Hydrate Powder Research Articles

Controls of Polymorphism and Morphology of Calcium Carbonate Compounds Formed by Crystallizing Amorphous Calcium Carbonate Hydrate

In this report, controls of polymorphism and morphology of calcium carbonate compounds were studied by suspending amorphous calcium carbonate hydrate (ACC) powder in water or MgCl2 solution. Characteristics of calcium carbonate compounds formed from ACC were determined by means of X-ray diffraction, thermal analysis (TG-DTA) and scanning electron microscopic observation. ACC was synthesized by adding 0.1mol⋅dm-3 CaCl2 solution into a mixed solution of 0.1mol⋅dm-3 NaOH and 0.1mol⋅dm-3 Na2CO3 at 0°C. The calcium carbonate compounds formed easily by suspending ACC in water and was affected remarkably by temperature (0-80°C) and pH (1.7-14.0). Thus ACC changed into hexagonal plate-like calcium carbonate hexahydrate at 0°C, rhombohedral calcite at 15-20°C, spherical vaterite at 30-50°C and needle-like aragonite above 80°C after aging for 1h. ACC was also changed into vaterite in the pH region of 7.0-9.5 and to basic calcium carbonate above pH 12.8 at 20-40°C. On the other hand, spherical calcium carbonate monohydrate was formed from ACC in MgCl2 solution (0.03-0.50mol⋅dm-3) and then changed finally to aragonite after long aging. For example, the amount of spherical monohydrate with a diameter of 30μm reached a maximum after aging for 3d, and it changed to needle-like aragonite with an average length of 50μm after 10d in 0.10mol⋅dm-3 MgCl2 solution. Accordingly, ACC changed easily to calcium carbonate anhydrides (calcite, aragonite, vaterite), calcium carbonate hydrates (monohydrate, hexahydrate) and basic calcium carbonate, when ACC was suspended in solutions of different conditions such as temperature, pH and concentration of MgCl2.

The Precipitation of Alkaline‐Earth Metal Polyacrylate Hydrate Powders from Aqueous Solution: Ionic Equilibria, Precipitate Compositions and Morphologies

AbstractThe precipitation of barium, strontium, calcium and magnexium polyacryate hydrates was studied from equivalent aqueous solutions of initial concentrations 0.03 M to 0.30 M at ambient temperature: sodium polyacrylate (m. wt = 30,000 to 300,000) was added to metal chloride solution. The final yields of precipitate increased with decreasing solubility and/or peptisation (Ba > Sr > Ca > Mg) and increasing molecular weight of the polyacrylate; the precipitates had the compositions [BaA(COO)2 · 1–2H2O]n, [SrA(COO)2 · 1–2 H2O]n, [CaA(COO)2 · 2 H2O]n and [MgA(COO)2 · 2 H2O]n.The final yields of the precipitates from sodium polyacrylate solutions were far lower and these had the compositions [Na2αM1‐αCA(COO)2 · 2 H2O]n; A = CHCH2CH.The metal polyacrylate hydrate powders consisted of microcrystalline ‘spherules’; their average diameters were from 0.03–0.05 μm (for lower m. wt products) to 0.01 to 0.02 μ,m (for higher m. wt products).

The coprecipitation of calcium aluminium hydroxide (calcium hydroxoaluminate hydrate) powders from aqueous solution with sodium hydroxide: Precipitate compositions and percipitation mechanisms

AbstractCalcium aluminium hydroxides were coprecipitated from different mixed metal cation solutions — at total CM = 0.1 M and Ca/Al2 ratios from 1 to 4 — with sodium hydroxide solution at ambient temperature. The coprecipitations were monitored by potentiometric (pH) titration and the final coprecipitate compositions were examined by chemical analysis, infra‐red spectrophotometry and thermal analysis Generally, microcrystalline aluminium hydroxide was first precipitated at pH about 4; this then redissolved on further addition of sodium hydroxide to form hydroxoaluminate anion and polyanion and calcium aluminium hydroxide coprecipitates were formed continuously at pHs from about 9 to above 12. Their compositions were similar to the calcium hydroxoaluminate hydrates formed by direct precipitation from high pH sodium hydroxoaluminate solutions.At Ca/Al2 ratio = 1, the main phase was probably Ca2(H2O)h[Al2(OH)4]2 with some Al(OH)3;At Ca/Al2 ratio = 2, the main phase was probably Ca2(H2O)h[Al2(OH)10] dehydrating to Ca2[Al2O(OH)8];At Ca/Al2 ratios = 3–4, the main phase was Ca2(H2O)h[Al2(OH)10] with increasing amounts of Ca4(H2O)h(OH)4[Al2(OH)10] and 5–10 percent adsorbed or post‐precipitated Ca(OH)2.

