Depletion of Grain-Boundary Phase and Elastic Creep Deformation Upon Ultra-Long Flexural Stress Rupture Experiments of NC-132 Silicon Nitride

A unique grain-boundary structure evolution was observed in two MgO-doped silicon nitride specimens (Norton, NC-132) that were tested in ultra-long flexure stress rupture experiments with an applied stress of 266 MPa and fractured at 14 941 and 17 376 h. Transmission electron microscopy showed that, although the starting material had a secondary glass phase both at multi-grain junctions and along grain boundaries, the tested specimens contained no residual glass phase. Concurrent with the elimination of the secondary glass phase, a continuous network of cracked grain boundaries was observed after long-term flexure testing consistent with the concept of elastic creep. It is, therefore, concluded that at ultra-long annealing times, this material is affected by creep deformation via microcrack nucleation and growth due to the depletion of the amorphous siliceous grain-boundary phase, which is seen as a truly transient, fugitive secondary phase.     

Statistical Analysis of the Intergranular Film Thickness in Silicon Nitride Ceramics

Silicon nitride materials typically reveal thin amorphous intergranular films along grain boundaries, with only the exception of special boundaries. It is known that such grainboundary films strongly affect the high-temperature properties of the bulk material. High-resolution electron microscopy (HREM) was used to study these amorphous films in different Si₃N₄ ceramics. The observed film thicknesses at grain boundaries in these materials varied between 5and 15 Å. It was shown that the grain-boundary film thickness strongly depends on film chemistry. Careful inspections of film-thickness measurements across grain boundaries in a given material suggest that the film widths vary on the order of 1 Å. Therefore, a quantitative evaluation should allow for the determination of the standard deviation of the film thickness. The amorphous film widths along grain boundaries in four materials were measured over the entire length (up to 1 μm) of the grain boundary between two triple points. Forty to fifty data points were evaluated for each boundary, giving a Gaussian-like distribution of the film thickness around a median value, which corresponded well with the film width measured from single HREM micrographs. The accuracy achieved by the statistical method was better than ± 1 Å.     

Ca15(CBN)6(C2)2O- a new cubic structure type containing CBN-anions together with acetylide and oxo anions

Ca₁₅(CBN)₆(C₂)₂O contains CBN⁴⁻ anions as well as C₂⁻ units and isolated O²⁻ anions. The compound is obtained by heating a stoichiometric mixture of CaO, C and BN with an excess of Ca in sealed niobium ampoules to 1270 K. It crystallizes in the space group Ia d with a = 1656.84(9) pm. Preparation, crystal structure, NMR and IR-spectroscopic properties are discussed.     

Datenschutz-Schutzziele — revisited

Zusammenfassung  Die Arbeit mit Schutzzielen hat sich grunds?tzlich bew?hrt. Sie sind so formuliert, dass sie die Anforderungen an technische und organisatorische Systeme sowohl abstrakt überblickbar als auch in Form von Ma?nahmen hinreichend konkret fa?bar machen. Der Beitrag empfiehlt, sie in Datenschutzgesetze und Vertr?ge aufzunehmen, als Leitlinien für den Entwurf und Betrieb von IT-Infrastrukturen heranzuziehen und in Mechanismen transformiert als WebService-Policies auszudrücken — und unterbreitet einen Strukturierungsvorschlag.     

Bioinspired Intervertebral Disc with Multidirectional Stiffness Prepared via Multimaterial Additive Manufacturing

Degenerative disc disease (DDD) has become a significant public health issue worldwide. This can result in loss of spinal function affecting patient health and quality of life. Artificial total disc replacement (A-TDR) is an effective approach for treating symptomatic DDD that compensates for lost functionality and helps patients perform daily activities. However, because current A-TDR devices lack the unique structure and material characteristics of natural intervertebral discs (IVDs), they fail to replicate the multidirectional stiffness needed to match physiological motions and characterize anisotropic behavior. It is still unclear how the multidirectional stiffness of the disc is affected by structural parameters and material characteristics. Herein, a bioinspired intervertebral disc (BIVD-L) based on a representative human lumbar segment is developed. The proposed BIVD-L reproduces the multidirectional stiffness needed for the most common physiological kinematic behaviors. The results demonstrate that the multidirectional stiffness of the BIVD-L can be regulated by structural and material parameters. The results of this research deepen knowledge of the biomechanical behavior of the human lumbar disc and may provide new inspirations for the design and fabrication of A-TDR devices for both engineering and functional applications.     

