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PubMed2006

Interaction between silicates and ionic surfactants in dilute solution.

Understanding the interaction between silicate ions and surfactants is critical for the design and development of mesoporous siliceous materials. We examined the interaction between sodium silicate ions and three different cationic surfactants [namely, cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB), and dodecyltrimethylammonium bromide (DTAB)] and an anionic surfactant [sodium dodecyl sulfate (SDS)] in dilute solution at room temperature. From the combination of several techniques, such as conductometric and potentiometric titrations, dynamic light scattering, and isothermal titration calorimetry, the phase behavior of the sodium silicate and CTAB system was determined. We observed that the aggregation behavior of the silicate-CTAB system is similar to that of a polymer-surfactant system. The formation of the silicate-CTAB complex is induced by the adsorption of SiOH and SiO- groups, aided by CTAB unimers. The electrostatic attraction and hydrophobic interaction are the dominant forces controlling the formation of silicate-CTAB complexes. When these complexes are saturated with CTAB unimers, free CTAB micelles are then produced. TEM micrographs revealed that a stable Si-O-Si network is absent within the silicate-CTAB complexes, and surprisingly, stable silicate-CTAB complexes with ordered structure were observed. The present finding is important for understanding the interaction between silicate and surfactant in the synthesis of mesoporous structure in the dilute solution regime.

Journal Article↗

PubMed2005

Sodium silicate as alternative to liming-reduced aluminium toxicity for Atlantic salmon (Salmo salar L.) in unstable mixing zones.

When acid aluminium (Al) rich water is limed, unstable mixing zones are formed until equilibrium is reached. In such mixing zones transient high molecular mass positively charged Al-species (HMM Al(i)) being extremely gill reactive are produced, causing toxic effects in fish. The transient HMM Al(i)-species are formed due to hydrolysis and polymerization of low molecular positively charged Al-species (LMM Al(i)), e.g. initiated by liming and the subsequent increase in pH. To counteract the toxicity of transient Al polymers in such mixing zones, sodium silicate, forming non-toxic hydroxyaluminosilicate (HAS) complexes, can be used as alternative to liming. In the present work the effect of sodium silicate on polymerization of LMM Al(i) in unstable mixing zones and subsequent gill reactivity and mortality of fish was compared to results obtained from liming. Diluted sodium silicate (<1.5 g l(-1)) and lime slurry (Ca(OH)(2)), respectively, were continually added to acidified Al-rich water in six different channel-tank systems, to obtain mixing zones with pH 5.9, 6.0 and 6.4, respectively. Utilising in situ size and charge fractionation techniques and following the exposure of Atlantic presmolt (Salmo salar L.) kept in cages at defined stations along the channel-tank systems, changes of Al-species in the mixing zones, the gill reactivity of Al-species and thus Al toxicity could be followed downstream the confluences (time of reaction after mixing: 1-100 min). By increasing the pH of the acid water to 6.0 or 6.4 by sodium silicate, the detoxification of Al was faster than using lime. Using sodium silicate, the transformation of LMM Al(i), the formation of HMM Al(i), the Al deposition in fish gills and fish mortality were lower than using lime. The formation of neutral LMM Al-species (Al(o)) was, however, higher and the formation of colloidal Al-species (Al(c)) lower in the presence of silicate compared to lime. Furthermore, the Al deposition in fish gills and fish mortality decreased by increasing concentration of sodium silicate dosed. Thus, sodium silicate is a good alternative to liming, and under certain circumstances when aging of water may represent a problem (e.g. aquaculture) sodium silicate should be the preferred agent.

Aluminum↗

PubMed2003

Highly dispersed green silicate and oxide pigments precipitated from model systems of postgalvanic waste.

