bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural states of dictyostelium myosin
Authors: Stewart Peter R. , Spudich James A.
Published: May 2005

Myosin purified from Dictyostelium amoebae has approximately 10% by weight of RNA associated with it, unless specific steps (DEAE cellulose chromatography or R Nase digestion) are taken to remove it. This RNA has significant effects on the structural states formed by the myosin at low ionic strength in the presence of Mg2+.

Rapid precipitation of Rna‐free myosin by dilution generates bipolar thick filaments (540 nm long, 33 nm thick), often with a bare zone and a 15‐nm transverse repeat. Rapid precipitation of myosin with copurified RNA yields linear aggregates of bipolar filaments, showing some lateral association.

Slow precipitation of RNA‐free myosin by dialysis yields very long filaments or ribbons (>5 μm, 30–60 nm wide) in which the myosin may be packed diagonally across the filament, similar to the “side‐polar” aggregates formed by other nonmuscle myosins and by smooth muscle myosin (Craig R, Megerman J: J Cell Biol 75:990, 1977; Hinssen H, D'Haese J, Small JV, Sobieszek A: J Ultrastruct Res 64:282, 1978). Slow precipitation of myosin with copurified RNA generates linear filaments with repeat intervals of 290 and 650 nm.

Other polyanions were tested for their effects on myosin aggregation. Total RNA and ribosomal RNA from Dictyostelium, when added to RNA‐free myosin, also induced the extensive linear aggregation seen with the copurified RNA/myosin complex, although higher concentrations of RNA were required to obtain quantitatively the same effect. DNA and heparin were also effective inducers of linear aggregation, whereas homopolymers of nucleotides and of acidic or basic amino acids were poorly effective.
Effects of the tumor promoter TPA on the induction of DNA synthesis in normal and RSV‐transformed rat fibroblasts
Authors: Magun Bruce E. , Bowden G. T.
Published: May 2005

Induction of DNA synthesis by the tumor promoter tetradecanoyl phorbol acetate (TPA) was studied in a line of cultured rat fibroblasts (Rat‐1) and their ffRous sarcoma virus‐transformed derivative (Rat‐1(RSV)). Following serum deprivation for 54 h to achieve quiescene, semiconservative DNA replication was measured by incubation of cells in BrdUrd and FdUrd after serum stimulation in the presence or absence of TPA. Optimal concentrations of TPA (0.1–0.5 μg/ ml) in serum‐free medium induced a small increase (10–15%) in the amount of DNA made over a 30‐h period in both Rat‐1 and Rat‐1 (RSV) cells. When Rat‐1 cells were stimulated by a 4‐h serum pulse, 30% of the DNA was replicated by 30 h. If the serum pulse was follwed by TPA addition, 702% DNA replication wass observed. If the serum pulse was preceded by TPA addition, the onset of DNA synthesis waas delayed by several hous, but stimulation of DNA synthesis occurred. In contrast, the Rat‐1 (RSV) cells did not show an increase in DNA synthesis induced by TPA in similar protocols, but the serum‐induced onset on DNA synthesis was delayed by several hours in the presence of TPA. Therefore, TPA acts as a co‐inducer of DNA synthesis in the Rat‐1 but not in the Rat‐(RSV) cells. The parent alcohol, phorbol, was inactive in Rat‐1 cells, but delayed the onset of DNA synthesis in the Rat(RSV) cells. We conclude that the co‐inducing and delaying activities of TPA on DNA synthesis appear to be distinct and to act at different points in the G1 phase of the cell cycle.
Analysis of cell surface interactions by measurements of lateral mobility
Authors: Elson Elliot L. , Reidler Jeffry A.
Published: May 2005

Interactions of cell surface components with one another and with structures inside and outside the cell may have important physiological functions in the transmission of signals and the assembly of specialized structures. These interactions may be detected and analyzed through their effects on the lateral mobility of cell surface molecules. Measurements by a fluorescence photobleaching method have shown that in general lipid‐like molecules diffuse rapidly and freely through the plasma membrane, whereas proteins move much more slowly or appear to be immobile. This dichotomy has been supposed to result from forces beyond the viscosity of the lipid bilayer, which specifically retard the diffusion of membrane proteins. This general picture should be qualified, however, by noting that the lateral mobility of lipid‐like molecules can be influenced in detail by changes in the state of the plasma membrane such as result from mitosis or fertilization. The interactions of cell surface proteins that limit their lateral mobility are unknown. The effects of binding concanavalin A to localized regions of cell surface show that these interactions can vary in subtle and complex ways. It may soon be useful to interpret mobility experiments in terms of simple reaction models that attempt to describe surface interactions in physicochemical terms. More experimental data are needed to carry out this program and to relate interactions that affect mobility to the structural connections between cell surface components and the cytoskeleton, which have been detected by biochemical methods and electron and immunofluorescence microscopy.
A comparative dielectric study of human serum low density lipoprotein before and after partial digestion by trypsin
Authors: Chana G. S. , Chapman M. J. , Sheppard R. J. , Mills G. L. , Goldstein Sonia , Grant E. H.
Published: May 2005

The relative permittivity of aqueous solutions of human serum low density lipoprotein (LDL) and partially trypsin digested lipoprotein (T‐LDL) has been determined for various concentrations at 20°C over the frequency range 0.15–100 MHz. Comparison of the dielectric dispersion curves for the digested lipoprotein with those for the native preparation revealed a larger low‐frequency dielectric increment, which may be attributed to an increase in the number of counterions moving over the surface of the molecule. An explanation of this observation is an elevation of 70% in the net negative charge on the surface of the trypsin‐treated particle as compared to its native counterpart.
The role of the Escherichia coli λ receptor in the transport of maltose and maltodextrins
Authors: Ferenci Thomas , Boos Winfried
Published: May 2005

