Impurities In Solid Solution Research Articles

Influence of Carbon Nanoparticle Addition (and Impurities) on Selective Laser Melting of Pure Copper.

The addition of 0.1 wt % carbon nanoparticles significantly improved the optical absorption and flowability of gas-atomized copper powder. This facilitated selective laser melting (SLM) by reducing the required laser energy density to obtain 98% dense parts. Moreover, the carbon addition led to an in situ de-oxidation of the copper parts during the SLM process. The properties of the as-built copper parts were limited to a tensile strength of 125 MPa, a ductility of 3%, and an electrical conductivity of 22.7 × 106 S/m, despite the advantageous effect of carbon on the powder characteristics and SLM behavior. The modest mechanical properties were associated with the segregation of carbon nanoparticles and other impurities, such as phosphorus and oxygen along grain boundaries of epitaxially grown grains. Whereas, the low electrical conductivity was mainly attributed to the phosphorus impurity in solid-solution with copper.

Microstructure and phase evolution of Indian magnesite‐derived MgAl2O4 as a function of stoichiometry and ZrO2 doping

AbstractTo aid development of cost‐effective sintered spinel as a refractory raw material, this paper presents an extensive analysis of microstructure and complex phase evolution of Al‐rich, Mg‐rich, and stoichiometric spinel aggregates derived from Indian magnesite and calcined alumina. Pore morphology in Al‐rich spinel was transformed upon sintering at 1650°C and corundum laths embedded in porous Al‐rich spinel matrix was formed. Stoichiometric spinel sintered at 1600°C consisted of mostly direct bonded angular equiaxed spinel grains which incorporated the impurities in solid solution. Mg‐rich spinel was composed of spinel grains with reduced angularity along with intergranular amorphous phase, small round monticellite grains, and periclase. EDS line scan revealed impurity‐free joins existed between direct bonded spinel grains. Mg‐rich spinel containing 0.65 wt% ZrO2 formed cubic ZrO2‐CaO‐MgO solid solution located along spinel boundaries, which reduced both intergranular amorphous phase and monticellite. This increased SiO2 and MgO content in spinel solid solution triggering exsolution of metastable cubic forsterite manifested as split spinel peaks in XRD pattern. A 14.7% reduction in slag penetration was exhibited upon doping Mg‐rich spinel with 0.21% ZrO2. Stoichiometric and Mg‐rich spinels attained 0.35% and 0.54% apparent porosity at 1600°C, which is better than most commercial sintered refractory spinels.

Reinforcement of the Cube texture during recrystallization of a 1050 aluminum alloy partially recrystallized and 10% cold-rolled

In high purity Aluminum, very strong {100}<001> recrystallization texture is developed after 98% cold rolling and annealing at 500 °C. On the contrary, in Aluminum alloys of commercial purity, the Cube component hardly exceeds 30% after complete recrystallization. Parameters controlling Cube orientation development are mainly the solute dragging due to impurities in solid solution and the stored deformation energy. In the present study, besides the 85% cold rolling, two extra annealings and a slight cold rolling are introduced in the processing route to increase the Cube volume fraction. The Cube development was analyzed by X-ray diffraction and Electron BackScattered Diffraction (EBSD). The nucleation and growth mechanisms responsible for the large Cube growth were investigated using FEG/EBSD in-situ heating experiments. Continuous recrystallization was observed in Cube oriented grains and competed with SIBM (Strain Induced Boundary Migration) mechanism. This latter was favored by the stored energy gap introduced during the additional cold-rolling between the Cube grains and their neighbors. Finally, a Cube volume fraction of 65% was reached after final recrystallization. ► EBSD in-situ heating experiments of aluminum alloy of commercial purity. ► A 10% cold-rolling after a partial recrystallization improved Cube nucleation and growth. ► Annealing before cold-rolling limited the solute drag effect and permitted a large Cube growth. ► Cube development is enhanced by continuous recrystallization of Cube sub-grains. ► The preferential Cube growth occurs by SIBM of small Cube grains.

