Nitric Acid Attack Research Articles

Evaluation of the phase composition, microstructure, mechanical performance, and resistance to acid attack of blended cement paste composed of binary trass-cement system

This study comprehensively investigated the viability of binary blended trass-cement system for being used as a competitive alternative to cement or other traditional blended cements. Concerning the phase composition, the trass blended sample had not only higher gel contents, but also faster rates of gel formation, which were 1.5 and 1.2 times greater than those of the plain cement sample during the periods of 7–28 and 28–90 days, respectively. Regardless of the samples types, the increase rate of ultrasonic pulse velocity was highest within the interval of 3–7 days, then decreased during the period of 7–28 days, and almost approached zero at 28–90 days. This indicated the minor change of the samples microstructure at prolonged ages compared to those earlier ones. Due to the pozzolanic effect of trass, the pore size distribution significantly shifted toward smaller pore diameters and also became more uniform. Furthermore, the filler effect of trass reduced the total intruded volume and total porosity by 11.7% and 9.2%, respectively. In the case of mechanical performance, the blended sample showed higher compressive strengths, whereas slightly lower flexural ones in comparison to its plain counterpart, which could be owing to the changes in phase composition and microstructure induced by blending cement with trass. Lastly, it was revealed that the nitric acid attack, by progressively decalcifying the exposed samples, gradually transformed them into soft, cracked, and highly porous materials with new microstructural morphology and mineralogical composition. This way, substantial losses in their performance and integrity happened over immersion time.

A Simple Method to Obtain Protective Film against Acid Rain

Acid rain is a major problem for animals, plants, buildings, and also for the top glass of photovoltaic (PV) solar panels and greenhouses. Air pollutants such as NOx, NH3, and H2S can mix with water in the atmosphere to form acid rain. It was discovered that atmospheric water vapor adsorbed on the surface of glass can also lead to corrosion of the glass surface. The purpose of this work is to obtain a protective film for glasses used in different domains such as solar cells, windows, stained glass windows from historical buildings, etc. Thin film deposited on glass must be protective against acid rain, transparent in the visible domain with a band gap up to 3.2 eV, and have a vitreous structure (glass). Electron beam (e-gun) technology is a deposition technique for producing high-purity and dense coatings in a short time. It is well known that Ta2O5 is an oxide with anticorrosive properties, but it is expensive and cannot form glass by itself. ZnO is an oxide known as a glass former, exhibiting good optical properties. In this paper, a thin film obtained by the deposition of ZnO and Ta2O5 on a glass substrate using e-gun technology are studied. The simulated acid rain effect on the structure, morphology, and optical properties of thin films are studied after a 65% nitric acid attack on the surface. The X-ray diffraction (XRD) pattern shows the vitreous state of the thin film with a composition 50%ZnO 50%Ta2O5 before and after the acid attack. The morphology, composition, and thickness of the film are investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and profilometry.

Properties and durability of partially replaced cement-based composite mortars co-using powders of a nanosilica superplasticiser and finely ground plastic waste

This paper was about an experimental work on properties and durability of partially replaced cement-based composite mortars. Substitutions equal to 0, 2, 4 and 6% of finely ground polyethylene (PE) in association with a 3% nanosilica superplasticiser (SP) were used to cast the composite mortars. Fresh properties concerned setting as well as compressive strength versus porosity accessible to water whereas hardened durability properties were investigated by carbonation according to FT-IR, chloride corrosion of reinforcement, total chloride ion content, steel bars losses of mass and nitric acid attack. The superplasticiser and polyethylene powder inhibited the hydration of the cement while the compressive strength decreased with the rise of the polyethylene content but remained higher than the control mortar one for a (PE) content not exceeding 4%. Composite mortars were less porous and experienced a 2.08% average porosity. Under carbonation, composite mortars exhibited similar performance with the control mortar while corrosion and steel bar mass losses readings revealed the passive condition of the composite mortars and a total chloride content less than 0.4%. Composite mortars demonstrated better resistance to nitric acid attack with (PE) content increase. Correlation of the SEM images and X-ray evidence with the experimental records may be an indication of the feasibility of providing composite mortars with an optimal 2% (PE) for concrete constructions under severe environmental conditions.