The λ receptor is a peptidoglycan‐associated integral protein that spans the outer membrane. Beside its function in phage λ adsorption it participates in transport. The latter function can be summarized as follows: (1) Receptor allows the nonspecific permeation of small molecules other than maltose and maltodextrins (in close analogy to a molecular sieve). Here the only criterion for selectivity is size and it has the properties of an unspecific pore. In this respect, it is similar to the outer membrane proteins Ia, Ib, and Ic, the porins. (2) It is a binding protein for maltodextrins. Binding affinity is low but increases by a factor of 500 as the chain length of the maltodextrins increases. In contrast, the affinity of the periplasmic maltose‐binding protein for maltose and maltodextrins is similarly high (in the μM range). (3) In the in vitro system of liposomes, the λ receptor facilitates specifically the diffusion of maltodextrins that exceed the size limit given by its porin function. This clearly demonstrates that the λ receptor alone is able to specifically overcome the permeability barrier of the outer membrane for maltodextrins. (4) From the genetic and kinetic analysis of maltose and maltodextrin transport, it can be concluded that the λ receptor interacts with the periplasmic maltose‐binding protein. (5) Electron microscopic studies indicate a location for the maltose‐binding protein in the outer cell envelope. This location is dependent on the presence of the λ receptor.
Interleukin 2 in cell‐mediated immune responses
Authors: Paetkau Verner , Shaw Jennifer , Caplan Barry , Mills Gordon B. , Lee Kwok‐Choy
Published: May 2005

The lymphokine Interleukin 2 (IL2) restores T cell responses in a number of in vitro systems where immunogenicity has been compromised. UV irradiation of the stimulating allogeneic cells in a mixed leukocyte culture eliminates the production of cytotoxic T lymphocytes and greatly reduces the DNA synthesis response. IL2 restores both parameters. UV‐irradiated stimulators are also unable to induce the normal production of IL2 which is observed in a mixed leukocyte culture. The cytotoxic activity of allogeneically stimulated thymocytes is almost completely lost within 24 hours after removal of IL2 at 5 days, indicating that the lymphokine is continuously required to maintain CTL. Thymocytes in 4‐day cultures do not adsorb IL2 unless they are simultaneously activated with a mitogen. Finally, IL2 does not adequately restore a secondary response to the purified protein derivative of tuberculin (PPD) in adherent‐cell‐depleted cultures, indicating that macrophages, in addition to being required for IL2 production, have other functions. These probably include the presentation of soluble antigens to responding cells.
Short‐latency ionic effects of nerve growth factor deprivation and readministration on ganglionic cells
Authors: Varon Silvio , Skaper Stephen D.
Published: May 2005

Nerve growth factor (NGF) is likely to exert its trophic action on dorsal root ganglion (DRG) and on sympathetic ganglion neurons by controlling a crucial function of these cells. This function would in turn regulate other cellular machineries and, ultimately, lead to the traditional NGF consequences, such as survival and neuritic growth. A corollary of this view is that the key to NGF action must lie in short‐latency events, occurring within minutes of NGF administration. Chick embryo DRG dissociates have proved to be an effective experimental system to investigate short‐latency responses to NGF, in that (1) measurable functional deficits develop over 6 h of NGF deprivation in vitro and (2) delayed presentation of NGF promptly and fully restores the defective function. The first deficit observed in this experimental system, a decline in RNA‐labeling capability, led to the recognition that NGF controls the transport of selected exogenous substrates, all of which are Na+‐coupled and depend on an Na+ gradient across the neuronal membrane. Subsequent work showed that NGF controlled such transport systems by actually regulating the neuronal ability to control intracellular Na+. Under NGF deprivation, the DRG cells accumulate Na+ to levels that reflect, and presumably equate, the extracellular Na+ concentrations. Conversely, on delayed NGF administration, the accumulated Na+ is actively extruded to an extent and at a speed that depends on the NGF concentration. The Na+ response is elicited by both Beta and 7S NGF, but not by other proteins tested. All ganglionic systems that display a requirement for exogenous NGF in culture have also displayed the Na+ response to NGF. The Na+ response is grossly paralleled by a K+ response. DRG dissociates, in which intracellular K+ has been pre‐equilibrated with extracellular 86Rb+, lose their 86Rb+ over 6 h of NGF deprivation and restore it on delayed NGF administration. The regulation by NGF of mechanisms controlling intracellular Na+ and K+ levels in their target neurons is likely to occupy an early and fundamentl place in the sequence of events underlying the mode of action of this factor.
Visualization of thrombin receptors on mouse embryo fibroblasts using fluorescein‐amine conjugated human α‐thrombin
Authors: Carney Darrell H.
Published: May 2005

The localization of thrombin receptors on mouse embryo (ME) cells has been examined by direct fluorescence microscopy using a fluorescein aminelabeled thrombin. Two fluorescein amines, 4‐(N‐6‐aminoethyl thioureal)‐fluorescein and 4‐(N‐6‐aminohexyl thioureal)‐fluorescein, were synthesized and attached to the carbohydrate moiety of highly purified human α‐thrombin by periodate oxidation of the carbohydrate and selective reduction of the Schiff's base using sodium cyanoborohydride. Preparations of fluorescent thrombin with from 1 to 4 fluoresceins per molecule of thrombin retained their ability to proteolytically cleave fibrinogin to form fibrin clots, to bind to thrombin receptors on ME cells, and to initiate cell division. After incubating mitogenic concentrations of the fluorescein amine labeled thrombin with ME cells at 4°C, a diffuse fluorescent pattern was observed over the surface of the ME cells. This diffuse pattern was specific: it was not observed on cells from parallel cultures incubated with fluorescent thrombin plus a 20‐fold excess of unlabeled thrombin. Thus, thrombin receptors appear to be distributed randomly over the surface of ME cells prior to interaction with thrombin. Increasing the temperature to 37°C following binding at 4° C resulted in a rapid dissociation of the fluorescent pattern from the cells leaving only the autofluorescent vesicles. This result may reflect the unique ability of thrombin to proteolytically cleave its own receptor.
Self‐renewal of factor‐dependent hemopoietic progenitor cell‐lines derived from long‐term bone marrow cultures demonstrates significant mouse strain genotypic variation
Authors: Greenberger Joel S.
Published: May 2005

