Equilibrium Solubility Product Research Articles

Carbide Precipitation during Tempering and Its Effect on the Wear Loss of a High-Carbon 8 Mass% Cr Tool Steel.

In this paper, the precipitation of carbide and wear loss of high-carbon 8 mass% Cr tool steel at two tempering conditions (i.e., 773–803 K and 823–853 K) were studied by INCA Steel, EPMA-1720H, XRD, and ML-10 tester. The results show that the particles of test steels include the carbides (Cr7C3 and Cr23C6) and carbides nucleated on Al2O3. When carbides are of the same size, the number of carbides in test steel at a tempering temperature of 773–803 K is greater than that at a tempering temperature of 823–853 K, especially when the size of carbides is less than 5 μm. Compared with the test steel tempered at 823–853 K, the distance between adjacent actual particles reduced by 80.6 μm and the maximum amount of reduction was 9.4% for single wear loss at the tempering temperature of 773–803 K. It can be concluded from thermodynamics results that Al2O3 inclusions began to precipitate in liquid, and the precipitation of carbides was at the solid–liquid region. Al2O3 can be used as the nucleation interface of carbide, thus promoting the formation of carbides. During the cooling of molten steel, a lower temperature can increase the difference of actual solubility product bigger than equilibrium solubility product, thus promoting the carbide formation.

Effect of Mg–Ti Deoxidation on the Formation Behavior of Equiaxed Crystals During Rapid Solidification of Iron Alloys

The effect of Mg–Ti deoxidation on the solidification structure of advanced high strength steel was investigated by observing the solidification structure and also the inclusion particles. The effect of precipitation of TiN, MgO, and “TiN–MgO” hybrid inclusion on the formation of fine equiaxed crystals was evaluated. The composition of inclusions was observed to change in the order of MgO → “MgO(core) + TiN(surface)” → Ti2O3 by reaction time, which corresponded to the change of solidification structure as “columnar → equiaxed → columnar.” This could be understood from the concept of lattice disregistry in between delta iron and MgO (3.97%), TiN (3.91%), and Ti2O3 (18.9%). However, even with very low disregistry between delta iron and MgO, the MgO itself did not work as an effective catalyst, indicating that there is another criterion for determining a good catalyst. The mechanism of the formation of TiN on MgO surface was schematically described. The precipitation of TiN on MgO surface was feasible although the content of Ti and N was lower than the equilibrium solubility product for the formation of TiN. Because disregistry between TiN and MgO is very low (0.05%), the precipitation of TiN on the surface of MgO is energetically more favorable.

Ikaite solubility in seawater-derived brines at 1 atm and sub-zero temperatures to 265 K

The concentration-based (stoichiometric) equilibrium solubility product of ikaite (CaCO3·6H2O) in seawater and cryogenic seawater-derived brines was determined at 1atm total pressure over the temperature range from −1.1 to −7.5°C and the salinity range from 34 to 124 in temperature–salinity pairs representative of sea ice brines. The solubility measurements were obtained in solutions that were undersaturated and supersaturated with respect to ikaite by equilibration with CO2/N2 gas mixtures of known pCO2 (20–400μatm). The solutions were then equilibrated with synthetic ikaite (seed) for up to 3months in a closed system. Arrival of the solid–solution system at a long-term chemical equilibrium was indicated by attainment of constant chemical solution composition with respect to total dissolved calcium, total dissolved inorganic carbon, and total alkalinity. Using these measurements, the stoichiometric equilibrium solubility product of ikaite (Ksp,ikaite∗=[Ca2+][CO32-], in mol2kgsolution-2) was determined, with the carbonate ion concentration computed from the measured total alkalinity and total dissolved inorganic carbon concentrations. The computed carbonate ion concentration and, by extension, the Ksp,ikaite∗ are both contingent on solving the system of equations that describe the parameters of the CO2 system in seawater by extrapolation to the experimental salinity and temperature conditions. The results show that the pKsp,ikaite∗=-logKsp,ikaite∗ in seawater of salinity 34 at −1.1°C was 5.362±0.004 and that the pKsp,ikaite∗ in sea ice at the freezing point of brines of salinity greater than 34 can be described as a function of temperature (T, in K) by the equation, pKsp,ikaite∗=-15489.09608+623443.70216T-1+2355.14596lnT, in the temperature range of 265.15K<T<271.15K (−8°C<t<−2°C). Brines of low pCO2 (20μatm) yielded a much slower (>1month) approach to chemical equilibrium when incubated without seeding ikaite crystals. Simple modeling indicated that ikaite should not precipitate from sea ice brines evolving under closed system conditions with respect to CO2 exchange. To facilitate ikaite precipitation, brine pCO2 reduction due to photosynthesis or CO2 degassing, or both, is necessary.

