Homogeneous Nucleation Limit Research Articles

Liquids at Large Negative Pressures: Water at the Homogeneous Nucleation Limit

An isochoric cooling method for obtaining unprecedented tensions on liquids was used to determine the homogeneous nucleation limit for stretching of water at a variety of water densities. At densities in the range 0.55 to 0.68 gram per milliliter (g/ml), the data agree with the homogeneous nucleation temperatures measured by Skripov for superheated water at positive pressures. At densities between 0.68 and 0.93 g/ml, cavitation occurred only at negative pressures (that is, under tension). The cavitation tensions measured were in excellent agreement with those predicted by Fisher's 1948 vapor nucleation theory. A maximum tension of 140 megapascals (=1400 bars) was reached at 42 degrees C, which lies on an extrapolation of the line of isobaric density maxima. At higher densities, cavitation of droplets that survived heterogeneous nucleation failed to occur at all unless provoked, at much lower temperatures, by freezing. This observation confirms the existence of a density maximum at 42 degrees C and -140 megapascals and hence greatly strengthens the basis for Speedy's conjecture of a reentrant spinodal for water.

Intermittency, Irreproducibility, and the Main Physical Effects in Cold Fusion

In this paper heterogeneous nucleation of D{sub 2} bubbles at the surface of the cathode is suggested as the cause of difficulties encountered in the reproduction of electrolytic cold fusion experiments. In some experiments, active nucleation centers are present only intermittently leading to a temporary increase in the chemical potential of deuterium in the cathode up to the homogeneous nucleation limit, which is {approximately}1.2 eV higher. The increase effective mass of electrons, expressed in the electronic specific heat and in the De Haas Van Alphen effect, is considered as a possible cause of cold nuclear fusion, along with the stronger heavy fermion effects directly observed at low temperatures, but localizability of these states remains a problem. Breakdown of the charge invariance of internucleonic forces at very low center-of-mass energies of the order of 1 eV applicable to this form of (non-{mu}-mesonic) cold fusion, leads to preferential tunneling of neutrons into nearby deuterons, which is suggested as an explanation for the conspicuous absence of neutrons and {sup 3}He.

Absence of the light effect in ultrasonic cavitation in liquid helium

Several years ago it was discovered that light can lower the homogeneous nucleation temperature of superheated liquid helium I. We report here on experiments involving the same homogeneous nucleation limit, reached now by acoustically reducing the pressure rather than by raising the temperature. It is found that in our present experimental setup the presence of light does not have any influence on the homogeneous nucleation limit. Thus, it seems that the presence of a solid surface in contact with the helium, such as the heater-thermometer surface in the superheating experiments, is important for observing the light effect.

Nucleation in bulk undercooled nickel-base alloys

The undercooling behaviour of binary Cu 1− x Ni x bulk melts was investigated over the entire concentration range 0 ⩽ × ⩽ 1 using an electromagnetic levitation technique in an ultraclean environment. The elimination of container-wall induced nucleation has led to undercooling levels of bulk melts up to 30 K larger than the highest values obtained so far by droplet dispersion. The analysis of the results within the framework of a nucleation theory for binary systems indicates that, despite the large undercoolings, the limit of homogeneous nucleation is not achieved. Microstructural investigations of the samples reveal heterogeneous surface nucleation as the prevailing nucleation mechanism. The role of surface oxidation as the responsible catalyst for nucleation is discussed with respect to the different undercooling behaviour of the samples in helium and HeH 2 atmospheres.

The density of supercooled water. II. Bulk samples cooled to the homogeneous nucleation limit

We have measured the density of supercooled water (H2O) in the range −33.41≤T≤−5.23 °C. Our samples were held in glass capillary tubing with an approximate inside diameter of 0.3 mm=300 μ. These samples were prepared by Mossop’s method and could be cooled to their homogeneous nucleation limit before freezing. We compare our density data to other measurements using capillaries and demonstrate what appears to be an excess density in smaller capillaries which is inversely proportional to the capillary inside diameter. The origins of this excess density are unknown, but we show its effect is insignificant on our measurement. The thermal expansivities derived from our data are fit to a power law in temperature relative to a singular temperature. These results are inconclusive due to a poor knowledge of the background expansivity.