Formation and Development of Strong Cube Recrystallization Texture in an Aluminium of Commercial Purity

The goal of the present study inspired by previous works on high purity aluminiun was to manufacture aluminium sheets of commercial purity, grade 1050, with a strong cube texture. In this preliminary work on AA1050, sheets which cube volume fraction reaches 65% have been manufactured. Parameters controlling cube orientation development are mainly the solute dragging due to impurities in solid solution and the stored deformation energy. Besides the 85% cold rolling (CR), two extra annealings and a slight cold rolling are introduced in the processing route to increase the cube volume fraction. The cube orientation, whose substructure is equiaxed, is important for its recovery. It develops thanks to the difference of stored energy relative to that of its first neighbors; the slight cold rolling enhances growth of these cube grains.

Effect of Solid Solution Impurities on Dislocation Nucleation During Nanoindentation

Dislocation nucleation in solid solutions of face-centered-cubic metallic materials was studied using nanoindentation. The effects of solute impurities in the copper–nickel system on the formation of dislocations in a previously dislocation-free region were demonstrated to be minimal. The shear stress required to nucleate dislocations in copper is approximately 1.6 GPa, while in nickel a 3.9 GPa shear stress is required. Changes in shear stress for nucleation track closely with changes in elastic modulus showing the nucleation stress is approximately 1/30 to 1/20 of the shear modulus. The expected solid-solution strengthening is identified within the same experimental method, demonstrating unambiguously the fact that solid-solution impurities in this system will impact the propagation of dislocations during plastic deformation but not alter the homogeneous nucleation of dislocations in these materials.

Potential anthropogenic mobilisation of mercury and arsenic from soils on mineralised rocks, Northland, New Zealand

Eroded roots of hot spring systems in Northland, New Zealand consist of mineralised rocks containing sulfide minerals. Marcasite and cinnabar are the dominant sulfides with subordinate pyrite. Deep weathering and leached soil formation has occurred in a warm temperate to subtropical climate with up to 3 m/year rainfall. Decomposition of the iron sulfides in natural and anthropogenic rock exposures yields acid rock drainage with pH typically between 2 and 4, and locally down to pH 1. Soils and weathered rocks developed on basement greywacke have negligible acid neutralisation capacity. Natural rainforest soils have pH between 4 and 5 on unmineralised greywacke, and pH is as low as 3.5 in soils on mineralised rocks. Roads with aggregate made from mineralised rocks have pH near 3, and quarries from which the rock was extracted can have pH down to 1. Mineralised rocks are enriched in arsenic and mercury, both of which are environmentally available as solid solution impurities in iron sulfides and phosphate minerals. Base metals (Cu, Pb, Zn) are present at low levels in soils, at or below typical basement rock background. Decomposition of the iron sulfides releases the solid solution arsenic and mercury into the acid rock drainage solutions. Phosphate minerals release their impurities only under strongly acid conditions (pH<1). Arsenic and mercury are adsorbed on to iron oxyhydroxides in soils, concentrated in the C horizon, with up to 4000 ppm arsenic and 100 ppm mercury. Waters emanating from acid rock drainage areas have arsenic and mercury below drinking water limits. Leaching experiments and theoretical predictions indicate that both arsenic and mercury are least mobile in acid soils, at pH of c. 3–4. This optimum pH range for fixation of arsenic and mercury on iron oxyhydroxides in soils is similar to natural pH at the field site of this study. However, neutralisation of acid soils developed on mineralised rocks is likely to decrease adsorption and enhance mobility of arsenic and mercury. Hence, development of farmland by clearing forest and adding agricultural lime may mobilise arsenic and mercury from underlying soils on mineralised rocks. In addition, arsenic and mercury release into runoff water will be enhanced where sediment is washed off mineralised road aggregate (pH 3) on to farm land (pH>6). The naturally acid forest soils, or even lower pH of natural acid rock drainage, are the most desirable environmental conditions to restrict dissolution of arsenic and mercury from soils. This approach is only valid where mineralised soils have low base metal concentrations.

The development of advanced vanadium alloys for fusion applications

As an alternative choice for fusion application, V alloyed with 6–8 wt%W has been studied. The results showed that W could strengthen the alloy at room temperature, more effectively than Ti or Cr. With both additions of Ti and W, the recovery and recrystallization of the alloys behaved similarly to V–4Cr–4Ti, but the behavior was strongly influenced by the concentration of the interstitial impurities in solid solution. Similar behavior to V–4Cr–4Ti was also found for V–6W–1Ti on hydrogen embrittlement. V–6W–1Ti seemed to have better properties for hydrogen embrittlement due to its low hydrogen absorption rate. Significant differences in oxidation behavior in air were not observed for the alloys investigated.