Long‐term bone marrow cultures established from C57Ks/J mice have been shown to spontaneously release endogenous ecotropic RNA type‐C virus (retrovirus). C57Ks/J marrow cultures produced granulocyte‐macrophage progenitor cells (GM‐CFUc) and immature and mature granulocytes for over 45 weeks. In contrast, NIH Swiss mouse marrow cultures failed to release detectable ecotropic virus and generated GM‐CFUc and granulocytes for 25–35 weeks and established WEHI‐3 conditioned medium (CM) dependent cell lines in vitro and did not establish permanent cell lines. To determine whether viral and/or cellular genes regulated the longevity of C57Ks/J marrow cultures, groups of cultures were established from the marrow of (NIH‐Swiss × C57Ks/J) F1 hybrid, F2 hybrid, and (NIH Swiss × C57Ks/J) X NIH Swiss backcross generations. Release of endogenous ecotropic virus was measured weekly in each culture as was the duration of production of immature granulocytic cells and GM‐CFUc over a 58‐week period. The results demonstrated a complex pattern of inheritance of longevity of long‐term in vitro hemopoiesis. Increased longevity did not absolutely correlate with detectable replication of the C57Ks/J N‐tropic virus.
The role of cells and their products in the regulation of in vitro stem cell proliferation and granulocyte development
Authors: Dexter T. M. , Spooncer E. , Toksoz D. , Lajtha L. G.
Published: May 2005

In long‐term marrow cultures haemopoiesis can be maintained in vitro for up to 6 months. Critical analysis of the cell populations produced has shown that the stem cells and their committed progeny have characteristics in common with the corresponding cell types in vivo. The maintenance of haemopoiesis in vitro is associated with the development of an appropriate inductive environment provided by bone marrow derived adherent cells. Analysis of the interactions between environmental and haemopoietic cells has been facilitated by the development of in vitro systems reproducing the naturally occurring genetic environmental defects and other systems where the development of a competent inductive environment shows a dependency upon corticosteroid hormones. Investigations have shown that stem cell proliferation may be controlled by production of opposing activities, one stimulatory for DNA synthesis, the other inhibitory. A model is proposed whereby modulation in the production of these factors is determined by the physical presence of stem cells in a proposed cellular milieu, within the adherent layer. The adherent layer, apart from acting at the level of stem cell proliferation, can also modify the response of differentiating cells (eg, GM‐CFC) to exogenous stimulatory activities. Addition of GM‐CSF or of CSF‐antiserum has no effect on haemopoiesis in long‐term cultures.
Oxytocin action: Lack of correlation between receptor number and tissue responsiveness
Authors: Goren H. J. , Geonzon R. M. , Hollenberg M. D. , Lederis K. , Morgan D. O.
Published: May 2005

Brattleboro rats exhibit diabetes insipidus (DI) because of a genetic autosomal recessive defect in the synthesis of vasopressin; oxytocin is synthesized normally. Preliminary work suggests that elevated circulating oxytocin levels may compensate for the absence of vasopressin. To evaluate the consequences of presumed elevations of oxytocin levels, oxytocin binding and tissue responsiveness have been measured in the uterus and epididymal fat cells of homozygous‐DI (HoDI) and heterozygous‐DI (HeDI) animals and Sprague‐Dawley and Long‐Evans controls. Surprisingly, whereas membranes from HoDI rat uteri exhibited an 85% reduction in oxytocin binding, the biological response (contraction) to oxytocin was indistinguishable from the uteri of HeDI or Sprague‐Dawley animals. The uterine response to carbachol was also normal in HoDI rats. In contrast, in adipocytes from HoDI animals, the biological response to oxytocin (glucose oxidation) was abolished, whereas the binding of oxytocin was normal; insulin‐stimulated glucose oxidation was, however, normal. These results indicate that receptor binding, while critical to hormone action, is not the sole determining factor. With oxytocin action, postreceptor mechanisms are most important in determining oxytocin responsiveness.
Studies on the biogenesis of an enzymatically active complex III of the respiratory chain from yeast mitochondria
Authors: Beattie Diana S. , Battie Cynthia A. , Weiss Robert A.
Published: May 2005

Complex III isolated from yeast mitochondria catalyzed an antimycin A and Diuron‐sensitive coenzyme QH2‐cytochrome c reductase activity with a turnover number of 15.7 sec−1 and contained 10 nmoles of cytochrome b and 4.6 nmoles of cytochrome c1 per mg of protein. Electrophoresis in sodium dodecyl sulfate acrylamide gels resolved Complex III into 10 bands with apparent molecular weights of 50,000, 40,000, 30,000, 29,000, 24,000, 17,000, 16,000, 12,000, 8,400, and 5,800. Yeast cells were labeled under nongrowing conditions with (35S)‐methionine in the absence or presence of inhibitors of cytoplasmiċ or mitochondrial protein synthesis. Labeled Complex III was isolated by immunoprecipitation from detergent‐solubilized mitochondria using antiserum raised against the purified complex. Analysis of the immunoprecipitates by polyacrylamide gel electrophoresis revealed that a 30,000‐dalton protein, cytochrome b, as well as 16,000‐dalton protein were labeled in the presence of cycloheximide, indicating that they are products of mitochondrial protein synthesis. Immunoprecipitates from mitochondria obtained from cells labeled in the presence of chloramphenicol contained a new radioactive peak with a molecular weight of 100,000. In addition, significant decreases in the labeling of the proteins with molecular weights of 50,000, 40,000, 30,000, and 16,000 were observed. When Complex III was isolated by immunoprecipitation from intact spheroplasts after a 5‐minute pulse with (35S)‐methionine, the 100,000‐dalton protein was labeled in the immunoprecipitate whether or not chloramphenicol was present; however, after a 1‐hour chase with unlabeled methionine, decreased labeling of the 100,000‐dalton protein was observed concomitant with an increased labeling of the 50,000‐ and 40,000‐dalton proteins. These results suggest that a protein with a molecular weight of 100,000 may either be a precursor or a partially assembled form of other proteins of Complex III, most probably the two largest polypeptides.
The cell substratum modulates skeletal muscle differentiation
Authors: Elson Hannah Friedman , Ingwall Joanne S.
Published: May 2005

