Mixed Sulfate Research Articles

Chemical Modification of Dust Particles during Different Dust Storm Episodes

Two dust episodes (D1: February 13 and D2: March 28–29, 2004) of long-range transport from desert and loess sources, and one dust episode (D3: March 30) mainly from local area, were investigated in spring 2004 in Beijing, China. Dust samples were collected in different dust episodes and scanning electron microscopy with X-ray energy dispersive detector (SEM/EDS) was applied to study the morphology, elemental composition, and chemical modification on the surfaces of dust particles with radius from 0.1 to 6.4 μm. The morphological features of the particles reveal that the three dust plumes carried both dust particles (90–98% by number) and anthropogenic pollutants (e.g., fly ash and soot, 2–10%). Particle compositions show that the amount of S-containing dust particles was higher in D1 and D2 than in D3. Sulfates were introduced into the dust particles through heterogeneous uptake of SO2 during their transport. In all three dust episodes, fine dust particles (radius < 1 μm) showed a higher degree of chemical modification by SO2 compared to the coarse particles (radius ≥ 1 μm). Furthermore, long-range transport dust particles were more deeply modified by SO2 than particles from local areas. The composition of the dust particles indicates that alkaline mineral components determined the level of chemical modification of individual particles. Heterogeneous uptake of SO2 on a large number of dust particles would increase mass of the internally mixed sulfates on their surfaces. The results suggest that the optical properties of dust particles during dust storm episodes are gradually altered based on how far they are transported.

Mechanochemical processing of serpentine with ammonium salts under ambient conditions for CO2 mineralization

This paper assesses the suitability of mechanochemistry as a convenient low-energy processing option in CO2 mineralization. Whereas some success has been reported in milling alkaline earth-containing minerals under gaseous CO2, this work focuses instead on a purely solid-state approach towards two key objectives: (a) Mg extraction from serpentine using ammonium bisulfate; and (b) direct or indirect CO2 sequestration using ammonium bicarbonate in a natural extension of its role as “CO2 carrier” in the chilled ammonia scrubbing process. In Mg extraction work, dry milling of serpentine with ammonium bisulfate gave respectable yields (>60% Mg) as boussingaultite [(NH4)2Mg(SO4)2·6H2O] in 2 to 4 h. In CO2 sequestration, dry milling anhydrous magnesium sulfate with ammonium bicarbonate yielded only mixed sulfate products. Carbonation of the heptahydrate, epsomite, was found to proceed via ammonium magnesium carbonate hydrate [(NH4)2Mg(CO3)2·4H2O], which dissolves incongruently to yield nesquehonite [MgCO3·3H2O]. The modest conversion (∼30%) is probably due to equipartition of Mg into the double sulfate co-product. A similar route is followed in magnesia and brucite, in which the existence of an amorphous native carbonate precursor to nesquehonite in the same molar ratio (Mg : CO2 = 1) was inferred from inconsistency in the XRD intensities. This was largely responsible for the high carbonation yields in the unwashed products, ∼70% and ∼85% in MgO and Mg(OH)2, respectively, as confirmed by TG-FTIR. The same intermediate is probably formed in serpentine, but it is apparently soluble in the aqueous mineral environment. When the unwashed product is subjected to mild thermal consolidation, stable hydromagnesite [Mg5(CO3)4(OH)2·4H2O] is formed in ∼20% yield after milling for 16 h. Possible identities for the amorphous precursor are briefly considered.

Wormlike Micelle Formation and Rheological Behavior in the Aqueous Solutions of Mixed Sulfate Gemini Surfactant without Spacer Group and Dodecyltrimethylammonium Bromide

AbstractThe rheological behavior of the aqueous solutions of mixed sulfate gemini surfactant with no spacer group, referred to as d‐C12S, and dodecyltrimethylammonium bromide (C12TABr) at a total concentration of 100 mmol·L−1 but different molar ratios of C12TABr to d‐C12S (α1) was investigated using steady rate and frequency sweep measurements. The wormlike micelles were formed over a narrow α1 range of 0.20–0.27. The viscoelastic solutions exhibited Maxwell fluid behavior. At the optimum molar ratio of 0.25, the zero‐shear viscosity was as high as 600 Pa·s and the length of the mixed wormlike micelle was about 0.45–0.85 µm. The present result provides an example to construct long wormlike micelles by anionic gemini surfactant.

