Long-term Dissolution Research Articles

Environmental Behaviour of Synthesized and Commercial Agricultural Zinc Products: Leaching, Migration, and Availability in Soils

The aim of this paper is to examine the environmental effect of different chemical characteristics of Zinc (Zn) sources, assessing the transport, leaching and accumulation in the environment in sand, acidic (AS) and calcareous (CS) soils. Comparative short- and long-term studies applying ZnO sources [bulk, laboratory-synthesized and commercial nanoparticles (NP)], ZnSO4, complexed Zn (Zn-lignosulfonate) and chelated Zn (Zn-diethylenetriamine-pentaacetate, Zn-hydroxy-ethylenediamine-tetraacetate and Zn-ethylenediamine-tetraacetate) were carried out. For all treatments and media, the medium- and long-term dissolution kinetic model was fitted to a logistic function. The applied Zn in the form of ZnO was mainly retained at the upper half (0–7.5 cm) of the columns and in very available form (ranging 40–61% of added Zn in AS and 29–31% in CS). Leached Zn reached values below 6% in AS and 3% in CS. The use of chelated Zn in both soils and complexed Zn, and ZnSO4 in AS resulted in excessive leaching of Zn (around 70%). The amount of Zn available at the upper half of the column was less than 5%. In the CS, these fertilizers showed a higher aging than ZnO sources, negatively affecting its availability as a nutrient for crops. ZnO NP showed short- and medium-term dissolution kinetics that allow gradual nutrient release and high availability at the medium-term. These products provide an effective solution for plant nutrition while mitigating the environmental problems observed with more traditional sources related to leaching.Graphical

Long-term in vivo dissolution of thermo- and pH-responsive, 19F magnetic resonance-traceable and injectable polymer implants.

19F magnetic resonance (19F MR) tracers stand out for their wide range of applications in experimental and clinical medicine, as they can be precisely located in living tissues with negligible fluorine background. This contribution demonstrates the long-term dissolution of multiresponsive fluorinated implants designed for prolonged release. Implants were detected for 14 (intramuscular injection) and 20 (subcutaneous injection) months by 19F MR at 4.7 T, showing favorable MR relaxation times, biochemical stability, biological compatibility and slow, long-term dissolution. Thus, polymeric implants may become a platform for long-term local theranostics.

A uniformly coloring electrochromic device based on a cardo fluorene-grafted viologen derivative with high dissolution stability

The conjugated and twisted structure of fluorene-based cardo enabled the FPV-based device to exhibit promising EC properties with a uniform coloring process (coloring difference <7%) and long-term dissolution stability (>22 days).

Dissolution of Silicon from Soilless Substrates and Additives

Silicon (Si) is a beneficial element that is usually ample in mineral soil solution, but it is minimally bioavailable from soilless substrates. Several Si additives are commercially available, but the rate of dissolution of Si is not well-characterized. The ideal additive would steadily release bioavailable Si over the crop lifecycle. We report the long-term (120 days) dissolution of Si from soilless substrates and substrate additives. Studies involving gently agitated containers with deionized water indicated that perlite, sphagnum peat, vermiculite, and coconut coir released less than 0.03 mmol Si per liter of substrate per day. Rice hulls and wollastonite (CaSiO3) had 7- to 130-times faster rates of dissolution in this system; therefore, they were further studied in peat-based media. Dissolution of Si from the addition of 1 g wollastonite per liter of peat peaked at day 10 at 2.1 mmol Si per liter of media per leaching event (15% by volume); then, it gradually decreased over 120 days. The peak dissolution of Si amended with 12% rice hulls was similar, but it gradually increased over time. The concentrations of nine heavy metals in plant tissue were compared with untreated control plants to determine wollastonite and steel slag. The concentration of some elements statistically increased, but all concentrations were well below the legal concentration limits of these elements for human consumption in the United States. These results indicate that both wollastonite and rice hulls steadily release Si for up to 4 months; therefore, they are good sources of Si for container-grown crops in soilless media.

