scholarly journals Use of ZnAl-Layered Double Hydroxide (LDH) to Extend the Service Life of Reinforced Concrete

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1769 ◽  
Author(s):  
Celestino Gomes ◽  
Zahid Mir ◽  
Rui Sampaio ◽  
Alexandre Bastos ◽  
João Tedim ◽  
...  
Keyword(s):  
Reinforced Concrete ◽  
Layered Double Hydroxide ◽  
External Solution ◽  
Chloride Ions ◽  
Nacl Solution ◽  
The Stability ◽  
Ph Range ◽  
Double Hydroxide ◽  
Corrosion Of Steel ◽  
Steel Rebars

This work investigated the use of ZnAl-layered double hydroxide (LDH) intercalated with nitrate or nitrite ions for controlling the corrosion of steel in reinforced concrete. The work started by analyzing the stability of the powder in the 1–14 pH range and the capacity for capturing chloride ions in aqueous solutions of different pH. The effect of the ZnAl-LDH on the corrosion of steel was studied in aqueous 0.05 M NaCl solution and in mortars immersed in 3.5% NaCl. It was found that the LDH powders dissolved partially at pH > 12. The LDH was able to capture chloride ions from the external solution, but the process was pH-dependent and stopped at high pH due to the partial dissolution of LDH and the preferential exchange of OH– ions. These results seemed to imply that ZnAl-LDH would not work in the alkaline environment inside the concrete. Nonetheless, preliminary results with mortars containing ZnAl-LDH showed lower penetration of chloride ions and higher corrosion resistance of the steel rebars.

scholarly journals The Stability and Chloride Entrapping Capacity of ZnAl-NO2 LDH in High-Alkaline/Cementitious Environment

2021 ◽  
Vol 2 (1) ◽  
pp. 78-99
Author(s):  
Zahid M. Mir ◽  
Celestino Gomes ◽  
Alexandre C. Bastos ◽  
Rui Sampaio ◽  
Frederico Maia ◽  
...  
Keyword(s):  
Binding Capacity ◽  
Cementitious Materials ◽  
Chloride Ions ◽  
Aqueous Environment ◽  
Chloride Ingress ◽  
The Stability ◽  
Ph Range ◽  
Secondary Mechanism ◽  
Double Hydroxide ◽  
Corrosion Of Steel

In this work, the ZnAl-NO2 LDH (layered double hydroxide) is investigated as a possible additive for mitigating the chloride-induced corrosion of steel in reinforced concrete. The investigation focused on the stability and chloride binding capacity of this LDH in the pH range typical of cementitious materials. Until pH = 12.5 the material was stable and effective in capturing chloride ions from the surrounding aqueous environment. For higher pH, precisely that of hydrated cement, the LDH was partially dissolved and OH− preferentially entrapped instead of Cl−. These results suggested that ZnAl-NO2 has excellent chloride entrapping capability at neutral pH, but this is reduced with increasing pH. However, when the LDH was incorporated into mortars, the chloride ingress was delayed, signifying that the dissolution of LDH leads to a secondary mechanism responsible for chloride capture.

The chemical stability of mendipite, diaboleïte, chloroxiphite, and cumengéite, and their relationships to other secondary lead(II) minerals

1980 ◽  
Vol 43 (331) ◽  
pp. 901-904 ◽  
Author(s):  
D. Alun Humphreys ◽  
John H. Thomas ◽  
Peter A. Williams ◽  
Robert F. Symes
Keyword(s):  
Chloride Ion ◽  
Stability Diagram ◽  
Chloride Ions ◽  
Ion Concentration ◽  
Stability Field ◽  
Cupric Ion ◽  
Free Energy Of Formation ◽  
High Concentrations ◽  
The Stability ◽  
Ph Range