Effect of ion irradiation on the thermoluminescence properties of K2Ca2(SO4)3 phosphor

This paper presents the thermoluminescence (TL) studies of ion-irradiated potassium–calcium mixed sulfate phosphor. The sample was prepared by the solid-state diffusion method. The X-ray diffraction study of the prepared sample suggests an orthorhombic structure with an average particle size of 0.16 μ m. The samples were irradiated with 1.2 MeV argon ions at fluences varying between 1011 and 1015 ions/cm2. The argon ions penetrate to a depth of 1.93 μ m and lose their energy mainly via electronic stopping. Due to ion irradiation, a large number of defects such as oxygen vacancies, radicals and color centers are formed in the sample. TL glow curves were recorded for each of the ion fluences. A linear increase in the intensity of TL glow peaks was found with an increase in the ion dose from 72 kGy to 720 MGy. The kinetic parameters associated with the prominent glow peaks were calculated using glow curve deconvolution, different glow curve shapes and sample heating rate methods.

Shapes of internally mixed hygroscopic aerosol particles after deliquescence, and their effect on light scattering

[1] Hygroscopic aerosol particles change the magnitude of light scattering through condensation and evaporation of water vapor. We collected aerosol particles from two megacities and observed the particle shapes at various values of relative humidity (RH) using an environmental cell within a transmission electron microscope. Many Mexico City samples had sulfate particles that were embedded within weakly hygroscopic organic aerosol, whereas the Los Angeles samples mainly consisted of externally mixed sulfate particles. For the Mexico City samples, when the RH was increased in the microscope, only the sulfate parts deliquesced, but the entire particle did not become spherical, i.e., particles containing deliquescent phases do not necessarily become spherical upon deliquescence. This result conflicts with the assumption used in many models, i.e., that deliquesced particles become spherical. Using a discrete-dipole approximation to calculate light scattering of simulated particles that resemble the observed ones, we show that, for particles >1.0 μm, the spherical-shape assumption used in Mie theory underestimates the light scattering by ∼50%, with the exact value depending on the sizes and relative volumes of the constituent phases.

Excitation of thermoluminescence in Eu doped Ba 0.12Sr 0.88SO 4 nanophosphor by low energy argon ions

In the present paper thermoluminescence properties of argon ions irradiated barium strontium mixed sulphate phosphor are reported. The Ba 0.12Sr 0.88SO 4 phosphor was prepared by chemical co-precipitation method. The X-ray diffraction study of prepared sample suggests orthorhombic structure with average grain size of 37 nm. The samples were irradiated with 1.2 MeV Argon ions at fluences varying between 10 11–10 15 ions/cm 2. The argon ions penetrate to the depth of 1.89 μm and lose their energy mainly via electronic stopping. Due to ion irradiation, a large number of defects in the sample are formed. Thermoluminescence (TL) glow curves were recorded for each of the ion fluence. These curves exhibit one broad peak with maximum intensity at 498 K composed of three overlapping peaks. This indicates that different sets of traps are being activated within the particular temperature range each with its own value of activation energy ( E) and frequency factor ( s). The peaks were observed due to formation of trap levels by ion irradiation and subsequently activation of traps on thermal stimulation. The TL response of the nanophosphor is linear in the dose range 59 kGy–590 MGy. Kinetic parameters associated with the prominent peaks were calculated using glow curve deconvolution (GCD) and verified by different glow curve shape and sample heating rate methods.

Hygroscopicity and cloud condensation nucleus activity of marine aerosol particles over the western North Pacific