Chloride diffusion of shotcrete lining structure subjected to nitric acid, salt–frost degradation, and bending stress in marine environment

The chloride diffusion of shotcrete lining at the middle and passageway of submarine tunnels subjected to chloride attack, combined action of NxOy from automobile exhaust and chloride attack, salt–frost degradation, and surrounding rock stress was investigated using 3.5%NaCl and HNO3+3.5%NaCl solution immersion method, accelerated salt–freezing-thawing method, and spring four-point bending loads method, respectively. Chloride content in shotcrete was measured using solid–liquid extraction and potential method. Meanwhile, the influence of chloride diffusion on nitric acid attack, salt–frost deterioration, bending stress, and shotcrete mixture parameters were analyzed. Nitric acid attack, salt–frost degradation and bending stress accelerated chloride migrate into shotcrete. When immersed in NaCl and HNO3+NaCl solution, shotcrete with low water–binder ratio and high steel fiber content had lower chloride content. With the increase in fly ash replacement, the chloride content decreased initially and then increased rapidly. Under salt–frost degradation, the shotcrete with low water–binder ratio and fly ash replacement had better chloride diffusion resistance. The distribution of chloride content in concrete conformed to Fick's second law. The chloride diffusion model was established based on the temperature of environmental and humidity of concrete, exposure time to solution, mixture parameters of shotcrete, nitric acid attack, salt–frost degradation, and bending stress.

Wear performance of UHMWPE based composites including nano-sized fumed silica

Fumed silica has been utilized in various applications due to its advanced mechanical properties. In addition to this advantage, the branch-like structure of fumed silica leads to a very high specific surface area in comparison to spherical nano-sized particles. Since the major contribution of the nano-sized fillers is growing the filler/matrix interaction surface, we used the fumed silica particles in the UHMWPE matrix to enhance the wear performance of the base material. The composites were produced by using the compression molding method and in order to determine the molding parameters such as molding pressure and molding temperature, a set of experiments was carried out by using the neat UHMWPE prior to the composite fabrications. After completing the molding stage, the specimens were subjected to the wear tests in a ball-on-disk configuration against a tungsten carbide (WC) counterpart. In addition, the composites were exposed to a nitric acid attack to investigate the effect of the fumed silica on the oxidation behavior. According to this work, fumed silica provides beneficial results for the wear performance of UHMWPE based composites. However, excessive loadings of the fumed silica lead to the formation of particle clusters in the microstructure and thereby reducing the wear resistance of the composites. The anti-oxidation performance of the composites was also enhanced with the addition of the fumed silica in the UHMWPE matrix.

Evaluation of the effectiveness of Cd stabilization by a low-temperature sintering process with kaolinite/mullite addition

This study first examined the phase transformation in the reactive sintering systems of cadmium-laden industrial sludge and Al-Si-rich precursors with different Cd/Al/Si molar ratios under various temperatures. X-ray diffraction results indicated that the Cd started to be incorporated at 750 °C by kaolinite or mullite (calcined from kaolinite). Three hours of processing at 950 °C can effectively incorporate Cd into Cd-Al-Si or Cd-Si materials. The amount of CdO in the reactive systems had significant influences on the Cd incorporation behavior into crystalline phases. With a small amount of CdO, product phase CdAl2Si2O8 dominated in the systems. Systems with considerable CdO produced notable amounts of Cd2SiO4 and Cd3SiO5. The production of Cd2SiO4 and Cd3SiO5 from CdO + mullite was more significant than that using kaolinite due to the preferred reaction between CdO and SiO2. To assess the effect of metal stabilization, single-phase products that host Cd (namely, CdAl2Si2O8, Cd2SiO4, and Cd3SiO5) were obtained, maintained at pH 4.0, and subjected to a constant-pH leaching test (CPLT) for 120 min. CPLT results evidently indicated that these phases were remarkably resistant to substantial acid (nitric acid) attack; the leaching behavior of CdAl2Si2O8 was incongruent dissolution. Finally, cadmium can be effectively incorporated into CdAl2Si2O8, Cd2SiO4, or Cd3SiO5 by using sludge ash from a secondary sewage treatment works, suggesting that precursors enriched with Al and Si can be promising materials in a cleaner production process for treating cadmium-laden industrial sludge.

