Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “SiO2”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Estimation of particle size based on LDV measurements in a de-accelerating flow field

The accuracy of velocity measurements made with a laser velocimeter is strongly dependent upon the response of the seeding particles to the dynamics of the flow field. The smaller the particle the better the response to flow fluctuations and gradients and therefore the more accurate velocity measurement. In direct conflict is the requirement of light scattering efficiency to obtain signals with the laser velocimeter which, in general, is better as the particle size is increased. In low speed flow fields these two requirements on particle size overlap and accurate measurements may be obtained. However in high speed flows, where the velocity gradients may be severe, very small particles are required to maintain sufficient dynamic response characteristics to follow the flow. Therefore if velocity measurements are to be made in these flows, the laser velocimeter must be designed with sufficient sensitivity to obtain signals from these small particles. An insitu determination of the size distribution of kaolin particles (Al2O3, .2 + or - SiO2 . 2H2O) in the 16-foot Transonic Tunnel and the sensitivity characteristics of the laser velocimeter system is described.

Meyers, J. F.↗
NASA NTRS1985

Phenomenological study of the behavior of some silica formers in a high velocity jet fuel burner

Samples of four silica formers: single crystal SiC, sintered alpha-SiC, reaction sintered Si3N4 and polycrystalline MoSi2, were subjected to a Mach 1 jet fuel burner for 1 hr, at a sample temperature of 1375 deg C (2500 deg F). Two phenomena were identified which may be deleterious to a gas turbine application of these materials. The glass layer formed on the MoSi2 deformed appreciably under the aerodynamic load. A scale developed on the samples of the other materials which consisted of particular matter from the gas stream entrapped in a SiO2 matrix.

Cawley, J. D.↗
NASA NTRS1985

Capsulation of moldings made from silicon ceramic material

Ceramic articles are potted for hot isostatic pressing by porous glass and/or ceramic coating which is sintered to a pressure-tight coating in vacuo. Thus, a powdered SiO2 glass mixture with saturated alcohol sterin is sprayed on a SI3N4 ceramic, dried, introduced into the press which is evacuated to less than 0.013 mbar and heated to approximately 1200 C to drive off the organic binder and leave a powdered glass coating on the ceramic. The coating is sintered by heating to approximately 1200 C for 0.5 to 2 hours and forms a tight gass-impermeable layer. The press is heated to approximately 1700 C at 1000-300 bar and isostatic pressing is performed in the conventional manner.

Rossmann, A.↗
NASA NTRS1986

Conductimetric determination of decomposition of silicate melts

A description of a procedure is given to detect decomposition of silicate systems in the liquid state by conductivity measurements. Onset of decomposition can be determined from the temperature curves of resistances measured on two pairs of electrodes, one above the other. Degree of decomposition can be estimated from temperature and concentration dependency of conductivity of phase boundaries. This procedure was tested with systems PbO-B2O3 and PbO-B2O3-SiO2.

Kroeger, C.↗
NASA NTRS1986

Technology for satellite power conversion

The work performed in this reporting period has concentrated on the metal-oxide-metal (MOM) diode. The fabrication procedure begins with the deposition of gold probing pads to provide a non-oxidizing contact to test the dc characteristics to the diode accurately. A thin patch capped with an insulating SiO2 layer, is deposited next to form the first half of the diode. The other half of the diode, typically Ni, is deposited completing the conduction path from the oxidized edge of the Ni patch to the opposite gold probing pad. It is important in this step that the last metallization take place without exposing the newly oxidized surface to the atmosphere. Successful production of diodes has been achieved. Work on millimeter wave frequency rectennas incorporating known semiconductor diode technology has been initiated.

Gouker, M. A.↗
NASA NTRS1985

Thermal regimes in the detachment fault environment as deduced from fluid inclusions

Extensional tectonism, which dominates middle- and late-Tertiary geology in western Arizona, southeastern California, and southern Nevada, is characterized by normal regionally extensive, low-angle detachment faults. The decollement movement of Fupper plate rocks relative to lower plate assemblages created extensive zones of dilatency, including synthetic and antithetic listric normal faults, tear faults, tectonic crush breccias, shatter breccias, and gash veins in lithologic units above and below the detachment. The tectonically enhanced permeability above and below the detachment fault permitted mass migration of large volumes of hydrothermal solutions along the fault zone during and following upper plate movement. Major quantities of MgO, CaO, K2O, FeO/Fe2O3, SiO2 and CO2 were added to rocks in and near the detachment and related structures. Also introduced were varying amounts of trace elements including Mn, Cu, S, Mo, Ba, Au, Pb, Zn, U and/or Ag. Minerals containing fluid incusions were collected from all of these loci at locations in detachment faulted terranes in western Arizona and southeastern California.

