Marion Gemeinert

Reliable nanomaterial classification of powders using the volume-specific surface area method

AbstractThe volume-specific surface area (VSSA) of a particulate material is one of two apparently very different metrics recommended by the European Commission for a definition of “nanomaterial” for regulatory purposes: specifically, the VSSA metric may classify nanomaterials and non-nanomaterials differently than the median size in number metrics, depending on the chemical composition, size, polydispersity, shape, porosity, and aggregation of the particles in the powder. Here we evaluate the extent of agreement between classification by electron microscopy (EM) and classification by VSSA on a large set of diverse particulate substances that represent all the anticipated challenges except mixtures of different substances. EM and VSSA are determined in multiple labs to assess also the level of reproducibility. Based on the results obtained on highly characterized benchmark materials from the NanoDefine EU FP7 project, we derive a tiered screening strategy for the purpose of implementing the definition of nanomaterials. We finally apply the screening strategy to further industrial materials, which were classified correctly and left only borderline cases for EM. On platelet-shaped nanomaterials, VSSA is essential to prevent false-negative classification by EM. On porous materials, approaches involving extended adsorption isotherms prevent false positive classification by VSSA. We find no false negatives by VSSA, neither in Tier 1 nor in Tier 2, despite real-world industrial polydispersity and diverse composition, shape, and coatings. The VSSA screening strategy is recommended for inclusion in a technical guidance for the implementation of the definition. Graphical abstractWe evaluate the extent of agreement between classification by electron microscopy (EM) and classification by Volume-Specific Surface Area (VSSA) on a large set of diverse particulate substances. These represent the challenges anticipated for identification of nanomaterials by the European Commission recommendation for a definition of nanomaterials for regulatory purposes.

Development of Advanced Low Temperature Co-Fired Ceramics (LTCC)

An important advantage of LTCC is the huge variability concerning an attainable property spectrum. Both crystalline and glassy raw materials can be combined and different material concepts (e.g. glass ceramic composites, glass bonded ceramics) are available. The combination of tapes with tailored properties (e.g. permittivity, sintering behaviour....) inside of one laminate further expands the variability of LTCC. Special miniaturized microwave modules were produced by combination of LTCC tapes with low and medium permittivities. Low shrinkage in lateral direction and low tolerances of shrinkage are an indispensable precondition for highdensity component configuration in LTCC modules. A proper combination of tapes with separate sintering ranges can be used to prevent lateral shrinkage. First results of this alternative “zero shrinkage” concept (without sacrificial tapes) are presented. Introduction LTCC are preferably used where integration of passive components (resistors, capacitors, inductors...), miniaturization (high savings in volume and mass) and high reliability is demanded. LTCC possesses great potentials on several promising application sectors like wireless communication, sensor technology, electronic control units and micro-systems [1]. But of course it exists a sharp competition with alternative solutions e.g. in the area of electronic application with polymer PCBs (Printed Circuit Boards), thick and thin film hybrid technology. LTCC has been available for many years. The technology has enjoyed a significant market growth in recent years, particularly in microwave applications and automotive electronics. But, to expand the application fields of LTCC, innovations in material development and ceramic processing as well as integration of process control methods in the LTCC technology are constantly necessary. One innovative research direction of advanced LTCC are “two-material” multilayer. Advanced LTCC by “two-material” multilayer challenge and chance Precondition for a successful production of “two-material” multilayer is the development of well adapted materials, respectively tapes. This task is very ambiguous, because both processing parameters (lamination, debindering, sintering) and material properties (high-temperature reactivity, thermal expansion.....) have to be matched. LTCC offers a broad variety of possibilities to tailor microstructure and phase composition. The microstructure of most LTCC materials consists of both glassy and crystalline phases. But the amount can strongly vary. Fig. 1 illustrates, that four types of LTCC materials with different glass amounts are known. Each type shows a characteristic sintering mechanism. Most of the current commercial LTCC materials possess a glass amount higher than 50 vol.-%. They can be classified either in “Glass Ceramic Composites (GCC)” (e.g. Du Pont 951, Heraeus CT 700) or in “Glass Ceramics (GC)” (e.g. Ferro A6) [2]. In the last years also “glass-free” LTCC was introduced, e.g. crystalline phases in the system Bi-Ti-Si-O. But LTCC can also be produced with a low glass amount (about 10 vol.-%), so-called “Glass Bonded Ceramics (GBC)”. In this case glasses with very low viscosity and high reactivity against the crystalline phase are necessary, to allow for solution-reprecipitation process below 950 °C. The multitude of LTCC material concepts expands the chances developing proper tapes for a “two-material” multilayer. Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 1181-1184 doi:10.4028/www.scientific.net/KEM.264-268.1181

LTCC Substrates for High Performance Strain Gauges

Recent advances in the development of high gauge factor thin-films for strain gauges prompt the research on advanced substrate materials. A glass ceramic composite has been developed in consideration of a high coefficient of thermal expansion and a low modulus of elasticity for the application as support material for thin-film sensors. Constantan foil strain gauges were fabricated from this material by tape casting, pressure-assisted sintering and subsequent lamination of the metal foil on the planar ceramic substrates. The sensors were mounted on a strain gauge beam arrangement and load curves and creep behavior were evaluated. The accuracy of the assembled load cells correspond to accuracy class C6. That qualifies the load cells for the use in automatic packaging units and confirms the applicability of the LTCC substrates for fabrication of accurate strain gauges. To facilitate the deposition of thin film sensor structures onto the LTCC substrates, the pressure-assisted sintering technology has been ref...