Untersuchungen zur Wechselwirkung von Polymerschmelze mit Metalloberflächen im Bereich der Kunststoffverarbeitung

In der Kunststoffverarbeitung wurde im Jahre 2012 in Deutschland ein Umsatz von 56 Milliarden Euro erwirtschaftet. Einen wichtigen Bereich der Kunststoffverarbeitung stellt dabei der Extrusionsprozess dar. Beim Extrusionsprozess werden Extruder zum Aufschmelzen von Kunststoffgranulat eingesetzt. Mit Hilfe eines anschließenden Werk-zeuges erfolgt die Formgebung der erkaltenden Kunststoffschmelze. Bei der Verarbei-tung von Kunststoffgranulat in Extrudern wird häufig eine Belagbildung- bzw. Stippen-bildung beobachtet. Durch die Belag- und Stippenbildung kommt es während der Pro-duktion zu einem Qualitätsabfall des extrudierten Kunststoffes. Es existiert keine ein-heitliche Lösung für die Vermeidung der Belagbildung. Mit der Aufklärung eines mög-lichen Mechanismus der Belag- und Stippenbildung könnten geeignete Maßnahmen zur Verringerung oder Vermeidung abgeleitet werden. Im Rahmen dieses Beitrags sollen Ergebnisse zur elementspezifischen Interaktion zwischen der Schmelze und den Be-standteilen des Stahls vorgestellt werden. Es soll zusätzlich auf die Bildung eines Me-tall-Polymerkomplexes als Folge dieser Interaktion eingegangen werden

Oxygen-Free Production—From Vision to Application

As oxygen negatively affects most production processes in the metalworking industry, a truly oxygen-free production environment appears attractive in terms of the resulting material and component properties. This overview summarizes research conducted within the Collaborative Research Centre (CRC) 1368. The objectives of this CRC are twofold. First, a fundamental understanding of the mechanisms that govern the interaction between a metal surface and the environment is established. Second, it is researched how this understanding can be exploited to improve current production processes and even develop completely new ones. Herein, data obtained within the first funding period, which already demonstrate that significant effects can be realized in processes such as thermal spraying, cold rolling, compound casting, laser brazing, milling or hot stamping to name just a few examples, are presented. In addition, key aspects such as initial deoxidation of the workpieces, their transport under conditions that prevent reoxidation, and the tools needed to establish and control an oxygen-free process environment are given, and the ramifications with respect to actual applications are discussed

Gas Phase Reaction of Silane with Water at Different Temperatures and Supported by Plasma

The interaction of silane and water is discussed controversially in literature: some authors suggest monosilane and water react kinetically and sufficiently fast enough to remove water, while others state the reaction occurs only at elevated temperatures. This question is of technological interest for the removal of unavoidable water residues in Ar gases. Thermodynamic calculations show that virtually complete removal of water is expected with superstoichiometric silane addition. However, mass spectrometric and infrared spectroscopic experiments give evidence that the addition of monosilane to such an Ar gas at room temperature is unable to remove residual water, which disagrees with some current hypotheses in the literature. This holds even for very high SiH4 concentrations up to 2 vol.-%. Silane reacts with water above temperatures of 555 °C, initiated by the thermal decomposition of silane. A cold dielectric barrier discharge-plasma used for silane and water dissociation enhances reactivity similar to elevated temperatures. Fourier-transformed infrared spectroscopy points toward silanol generation at temperatures between 400 and 550 °C, while quadrupole mass spectrometry indicates the creation of SiOH+, SiHOH+, SiH2OH+, and SiH3OH+. Cold plasmas generate smaller amounts of SiOH+, SiHOH+, and SiH2OH+ compared to elevated temperatures. Reaction products are hydrogen and nanoscaled particles of non-stoichiometric silicon oxides. The silicon-oxide particles produced differ in elemental composition and shape depending on the prevailing water content during decomposition: SiOx generated with residual water appears with relatively smooth surfaces, while the addition of water supports the formation of significantly rougher particle surfaces. Higher initial water contents correlate with higher oxygen contents of the particles

Silver nano particle formation on Ar plasma : treated cinnamyl alcohol

Metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy are employed to study the adsorption of silver on cinnamyl alcohol films prepared on Au(111) substrates by thermal evaporation. Additionally, the impact of an Ar atmosphere dielectric barrier discharge plasma applied to the cinnamyl alcohol film preliminary to the Ag adsorption is investigated. In both cases silver nano particles with an average diameter of 9 nm are formed. These particles do not interact chemically with the underlying cinnamyl alcohol film. We do not find any influence of the preliminary Ar plasma-treatment on the adsorption behavior at all

Influence of an oxygen-free atmosphere on laser beam brazing of aluminium with prior surface deoxidation by pulsed laser radiation