Ceramic micro parts produced by micro injection molding: latest developments

Powder injection molding is a preferred technology for the production of micro parts or microstructured parts. Derived from the well known thermoplastic injection molding technique it is suitable for a large-scale production of ceramic and metallic parts without final machining. To achieve good surface quality and control the part size and distortions is an important goal to allow mass production. This means that all process steps like part design adjusted for MIM/CIM-technology, appropriate choice of powder and binder components and injection molding simulation to design the sprue are required. Concerning the injection molding itself high quality mold inserts, high-precision injection molding with suitable molding machines like Battenfeld Microsystem50 or standard machine with special equipment like variotherm or evacuation of the molding tool and an adjusted debinding and sintering process have to be available. Results of producing micro parts by powder injection molding of ceramic feedstock will be presented.     

Zur Messung der Oberfläche von Spanplatten

Zusammenfassung Die Oberfl?chen von Spanplatten sind für deren Weiterverarbeitung von Bedeutung. Die Frage der Technik zur Messung der Oberfl?chengüte von Spanplatten wird er?rtert. Im Zusammenhang mit eigen Untersuchungen werden Vorschl?ge für die Oberfl?chenmessungen mit Hilfe des Tastschnittverfahrens gemacht. Die zur Durchführung des Verfahrens notwendige Quellung der zu prüfenden Spanplattenobertl?chen erfolgt bei Wasserlagerung rund hundertmal schneller als bei Lagerung in feuchter Luft. Eine Erh?hung des Hydrophobierungsmittel-Gehaltes der Decklagenp?ne, zeigt keinen nennenswerten Einflu? auf den Verlauf der Decklagenquellung. Mit hoher Decklagen-Spanfeuchtigkeit hergestellte Platten weisen nach 24 h Wasserlagerung eine nur geringe Rauhtiefenzunahme auf. Spanplatten, die mit Schleifpapier feinerer K?rnung geschliffen werden, zeigen auch nach einer Wasserlagerung glattere Fl?chen als mit grober K?rnung gechliffene Platten. Das Befeuchten der Spanplattenoberfl⇂hen vor dem Schleifen ergibt eine merkliche Verminderung der Rauhtiefenzunahme gegenüber nicht befeuchteten Oberfl?cher. Für die Untersuchung unbehandelter Spanplatten-oberfl?chen ist das Pastentestverfahren nach H. Flemming gut geeignet.

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Measuring of the surface of particleboard

Summary The surfaces of particleboard are of importance for their finishing. The problem of technics concerning the measurement of surface quality of particleboard is discussed. In connection with own investigations proposals for surface measurements with the tracer method are made. The swelling of the particle-board to be tested necessary for the procedure is, with watering achieed about a hundred times quicker than in humid air. An increase in the content of water-repellent agent in the outer layer does not show any significant effect on the swelling of surface layers. After 24 h of watering, boards produced with a high moisture content of the surface layers show merely a slight increase in roughness. Particleboard sanded with sandpaper of a finer grit even after watering shows a smoother surface than boards sanded with a coarser grit. The wetting of the particleboard surfaces prior to sanding yields a notable diminishing of the roughness increase as against not wetted surfaces. For the investigation of untreated particleboard surfaces the Pastentest procedure according to H. Flemming is well suited.

     

Oxidation Kinetics of an Amorphous Silicon Carbonitride Ceramic

The oxidation kinetics of amorphous silicon carbonitride (SiCN) was measured at 1350°C in ambient air. Two types of specimens were studied: one in the form of thin disks, the other as a powder. Both specimens contained open nanoscale porosity. The disk specimens exhibited weight gain that saturated exponentially with time, analogous to the oxidation behavior of reaction-bonded Si₃N₄. The saturation value of the weight gain increased linearly with specimen volume, suggesting the nanoscale pore surfaces oxidized uniformly throughout the specimen. This interpretation was confirmed by high-resolution electron microscopy and secondary ion mass spectroscopy. Experiments with the powders (having a particle size much larger than the scale of the nanopores) were also consistent with measurements of the disks. However, the powder specimens, having a high surface-to-volume ratio, continued to show measurable weight gain due to oxidation of the exterior surface. The wide range of values for the surface-to-volume ratio, which included all specimens, permitted a separation of the rate of oxidation of the free surface and the oxidation of the internal surfaces of the nanopores. Surface oxidation data were used to obtain the rate constant for parabolic growth of the oxidation scale. The values for the rate constant obtained for SiCN lay at the lower end of the spectrum of oxidation rates reported in the literature for several Si₃N₄ and SiC materials. Convergence in the behavior of SiCN and CVD-SiC is ascribed to the purity of both materials. Conversely, it is proposed that the high rates of oxidation of sintered polycrystalline silicon carbides and nitrides, as well as the high degree of variability of these rates, might be related to the impurities introduced by the sintering aids.