Crystal Habit Modification Research Articles

Adsorption of Organic Phosphonates on Calcium Sulfate Dihydrate Crystals

Abstract 14C labeled ethylenediaminetetra (methylene phosphonic acid) and triethylenediaminetetra (methylene phosphonic acid) have been used to study their adsorption on calcium sulfate dihydrate crystals radiometrically under different conditions. Kinetics of crystal growth of calcium sulfate dihydrate crystals was studied both in solution and on heated metal surface. The growth of gypsum has been shown to follow an equation second order in supersaturation. The heterogeneity of surface sites is responsible for crystal habit modification in the presence of impurities. Blocking of the active growth sites by the inhibitors results in inhibiting the scale formation.

Size Reduction of Crystals in Slurries by the Use of Crystal Habit Modifiers

Size Reduction of Crystals in Slurries by the Use of Crystal Habit Modifiers

Morphology of inhibitor-treated CaCO 3 precipitate

The modification of the habit of CaCO 3 crystals spontaneously deposited from highly supersaturated solutions treated with scale inhibitors is reported. Scanning-electron-microscope investigations reveal the marked effect of the scale-inhibitor on the crystallization and the modification of crystal habit. The method described is suitable for determining the inhibitor efficiency. On the basis of the alterations of the morphology of water-formed deposits the production of removable aggregates could be expected.

Precipitation of calcium phosphates from electrolyte solutions. V. The influence of citrate ions.

The influence of citrate ions on the precipitation of crystalline apatitic precipitates with low Ca/P molar ratios [octacalcium phosphate (OCP) and calcium-deficient apatites (DA) (system A)] and of the intercrystalline mixtures of calcium hydrogen phosphate dihydrate (DCPD) and DA (system B) was investigated. Samples were prepared by direct mixing of calcium chloride solutions (A, 6.10(-3) mol dm-3; B, 1.10(-1) mol dm-3) and sodium phosphate solutions (A, 6.10(-3) mol dm-3; B, 2.10(-2) mol dm-3) containing citrate (0-2.10(-3) mol dm-3) and preadjusted to pH 7.4. In the presence of citrate ions: (a) crystal growth of OCP and DA was slowed down; (b) habit modification of DCPD crystals occurred; and (c) equilibration in intercrystalline mixtures of DCPD and DA's was slowed down. All phenomena were caused by surface adsorption of negatively charged ions, most probably CaC6H5O7-, which is the prevalent calcium citrate species under the given experimental conditions. Habit modification of DCPD was induced by preferential adsorption at the (001) crystal plane.

The growth and habit modification of rutile crystals using Li2WO4–WO3 flux

The single crystals of rutile were grown from the flux of the system Li2WO4–WO3. Their growth habits varied through three types, {110}>{101}, {110}>{111} and {111}>{110}≈{253}, with increasing WO3 in the flux melt. TiO2 solubility was measured to determine the reactivity between TiO2 and WO4 or WO6 species in the flux melt. The heat of solution of TiO2 into the Li2WO4 melt was determined to be 49 kcal/mol, and decreased markedly by adding WO3 owing to the large reactivity of TiO2 with WO3 (or WO6).It is inferred that the habit modification of rutile was attributed to the steric interaction of WO6 species which were epitaxially adsorbed on the growing surfaces.

A mechanism for the habit modification of ammonium dihydrogen phosphate crystals in the presence of ionic species in aqueous solution

AbstractAmmonium dihydrogen phosphate (ADP) crystals develop new high index faces when grown from aqueous solution containing up to 1000 ppm of added CrCl3 · 6 H2O. The crystallographic nature of these faces has been studied as a function of the CrCl3 · 6 H2O concentration in the growth solution (24.0°C, σ = 0.06) and their high morphological importance is explained, using a modification of the Hartman‐Perdok theory of crystal morphology, but postulating that the adsorption of impurity species at specific sites transform K‐faces into pseudo‐F‐faces.

Crystal habit modifiers: I. The relationship between the structure of the additive and the crystal lattice

The crystal habits of NaCl and KCl are significantly modified by nitrilotriacetamide (NTAA) and nitrilotripropionamide (NTPA), as shown by scanning electron microscope photomicrographs. The various effects are correlated with the fit between the molecular structures of the additives and the lattice of the crystals.