Mortar incorporating supplementary cementitious materials: Strength, isothermal calorimetry and acids attack

Supplementary cementitious materials (SCMs) prove to be effective to meet most of the requirements of durable concrete and leads to a significant reduction in CO 2 emissions. This research studies the effect different SCMs (natural pozzolan (PN) / limestone fine (FC) at various replacement levels) on the physical and mechano-chemical resistance of blended mortar. The paper primarily deals with the characteristics of these materials, including heat of hydration, strength and effects of aggressive chemical environments (using sulphuric acid and nitric acid). Over 6 mixes were made and compared to the control mix. Tests were conducted at different ages up to 360 days. The experimental results in general showed that Algerian mineral admixtures (PN/FC) were less vulnerable to nitric and sulphuric acid attack and improved the properties of mortars, but at different rates depending on the quantity of binder. Keywords: natural pozzolan; portlandite; limestone fine; durability; blended cements

Evaluation of nitric and acetic acid resistance of cement mortars containing high-volume black rice husk ash

This paper presents the performance of cement mortar containing black rice husk ash (BRHA) under nitric and acetic acid attacks. The BRHA, collected from an electrical generating power plant that uses rice husk as fuel, was ground using a grinding machine. The compressive strength loss, weight loss, and expansion of mortars under nitric and acetic acid attack were investigated. The test results of BRHA properties in accordance with the ASTM C 618 standard found that the optimal grinding time was 4 h as this achieved a Blaine fineness of 5370 cm2/g. For parametric study, BRHA were used as a Portland cement Type 1 replacement at the levels of 0%, 10%, 20%, 30%, 40%, and 50% by weight of binder. The water-to-binder ratios were 0.55, 0.60, and 0.65. From test results, when the percentage replacements of BRHA in cement increased, it was observed that the strength loss and weight loss of mortars containing BRHA under acetic acid attack were higher than those of the mortars against nitric acid attack. It was found that, of the various BHRA mortars, the strength loss and weight loss due to nitric and acetic acid attacks were the lowest in the mortar with 10% BRHA replacement. For 10%, 20% and 30% BRHA replacements, the rate of expansion of the BRHA mortar decreased when compared with the control mortar. For the mortars with other percentage replacements of BRHA, the rate of expansion increased. Furthermore, the effective water-to-binder ratios of control and BRHA mortars were the primary factor for determining the durability of mortar mixed with BRHA.

DURABILITY OF FLY ASH GEOPOLYMER MORTARS IN NITRIC ACID–EFFECT OF ALKALI (NA2O) CONTENT / GEOPOLIMERINIO SKIEDINIO, PAGAMINTO NAUDOJANT LAKIUOSIUS PELENUS, ILGAAMŽIŠKUMAS AZOTO RŪGŠTYJE: ŠARMŲ (NA2O) KIEKIO POVEIKIS