Effects of Al/Si ratio and crystallite size on the dissolution rate of aluminosilicate glass and low-calcium SCMs under alkaline condition

The dissolution of supplementary cementitious materials (SCMs) can significantly affect pozzolanic reactions in cement systems. The long-term dissolution of synthesised aluminosilicate glass and low-calcium SCMs were investigated at pH 13 for cement systems. Experimental and analysis results show that the dissolution rate of aluminosilicate glass depended on their Al/Si ratio and crystallite size. The dissolution rate of aluminosilicate glass increased as the Al/Si ratio increased. Molecular dynamics analysis showed that this was largely because the bonding dissociation energy of Al–O was lower than that of Si–O. The secondary effect was that the incorporation of Al broke the Si–O tetrahedrons when the Al/Si ratio was >0.5. In addition, the crystallite size of aluminosilicate glass decreased as the Al/Si ratio increased. The dissolution rate and the dissolvable content of aluminosilicate glass and low-calcium SCMs increased as the crystallite size decreased. Given their Al/Si ratio and crystallite size, two semi-empirical relationships were proposed to estimate the dissolution rates of aluminosilicate glass and low-calcium SCMs. These relationships provide a basis for assessing the reactivity of various SCMs.

Customizable 3D Printed Implants Containing Triamcinolone Acetonide: Development, Analysis, Modification, and Modeling of Drug Release.

Three-dimensional-printed customizable drug-loaded implants provide promising opportunities to improve the current therapy options. In this study, we present a modular implant in which shape, dosage, and drug release can be individualized independently of each other to patient characteristics to improve parenteral therapy with triamcinolone acetonide (TA) over three months. This study focused on the examination of release modification via fused deposition modeling and subsequent prediction. The filaments for printing consisted of TA, ethyl cellulose, hypromellose, and triethyl citrate. Two-compartment implants were successfully developed, consisting of a shape-adaptable shell and an embedded drug-loaded network. For the network, different strand widths and pore size combinations were printed and analyzed in long-term dissolution studies to evaluate their impact on the release performance. TA release varied between 8.58 ± 1.38 mg and 21.93 mg ± 1.31 mg over three months depending on the network structure and the resulting specific surface area. Two different approaches were employed to predict the TA release over time. Because of the varying release characteristics, applicability was limited, but successful in several cases. Using a simple Higuchi-based approach, good release predictions could be made for a release time of 90 days from the release data of the initial 15 days (RMSEP ≤ 3.15%), reducing the analytical effort and simplifying quality control. These findings are important to establish customizable implants and to optimize the therapy with TA for specific intra-articular diseases.

Computational Materials Design for Ceramic Nuclear Waste Forms Using Machine Learning, First-Principles Calculations, and Kinetics Rate Theory.

Ceramic waste forms are designed to immobilize radionuclides for permanent disposal in geological repositories. One of the principal criteria for the effective incorporation of waste elements is their compatibility with the host material. In terms of performance under environmental conditions, the resistance of the waste forms to degradation over long periods of time is a critical concern when they are exposed to natural environments. Due to their unique crystallographic features and behavior in nature environment as exemplified by their natural analogues, ceramic waste forms are capable of incorporating problematic nuclear waste elements while showing promising chemical durability in aqueous environments. Recent studies of apatite- and hollandite-structured waste forms demonstrated an approach that can predict the compositions of ceramic waste forms and their long-term dissolution rate by a combination of computational techniques including machine learning, first-principles thermodynamics calculations, and modeling using kinetic rate equations based on critical laboratory experiments. By integrating the predictions of elemental incorporation and degradation kinetics in a holistic framework, the approach could be promising for the design of advanced ceramic waste forms with optimized incorporation capacity and environmental degradation performance. Such an approach could provide a path for accelerated ceramic waste form development and performance prediction for problematic nuclear waste elements.