Received 14 July 2010; revised 12 October 2010; accepted 27 October 2010; published 19 March 2011. [1] Hygroscopic growth of aerosol particles at 85% relative humidity and the number fraction of cloud condensation nuclei (CCN; 0.42%, 0.23%, and 0.10% supersaturation) as a function of dry diameter (24.1–359 nm) were measured simultaneously on board R/V Hakuho‐Maru over the western North Pacific during August–September 2008. Highly hygroscopic and unimodal growth distributions were observed, except for aerosols, which showed lower hygroscopic growth over the northern Pacific. The measured particle hygroscopicity, CCN activation diameters, and chemical composition data suggest the dominance of internally mixed sulfate aerosols. Backward air mass trajectory analysis exhibits an intrusion of free tropospheric aerosol, which was likely influenced by Kasatochi’s volcanic plume and which was linked to the low‐hygroscopicity event. Frequent observation of the Hoppel minimum suggests that in‐cloud processing over the Pacific enhanced and/or maintained the high hygroscopicity of accumulation mode particles. The CCN activation diameters predicted from median hygroscopic growth factors (gmedian) agreed well with those determined from the CCN efficiency spectra, without assuming surface tension reduction caused by organics or enhancement of bulk hygroscopicity at high RH caused by sparingly soluble or polymeric compounds. The CCN spectra predicted from gmedian and measured CCN activation diameters suggest that the high CCN activities of particles over the North Pacific are sustained by high hygroscopicity, while sporadic changes of aerosol origins produce the diversity of the aerosol properties.

Biological removal of cationic fission products from nuclear wastewater

Nuclear energy is becoming a preferred energy source amidst rising concerns over the impacts of fossil fuel based energy on global warming and climate change. However, the radioactive waste generated during nuclear power generation contains harmful long-lived fission products such as strontium (Sr). In this study, cationic strontium uptake from solution by microbial cultures obtained from mine wastewater is evaluated. A high strontium removal capacity (q(max)) with maximum loading of 444 mg/g biomass was achieved by a mixed sulphate reducing bacteria (SRB) culture. Sr removal in SRB was facilitated by cell surface based electrostatic interactions with the formation of weak ionic bonds, as 68% of the adsorbed Sr(2+) was easily desorbed from the biomass in an ion exchange reaction with MgCl₂. To a lesser extent, precipitation reactions were also found to account for the removal of Sr from aqueous solution as about 3% of the sorbed Sr was precipitated due to the presence of chemical ligands while the remainder occurred as an immobile fraction. Further analysis of the Sr-loaded SRB biomass by scanning electron microscopy (SEM) coupled to energy dispersive X-ray (EDX) confirmed extracellular Sr(2+) precipitation as a result of chemical interaction. In summary, the obtained results demonstrate the prospects of using biological technologies for the remediation of industrial wastewaters contaminated by fission products.

Solvent Extraction Separation of Co(II) from Synthetic Leaching Sulfate Solution of Nickel Laterite Ore with High Magnesium Content

Leaching of nickel garnierite ore with sulfuric acid resulted in a mixed sulfate solution of Co(II) and Ni(II) with high magnesium content. In order to find an optimum condition to separate cobalt, solvent extraction experiments have been performed from the synthetic leaching sulfate solution with the following composition: Co(II) ¼ 0:08 g/L, Ni(II) ¼ 4:4 g/L, Mg(II) ¼ 32:2 g/L. The effects of extraction variables on the separation of Co(II) from nickel and magnesium were investigated by using D2EHPA, PC88A, Cyanex272, and Alamine336. Saponifiaction degree of cationic extractants, extractant concentration, and volume ratio were changed. In our experimental range, extraction of nickel was negligible. Among the cationic extractants tested in this study, the highest separation factor between Co(II) and Mg(II) was obtained with saponified Cyanex272. Alamine336 in the presence of MgCl2 extracted only Co(II), while the extraction percentage of Mg(II) was nearly zero. [doi:10.2320/matertrans.M2011027]

Argon ions induced thermoluminescence properties of Ba 0.12Sr 0.88SO 4 phosphor

Thermoluminescence properties of barium strontium mixed sulfate have been studied by irradiation with Argon ions. The sample was recrystallized by chemical co-precipitation techniques using H 2SO 4. The X-ray diffraction study of prepared sample suggests the orthorhombic structure with average grain size of 60 nm. The samples were irradiated with 1.2 MeV Argon ions at fluences varying between 10 11 and 10 15 ions/cm 2. The argon ions penetrate to the depth of 1.89 μm and lose their energy mainly via electronic stopping. Due to ion irradiation, a large number of defects in the sample are formed. Thermally stimulated luminescence (TSL) glow curves of ion irradiated Ba 0.12Sr 0.88SO 4 phosphor exhibit broad peak with maximum intensity at 495 K composed of four overlapping peaks. This indicates that different sets of traps are being activated within the particular temperature range each with its own value of activation energy ( E) and frequency factor ( s). Thermoluminescence (TL) glow curves were recorded for each of the ion fluences. A linear increase in intensity of TL glow peaks was found with the increase in ion dose from 59 kGy to 5.9 MGy. The kinetic parameters associated with the prominent glow peaks were calculated using glow curve deconvolution (GCD), different glow curve shape and sample heating rate methods.