Aluminium alloys, like AlMgSi1 and AlMg3, cannot be joined in industrial processes by laser beam brazing without the use of fluxes due to their resistant oxide layer. The aim of this study is to dispense with the use of flux. For the investigations, an oxygen-free atmosphere was created by using the highly reactive gas monosilane and thus achieving O2 partial pressures of 10-18 mbar. After removal of the oxides by a laser source with 1064 nm wavelength, pulse energies of max. 0.3 µJ and pulse durations of 45 ns, reoxidation is prevented by the oxygen-free atmosphere, so that brazing is carried out on an oxide-free material surface. The bead on plate seams show a materially bonded brazed joint in cross-section. Reference experiments without monosilane either show no wetting or an increased melting of base material. The influence of laser beam power for brazing, pulse energy for deoxidation and wire feed was investigated

Towards dry machining of titanium-based alloys : A new approach using an oxygen-free environment

In the current study, the potential of dry machining of the titanium alloy Ti-6Al-4V with uncoated tungsten carbide solid endmills was explored. It is demonstrated that tribo-oxidation is the dominant wear mechanism, which can be suppressed by milling in an extreme high vacuum adequate (XHV) environment. The latter was realized by using a silane-doped argon atmosphere. In the XHV environment, titanium adhesion on the tool was substantially less pronounced as compared to reference machining experiments conducted in air. This goes hand in hand with lower cutting forces in the XHV environment and corresponding changes in chip formation. The underlying mechanisms and the ramifications with respect to application of this approach to dry machining of other metals are discussed. © 2020, MDPI AG. All rights reserved

Towards dry machining of titanium-based alloys: a new approach using an oxygen-free environment

In the current study, the potential of dry machining of the titanium alloy Ti-6Al-4V with uncoated tungsten carbide solid endmills was explored. It is demonstrated that tribo-oxidation is the dominant wear mechanism, which can be suppressed by milling in an extreme high vacuum adequate (XHV) environment. The latter was realized by using a silane-doped argon atmosphere. In the XHV environment, titanium adhesion on the tool was substantially less pronounced as compared to reference machining experiments conducted in air. This goes hand in hand with lower cutting forces in the XHV environment and corresponding changes in chip formation. The underlying mechanisms and the ramifications with respect to application of this approach to dry machining of other metals are discussed

Chemical improvement of surfaces. Part 2: Permanent hydrophobization of wood by covalently bonded fluoroorganyl substituents

A recently developed esterification method in our laboratory was applied to permanent hydrophobization of wood surfaces. Specifically, the covalent attachment of fluoroorganyl substituents to wood hydroxy groups via benzotriazolyl-activated, substituted benzoic acids was in focus. Weight percent gain values from 10% to 28% were obtained on Scots pine (Pinus sylvestris) sapwood veneer chips. It proved feasible to lower the temperature for wood modification from 150°C to 120°C, or even to 70°C so that thermal decomposition of wood during modification can be neglected. The modified chips were analyzed by attenuated total reflection – infrared and X-ray photoelectron spectroscopy. Covalent attachment of the fluorobenzoic acids led to a very high, permanent hydrophobicity of the wood surface, documented by outstanding contact angles of up to 143

Switchable mesomeric betaines derived from pyridinium-phenolates and bis(thienyl)ethane

Syntheses of push–pull substituted non-symmetric bis(thienyl)ethenes (BTEs) possessing a central perfluorocyclopentene core are described. The substituent effects of anisole, phenole, and phenolate as well as pyridine, pyridinium, and N-methylpyridinium substituents, joined through their 3- or 4-positions to the central BTE core, respectively, cover the range from very strongly electron-donating [σ(4-phenolate)=−1.00] to extremely strongly electron-withdrawing [σ(pyridinium-4-yl)=+2.57] in the title mesomeric betaines. The different isomers possessing 4-yl/4-yl, 4-yl/3-yl and 3-yl/3-yl substituents represent different combinations of conjugated and cross-conjugated partial structures and cause different spectroscopic properties. In addition, through-space conjugation between the 2- and 2′-position of the thiophenes can be observed which circumvents the charge-separation of through-bond cross-conjugation. The BTE possessing the push–pull chromophore consisting of 3-anisole and 4-pyridinium substituents (24) displays the best extinction coefficients within the series of compounds described here (ϵ=33.8/15.7 L/mol ⋅ cm), while the mesomeric betaine possessing an N-methylpyridinium-4-yl and a 4-phenolate substituent (29) displays considerable bathochromic shifts to λmax=724 nm in its closed form

The influence of protecting polyelectrolyte layers on the temperature behavior of NaBD₄

The use of NaBH4 as a hydrogen storage material suffers to some extent from its deficient stability against chemicals and degradation at elevated temperatures. This disadvantage can be overcome by the use of polyelectrolytes as protective layers. Furthermore, the coating of NaBH4 with polyelectrolytes significantly enhances the release of hydrogen from the storage material. In this work, the influences of polyethyleneimine (PEI) and poly(acrylonitrile-co-butadiene-co-acrylic acid), dicarboxy terminated (PABA) as protective polyelectrolytes coatings have been investigated on deuterated sodium borohydride, thus being able to determine hydrogen release from the polyelectrolyte and the hydrogen storage material. The release rates have been investigated by temperature-programmed desorption measurements of significant species as preliminarily identified by mass spectrometry. Furthermore, the geometrical structures of the polyelectrolyte films were characterized by confocal laser scanning microscopy studies prior and posterior to the temperature treatment