A procedure was worked out to obtain highly dispersed green silicate and oxide pigments precipitated from postgalvanic waste. The highly dispersed chromium(III) silicates and oxides were produced from the waste, originating from chromium plating, by reduction of Cr(VI) to Cr(III) employing various reducing agents. All the reductions were conducted in an acidic medium. Solutions of Cr(III), obtained in reducing processes, were employed to precipitate silicate pigments (using sodium metasilicate solution and containing mainly chromium(III) silicates) and oxide pigments (using sodium hydroxide and containing chromium(III) oxides). The precipitated silicates and oxides were subjected to a comprehensive physicochemical analysis (estimating bulk density, capacities to absorb water, dibutyl phthalate, paraffin oil, particle size distribution, and morphology of particle surface). Precipitation process (its parameters) and heating of the reactive mixture exerts a significant effect on the principal physicochemical properties of the pigments. The heating significantly affects first of all color shade of the obtained silicate and oxide pigments as well as their dispersion. Coprecipitated chromium(III) and iron(III) silicates exhibit a brownish color and a reasonably uniform character. Apart from primary agglomerates (in the range of 414-717 nm), they contain small amounts of secondary agglomerates (in the range of 4154-6445 nm). Best physicochemical parameters have been demonstrated by chromium pigments which have been precipitated from chromium solutions reduced using hydrogen peroxide. Chromium(III) oxides deserve particular distinction since their structure includes primary particles, primary agglomerates but is completely free of secondary agglomerates. The pigments manifest a brightly green color and a low capacity to absorb water (100 cm3 x 100 g(-1)). Application of hydrophobicity-inducing agents in the course of precipitation has corrected physicochemical parameters of both the oxides and silicates of chromium(II). Their bulk densities have been clearly decreased (to as low as below 250 g x L(-1) in the case of chromium(III) silicate), while capacities to absorb paraffin oil have increased to as much as 750 cm3 x 100 g(-1) for chromium(II) oxide. The respective particle size distribution has shown a tendency for disappearance of large accumulations of secondary agglomerates.

Carcinogens, Environmental↗

PubMed1978

Role of silicon on diatom metabolism. IX. Differential synthesis of DNA polymerases and DNA-binding proteins during silicate starvation and recovery in Cylindrotheca fusiformis.

During recovery from silicate-starvation, a period of active DNA synthesis, synchronized cells of Cylindrotheca fusiformis incorporated 3 times more L-[U-14C]aspartate than did starved cells. Of the diatoms's four DNA polymerases, A and D are synthesized during silicate recovery, indicating that they are involved in silicate-dependent DNA replication. Polymerase B, and the chloroplast enzyme, polymerase C, are synthesized during silicate-starvation and their levels are unaffected by the addition of silicate. DEAE-Sephadex analysis of the DNA-binding proteins, labeled with [14C]- and [3H]asparate, shows that only three proteins are synthesized in cells recovering from silicate-starvation. Two of these proteins correspond to polymerases A and D, while the function of the third protein is not known. At least 15 other proteins are present in silicate-starved cells and their synthesis is repressed upon the addition of silicate. Models are proposed which describe the modes by which silicate might regulate DNA synthesis in the diatom.

Amino Acids↗

PubMed2005

Molecular manipulation of two- and three-dimensional silica nanostructures by alkoxysilylation of a layered silicate octosilicate and subsequent hydrolysis of alkoxy groups.

A novel methodology for constructing molecularly ordered silica nanostructures with two-dimensional (2-D) and three-dimensional (3-D) networks has been developed by using a stepwise process involving silylation of a layered silicate octosilicate with alkoxytrichlorosilanes [ROSiCl(3), R = alkyl] and subsequent reaction within the interlayer spaces. Alkoxytrichlorosilanes react almost completely with octosilicate, bridging two closest Si-OH (or -O(-)) sites on the silicate layers, to form new five-membered rings. The unreacted functional groups, Si-Cl and Si-OR, are readily hydrolyzed by the posttreatment with a water/dimethyl sulfoxide (DMSO) or water/acetone mixture, leading to the formation of two types of silicate structures. The treatment with a water/DMSO mixture produced a unique crystalline 2-D silicate framework with geminal silanol groups, whereas a water/acetone mixture induced hydrolysis and subsequent condensation between adjacent layers to form a new 3-D silicate framework. The 2-D structure is retained by the presence of DMSO molecules within the swelled interlayer spaces and is transformed to a 3-D silicate upon desorption of DMSO. The structural modeling suggests that both of the 3-D silicates contain new cagelike frameworks where solvent molecules are trapped even at high temperature (up to 380 degrees C, in the case of acetone). Both 2-D and 3-D silica structures are quite different from known layered silicates and zeolite-like materials, indicating the potential of the present approach for precise design of various silicate structures at the molecular level.

Journal Article↗

PubMed2005

FTIR spectroscopic study of titanium-containing mesoporous silicate materials.