Adsorption and Molecular Structuring at the Solid/Liquid Interface

AbstractAdsorption at the solid/liquid interface plays a decisive role in a wide range of phenomena including the stabilisation of colloidal dispersions, clarification and purification of liquid media (e.g., oil, sugar, liquors, wine), lubrication, and crystal habit modification. Not only the extent of adsorption but the chemical nature and the structure of the adsorbed layer is important. In recent years increasing interest has been attached to the study of molecular structuring phenomena in adsorbed layers. In aqueous media adsorption studies are complicated by the simultaneous influence of elecrical double layer effects, so that, so far, most progress has been made in nonaqueous media. This paper surveys briefly the general problems, and discusses in particular the structuring of n‐alkanes, n‐alkanols and n‐alkanoic acids from the pure liquids and from solution at carbon surfaces. Consideration is given to the possibility that similar phenomena may occur at the aqueous solution/solid interface.

Crystal habit modification by water soluble polymers

The crystal habits of SrSO 4 crystals grown from 0.015 M solution with and without the addition of polyvinyl sulfonate are compared. Pure strontium sulfate precipitate consists of single crystals, about some tens of microns long, with distinctly visible growth steps. Crystals grown with polyvinyl sulfonate in stirred solutions show a striking change of habit: they are sponge-like structures, composed of minute crystallites, of size in the nm range. The different modes of growth and the time-lag for precipitation in the presence of the polymer are explained by the stabilization of the critical nuclei of SrSO 4, possibly nucleating on the polymer molecules.

Crystal Habit Modification of Agel by Impurities Determining the Solvation

AbstractFor the first time the formation of AgCl crystals consisting of rhombic dodecahedra is shown in a photographic emulsion. Different substances, selected for their influence on the structuredness of water have been found to modify the usual growth directions of AgCl crystals. The structure of the water that promotes the {110} and {111} habits of AgCI also enhances the monomer formation of methylene blue in aqueous solutions. Adsorption of methylene blue on crystals with a {110} habit occurs 10 the monomeric form.

Crystal habit modification studies with ammonium and potassium dihydrogen phosphate

AbstractFace rates of growth of ammonium and potassium dihydrogen phosphate crystals have been measured for crystallisation from pure solutions and from solutions that contained known amounts of foreign ions. The level of supersaturation and the solution pH both effect the crystal habit. Low supersaturation at normal pH (3.8) tends to give tapered crystals, and at a slightly higher pH (˜5), the linear growth rates of both principal axes are considerably increased. The presence of foreign ions such as Cr3+, Fe3+ and Al3+ in low concentrations (˜ 1 × 10−3 g ion/1 or ˜ 50 ppm) also causes a tapering habit.A mechanism of habit modification based on the presence of aquo ions at the crystal face is suggested.

Growth studies of calcium oxalate in the presence of various ions and compounds.

SUMMARY The well-known techniques of modification of crystal habit and composition or inhibition (prevention or slowing down) of crystal growth by addition of foreign substances to the crystallising solution have been successfully applied to the crystallisation of calcium oxalate. Several ions, notably A13+, many dyestuffs, including thosepermitted as colouring matter in foods, and some compounds of therapeutic value are particularly effective. It is hoped that some of these may prove to be of use in the control of the formation of calcium oxalate renal calculi.

Carbonate Scale Formation on Steel Surfaces

Abstract This study was concerned with scale deposition on heated steel disks under controlled laboratory conditions. Produced brines from fields in South and West Texas were used as the scaling solutions. These brines exhibited a wide range of salt concentration. A laboratory testing apparatus was developed. The main feature of the new apparatus is its ability to measure the skin temperature (i.e., the temperature at the brine-steel interface). A series of tests were made covering a temperature range of from 120 to 190°F. This temperature range represents a variety of field conditions, from surface to downhole. A quantitative measurement of calcium carbonate deposition vs temperature was obtained. Thirteen selected chemicals were tested for possible use as scale inhibitors. The selection was based on the properties that might affect scale deposition, such as dispersion, sequestration, interionic action, film formation ... etc. The inhibition of scale by the various chemicals used was found to vary considerably. Film-forming compounds in the presence of crude oil proved highly effective. The nature of the scale crystals and the influence of the additives on crystal habit modification was studied through microscopic examination and photomicrographs. X-ray studies were used to indicate the chemical nature of the scale. The experimental procedure and conditions under which scale is deposited were found to be of great importance. In view of the encouraging results, the field application of film-forming compounds as scale inhibitors is highly recommended.