Long-term dissolution behavior of amorphous aluminosilicate in sodium hydroxide solution for geopolymer synthesis using circulating fluidized bed combustion fly ash

The dissolution behaviors of silicon (Si) and aluminum (Al) in the alkaline solution is vital for revealing the reaction mechanism during geopolymer synthesis from fly ash. Most of the relevant reported studies reported were performed under constant agitation for a short period (several hours), which is insufficient because during geopolymer formation, the Si and Al are generally dissolved slowly and continuously in the static state with no agitation. In this study, the circulating fluidized bed combustion fly ash (CFBFA) was immersed in NaOH solutions in the static state for specified times (1–35 d), and the dissolution behaviors of Si and Al were investigated. The effects of the NaOH concentration, curing temperature and liquid-to-solid ratio (L/S) on the dissolution behavior were investigated. The phase and structure changes of CFBFA before and after dissolution were revealed by X-ray diffraction and nuclear magnetic resonance spectroscopy. The obtained results revealed that the dissolution of Si was slower in the static state than that under the continuous agitation, whereas the dissolution of Al under these two conditions was similar. The dissolution activity of amorphous Si in CFBFA in the NaOH solution was significantly higher than that of amorphous Al. Increasing the NaOH concentration promoted the dissolution of Si more than that of Al. The dissolved Si and Al combined easily to form some precipitates when the temperature was above 60 °C or the L/S was 10:1 mL/g. The formation of precipitates was not conducive to the further dissolution of Si and Al. The rate-determining step for the dissolution of amorphous Si and Al in the static state was the diffusion of OH– ions and the reaction products. The order of the dissolution activity of amorphous aluminosilicates in the NaOH solution was Q4(0Al) > Q4(1Al) > Q4(2Al). These results provide reference information for the evaluation of active Si and Al amounts in CFBFA during geopolymer synthesis.

Comparing the effects of two different progesterone vaginal gels, Progeson™ and Crinone™, from pharmacokinetics study to clinical applications in patients undergone fresh embryo transfer and frozen-thawed embryo transfer via natural cycle endometrial preparation protocol.

The pharmacokinetics performance and clinical pregnancy rate of two vaginal progesterone gel, Progeson™ and Crinone™, were compared in this study. In the pharmacokinetics performance, Progeson showed similar long-term dissolution rate as Crinone. In the clinical study, 141 subjects undergone invitro fertilization (IVF) treatments were included to compare serum progesterone level and clinical pregnancy rates. Among the subjects, 78 subjects received fresh embryo transfer and 63 subjects received frozen embryo transfer via natural cycle endometrial preparation protocol. In each group, subjects were given either Crinone™ or Progeson™ for luteal phase support without combination with other progesterone products. The study showed that Crinone™ group led to higher estrogen level at mid-luteal phase in the fresh embryo transfer group, and Progeson™ group led to higher progesterone level at mid-luteal phase and pregnancy test day in the frozen-thawed embryo transfer group. Subjects received Crinone™ or Progeson™ had similar rate of pregnancy, live birth, and stillbirth in both fresh embryo transfer and frozen-thawed embryo transfer group. Thus, Progeson™ might be a suitable substitute for Crinone™ in assisted reproductive therapy.

Dissolution of Glass–Ceramic Scaffolds of Bioactive Glasses 45S5 and S53P4

Although the initial in vitro dissolution of bioactive glasses (BAG) is well characterized, the long-term behaviour of crystallized BAG scaffolds in a continuous fluid flow is incompletely understood. A detailed understanding of the long-term dissolution of scaffolds is vital for predicting their behaviour in clinical applications. Here, we explored the dissolution and reaction mechanisms of partly crystalline and glass–ceramic scaffolds based on the bioactive glasses S53P4 and 45S5 using a continuous flow-through method in Tris-buffer (Tris) and simulated body fluid (SBF) for up to 21 days. Granules of the parent glasses were used as references. The main crystalline phase in both scaffolds was sodium-calcium-silicate. The scaffolds’ dissolution suggested that the sodium-calcium-silicate crystals dissolved incongruently to yield hydrous silica. The silica phase then provided abundant nucleation sites for hydroxyapatite precipitation, resulting in fine-grained crystalline structures. When exposed to Tris, the scaffolds almost completely dissolved within the test period, leaving only highly porous remnant phases. For the 45S5 scaffolds, the calcium phosphate reaction layers that formed on their surfaces effectively slowed the dissolution in SBF. In contrast, this effect was less apparent for the S53P4 specimens.