Optical-chemical-microphysical relationships and closure studies for mixed carbonaceous aerosols observed at Jeju Island; 3-laser photoacoustic spectrometer, particle sizing, and filter analysis

Abstract. Transport of aerosols in pollution plumes from the mainland Asian continent was observed in situ at Jeju, South Korea during the Cheju Asian Brown Cloud Plume-Asian Monsoon Experiment (CAPMEX) field campaign throughout August and September 2008 using a 3-laser photoacoustic spectrometer (PASS-3), chemical filter analysis, and size distributions. The PASS-3 directly measures the effects of morphology (e.g. coatings) on light absorption that traditional filter-based instruments are unable to address. Transport of mixed sulfate, carbonaceous, and nitrate aerosols from various Asian pollution plumes to Jeju accounted for 74% of the deployment days, showing large variations in their measured chemical and optical properties. Analysis of eight distinct episodes, spanning wide ranges of chemical composition, optical properties, and source regions, reveals that episodes with higher organic carbon (OC)/sulfate (SO42−) and nitrate (NO3−)/SO42− composition ratios exhibit lower single scatter albedo at shorter wavelengths (ω405). We infer complex refractive indices (n–ik) as a function of wavelength for the high, intermediate, and low OC/SO42− pollution episodes by using the observed particle size distributions and the measured optical properties. The smallest mean particle diameter corresponds to the high OC/SO42− aerosol episode. The imaginary part of the refractive index (k) is greater for the high OC/SO42− episode at all wavelengths. A distinct, sharp increase in k at short wavelength implies enhanced light absorption by OC, which accounts for 50% of the light absorption at 405 nm, in the high OC/SO42− episode. Idealized analysis indicates increased absorption at 781 nm by factors greater than 3 relative to denuded black carbon in the laboratory. We hypothesize that coatings of black carbon cores are the mechanism of this enhancement. This implies that climate warming and atmospheric heating rates from black carbon particles can be significantly larger than have been estimated previously. The results of this study demonstrate ways in which atmospheric processing and mixing can amplify particle light absorption for carbonaceous aerosol, significantly at short wavelength, underscoring the need to understand and predict chemical composition effects on optical properties to accurately estimate the climate radiative forcing by mixed carbonaceous aerosols.

Resistance of concrete mixtures to cyclic sulfuric acid exposure and mixed sulfates: Effect of the type of aggregate

The behavior of different concrete mixtures was examined in relation to their exposure both to different metal sulfate solutions and alternately to metal sulfates and sulfuric acid, recording the expansion and mass loss of the test specimens for about three years. The test method adopted in this study can be considered a model of accelerated deterioration, more closely resembling the situation in sewer pipes than in sulfate-bearing soil. Three different cements – i.e. Portland limestone (PLC), blast furnace slag (BFC) and pozzolanic (PZC) cement (this last with silica fume, SF) – were used to prepare the concretes mixtures. Half of the samples were prepared using a ground dolomitic limestone and the other half with a natural aggregate. The greatest expansion and most severe damage were surprisingly recorded for the BFC and PZC + SF samples, in a two-stage process of deterioration. The degradation was particularly severe when the samples contained natural aggregate and under cyclic exposure to solutions of mixed sulfates and sulfuric acid. A continuous web of cracks within the cement paste and through the aggregate particles was seen on SEM. EDX analyses enabled us to establish gypsum nucleates in the cracks, causing expansion and aggregate detachment. Portland limestone cement is the best choice when a concrete is liable to attack by these different aggressive species, regardless of the type of aggregate used. For comparison, the same types of sample were exposed to attack by mixed sulfates alone.

Selective precipitation of mixed nickel–cobalt hydroxide

The precipitation parameters of mixed hydroxide precipitate (MHP) using caustic calcined magnesia were evaluated at simulated industrial conditions using a mixed sulphate–chloride feed solution and fine magnesia powder. Controlling the rate of magnesia addition was found to decrease the manganese content of the precipitate but the benefit was minimal. Thermodynamic analysis combined with oxidation–reduction potential measurements suggests that some of the manganese is reporting to the solids by an oxidative precipitation reaction. The oxidative precipitation of manganese in air was confirmed experimentally. Contacting MHP with feed solution was found to substantially improve the solids' nickel and cobalt grade while decreasing the manganese and magnesium content. Precipitate contacting with the feed solution also resulted in a higher concentration of sulphate and chloride in the precipitate.

