Optimization of the gelcasting of a silicon nitride formulation

An optimum gelcasting condition for a silicon nitride formulation was determined using the Taguchi statistical method. An L{sub 8}(4{sup 1} {times} 2{sup 4}) design, in which the effects of one factor at four levels and four factors at two levels were evaluated in only eight experiments, was used. The factors at two levels were: the total monomer concentration, the monomer/crosslinker ratio, the initiator concentration, and the initiator/catalyst ratio; the factor at four levels was the initiator concentration per mass of the slip. The primary criterion used to determine optimum design was the green strength of the dried part, although three other parameters were measured: initial slip viscosity, time for the slip viscosity to reach 300 mPa.s. at 25 C, and time for the slip to gel at 50 C. The optimum gelcasting conditions from the designed experiments predicted 80% increase in green strength (4.3 MPa versus 2.4 MPa, the initial value). The confirmation runs showed only a 60% increase (3.8 MPa)

Nondestructive evaluation development for process control

A joint project between Garrett Ceramic Components (GCC) of Allied Signal Aerospace Corporation and Argonne National Laboratory (ANL) is ongoing to evaluate nondestructive characterization (NDC) methods to detect and measure process-induced variations in ceramic materials. The process methods of current focus on slip-casting and injection molding and the NDC methods being evaluated are microfocus X-ray computed tomography (XCT) and nuclear magnetic resonance computed tomography (MRCT). As part of this work, SiC whisker reinforced Si{sub 3}N{sub 4} (GCC's GN-10 material) has been pressure slip-cast at two casting pressures, 15 and 40 psi; and at length/diameter ratios of 1.5, 2.5 and 3.0 with whisker contents of 20, 23, 27 and 30 wt %. Three-dimensional microfocus XCT has been used to study density variations in billets produced by different process conditions. Destructive measurement of density variation has been compared to the XCT measurements and correlations established. XCT has been shown to be able to detect <5% variations in as-cast density and these were destructively verified

Metrology for long distance surveying – a joint attempt to improve traceabili - ty of long distance measurements

A number of applications, e.g., the estab ~ ishment of local ties at geodetic fundamental stations, but also the maintenance of surveillance networks require distance measurements over hundred metres or more with uncertainties at the millimetre level or even below. However, based on the current state of technology and understanding of perturbing influences, a measurement traceable to the Sl definition of the metere with such uncertainties is extremely challenging or even impossible. The accuracy of electrooptic distance metres (EDMs) on one hand is primarily limited by the imperfect knowledge of the index of refraction of air, the measurement uncertainty of distance measurements based on Global Navigation Satellite Systems (GNSS) is even more difficult to quantify. In a joint research projects of 12 European institutions, scientists from national metrology institutes have united with partners from geodesy to develop novel technological and methodical solutions to understand, to quantify better, and to reduce the uncertainty of this kind of measurements, in particular fostering traceability to the Sl unit metre. In case of optical distance metrology, refractivity-compensated primary and transfer standards will be developed and applied to reference baselines in Europe. Furthermore, completely novel approaches based on femtosecond laser sources will be explored and set up. In case of GNSS-based distance metrology, a systematic investigation of sources of uncertainty will performed, leading to a sound uncertainty budget. Two different near real-time 3D monitoring systems will be developed and compared at geodetic fundamental stations. The contribution wants to present the concept and the scientific and technological ideas of the project which starts on July 1st 2013, inviting the geodetic community to provide guidance and feedback

Use of volume x-ray tomography for characterizing density variations in as-cast ceramic bodies

A joint project is ongoing to evaluate nondestructive characterization (NDC) methods to detect and measure process-induced variations in ceramic materials. The process methods of current focus are slip-casting and injection molding, and a primary NDC method being evaluated is microfocus X-ray computed tomography (XCT). SiC-whisker-reinforced Si[sub 3]N[sub 4] has been pressure-slip-cast at two casting pressures, 0.103 and 0.276 MPa (15 and 40 psi); and at length/diameter ratios of 1.5, and 2.67 with whisker contents of 20, 23, 27, and 30 wt.%. Three-dimensional microfocus XCT has been used to study density variations in billets produced by different process conditions. Destructive measurement of density variation has been compared to the XCT measurements and correlations have been established. XCT has been proven (by destructive verification) to be capable of detecting <5% variations in as-cast density