Carbonation, Neutralization, and Reinforcement Corrosion for Concrete in Long-Term Atmospheric Exposures

This paper presents observations of carbonation and alkali loss for well-compacted reinforced concrete columns from the exterior and interior of a 60-y-old in-land building. Calcium carbonate formation was detected only in the outermost 10 mm to 15 mm. However, alkali loss and concrete pH reduction extended much further inward but reinforcement corrosion was not observed. Theoretical thermodynamic conditions dictate that corrosion initiation of reinforcement can result only from the long-term dissolution and loss by leaching of calcium hydroxide from the concrete matrix. These appear rate-limited by the barrier effect of carbonated concrete. These interpretations provide a new model for “carbonation” initiation of reinforcement corrosion. The results also show the potential for concretes to absorb atmospheric carbon dioxide (greenhouse gases) for an extended time without significant risk of reinforcement corrosion.

Modeling and verification of non-linear mineral dissolution processes with buoyancy effects

A new methodology for the simulation of salt cavity development by dissolution is presented, verified and qualitatively validated by experiments. Starting from an initial cavity, the simulator models the injection of fresh water, natural and forced convection of the brine, and the evolution of the cavity walls due to dissolution. The nonlinear model couples brine mass and momentum conservation (governed by incompressible Navier–Stokes equations) with the buoyancy effect due to the brine density variations. Vortex generation and density-driven brine plume rise demonstrate the impact of complex brine flow patterns on the dissolution front evolution. A new explicit interface tracking strategy is employed to investigate the dissolution front movement and an improved smoothing algorithm to enhance the model robustness, contributing to low computational cost and stable simulation for the long-term dissolution process simulation. The proposed model is verified by conducting spatial and temporal convergence studies and qualitatively validated using lab-scale experiments. The agreement between experiments and simulations of horizontal and vertical dissolution cases demonstrates the utility of the model. The simulation results indicate that the rising plume of brine results in a “morning glory” shape cavity under a vertical dissolution scenario and a significant difference between upper and lower fronts dissolution rates for the horizontal dissolution case. The coupling effect of eddy development and cavity shape evolution is also discussed. This work furthers the understanding of the interaction between brine transport in an initially-formed cavity and dissolution patterns of the cavity boundaries, driven by gravity and convective flows.

Potential mobilization of cadmium and zinc in soils spiked with smithsonite and sphalerite under different water management regimes

Particulate cadmium (Cd) and zinc (Zn) are ubiquitous in agricultural soils of Pb–Zn mining regions. Water management serves as an important agronomic measure altering the bioavailability of Zn and Cd in soils, but how this affects particulate Cd and Zn and the underlying mechanisms remain largely unknown. Microcosm soil incubation combined with spectroscopic and microscopic characterization was conducted. During a two-year-long incubation period we observed that the concentrations of soil CaCl2-extractable Zn and Cd increased 3–10 times in sphalerite-spiked soils and 1–2 times in smithsonite-spiked soils under periodic flooding conditions due to the long-term dissolution of sphalerite (SP) and smithsonite (SM). However, the increase in the concentration of CaCl2-extractable metals (Zn: from 0.607 mg kg−1 to 1.051 mg kg−1 and Cd: from 0.047 mg kg−1 to 0.119 mg kg−1) was found only in SP-treatment under continuous flooding conditions, indicating the mobilization of metals. Ultrafiltration analysis shows that the nanoparticulate fraction of Zn and Cd in soil pore water increased 5 and 7 times in SP-treatments under continuous flooding conditions, suggesting the increment of metal pools in soil pore water. HRTEM-EDX-SAED further reveals that these nanoparticles were mainly crystalline ZnS and Zn-bearing sulfate nanoparticles in the SP-treatment and amorphous ZnCO3 and ZnS nanoparticles in the SM-treatment. Therefore, the formation of the stable crystalline Zn-bearing nanoparticles in the SP-treatment may explain the elevation of the concentration of soil CaCl2-extractable Zn and Cd under continuous flooding. The potential mobility of particulate metals should therefore be expected in scenarios of continuous flooding such as paddy soils and wetland systems.