The surface acidity of different mesoporous titanium-silicates, such as well-organized hexagonally packed Ti-MMM, Ti-MMM-2, Ti-SBA-15, and amorphous TiO(2)-SiO(2) mixed oxides (aerogels and xerogels), was studied by means of FTIR spectroscopy of CO adsorbed at 80 K and CD(3)CN adsorbed at 293 K. The surface hydroxyl groups of mesoporous titanium-silicates with 2-7 wt % Ti revealed a Brönsted acidity slightly higher to that of pure silicate. TiO(2)-SiO(2) xerogels revealed the highest Brönsted acidity among the titanium-silicates studied. CO adsorption revealed two additional sites on the surface in comparison to pure silicate, characterized by nu(CO) from 2185 (high pressure) to 2178 (low pressure) cm(-1) and from 2174 (high pressure) to 2170 (low pressure) cm(-1). These bands are due to CO adsorbed on isolated titanium cations in the silica surrounding or having one Ti(4+) cation in their second coordination sphere and due to CO interactions with Ti-OH groups, respectively. CD(3)CN adsorption similarly revealed the existence of two additional sites, which were not detected for pure silicate: at 2289 cm(-1) due to CD(3)CN interaction with titanol groups and from 2306 (low pressure) to 2300 (high pressure) cm(-1) due to acetonitrile interaction with isolated framework titanium cations with probably one Ti(4+) cation in their second coordination shell. The spectroscopic results are compared with computational data obtained on cluster models of titanium-silicate with different titanium content. According to the IR data, the Ti accessibility on the surfaces for mesoporous titanium-silicates with similar Ti loading (2 wt %) was found to fall in the order TiO(2)-SiO(2) aerogel approximately TiO(2)-SiO(2) xerogel > Ti-MMM approximately Ti-MMM-2 > Ti-SBA-15. This order (except TiO(2)-SiO(2) xerogel) correlates with the catalytic activity found previously for titanium-silicates in 2,3,6-trimethylphenol oxidation with H(2)O(2).

Journal Article↗

PubMed2004

In vitro tobramycin elution analysis from a novel beta-tricalcium phosphate-silicate-xerogel biodegradable drug-delivery system.

This in vitro research analyzed local tobramycin elution characteristics from a novel, biodegradable drug delivery system, consisting of a beta-TCP bone substitute, VITOSS trade mark, encapsulated with silicate xerogel prepared by the sol-gel process. Tobramycin elution from silicate-xerogel-encapsulated VITOSS was compared directly with non-silicate-xerogel-encapsulated VITOSS to assess whether xerogels are effective in delivering greater tobramycin quantities in a controllable, sustained manner crucial for microbial inhibition. Tobramycin elution characteristics indicate an initial release maximum during the first 24 h that diminishes gradually several days after impregnation. The copious tobramycin quantity eluted from the VITOSS/silicate-xerogel systems is attributed to various factors: the intrinsic ultraporosity and hydrophilicity of VITOSS, the ability of tobramycin to completely dissolve in aqueous media, tobramycin complexation with highly polar SO(4) (2-) salts that further assist dissolution, and ionic exchanges between VITOSS and the environment. Silicate-xerogel-encapsulated VITOSS eluted 60.65 and 61.31% of impregnated tobramycin, whereas non-silicate-xerogel-encapsulated VITOSS eluted approximately one-third less impregnated tobramycin, at 21.53 and 23.60%. These results suggest that silicate xerogel optimizes tobramycin elution because of its apparent biodegradability. This mechanism occurs through xerogel superficial acidic sites undergoing exchanges with various ions present in the leaching buffer. Tobramycin elution kinetics were evaluated, and demonstrate that first-order elution rate constants are considerably less when silicate xerogels are employed, following a more uniform exponential decay-type mechanism, thus bolstering controlled release. Overall, tobramycin elution rates adhere to linear-type Higuchi release profiles. Elution rate constants are initially first order, and taper into zero-order elution kinetics in the latter stages of release. Because VITOSS and silicate xerogel are completely biodegradable, essentially all impregnated tobramycin will be delivered to the surgical site after implantation.

Anti-Bacterial Agents↗

PubMed1987

Silicate minerals and the interferon system.

