不锈钢在湿法磷酸中的应用

介绍湿法磷酸生产中杂质、操作条件、酸浓度、温度、搅拌、有饥物等对腐蚀的影响和材料选择的基本要素，并列出多种不锈钢的主要化学成份和几种工艺流程的材料选用表。     

Preparation, characterization and Methylene Blue adsorption of phosphoric acid activated carbons from globe artichoke leaves

Activated carbons were prepared by the pyrolysis of artichoke leaves impregnated with phosphoric acid at 500 °C for different impregnation ratios: 100, 200, 300 wt.%. Materials were characterized for their surface chemistry by elemental analysis, “Boehm titrations”, point of zero charge measurements, infrared spectroscopy, as well as for their porous and morphological structure by Scanning Electron Microscopy and nitrogen adsorption at 77 K. The impregnation ratio was found to govern the porous structure of the prepared activated carbons. Low impregnation ratios (~ 100 wt.%) led to essentially microporous and acidic activated carbons whereas high impregnation ratios (> 100 wt.%) gave essentially microporous-mesoporous carbons with specific surface areas as high as 2038 m²·g^− 1, pore volume as large as 2.47 cm³·g^− 1, and a slightly acidic surface. The prepared activated carbons were studied for their adsorption isotherms of Methylene Blue at pH = 3 and pH = 9. The supermicroporous structure of the material produced at 200 wt.% H₃PO₄ ratio was found to be appropriate for an efficient adsorption of this dye controlled by dispersive and electrostatic interactions depending on the amount of oxygen at the surface.     

Effects of fly ash,phosphoric acid,and nano-silica on the properties of magnesium oxychloride cement

This study investigates the effects of fly ash, phosphoric acid, nano-silica additives on the hydration process, setting time, compressive strength, water resistance, and thermal stability of magnesium oxychloride cement (MOC). MOC samples incorporating different combinations of additives are prepared, and their hydration products and microstructures are studied via X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry-differential scanning calorimetry (TGA-DSC), and scanning electron microscopy (SEM). Results indicate that the addition of nano-silica to MOC containing fly ash and phosphoric acid reduces initial and final setting times, decreases the thermal stability, and increases compressive strength. Furthermore, the water resistance of modified MOC pastes is significantly improved through the combined use of additives. Hydration mechanisms arising in MOC are elucidated, and the remarkable enhancement of water resistance is attributed to secondary hydration of the 5 Mg(OH)₂·MgCl₂·8H₂O (5·1·8 phase) and the formation of amorphous gel facilitated by nano-silica inclusion.     

Effects of ionic impurities on the crystal morphology of phosphoric acid hemihydrate

The adsorption of foreign molecules on the crystal surface is generally believed to contribute to modify crystal morphology and the different adsorption energies on different crystal faces may lead to different modifications of crystal morphologies. In order to obtain a deep understanding of the face growth intervening mechanism, phosphoric acid hemihydrate (H₃PO₄·0.5H₂O) is taken as an example to investigate the influence of several typical ionic impurities on its crystal morphology by applying a molecular simulation study using Cerius 2 software. The absolute values of the calculated binding energies for cations are larger than that for anions. Therefore, it is concluded from the simulation that cations inhibit the growth of some crystal faces, while anions has no significant inhibition to a particular crystal surface, which is in good agreement with the experimental observation. It is also noticed that significant differences of binding energies to the different crystal faces will lead to obvious modifications of crystal morphologies and higher charged cations have more obvious effects than lower charged cations on the crystal morphology modification.     

磷酸活化法制备污泥含碳吸附材料的研究

研究了磷酸活化法制备污泥含碳吸附剂的工艺条件,探讨了活化剂质量分数、活化温度、活化时间和浸渍质量比对活化效果的影响.结果表明,在磷酸质量分数为50%、活化温度450℃、活化时间1 h、浸渍质量比1.5:1的条件下,制得的含碳吸附剂碘值在210 mg/g以上,产品收率50%,应用该吸附材料处理废水效果较好.     

Effect of glycerol on micro/nano structures of catalyst layers in polymer electrolyte membrane fuel cells

Effect of glycerol in catalyst ink on the micro/nano structures of polymer electrolyte membrane fuel cells (PEMFCs) catalyst layers was investigated. Catalyst layers were fabricated by the decal method for various mass ratios of glycerol to carbon in the catalyst ink r_gc (=m_g/m_c) from 0 to 20, and thus change the micro/nano structures of catalyst layer. The structures were evaluated by measuring the pore size with a mercury porosimeter and by observing the surface with a field emission scanning electron microscope (FE-SEM). At r_gc < 5, although the residual glycerol was almost zero, the cell performance decreased with decreasing r_gc, suggesting that the structure of the catalyst layers significantly depended on r_gc. At r_gc > 5, the remaining glycerol was proportional to r_gc. Because remaining glycerol blocks the pores and reduces the reaction sites, the cell performance decreased with increasing r_gc. If the remaining glycerol is removed by steam water, the performance is improved to the same level of the maximum performance for not steamed MEAs.     