The precipitation of magnesium hydroxoaluminate hydrate powders from sodium hydroxoaluminate solutions: Precipitate phases and precipitation mechanisms

AbstractMagnesium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate and hydroxoaluminate‐hydroxide solutions at ambient temperature, at CAl = 0.1 M, OH/Al ratios = 4–9 and XS OH/Al ratios = 1–6. The precipitations were monitored by potentiometric (pH) measurements while the final precipitate compositions were examined by chemical analysis, infra‐red spectrophotometry and thermal analysis.At solution OH/Al ratio = 4, the main precipitate phase at 20°C was Mg(H2O)n[Al(OH)4]2 admixed with some Al(OH)3; at solution OH/Al ratio = 5, the main phase was Mg2(H2O)4[Al2(OH)10]; at solution OH/Al ratio = 7, the main phase was Mg4(H2O)n(OH)4[Al2(OH)10] while at solution OH/Al ratio = 9, the main phase was Mg6(H2O)n(OH)8[Al2(OH)10] admixed with some Mg(OH)2.These hydrates were dehydrated at 60–100°C probably to the compounds Mg2[Al2O3(OH)4], Mg4(OH)4[Al2O3(OH)4] and Mg6(OH)8[Al2O3(OH)4], respectively.

STUDIES ON ALKALINE-EARTH METAL POLYMETAPHOSPHATES PREPARED BY PRECIPITATION AND DEHYDRATION

Abstract Barium, strontium, calcium and magnesium polymetaphosphate hydrate powders were prepared by precipitation from aqueous solution and their dehydrations to amorphous anhydrous powders were studied in detail by a variety of physico-chemical methods. Anhydrous barium and strontium polymetaphosphates were formed through two dehydration processes whereas calcium and magnesium polymetaphosphates were formed through dehydration, hydrolysis (with depolymerisation) and repolymerisation processes, over the temperature range 20–450°C. Batch samples of amorphous anhydrous alkaline-earth metal polymetaphosphate powders were then prepared by controlled dehydration and their properties studied. All these powders consisted of “peapod”-shaped aggregates of three to fourteen “spherules” of highly microcrystalline material of average diameter d av = 0.17 μm. Their general composition was [MP2O6] n ; chain-lengths (n) varied from 8 to 22 (and molecular-weights varied from about 800–2200). Their glass transition temperatures (Tg ) were similar to the values reported for amorphous polymetaphosphates prepared by high-temperature methods and increased with reciprocal cation radius from 453–530°C. The annealing of the amorphous powders above Tg was also studied by the above techniques: crystallisation started onto heterogeneous nuclei at initial temperatures Ti [dbnd] Tg + 20–30°C and reached maximum rates at temperatures T xmax [dbnd] Tg + 50–70°C.

The precipitation of calcium hydroxoaluminate hydrate powders from sodium hydroxoaluminate solutions: Precipitate phases and precipitation mechanisms

AbstractCalcium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate and hydroxoaluminate‐excess hydroxide solutions at ambient temperature (at CAl = 0.1 to 0.3 M and at XS OH/Al = 0 to above 8). The precipitations were monitored by potentiometric (pH) measurements. Precipitate morphologies were examined by optical microscopy and precipitate compositions were determine by chemical analysis, infra‐red spectrophotometry and thermal analysis.Generally at OH/Al ratios of 4 to 4.5 (XS OH/Al = 1 to 1.5), the compound 2 CaO · · Al2O3 · 8 H2O (C2AH8) was precipitated with some aluminium hydroxide; then at OH/Al ratios of 5 to above 11 (XS OH/Al = 2 to above 8), the compound 2 CaO · Al2O3 · 8 H2O was precipitated with increasing amounts of the compound 4 CaO · Al2O3 · 13 H2O (C4AH13).

The precipitation of barium hydroxoaluminate hydrate powders from sodium hydroxoaluminate solutions: Precipitate phases and precipitation mechanisms

AbstractBarium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate solutions at 20 °C; CAl varied from 0.1 to 0.5 M and initial Ba/Al2 ratios ( = excess OH/Al ratios) varied from 1 to 7. Precipitate compositions were determined by chemical analysis, infra‐red spectrophotometry and thermal analysis. The compound BaO · Al2O3 · 7 H2O was precipitated at initial Ba/Al2 ratios of one to well above two while the compound 2 BaO · Al2O3 · 5 H2O was only precipitated over a narrow range of concentrations. The compound Ba(OH)2 · 8 H2O was precipitated from solutions of high hydroxide and barium ion concentrations. The ionic equilibria and precipitation mechanisms in different solutions are discussed.