The use of thermal analysis in the assessment of crystal disruption

The highly ordered crystal lattice of small organic molecules, such as drugs, contains defects resulting from the crystallization process. Pharmaceutical processing and impurities introduce further defects which cause partial disruption of the crystalline order decreasing the crystallinity and increasing the crystal energy, enthalpy, entropy and free energy. As a result, the intrinsic dissolution rate increases and other solid state properties, including the compaction (tableting) behavior, are changed, thereby accounting for interbatch variations. Differential scanning calorimetry (DSC) or differential thermal analysis (DTA) are used to measure the enthalpy of fusion at the melting point and hence the entropy of fusion. The negative slope of the plot of the entropy of fusion against the ideal entropy of mixing of a guest impurity in solid solution in the host solid affords the disruption index (d.i.) resulting from the presence of the guest. The significance and magnitude of d.i. are discussed. The change in the entropy of fusion resulting from the processing of the solid is used to calculate the entropy of processing, ΔSp, which is related to changes in various pharmaceutical properties. The uses of d.i. and ΔSp are illustrated using a variety of pharmaceutical examples.

Comparative study to enhance the phase formation of Tl-based superconductor with three CuO layers

Characteristics of the “1223” phase in the (Tl, Bi, Pb)SrCaCuO superconductor system have been enhanced using an over-stoichiometric “1234” precursor (Tl 0.64Pb 0.2Bi 0.16)Sr 2Ca 3Cu 4O y . The quality of the 1223 phase heavily depends on the synthetic condition of the 1234 precursor. The precursor synthesized from Sr 2Ca 2Cu 3O y yields the most “1223” phase after 920°C sintering for 10 h, whereas a remarkable amount of the “1212” phase containing two CuO layers was accompanied in other synthetic courses. Although some solid solution impurities are observed, they are not inevitable with a Ca-rich composition. Quality of the superconducting phase was examined by X-ray diffraction, resistivity and magnetization measurements.

Deformation-related recrystallization processes

Recrystallization is a common microstructural transformation that occurs during deformation, metamorphism and diagenesis of rocks. Studies on minerals and rock analogues have demonstrated that a wide range of recrystallization mechanisms can occur. The range of mechanisms is related to the various ways in which two basic processes, grain boundary migration and new grain boundary formation combine to transform the microstructure. Two recent papers (Drury et al., 1985; Urai et al., 1986) have proposed different schemes for the description of recrystallization mechanisms. The purpose of this paper is to provide a unified framework for the description of mechanisms. Recrystallization mechanisms are divided into three main types; rotation mechanisms which principally involve the formation of new grain boundaries; migration mechanisms which principally involve grain boundary migration; and general mechanisms which involve both basic processes. A further distinction is made on the basis of the continuity of the microstructural transformation with respect to time. Each of the three main types of mechanism can be divided into a number of sub-types depending on whether the processes of grain boundary migration, new grain boundary formation and new grain formation occur in a discontinuous or continuous manner with respect to time. As the terms continuous and discontinuous have been used in the metallurgical literature to signify the spatial continuity of the microstructural transformation, the terms discontinuai and continual are used to refer to the temporal continuity of the transformation. It is recommended that the following aspects should be specified, if possible, in a general description of recrystallization mechanisms: 1. (1) How do the basic processes combine to transform the microstructure. 2. (2) If new grain development occurs, what is the development mechanism, and does new grain formation occur in a continual or discontinuai manner. 3. (3) If grain boundary migration is involved in the transformation, what is the migration mechanism (i.e. fast solute escape migration, slow solute loaded migration, fluid assisted migration, etc.), and is migration a continual or discontinuai process. The application of the unified scheme is illustrated by reviewing studies that have provided detailed information on the recrystallization mechanisms involved. The complicating effects of solid solution impurities, dispersed second phase particles and grain boundary fluid films are also considered and it is demonstrated that variations in content of these types of impurity can significantly effect the types of recrystallization that occur in a given material.