Aggregate dissolution kinetics

The alkali–silica reaction (ASR) starts with the dissolution of silica in alkali-reactive aggregates. Besides the thermodynamic basics of silica dissolution, kinetic data are needed to model ASR in order to describe the temporal course of the reaction. Although the dissolution kinetics of silica has been investigated frequently, data for concrete-like environments (pH > 12) and under special influences, such as de-icer impact by sodium chloride (NaCl) or the release of aluminium (Al) from feldspars, are rare or missing. In the present study, long-term (2.5 years) dissolution tests were performed to obtain kinetic data for two types of aggregate (granodiorite, rhyolite) under concrete-like conditions (pH 13.8, with/without calcium hydroxide (Ca(OH)2) and sodium chloride) at temperatures of 25, 45 and 60°C. The findings show that silica dissolution rates effective for ASR differ up to four orders of magnitude, ranging from (log r1) −13.13 to −9.96 mol/m2s as a function of aggregate type, temperature, sodium chloride concentration and calcium hydroxide. Besides a predominant influence of temperature and calcium hydroxide, sodium chloride promotes the dissolution of silica and lowers the aluminium concentration, especially at higher temperatures. The activation energy for silica dissolution (84 ± 4 kJ/mol) did not change significantly in the presence of sodium chloride.

Influence of Environmental Parameters and Fiber Orientation on Dissolution Kinetics of Glass Fibers in Polymer Composites

Glass fibers slowly dissolve and age when exposed to water molecules. This phenomenon also occurs when glass fibers are inside fiber-reinforced composites protected by the matrix. This environmental aging results in the deterioration of the mechanical properties of the composite. In structural applications, GFRPs are continuously exposed to water environments for decades (typically, the design lifetime is around 25 years or even more). During their lifetime, these materials are affected by various temperatures, pH (acidity) levels, mechanical loads, and the synergy of these factors. The rate of the degradation process depends on the nature of the glass, sizing, fiber orientation, and environmental factors such as acidity, temperature, and mechanical stress. In this work, the degradation of typical industrial-grade R-glass fibers inside an epoxy fiber-reinforced composite was studied experimentally and computationally. A Dissolving Cylinder Zero-Order Kinetic (DCZOK) model was applied and could describe the long-term dissolution of glass composites, considering the influence of fiber orientation (hoop vs. transverse), pH (1.7, 4.0, 5.7, 7.0, and 10.0), and temperature (20, 40, 60, and 80 °C). The limitations of the DCZOK model and the effects of sizing protection, the accumulation of degradation products inside the composite, and water availability were investigated. Dissolution was experimentally measured using ICP-MS. As in the case of the fibers, for GFRPs, the temperature showed an Arrhenius-type influence on the kinetics, increasing the rate of dissolution exponentially with increasing temperature. Similar to fibers, GFRPs showed a hyperbolic dependence on pH. The model was able to capture all of these effects, and the limitations were addressed. The significance of the study is the contribution to a better understanding of mass loss and dissolution modeling in GFRPs, which is linked to the deterioration of the mechanical properties of GFRPs. This link should be further investigated experimentally and computationally.

Surfactant Adsorption to Gypsum Surfaces and the Effects on Solubility in Aqueous Solutions.