Natural-occurring minerals representative of six silicate classes were examined for their influence on interferon induction by influenza virus in Rhesus monkey kidney (LLC-MK2) cell monolayers. Minerals within the classes nesosilicate, sorosilicate, cyclosilicate, and inosilicate exhibited either little or marked (50% or greater) inhibition of interferon induction. Within the inosilicate class, however, minerals of the pyroxenoid group (wollastonite, pectolite, and rhodonite) all significantly showed a two- to threefold increase in interferon production. Silicate materials in the phyllosilicate and tectosilicate classes all showed inhibitory activity for the induction process. When silicate minerals were coated with the polymer poly(4-vinylpyridine-N-oxide), the inhibitory activity of silicates on viral interferon induction was counteracted. Of nine randomly selected silicate minerals, which inhibited viral interferon induction, none adversely affected the ability of exogenous interferon to confer antiviral cellular resistance. Increased levels of influenza virus multiplication concomitant with decreased levels of interferon occurred in cell monolayers pretreated with silicates. The findings of this study demonstrate the diverse effects of minerals representative of different silicate classes on the interferon system and indicate that certain silicates in compromising the viral interferon induction process may increase susceptibility to viral infection.

Cell Line↗

PubMed2004

Inhibition of pyrite oxidation by a phospholipid in the presence of silicate.

The influence of sodium silicate on the ability of a diacetylene-containing phospholipid (23:2 diyne PC) to inhibit the oxidation of pyrite at pH 2 and pH 6 was investigated. The phospholipid used has previously been reported to show up to 80% suppression of pyrite oxidation and to show excellent stability down to at least pH 2. Pyrite was leached with a solution containing Fe3+ but no coating agent and three different solutions or treatments: a lipid treatment, a silicate treatment, and a lipid + silicate treatment. Pyrite oxidation was based on iron (Fe3+, Fe2+) leached out of a continuous-flow porous-bed reactor system. The results show that at pH 6 the silicate and lipid both bind strongly to the pyrite surfaces, providing a barrier that inhibits the production and subsequent release of oxidation products. The lipid is superior to the silicate in suppressing pyrite oxidation at both pH 2 and pH 6. Also, the presence of silicates decreased the ability for the lipid to suppress pyrite oxidation, both at pH 2 and pH 6. The reaction mechanism for pyrite oxidation at pH 2 is first order for pyrite leached by solutions containing only ferric, ferric together with silicate, and ferric combined with silicate and lipid. The only treatment that effectively prevented pyrite oxidation at pH 2 was the lipid treatment. The Fe speciation results are supported by both SEM images and EDS calculations.

Hydrogen-Ion Concentration↗

PubMed1956

Effect of silicate on Gram staining and viability of pneumococci and other bacteria.

Application of silicate solutions to living or heat-killed pneumococci and to certain "viridans" streptococci causes their conversion from a Gram-positive to a Gram-negative state. The original staining properties can be restored by suspending the silicate-treated bacteria in alkaline solutions of various salts but not by simple washing in water. Living pneumococci and the strains of streptococci whose staining properties are similarly affected are killed when suspended in silicate solutions. In other Gram-positive species silicate causes conversion to Gram negativity but restoration to positivity occurs upon washing in water. In a third group of Gram-positive organisms silicate has no effect on the Gram reaction. The viability of organisms in these two groups is unaffected by silicate under the conditions employed. No effect on staining or viability of Gram-negative bacteria has been observed. The effects of silicate on staining and viability are inhibited by nutrient broth or whole serum but not by purified serum albumin. Lecithin, choline, and other substituted ammonium compounds also inhibit the effects of silicate on pneumococci.

Bacteria↗

PubMed1984

Adjuvant effects of aluminum silicate on IgE and IgG1 antibody production in mice.

The adjuvant effects of aluminum silicate on IgE and IgG1 antibody production were investigated. BALB/c mice were immunized intraperitoneally with 10 micrograms ovalbumin (OA) adsorbed on 0.2, 2, or 20 mg aluminum silicate. The enhancement of anti-OA IgE antibody production was observed in the mice injected with aluminum silicate and antigen compared with the mice injected with antigen alone. Anti-OA IgE antibody production with 2 and 20 mg aluminum silicate was greater than that with aluminum hydroxide (alum) as an adjuvant. Similar adjuvant effects with 2 mg aluminum silicate or alum were observed in AKR and C57BL/6 mice using 10 micrograms OA, and in BALB/c mice using 2 micrograms DNP-KLH (dinitrophenyl keyhole limpet hemocyanin): IgE antibody production induced by aluminum silicate adjuvant persisted for weeks in these experiments. The enhancement of IgG1 antibody production to OA mixed with aluminum silicate was also demonstrated. However, no difference between aluminum silicate and alum was observed on the IgG1 antibody production.