During chick embryogenesis, massive alterations occur in the migrating cell's substratum, or extracellular matrix. The possibility that some of the components of this milieu play a regulatory role in cell differentiation was explored in a cell‐culture system derived from embryonic chick skeletal muscle tissue. In particular, the effects of collagen and the glycosaminoglycans were studied. Collagen is required for muscle cell attachment and spreading onto plastic and glass tissue‐culture dishes. A major constituent of the early embryonic extracellular space, hyaluronate (HA), while having no significant effect on collagen‐stimulated cell attachment and spreading, was found to inhibit myogenesis. The muscle‐specific M subunit of creatine kinase was preferentially inhibited. Control experiments indicated that the inhibition was specifically caused by HA and not by other glycosaminoglycans. A general metabolic inhibition of the cultures was not observed. Muscle cells could bind to HA‐coated beads at all stages of differentiation but were inhibited only when HA was added within the first 24 h of culture. Endogenous GAG in the culture is normally degraded during the first 24 h after plating as well; this may parallel the massive degradation of HA that occurs in the early embryo in vivo. These findings suggest a regulatory role for HA in modulating skeletal muscle differentiation, with degradation of an inhibitory component of the cell substratum a requirement for myogenesis.
Hormonal regulation of the adrenocortical cell
Authors: Gill Gordon N. , Hornsby Peter J. , Simonian Michael H.
Published: May 2005

Monolayer cultures of bovine and human adrenocortical cells have been used to study regulation of growth and function. Homogeneous bovine adrenocortical cells exhibit a finite life span of ∼60 generations in culture. Full maintenance of differentiated function (steroid hormone synthesis) requires an inducer such as ACTH and antioxidizing conditions. Full induction of differentiated function occurs only when cellular hypertrophy is stimulated by growth factors such as fibroblast growth factor and serum. ACTH and other agents that increase cellular cAMP inhibit replication but do not block growth factor‐induced cellular hypertrophy. ACTH and growth factors together result in a hypertrophied, hyperfunctional cell. Replication ensues only when desensitization to the growth inhibitory effects of ACTH occurs.

Cultures of the definitive and fetal zones of the human fetal adrenal cortex synthesize the steroids characteristic of the two zones in vivo. ACTH stimulates production of dehydroepiandrosterone (DHA), the major steroid product of the fetal zone, and of cortisol, the characteristic steroid product of the definitive zone. Prolonged ACTH treatment of fetal zone cultures results in a preferential increase in cortisol production so that the pattern of steroid synthesis becomes that of the definitive zone. The preferential increase in cortisol production by fetal zone cultures results from induction of 3β‐hydroxysteroid dehydrogenase, Δ4,5 isomerase activity, which is limiting in fetal zone cells. ACTH thus causes a phenotypic change in fetal zone cells to that of definitive zone cells.

In both bovine and human adrenocortical cells, the principal effect of ACTH is to induce full expression of differentiated function. This occurs only under conditions where growth substances and nutrients permit full amplication.
Genetics of receptors for bioactive polypeptides: A variant of swiss/3T3 fibroblasts resistant to a cytotoxic insulin accumulates lysosome‐like vesicles
Authors: Miskimins W. Keith , Ferris Wayne R. , Shimizu Nobuyoshi
Published: May 2005

Recently we have isolated six variants of Swiss/3T3 mouse fibroblasts that are resistant to the cytotoxic insulin‐diphtheria toxin A fragment. All of the variants proved to have greatly reduced or no insulin binding capacity, and several variants showed altered morphologies and growth characteristics. We now report on the further characterization of one of these variants, CI‐3. which displays a massive accumulation of membranous vesicles in its cytoplasm. By electron microscopy these vesicles resemble lysosomes. They also appear to fluorcsce bright orange after treatment of viable cells with acridine orange. However, the specific activity of several lysosomal enzymes is depressed in CI‐3. Additionally, there is an apparent shift in the density of vesicles containing lysosomal enzymes in this variant. These alterations may be directly related to CI‐3′s resistance to the cytotoxic insulin and have some important bearings on the mechanism of insulin action.
Tannic acid‐glutaraldehyde fixation reveals calcium ionophore‐induced changes in rabbit polymorphonuclear leukocyte membranes
Authors: Shannon W. Allen , Zellmer Daniel M.
Published: May 2005

TAG fixation of normal and Ca2+ ionophore‐treated rabbit polymorphonuclear leukocytes (PMN) has revealed membrane components not apparent with conventional glutaraldehyde fixation. These included a 30 Å external electron‐dense coating on untreated cells. A somewhat thicker coat (40 Å) was observed in ionophore‐treated, nondegranulating PMN. In ionophore‐treated, degranulating PMN, a 65 Å cell membrane coat was observed. A similar coat was observed on the inner side of the membrane of some azurophil‐type granules, but the electron density and thickness were not so pronounced. Cytoplasmic granules were often closely apposed and often protruded outward at the plasma membrane. Extracellular lamellae, sometimes stacked apposed to the plasma membrane, possibly represent remnants of intense granule extrusion. Sequential degranulation of the respective granules was not apparent.
Antigenic and genetic parameters in the stimulation and in the lytic phases of anti‐hapten + self cytotoxic T cells and their derived clones: Role of the T helper cell
Authors: Schmitt‐Verhulst A.‐M. , Albert F. , Guimezanes A. , Buferne M.
Published: May 2005

