble diameter up to a minimal diameter d_K of the contact area with the solid. This condition seems to be a universal one and should always be checked to ensure that the measured values are comparable. Contact angles calculated from the geometrical parameters of a drop or bubble should be used with care. The surface energetic characters for the PTFE/water are δθ = 19.5°, θ_{a, e} = 108.5° and θ_{r, e} = 89°.