Polymers that inhibit the deposition of calcium sulphate: Some interesting conductance observations

The crystal habit modification of gypsum deposited from polymer-treated supersaturated solutions at 100°C is reported. Conductance measurements reveal the marked effect of the polymer on the crystallization kinetics and are consistent with observations of the modification of crystal habit. The test method described is advanced as a rapid and reliable tool for determining the inhibiting efficiency of a range of polyelectrolytes over a range of temperatures and concentrations.

Modification of Crystal Habit of Gypsum by Aluminium Ion and Cromic Ion

Modification of Crystal Habit of Gypsum by Aluminium Ion and Cromic Ion

Sodium Chloride: Modification of Crystal Habit by Chemical Agents

Microscopic investigation of drops of brine evaporating in air revealed crystal forms of sodium chloride other than the cube, when cysteine, creatinine, papain, monosodium glutamate, sodium hexametaphosphate, a combination of sodium hexametaphosphate and aluminum salt, or aluminon were added to the brine in small amounts. Some of these have a definite effect in parts per million concentration.

A Phenomenological Theory of Spherulitic Crystallization

To account for spherulitic crystallization from the melt, one must explain the origins (i) of fibrous crystal habits in the absence of appreciable temperature gradients and (ii) of profuse noncrystallographic branching. Attention is drawn to properties held in common by spherulite-forming melts of various types and, in particular, to the facts that (a) they are multicomponent systems, (b) they exhibit small coefficients of self-diffusion, and (c) they crystallize slowly. It is shown that a consequence of these properties is that a plane crystal face cannot grow without suffering an instability of profile. Analagous instabilities lead in metal crystals to a cellular interface but, because of unusual growth kinetics, instability in spherulite-forming melts gives rise to a drastic modification of crystal habit. Bundles of discrete fibers are formed whose widths are determined by δ = D/G, D being the coefficient of self-diffusion and G being the growth rate. δ is generally small in these systems and commensurate with the scale of crystalline disorder in the fibers. It is this circumstance that allows noncrystallographic branching to occur.

Modification of Crystal Habit of Gypsum by Ferric Ion

Modification of Crystal Habit of Gypsum by Ferric Ion

Crystal Habit Modification of Strontium Sulfate. II. Characteristic Effect of Sodium Triphosphate on Crystallization and Mechanism of Spherulite Formation

Abstract 1) The peculiar effect of sodium triphosphate (STP) on the crystallization and the crystal habit of strontium sulfate was studied systematically by measuring (a) the deposition rate and (b) the dissolution rate of strontium sulfate at various STP concentrations, (c) the surface adsorption of STP on strontium sulfate crystal, and (d) the coprecipitation of these salts. 2) The inhibiting action of STP on the deposition and dissolution of strontium sulfate is attributed to the adsorption of STP. 3) The fact that STP makes the growth rate predominant in the direction of c axis of strontium sulfate is ascribed to the small adsorption of STP on the (001) faces compared with that on the other faces. 4) The occurrence of the branching of crystallite was ascertained experimentally, and attributed to the ruptures appearing on the crystal faces as a result of the unfitness in the size and ionic charge of the adsorbed triphosphate. 5) The formation process of the spherulite can be interpreted from the fact that the frequent branchings are accompanied by the nearly one-dimentional growth of crystallite. 6) Possibilities of preparing spherulites from other substances are discussed.

The crystal habit modification of inorganic salts with dyes. Part 2.—The relationship between the structure of crystals and habit modifying dyes

The crystal habit modification of inorganic salts with dyes. Part 2.—The relationship between the structure of crystals and habit modifying dyes