Vibrational sum frequency generation (VSFG) spectroscopy, conductometric titration measurements, and EDX elemental mapping were used to examine surfactant adsorption to the gypsum (010) surface and assess the effects of surfactant adsorption on gypsum solubility in aqueous solutions. Sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium chloride (DTAC) were used as anionic and cationic surfactants, respectively. Gypsum/SDS interactions result in an ordered precipitate layer on the gypsum surface after water evaporation; gypsum/DTAC interaction did not show a similar effect, despite exposure of gypsum to equivalent amounts of surfactant. VSFG spectra showed that SDS molecules adsorb with their chains parallel to the gypsum surface; spectra from gypsum surfaces treated with DTAC, however, showed no measurable response, implying that these surfactants form disorganized aggregates with no polar ordering. Vibrational data were supported by independent EDX measurements that show a uniform distribution of SDS across the gypsum surface. In contrast, element-specific EDX images showed that DTAC clustered in tightly localized patches that left most of the gypsum surface exposed. The uniform adsorption of SDS on the gypsum surface suppresses long-term dissolution up to 40% when compared to samples exposed to DTAC. Gypsum samples in DTAC-containing solutions lose approximately the same amount of material to dissolution as samples immersed in pure water.

A novel Ti-Au alloy with strong antibacterial properties and excellent biocompatibility for biomedical application

In order to avoid the toxic and side effects on human body of long-term dissolution of metal ions from antibacterial titanium alloys, Au element with non-toxicity and non-side effect was selected as the alloying element to prepare a new Ti-Au alloy with strong antibacterial property. We produced Ti-Au(S) sintered alloy by powder metallurgy and Ti-Au ingot alloy by ingot metallurgy, and investigated the influence of the secondary phase on the relative antimicrobial properties and antibacterial mechanism in this work. The results indicated that the aged Ti-Au(T6) alloy and Ti-Au(S) sintered alloy exhibited strong antibacterial rate against S. aureus due to the formation of Ti3Au phases. In vitro cell culture (MC3T3 cells) experiments showed that Ti-Au alloys had good cytocompatibility and osteogenic properties. The following viewpoints of antibacterial mechanism are that the Ti3Au destroyed the ROS homeostasis of bacteria, causing oxidative stress in bacterial cells and preventing from the biofilms formation.

Aqueous solubility of Zn incorporated into Mg-Al-layered double hydroxides

Hydrotalcite minerals are layered double hydroxides (LDH) which play an important role in immobilizing hazardous compounds to decontaminate industrial wastewaters. The stability of an LDH is mostly evaluated in terms of its low solubility in water. However, the solubility of divalent trace metals immobilized by Mg-Al-type LDHs is not well known. Hydrotalcites containing Zn in solid solution, (Mg+Zn)3-Al-LDH, were synthesized by alkaline co-precipitation. A series of eleven LDH phases with Zn mole fractions XZn = Zn/(Mg+Zn) of 0–1 were characterized by powder X-ray diffractometry (XRD), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetry (TGA), scanning and transmission electron microscopy (SEM/TEM), Brunauer-Emmett-Teller (BET) surface area analysis, and inductively coupled plasma mass (ICP-MS) spectrometry. The XRD analysis provided sharp characteristic spacings for d003 and d006 which occurred for all samples, confirming a layered LDH structure. Cell parameters (a, c) obeyed Vegard’s law and confirmed the formation of a regular solid-solution series without a mixing gap. An aqueous equilibrium time was determined by kinetic dissolution experiments. Steady-state solubility occurred after 120 days, but the experiments continued up to 240 days. The XRD and SEM/TEM analyses indicated no phase changes during the long-term dissolution experiments; neither were phase impurities detected after 240 days. The solubility products of the Mg- and Zn-bearing endmember compositions were calculated from experimentally determined total cation and anion concentrations using the Visual Minteq code for considering element speciation and ion pairing. The solubility product decreased as the Zn mole fraction increased, suggesting that the Zn-bearing LDH phases were more stable than the pure Mg3-Al-LDHs. Solid-solution aqueous-solution thermodynamic equilibrium modeling using the Lippmann “total solubility product” approach and applying Lippmann diagrams with logarithmic x-axes revealed a log-linear decrease in aqueous Zn solubility. The results are promising for remediation of metal-bearing liquid wastes because the metals that co-precipitated with the LDH were more strongly retained and, therefore, less soluble than the hydroxides or carbonates of the trace metal.