Beane, R. E.↗
NASA NTRS1986

Correlation of processing and sintering variables with the strength and radiography of silicon nitride

A sintered Si3N4-SiO2-Y2O3 composition, NASA 6Y, was developed that reached four-point flexural average strength/standard deviation values of 857/36, 544/33, and 462/59 MPa at room temperature, 1200 and 1370 C respectively. These strengths represented improvements of 56, 38, and 21 percent over baseline properties at the three test temperatures. At room temperature the standard deviation was reduced by over a factor of three. These accomplishments were realized by the iterative utilization of conventional x-radiography to characterize structural (density) uniformity as affected by systematic changes in powder processing and sintering parameters. Accompanying the improvement in mechanical properties was a change in the type of flaw causing failure from a pore to a large columnar beta- Si3N4 grain typically 40 to 80 microns long, 10 to 30 microns wide, and with an aspect ratio of 5:1.

Sanders, W. A.↗
NASA NTRS1986

Simulation of cosmic irradiation conditions in thick target arrangements

One approach to simulate 2-pi irradiation conditions of planetary surfaces which has been widely applied in the past are bombardments of so called thick targets. A very large thick target was exposed recently to 2.1 GeV protons at the Bevatron-Bevalac in Berkeley. In a 100x100x180 cm steel-surrounded granodiorite target radioactive medium and high energy spallation products of the incident primary and of secondary particles were analyzed along the beam axis down to depths of 140 g/cm(2) in targets such as Cu, Ni, Co, Fe, T, Si, SiO2 and Al. Activities of these nuclides were exclusively determined via instrumental gamma-ray spectroscopy. Relative yields of neutron capture and spallation products induced in Co and Cu targets during the thick target bombardment are shown as a function of depth. The majority of the medium energy products such as Co-58 from Co targets exhibit a maximum at shallow depths of 40-60 g/cm(2) and then decrease exponentially. In a comparable 600 MeV proton bombarded thick target such a slight maximum for medium energy products was not observed. Rather, Co-58 activities in Co decreased steadily with the highest activity at the surface. The activities of the n-capture product Co-60 increase steadily starting at the surface. This indicates the rapidly growing flux of low energy neutrons within the target.

Theis, S.↗
NASA NTRS1985

Calculation of recoil implantation profiles using known range statistics

A method has been developed to calculate the depth distribution of recoil atoms that result from ion implantation onto a substrate covered with a thin surface layer. The calculation includes first order recoils considering projected range straggles, and lateral straggles of recoils but neglecting lateral straggles of projectiles. Projectile range distributions at intermediate energies in the surface layer are deduced from look-up tables of known range statistics. A great saving of computing time and human effort is thus attained in comparison with existing procedures. The method is used to calculate recoil profiles of oxygen from implantation of arsenic through SiO2 and of nitrogen from implantation of phosphorus through Si3N4 films on silicon. The calculated recoil profiles are in good agreement with results obtained by other investigators using the Boltzmann transport equation and they also compare very well with available experimental results in the literature. The deviation between calculated and experimental results is discussed in relation to lateral straggles. From this discussion, a range of surface layer thickness for which the method applies is recommended.

Fung, C. D.↗
NASA NTRS1986

Distribution of nitrogen and defects in SiO(x)N(y)/Si structures formed by the thermal nitridation of SiO2/Si

Previously reported nitrogen distributions in SiO2 films on Si which have been thermally nitrided at 1000 C have been explained by a kinetic model of the nitridation process which rests upon the effects of interfacial strain. A critical test of this kinetic model is the validity of the predictions regarding nitrogen distributions obtained at other nitridation temperatures. In this work, nitrogen distributions determined via X-ray photoelectron spectroscopy are reported for samples nitrided at 800 and 1150 C, and are shown to be consistent with the kinetic model. In addition, the intensity of a fluorine marker is found to correlate with the nitrogen distribution, and is postulated to be related to kinetically generated defects in the dielectric film, consistent with the strain-dependent energy of formation of defects proposed recently to explain electrical data.

Vasquez, R. P.↗
NASA NTRS1986

Effect of grain-boundary crystallization on the high-temperature strength of silicon nitride

Si3N4 specimens having the composition 88.7 wt pct Si3N4-4.9 wt pct SiO2-6.4 wt pct Y2O3 were sintered at 2140 C under 25 atm N2 for 1 h and then subjected to a 5 h anneal at 1500 C. Crystallization of an amorphous grain-boundary phase resulted in the formation of Y2Si2O7. The short-time 1370 C strength of this material was compared with that of material of the same composition having no annealing treatment. No change in strength was noted. This is attributed to the refractory nature of the yttrium-rich grain-boundary phase (apparently identical in both glassy and crystalline phases) and the subsequent domination of the failure process by common processing flaws.

Pierce, L. A.↗
NASA NTRS1986

Roedderite in the Qingzhen (EH3) chondrite

The rare mineral roedderite, (Na1.09 K0.89 Ca0.02)2.00 (Mg4.71 Fe0.27)4.98 (Si11.80 Al0.09)11.89 O30 has been found in accessory amounts in the highly unequilibrated enstatite chondrite, Qingzhen. It occurs in association with minor amounts of albite and SiO2 as inclusions within the metal or sulfide phases of metal-sulfide assemblages. The roedderite crystals are connected through oxide and silicate veins to the surrounding matrix. The presence of glass coated vesicles on the surface of the assemblages strongly suggests that roedderite originated in the presence of a fluid phase, presumably during post-accretional planetary processes.