Requirements for stimulation of cytotoxic T cells (CTL) and for their lytic recognition have been compared in T cell lines repeatedly stimulated with trinitrobenzene sulfonate‐treated syngeneic murine spleen cells. Differences were observed between the requirements for cells to stimulate or to be lysed by the CTL, which included: (a) the expression of major histocompatibility complex (MHC = H‐2) encoded allelic products, and (b) the hapten density. Propagation of the CTL within the line required I‐A intra‐H‐2 homology between hapten‐treated stimulating cells and the line cells, whereas the lytic interaction required H‐2K region homology between hapten‐treated target cells and CTL. The hapten density requirement was analyzed for a responder (H‐2k) and a non‐responder (H‐2b) strain to low hapten density modified syngeneic cells. This property was found to be a characteristic of the lytic phase rather than of the stimulation of CTL. CTL clones could be derived by growing the line cells under conditions of limiting dilution in the presence of T cell growth factors. Such CTL clones were unable to be stimulated by their target antigens and were dependent on T cell growth factors for their propagation. These results are discussed in terms of the dependence of the development and growth of CTL on T helper cells.
Neue Untersuchungen über die Adsorption von Wasserstoff bei der Auflösung von Eisen
Authors: Cavallaro L. , Bolognesi G. P. , Felloni L.
Published: May 2005

Es wurden die Auflösungsvorgänge von Eisen in In‐HCL untersucht und ein Zusammenhang zwischen der Menge des vom Eisen aufgenommenen Wasserstoffs und der Auflösungsgeschwindigkeit des Metalls gefunden. Es stellt sich dabei ein dynamisches Sättigungsgleichgewicht im Innern des Metalls ein. Daraus läßt sich die Bedeutung der Teil‐Reaktionen ableiten und das Eingreifen von Inhibitoren erklären.
Erörterung der Aus‐ oder Umschalttechnik bei der Potentialmessung für den kathodischen Korrosionsschutz
Authors: Schwenk Wilhelm
Published: May 2005

Beim kathodischen Korrosionsschutz ist die Potentialmessung für die Kontrolle eines ausreichenden Schutzes notwendig. Bei der Potentialmessung einer stromdurchflossenen Elektrode wird immer ein Ohmscher Spannungsabfall miterfaßt, so daß der Meßwert zu negative erscheint. Durch eine Aus‐ bzw. Umschalttechnik kan dieser Spannungsabfall eliminiert werden. Hierbei ist es aber möglich, daß ein zu hoher Spannungsbetrag abgezogen wird, so daß der Meßwert zu positiv erscheint.

Der bei der Aus‐ bzw. Umschalttechnik verursachte Fehler ist vernachlässigbar klein. Für Umschaltprozesse kann theoretisch hergeleitet werden, daß der Fehler kleiner als 50 mV ist. Für Ausschaltprozesse kann eine ähnliche Abschätzung nicht durchgeführt werden. Jedoch zeigen Versuchsergebnisse, daß auch in diesem Falle der Fehler sehr klein ist. Die Aus‐ bzw. Umschalttechnik kann für Potentialmessungen beim kathodischen Korrosionsschutz mit vernachlässigbarem Fehler angewendet werden.
Über die derzeitigen Kenntnisse vom Alterungsverhalten der glasfaserverstärkten Kunststoffe und Versuche einer mechanisch‐technologischen Deutung des Phänomens
Authors: Matting A. , Müuller D.
Published: May 2005

Kunststoffe zeigen eine ausgeprägtere Zeit‐ und Umweltabhängigkeit ihrer Eigenschaften, insbesondere der Festigkeitseigenschaften, als die meisten anderen Werkstoffe der Technik. Der zunehmende Einsatz glasfaserverstärkter Kunststoffe machte deshalb grundlegende Untersuchungen über das Langzeitverhalten not‐wendig.

Der Einfluß langandauernder statischer und dynamischer Belastung sowie von Temperatur und Klimaten auf die Festig‐keitseigenschaften der glasfaserverstärkten Kunststoffe wird dargestellt und an Hand spannungsoptischer Untersuchungen der Grenzfläche zwischen Harz und Glas gedeutet.
Zur Korrosion milchwirtschaftlicher Geräte aus Kunststoffen und ihre Folgeerscheinungen
Authors: Kiermeier Friedrich
Published: May 2005

Die wiedergegebenen Wechselbeziehungen zwischen Kunststoff und Lebensmittel wird der Theoretiker nur widerwillig unter den Begriff „Korrosion”︁ einreihen wollen. Der Verfasser möchte jedoch zu bedenken geben, daß der Lebensmittelchemiker einen wesentlich strengeren Maßstab anlegen muß. Beispielsweise macht die an sich geringfügige Porosität einer verzinnten Dose die darin aufbewahrte Kondensmilch auf Grund des Übertritts von wenigen mg Eisen als Weißungsmittel für Kaffee unbrauchbar; ebenso genügen wenige mg von Kupfer einer Rahmpumpe, daß die Butter in kurzer Zeit ranzig wird. Bei der Korrosion der Kunststoffe liegt für den Lebensmittelchemiker meines Erachtens nach die gleiche Situation vor. Das Ausmaß der Korrosion der Kunststoffe auf dem Lebensmittelsektor ist im allgemeinen zwar geringfügig, durch die ausgelösten mikrobiologischen und sinnesphysiologischen Folgeerscheinungen kann jedoch die Korrosionswirkung so potenziert werden, daß das Lebensmittel für den Verbraucher nicht mehr zumutbar wird.
Erfahrungsaustausch und Schadensfälle. Schadensfälle durch falsche Werkstoffwahl und falsche Werkstoffkombinationen
Authors: Oeteren K. A.
Published: May 2005