An investigation of zincite from spent anodic portions of alkaline batteries: An industrial mineral approach for evaluating stock material for recycling potential

The mineralogy of anodic portions of spent alkaline batteries from a leading brand (Duracell) that had been equilibrated in ambient air for approximately 4 months was investigated to determine if material generated from this low energy process may be suitable stock material for recycling. Powder X-ray diffraction (XRD) identified the bulk of the ambient air oxidized anodic material as zincite (ZnO). Scanning electron microscopy investigation indicates a variety of textures of zincite are present with euhedral hexagonal prisms being the most common crystal form. Energy dispersive spectroscopy (EDS) analysis indicates that there are no minor amounts of Mn within the zincite. Transmission electron microscopy investigation indicates a variety of textures exist in the <2 μm size fraction including near euhedral prismatic crystals, crystals with step-fashion terminations and indentations, heavily corroded zincite and near amorphous aggregates of anastomozing zinc oxide. Impurities in the <2 μm size fraction include minor amounts of unidentified mixed sulfate materials and are interpreted as dominantly occurring as thin coatings on zincite particles. Discrete submicrometer-sized spherical and rhomboid particles of Zn–Mn oxides are also common impurities in the <2 μm size fraction but occurr at abundance of <1% by volume. This study provides new baseline information that can be used to develop large scale recycling of zincite from spent alkaline batteries. A promising applications of zincite are numerous, including the development of new solar cell materials. The spent alkaline battery waste stream may serve as promising resource for driving further development of this sector of the economy.

Separation and Recovery of Zinc(II) and Cobalt(II) from a Mixed Sulfate/Thiocyanate Solution using some Commercial Organophosphorus Extractants

The separation and recovery of divalent zinc and cobalt ions from mixed sulfate and thiocyanate solutions have been carried out using CYANEX 921 (trioctylphosphine oxide), CYANEX 923 (a mixture of straight chain alkylated phosphine oxides), and CYANEX 925 (a mixture of branched chain alkylated phosphine oxides) in kerosene. Different parameters affecting the extraction equilibrium of Zn(II) and Co(II) in addition to temperature, were studied and the stoichiometry of the extracted Zn(II) and Co(II) species were postulated based on the slope analysis method. The extraction percent of the metal ions was found to increase with increasing pH and zinc was preferentially extracted over cobalt with CYANEX 925. The respective loaded organic phases were stripped with different mineral acids. The highest separation factor was obtained when using 0.015 M CYANEX 925 as extractant. Based on the obtained results, the application of the method was tested to separate Zn(II) and Co(II) from Nickel Metal Hydride batteries (Ni-MH batteries) leached by 2.0 M H2SO4 and good results were obtained.

Prospects for solvent extraction processes in the Indian context for the recovery of base metals. A review

Details of the research and development work carried out in India using SX for the treatment of the leach/waste solutions and effluents containing base metals are reviewed, focusing on solutions obtained from low-grade or complex ores, secondary resources or industrial wastes. Commercially available organic extractants, such as hydroxyl-oximes, hydroxyl-quinoline, tertiary amines, substituted phosphoric acid and other phosphate based extractants, have been used for the recovery of metals from acidic, alkaline and mixed sulfate–chloride solutions containing copper, nickel, cobalt, zinc and associated metals. The applicability of commercially available tailor-made extractants is described for the purification and enrichment of the metal contents of lean and complex solutions in an Indian context. Research efforts for the separation and recovery of valuable metals by SX are also highlighted. Treatment of solutions for producing metals by crystallization or electrowinning is described.

Совместное электролитическое осаждение оксида кобальта (III) с оксидами никеля (III) и хрома (III) и образование бинарных оксидных систем

With the help of the polarization curves method (E-lgIa) there are investigated the anode processes at Co2O3 anode deposition together with the doping additives – nickel (NiO, Ni2O3) and chromium (Cr2O3) oxides at the electrolysis from the mixed sulfate solutions. The possible mechanisms of these processes interconnection with nucleation and crystal growth of binary oxide compounds of Co-Ni and Co-Cr and crystal structure formation of anode deposits are considered.