Durability of fly ash based geopolymer mortar specimens in Nitric acid solution was investigated on three different series of specimens manufactured by activating fly ash with a mixture of sodium hydroxide and sodium silicate solution containing Na2O ranging from 5% to 8% of fly ash. Specimens were exposed in 10% by weight Nitric acid solution up to 24 weeks. The effect of alkali (%Na2O) content on durability of geopolymer mortar specimens were studied in terms of visual appearance, change in weight and change in compressive strength. Mineralogical and microstructure changes due to nitric acid attack were also investigated. Geopolymer mortar specimens showed excellent durability in terms of extremely less weight loss as well as high retention of compressive strength. Specimens with higher alkali content exhibited better durability in nitric acid. Santrauka Buvo tiriamas geopolimerinio skiedinio bandinių, pagamintu naudojant lakiuosius pelenus, ilgaamžiškumas azoto rūgšties tirpale. Buvo tiriami trijų skirtingų partijų bandiniai, pagaminti pridėjus lakiųjų pelenų, kurie turi natrio hidroksido ir natrio silikato mišinį, jo sudėtyje Na2O svyruoja 5–8% nuo lakiųjų pelenų kiekio. Bandiniai 24 savaites buvo veikiami 10% (pagal masę) azoto rūgšties tirpalu. Šarmų (% Na2O) kiekio poveikis geopolimerinio skiedinio bandinių ilgaamžiškumui buvo tiriamas įvertinant išvaizdą, nustatant masės ir gniuždomojo stiprio pokytį. Taip pat buvo nustatyti mineraloginiai ir mikrostruktūriniai pokyčiai veikiant azoto rūgštimi. Geopolimerinio skiedinio bandinių ilgaamžiškumas buvo labai didelis, masės nuostoliai nedideli ir didelis gniuždomasis stipris. Bandiniai su didesniu šarmų kiekiu buvo ilgaamžiškesni azoto rūgštyje.

The water-soluble fraction of carbon, sulfur, and crustal elements in Asian aerosols and Asian soils

We quantified the water-soluble species in 24 h average TSP (Dunhuang and Gosan) and PM1.0 (Gosan only) samples associated with the Spring 2001 Asian Dust season. Samples were analyzed for water-soluble organic carbon, water-soluble sulfur, and water-soluble crustal elements, as well as their bulk chemical composition. Water-soluble organic carbon in Gosan accounted for 28–83% (average=63%) of the particle-phase TSP total organic carbon, and 1–69% (average=23%) of the particle-phase PM1.0 organic carbon. Water-soluble sulfur, primarily in the form of sulfate, accounted for 2–22% of the TSP mass in Gosan, and 0.9–11% of the TSP mass in Dunhuang. The absolute concentrations and the soluble fraction of crustal elements in TSP samples collected at Gosan were found to correlate with the air mass source region as determined by back-trajectory analysis. For example, elevated levels of water-soluble sodium, potassium, and calcium were observed during dust events. These observations are likely the result of differences in anthropogenic sources, mineralogical composition of resuspended crustal materials, and atmospheric processing of the aerosols. Experiments were conducted using Asian soil samples to study the impact of acidification by nitric acid vapor on the solubility of crustal elements present in Asian desert and non-desert dusts. These experiments demonstrated that gaseous nitric acid attack leads to significant increases (>100% increase) in water-soluble calcium, magnesium, aluminum, manganese, and iron, while little or no increases in water-soluble sodium and potassium were observed in the soils.

Preparation and characterisation of high surface area stannic oxides: structural, textural and semiconducting properties

Nanosized cassiterite-type samples have been prepared following two different methods: nitric acid attack on metallic tin and neutralisation of SnCl 4 solution by hydrazine. Samples have been characterised by different physico-chemical techniques (X-ray diffraction (XRD), isotherm measurements of N 2 adsorption–desorption, scanning electronic microscopy (SEM), FTIR and UV–VIS spectroscopy). Structural, textural and semi-conductive properties have been thus investigated and their evolution as a function of the temperature of calcination in flowing oxygen up to 600 °C has been studied. The progressive formation of oxygen vacancies, leading to non-stoichiometric SnO 2, was observed during this treatment for both samples. An important feature is that, after this treatment, no oxygen vacancies could be observed at the crystallites surface, their formation requiring specific treatments like outgassing at high temperatures. Strong differences in textural properties, types of surface hydroxyl species and concentration of oxygen vacancies at the crystallites surface have been also evidenced between the two samples.