A theoretical treatment of changes in energy and entropy of solids caused by additives or impurities in solid solution

A dimensionless entropy increment ratio, termed the “disruption index” (d.i.), has previously been defined and evaluated from heats of fusion, ΔH f ( Int. J. Pharm., 25 (1985) 57–72), and from heats of solution, ΔH s ( Int. J. Pharm., 28 (1986) 103–112). The d.i. quantifies the disruptive influence of an additive or impurity (the guest substance), when present at low mole fractions ( x 2 < 0.05), in solid solution in the crystal lattice of a host substance. The present report places the thermodynamics in the previous papers on a more rigorous foundation. (1) The previously defined “enthalpy of fusion of the solid”, ΔH f, and “enthalpy of solution of the solid”, Δ H s θ , are defined in terms of the partial molar enthalpies of the two components. (2) The d.i., previously calculated from ΔH s θ , is expressed in terms of the excess entropy of the solid, S E. The original definition of d.i. is found to involve the assumption that the partial molar excess entropy of the guest, S E 2, is directly proportional to the ideal entropy of mixing. (3) The pseudo-d.i. (p.d.i.), originally defined by assuming enthalpy-entropy compensation, is expressed in terms of the excess enthalpy of the solid, H E. (4) The d.i. previously calculated from ΔS f is expressed in terms of S E 2 . The d.i. derived from ΔS f and tha from ΔS s θ differ by about a unit in theory and are approximately equal when d.i. ⪢ 1; however, the experimentally observed differences express the temperature dependence of S E, which is reflected in the annealing of the solid between ambient temperatures and the melting point. (5) The d.i. is compared with an alternative approach based on the limiting value of ( ∂ΔS/ ∂Δx 2) at low x 2, i.e. ( S E 2) 0 . The empirical relationship between these two approaches is d.i. = 0.035 · [( S E 2) 0] 0.912 with ( S E 2) 0 in JK −1 mol −1 and d.i. from 10 −1 to 4 × 10 3. It is concluded that the present rigorous thermodynamic treatment does not alter the main conclusions derived from the previous intuitive treatment but defines better the approximation inherent in the evaluation of d.i. and shows that d.i. is directly related to S E.

Hardening and serrated flow behaviour in the 300–500 K range for Eu-doped alkali halides

The hardening behaviour of Eu-doped alkali halides has been investigated in the 300–500 K temperature range. The aggregation/precipitation state of the europium has been monitored by means of optical and electron spin resonance spectroscopy. Main attention has been paid to investigate dynamic effects on the yield-stress as well as the occurrence of serrated flow behaviour. In fact, jerky flow, which increases with impurity concentration, has been found for Eu-doped NaCl, KCl and KBr, although the active temperature range is different for the three systems. This behaviour is characteristic of the impurity in solid solution and disappears or markedly decreases when precipitates are formed. On the other hand, yield-stress σ increases with temperature above RT for NaCl, keeps essentially constant for KCl and decreases for KBr. The enhancement of σ observed in NaCl has been shown to be a dynamic effect, not related to either impurity aggregation or static strain hardening. These results as well as those on serrated flow are, consequently, discussed in terms of available dynamic strain ageing models. It has been concluded after some numerical estimates, that formation of a Cottrell cloud, probably involving diffusion of cation vacancies, may be an appropriate dynamic aging mechanism to account for the observed effects. On the other hand, the Snoek mechanism of dipolar reorientation, has to be ruled out.

Entropy of processing: a new quantity for comparing the solid state disorder of pharmaceutical materials

During the pharmaceutical processing of a solid (e.g. crystallization, drying, gain or loss of impurities or additives, milling. compression, heating or irradiation), defects and other imperfections develop, wander or disappear in the crystal lattice. Crystal imperfections contribute to the disorder of the crystal lattice, and entropy is here proposed as a practical and fundamental measure of this effect. The difference between the entropy of a given sample and that of the same amount of the reference material is designated the “entropy of processing (or imperfection)”, ΔS p, of the sample. Thermodynamic cycles are described for evaluating ΔS pof a sample from differential scanning calorimetry or from solution calorimetry with solubility studies. ΔS p may be evaluated for polymorphs, solvates (e.g. hydrates), amorphous forms, glasses, impure, or variously processed samples of a given substance. ΔS p calculated from literature data for processed pharmaceutical solids is found to be positive with respect to a highly pure. stable. crystalline reference material and to range from 0 to 200 J. K −1 · mol −1. Small values of ΔS p (0–10 J · K −1 · mol −1) are given by crystals which have been “doped” with additives or impurities in solid solution. Literature data for milled calcium gluceptate suggest that enthalpy-entropy compensation occurs and may be exploitable. ΔS pof ground samples of chloramphenicol palmitate A or B parallels their dissolution rate and bioavailability. Data for β-lactam antibiotics and calcium gluceptate indicate that ΔS p increases with decreasing X-ray crystallinity, purity and stability and with increasing processing stress. ΔS p may decrease during annealing and/or storage and appears to be useful for quantifying, understanding and predicting batch-to-batch differences in pharmaceutical solids.