Adjuvants, Immunologic↗

PubMed2002

Aggregation and decomposition of a pseudoisocyanine dye in dispersions of layered silicates.

The optical properties of reaction systems composed from a pseudoisocyanine (PIC) solution and dispersed layered silicates were studied using visible spectroscopy. Two series of reduced-charge montmorillonites were used as the silicate materials. Each series consisted of eight samples with different layer charges, which were prepared from one parent material. Observed trends were verified with another series of dioctahedral and trioctahedral smectites of different layer charges, structure, and origin. The layer charge density of the silicates significantly affected the aggregation of PIC cations. In addition to the formation of J-aggregates, dye spectral bleaching was also observed. Silicates with very low charge densities induced neither significant aggregation nor spectral bleaching of the dye. The highest levels of PIC J-aggregate formation were found in dispersions of the layered silicates with a medium surface charge. However, reversible spectral bleaching was also observed in some cases. PIC dye cations probably change their conformations during the adsorption process, due to the tension resulting from the large size of the cations and the relatively high charge density at the silicate surface. The bleached dye recovers, at least partially, with the rearrangement and redistribution of the dye cations over the time. In contrast, the presence of silicates with very high charge densities (synthetic taeniolite and fluorohectorite) led to the very fast and irreversible decomposition of the PIC. Perhaps, the tension in adsorbed dye cations, induced by the high charge density at the silicate surface, resulted in significant destabilization and a decomposition reaction of the chromophore.

Journal Article↗

PubMed1982

Electron micrographic study of precipitates formed by interaction of silicic acid and alkaline phosphatase: contribution to a study of silica urolithiasis in cattle.

Association of alkaline phosphatase with silicic acid in precipitates formed in dilute solution was studied as a model for the nonspecific reaction between silicic acid and protein. Precipitates contained 68-83% of the silicic acid and 52-83% of the enzyme in the original mixture and were in the form of aggregates of roundish particles 150-800 nm in diameter. Enzyme protein formed a tightly bound layer on the surface of particles formed in solutions of freshly prepared silicic acid. The similarity between the ultrastructural features of precipitates from solutions of silicic acid and of internal portions of siliceous urinary calculi from cattle suggests that deposition of silica during development of such calculi is due, at least in part, to the interaction of protein with silicic acid in urine.

Acid Phosphatase↗

PubMedDate not supplied

Protease-containing silicates as active antifouling materials.

Biocatalytic silicates, composite materials composed of alpha-chymotrypsin and a silicate prepolymer, were prepared via a two-step polymerization process following solubilization of the enzyme in the polymerization media. This new approach resulted in active and stable composites, and a calculated half-life of over 350 days in aqueous buffer at 30 degrees C. The high stability and activity of this biocatalytic silicate was likely due to the covalent attachment between alpha-chymotrypsin and the silicate matrix. The protease-containing silicate was resistant to fouling by nonselective protein binding, as demonstrated by the dramatically reduced binding of human serum albumin to the silicate material when compared to that of a silicate containing pre-inactivated alpha-chymotrypsin.

Catalysis↗

PubMed2005

Interactions of silicate ions with zinc(II) and aluminum(III) in alkaline aqueous solution.

We present (29)Si, (27)Al, and (67)Zn NMR evidence to show that silicate ions in alkaline solution form complexes with zinc(II) (present as zincate, Zn(OH)(3)(-) or Zn(OH)(4)(2-)) and, concomitantly, with aluminate (Al(OH)(4)(-)). Zincate reacts with monomeric silicate at pH 14-15 to form [(HO)O(2)Si-O-Zn(OH)(3)](4-) and with dimeric silicate to produce [HO-SiO(2)-O-SiO(2)-O-Zn(OH)(3)](6-). The exchange of Si between these free and Zn-bound sites is immeasurably fast on the (29)Si NMR time scale. The cyclic silicate trimer reacts relatively slowly and incompletely with zincate to form [(HO)(3)Zn{(SiO(3))(3)}](7-). The concentration of the cyclic trimer becomes further depleted because zincate scavenges the silicate monomer and dimer, with which the cyclic trimer is in equilibrium on the time scale of sample preparation. Identification of these zincate-silicate complexes is supported by quantum chemical theoretical calculations. Aluminate and zincate, when present together, compete roughly equally for a deficiency of silicate to form [(HO)(3)ZnOSiO(2)OH](4-) and [(HO)(3)AlOSiO(2)OH](3-) which exchange (29)Si at a fast but measurable rate.