Uranium and Rare Earth Recovery from Phosphate Fertilizer Industry by Solvent Extraction

The paper presents a comprehensive review of the fundamental and applied aspects of the recovery of uranium and rare earths from phosphoric acid used for fertiliser production, by solvent extraction, with emphasis on the data from the pilot plant operated in Romania. The occurrence of uranium and rare earths in various phosphatic deposits is described and variations discussed. The radioactivity of the phosphatic rock is shown to be a cause for concern for control over pollution. History of the commercial recovery operations is decribed and the role of economic factor highlighted. The acidulation of phosphate rock, behavior of uranium and rare earths, influence of iron and effect of humic matter in the sulphuric acid process and the nitric acid process is discussed- Uranium extraction from the phosphoric acid by acidic organophosphorus esters is discussed in detail. The industrial flowsheets are described. Details are presented for the single cycle extraction process developed in Romania. Cost estimates are given which show the superiority of the single cycle process and its capability to produce uranium at a competitive price, while also producing rare earths as a by-product. Process flowsheet with stream data is also given for treatment of the solution obtained by nitric acid attack of the phosphate rock. Analysis of the uranium green cake (UF4) and the rare earth concentrate is given.

Raman Spectroscopic Study of the Aging and Nitration of Actinide Processing Anion-Exchange Resins in Concentrated Nitric Acid

Degradation of two types of anion exchange resins, Dowex 11 and Reillex HPQ, from the action of concentrated nitric acid (4 to 12 M) and radiolysis [from depleted uranium as UO22+ nitrate species and 239Pu as Pu(IV) nitrate species] was followed as a function of time with Raman vibrational spectroscopy. Elevated temperatures (∼ 50 °C) were used in the absence of actinide metal loading to simulate longer exposures of the resin to a HNO3 process stream and waste storage conditions. In the absence of actinide loading, only minor changes in the Dowex resin at acid concentrations ⩽10 M were observed, while at 12 M acid concentration, the emergence of a Raman peak at 1345 cm−1 indicates the addition of nitro functional groups to the resin. Similar studies with the Reillex resin show it to be more resistant to nitric acid attack at all acid concentrations. Incorporation of weakly radioactive depleted uranium as the UO22+ nitrate species to the ion-exchange sites of Dowex 11 under differing nitric acid concentrations (6 to 12 M) at room temperature showed no Raman evidence of resin degradation or nitration, even after several hundred days of contact. In contrast, Raman spectra for Dowex 11 in the presence of 239Pu as Pu(IV) nitrate species reveal numerous changes indicating resin alterations, including a new mode at 1345 cm−1 consistent with a Pu(IV)-nitrate catalyzed addition of nitro groups to the resin backbone.

Thermally stimulated oxidative degradation of high impact polystyrene with nitric acid

AbstractThe practical application of high impact polystyrene (HIPS) depends on the resistance to aging in aggressive environments. The investigation of morphological, mechanical, and chemical properties was made on HIPS samples of various thickness. The property deterioration of HIPS caused by concentrated nitric acid and heat was studied. The diffusion through micropores formed visible cracks that finally led to the complete destruction into a powder. The rapid loss in mechanical properties was explained in terms of scission reaction of the graft polybutadiene (PB) with the homopolystyrene (PS) matrix. Comparative measurements of pure PS and PB under the same conditions were helpful in resolving parallel reactions that preferentially take place in PS and/or in PB sequences. It was established that higher degree of nitration caused by higher temperature results in increased insolubility owing to parallel crosslinking reactions. The nitric acid attack on HIPS caused scission reactions, which also led to the oxidative degradation, more pronounced in the PS phase in the soluble part of HIPS.

Dependence of the velocity and attenuation of ultrasound in bone on the mineral content

Measurements of the attenuation and velocity of ultrasound from 0.3 to 0.8 MHz have been performed on a number of bovine cancellous bone samples. The influence of bone mineral content has been isolated by measuring the acoustic properties of the samples at various stages of demineralization resulting from controlled nitric acid attack. The correlation coefficient r, between the attenuation at different frequencies and bone density was found to be in the range 0.68-0.97. Broadband ultrasonic attenuation (BUA) was also calculated and produced r values between 0.84 and 0.99. The velocity measurements indicated a correlation greater than 0.97 in all cases. Thus velocity is the parameter most sensitive to changes in bone mineral density alone. Attenuation and BUA are less well correlated presumably because of a sensitivity to minor structural change.