The precipitation of alkaline‐earth metal polymetaphosphate hydrate powders from aqueous solution. Nucleation and crystal growth processes, final precipitate compositions and crystal sizes

AbstractThe precipitation of barium, strontium, calcium and magnesium polymetaphosphate hydrates was studied from aqueous solutions of initial metal salt concentrations from 0.001 to 3 M at 20 °C; equivalent sodium polymetaphosphate solutions were added to the alkaline‐earth metal chloride solutions. Precipitate compositions were determined by chemical analysis, paper chromatography, potentiometric analysis, thermogravimetric and differential thermal analysis and infra‐red spectrophotometry; final crystallite morphologies and sizes were studied by scanning electron microscopy and X‐ray powder diffraction.Nucleation rates and nucleus numbers (at the end of the induction periods) were very high; crystal numbers varied from 1014 to 1015 at the critical concentrations to above 1017 per 1. solution.Crystal growth rates were also very high and varied as the fourth power of the initial metal salt concentration. High molecular‐weight metal polymetaphosphate hydrates were precipitated from the more dilute solutions (0.001 to 0.025 M) while increasing amounts of the more soluble intermediate and low molecular‐weight products were precipitated from the more concentrated solutions. Washing with cold water removed the tri‐ and tetralinear and cyclic phosphate products. The magnesium salts were not precipitated even from 3 M aqueous solutions.The precipitates from aqueous (NaPO3(I))n (n = 12) solutions had the compositions (BaP2O6 · 2.5 H2O)6, (SrP2O6 · 3 H2O)n and (CaP2O6 · 4 H2O)n while the magnesium salt precipitate from 20 percent aqueous acetone solution had the composition (MgP2O6 · 4 H2O)n, the precipitate n values varied from 19 to 13. The precipitates from aqueous (NaPO3(II))n (n = 20) solutions contained 0.5n to n additional adsorbed water molecules; these precipitate n values varied in turn from 40 to 26.The final precipitate powders consisted of ‘spherules’ of highly microcrystalline or amorphous polymer glass; the spherule diameters were about 0.2 μm at the critical concentrations and decreased to below 0.05 μm with increasing solution concentrations.

Electrical characteristics of a highly hydrated battery grade manganese dioxide powder

The manganese dioxide powder under study, called Permanox is a byproduct of saccharin manufacture. It contains about 10% by weight of water and 7.5% KOH. The electric conductivity is highly dependent on pressure, water content, temperature and not least, the measuring procedure. Conductivity rises considerably in transverse electric fields. From Argand diagrams, the apparent powder resistivity can be split into two parts. To a first approximation, the first part belongs to the grain cores, the second to intergranular contacts.

The fabrication of ?-alumina by reactive hot-pressing

Polycrystalline α-alumina has been fabricated by reactive hot-pressing, in which low temperature forms of alumina have been transformed to α-alumina at temperature, under pressure. The influence of the phase transformation upon the densification during hot-⌕essing was studied for a number of commercial aluminium hydrate powders, including gibbsite and boehmite.

Effect of organic surface agents on properties of hydrated cement compacts

This paper reports the treatment of bottle-hydrated portland cement with organosilanes, oleic acid and octadecylamine intended to reduce the sorption of water and the corresponding dimensional changes. Compacts were made from the treated hydrated cement powder to simulate cement paste and allow measurements of sorption-dimensional change characteristics and microhardness. It was found that organochlorosilanes are not suitable for the treatment because the HCl released during the reaction produced undesirable side effects and in some cases increased the adsorption and expansion of the cement. Hexamethyldisilazane was more effective, reducing odsorption by 10 to 20%. Oleic acid was effective at concentrations as high as 25% by weight, but serious loss in mechanical property of microhardness was experienced.

Investigation of lateral pressure at small compaction forces

1. An installation has been developed for measuring the lateral pressure of powders at small compaction pressures. It was established that, at low compaction pressures (2–42.5 daN/cm2), the coefficient of lateral pressure is constant and practically independent of powder particle size. 2. The coefficients of lateral pressure were determined for powders of Kh17N2, Kh18N15, and 1Kh18N9T stainless steels, copper, tin, tungsten, molybdenum, chromium, aluminum, iron, and titanium, as well as for hydrate, carbonyl, and electrolytic nickel powders. The highest value of the coefficients of lateral pressure (0.39) is exhibited by tungsten, molybdenum, and tin powders, and the least value (0.33) by Kh18N15 stainless steel powder. 3. In spite of the pronounced porosity of powders in this range of compaction pressures, the values of the coefficients of lateral pressure are high. For instance, for the iron powder produced by the Sulinsk Factory the mean value of ɛ is 0.35, which is very close to the values obtained in measurements of the lateral pressure of iron powder at high compaction pressures [1, 2]. Equation (3) may be employed for the approximate determination of the coefficient of lateral pressure at small compaction forces.

The Dielectric Characteristics of the Hydrate Powder

The Dielectric Characteristics of the Hydrate Powder