Influence of impurities on stainless steels corrosion in wet process phosphoric acid

The corrosion behaviour of stainless steels in wet process phosphoric acid was studied by means of polarization curves and corrosion tests; in this context the influence of impurities that enhance the corrosivity of the acid, such as chlorides, fluorides and sulphates, was evaluated. Moreover the efficiency of some corrosion inhibitors, present as impurities in wet-process phosphoric acid, was evaluated by means of polarization curves and corrosion tests. Inhibitors of fluoride aggressiveness such as compounds of silicon, aluminum, magnesium were tested both separately and together. Trivalent iron as an oxidizing agent was also evaluated in order to minimize chloride-induced corrosion. Different grades of stainless steels such as AISI 316 L, Alloy 20, Alloy 28 and a duplex stainless steel 22Cr5Ni type, were taken into consideration.     

Effects of temperature and phosphoric acid addition on the solubility of iron phosphate dihydrate in aqueous solutions

As important controlling factors for the synthesis of iron phosphate materials by liquid-phase precipitation, the solubilities of iron phosphate dihydrate were systematically measured at H_3PO_4 concentrations from 1.13 wt%to 10.7 wt%, temperature from 298.15 to 363.15 K, and atmosphere pressure in this work. The solubility was found to increase 5 orders of magnitude or more with increasing the concentration of phosphoric acid, and decrease 1 to 2 orders of magnitude with increasing the equilibrium temperature. The phosphoric acid addition and temperature were found to affect the solubility of iron phosphate dihydrate by the formation or dissociation of coordination species, which could further accelerate the phase transformation from the amorphous iron phosphate dihydrate to orthorhombic iron phosphate dehydrate by dissolution–recrystallization mechanism.The high dependences of the solubility of iron phosphate materials on H_3PO_4 concentration and temperature were also well predicted by calibration equations, which are meaningful for quantitatively understanding the precipitation process and sequential crystalline structure transformation and pursuing a rational strategy for synthesizing specific iron phosphate materials.     

Effect of pH and application times of a meta-phosphoric acid on resin-dentin bonding properties

PurposeTo evaluate the effect of different pHs of 40% meta phosphoric acid (MPA) in comparison with a conventional 37% ortho-phosphoric acid under different application times in terms of resin-dentin bond strength (μTBS), nanoleakage (NL) and the dentin-etching pattern.Materials and methodsNinety-six molars were randomly assigned into 12 experimental conditions according to the combination of the independent variables: Acid [37% ortho-phosphoric acid (OPA), 40% meta-phosphoric acid (MPA) in the following pHs – 0.5, 1 and 2] and Application Time [7, 15 and 30 s]. After restorations, specimens were sectioned into resin–dentine beams (0.8 mm²) tested under tension (0.5 mm/min). Selected beams from each tooth were used for NL evaluation. The dentin-etching pattern of the OPA and MPA was examined under a scanning electron microscop. Acid vs application time data were subjected to two-way ANOVA and Tukey's test (α=0.05)ResultsMPA pH 0.5 showed μTBS means similar to OPA, independently the application time (p>0.05). A statistically higher NL was observed for OPA in comparison with MPA, regardless the application time (p<0.03). When MPA pH 0.5 was applied at the different times, the demineralised substrate showed presence of minerals along dentin surface.ConclusionThe use of 40% meta-phosphoric acid with pH 0.5 is an alternative acid-etching agent with similar immediate bond strength and lower nanoleakage than the traditional 37% ortho-phosphoric acid.     

磷酸活化烟草杆制备中孔活性炭的研究

以烟草杆为原料,以磷酸为活化剂,采用一步炭化法制备了活性炭。采用正交实验研究了磷酸质量分数、浸渍时间、炭化温度及保温时间对活性炭得率和吸附性能的影响,在最佳工艺条件(磷酸质量分数30%,浸渍时间48 h,炭化温度750℃,保温时间20 min)下,所制备的活性炭其碘吸附值为889.36 mg/g,亚甲基蓝吸附值为21.5 mL/(0.1 g),得率为36.90%。同时测定了该活性炭的液氮吸附等温线,并通过BET、H K方程、D A方程和密度函数理论(DFT)表征了活性炭的孔结构。结果表明,该活性炭为中孔型,BET比表面积为892 m2/g,总孔体积为0.467 8 mL/g,微孔占总孔体积的37.06%,中孔占62.85%,大孔占0.07%。最后采用电子探针和透射电镜分析了活性炭的微观结构,其结构与氮吸附测定的结果较为一致。     

