Bestimmung der Bioabbaubarkeit von nicht wasserlöslichen Flüssigkeiten (Schmieröle etc.) nach CEC L-33-A-94

The use of biodegradable lubricants as substitutes for lubricants based on mineral oils is necessary in areas where an impact on ecosystems is inevitable and cannot be excluded. These are applications in which a partial loss of lubricant into the environment occurs, e.g. chain saw oils, two-stroke oils for outboard motors, and hydraulic oils, which are used in sensitive areas as dredging-machines near rivers or ground water sources. The use of commercially available biodegradable base liquids for lubricants is discussed and several current examples are given. These water-insoluble products are frequently examined with the CEC test that can be used for a rough determination of the biodegradability. The development and application of this method has a long tradition at the EMPA Dübendorf. Experimental details, limits, advantages, and disadvantages will be discussed in this paper. Longterm measurements with the calibrating oils RL 130 and RL 110 together with results from a biodegradation study of several hydraulic fluids that are used in agricultural machinery are presented

Untersuchung der thermisch-oxidativen Stabilität von Gasölen mittels Druckdifferenz-Kalorimetrie (PDSC)

Thermoanalytical techniques have found widespread use as a quality-control tool for petroleum and related products. Pressure differential scanning calorimetry (PDSC) has been effectively used as an alternative method to estimate thermal-oxidation stability of middle-destillate fuels. In this paper, the fuels were rated on thermal stability on the basis of their enthalpy of the exothermic reaction 'Oil + O2 → Oxidation Products' under isothermal conditions. The thermograms before and after a certain period of time under thermal-oxidative strain have been compared in order to determine the average heat flow during that period and, therefore, to obtain an indication to fuel storage stability. Six heating oils of diverse composition and origin were selected for the investigation. On the basis of these examples a correlation between the physical-chemical properties and the DSC data has been shown and the factors influencing the thermal-oxidation stability have been evaluated. The reliability of the method with regard to predicting long-term storage stability has been discussed

Small-Angle Excess Scattering: Glassy Freezing or Local Orientational Ordering?

We present Monte Carlo simulations of a dense polymer melt which shows glass-transition-like slowing-down upon cooling, as well as a build up of nematic order. At small wave vectors q this model system shows excess scattering similar to that recently reported for light-scattering experiments on some polymeric and molecular glass-forming liquids. For our model system we can provide clear evidence that this excess scattering is due to the onset of short-range nematic order and not directly related to the glass transition.Comment: 3 Pages of Latex + 4 Figure

Is the Stillinger and Weber decomposition relevant for coarsening models?

We study three kinetic models with constraint, namely the Symmetrically Constrained Ising Chain, the Asymmetrically Constrained Ising Chain, and the Backgammon Model. All these models show glassy behavior and coarsening. We apply to them the Stillinger and Weber decomposition, and find that they share the same configurational entropy, despite of their different nonequilibrium dynamics. We conclude therefore that the Stillinger and Weber decomposition is not relevant for this type of models.Comment: 14 pages, 12 figure

Dynamic criticality in glass-forming liquids

We propose that the dynamics of supercooled liquids and the formation of glasses can be understood from the existence of a zero temperature dynamical critical point. To support our proposal, we derive from simple physical assumptions a dynamic field theory for supercooled liquids, which we study using the renormalization group (RG). Its long time behaviour is dominated by a zero temperature critical point, which for dimensions d > 2 belongs to the directed percolation universality class. Molecular dynamics simulations confirm the existence of dynamic scaling behaviour consistent with the RG predictions.Comment: 4 pages, 2 figure

Free Energy Landscape Of Simple Liquids Near The Glass Transition

Properties of the free energy landscape in phase space of a dense hard sphere system characterized by a discretized free energy functional of the Ramakrishnan-Yussouff form are investigated numerically. A considerable number of glassy local minima of the free energy are located and the distribution of an appropriately defined ``overlap'' between minima is calculated. The process of transition from the basin of attraction of a minimum to that of another one is studied using a new ``microcanonical'' Monte Carlo procedure, leading to a determination of the effective height of free energy barriers that separate different glassy minima. The general appearance of the free energy landscape resembles that of a putting green: deep minima separated by a fairly flat structure. The growth of the effective free-energy barriers with increasing density is consistent with the Vogel-Fulcher law, and this growth is primarily driven by an entropic mechanism.Comment: 10 pages, 6 postscript figures, uses iopart.cls and iopart10.clo (included). Invited talk at the ICTP Trieste Conference on "Unifying Concepts in Glass Physics", September 1999. To be published in J. Phys. Cond. Ma

Evidence against a glass transition in the 10-state short range Potts glass

We present the results of Monte Carlo simulations of two different 10-state Potts glasses with random nearest neighbor interactions on a simple cubic lattice. In the first model the interactions come from a \pm J distribution and in the second model from a Gaussian one, and in both cases the first two moments of the distribution are chosen to be equal to J_0=-1 and Delta J=1. At low temperatures the spin autocorrelation function for the \pm J model relaxes in several steps whereas the one for the Gaussian model shows only one. In both systems the relaxation time increases like an Arrhenius law. Unlike the infinite range model, there are only very weak finite size effects and there is no evidence that a dynamical or a static transition exists at a finite temperature.Comment: 9 pages of Latex, 4 figure

Relaxation properties in a lattice gas model with asymmetrical particles

We study the relaxation process in a two-dimensional lattice gas model, where the interactions come from the excluded volume. In this model particles have three arms with an asymmetrical shape, which results in geometrical frustration that inhibits full packing. A dynamical crossover is found at the arm percolation of the particles, from a dynamical behavior characterized by a single step relaxation above the transition, to a two-step decay below it. Relaxation functions of the self-part of density fluctuations are well fitted by a stretched exponential form, with a $\beta$ exponent decreasing when the temperature is lowered until the percolation transition is reached, and constant below it. The structural arrest of the model seems to happen only at the maximum density of the model, where both the inverse diffusivity and the relaxation time of density fluctuations diverge with a power law. The dynamical non linear susceptibility, defined as the fluctuations of the self-overlap autocorrelation, exhibits a peak at some characteristic time, which seems to diverge at the maximum density as well.Comment: 7 pages and 9 figure

Finite-size scaling at the dynamical transition of the mean-field 10-state Potts glass

We use Monte Carlo simulations to study the static and dynamical properties of a Potts glass with infinite range Gaussian distributed exchange interactions for a broad range of temperature and system size up to N=2560 spins. The results are compatible with a critical divergence of the relaxation time tau at the theoretically predicted dynamical transition temperature T_D, tau \propto (T-T_D)^{-\Delta} with Delta \approx 2. For finite N a further power law at T=T_D is found, tau(T=T_D) \propto N^{z^\star} with z^\star \approx 1.5 and for T>T_D dynamical finite-size scaling seems to hold. The order parameter distribution P(q) is qualitatively compatible with the scenario of a first order glass transition as predicted from one-step replica symmetry breaking schemes.Comment: 8 pages of Latex, 4 figure