Der Verfasser betont die Notwendigkeit der Wahl von Werkstoffen, die unter den vorgesehenen Korrosionsbedingungen beständig und miteinander verträglich sind. Dieser Grundsatz wird anhand von einigen Schadensfällen aus der industriellen Praxis erlätert, wo die Verwendung von Werkstoffen, Überzügen und ungeeigneten Werkstoffkombinationen zu Veränderungen des Aussehens sowie zu Kontaktkorrosion, Lochfraß und Spaltkorrosion geführt hat. Derartige nichtverträgliche Kombinationen sind z. B. Al/Cu, Zn/Cu, Stahl/Edelstahl, Al/Stahl und Cu/Stahl. Ebenso wird gezeigt, daß es notwendig ist, eine Gesamtbeschichtung und nicht nur eine Teilbeschichtung vorzusehen, da schon im Falle von unterschiedlichen Schichtdicken (z. B. Schmelztauchverzinkung neben elektrolytischer Verzinkung) unterschiedliche Lebensdauern resultieren können.
High‐temperature corrosion of NiCrAl alloy in oxygen‐chlorine mixtures
Authors: Viswanath R. P. , Rein D. , Hauffe K.
Published: May 2005

In order to decrease the attack of chlorine in O2Cl2N2 mixtures to NiCr alloys at high temperatures, the corrosion of a preoxidized Ni 20 Cr 4 Al alloy was investigated in N2O2 mixtures with 5 to 150 torr O2 and 20 torr Cl2 at 800°. For the generation of a protective layer of Al2O3 both the untreated and Al evaporated alloy sample was preoxidized in a H220 torr H2O atmosphere at 900° C. As was found, the catastrophic corrosion by Cl2 in a N2Cl2 gas mixture with 20 torr Cl2 could not be prevented by an Al2O3 layer. However, in the simultaneous presence of an oxygen content in the corroding gas mixture not lower than 10 torr, the attack of chlorine could be drastically decreased. The presence of 50 torr Cl2 postulates an oxygen pressure which is technically unrealistic. Since the formed oxide layer spalled off during the cooling period, the Ni 20 Cr 4 Al alloy cannot be used as material for cyclic oxidation. To what extent ThO2 particles dispersed in the alloy can prevent a spalling effect of the oxid film is at present an open question.
A cast low carbon stainless steel for use in nitric acid at higher concentrations and temperatures
Authors: Tischner Hermann , Pieger Bernd , Kratzer Adolf , Horn Elmar‐Manfred
Published: May 2005

This paper introduces three modifications of cast, low carbon stainless steels with about 15 to 20% Cr, 13% Ni and 4.5 to 6.5% Si which can be used for pumps and valves in nitric acid plants. Mechanical and structural properties, castability, machinability and weldability are discussed to characterize the practical applicability of these alloys for producers and users of such cast components. Laboratory corrosion tests in boiling nitric acid between 50 and 98 wt% prove the superior resistance of the Si‐bearing alloys in the 90% and 98% acid compared to standard CrNi‐steels without Si. Comparative field tests with cast pump impellers and casings confirm the very good corrosion resistance of the Si‐bearing alloys in highly concentrated nitric acid under service conditions.
Hochlegierte nichtrostende Stähle und Nickelbasislegierungen im Chemie‐Apparatebau
Authors: Diekmann Helmut
Published: May 2005

Die in den letzten Jahren vorgestellten neuen Legierungen der ferritischen Chromstähle, ferritisch‐austenitischen Stähle, höher und hoch‐legierten austenitischen Stähle und Nickelbasislegierungen können heute in mehreren gezeigten Anwendungen zumindest auf mehrjährige positive Betriebserfahrungen zurückblicken. Die Gruppe der austenitischen Stähle mit 6 Massenanteilen Molybdän stehen im chemischen Apparatebau an der Schwelle zu größeren Anwendungen. Die ersten vergleichenden Untersuchungen mit anderen hochlegierten Stählen sind vielversprechend. Die Nickelbasislegierungen werden sicher durch das Hastelloy alloy C‐22 ergänzt werden, so daß auch für stark oxidierend wirkende Medien neben Titan und anderen Legierungen dieser Werkstoff eingesetzt werden kann.
HASTELLOY® Alloy C‐22 –ein neuer und vielseitig anwendbarer Werkstoff für die chemische Industrie
Authors: Manning P. E. , SchßOubel J.‐D.
Published: May 2005

Der HASTELLOY®‐Legierung C‐22 liegt eine kritische Abstimmung der Legierungselemente Chrom, Molybdän und Wolfram zu Grunde. Dieses Verhältnis bewirkt eine optimale Korrosionsbestän‐digkeit im Ni‐Cr‐Mo‐System gegen oxiderende und nichtoxidierende Säuren sowie gegen Loch‐ und Spaltkorrosion. Legierung C‐22 verfügt darüber hinaus über eine ausgezeichnete thermische Stabilität bei Schweißverfahren mit hohem Wärmeeinbringen.

Die bisherigen Anwendungen von HASTELLOY alloy C‐22 bestätigen, daß dieser Werkstoff schwierige Korrosionsprobleme in der Praxis selbst dort löst, wo andere hochkorrosionsbeständige Legierungen versagen.
Der Einfluß von Kriechverformung auf die Ausbildung der Oxidschicht auf der Hochtemperaturlegierung Ni20Cr
Authors: Berchtold L. , Welker M. , Sockel H. G.
Published: May 2005

Die Ausbildung der Cr2O3‐Schicht auf Ni20Cr ist bei 850°C in H2/H2O (p(O2) = 10−19 bar) unter gleichzeitiger Kriechverformung an Flachproben untersucht worden. Die Schädigung der schützenden Oxidschicht durch Risse wurde in Abhängigkeit von der Verformungs‐geschwindigkeit und der Dehnung des Grundwerkstoffes beobachtet. Zur Trennung des Einflusses der plastischen Verformung der Oxidschicht und der Rißheilung wurden ergänzend voroxidierte Proben in reiner Ar‐Atmosphäre verformt.

