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- Englisch (14) (entfernen)
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- LTCC (5)
- Coefficient of thermal expansion CTE (2)
- Design (2)
- Glass ceramic composites (2)
- Particle size distribution (2)
- Strain gauge (2)
- Thin-film substrate (2)
- Accuracy experiment (1)
- Alumo-sol (1)
- Analytical centrifuge (1)
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 (9.4 ppm/K) and a low modulus of elasticity (82 GPa) for the application as support material for thin-film sensors. In the first part, 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 accuracy of the assembled load cells corresponds to accuracy class C6. That qualifies the load cells for the use in automatic packaging units and confirms the applicability of the low-temperature co-fired ceramic (LTCC) substrates for fabrication of accurate strain gauges. In the second part, to facilitate the deposition of thin-film sensor structures to the LTCC substrates, pressure-assisted sintering step is modified using smooth setters instead of release tapes, which resulted in fabrication of substrates with low average surface roughness of 50 nm. Titanium thin films deposited on these substrates as test coatings exhibited low surface resistances of 850 Ω comparable to thin films on commercial alumina thin-film substrates with 920 Ω. The presented material design and advances in manufacturing technology are important to promote the development of high-performance thin-film 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 refined. By the use of smooth setters instead of release tapes substrates with minimal surface roughness were fabricated. Metallic thin films deposited on these substrates exhibit low surface resistances comparable to thin films on commercial alumina thin-film substrates. The presented advances in material design and manufacturing technology are important to promote the development of high performance thin-film strain gauges.
Alumina sols were prepared using a modified
Yoldas procedure, thus resulting in sols with high solids
content, excellent long term stability and small particle size.
PH-value ranged between 3.7 and 0.6. Sols were characterised
using rheological, UV-vis transmission and particle
size measurements. Depending on NO3-/Al molar ratio as
well as solids content, sols vary. Analysis of reduced viscosities
indicate the formation of chainlike polymeric species
above a critical solids fraction.
Presented are results of an inter-laboratory study (ILS) for measurements of the particle size distribution of fine powders in wet dispersion by laser diffraction. In this proficiency test 32 participants from four countries took part. They utilized 13 different devices from 7 manufacturers.
Three commercial powders (glass spheres and two silicon carbide powders) showing a median diameter of about 30, 10 and 1 µm (volume distribution), respectively, were chosen for the procedure. A homogeneity study was carried out after the units had been separated and bottled.
All participants received their test samples including a description of the standard operating procedures based on ISO 13320:2009 – to ensure that experiments were performed in a consistent manner. Results were calculated using the Mie Theory. The general means and the precision of the results were estimated in accordance with ISO 5725-2:2002.
The evaluation showed excellent values of repeatability standard deviation. Values of 4 to 21?% of the reproducibility standard deviation of the results were found in the particle size range above 1 µm. Much larger deviation between the labs was detected in the case of smaller particles. Differences in the design of the analyzers were unambiguously identified as the main reason for the large deviations.
Resolution of capacitive sensors can be improved enormously by replacement of the dielectric material between the capacitor plates (e.g. air-dielectric) by a dielectric fluid with high permittivity. High dielectric liquid dispersions of ceramic micro and nano powders should be qualified as dielectric fluid with longtime shelf life.
For this purpose it was necessary to produce stabilized ceramic suspensions with high particle concentration and to investigate sedimentation processes of the particles. Characterization of particles was done by use of zeta potential measurement, gas adsorption measurements (BET), density measurement with gas pycnometer as well as particle sizing by ultrasound spectroscopy and by use of an optical centrifuge.
Shelf life of optimized electrostatic and steric stabilized ceramic suspension was investigated by use of an optical centrifuge, a LUMISizer 651 MW (LUM Ltd.) with STEP technology and front tracking analysis. Two different wave lengths – NIR (865 nm) and blue light (470 nm) were available for examination. Centrifugation measurements with different rotation speed were used to study the rheological behavior and the sedimentation process. By this way it was possible to achieve accelerated stability determination. Measured values could be used to simulate the sedimentation process under gravity acceleration and to predict shelf life for suspensions with different dispersants.
New applications of low-temperature co-fired ceramics (LTCC), such as pressure sensors or integrated functional layers, require materials that possess higher coefficients of thermal expansion (CTE). To fabricate LTCC with elevated CTE, two methods of material design are examined: firstly, glass ceramic composites (GCC), which consist of >50 vol% glass in the starting powder, and, secondly, glass-bonded ceramics (GBC), where glass is added as a sintering aid only. The CTE of GBC is mainly determined by the crystalline component. For GCC, the CTE can be well predicted, if CTE and elastic data of each phase in the microstructure are known. A nonlinear characteristic of the CTE versus phase composition was found with increasing Ecrystals/Eglass ratio and absolute CTE difference between the components. The glass composition and glass amount can be used to compensate the fixed properties of a crystalline material in a desired way. However, because the CTE and permittivity of a glass cannot be chosen independently, an optimum glass composition has to be found. For a given LTCC, it is possible to control the devitrification by shifting the glass composition. In this way, the resulting CTE values can be predicted more exactly and tailoring becomes possible. Different LTCC materials, based on the crystalline compounds Ba(La,Nd)2Ti4O12, ZrO2 (Y-TZP), SiO2 (quartz), and specially developed glasses, possessing an elevated CTE of around 10 × 10-6 K-1 while showing permittivity εr between 6 and 63, are introduced.