Mechanochemical synthesis of kaolin-KH2PO4 and kaolin-NH4H2PO4 complexes for application as slow release fertilizer

A milling process to reduce kaolin to amorphous phase in the presence of KH₂PO₄ or NH₄H₂PO₄ and allow mechanochemical (MC) reaction for incorporation of KH₂PO₄ and NH₄H₂PO₄ into the kaolin structure was investigated in this work. Mixtures of kaolin and KH₂PO₄ and NH₄H₂PO₄ in separate systems were prepared by milling in a planetary ball mill. Tests with kaolin contents ranging from 25 to 75 wt.% and mill rotational speeds from 200 to 700 rpm were performed to evaluate incorporation of KH₂PO₄ and NH₄H₂PO₄ and release of K⁺, NH₄⁺ and PO₄³⁻ ions into solution. Analyses by XRD, DTA and ion chromatography indicated that the MC process was successfully applied to incorporate both KH₂PO₄ and NH₄H₂PO₄ into the amorphous kaolin structure. Release of K⁺ and PO₄³⁻ ions from the system (kaolin-KH₂PO₄) when dispersed in water for 24 h reached only up to 10%. Under similar conditions for the system (kaolin-NH₄H₂PO₄), release of NH₄⁺ and PO₄³⁻ ions reached between 25 and 40%. These results indicated that the MC process can be developed to allow amorphous kaolin to act as a carrier of K⁺, NH₄⁺ and PO₄³⁻ nutrients to be released slowly for use as fertilizer.     

The mechanism for soluble phosphates to improve the water resistance of magnesium oxychloride cement

This paper discusses the reasons why the addition of some soluble phosphates to magnesium oxychloride cement (MOC) can greatly improve its water resistance. With the XRD analysis and the determination of the strength retention coefficients (a judging index for the water resistance), it has been shown that the addition of small quantity of the soluble phosphates, such as H₃PO₄, NaH₂PO₄·2H₂O, and NH₄H₂PO₄, to MOC pastes does not influence the phases formed in the MOC pastes, but can result in the great increases of the strength retention coefficients of hardened MOC pastes, i.e., the great improvement of the water resistance of MOC. It was considered that the key components being responsible for the improvement of the water resistance could be the anions H₂PO₄⁻, HPO₄²⁻, and PO₄³⁻ yielded by the ionization of these phosphates in the solution of MOC pastes. These anions can decrease the lowest concentration of Mg²⁺ ions in the solution required by the formation of 5Mg(OH)₂·MgCl₂·8H₂O (5-phase) or 3Mg(OH)₂·MgCl₂·8H₂O (3-phase) in the MOC pastes and increase the stability of these phases in water. Thus, when the hardened MOC pastes with small quantity of the soluble phosphates are immersed in water, the 5-phase or 3-phase in them will not be decomposed by water, which makes the strength of the hardened MOC pastes remain unchanged in water.     

Mass transportation in diethylmethylammonium trifluoromethanesulfonate for fuel cell applications

To use the protonic mesothermal fuel cell without humidification, mass transportation in diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), trifluoromethanesulfuric acid (TfOH)-added [dema][TfO], and phosphoric acid (H₃PO₄)-added [dema][TfO] was investigated by electrochemical measurements. The diffusion coefficient and the solubility of oxygen were ca. 10⁻⁵ cm² s⁻¹ and ca. 10⁻³ M (=mol dm⁻³), respectively. Those of hydrogen were a factor of 10 and one-tenth compared to oxygen, respectively. The permeability, which is a product of the diffusion coefficient and solubility, of oxygen and hydrogen were almost the same for the perfluoroethylenesulfuric acid membrane and the sulfuric acid solution; therefore, these values are suitable for fuel cell applications. On the other hand, a diffusion limiting current was observed for the hydrogen evolution reaction. The current corresponded to ca. 10⁻¹⁰ mol cm⁻¹ s⁻¹ of the permeability, and the diffusion limiting species was the hydrogen carrier species. The TfOH addition enhanced the diffusion limiting current of [dema][TfO], and the H₃PO₄ addition eliminated the diffusion limit. The hydrogen bonds of H₃PO₄ or water-added H₃PO₄ might significantly enhance the transport of the hydrogen carrier species. Therefore, [dema][TfO] based materials are candidates for non-humidified mesothermal fuel cell electrolytes.     

Effect of physico-chemical properties of simulated body fluids on the electrochemical behaviour of CoCrMo alloy

The behaviour of the CoCrMo alloy was studied under different experimental conditions of solution pH, chemical composition (phosphate buffer solution with and without addition of bovine serum albumin) and aeration (presence and absence of oxygen in the solution). With this purpose, electrochemical techniques such as open circuit measurements (OCP), potentiodynamic curves, potentiostatic tests and electrochemical impedance spectroscopy (EIS) were employed.The results show that the general corrosion behaviour of CoCrMo alloy depends on the solution pH. Thus, the effect of BSA and the aeration conditions are related to the solution pH. At pH 3 no influence of BSA was observed in deoxygenated solutions which imply that BSA acts over the oxygen reduction reaction in acidic media. On the contrary, a noticeable influence of BSA addition was observed at pH 7.4 (independently on the gas content). Finally, at pH 10, the influence of BSA was only significant in oxygenated solution. It was found that H₂PO₄⁻ favours the formation of passivating compounds which improves the resistance of the CoCrMo alloy to passive dissolution. Therefore, when the concentration of the H₂PO₄⁻ increases (when pH decreases) the polarization resistance of the alloy also increases. On the other hand, the oxygen (aerated conditions) decreases the polarization resistance of the alloy in all the studied conditions.     