Selective extraction techniques in exploration for volcanogenic sulphide deposits, Eastern Black Sea region, Turkey

Selective extraction techniques employing 0.05 M EDTA, 1 M hydroxylamine hydrochloride (Hxl) in acetic acid and 0.157 M ammonium oxalate in oxalic acid were used to assess the mode of occurrence of the trace elements in the various geochemical sample media and to increase the anomaly contrast over the concealed massive ore bodies in the the Eastern Black Sea region of Turkey. In hematitized pumice tuffs, an exhalate horizon overlying the Madenköy massive sulphide ore body, the trace elements such as As, Cu, Zn, Pb and Mo are partly associated with sulphides and partly occur in clays, and Fe- and Mn-oxides. The extraction data on stream sediments suggest that a hot nitric acid attack is the best digestion procedure for detecting mechanical dispersion trains in regional geochemical programmes. Comparison of the extractabilities of metals in soils from mineralized areas with those from the background Sirtköy soils by the different extraction procedures demonstrates that EDTA, and to lesser extent Hxl are the best extraction procedures for increasing the anomaly/background ratio. These two extraction procedures were found to also enhance Zn and Pb anomalies over the cover rocks of the Madenköy massive ore body relative to the largely exposed stockwork-impregnation zones. Among the EDTA, Hxl and ammonium oxalate extractions, only the last procedure extracted considerable amounts of As from the soil samples. Vapor-phase analysis suggests that mercury occurs mainly in sulphide form which is leachable only by ammonium oxalate solution that also leaches adsorbed mercury. The EDTA and the Hxl solutions only extracted adsorbed mercury. These three extractants have no effect on either mercuric oxide or mercuric sulphate. Arsenic, a very useful pathfinder in this region, can only be partly extracted from the pumice tuff and soil samples by ammonium oxalate solution.

Degradation of nitric acid-treated bulk polyethylene

The Selective removal of Chain Defects (branches, unsaturations) by nitric acid from melt crystallized polyethylene is examined with reference to the question of the distribution of defects between crystalline and “amorphous” domains. The results obtained using the IR methyl band at 1376 cm−1 together with weight-loss measurements support the view that the majority of defects, which are situated in the non-crystalline regions, are selectively digested by the nitric acid attack. After removal of the non-crystalline phase the small remaining branch content located within the crystal cores confirms the levels of defect inclusion previously derived from unit cell expansion data.

Determination of silver in rocks and minerals by atomic absorption spectrophotometry

Methods have been proposed for the determination of trace quantities of silver in sulphide ores and silicate rocks. For sulphide ores the samples have been decomposed by nitric acid-perchloric acid attack and the chloride interference eliminated by use of ammonium citrate-ammonium hydroxide. Silicate rock samples have been decomposed by hydrofluoric acid-perchloric acid attack and silver is determined in the organic phase after extraction with dithizone in MIBK. The methods are very simple and accurate and silver in amounts as low as 0.05 μg in a sample can be determined with confidence.

Nitric acid attack on polypropylene. Weight and density changes and blister formation during the initial stages

AbstractWeight loss and density change results are presented to indicate the manner in which fuming nitric acid at 70°C attacks three grades of polypropylene of different crystallinity. The phenomenon of surface blistering is discussed in relation to the spherulitic structure at the surface of the bulk specimen.

Chromic acid as an etchant for bulk polypropylene and its use to study (i) nitric acid attack on polypropylene (ii) cracks in polypropylene induced by tensile stress

This paper describes an etchant, chromic acid, which reveals the microstructures present in bulk samples of annealed isotactic polypropylene. It is shown how this reagent may be used first, to follow the attack of fuming nitric acid on polypropylene, and second, to identify the types of crack which occur when a bulk sample of annealed polypropylene fractures under tensile load.