A disruption index for quantifying the solid state disorder induced by additives or impurities. I. Definition and evaluation from heat of fusion

A dimensionless disruption index (d.i.) is proposed for quantifying the solid state disorder induced by an additive or impurity (the guest substance), when present in solid solution in the crystal lattice of a host substance at mole fractions, x 2, less than 0.05. The d.i. value is defined as the rate of change of the difference between the entropy of the solid and that of the liquid, with respect to the ideal entropy of mixing of the components of the solid, ΔS m ideal. From fundamental thermodynamic considerations d.i. is closely approximated by the slope of the plot of the entropy of fusion of the solid, ΔS f, against ΔS m ideal for x 2 < 0.05. ΔS f is given by the heat of fusion divided by the absolute melting point, while ΔS m ideal = − RΣx j ln x j is calculated from the analytical data of the crystals, where x j is the mole fraction of a given component. The linear relationship was tested using the limited literature data available for 7 systems and was found to be obeyed for x 2 < 0.05. Values of d.i. range from zero for ideal solutions through about 10 −1 for doping of the intermetallic compound InCd 3 with either of its components, (somewhat higher, 0.423, for cadmium doped with InCd 3), to about 10 for the doping of a stable, ordered organic crystal with an organic additive. The d.i. values for phenacetin doped with benzamide, griseofulvin + lecithin, acetaminophen + water + p-acetoxyacetanilide, and pp-DDT + op-DDT, are 7.94, 5.09, 6.53 and 15.1, respectively. The d.i. values are discussed in relation to the properties of the host and guest. The method of determining d.i. from ΔS f is critically assessed. The d.i. values may be useful in predicting the sensitivity of the crystal lattice of a drug or excipient to the presence of traces of a given impurity in solid solution. If the presence of impurities gives rise to batch-to-batch variations, d.i. values may also be useful for quantifying the observed differences in properties between batches of materials.

Anharmonic Study on the Debye‐Waller Factor for a Vacancy‐Trapped Mössbauer Impurity in Solid Solution of Aluminium

AbstractThe effect of anharmonicity on the Debye‐Waller factor for a simple cubic lattice containing Mössbauer atoms as impurity along with vacancies at the lattice points is evaluated theoretically using the double‐time Green's function technique in the high‐temperature limit. The contributions of the anharmonic lattice vibrations to the Debye‐Waller factor for 57Fe atoms present as a dilute impurity in solid solution of aluminium are also estimated. The exponent of the Debye‐Waller factor is found to increase much more rapidly at higher temperature for a defect lattice than that for a perfect lattice due to the presence of the anharmonic terms in the expansion of the potential energy of the crystal.

Debye‐Waller Factor for a Vacancy‐Trapped Mössbauer Impurity in Metallic Solid Solutions

AbstractThe effect of vacancy trapping of 57Fe atoms present as a dilute impurity in solid solution of aluminium, on the Debye‐Waller factor is evaluated theoretically in the harmonic approximation in the high temperature limit with the help of the double‐time Green function technique. The change in the recoil‐free fraction for the impurity atoms in the presence of nearby vacancies is estimated by using the force constants obtained from the usual Debye relation. A significant change in the Debye‐Waller factor is found with the rise in temperature indicating the effect of temperature on the amount of trapping of point defects by the impurity atoms. The contributions due to the substitutional impurity alone and that in presence of a vacancy adjacent to it are evaluated for a simple cubic crystal with nearest‐neighbour central‐force interactions and are discussed for the zero phonon process.