Modelling early age hydration kinetics of alite

The modelling platform μic [1] has been used to investigate the mechanisms occurring during the hydration of alite. It is shown that it is possible to obtain a good simulation of the hydration kinetics through the implementation of two mechanisms: a dissolution mechanism combined with nucleation and growth of products. The dissolution rate is varied according to the ratio β, between the ion activity product and the equilibrium solubility product according the theory published by Juilland et al. [2]. The solution concentrations are computed directly from the amount of alite dissolved taking into account the amount of water present and the amount of products formed, with activities and complex ion formation calculated according to standard methods. Saturation index calculations are implemented to compute the time of precipitation of C–S–H and portlandite (CH) individually. For the main heat evolution peak, the rate controlling mechanism switches to a modified form of boundary nucleation and growth. C–S–H grows in a diffuse manner in which the density of packing of the C–S–H phase increases with hydration [3]. The rate of heat evolution obtained from the simulations is compared with isothermal calorimetry data and good agreement is found.

Solubility Product of MoC with NaCl Type Cubic Crystal Structure in Iron

In this paper, firstly, the equilibrium solubility product formula of MoC with NaCl type cubic crystal structure in ferrite has been deduced by thermodynamic method, according to the free energy change of molybdenum and carbon dissolved in ferrite and the formation energy of MoC. On the basis of deducing activity coefficients of Mo in iron, the solubility product formula of MoC in austenite has been obtained according to the relationship of solubility product of MoC in austenite and ferrite. Finally, the solubility products for MoC and NbC in iron are compared. The solubility product formulae of MoC deduced would play an important role in related theoretical research and practical production.

Modelling early age hydration kinetics of alite

The modelling platform μic [1] has been used to investigate the mechanisms occurring during the hydration of alite. It is shown that it is possible to obtain a very good simulation of the hydration kinetics through the implementation of two mechanisms: a dissolution mechanism combined with nucleation and growth of products. The dissolution rate is varied according to the ratio β, between the ion activity product and the equilibrium solubility product according the theory published by Juilland et al. [2]. The solution concentrations are computed directly from the amount of alite dissolved taking into account the amount of water present and the amount of products formed, with activities and complex ion formation calculated according to standard methods. Saturation index calculations are implemented to compute the time of precipitation of C-S-H and portlandite (CH) individually. Once the pore solution is saturated with respect to portlandite, the rate controlling mechanism switches to a modified form of boundary nucleation and growth. C-S-H grows in a diffuse manner in which the density of packing of the C-S-H phase increases with hydration [3]. The kinetics parameters are calibrated and the same values are used consistently across a range of particle sizes. The rate of heat evolution obtained from the simulations is compared with isothermal calorimetry data and good agreement is found.

Aqueous Pb sorption by hydroxylapatite; applications of atomic force microscopy to dissolution, nucleation, and growth studies

Other| February 01, 1998 Aqueous Pb sorption by hydroxylapatite; applications of atomic force microscopy to dissolution, nucleation, and growth studies Steven K. Lower; Steven K. Lower Kent State University, Department of Geology, Kent, OH, United States Search for other works by this author on: GSW Google Scholar Patricia A. Maurice; Patricia A. Maurice Search for other works by this author on: GSW Google Scholar Samuel J. Traina; Samuel J. Traina Search for other works by this author on: GSW Google Scholar Ernest H. Carlson Ernest H. Carlson Search for other works by this author on: GSW Google Scholar Author and Article Information Steven K. Lower Kent State University, Department of Geology, Kent, OH, United States Patricia A. Maurice Samuel J. Traina Ernest H. Carlson Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online Issn: 1945-3027 Print Issn: 0003-004X GeoRef, Copyright 2004, American Geological Institute. American Mineralogist (1998) 83 (1-2): 147–158. https://doi.org/10.2138/am-1998-1-215 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Steven K. Lower, Patricia A. Maurice, Samuel J. Traina, Ernest H. Carlson; Aqueous Pb sorption by hydroxylapatite; applications of atomic force microscopy to dissolution, nucleation, and growth studies. American Mineralogist 1998;; 83 (1-2): 147–158. doi: https://doi.org/10.2138/am-1998-1-215 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract A combination of atomic force microscopy, scanning election microscopy, transmission electron microscopy, energy dispersive spectroscopy, electron diffraction, and X-ray diffraction were used to study reactions of 0.5-500 mg/L aqueous Pb with Ca 5 (PO 4 ) 3 OH, hydroxylapatite (HAP), at pH 6 and 22 degrees C. Following 2 h reaction time, concentrations of Pb aq ([Pb aq ]) decreased from 500 mg/L to <100 mg/L, and from 0.5-100 mg/L to <15 mu g/L. This loss of Pb aq from solution (i.e., sorption) resulted partially from simultaneous dissolution of HAP and precipitation of Pb 5 (PO 4 ) 3 OH, hydroxypyromorphite (HPY), or another solid Pb phase. The initial saturation state with respect to HPY (defined as the ratio of the ion activity product to equilibrium solubility product) influenced strongly precipitation processes. At a high degree of saturation (initial [Pb aq ]>100 mg/L), small nuclei or aggregates of poorly crystalline HPY precipitated homogeneously in solution. At intermediate saturation (initial [Pb aq ] approximately 10-100 mg/L), large, euhedral needles of HPY precipitated homogeneously in solution. At a low degree of saturation (initial [Pb aq ]<10 mg/L), a needle-like Pb-containing phase grew heterogeneously on HAP. These results agree well with concepts derived from nucleation and growth theories and demonstrate that initial saturation state influences strongly the sorption process. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Design of coatings to minimize tool crater wear

