The Adhesion of Maleic Anhydride on Native Aluminum Oxide: An Approach by Infrared Spectroscopy and Quantum Mechanical Modeling

The bonding between maleic anhydride, a curing agent for epoxy resins, and natively oxidized aluminum is studied by a combination of infrared spectroscopy and quantum mechanical modeling. On native aluminum oxide, maleic anhydride is hydrolyzed to maleic acid in the early stages of adhesion. The acid prefers a bridged chelate bond of one of its acid groups to two Al atoms of the metal oxide. Furthermore, a monodentate bond between a carbonyl oxygen of an acid group and an Al atom is identified. The anhydride itself shows no tendency to adhere on the native aluminum oxide. Since maleic acid is less reactive in the polymerization than the anhydride, the results imply that the chemical curing reaction could be hampered in the vicinity of the Al substrate.     

Modification of the vermont test for monitoring fat adulteration of dairy products

The Vermont test was developed for the routine screening of dairy products for vegetable fat adulteration. A slight modification of the test procedure made it more rapid and reduced costs. Gas-liquid chromatographic analysis of saponified fatty acids in the first and second Mojonnier extractions were proportional; thus, only the first extraction was needed to determine the purity of a milk lipid sample. This modification saves about 8 min/series of four samples and conserves 48% of the volume of organic solvents necessary to perform the classical Mojonnier extraction.     

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.     

The Adhesion of Maleic Anhydride on Native Aluminum Oxide: An Approach by Infrared Spectroscopy and Quantum Mechanical Modeling

The bonding between maleic anhydride, a curing agent for epoxy resins, and natively oxidized aluminum is studied by a combination of infrared spectroscopy and quantum mechanical modeling. On native aluminum oxide, maleic anhydride is hydrolyzed to maleic acid in the early stages of adhesion. The acid prefers a bridged chelate bond of one of its acid groups to two Al atoms of the metal oxide. Furthermore, a monodentate bond between a carbonyl oxygen of an acid group and an Al atom is identified. The anhydride itself shows no tendency to adhere on the native aluminum oxide. Since maleic acid is less reactive in the polymerization than the anhydride, the results imply that the chemical curing reaction could be hampered in the vicinity of the Al substrate.     

Measurement of gold ballbond intermetallic coverage

An important characteristic of gold ballbonds is intermetallic coverage (IMC), defined as the percentage of the total area on which gold aluminide compounds are formed by reaction between the gold ball and aluminium alloy metallization during thermosonic bonding. IMC measurement complements mechanical measurements such as ball pull and shear strength and in general, IMC should be maximised to aid in achieving a high degree of initial mechanical robustness so that devices can withstand subsequent processing steps and maintain high reliability. Too little IMC can result in weak bonds and erratic intermetallic growth patterns during subsequent thermal processing of bonded devices and may result in mechanical and electrical malfunction and failure. Optical microscopy of the underside of ballbonds is often used to determine IMC, but usually without consideration of certain key physical effects such as lighting, resolution and surface roughness. This paper compares the relative merits of IMC measurement by scanning electron microscopy (SEM) and optical microscopy and includes practical guidelines for the use of each technique.     

Annealing of a Cyanurate Prepolymer Adhesive on Aluminium and Gold Substrates

Two major effects are observed during annealing. First, some cyanate groups hydrolyze into carbamate structures on Al and Au. The reaction is driven by the metal surface and both hydroxyl groups and adsorbed water can be involved. On Al, where the carbamate production is most prominent, a part of the cyanate groups in the prepolymer is expected to react with substrate hydroxyl groups. The resulting carbamate coupling to the oxide provides a new chemical adhesion mechanism.

As a second effect, an unexpected strong loss of monomer molecules from the prepolymer layers is observed on both substrates at elevated temperatures. It is concluded that the monomer molecules are pushed out of the interphase layer with the substrates due to negative adsorption. Hence, the less mobile, bulky oligomers remain on the substrate and thermal curing of the adhesive must result in a polycyanurate network which is much weaker than in the bulk polymer. This could reduce the mechanical strength of an adhesive joint made with pure polycyanurates and could afford additional chemical modification for practical applications.