Molecular dynamics simulation of microscopic structure and hydrogen bond network of the pristine and phosphoric acid doped polybenzimidazole

The microscopic structure and hydrogen bonding characteristics of the pristine and phosphoric acid (PA) doped polybenzimidazoles (poly[2,2′-(meta-phenylene)-5,5′-benzimidazole] or m-PBI, and poly[2,2′-(para-phenylene)-5,5′-benzimidazole] or p-PBI) were studied by molecular dynamics simulations based on a united-atom force field model. In all the simulated systems, a benzimidazole group and an adjacent phenylene group are almost in coplanar configuration, while two adjacent benzimidazole groups are in twisted configuration. In pristine PBIs, the p-PBI is more ordered and stretched than the m-PBI. In PA doped PBIs, hydrogen bonding network is formed by donating phosphoric acid proton to imine nitrogen, phosphoric acid proton to phosphoric acid oxygen, and amine proton to phosphoric acid oxygen. In addition, the structural transport of proton is attributed to the formation of hydrogen bonding network in PA doped PBIs.     

HEMP-derived activated carbon fibers by chemical activation with phosphoric acid

Activated carbon fibers were prepared by chemical activation of hemp fibers with phosphoric acid at different carbonization temperatures and impregnation ratios. Surface properties of the activated carbons fibers were significantly influenced by the activation temperature and the impregnation ratio. An increase of either of these parameters produced a high development of the porous structure of the fibers. Activated carbon fibers with apparent surface area of 1350 m²/g and mesopore volume of 1.25 cm³/g were obtained at 550 °C with an impregnation ratio of 3. The activated carbon fibers presented a high oxidation resistance, due to the presence of phosphorus compounds on the carbon surface. The oxidation resistance results suggest that C-O-PO₃ and mainly C-PO₃ and C-P groups act as a physical barrier, blocking the active carbon sites for the oxidation reaction.     

Performance improvement of electrode for polymer electrolyte membrane fuel cell

The very high power density output available from polymer electrolyte membrane fuel cells combined with low cost has high potential for commercialization. Such high power densities are attained via better utilization of Pt crystallites in the reaction layer. This enhanced performance can be achieved by making a thin catalyst layer on the membrane surface. The robustness in the front surface catalysts is essential to minimize the coagulation of Pt particles when the fuel cells are subjected to long-term operation. This robustness of the catalyst structure depends on the manufacturing processes and also the organic solvents used to make the slurry. In this work, five different electrodes were fabricated by using different fabrication procedures, and the poison effect of CO was investigated at the anode interface.     

Phosphoric acid distribution in the membrane electrode assembly of high temperature proton exchange membrane fuel cells

The ionomer content in electrode is one of the most important parameters for the high performance of fuel cells. The high temperature PEMFC based on phosphoric acid (PA)-doped polymer membrane with unhumidified reactant gases has a difficulty in controlling the liquid state PA ionomer content in electrode. To evaluate the PA content in electrode, the three techniques of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and acid–base titration (ABT) are carried out in situ or ex situ. The properties of membrane electrode assembly (MEA) such as electrochemical surface area (ESA), ohmic resistance, charge transfer resistance, double layer capacitance and the amount of PA in MEA components (anode, cathode and membrane) are extracted by each technique. Ex situ CV with the usage of dry gases has a limitation in assessing the reliable ESA of unhumidified PEMFC. While in situ EIS presents some informative values of resistance and capacitance for understanding the PA distribution in MEA, its sensitivity to the PA content in MEA components needs to be higher for detecting a subtle change in PA distribution. Ex situ ABT supplies a clear PA distribution in MEA at room temperature but does not seem to reflect the operating state well at high temperatures. However, it can be used as a detection tool for the loss of the initial acid content in membrane during a long-term MEA durability study.     

Classic and local analysis of corrosion behaviour of graphite and stainless steels in polluted phosphoric acid

In phosphoric acid solution (40% H₃PO₄), the corrosion behaviour of graphite and stainless steels was studied by the use of different electrochemical methods, namely polarization curve analysis, electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). The combined effect of chemical impurities and the increase of medium temperature was studied to approach the real conditions in the process of phosphoric acid manufacturing. It was found that the current density measured by polarization curves increased with the presence of chloride and sulphate ions in the acid solution whatever the tested material. Compared to stainless steels, graphite had the best corrosion resistance in polluted phosphoric acid. However, for graphite the increase of temperature from 20 to 80 °C induced an increase of the corrosion rate and potential and a decrease of the resistance confirmed by EIS results. Subsequently, local currents were detected at the surface of the sample by using the scanning vibrating electrode technique. From the data obtained, graphite surface manifested a distinctive behaviour from that of stainless steels. A generalized corrosion was occurred on graphite whereas a localized corrosion was observed for stainless steels. These results show a clear interest of graphite as component material in some of the equipments of the phosphoric acid industry.     