Structure and electrochemical properties of novel mixed Li(Fe1−xMx)SO4F (M = Co, Ni, Mn) phases fabricated by low temperature ionothermal synthesis

In the current scenario, Li-ion batteries are no longer limited to portable electronic devices, but are rapidly gaining momentum to enter the large-scale hybrid automotive market owing to their adequate energy density coupled with their low cost and safety. LiFePO4 is the front-runner candidate in this sector mainly due to its economic cost and operational safety. Recently, our group has discovered a novel 3.6 V metal fluorosulfate (LiFeSO4F) electrode system, which combines sulfate polyanions with fluorine chemistry to deliver excellent conductivity and electrochemical capacity. In the current study, we extend our effort to investigate the structure and electrochemical properties of 3d-transition metal (M = Co, Ni, Mn) substituted fluorosulfates. Toward this goal, we have adopted ionothermal synthesis to fabricate three families of solid-solution systems, namely Li(Fe1−xCox)SO4F, Li(Fe1−xNix)SO4F and Li(Fe1−xMnx)SO4F at temperatures as low as 300 °C. The structure, thermal stability and electrochemical properties of these mixed sulfate phases along with the end members (LiCoSO4F, LiNiSO4F and LiMnSO4F) have been examined using a suite of characterization techniques. Overall, a 3.6 V Fe2+/3+ redox reaction is observed with no signature of Co2+/3+, Ni2+/3+ or Mn2+/3+ reaction. These metal fluorosulfate systems, delivering near theoretical capacity, stand as an alternative new class of electrodes for varied commercial applications.

New particle formation and growth at a remote, sub-tropical coastal location

Abstract. A month-long intensive measurement campaign was conducted in March/April 2007 at Agnes Water, a remote coastal site just south of the Great Barrier Reef on the east coast of Australia. Particle and ion size distributions were continuously measured during the campaign. Coastal nucleation events were observed in clean, marine air masses coming from the south-east on 65% of the days. The events usually began at ~10:00 local time and lasted for 1–4 h. They were characterised by the appearance of a nucleation mode with a peak diameter of ~10 nm. The freshly nucleated particles grew within 1–4 h up to sizes of 20–50 nm. The events occurred when solar intensity was high (~1000 W m−2) and RH was low (~60%). Interestingly, the events were not related to tide height. The volatile and hygroscopic properties of freshly nucleated particles (17–22.5 nm), simultaneously measured with a volatility-hygroscopicity-tandem differential mobility analyser (VH-TDMA), were used to infer chemical composition. The majority of the volume of these particles was attributed to internally mixed sulphate and organic components. After ruling out coagulation as a source of significant particle growth, we conclude that the condensation of sulphate and/or organic vapours was most likely responsible for driving particle growth at sizes greater than 10 nm during the nucleation events. Although there was a possibility that the precursor vapours responsible for particle formation and growth had continental sources, on the balance of available data we would suggest that the precursors were most likely of marine/coastal origin. Furthermore, a unique and particularly strong nucleation event was observed during northerly wind. The event began early one morning (08:00) and lasted almost the entire day resulting in the production of a large number of ~80 nm particles (average modal concentration during the event was 3200 cm−3). The Great Barrier Reef was the most likely source of precursor vapours responsible for this event.

Editorial: A Light Breakfast, a Jug of Salt Water and Bowel

Successful colonoscopy is predicated on achieving adequate colon cleansing. An ideal bowel preparation would be low in volume, acceptable to patients, reliable in cleansing efficacy, and safe. The study by Di Palma et al. in this issue shows that a novel, low-volume (960 ml) preparation of mixed sulfate salts can achieve excellent bowel cleansing with acceptable tolerability and minimal electrolyte shifts. A split-dosing strategy, with a proportion of the preparation administered on the day of colonoscopy, achieved a 97.2% preparation success rate vs. 82.4% using a regimen provided entirely the day before colonoscopy. These results were comparable with control groups using a commercially available polyethylene glycol solution. Endoscopists and patients alike should be encouraged by the trend toward lower-dose bowel cleansing regimens that achieve equivalent efficacy compared with large-volume preparations.