Dislocation damping in Cu-Ni alloys at low temperatures and high strain amplitudes

Dislocation damping was studied in 〈110〉 Cu crystals containing 0≲c0≲4×10−2 atom fraction Ni at 95≲T≲297 °K, strain amplitudes ε0 from the mid-10−7 to the mid-10−4 range, and frequencies f≈22 kHz. Dislocation interactions with the combined Suzuki-Cottrell atmosphere are analyzed to explain the composition dependence and propose a model for amplitude-independent damping Q−1I in alloys consisting sequentially of (1) the fault narrowing, (2) the escape of one partial, and (3) the complete breakaway from the combined Suzuki-Cottrell atmosphere. Consideration of both the multiplicity of Cottrell pinning sites and the stacking-fault width demonstrate the role of the pinning-point amplification factor in determining the impurity-dislocation binding energy and the distribution of impurities in the combined atmosphere. The transition ε0 from Q−1I to amplitude-dependent damping Q−1H showed a linear correlation with the calculated Suzuki yield stress. Two distinct stages of Q−1H were observed: at the lower ε0, Q−1H1 is thermally activated and characterized by an escape enthalpy of ≈0.04 eV, while at the higher ε0, Q−1H2 is nearly independent of temperature. A qualitative static-hysteresis model is proposed to account for the interaction between dislocations in the breakaway configuration and solid-solution impurities located outside of the Suzuki-Cottrell atmosphere, which predicts a squared hysteresis loop and the observed nearly temperature-independent behavior for Q−1H2.

Mo¨ssbauer effect measurement in single crystal iron subjected to cyclic stress

High purity single crystal iron specimens, in the form of rectangular strips with appropriate stress concentrators in the midplane, were cyclically fatigued in the stress range of (3–7) kg/mm 2 and their backscattered Mo¨ssbauer spectra recorded at different fatigue levels. From the data on hyperfine spacing, it is observed that the effective field increased by about 1% per 2 × 10 6 fatigue cycles. This roughly equivalent to an order of magnitude increase in the interstitial impurity in solid solution in the region of stress concentration. This change in H (effective) at the absorber nuclei is accompanied by a corresponding line broadening from the superposition of spectra due to several nonequivalent absorber nucleus sites as well as inhomogeneous quadrupole interaction. It thus appears that this technique can be used to follow (measure) the interstitial impurity increase which is presumed to be the eventual cause of fatigue crack initiation and metal failure.

Effect of Oxygen Partial Pressure on the Creep of Polycrystalline Al2O3 Doped with Cr, Fe, or Ti

Steady‐state creep was studied in hot‐forged polycrystalline Al2O3 (3 to 42 μm) of nearly theoretical density doped with≤1 cation % of Fe, Ti, or Cr. Tests were conducted at stresses between 10 and 550 kg/cm2 at 1375° to 1525°C under O2 partial pressures of 0.88 to 10−10 atm. Except in the 10‐μm Fe‐doped material tested at very small stresses, slightly nonviscous creep behavior was generally observed. The effects of Po2 on the creep rate indicated that increased concentration of a divalent (Fe2+) or quadrivalent (Ti4+) impurity in solid solution enhances the creep rate of polycrystalline Al2O3. The activation energies for the creep of Fe‐ and Ti‐doped Al2O3 samples (148 and 145 kcal/mol, respectively) were significantly higher than that for Cr‐doped material (114 kcal/mol). Taking into account the effects of Po2, temperature, and grain size, it was concluded that the steady‐state creep of transition‐metal‐doped Al2O3 is controlled by cation lattice diffusion.

Electron Beam Float Zone Melting and Vacuum Degassing of Niobium Single Crystals

Niobium metal powder produced by electrodeposition from molten salts was electron beam float zone melted (EBFZM) for purification and growth of single crystals. It was necessary to EBFZM with a high oxygen partial pressure to reduce the carbon level. A high resistance ratio (R300 K/R4.2 K(15 kG)=6500) and low flow stress (τly=460 gm/mm2) was obtained after a high temperature anneal (2350 °C) in high vacuum (2×10−10 Torr). Extensive material characterization results are reported for the niobium at various stages in the purification process. The impurity content determined by chemical analyses did not correlate with the resistance ratios; however, the flow stress exhibited an excellent correlation with resistance ratio. These results imply that interstitial impurity in solid solution is the impurity distribution most affecting disslocation motion.