An experimental study of high-pressure bubble growth within multicomponent liquid droplets levitated in a flowing stream of another immiscible liquid

Measurements of vaporization rates of highly superheated liquid droplets are reported at reduced pressures up to 0.4 and reduced temperatures up to 0.95. Binary and ternary mixtures of n -pentane, n -hexane, and n -decane, were studied. The experimental method involved levitating a test droplet in a flowing stream of another immiscible liquid (glycerine). Levitation was achieved by balancing the buoyancy and drag force on the droplet. Bubble formation within the droplet was induced by isothermally decompressing the field liquid to pressures approaching the homogeneous nucleation limit of the levitated droplet. It was observed that a droplet consisting of a binary n -pentane- n -hexane mixture vaporized faster than either an n -pentane or n -hexane droplet, and that the vaporization rate decreased with increasing press­ure. Replacing part of the non-volatile component of a n -pentane— n -hexane mixture by a yet more non-volatile liquid ( n -decane), thus forming a ternary pentane-hexane-decane mixture, was found to increase the vaporization rate above that of a droplet consisting of a binary mixture of the most volatile component with any one of the other two components. The results are discussed from the perspective of bubble growth within a liquid mixture of infinite extent.

Containerless undercooling of bulk Fe-Ni melts

Bulk samples of Fe1−xNix, with x covering the whole concentration range 0≤x≤1, have been undercooled in a containerless state by electromagnetic levitation, yielding undercooling levels not achieved to date by any other technique. Comparison with a theoretical approximation indicates that, despite the large undercoolings attained, the limit of homogeneous nucleation is not yet reached. The solidification of the undercooled melts is initiated rather by heterogeneous surface nucleation originating from surface oxidation processes.

Use of a Cubic Equation to Predict Surface Tension and Spinodal Limits

The very general Shamsundar–Murali cubic equation is used to interpolate p–v–T data into the metastable and unstable regions. This yields a spinodal line that closely matches the homogeneous nucleation limit predicted by an improved kinetic theory. Only the pressure, the saturated liquid and vapor volumes, and the liquid compressibility at saturation, as well as one compressed liquid data point, are needed to use the cubic equation for the interpolation process. The equation also yields an accurate prediction of the temperature dependence of surface tension when it is substituted in van der Waals’ surface tension formula. Thus, by capitalizing on the inherent relation among the p–v–T equation, the spinodal prediction, and the surface tension—all three—it is possible to obtain each with high accuracy and minimal experimental data.

Neutron-Induced Vaporization of Superheated Liquids: Theory and Experiment

AbstractMy interest in neutron-induced nucleation began with a simple and elegant demonstration in one of David Turnbull's classes in which a drop of water was superheated to about 250°C as it rose in a column of heated oil. As David Glaser, the inventor of the bubble chamber, so ably demonstrated, such superheated liquids are radiation sensitive. Our test system is a simple one. Halocarbon and hydrQcarbon drops are introduced into an aqueous holding gel under pressure at room temperature. As the pressure is released, the drops become superheated. Neutrons of sufficient energy will trigger vaporization of these moderately superheated drop detectors (SSDs), but gammas and x-rays will not unless the homogeneous nucleation limit is approached. We have performed measurements on the neutron energy threshold to produce nucleation in a number of different superheated materials at different temperatures. We have also developed a theory which indicates that of the energy deposited in a critical radius, only about 5% is effective in producing bubble formation. Both theory and experiment are discussed.

Homogeneous Nucleation and the Spinodal Line

The limit of homogeneous nucleation in a liquid is shown to lie very close to its liquid spinodal line. It is also argued that the homogeneous nucleation prediction should be based on a comparison of the critical work of nucleation with the “potential well” energy instead of the kinetic molecular energy. The result is a new prediction of the liquid spinodal line for water that is valid to large negative pressures. This prediction compares well with spinodal points obtained by extrapolating liquid and vapor water data with the Himpan equation.

Supercooling and nucleation of ice in single cells

An emulsion droplet formation procedure was employed to isolate yeast cells and, in separate experiments, human red blood cells, one from another in individual droplets, and to segregate extraneous materials catalyzing the formation of ice. Emulsification succeeded in isolating the cells and permitted the observation of the supercooling of droplets containing cells whereby each droplet was observed to nucleate ice at a temperature that depended only upon the components of the droplet. The droplet formation procedures were characterized. It was shown that the surface coatings and the carrier fluids used in the preparation of the emulsions did not act as ice nucleators. It was, in this manner, possible to study the nucleation of ice brought about by supercooling and homogeneous nucleation in the volume of the droplet or by the catalysis of nucleation on or in the cells contained in the droplets. It was shown that yeast cells and red blood cells could each be supercooled to about −40 °C in short-term experiments. The results also revealed that yeast cells did not store for infinite times at temperatures above the observed upper limit of homogeneous nucleation. The yeast cells died at rates that were exponential functions of time at −20, −22.5, −25, −29 and −33 °C. The temperature dependence of the death rate did not correspond to a process with a normal Arrhenius activation energy. The temperature dependence did, however, suggest a potentiated heterogeneous catalysis of ice resulting in the death of the yeast cells.