Unterhalb der Kriechgeschwindigkeit

von 10−9s−1 werden keine Risse mehr festgestellt. Bei

< etwa 3 × 10−8s−1 treten Risse nur oberhalb Legierungskorngrenzen auf, bei höheren

liegen sie auch in Bereichen über den Legierungskörnern. Für

> etwa 3 × 10−8s−1 hängt die Rißdichte nicht mehr von

ab. Aus der unterschiedlichen Schädigung der Oxidschicht in den beiden Gasatmosphären kann geschlossen werden, daß bei

zwischen 10−9s−1 und 10−7s−1 neben einer Plastizität der Oxidschicht insbesondere die Rißheilung meßbare Einflüsse bei der Summe der Rißöffnungen hervorruft, mit steigendem

wird der Beitrag der Plastizität vernachlässigbar klein.
Einige Anmerkungen zur Arbeit von H. Leyerzapf „Zur Bedeutung und Geschichte des Wortes ‚Korrosion’︁”︁ (Werkstoffe und Korrosion 36 (1985) 88–96) [1]
Authors: Hübner Wolfgang
Published: May 2005

Die Arbeit von H. Leyerzapf (Werkst. Korros. 36 (1985) 88–96) wird kritisch kommentiert. Danach erscheint seine Beschränkung auf den Begriff „Korrosion”︁ nicht gerechtfertigt, denn im historischen Zusammenhang kommt dem Wort „Rost”︁ (und seinen Entsprechungen in allen Sprachen) mindestens die gleiche Bedeutung zu, auch dieses Wort wurde zum Fachterminus. Aus eigenen Untersuchungen zur Geschichte der Korrosionsforschung wurden dafür Beispiele genannt. Auch die Behauptung, in früherer Zeit fehle es an Theorien der Korrosion, ist nicht ganz korrekt.

Mit dem Hinweis auf den interdisziplinären Charakter des Forschungsgebietes wird gezeigt, daß Phasen geringerer Aktivität nur scheinbar Pausen waren, da die Entwicklung in dieser Zeit in anderen Disziplinen stattfand.
Effect of temperature on the Electrochemical corrosion behaviour of titanium
Authors: Rauscher Á. , Lukács Z.
Published: May 2005

The influence of variations in temperature on the electrochemical corrosion properties of VT 1‐0 commercial titanium was studied in deaerated 1 mol/dm3 sulphuric acid between 293 and 353 K. Galvanostatic and quasi‐potentiostatic polarization measurements were carried out. Corrosion rates were determined by mass loss measurements, too. The slopes of the cathodic Tafel‐like lines obtained with galvanostatic polarization change anomalously with temperature. The corrosion rates calculated from the mass loss data increase with increasing temperature at a higher rate than those determined with the polarization method, pointing to a self‐dissolution process. The results are attributed to a hydride layer with a H/Ti ratio increasing with temperature. Titanium hydride may play a dominant role both in the hydrogen evolution reaction and in the self‐dissolution process.
CORIS®: Wissensbasiertes System zur Lochkorrosion
Authors: Gervens T. , Gunia H. , Schlagner W.
Published: May 2005

Es wird ein flexibles, wissensbasiertes System über die chloridinduzierte Lochkorrosion vorgestellt. Der Anwender kann dieses System zu Zwecken der Wissensanfrage für eine Werkstoffüberprüfung oder eine Werkstoffauswahl nutzen. Gleichzeitig kann er neues Wissen hinzufügen. Das System stellt eine Kombination von herkömmlicher Expertensystemtechnik und der Technik neuronaler Netzwerke dar.
High‐pressure electron capture mass spectrometry
Authors: Knighton W. B. , Sears L. J. , Grimsrud E. P.
Published: May 2005

High‐pressure Electron Capture Mass Spectrometry (HPECMS) has demonstrated extraordinarily high chemical specificity and sensitivity in the analysis of numerous compounds of environmental and biomedical interest. In the application of this technique, however, difficulties in the form of unexpected EC mass spectra and unexplainable variations of sensitivity are often noted. In this review article, two distinct sets of processes that determine the nature of the ions produced in an HPEC ion source are reviewed and discussed. The first set of gas‐phase processes comprises the electron capture mechanism, leading to simple fragment and molecular anions. The second set of processes is imposed by physical realities of the typical HFEC ion source, These secondary processes can have large effects on the sensitivity of HPECMS to various types of EC‐active compounds and can lead to the production of unexpected ions in HPEC mass spectra. It will be shown that the successful use of HPECMS is greatly facilitated by an understanding of all of the above interactive factors. The scope of this review is limited to the processes that will be important only under the relatively pristine ion source conditions that are typically established for the trace analysis of EC‐active compounds introduced in very small quantities by capillary‐column gas chromatography. © 1996 John Wiley & Sons, Inc.
Stand der Entwicklung und Anwendung des Kaltpreßschweißens
Authors: Ruge J. , Böhme K.
Published: May 2005

Für das Kaltpreßschweißen wird eine Begriffsbestimmung gegeben. Zum Kaltpreßschweißen herangezogene Umformverfahren werden beschrieben und Einflußgrößen besprochen, die die Güte der Schweißverbindung beeinflussen. Den Abschluß bildet eine Zusammenstellung zahlreicher Anwendungsbeispiele aus der Praxis.
Wasserstoffversprödung von Feinkornbaustählen in Abhängigkeit von der Legierungszusammensetzung, der Gefügeausbildung und der mechanischen Belastung
Authors: Günther T. , Gräfen H.
Published: May 2005