Synthesis of LiVOPO4 for cathode materials by coordination and microwave sintering

Lithium vanadyl phosphate (LiVOPO₄) sample, as one potential cathode materials, was synthesized via a route of coordination and microwave sintering. The precursors were prepared by coordination reactions among LiOH·H₂O, NH₄VO₃, NH₄H₂PO₄, C₆H₈O₇·H₂O and a small amount of water, and then they were sintered in a microwave furnace at 600 °C for 50 min. X-ray diffraction (XRD) results confirmed the formation of crystallized LiVOPO₄ with orthorhombic structures belonging to the space group of Pnma. Scanning electron microscopy (SEM) measurements indicated that the average particle size was less than 500 nm. After undergone an “activation” process, the sample exhibited a high discharge capacity for about 154 mA h g⁻¹ by the 22nd cycle at a current of 18.5 mA g⁻¹, which was very close to the theoretical values. Though the discharge capacity decreased obviously with the increased current, 110 as well as 80 mA h g⁻¹ can still be sustained within 40 cycles at 38 and 75 mA g⁻¹ respectively. This paper showed that submicron-sized LiVOPO₄ materials prepared through above way should be prospective for the application to 4 V system of lithium ion batteries.     

Application of PEDOT layers for the electrogravimetric detection of sulphate and phosphate in aqueous media

Poly(3,4-ethylenedioxythiophene), PEDOT, films were electrochemically prepared from aqueous solutions containing different supporting electrolytes (ClO₄⁻, SO₄²⁻ and H₂PO₄⁻). Characterization of the resulting films was carried out using cyclic voltammetry and potential step experiments combined with the dissipative quartz crystal microbalance technique. The ion incorporation caused an increase of the film mass and below 10⁻² M depended on the concentration of the solutions. Potential step experiments showed that the pH of the solutions also has an influence on the mass change of the films, which can only be partially attributed to the pH dependence of the charge of the anions. In principle, the ratio of the mass and the passed electric charge (apparent molar mass) during the redox switching of the polymer can be used to identify the ionic species.     

Modification of titanium oxide layer by calcium and phosphorus

The aim of the study was to investigate the possibility of calcium and phosphorus ion implantation into an oxide film applied onto titanium during anodic passivation. The corrosion resistance of modified titanium in Tyrode's physiological solution has been identified. Anodic oxidation was carried out in two solutions. The first contained 20 g dm⁻³ NaH₂PO₂ in 4.3 M H₃PO₄ (K1), whereas the other, 20 g dm⁻³ Ca(H₂PO₂)₂ in 4.3 M H₃PO₄ (K2). Voltage of 100 and 150 V was applied. It has been found out that it is possible to incorporate Ca and P into the emerging passive layer. The application of the voltage of 150 V makes it very porous. It has been also demonstrated that titanium so modified presents higher resistance to corrosion in the investigated environment than titanium not modified in Tyrode's solution.     

Anion complexation by calix[4]arene-TTF conjugates

Calix[4]arenes bearing tetrathiafulvalene (TTF) moieties appended to the upper rim via the amidic functions were synthesized and used for ¹H NMR and UV/Vis complexation studies towards selected anions. It was found that the complexation affinity towards H₂PO₄⁻ dramatically depends on the substitution pattern of the calixarene moiety. As a result, the proximally disubstituted derivative has a complexation constant by two orders of magnitude higher than the distally disubstituted analogue. The differences between proximal and distal receptors were also documented by their behaviour during the oxidation of the attached TTF units.     

Effects of neodymium aliovalent substitution on the structure and electrochemical performance of LiFePO4

LiFe_1−xNd_xPO₄/C (x = 0-0.08) cathode material was synthesized using a solid-state reaction. The synthesis conditions were optimized by thermal analysis of the precursor and magnetic properties of LiFePO₄/C. The structure and electrochemical performances of the material were studied using XRD, FE-SEM, EDS, electrochemical impedance spectroscopy and galvanostatic charge-discharge. The results show that a small amount of aliovalent Nd³⁺ ion-dopant substitution on Fe²⁺ ions can effectively reduce the particle size of LiFePO₄/C. Cell parameters of LiFe_1−xNd_xPO₄ (x = 0.04-0.08) were calculated, and the results showed that LiFe_1−xNd_xPO₄/C had the same olivine structure as LiFePO₄. LiFe_0.4Nd_0.6PO₄/C delivers the discharge capacity of 165.2 mAh g⁻¹ at rate of 0.2 C and the capacity retention rate is 92.8% after 100 cycles. Charge-transfer resistance decreases with the addition of glucose and Nd³⁺ ions. Poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) was synthesized and PZS nanorods were used as a carbon source to coat LiFePO₄. All of the results show that aliovalent doping substitution of Fe in LiFePO₄ is well tolerated.     

Synthesis and properties of imidazole-grafted hybrid inorganic-organic polymer membranes

Imidazole rings were grafted on alkoxysilane with a simple nucleophilic substitute reaction to form hybrid inorganic-organic polymers with imidazole rings. Proton exchange membranes (PEM) based on these hybrid inorganic-organic polymers and H₃PO₄ exhibit high proton conductivity and high thermal stability in an atmosphere of low relative humidity. The grafted imidazole rings improved the proton conductivity of the membranes in the high temperature range. It is found that the proton conductivities increase with H₃PO₄ content and temperature, reaching 3.2 × 10⁻³ S/cm at 110 °C in a dry atmosphere for a membrane with 1 mole of imidazole ring and 7 moles of H₃PO₄. The proton conductivity increases with relative humidity (RH) as well, reaching 4.3 × 10⁻² S/cm at 110 °C when the RH is increased to about 20%. Thermogravimetric analysis (TGA) indicates that these membranes are thermally stable up to 250 °C in dry air, implying that they have a good potential to be used as the membranes for high-temperature PEM fuel cells.