Rambaldi, E. R.↗
NASA NTRS1986

Effect of oxygen barrier coatings on oxidation and embrittlement of Ti-6Al-2Sn-4Zr-2Mo foil in heat shield applications

Because of the loss of ductility with exposure to oxidizing conditions, long time applications of titanium alloys have been limited to temperatures below 700 K and short time applications have been limited to temperatures below 815 K. Oxygen barrier coatings for shielding Ti-6Al-2Sn-4Zr-2Mo alloy from oxidation during exposure to high temperatures were studied using foil gage specimens. The coatings included micrometer-thick sputtered SiO2 and chemical-vapor-deposited silicate layers both with and without an aluminum basecoat. The oxidation rates and resistance to embrittlement of the coated specimens were significantly better than those of the uncoated specimens.

Clark, R. K.↗
NASA NTRS1985

Design, fabrication, and performance of a whiskerless Schottky diode for millimeter and submillimeter wave applications

Design considerations, fabrication techniques, and performance predictions are presented for a planar whiskerless Schottky diode to be used (in radio astronomy applications) at 100-300 GHz. The anode and ohmic contacts are on the same side of the device, and proton bombardment is used to establish the divided surface (by making some regions of the GaAs wafer semiinsulating) prior to definition of a B-doped SiO2 finger, ohmic contacting, anode formation, and anode contact metallization (all using photolithographic techniques). The contributions of parasitic elements are calculated for a device with a 3.5-micron-deep n(+) layer doped at 2 x 10 to the 18th/cu cm, a 250-nm-thick epitaxial layer doped at 5 x 10 to the 16th/cu cm, and a 1-micron-radius anode (providing zero-bias junction capacitance 7 fE). It is predicted that such a device would have total series resistance 12.58 ohm and total shunt capacitance 1.37 fF, compared with 14.27 ohm and 0.93 fF for the corresponding whiskered device.

Mckinney, K.↗
NASA NTRS1986

An X-ray photoelectron spectroscopy study of the thermal nitridation of SiO2/Si

The dependence of the nitrogen distribution in thermally nitrided SiO2 films on the nitridation time and temperature has been studied by means of X-ray photoelectron spectroscopy (XPS). The photoelectron peak intensities were measured by fitting Voigt profiles to the XPS spectra and were used to calculate the film composition as a function of film depth, applying an analytical method described in detail. The times of appearance of the maxima in interfacial nitrogen concentration are shown for 800, 1000, and 1150 C, and the data are related to a kinetic model of Vasquez and Madhukar (1985), which considers the effect of interfacial strain on the nitridation kinetics. In addition, the intensity of a fluorine marker (from the HF used in the etching step) was found to correlate with the nitrogen concentration. It is postulated that the F bonds preferentially to defects. This hypothesis and the measured F intensities are consistent with the proposed strain-dependent energy of defect formation.

Vasquez, R. P.↗
NASA NTRS1986

The parental magma of the Nakhla achondrite - Ultrabasic volcanism on the shergottite parent body

An examination of chemical and mineral chemical data available for the cumulate and the intercumulus magma of the Nakhla meteorite is presented. The composition of the intercumulus magma, calculated by mass balance, is found to be ultrabasic (SiO2 is less than 45 percent), and the magma is enriched in incompatible elements (La/Lu=6 x Cl). The cumulus augite and intercumulus magma are in chemical equilibrium, implying that the intercumulus magma is a sample of Nakhla's parental magma. The possibility of Nakhla's Martian origin is discussed.

Treiman, A. H.↗
NASA NTRS1986

Correlation of processing and sintering variables with the strength and radiography of silicon nitride

A sintered Si3N4-SiO2-Y2O3 composition, NASA 6Y, was developed that reached four-point flexural average strength/standard deviation values of 857/36, 544/33, and 462/59 MPa at room temperature, 1200 and 1370 C, respectively. These strengths represented improvements of 56, 38, and 21 percent over baseline properties at the three test temperatures. At room temperature the standard deviation was reduced by over a factor of three. These accomplishments were realized by the iterative utilization of conventional X-radiography to characterize structural (density) uniformity as affected by systematic changes in powder processing and sintering parameters. Accompanying the improvement in mechanical properties was a change in the type of flaw causing failure from a pore to a large columnar beta-Si3N4 grain typically 40-80 micron long, 10-30 micron wide, and with an aspect ratio of 5:1.

Sanders, W. A.↗
NASA NTRS1986

Characterization of the heavily doped emitter and junction regions of silicon solar cells using an electron beam

Heavily doped emitter and junction regions of silicon solar cells are investigated by means of the electron-beam-induced-current (EBIC) technique. Although the experimental EBIC data are collected under three-dimensional conditions, it is analytically demonstrated with two numerical examples that the solutions obtained with one-dimensional numerical modeling are adequate. EBIC data for bare and oxide-covered emitter surfaces are compared with theory. The improvement in collection efficiency when an emitter surface is covered with a 100-A SiO2 film varies with beam energy; for a cell with a junction depth of 0.35 microns, the improvement is about 54 percent at 2 keV.

Luke, K. L.↗