SummaryThe chemical stabilities of mendipite, Pb3O2Cl2, diaboleïte, Pb2CuCl2(OH)4, chloroxiphite, Pb3CuCl2O2(OH)2, and cumengéite, Pb19Cu24Cl42 (OH)44, have been determined in aqueous solution at 298.2 K. Values of standard Gibbs free energy of formation, ΔGf°, for the four minerals are −740, −1160, −1129, and −15163±20 kJ mol−1 respectively. These values have been used to construct the stability diagram shown in fig. I which illustrates their relationships to each other and to the minerals cotunnite, PbCl2, paralaurionite, PbOHCl, and litharge, PbO. This diagram shows that mendipite occupies a large stability field and should readily form from cold, aqueous, mineralizing solutions containing variable amounts of lead and chloride ions, and over a broad pH range. The formation of paralaurionite and of cotunnite requires a considerable increase in chloride ion concentration, although paralaurionite can crystallize under much less extreme conditions than cotunnite. The encroachment of the copper minerals on to the stability fields of those mineral phases containing lead(II) only is significant even at very low relative activities of cupric ion. Chloroxiphite has a large stability field, and at given concentrations of cupric ion, diaboleïte is stable at relatively high aCl−. Cumengéite will only form at high concentrations of chloride ion.

scholarly journals Ammonium Phosphate as Inhibitor to Mitigate the Corrosion of Steel Rebar in Chloride Contaminated Concrete Pore Solution

Molecules ◽  
2020 ◽  
Vol 25 (17) ◽  
pp. 3785
Author(s):  
Soumen Mandal ◽  
Jitendra Kumar Singh ◽  
Dong-Eun Lee ◽  
Taejoon Park
Keyword(s):  
Passive Film ◽  
Ammonium Phosphate ◽  
Corrosion Current ◽  
Iron Phosphate ◽  
Nacl Solution ◽  
Steel Rebar ◽  
Prolonged Duration ◽  
Corrosion Inhibition Efficiency ◽  
Corrosion Of Steel ◽  
Steel Rebars

In the present study, different amounts, i.e., 1–3 v/v% of 1 M ammonium phosphate monobasic, were used as an eco-friendly corrosion inhibitor to mitigate the corrosion of steel rebar exposed to simulated concrete pore (SCP) + 3.5 wt% NaCl solution at a prolonged duration. Potentiodynamic polarization results show that as the amount of inhibitor is increased, the corrosion resistance of steel rebar is increased. The steel rebar exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution exhibited nobler corrosion potential (Ecorr), the lowest corrosion current density (icorr), and 97.62% corrosion inhibition efficiency after 1 h of exposure. The steel rebars exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution revealed higher polarization resistance (Rp) and film resistance (Ro) with exposure periods compared to other samples owing to the formation of passive film. The scanning electron microscopy (SEM) of steel rebar exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution showed homogenous and uniform dendritic passive film which covers all over the surface, whereas, bare, i.e., SCP + 3.5 wt% NaCl solution exposed samples exhibited pitting and irregular morphology. Raman spectroscopy results confirm the formation of goethite (α-FeOOH), maghemite (γ-Fe2O3), and iron phosphate (FePO4) as a passive film onto the steel rebar surface exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution. These phases are responsible for the corrosion mitigation of steel rebar which are very protective, adherent, and sparingly soluble.

scholarly journals Recovery of Palladium and Gold from PGM Ore and Concentrate Leachates Using Fe3O4@SiO2@Mg-Al-LDH Nanocomposite

Minerals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 917
Author(s):  
Nkositetile Raphael Biata ◽  
Silindokuhle Jakavula ◽  
Richard Motlhaletsi Moutloali ◽  
Philiswa Nosizo Nomngongo
Keyword(s):  
Layered Double Hydroxide ◽  
Fe3o4 Nanoparticles ◽  
Analytical Techniques ◽  
Magnetic Composite ◽  
Secondary Sources ◽  
Adsorption Sites ◽  
Quantitative Extraction ◽  
Magnetic Fe3o4 Nanoparticles ◽  
The Stability ◽  
Double Hydroxide