The influence of Pt on the electrooxidation behaviour of carbon in phosphoric acid

The electrooxidation behaviour of Pt/C catalysts for phosphoric acid fuel cells (PAFC) has been investigated by potentiostatic tests in the potential range 0.6 ÷ 1.0 V (rhe). Results indicate that the corrosion rate increases with an increase in Pt content, and is most noticeable at 0.6 V. At higher potentials anodic dissolution of Pt takes place, thus no metal is available to catalyze the corrosion of carbon. It is concluded that a definite influence of the presence of the supported metal on the extent of carbon corrosion under practical conditions does exist, but the understanding of mechanisms involved in the Pt-promoted carbon corrosion requires further studies.     

Removal of cadmium from phosphoric acid solution by solvent-impregnated resins (sirs) - sorption kinetics and equilibria studies

Cyanex-302 (bis [2,4,4-trimethylpentyl] monothiophosphinic acid) was impregnated into macroporous Diaion HP-10 and HP-1MG polymeric resin matrices and used as an extractant to recover cadmium from concentrated phosphoric acid. The optimum conditions for batchwise extraction of cadmium were established, and equilibrium data in the concentration range 0-200 mg/L Cd were obtained in 40% H 3 PO 4 solution. A Langmuir adsorption isotherm gave the best fit of the adsorption equilibrium data. A preliminary kinetic study was carried out in order to elucidate the rate-controllingmechanism. The uptake of trace cadmium onto Cyanex 302 containing solvent-impregnated resins from 40% phosphoric acid appears to be particle diffusion controlled.     

CFD investigation of the agitation in the desupersaturation during the wet-process phosphoric acid(WPPA) process

Desupersaturation is a complex cooling operation that involves hydrodynamic, thermal and mechanical phenomena. This process requires continuous agitation to avoid fouling problems and sludge deposition. The current work aims to investigate the well mixedness in the desupersaturation tank for optimal performance. For this purpose, a multi-fluid CFD study was conducted based on the Euler–Euler modeling approach, considering a multiphase flow involving a liquid phase(phosphoric acid) and a poly-dispersed solid phase, i.e. a sludge with three different sizes where each size is considered as a separate phase. First, the hydrodynamic behavior of the flow within the agitated desupersaturator is analyzed through the investigation of the velocity fields as well as the power and pumping numbers, to determine both the agitator capacity to pump the flow and its power consumption during the operation. Then, in order to assess the mixture homogeneity, we evaluated the solid suspension in the desupersaturation reactor following conventional methods and two new proposed methodologies: the first approach is to evaluate the suspension quality in the mixing system by compartment and the second consists on the assessment of the uniform convergence of the solid concentration. Furthermore, we calculated the time required to achieve a full suspension at different solid concentrations. On other hand, we conducted a detailed analysis of the solid distribution dependency on the impeller rotational speed at different solid volume fraction,which allows a good understanding of the parameters controlling the homogenization in the desupersaturator.     

Preparation and the physical/electrochemical properties of a Pt/C nanocatalyst stabilized by citric acid for polymer electrolyte fuel cells

Pt/C nanocatalysts were prepared by the reduction of chloroplatinic acid with sodium borohydride, with citric acid as a stabilizing agent in ammonium hydroxide solution. These nanocatalysts were obtained by altering the molar ratio of citric acid to chloroplatinic acid (CA/Pt) from 1:1, 2:1, 3:1 to 4:1. Transmission electron microscopy and X-ray diffraction analyses indicated that the well-dispersed Pt nanoparticles of around 3.82 nm in size were obtained when the CA/Pt ratio was maintained at 2:1. X-ray photoelectron spectroscopy measurements revealed that the 2:1, 3:1 and 4:1 molar ratio catalysts had a relatively higher amount of Pt in their metallic state than did the 1:1 molar ratio catalyst. Cyclic voltammetry results demonstrated that the Pt/C nanocatalysts annealed at 400 °C in an N₂ atm provided higher electrocatalytic activity. Among all the molar ratio catalysts, the 2:1 molar ratio catalyst exhibited the largest electrochemical active surface (EAS) area, and its methanol oxidation reaction current was superior to the E-TEK catalyst. The oxygen reduction reaction of the catalysts studied by linear sweep voltammetry and tested in a fuel cell indicated that the catalytic activity of the 2:1 molar ratio catalyst was comparable to that of an E-TEK catalyst.