An den Feinkornbaustählen StE 51 und StE 36 wurden Versuche zur dehnungsinduzierten Wasserstoffversprödung bei zügiger, bei schwellender und bei ruhender Belastung in Wasserstoff und Schwefelwasserstoff unter Variation der Dehngeschwindigkeit, des Gasüberdruckes, der Gasreinheit und der Oberflächengüte durchgeführt. Beide Stähle verhielten sich nicht grundsätzlich empfindlicher als weichere Baustähle. Eine Wasserstoffaufnahme erfolgte nur im Fließbereich und äußerte sich vornehmlich durch eine Abnahme der Brucheinschnürung oder zumindest durch Nebenrisse im Einschnürbereich. Diese Art der Versprödung kann z.B. für Konstruktionen bedeutsam sein, wenn es unter wechselndem Innendruck an Kerbstellen zu Fließvorgängen kommt.
Electrochemical Polarization and Passivation of Tin in neutral solutions of chloride, bromide and iodide ions
Authors: Ammar I. A. , Darwish S. , Khalil M. W. , Galal A.
Published: May 2005

Passivation of commercial grade tin (99.5%) was studied in 0.1 M KCl, KBr and KI solutions using the potentiodynamic technique involving cathodic and anodic polarization at various scan rates. While low scan rates (0.1 mV/sec) lead to the complete deterioration of the anode in chloride solutions, higher scan rates of 1 and 5 mV/sec lead to the appearance of two anodic peaks. These peaks disappear at still higher rates (10 mV/sec). In bromide solutions, two anodic peaks appear with scan rates of 1 and 5 mV/sec, and only one peak is observed with 50 mV/sec. A white precipitate is formed in both chloride and bromide solutions during anodic scanning. No gas evolution (O2, Cl2 or Br2) could be detected up to anode potentials of 3–4 V (SCE). At scan rates of 1 mV/sec and higher values, pitting does not occur, and thick anode films are formed. The film is gray in chloride solutions, and yellowish gray in bromide solutions. Values of the corrosion potential Ecor are recorded for the forward and reverse scanning. The corrosion cd Icor is calculated both by the Tafel extrapolation procedure and by the linear polarization technique. The latter gives more accurate results. In Cl− and Br− solutions, the first anodic peak associated with passivation is more anodic than the equilibrium potentials for the tin/tin oxides or hydroxides. Passivation is explained as a result of the formation of the sparingly soluble salts Sn(OH)Cl, Sn(OH)Br which appear both in the precipitate and in the anode film. The passivating films are constituted at least partially of these basic salts, and contain a proportion of the oxides and hydroxides of Sn. From the effect of scan rates on the characteristics of the anodic peaks, it appears that the formation of thick anode films is governed by the diffusion kinetics for porous films. Of the three possibilities considered as explanations for the second anodic peak (oxidation of impurities, oxidation of halides to oxyacids, and structural changes in the film) the latter appears to be the most probable one.

Thick anodic films are not formed in iodide solutions (scan rates 1, 5, 10 mV/sec), and the anode surface remains very bright. Dense evolution of I2 occurs during anodic polarization, and apart from I2 which dissolves in solution, the latter remains clear. Only one peak is observed in the forward anodic scanning. The polarization resistance technique gives Icor = 0. Thermodynamic calculations show that I3−, HIO, IO−, HIO3, IO3−, HIO4, and IO4− occur in 0.1 M KI solutions at potentials less anodic than the potential of the anodic peak (1.32 to 1.37 V, vs SCE). This peak potential is more anodic than the quilibrium potential for I2 evolution.
Nachsintern von reaktionsgebundenem Siliciumnitrid unter erhöhtem Stickstoff‐Druck
Authors: Kleebe H.‐J. , Ziegler G.
Published: May 2005

Nachsintern von reaktionsgebundenem Siliciumnitrid (RBSN) unter hohem Stickstoffdruck stellt ein vielversprechendes Verfahren zur Herstellung dichter Si3N4‐Materialien dar. Diese Herstellungsmethode beinhaltet zwei thermische Behandlungsschritte, die Nitridierung und Sinterung. Daher ergibt sich, verglichen mit der Sinterung von Si3N4‐Pulverkörpern, eine größere Anzahl von Einflußparametern.

In dieser Arbeit wird der Einfluß der Si‐Pulvercharakteristika (speziell der Korngrößenverteilung) der Art und Menge der Additive sowie der Prozeßparameter Sinterdauer und Sintertemperatur auf das Verdichtungsverhalten und auf die resultierenden Eigenschaften des nachgesinterten reaktionsgesinterten Si3N4 (SRBSN), wie Dichte und Biegefestigkeit, diskutiert. Insbesondere bei Materialien mit geringer Additivkonzentration konnte eine deutliche Korrelation zwischen Pulvercharakteristika und den Eigenschaften des SRBSN gefunden werden.
Querrißbildung in 0/90/0 CFK‐Laminaten
Authors: Peters P. W. M.
Published: May 2005

Querrißbildung in kohlefaserverstärkten Kunststoffen (CFK) mit sowohl duromerer als auch thermoplastischer Matrix wurde untersucht an 0/90/0 Laminaten mit unterschiedlicher 90°‐Schichtdicke. Da die 90°‐Schicht in einem Mehrschichtverbund zuerst versagt, kann die höhere Festigkeit der anderen Schichten nicht ausgenutzt werden. Aus diesem Grunde muß nach Möglichkeiten gesucht werden, die Querzugfestigkeit (Festigkeit senkrecht zur Faser) von Faserverbundwerkstoffen zu erhöhen. Zunächst ist es deshalb notwendig, den Einfluß der Parameter, die die Querzugfestigkeit beeinflussen, zu untersuchen. In dieser Arbeit ist der Einfluß der Matrix(‐Bruchdehnung), der Faser/Matrix‐Grenzschicht, der Lunker und der Stützwirkung von Nachbarschichten ermittelt worden. Mit Hilfe von zweiparametrigen Weibull‐Verteilungen der 90° ‐Schicht‐Bruchdehnung, die das Phänomen der mehrfachen Rißbildung in einer Probe beschreiben, wurde festgestellt, daß die Stützwirkung der Nachbarschichten, verbesserte Faser/Matrix‐Haftung und Matrixduktilität die Bruchdehnung erhöhen und Lunker die Bruchdehnung verkleinern.