Algorithms↗

PubMed2005

A randomized double-blind study to assess the effects of silicic acid compared to placebo in patients with mild to moderate acne.

OBJECTIVE: To establish the efficacy and safety of silicic acid in comparison to placebo in patients with mild to moderate acne vulgaris. PATIENTS AND METHODS: Forty adult patients with facial acne vulgaris were randomized to silicic acid or placebo applied twice daily for 8 weeks. Efficacy was assessed by number of acne lesions, acne grade and sebum excretion rate (SER). Clinical safety and tolerance were also assessed and global assessments and psychological profile questionnaires were completed. RESULTS: There were no significant differences between silicic acid and placebo in the number of inflamed lesions (the primary efficacy variable). In contrast, silicic acid significantly reduced the number of non-inflamed lesions, total acne lesions and the acne grade after 8 weeks and SER over 4 weeks when compared with placebo. There were no significant differences between silicic acid and placebo in the responses to the questionnaires or the global assessments after 8 weeks. Silicic acid was well tolerated with few adverse events. CONCLUSIONS: Silicic acid may have a positive treatment effect on the non-inflammatory component of mild to moderate facial acne. These preliminary findings now need to be confirmed by similar studies.

Acne Vulgaris↗

PubMed2005

Collagen-silica hybrid materials: sodium silicate and sodium chloride effects on type I collagen fibrillogenesis.

Collagen-silica hybrid materials have been considered for potential biomedical applications. Understanding of the collagen-silica interactions is the key to control hybrids structure and properties. For this purpose, the effect of sodium silicate and sodium chloride addition at two concentrations, 0.83 and 10 mM, on the kinetic of the type I collagen fibrillogenesis at 20 degrees C, and pH 7.4 were studied. Absorbance profiles of fibrillogenesis experiments were collected together with measures of silicic acid concentration and transmission electron microscopy analysis. The specific effect of silica addition on the collagen fibrils self-assembly mechanisms was demonstrated by comparison with the sodium chloride. Sodium silicate at 10 mM inhibited the collagen fibrillogenesis. At the same concentration, the sodium chloride decreased the rate of the collagen fibril assembly. Collagen fibrillogenesis kinetic was not significantly disturbed by the presence of 0.83 mM of sodium chloride. However, the same concentration of sodium silicate modified the collagen fibrillogenesis kinetic. Transmission electron microscopy indicated for experiment with 0.83 mM of sodium silicate, the formation of longer and wider fibrils than for the equivalent collagen fibrillogenesis experiment with sodium chloride. The effect of sodium chloride is explained in terms of osmotic exclusion and influence on electrostatic interactions between collagen fibrils. The specific involvement of silicic acid in collagen helices hydrogen-bond interactions is suggested. Finally, the results of this study are discussed regarding the preparation of composites by co-gelation of type I collagen and sodium silicate, for potential application as bone repair device.

Animals↗

PubMed1998

The Silicate Garden Reaction in Microgravity: A Fluid Interfacial Instability.

In the "silicate garden" reaction, crystals of a metal salt are placed in sodium silicate solution. The crystals become coated with a semipermeable membrane of metal silicate reaction product, from which hollow tubes of metal silicate rise convectively upward, against gravity. In the absence of gravity, and free of convective influences, the reaction might be expected to reveal more fundamental organizing principles. Accordingly, we have grown silicate gardens in microgravity, from salts of calcium, cobalt, and magnesium with added nickel. Even in these isotropic conditions, complex structures developed. They included tubes and hollow spheroids, and also novel dendritic "fingers" which grew by continuous plastic deformation. This new mode of growth is favored by the slow, diffusion-limited rate of reaction in microgravity, which greatly reduces the rate of hardening of the reaction products. The magnesium-nickel garden grew almost entirely as a fluid interfacial instability between the metal salt solution inside and the silicate solution outside, by deformation of the semipermeable fluid membrane between them. The resulting shape had similarities to that of a solid front advancing through a supercooled melt. The morphology of such a solid is determined by the diffusion of released latent heat away from it, according to the Laplacian diffusion equation. We suggest that Laplacian-growth morphology arises in a microgravity silicate garden when its development is controlled by the analogous diffusion of dissolved ions away from it. Copyright 1998 Academic Press.

Journal Article↗