The physical capacity of the feeder and conveyors was not reached even at feed rates as high as -2,000 kg/hr, where the aluminum fraction is still 93-percent pure while recovering 99.6 percent of the available aluminum. The Bureau of Mines has used colloidal solutions of magnetite in a magnetic field to segregate non-magnetic materials such as non-ferrous scrap metals and to concentrate precious minerals. The reactions were completed in a 55-gallon stainless steel tank fitted with an electric immersion heater and an air-driven stirrer. The power supply is rated for the regulation of the output current to better than 1 percent over the full operating range. Figure 8 shows some of the diamonds that were visible in the float product from the second pass. /CropBox [ 0 0 609 791 ]/Contents [ 28 0 R ]/Rotate 0/Parent 1 0 R/Resources << Comparing the first and the last row of this table indicates the desirability of using the belt feeder. In this new magnetic separation of the second kind, a magnetic fluid rather than air or water acts as the separation medium. When the medium of separation rather than the separated particles are made magnetizable, a new system of gravity separation results. Magnetic Separation [Practical Experiment]. The separation of nonferrous automobile scrap was studied with the goal of upgrading the mixed useless scrap into useful metallic groupings. /Type /Page/MediaBox [ 0 0 609 791 ]>> The system has also been used to upgrade diamondiferous jig concentrates from certain river gravels in order to facilitate the sorting and recovery of their diamond content. In these tests the separation zone was maintained at an apparent specific gravity of 7.0 (magnetic fluid saturation magnetization of 400 gauss and electrical power supply setting at 70 amperes). No sales to private individuals. Figure 3A shows the principles of a continuous magnetogravimetric separation technique that orients the magnetic reactionary force in a nonvertical direction. off the sand from the salt water solution. unwrapping the plastic from the magnet carefully! %0]x2&v\O_0oC 8TSSL2F4B.t /F2 17 0 R/F1 14 0 R/F3 20 0 R>> The reshredding step resulted in an added benefit of pulverizing the glass and other nonmetallics, thereby facilitating their screening from the metallic portion to be segregated with magnetic fluids. fluid of 130 gauss along with a power supply setting at 65 amperes to float the light gangue minerals from the diamonds. endobj Hence, the magnetic force per unit fluid volume, Fm, will be given by the negative gradient of the scalar function U/V: Fm = 1/V grad U = u grad H..(3). Figure 4 is a photograph of the separator used in these bench-scale experiments and illustrates a method for returning the skimmed fluid to the separation cell. To aid in determining the proper separation settings, colored cubic-shaped tracers of specific gravity 3.5 from J. E. Encapsulations, Essex, England, in the same size ranges as the feed, were used to monitor the results. This approach allows continuous separation of materials by means of a single magnetic fluid-magnetic field combination. and distillation. After hand sorting they reported that all of the diamonds in the minus 3/8-inch plus 4-mesh fraction had reported to the middling product. endobj Naturally, these constituents will sink in the magnetic fluid. Conventional magnetic separation relies on the inherent magnetic susceptibility of the material to be separated and may be designated as magnetic separation of the first kind. Practical laboratory experiment using magnetism to separate a mixture of sand and iron filings. /F2 17 0 R/F1 14 0 R/F3 20 0 R>> 2 0 obj The next time you visit our online store all you need to view your personal details is your email address and password. hysteresisless magnetization curve is typical of superparamagnetic substances and indicates that magnetic colloids can become magnetically saturated at reasonably attainable magnetic fields. Meticulous crushing of the jig concentrate is important to preserve the precious stones intact and to avoid their catastrophic degradation through size reduction. Both methods utilized the magnetic levitation force created within the fluid in an inhomogeneous magnetic field as an anti-gravity force; that is, the former force was always oriented in the vertical direction, as illustrated in figure 2. Kaiser used an on-off magnetic field for the separation of particles (positioned at different elevations in the fluid) according to density, while Rosensweig employed the fluid as a horizontal sieve. /CropBox [ 0 0 609 791 ]/Contents [ 32 0 R ]/Rotate 0/Parent 1 0 R/Resources << Screening the incinerator residue. 11 0 obj Among these media, water-based magnetic fluids may improve the process economics by eliminating the need to dry the feeds and by simplifying the media recovery procedure. Separation theory In this method the vibratory feeder previously described discharges directly onto the surface of the magnetic fluid pool. one component at a time, which means that this experiment can be expected /CropBox [ 0 0 609 791 ]/Contents [ 29 0 R ]/Rotate 0/Parent 1 0 R/Resources << properties. The results also seem to indicate that both systems of scrap feeding were adequate for the separation of aluminum. salt and sand in water and stir. Sedimentation This practical experiments is included in the Year 7 Chemistry Workbook (Australian Curriculum), which includes the following worksheets, activities and practical experiments: Teachers Pay Teachers is an online marketplace where teachers buy and sell original educational materials. With this configuration, the zinc fraction was separated from the heavy metals: copper, stainless steel, and lead. The magnet assembly is sloped forward, and the float product is skimmed off using a fixed tray. The higher power setting was used when separating the coarse feed. Mix the remaining In this topic, you will be taken through the experiment and the theory be sped up in an oven. x|g`3;HV$Iad .B6nyqzK{c+8 v~${i5s-s9vumC4YZaM]oMB{YgZv B.Yy/'iZtvi_OuCP0Y^pme+,[zY NU}pC\~wK5Iu}k^;y!$2?P% (f!! ! Generally, materials are separated according to differences in their physical /CropBox [ 0 0 609 791 ]/Contents [ 11 0 R ]/Parent 1 0 R/Resources << and the sand will not. 6 0 obj An alternative method of feeding materials and discharging products is shown in figure 6B. easier. separated solids and compare them with their original weights. Figure 2A depicts a magnetic fluid sample of about 0.8 g/ml density containing water and some alumina beads with a density of 3.8 g/cm. "~m.xgwK&H0pu The first one deals with materials recycle by segregating metals of common identity from the nonferrous segment of automobile scrap. The following is a description of the density separation equipment, the separation procedures and the material used. :-EVhz0X_RyDd.Nh -0/(5VR7P!? $ Tv;yt ?yr(sW. The bulk of the magnetic fluid that adhered to the separated particles was recovered by floating it on water and skimming it off with the aid of moving magnets. endstream << /F5 26 0 R/F2 17 0 R/F4 23 0 R/F1 14 0 R/F3 20 0 R>> and filtration, Recrystallisation These methods will be the subject of subsequent publications. does a filter paper work? The mill contents are then screened and hand sorted to recover the diamonds. State of Victoria (Department of Education and Early Childhood Development). As the density mismatch becomes smaller (for example, in separating zinc from copper), the effect of feed velocity begins to be of significance. The << of the three materials. /Type /Page/MediaBox [ 0 0 609 791 ]>> Twenty-two carats of diamonds (4.4 g) were recovered from the 2,750 lb of feed. This. /ProcSet [ /PDF /Text /ImageB /ImageC /ImageI ]/Font << Recovery of aluminum was excellent using either a conveyor belt or a direct feeding mode. The minerals were mined by dredging river gravels followed by concentration by jigging. sand. Separation of this residue into its components was accomplished using a permanent magnet and a magnetic fluid with a saturation magnetization of 80 gauss (8 x 10 -3 Tesla). One can, therefore, increase the levitating force either by increasing the fluid magnetization (stronger magnetic fluid) or by increasing the field gradient, or both. One diamond was about 0.5 cm in size and weighed slightly more than 1 carat. %PDF-1.7 This follows Newtons third law of motion, to every action there is always opposed an equal reaction. A magnetic levitation force Fl will therefore be exerted per unit volume of an immersed body in a magnetic fluid placed in an inhomogeneous magnetic field. 7 0 obj Magnetic fluids with magnetization values from 100 to over 400 gauss were produced by varying the quantity of magnetite dispersed in the kerosine carrier. The technique has been applied to two main beneficiation areas involving material recycle and mineral recovery. The diamondiferous concentrate was provided by a U.S. mining company, which prefers to be anonymous, having properties in South America. The scrap metal used in this work was obtained from an automobile shredding operation. << The principles underlying the magnetogravimetric separation technique with magnetic fluids have been outlined. /ProcSet [ /PDF /Text /ImageB /ImageC /ImageI ]/Font << In this work, the fluid magnetization is represented by M, while the symbol u represents the magnetic moment per unit volume, sometimes called the intensity of magnetization. /ProcSet [ /PDF /Text /ImageB /ImageC /ImageI ]/Font << 1). /Type /Page/MediaBox [ 0 0 609 791 ]>> Using a funnel, flask and filter paper, filter For the second pass through the separator, the magnetic fluid was not changed, but the power supply was adjusted in a range of 100 to 110 amperes to float the diamonds from the heavier gangue minerals. The white alumina was partially covered with the dark fluid in the front beaker. /CropBox [ 0 0 609 791 ]/Contents [ 31 0 R ]/Rotate 0/Parent 1 0 R/Resources << In this case all three are solids, which means /Type /Page/MediaBox [ 0 0 609 791 ]>> At present, material separation processes based on magnetic fluid technology can be envisaged in reclaiming nonferrous metals from concentrated unburned urban refuse, recovering titanium and lead, and unalloyed copper and zinc from wasted nonferrous scrap, recovering lead-free zinc die-cast alloys (trade name, Zamac) from the nonferrous segments of automobile scrap, separating the gangues from native copper ores to upgrade their copper content, and recycling military wastes and scrap and processing their electronic scrap for precious metals. Because the fluid is constrained in its position by being confined in an immovable vessel, a reactionary force of equal and opposite sign will be created within the fluid and will manifest itself on immersed objects. Are you getting the free resources, updates, and special offers we send out every week in our teacher newsletter? stream of salt water becomes a problem. The data in table 3 indicate that diamonds were concentrated with magnetic fluids into a product containing about 8 and 30 percent, respectively, of the starting weight for the coarser and finer sizes. /Filter /FlateDecode/Length1 31600/Length 20351>> The scrap metal used in these series of tests had the following approximate composition as determined by hand sorting: zinc-48 percent, aluminum-39 percent, copper and brass7 percent, non- metals4 percent, and less than 1 percent each of lead, stainless steel, and insulated copper wire. solids with significantly different physical properties, which makes separation Separation of zinc from heavier metals was improved where a conveyor belt system was used. /ProcSet [ /PDF /Text /ImageB /ImageC /ImageI ]/Font << for a difference in a physical property. Weigh each of the These differences form the basis for separation If a small volume of magnetic fluid is placed in an inhomogeneous magnetic field such that the lowest value of the ambient field saturates the fluid magnetization, then equation 1 becomes applicable since u is a constant independent of H. Because the fluid magnetizes along the local field direction, =0, and. BZtga:0 A&D*G-WwDhCb3j| By contrast, a magnetic colloid behaves as a one-phase system and will be attracted as one unit to the magnet. 3 0 obj A schematic drawing of the electromagnet assembly is illustrated in figure 5A, while figure 5B shows a pool of magnetic fluid held in an open-ended trough. $ Wrap a magnet in plastic Before you prepare the mixture, weigh each of the << Total combined weight of the sample was 1,250 kg. /CropBox [ 0 0 609 791 ]/Contents [ 27 0 R ]/Rotate 0/Parent 1 0 R/Resources << The composition of the float products from automobile scrap was determined as. A diagram of the orientation of these forces is shown in figure 3B. Theory predicts that the magnetic levitation force per unit volume of an immersed object is equal to the product of the fluid magnetization by the magnitude of the magnetic field gradient. endobj endobj Give In the latter procedures, either the magnetic field gradient was changed by use of an intermittent variable electromagnet, or a bottomless vessel containing the magnetic fluid was placed between the inclined poles of a magnet with the magnetomotive force holding the fluid in place. three solids and record the weights for reference at the end of the experiment. The composition and recovery of the float product with feed rate are given in table 1. Salt is a non-magnetic solid which is soluble in water. The concept in this continuous method is quite different from that of previous separation procedures that utilized the magnetic levitation force in a vertical direction. Quizzes with auto-grading, and real-time student data. In figure 3A, a mixture of alumina balls (white) and lead shot (black) was poured into the magnetic fluid contained in a cell that was obliquely sandwiched between two steel blocks on the poles of a laboratory magnet. Two operational modes of material feeding were compared for the separation of metals from nonferrous automobile scrap. Iron is magnetic and the other two not, which An extension was added to the feeder tray to narrow the discharge end to fit between the separation trough. This second method does not give close control of the velocity of feed materials entering the magnetic pool, but it does allow the separation of materials that would tend to clog the conveyor belts. Although these separations were conducted on a relatively large scale, commercial application would be more attractive by achieving larger throughputs. Their individual properties are best set out as a table: Separation technique Similar relationships were rigorously derived by Epstein for an electrostatic field and by Rosensweig for a magnetic field by integrating the surface and volume forces experienced by an immersed body, and differentiating a modified Bernoulli equation to evaluate the pressure gradient. /Filter /FlateDecode/Length 1490>> a prize for the best set of results. The filings can be removed by Used with Permission. /Type /Page/MediaBox [ 0 0 609 791 ]>> /F2 17 0 R/F1 14 0 R/F3 20 0 R>> This liquid would be effective only for this separation; in contrast, the magnetic fluid can separate components over the entire density spectrum. Sand is a non-magnetic solid which is insoluble in water. experiments that can be undertaken by students investigating the principles Separating iron filings, salt and products with water. We only supply companies, institutions and educational facilities. << << /ProcSet [ /PDF /Text /ImageB /ImageC /ImageI ]/Font << The sink product drops onto a conveyor positioned in the lower regions of the pool. Copyright 2012-2021 911Metallurgist | All Rights Reserved, Electromagnet Powered Magnetic Fluid Separation Unit. Methods have bean devised to clean up rhe separated products from the adhering separation medium, and to recover the latter for recycle to the separation cell. )B&SRAZdA#?pAKIC}@XG7fT@h :9%hu5`G#{D\\xj(|B}(t?mD@H W@ When operated at full power the lower region of the separation zone has a magnetic field of about 10 koe. Separating iron filings, salt and sand is one of the most interesting How Gib bitte einen Namen an unter dem dein Warenkorb gespeichert werden soll. << Preliminary testing on the jig concentrates indicated a problem with the conveyor belts clogging with fines. and evaporate off the water. of separation of materials. The net force per unit volume, f, exerted on the immersed body is the vectorial sum of the magnetic levitation force and the gravitational force and is given by, F = Fg + Fl = (p-p)gk grad H(6). The material used in this phase of investigation consisted of a jig concentrate produced from river gravels dredged in South America. The salt will dissolve A hinged deflector is used at the end of the conveyor to assist in submerging pieces of scrap into the magnetic fluid pool. This may take some time in the Sun or may Tests were also conducted using a feed composed of the sink product from the aluminum beneficiation step. In deciding how to separate two or more materials, you should first look Physical properties For the separation tests the scrap sample was pre-treated by sizing to minus 2- plus -inch and removing the magnetic pieces. The assumption made is that the magnetic moment, u, per unit volume of the fluid is independent of the spatial coordinates within the magnetic field, and that it is relatively constant independent of H. The force Fm, is in the same direction of the vector quantity grad H and tends to move the fluid towards the magnet. Because the true body weight is pg per unit volume, the magnitude of the gravitational force, Fg, on the immersed object is (p-p)g, and the gravitational force vector is, where k is the unit vector in the vertical direction. Please note: To comply with EU regulation 1272/2008 CLP, PHYWE does not sell any chemicals to the general public. Du findest deine gespeicherten Warenkrbe im Mein Konto Bereich, Mixture separations by magnetic separation, Mixtures of Substances & Separation of Substances, Exhaust Gas Cleaning, Environmental Protection, Stabilised or Regulated Power Supply Units, Gas, Density & Pressure Measuring Instruments, Glass Apparatus for Distillation & Calorics, Round-bottom, Measuring & Volumetric Flasks, Plastic Laboratory Beakers & Measuring Cylinders, PHYWE XR 4.0 X-ray Equipment & Accessories. To eliminate the energy- and timeconsuming grinding method, the magnetic fluid beneficiation technology was attempted as an alternate route. The final choice consisted of a magnetic. 'G~*p:_rxc12CST! T,#_2>h&C12Wq) g vM"9A9tZEc&y^*aLrW2t>^I:zy{NHA9Fyeuy2T>lBq^wHHG|#,/_hF}l7rM'?X4QN Q;.A7v\Q%U5^FoAWX!3p'eiDHCsR GZj /ProcSet [ /PDF /Text /ImageB /ImageC /ImageI ]/Font << Following the separation tests the products were returned to the mining company. Two beneficiation systems were studied in this paper. Figure 2B illustrates the creation of a magnetic levitation force, sometimes called an antigravity force, in a magnetic fluid-magnetic field combination. Make sure you have used enough water [/+Hi: 1 0 obj /Type /Catalog/PageMode /UseNone/Pages 1 0 R>> The technique has been applied to segregate nonferrous metals from automobile and appliance shredders and mixed scraps. Approximately 5 gallons of magnetic fluid is used to fill the open-ended aluminum trough that is mounted between the magnet pole pieces. This conveyor belt feeding system is schematically illustrated in figure 6A. It should be noted that the horseshoe magnet in figure 3A was tilted to make the magnetic field gradient vector deviate from the vertical axis. Because the fluids apparent density can be varied as desired by varying the magnetic field, one should be able to selectively separate particles according to their density spectrum. The mixture is fed from a chute, and the components are received at different receptacles in the exit section. Reported resources will be reviewed by our team. =F}FP2Br. 5 0 obj -1,yqNUboK5X?!c7J"ccOX=2{:jI]};Z;\ sVh >> Separation tests were conducted in a kerosine-base magnetic fluid prepared in bulk following the Bureau of Mines peptization method. The light fraction collector contained 58 percent of the sample and was rich in aluminum (84.7 percent). Several magnetic fluid and power supply settings were initially tried in attempts to develop a two-stage separation scheme. The particles essentially impart their magnetic character to the continuous phase, both phases becoming magnetically indistinguishable in a true colloid. A head sample weighing 2,750 pounds (1,250 kg) of the jig concentrate was beneficiated with magnetic fluids in presence of the mining company personnel who took the separated fractions back to their company headquarters for analysis. Pre-made digital activities. K*S;MD6:{R2NKjr4wq9=b9[*J.)] ryfTY.8 f Ch%uPV<8JlcfIWLceA' 1}!&_ }4x|o88Zwbb^b_%Nh ef The Walker/Magnion levitation magnet system consists of a 31.25-kw DC-regulated power supply and an electromagnet designed to provide a constant magnetic field gradient in the air gap between the pole caps. /Kids [ 2 0 R 5 0 R 6 0 R 7 0 R 8 0 R 9 0 R 10 0 R ]/Type /Pages/Count 7>> Evidently, for aluminum at least, the velocity of the scrap pieces at the point of entry in the magnetic fluid does not influence the separation efficiency. mixture, leaving the salt and sand. 12 0 obj /CropBox [ 0 0 609 791 ]/Contents [ 33 0 R ]/Rotate 0/Parent 1 0 R/Annots [ 34 0 R 35 0 R ]/Resources << H = H cos = u HV cos (1), where is the angle between the two vectors and H, and H are their magnitudes, respectively, and u is the volume-averaged magnetic moment. We offer the storage of your personal details in a password-protected customer account, in order for you not to have to enter your name and address during your next purchase. >> water to remove the last of the salt from the sand in the filter paper. 8R~s^;k \)CK4k`g=TmL(9*]@i(R2>vSG)>7s~;0wR1F`Z % We only accept orders from resellers, professional users and research, study and educational institutions. >> Thus, in a magnetic field the fluid appears to have a density greater than 3.8 g/ml. Beneficiations based on these techniques would therefore benefit from the rapidly evolving technology of superconducting magnets. /ProcSet [ /PDF /Text /ImageB /ImageC /ImageI ]/Font << /Type /Page/MediaBox [ 0 0 609 791 ]>> three solids and record the weights for reference at the end of the experiment. Iron is a magnetic solid which is insoluble in water. !]!YBglw_s V9z#/`ZKaI`niwvXw mmf!>84i_2NJrw'x'K`)d0/}e+$i8~@}jWOaBe!); [pp'_nYC~s/>RKN}z z-}7 })g This avoids costly >> Put the sand to one side and allow it to dry It is best to try to separate endobj /CreationDate (D:20100830123129Z)/Author (benmens)/Creator (vspdflib \(www.visagesoft.com\))/Producer (vspdflib \(www.visagesoft.com\))/ModDate (D:20100830123129Z)>> Since grad H can be impressed upon the system in any desired direction, it is possible to overcome gravity by orienting the field gradient in a direction opposite to k. This means that a nonuniform magnetic field whose magnitude decreases in an upward direction, and hence whose gradient vector is directed downward, will tend to lift an immersed body upward. The main minerals in these beach sands were quartzite, iron silicates, goethite, and kyanite. In this figure, the same container shown in figure 2A is placed on a laboratory horseshoe magnet whereby both the water and alumina are floated on top of the fluid. When the sink products reach the sloped bottom of the separation trough, they also slide forward for collection. << This force will be equal, and opposite in direction, to Fm, and, per unit volume of the immersed body, will be given by, Fl = grad H = M/4 grad H(4). In all these tests the separation zone was maintained at an apparent specific gravity of 4.0 using a magnetic fluid of 200 gauss saturation magnetization and an electric power setting at 70 amperes. Collect all the salt water in a weighed container `; * /F2 17 0 R/F4 23 0 R/F1 14 0 R/F3 20 0 R>> endobj This method was also successfully applied to fractionate nonferrous metals from the residue of an experimental solid waste incinerator. The second system covers the upgrading of diamondiferous concentrates obtained from certain river gravels. In such cases, the conveyor belt method of feeding will be more advantageous, since feed rates with the vibratory feeder cannot be varied independently from feed velocities within the separation cell. Click the green View Preview button for a full preview of this practical experiment. change any of the parts of the mixture if possible. In the first system, scrap metal is loaded into a Syntron Model SF-212 Vibro-Flow feeder having an 8-inch-wide tray. /F2 17 0 R/F1 14 0 R/F3 20 0 R>> The composition of the products listed in tables 1 and 2 was determined by hand sorting of the metals into their specific groupings. >> endobj Before you prepare the mixture, weigh each of the Materials from this tray are then fed onto a Dorner conveyor constructed of nonmagnetic materials and fitted with a 5-inch belt. Separation technique To generate the magnetic field profile for density separation the special pole pieces provide a magnetic field gradient of approximately 230 oe/cm in the separation zone. Full prac report format, including discussion questions. 9 0 obj << Modern magnetic fluids can easily provide transient zero-gravity conditions when placed in inhomogeneous magnetic fields. Because of the large density mismatch between aluminum and the zinc-copper fraction, it was possible to use very large feed rates and still obtain relatively efficient separations. The results of these separation tests are listed in table 3. to have at least three stages, corresponding to the removal of each component This force, sometimes called the levitation force, can be made to segregate nonmagnetic particles in a flowing stream according to their specific gravity. Two systems for feeding the input materials into the levitation electromagnet and discharging the separated products have been devised and tested. that differences in state are of no use. At present the jig concentrates are carefully ball milled for about 60 hours to crush the softer gangue minerals. endobj << means the two can be mixed in water and stirred. /Type /Page/MediaBox [ 0 0 609 791 ]>> in the Sun or warm oven. The magnetization curves of magnetic colloids did not exhibit the hysteresis loop expected for ferrimagnetics or ferromagnetics, but produced instead a symmetrical sigmoid curve about the origin (fig. In a two-phase system of large magnetic particles in a nonmagnetic fluid, the particles alone will move in the direction of maximum field (separation of the first kind). The other hydrodynamic force exerted per unit volume of an immersed object of density, p, is the Archimedes buoyancy force, which is equal to the weight, Pg, of the fluid displaced by unit volume of the solid, where p is the fluid-density. The emu unit of both quantities is the same; namely; erg per oe.cm, or gauss. Includes detailed teacher notes and answers. Ordinary magnetic reclamation of the major ferrous constituents left a reject containing the nonferrous and valuable metals of the automobile scrap. theory About the limitations of magnetic separation. cY JF?DE@v7x =Kj#w= }3rIO6x:=/xx^ } xq-QkZNSkhL;iw1n c}|0UH 7rZ\-@. iron filings will stick to the magnet. to dissolve all of the salt, but not too much that handling large quantities This The vibratory feeder gave inefficient separations of zinc, even at the smallest feed rate as shown in the first row of table 2. You can delete your customer account at all times. Wash the sand with some fresh A motor-driven variable output transformer provides the capability of current adjustment from 45 to 125 amperes with a maximum output voltage of 250 volts. a function of feed rate using both methods of material feeding to the separator. endobj The rejects were further reshredded so that the bulk of the metallics was fragmented to pieces smaller than 3 inches (76 mm). A higher purity zinc product with greater recovery was obtained with the conveyor belt even though the feed rate was five times faster than with the vibratory feeder.