Solution-precipitation Process Research Articles

Oxygen isotope fractionation between rutile and water and geothermometry of metamorphic eclogites

SummaryOxygen isotope fractionation between rutile and water has been studied from 300 °C to 700 °C, PH2O = 1 kb, using aqueous oxidation of titanium metal as the equilibration reaction. The mechanism of rutile formation (which is critical to the assessment of isotopic equilibrium) is an ‘armouring’ reaction in which rutile grows around grains of titanium metal by solution-precipitation processes. Mean fractionation factors expressed as 103 In αTiO2-H2O obtained in the present study are:−6.20±0.23‰ at 304±5 °C−6.64±0.27‰ at 405±6 °C−6.11±0.16%. at 508±6 °C−4.45±0.28%. at 608±6 °C−3.38±0.15%. at 698±6 °C.These data agree with those obtained at temperatures above 500 °C by Addy and Garlick (1974) but do not accord with theoretical predictions by Bottinga and Javoy (1973). A minimum in the calibration curve 103 ln α versus 106T−2 occurs between 300 °C and 500 °C but from 500 °C to 700 °C 18O fractionation between rutile and water may be expressed by the equation:103 ln α = −(4.72±0.40)106T−2+(1.62±0.53).Oxygen isotope analyses of rutile and quartz from metamorphic eclogites and schists from the Tauern Window, Austria, yield isotopic temperatures at about 550 °C in agreement with results obtained on similar rocks from the Sesia Zone (Western Alps, Italy) and elsewhere by other workers. Petrologic studies indicate that the latest metamorphism of the Tauern eclogites reached about 450 °C Thus the measured partitions of 18O between rutile and quartz indicating temperatures around 550 °C have been inherited from an earlier metamorphic event.

Analysis of superplastic deformation mechanisms in Zn-22% Al alloy on the basis of electron microscopy topographic investigations

Mechanisms of superplastic flow of Zn-22% Al alloy with strain rates in the intervals between 3.6 × 10 −4 and 7.1 min −1 at 250°C are discussed on the basis of quantitative investigation of relief peculiarities of deformed specimens under an electron microscope. The regularities of changes of striated band parameters such as the width, summary length and inclination angle to the specimen surface are established as functions of strain and strain rate. The probability of appearance of striated bands on different boundary types ( α β , α α and β β ) was studied with the help of statistical analysis. The striated bands' nature is discussed with regard to the diffusion creep and grain boundary sliding in their formation. It is concluded that a solution-precipitation mass transfer process ought to take place during diffusion creep; contributions to the total specimen elongation are quantitatively estimated as a function of strain rate.

Liquid phase sintering of TiN - Co and TiN - Wc - Co systems.

1) A mutual solubility of titanium nitride and cobalt was observed in the sintering of the TiN-Co system at 1600°-1800°C.2) In the sintering of the TiN-WC-Co system, in addition to the above fact, tungsten carbide seemed to be dissolved into the other two phases, in the way that W atoms were mainly dissolved into the cobalt phase whereas C atoms were dissolved into the titanium nitride phase.3) The microstructure of TiN-10wt% WC-20wt% Co alloy was analysed by E. P. M. A. and I. M. A.. Grains were titanium nitride phase and a binder phase was cobalt phase.4) The solid skelton forming for grains during sintering for the binary systems was observed and it is indicating the incomplete wetting of tungsten carbide to this binary alloy resulted in an improvement of the wettability of titanium nitride phase to the binder phase.5) The solution-precipitation process in the sintering for the TiN-WC-Co system was controlled by the solution reaction of granular particles at solid-liquid boundaries.6) The maximum mechanical strength obtained for the TiN-WC-Co ternary alloys at any sintering conditions was essentially higher than that for the TiN-Co binary alloys.

The impact of ion implantation on silicon device and circuit technology : H. G. Dill, R. M. Finnila, A. M. Leupp and T. N. Toombs. Solid St. Technol., December (1972), p. 27

To date, there have been few reports of the fabrication of hardened, pure calcium carbonate specimens beginning from the powder state. In this study, hardened calcium carbonate bodies exhibiting high densities and compressive strengths were produced using a warm press method. The warm press conditions consisted of temperatures from 150 to 280 °C and a uniaxial pressure of 240 MPa, applied for durations of 10–180 min to powder compacts composed of pure calcium carbonate powder or powder mixed with 10% water (by mass). Heating at 150 °C and 240 MPa for 180 min with 10% water generated a relative density of 87% and an average compressive strength of 40 MPa. The added water was found to play an important role to promote a solution-precipitation process inside the calcium powder compact, allowing low temperature sintering to form dense calcium carbonate.

Scleractinian Coral Alteration in Subaerial Vadose Diagenetic Environment: ABSTRACT

Exoskeletons of scleractinian corals in the elevated late Pleistocene reefs on northern Barbados illustrate a series of diagenetic textures that document aragonite coral alteration under subaerial vadose conditions. Two major solution-precipitation processes are recognized: (1) concomitant solution-precipitation on a fine scale leading to preservation of coral microstructure; and (2) total leaching and destruction of the microstructure followed by later precipitation of void-filling spar. The pathway of aragonite solution in both processes is similar and controlled by the original coral microstructure. Solution is initiated in the fine equant crystallites forming the axis (center of calcification) of each trabecula and moves outward into the surrounding zone of closely packed aragonite needles by preferential solution along the linear intercrystalline contacts between needles. This results in the friable aragonite chalk commonly observed in Pleistocene corals. Aragonite chalk is also observed as a zone between aragonite and calcite in corals undergoing solution-precipitation on a fine scale. The coral microstructure is preserved by concomitant precipitation of calcite between separated aragonite needles adjacent to the calcite alteration front, incorporating minor impurities and irregularities of the original structure into the calcite crystals. This results in a new calcite texture that mimics the original aragonite one. Corals completely altered to calcite by concomitant solution-precipitation on a fine scale exhibit a coarse mosaic of blocky calcite with a relict fibrous texture. The once dark trabecular axes are preserved as a clear central canal. A similar calcite trabecular texture is observed in certain Devonian tabulate corals and other fossil calcareous organisms, suggesting that their skeletons may have been aragonite and altered in a manner similar to that described. End_of_Article - Last_Page 630------------

Study of consolidation processes in sintering in the presence of a liquid phase

1. By using the dilatometric method, we investigated the sintering of W-Cu and TiC-Ni systems in the presence of a liquid phase in dependence on the porosity, the amount of liquid phase, and the temperature. 2. In correspondence with theoretical considerations, two sintering stages were observed: the regrouping and the solution-precipitation processes. The shape of the shrinkage vs. time curve for these processes qualitatively agrees with theoretical data [4]. 3. For the copper-tungsten system, a sharp increase in the amount of shrinkage with an increase in temperature was observed, the probable cause of which was an increase in the wettability of tungsten in copper. 4. Complete consolidation of the W-Cu system was not achieved. A higher degree of consolidation in this system can be secured for a higher degree of initial porosity. The optimum temperature for producing W-Cu specimens with the greatest density lies in the 1300–1350° interval. 5. It was shown that, owing to the solution-precipitation mechanism, complete consolidation of the TiC-Ni system can be secured if the amount of liquid phase is not less than 20–25% by volume.

Phenomenological Study of Liquid Phase Sintering (3 rd Report)

Microstructure changes, particle growth and the rate of densification during sintering of Cu-Ag in the presence of a liquid phase have been observed. Rapid densification occurred in the early stage of sintering, and more rapidly as the amount of liquid phase and temperature increased.Particle growth by the solution-precipitation process was observed in this system. In a large amount of liquid, particles were larger in initial stage and smaller in final stage than in a small amount.Using spherical copper powders, it has been found that the starting particles was disintegrated into smaller particles.

Phenomenological Study of Liquid Phase Sintering (1st Report)

Microstructure changes, particle growth and the rate of densification during sintering of Cu-Ag in the presence of a liquid phase have been observed. Rapid densification occurred in the early stage of sintering, and more rapidly as the amount of liquid phase and temperature increased.Particle growth by the solution-precipitation process was observed in this system. In a large amount of liquid, particles were larger in initial stage and smaller in final stage than in a small amount.Using spherical copper powders, it has been found that the starting particles was disintegrated into smaller particles.

Densification during Sintering in the Presence of a Liquid Phase. I. Theory

The driving force leading to densification during sintering in the presence of a liquid phase and the material transport phenomena have been analyzed and relationships for the densification rate during the rearrangement process, the solution-precipitation process, and the final coalescence process have been determined. These relationships allow an experimental determination of the mechanism of sintering in the presence of a liquid phase on the basis of the time, particle size and temperature dependence of the densification rate. In addition, they allow direct calculations of densification rates to be made for certain simple systems for which property data are available.