A quantitative study of the micromechanisms of crater during the high speed machining of an AISI 1045 grade steel with a tungsten carbide tool has confirmed that diffusional wear is the dominant mechanism of crater wear. Neutron activation analysis is used to determine the amount of tungsten dissolved in the chips as a function of cutting speed. The concentration of tungsten dissolved in the chips increases from a negligible amount (0.2 ppm) to as much as 10.5±0.5 ppm as the cutting speed is increased from 100 to 240 m min -1, whereas the contribution from mechanical wear as given by tungsten carbide content remains nearly constant at 0.8 ppm. The depth of penetration of tungsten into the chips machined at 150 m min -1 and 240 m min -1 respectively were determined using secondary-ion mass spectrometry analysis. The tungsten concentration distribution from the interface into the chip in each case is characteristic of a diffusion profile. Ultrafine grains (0.5 μm) observed in the secondary shear zone contribute to grain-boundary-enhanced diffusion of tungsten into the chips. Diffusional wear of tungsten carbide was decreased markedly by coating the tool with HfN. The thermodynamic potential for dissolution of HfN in steel as measured by the equilibrium solubility product of HfN at 1200δC in austenite is six orders of magnitude less than that of WC. Thus, the magnitude of the thermodynamic potential for dissolution of a coating into the workpiece at typical tool-workpiece interface temperatures is an important criterion in the design of a coating to minimize tool crater wear.

Contribution to the theory of diffusion-reaction controlled Liesegang patterns

A Turing-type reaction-diffusion model is explored which may be applicable to Liesegang bands, rings, and spirals evolving by precipitation in the environs of an equilibrium solubility product relation. Because of their incompletely specified initial and (or) boundary conditions the solutions exhibit a bivariate free boundary degeneracy. We find that one degree of freedom may be removed by the specification of a global rate constant and the other by the specification of a principle of optimal wave number selection within linear stability theory. Existence conditions for banding in one dimension are established and these agree with particular observations.

LABILE RESIDUAL FERTILIZER PHOSPHORUS IN CHERNOZEMIC SOILS. I. SOLUBILITY AND QUANTITY/INTENSITY STUDIES

Granular monoammonium phosphate (500 μg P/g soil) was applied in the field to three soils of an Oxbow catena. Changes in the inorganic P forms controlling P concentration or intensity (Ie) in soil solution during the ensuing 2½ yr were determined by equilibrium solubility product and related quantity/intensity analyses. In the Calcareous and Orthic control soils, Ie was controlled by impure hydroxyapatite. After P addition, it was controlled by dicalcium phosphate dihydrate and octocalcium phosphate. Marked changes in the quantity of labile P caused negligible changes in values for Ie. Therefore, in these and similar Chernozemic soils, Ie should adequately reflect the availability of residual P to plants. In the Gleysol after P addition, Ie was determined by adsorbed P or by the solubility of aluminum/iron-bound P forms. For this and similar Chernozemic soils, the quantity/intensity data indicated that estimates of the availability of residual P will require a measurement of its capacity to maintain Ie at the root–soil interface against depletion by plant uptake rather than a measurement of Ie alone.