In this work, we developed a core–shell nanostructured magnetic composite by functionalizing layered double hydroxide (Mg-Al-LDH) microspheres with Fe3O4@SiO2, for the recovery of Au(III) and Pd(II). The magnetic Fe3O4 nanoparticles provided effective magnetic separation of the adsorbent from aqueous solutions. While silica protected the Fe3O4 nanoparticles, increased the adsorption sites and the stability of the material. Finally, Mg-Al-LDH was chosen because of its large anion sorption capacities which lead to the improved adsorption capacity of Fe3O4@SiO2@ Mg-Al-LDH nanocomposite. The morphology and structural composition of the nanocomposite were characterized using various analytical techniques. It was satisfactorily established that silica was coated on iron oxide and layered double hydroxide was immobilized on Fe3O4@SiO2. Parameters affecting adsorption of the composite towards Au(III) and Pd(II), such as effects of sample pH, mass of adsorbent, extraction time, eluent type and concentration were investigated using response methodology based on central composite design. Maximum adsorption capacities of Fe3O4@SiO2@ Mg-Al-LDH for Au(III) and Pd(II) were 289 mg g−1 and 313 mg g−1, respectively. Under optimum conditions, the proposed method displayed good analytical performance suggesting that the adsorbent is a good candidate for quantitative extraction of Au(III) and Pd(II) from secondary sources. Additionally, %recoveries ranging from 85%–99.6% were obtained revealing that Fe3O4@SiO2@ Mg-Al-LDH could selectively extract Au(III) and Pd(II) from leaching solutions of SARM 107 PGM ore and SARM 186 PGM concentrate.

scholarly journals Ion specific effects on the stability of layered double hydroxide colloids

Soft Matter ◽  
2016 ◽  
Vol 12 (17) ◽  
pp. 4024-4033 ◽  
Author(s):  
Marko Pavlovic ◽  
Robin Huber ◽  
Monika Adok-Sipiczki ◽  
Corinne Nardin ◽  
Istvan Szilagyi
Keyword(s):  
Layered Double Hydroxide ◽  
Layered Double Hydroxides ◽  
Particle Surface ◽  
Specific Effects ◽  
Strong Adsorption ◽  
The Stability ◽  
Double Hydroxide ◽  
Double Hydroxides

Multivalent counterions are effective destabilization agents for layered double hydroxides due to their strong adsorption on the particle surface.

scholarly journals Passivity and Semiconducting Behavior of a High Nitrogen Stainless Steel in Acidic NaCl Solution

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Yanxin Qiao ◽  
Xiang Cai ◽  
Jie Cui ◽  
Huabing Li
Keyword(s):  
Stainless Steel ◽  
Manganese Oxides ◽  
Chloride Ions ◽  
Passive Films ◽  
Molybdenum Oxides ◽  
Nacl Solution ◽  
High Nitrogen ◽  
Pitting Corrosion Resistance ◽  
The Stability ◽  
Corrosive Environments

The passivity and semiconducting behaviors of a high nitrogen-containing nickel-free stainless steel (HNSS) in 0.05 mol/L H2SO4+ 0.5 mol/L NaCl have been investigated. Results indicated that HNSS offered excellent pitting corrosion resistance in corrosive environments. Three corrosion potential values were observed in potentiodynamic polarization response, indicating the existence of an unstable system. The current transient and Mott-Schottky plots demonstrated that the stability of passive films decreased with the increase of applied potentials. The angle resolved X-ray photoelectron spectrometric results revealed that the primary constituents of passive films formed in 0.05 mol/L H2SO4+ 0.5 mol/L NaCl solution were composed of iron oxides, manganese oxides, Cr2O3, and Cr(OH)3. Meanwhile, it indicated that molybdenum oxides did not exist in the oxide layer, but chloride ions were present in the passive films.

Promoting the Chloride Ions Uptake by ZnCo-Cl Layered Double Hydroxide Electrodes towards the Enhanced Capacitive Deionization

2021 ◽  
Author(s):  
Zehao Zhang ◽  
Haibo Li
Keyword(s):  
Layered Double Hydroxide ◽  
Chloride Ions ◽  
Capacitive Deionization ◽  
Removal Capacity ◽  
Double Hydroxide ◽  
Research Domain

Hybrid capacitive deionization (HCDI) has gained a lot attentions in desalination research domain due to the remarkable salt removal capacity. In this work, the ZnCo-Cl layered double hydroxide (LDH) has...

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