Conditions for the formation of glasses by cooling melts of one-component systems

Well-known conditions for the formation of glass from the melt are sufficiently fast cooling rates and directed bonding between the constituents. These conditions, however, are not specific enough to select promising melts which may form glasses upon cooling. Therefore, the phase transition from a solid to a melt and the accompanying flow and storage of enthalpy and entropy are considered in detail. The melting entropy is stored in the new configuration of the constituents. Upon cooling a melt, this entropy can only be removed by thermal conduction after it has been reloaded onto the vibrations of crystals. This reloading may be a botdeneck. The smaller the temperature interval where crystallisation is possible, the easier is glass formation. Extrapolating the enthalpy function from the molten state to lower temperatures, that temperature interval (relative to the melting temperature Tm) has been estimated to be ΔTmin/Tm = ΔHm/[Tm(2Cpl - Cps)] = ΔSm/(2Cpl - Cps) ≈ ΔSm/Cpl wherein ΔHm and ΔSm are the molar melting enthalpy and entropy, respectively, and Cpl and Cps are the molar specific heat capacities at constant pressure in the molten (index "l") and crystalline (index "s") states. In fact, ΔTmin/Tm is small for all known one-component systems forming glasses by cooling their melts, which seems to characterize their glass forming capability quite well

Does Shelyubskii's evaluation method characterize the homogeneity of glass?

Α formula given by Shelyubskii has been used in several publications to characterize the homogeneity of glasses from internal spectral transmittance curves of Christiansen filters. It is shown that this evaluation method cannot provide any useful data on the homogeneity of glass

Energy and entropy of crystals, glasses and melts

The molar entropy, S, and enthalpy (energy), H, of crystals, glasses and melts of the same one-component systems have been suitably visualized including the transformadon from the melt into a glass or crystallization. For the temperature T → 0 Κ the enthalpy and entropy of the glass are larger by ΔH0 and ΔS0 as compared to the stable crystal. The S and Η functions of glasses correspond to a simple continuation of these functions from the molten State to lower temperatures. Crystallization occurs as a spontaneous process under production of entropy. Extrapolating the entropy of the molten and crystalline states from the melting range to lower temperatures, which is the basis of "Kauzmann's paradox", is ambiguous and misleading, as the extrapolated data deviate considerably from the experimental temperature dependencies of S of glasses and crystals. Α proper extrapolation does not cause an entropy catastrophe as claimed in "Kauzmann's paradox", since the enthalpy difference between the undercooled melt and the corresponding crystals must be taken into account, and the respective entropies in both states are not connected by an isothermal process. The molar entropy and enthalpy are visualized as functions of temperature by numerical results of a Debye model. The molar entropy is a universal function of the ratio T/TD, wherein TD is the Debye temperature of the well known specific heat capacity, CD. Between 0 K and TD the entropy increases by 1.36 × 3R ≈ 4R irrespective of TD. Above TD it increases approximately as 3R × ln (T/TD). The entropy capacity, CD/T scales with 1/TD and the enthalpy with TD, both considered as functions of T/TD. The entropy capacity shows a maximum of 2.033 × 3R/TD for T/TD = 0.28

Spectral transmittance of Christiansen filters - Experimental observations

Powder of the optical glass K5 has been immersed into methyl benzoate as refractice index matching fluid to fabricate Christiansen filters. The internal spectral transmittance of these filters has been investigated in the visible spectral region as a function of the filter thickness, the mean diameter of the powder grains, and the difference between the refractive indices of the fluid and the K5 glass. The minimum internal spectral extinction of the filter curve is approximately proportional to the thickness of the filter. Furthermore, it scales inversely with the average diameter of the glass grains. Hence, one can deduce that the minimum spectral extinction is proportional to the total interface area between grains and Immersion liquid. According to the experimental results it can be concluded further that this extinction is mainly due to Rayleigh scattering. The halfwidth of the spectral transmission passband decreases with increasing thickness of the filters and with decreasing average diameter of the grains. The spectral extinction at wavelengths sufficiently far from its minimum increases sublinearly with the filter thickness and the inverse mean diameter of the grains. In the same spectral region, the extinction increases also sublinearly with the absolute difference between the refractive indices of the matenal of the grains and of the Immersion liquid. Undl now, a theory predicting all of these observations correctly seems to be still missing

Der „Dialog über die Vögel“ von G. LONGOLIUS (Köln 1544). Lateinischer Originaltext, deutsche Übersetzung, Kommentierung

GISBERT LONGOLIUS (*1507 - †1543) lebte zeitweilig und verstarb in Köln, studierte an der Alten Universität Köln und war hier auch später (mit gerade 30 Jahren) Professor (s.u.). Sein in Latein verfasstes Werk „Dialogus de avibus …“ erschien 1544 ebenfalls in Köln, weshalb das Kölner Autorenteam aufmerksam wurde. Die nachfolgende erstmalige Übersetzung ins Deutsche basiert auf dem Band in der Privatbibliothek des Kölner Zoologen Prof. Dr. Dr. HANS ENGLÄNDER († 2011). Das Original befindet sich nunmehr in der Universitätsbibliothek in Köln. Die Übersetzung übernahm dankenswerter Weise der mit dem Erstautor befreundete Drittautor A. PEUSTER († 2013) mit sehr großer Sorgfalt und viel Einfühlsamkeit

Objektorientierte Analyse und Migration diffraktierter Wellenfelder unter Verwendung der Strahlenmethode und der Edge-Wave-Theorie

Summary in English; Available from TIB Hannover: RR 1846(55) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman