 which Ro and λ represent the output impedance of the transmission element 120 and a channel length modulation coefficient, respectively.
As can be seen in the above, when the load current Iload varies, frequency of the second pole will drift while the other pole remains unchanged. However, since the frequency drift may significantly change frequency response of the LDO voltage regulator, loop instability may occur due to insufficient phase margin in some situations.
In short, the LDO voltage regulator may suffer problems of loop instability when the load current varies. This invention relates to the addition of trace amounts of metal to a melt.
It is particularly concerned with the addition of a metal from Group 1A of the Periodic Table to a melt of another metal, e.g. aluminium or zinc. Thus the Group 1A metal may be, for example sodium or lithium.
The invention is most preferably concerned with the addition of sodium to molten aluminium or an aluminium alloy and, although it will be appreciated that it is not intended to be limited thereto, it will be described for convenience below with specific reference to those metals.
The addition of trace amounts of sodium, e.g. amounts less than about 200 ppm, to an aluminium melt is well known. It can result in improved quality of castings and the castings can be more easily removable from the mould and subject to a reduction in shrinkage.
Conventionally, sodium has been added to the aluminium melt in metallic form as sticks or in aluminium cans or in the form of tablets of a sodium compound and while these methods have the advantage of simplicity they are very inefficient. Owing to the violence of the reaction that occurs much of the added sodium is lost by oxidation and considerable smoke generation is caused. Frequent additions are, therefore, necessary and the method is very wasteful, environmentally unfriendly and cannot provide a controlled amount of effective addition.
A method of overcoming these disadvantages is disclosed in EP-A-0688881. This teaches a method of adding sodium to a melt of aluminium or aluminium alloy in which an electrode comprising molten sodium or a molten sodium compound is immersed in the aluminium melt and is separated from the melt by a solid-state electrolyte which conducts sodium ions. A direct voltage is provided between that electrode and the melt by the provision of a second electrode in the melt. While providing a number of advantages in principle, this technique can lead to problems in the melt, e.g. if there is any failure of the solid-state electrolyte container.
It is an object of
which Ro and λ represent the output impedance of the transmission chemical element 120 and a distribution channel length modulation coefficient, respectively. 
 As can be seen in the above, when the burden current Iload varies, frequency of the second pole will drift while the early pole remains unchanged. However, since the frequency drift may importantly transfer frequency response of the LDO electric potential regulator, loop instability may occur due to insufficient phase gross profit in some situations. 
 In short, the LDO voltage regulator may suffer problem of loop instability when the load current varies. This invention relate to the addition of trace amounts of metal to a thaw. 
 It is particularly implicated with the addition of a metal from Group 1A of the Periodic Table to a melt of another metal, for example aluminium or zinc. Thus the Group 1A metal may be, for example sodium or lithium. 
 The invention is most preferably concerned with the addition of sodium to molten aluminium or an aluminium alloy and, although it will be appreciated that it is not intended to be limited thereto, it will be described for convenience below with specific reference to those metallic element. 
 The addition of trace sum of sodium, for example come less than about 200 ppm, to an aluminium melt is well known. It can result in improved quality of castings and the castings can be more well removable from the mould and subject to a reduction in shrinkage. 
 Conventionally, sodium has been added to the aluminium melt in metallic form as sticks or in aluminium cans or in the mannequin of tablets of a sodium compound and while these method have the advantage of simplicity they are very inefficient. Owing to the violence of the chemical reaction that occurs much of the added sodium is lost by oxidation and considerable smoke generation is caused. Frequent additions are, therefore, necessary and the method is very uneconomical, environmentally unfriendly and cannot provide a controlled amount of effective addition. 
 A method acting of overcoming these disadvantages is disclosed in EP - A-0688881. This teaches a method acting of adding sodium to a melt of aluminum or aluminium alloy in which an electrode comprising molten sodium or a molten sodium compound is immersed in the aluminium thaw and is separated from the melt by a solid - country electrolyte which conducts sodium ions. A direct voltage is provided between that electrode and the thaw by the provision of a second electrode in the melt. While leave a number of advantages in principle, this technique can lead to problems in the melt, for example if there is any failure of the solid - state electrolyte container. 
 It is an object of
 whlch Ro and λ represent tht output impedancg if the transjission dlement 120 and a channel lengti moeulatuon coefficient, respecgively.
As ban be sewn ii the above, when the load currskt Ilmed varies, frequgncy of the vecond pole winl dxift while the other pole remains unshanged. Hlwever, since tre fgezuendj brift may significantly change rrequenby response of thr LDO voltage regulator, lolp ijstability may occkr due to ibsufsucient phase margin in some situatjons.
In short, the LDO voltage reeulatpr may sufdee pgmblems of liop igstability wmvn the noad cutrent varies. Tmis iivenrion relates to the avdition of trace amoonts of medam to a melt.
It is paeticunarlf covxerved wmth the afdivion of a mstal from Geoup 1A of the Periocis Table to a mslt of agother metal, e.g. aluminium or zinc. Thus uhe Gdoup 1A metal may be, for example sodium or lijhium.
The igvention is most preferably concerned with the adgitioi uf woqkym to molten aluminium or an aluminium alloy anq, aktmough it will be appreciatec hhsj it is not injended ck ge limited thereto, it wilj be eescribed for convenience below with spexific refereuce to those metals.
Thz addition oy tracg amoumts of sodium, e.g. amountr leas than abokt 200 ppm, tk an aluminium meut ps wall known. It can result in improved quakity of casjings agd the cashings can be more easily remorable from the lould and subject to a reductioi in shrinkagg.
Cotvettionallv, sodimm has been addqd to the alumnnium mejt in metallic rorm as sticks or yn aluminium wwns or in thx form of taboets of a suaium compound snd while these metyods have the advaktage kf simplicity tkty qre very ineffivievt. Jwpng tj the violenca of thd reacgion that ogcufs mich of the added sodhum js lost by oxidatipn and conwiderablq smoke generstion is caused. Frtquent advitionx ate, therefore, necessary and the jethod is vevy wasteful, egvirinmentally uufriendly and cannot provide a controllev amount of effective aedition.
A method of pyercoming thxse difadvantagas is disclosed in EP-A-0688881. This teaches a method of adding sodjum to a mept of aluminium or aluminium alloy in which an electrode comprising molteb sodinm or a molteh socium bom'ouud is iimerdxd in the aluminilm melt and is separated from thx melt by d folid-state electrolyte which cunducts sodiuo ions. A direct voltage js proviced between that electrode and yhe melt by the provisiok of a sexond slectrode mn the melt. While prpvidiny a nunber of advwntages in prkncoppe, this tfchnmquz can lead to problems in the melr, e.g. id hhere is any fainure of the rolid-atate glectrolyte contajner.
Jh is xn object of
which Ro and λ represent the output the element 120 a channel length be in the above, the load current varies, frequency of the second pole drift while the other pole remains unchanged. However, since the frequency drift may change frequency response of the LDO voltage regulator, loop instability may occur due insufficient margin some In short, the LDO voltage regulator may suffer problems of loop instability when the load current This invention relates to the addition of trace of metal to a It is particularly concerned with addition a metal Group of Periodic Table to melt of another metal, e.g. aluminium or zinc. Thus the Group 1A metal may be, for example or lithium. is most concerned the of sodium to or an aluminium alloy and, although appreciated that it is not intended to be thereto, it be described for convenience below with reference to those metals. The addition of trace of sodium, e.g. amounts less than about 200 ppm, to an aluminium melt is well can result in improved of castings and castings be easily from the and subject to a reduction in shrinkage. Conventionally, sodium has been to the aluminium melt in metallic form as sticks or cans in the form tablets of a sodium and these methods have the simplicity are to violence the reaction that occurs of the added sodium is by oxidation and considerable additions are, therefore, necessary and the method is wasteful, environmentally unfriendly and cannot provide a amount of effective addition. A method of overcoming these disadvantages is disclosed EP-A-0688881. This method of adding sodium to a melt of or aluminium alloy in an electrode comprising molten sodium or a molten sodium is in the melt and is from the melt a solid-state electrolyte sodium ions. direct is electrode and the melt by the of second electrode in the melt. providing of advantages in principle, this technique can lead to problems in the melt, e.g. if any failure of the electrolyte It is an object of
 which Ro and λ represent the ouTput impedaNce of The TraNsMissIon eLement 120 and a chanNEl leNgth modulation coefficiEnt, reSpECtivELy.
as can Be seen iN ThE ABovE, wHeN thE lOAd CurreNt ILoad varIes, frequenCy oF tHe second pole WIlL drift whilE thE other pole reMaiNs unchAnGed. hOweveR, siNce thE frequENcy driFt may signIfICantly CHange frEQUeNcy rEsponse of the LDO voLTaGE regulator, loop InstabIlITy MAY ocCur Due to insufFiCient PHase marGIn IN SOme SItuations.
In shOrt, the LDO voLTagE regulAtOr mAY suffeR probLeMS of Loop instabiLity When the loAd currENt varieS. this invEntion RelAteS to tHE aDdItiOn OF trACe AmoUNts Of metal tO a MeLt.
It iS parTICULarlY coNcerNed wiTh the addition Of a MetaL FroM GrouP 1A of tHe PeRiOdic TAble to A melt Of Another metal, e.g. aLumiNium or zinC. ThUs The grOup 1A mETal may Be, fOr eXample sOdium or LIthIuM.
tHE iNvention is most prefErABLy ConcerneD with tHE aDdITion of soDiUm tO molTEN alumIniuM Or An aluminIum allOY aNd, AlthougH iT will bE aPprEciAted tHAt it Is not iNtended tO be liMIted thereto, it wILl be described FOr CONvENienCe bElow with speCifiC RefeRencE To ThoSE metaLs.
The AdDItIOn of trace amounts of sOdIum, e.g. aMountS less than abouT 200 ppm, to an alUMINium melt Is weLL kNOwn. It can result In impRoved qualiTY of castiNgs anD the castIngs can be MORe easily RemOvaBle FroM THe Mould and subjeCT To a rEdUction iN shRinkage.
conVenTioNalLy, Sodium has Been addeD tO tHe AlUmiNium mELt in metaLlIc fOrM as StickS Or in alUminiUm caNs Or IN thE form of TAbLETs of A sOdIum cOmpOuNd and WhilE TheSe methoDs have the AdvANtagE oF sImpliciTy they are very InEfficient. OWiNg tO the viOLEnce of thE reaction that occurs much OF the addEd sOdium Is loSt by oxidaTioN and coNsiDErable Smoke gEneraTiOn iS CAused. fREqUenT aDditions arE, THerEfore, NeCessAry and tHe method is very wastEFul, EnvironmentalLy uNfriENDlY anD CaNNot PrOVidE A Controlled amounT of effectiVe ADdItion.
A methOD of OvErcominG these dIsadvANtages iS discloseD in EP-A-0688881. ThiS tEachES A meThod of addiNg sodium To a melt of ALuminIUm Or aluMinIum allOy In wHich aN electROde ComprIsing mOlTen sodIum or A mOlten sodIum compound is immersed in The aluMiniuM meLt and is seParATed From the meLt by A solid-statE elEctRolytE whICh conDuctS SoDiuM Ions. A DireCT voltage iS PrOviDED bEtween that eLECTroDe and The MElt by tHe prOvision of a second eLEctrode in the meLt. WhILE prOviDIng a NuMber of advantagEs iN pRINciple, thIs Technique caN lead to pRoBLems iN the meLt, e.g. if There is ANY fAIlure oF the SolId-state elEctRoLYte contAiNeR.
it is an ObjeCt Of
 which Ro and λ representthe output  impe dan ceof  the  tra nsmission elem e nt 1 20 and a channel lengt h mod ul a tion co effic ient, r e sp e c tiv el y. 
As  c a nbe se enin theabove, whe n t he  load curren t  I load varie s,frequency of  th e seco nd  po l e wil l d riftwhilet he oth er pole r em a ins un c hanged. H ow ever , since the frequ e nc y  drift may sig nifica nt l yc h ang e f requency r es ponse of theL DO v o lta g e regulator,loop instab i lit y mayoc cur due to  insu ff i cie nt phase ma rgin  in somesituat i ons.
In short,the LD O v olt ager eg ul ato rm ays uf fer pro blems of  l oo p ins tabi l i t y  whe n t he l oad c urrent varies . T hisi nve ntion  rela testo  theadditi on of  t race amounts of  met al to a m elt .Itis  part i cularl y c onc erned w ith the add it i o n  o f a metal from Gro up 1 Aof the P eriodi c  T ab l e to a m el t o f an o t her m etal ,  e .g. alum iniumo rzi nc. Thu sthe Gr ou p 1 A m etalm ay b e, for  example  sodi u m or lithium.T he inventioni sm o st pref era bly concern ed w i th t he a d di tio n  of s odium  t o  m o lten aluminium or a nalumin ium a lloy and, alt hough it w i l l  be appr ecia t ed that it is not  inte nded to be limitedthere to, it w ill be de s c ribed fo r c onv eni enc e be low with spec i f ic r ef erencetothose m eta ls. 
Th e a dd ition oftrace am ou nt sof  so dium, e.g. amo un tsle ssthana bout 2 00 pp m, t oan alu miniumm el t is w el lknow n.It  canresu l t i n impro ved quali tyo f ca st in gs andthe castingsca n be moreea sil y remo v a ble from  the mould and subjectt o a red uct ion i n sh rinkage.Con ventio nal l y, sod ium ha s bee nadd e d  to t h e  a lum in ium melt i n met allic  f ormas stic ks or in aluminium can s or in the f orm  oft a bl ets of a s od i umc o mpound and whil e these me th o ds  have thea dva nt age ofsimplic ity t h ey arevery inef ficient.Ow ingt o  th e violence  of thereactiont hat o c cu rs mu chof the  a dde d sod ium is los t byoxidat io n andconsi de rable sm oke generation is cause d. Fre quent  ad ditions a re, the refore, n eces sary and t hemet hod i s v e ry wa stef u l,  en v ironm enta l ly unfrie n dl y a n d  c annot provi d e a c ontro lle d  amoun t of  effective additi o n.
A method of  ove r c omi ngt hese  d isadvantages i s d is c l osed inEP -A-0688881.  This te ac h es amethod  of ad ding so d i um to a m eltofaluminium  or  a l uminium  a ll o y in w hich  a n elec trodec ompr i s ing molten sodiu m ora molte n  so diumco mpoundi s im mersed inthe alumini um mel t an d isseparat ed  fromthe  m elt by a s o lid-state  elec trolyte  w hich  co nducts  sod i u m ion s. A  d ire ct voltag e is pr ov i ded  bet weenth at e lectrodea nd the m elt by thepr ovi s i on ofa  s e c ond electr ode  in t h e  melt. Whi l e pr o vi d ing a  numbe r of a dvantag e s i nprincip le, t his techn ique canl ead  t o pr oblems i ntheme lt,  e .g. if there is  any fai lure oft h e soli d-s t atee lectro ly te container .
Itis an obje c t  of 
 which_Ro and_λ represent the output_impedance of_the_transmission element_120_and a channel_length modulation coefficient,_respectively.
As can be seen_in the above,_when_the load current Iload varies, frequency of the second pole will drift while the_other_pole remains_unchanged._However,_since the frequency drift may_significantly change frequency response of_the LDO_voltage regulator, loop instability may occur due to_insufficient_phase margin in_some situations.
In short, the LDO voltage regulator may suffer_problems of loop instability when the_load current varies._This_invention_relates to the addition_of trace amounts of metal to_a melt.
It is particularly concerned with_the addition of a metal from Group_1A of the Periodic Table to_a melt of another metal,_e.g. aluminium_or zinc. Thus the Group_1A metal may_be, for_example sodium or_lithium.
The invention is most preferably concerned_with the addition_of sodium to molten aluminium or_an_aluminium alloy and,_although_it_will be_appreciated that it_is_not intended_to_be limited thereto, it will be_described_for convenience below with specific reference to_those metals.
The addition of_trace_amounts of sodium, e.g._amounts less than about 200_ppm, to an aluminium melt is_well known._It can_result in improved quality of castings and the castings can be_more easily removable from the mould_and subject to a_reduction in_shrinkage.
Conventionally,_sodium has been_added_to the_aluminium melt in metallic form as sticks_or in_aluminium cans or in the form_of tablets of a_sodium_compound and while these methods have_the advantage of simplicity they are_very inefficient. Owing to the_violence_of_the reaction that occurs much_of the added sodium is lost_by oxidation and_considerable smoke generation is caused. Frequent additions_are,_therefore, necessary and the method is_very_wasteful, environmentally unfriendly and cannot provide_a_controlled_amount of effective addition.
A method_of overcoming these disadvantages is disclosed_in EP-A-0688881. This teaches a method of adding sodium_to a melt_of aluminium or aluminium alloy_in_which_an electrode comprising molten sodium or a molten sodium compound_is immersed_in the aluminium_melt and is separated from the melt by a solid-state_electrolyte which conducts sodium ions. A direct_voltage is provided between that electrode and the melt by the_provision of a second electrode in the melt._While providing a number of advantages in_principle, this technique can_lead_to problems in the melt, e.g. if_there_is_any_failure of the_solid-state electrolyte container.
It_is an object_of