On the dissolution of a borosilicate glass with the use of isotopic tracing – Insights into the mechanism for the long-term dissolution rate

An understanding of the mechanisms responsible for controlling the long-term corrosion rate of nuclear waste glass is paramount if reliable glass dissolution models are to be used to calculate the controlled release of radionuclides from nuclear waste glass under geologic disposal conditions. Understanding the mechanism that controls silicate glass dissolution rates is also important for natural glasses to understand the role from the dissolution of these glasses has on the composition of natural aquatic systems. Two general mechanisms appear to be responsible for the elemental release from glass to the surrounding biosphere – ion exchange (release principally of alkalis) and matrix dissolution (release of the structural components of the glass). Key unknowns related to these mechanisms are the impact of surface layers on the altered glass and how these layers participate in corrosion. To better understand the impact of these layers on the long-term glass corrosion rate, we made two glasses of the same elemental composition, but with selected elements enriched in specific isotopes for B (11B), Li (6Li), and Si (29Si). We reacted these glasses for 1 y then the solutions from each were exchanged and the chemistry of the solutions and the solids were followed for another 2 y (a total of 3 y). This allowed us to follow changes in the glasses with respect to these elements and how these elements were transported through the alteration layers with time and, for at least one element, into the glass and to deconvolute some competing kinetic steps, such as matrix dissolution and ion exchange. Results from these experiments demonstrate that the release behavior of different elements is strongly dependent on their structural role in the glass (e.g. network formers and modifiers), but, more importantly, the role of water transport and subsequent ion exchange has in the long-term dissolution of the glass studied here. In this article, we highlight the behavior of four elements: lithium, sodium, silicon, and boron. Lithium and sodium, network modifying elements, have similar chemistries. The behavior of Li could be tracked in more detail by following both 6Li and 7Li; Li penetrates through the gel layer in both directions without hinderance and is released from the glass deeper than Na. Silicon, a network forming element, reacts with the silica-rich alteration layer. Boron, a network forming element, does not accumulate in the gel or the pristine glass and has a very sharp elemental profile between the pristine glass and alteration layer. Boron, lithium, and sodium elemental profiles suggest that there is little if any transport control within the alteration layer. These results are similar to those found for basalt glass. However, the correlation between the Li and Na profiles and that of a water species suggest that the limiting release is not controlled by the formation of the gel but rather is a steady state between the diffusion of a water species and matrix dissolution that results in a low release rate for alkali and this provides a steady driving force for the long-term dissolution of glass.

Structural properties and dissolution behavior of new generation controlled release phosphate glass fertilizers

In this work, different phosphate glasses in the Na2O–K2O–CaO–P2O5, Na2O–K2O–CaO–Al2O3–P2O5 and Na2O–K2O–CaO–Al2O3–SiO2–P2O5 systems are synthesized by conventional melt quenching technique and investigated in terms of physical, thermal, and structural properties along with long-term dissolution behavior in different solvent media, i.e., deionized water, and 2% citric acid solution simulating the neutral soil environment and pH value of the plant root zone. In addition, the effect of selected glasses (with and without microconstituent doping) on the growth of tomato plants are examined and their potential use as controlled release glass fertilizers is evaluated by linking their chemical durability behavior with structural changes in the glass network. Consequently, studied glass compositions — exhibiting long term (over 90 days) nutrient release during plant growth along with insignificant change in pH and no toxic compound release during dissolution process — are evaluated as promising controlled release fertilizers for tomato plants.