Th e effect of sm all oxid e a dd itions on t he p olym orp hism of Bi,03 was studied by m eans of high-temperat ure x-ray diffrn,ctom etr y. Soli d us a nd occasiona l li q uidus temperatu res were approximated, so t hat te ntat ive partial phase diagra ms for 33 ox ide a dd ilions were con stru cted. Only t he m on ocli ni c a nd t he cubic f orms of B i, 0 3 were f ound to be stab le. Oth er phases, frequ en tly reported by p revious in vestigators, s uch as tetrago na l a nd bod ycentered cubic (b .c.c.), were shown to f orm m etastably fr om cooled liquid or eu bie. Au impure b. c.c. ph ase of distin ct but varia~~e e om pos i~i o n apI;eared in systems of ZnO,. Pb O, 1320 3, AI,03, Ga203, Fe, 0 3, S10 " GeO" 110 " a nd 1 , 0 5, lhe Im p ure b.c.c. p hase 111 t he s~' stem s with SiO" GeO" and Ti O, m elted congruently abo ut 100°C above the m .p. of 13 i,0 3' Th e im p ure b.c.c. p hase was f orm ed m etastably in s. vstems w it h R.b20, N iO, MnO, C d O, V, 0 5, an d Nb, 0 5; t he cond itions of fo rmation we re dependent on COHlposit ion, preparation, and heatin g sc hed ules. The impure b.c.c. p hases, bolh stabl e and metastable, had sm a ll er uni t cell dim ensions l han thal of pure Bi,0 3'

Stabili ty relationships of t he four p oly m orp hs of bismu t h oxide have been dct erJlIin ed by m eans of DTA a nd high-temperat ure x-ray studies. The stable low-temperature m onoclinic form t ransform s to the stabl e cubic form at 730 ± 5 ac, whi ch then m elts at 825 ± 5 ac.By controlled coolin g, t he m etastable tetragonal ph ase and/ o r t he metastable bod v-ce n te red cubic (b. c.c.) phase ap pear at about 645 ac. Wh ereas b. c.e. can be prese r ved to i·oom temperature, tetrago na l \\"ill transform to m onocli nic bct\\'een 550 a nd 500 ac. T etragona l Bi, 0 3, h owever, is easil y prepa red by decom posin g bismu t ite (B i, 0 3·CO,) at 400 ac for se vera l h ours. Th e g reatest transit ion expa nsion occurs at t h e m on ocl inic to cubic in versio n, an d cubi c 13i,03 shows t he g reatest coeffi cient of vo lum e expansion. vVi th exposure to a ir, 13 i, 0 3 carbo nates a nd pa r tiall y t ra nsforms to bismu tite a nd a n u nkno,yn ph ase.

The phase diagram for the system Bi2O3‐B2O3 has been determined experimentally. The melting point of Bi2O3 has been redetermined as 825° C with an estimated overall uncertainty of about ±3°C, and the molal heat of fusion of Bi2O3, calculated from the slope of the liquidus curve, is 2050 cal per mole. The system contains a body‐centered cubic phase of approximate composition 12Bi2O3·B2O3, which melts incongruently at 632°C. Four congruently melting compounds exist in the system: 2Bi2O3· B2O3·5B2O3, Bi2O3·3B2O3, and Bi2O3·4B2O3, with melting points, respectively, of 675°, 722°, 708°, and 715°C. The Bi2O3·4B2O3 compound exhibits a sluggish transformation at 696°C. Compositions containing up to 97.5 wt% (85 mole %) Bi2O3 can be partly or totally quenched to glass. Indices of the quenched glasses are greater than 1.74. A region of liquid immiscibility extends at 709°C from almost pure B2O3 to 19.0 mole % Bi2O3. The extent of immiscibility theoretically calculated agrees with the experimentally determined value when 1.20 A is used for the ionic radius of Bi3+.

The phase equilibrium diagram for the system Laz03-Bz03 has been determined experimentally. The compounds Laz03.3Bz03 and Laz03.-BzO3 melt congruently at 1141" f 5°C. and 1660" f 15"C., respectively. At 1488' f SOC., Laz03.-Bz03 inverts from the aragonite-type structure to a high-temperature form. Trilanthanum borate, 3LaZO3.BZO3, melts incongruently at 1 3 8 6 O f 5OC. to give liquid and La208. No solid solutions exist in the system. A region of liquid immiscibility exists in the system and extends at 1136' f 5°C. from almost pure B 2 0 3 to 21.5 mole ' % La203. The eiperimental value for the extent of immiscibility agrees with that calculated from theoretical considerations. A second method for estimating immiscibility in the system is demonstrated, which requires experimentally only the determination of t h e index of refraction of the modifier-rich liquid. FVinciples governing immiscibility are discussed.

A phase equilibrium diagram of the system BaO-B20 3 has been constructed fr om data obtained essentiall y by the quenching method. Four congruently m elting compounds were identifi ed: BaOAB20 3, melting at 879° ± 5° C; BaO.2B20 3, melting at 900° ± 5° C; BaO.B20 3, melting at 1,095° ± 5° C; and 3BaO.B20 3, melting at 1,383° ± 5° C . Some optical properties of these compounds were determined with the petrographic microscope, and X-ray d.ffraction data suitable for their id entification were obtained. Barium m etaborate, BaO.B20 3, s howed an inversion occurring between 100° and 400° C. Mixtures contain ing less than 30 p ercent of BaO were found to eparate on fu sion into two li quid layers, one of which contained 30 p ercent of BaO, wherea t he other was nearly pure 1320 3• A curve showing indices of refraction of the quenched glasses is also presc ntcd.

A phase equilibrium diagram for t he system BaO-B, 0 3-S iO, has bee n co n s~ru c te d fr·om data, o btained esse ntiall y by th e quenching met hod, o n 178 te rnary co mpOS it IOn s . One ne w co mpo und, 3Ba· 03B, 9 3· 28 i9" melt in g .at 1,009: C a n.d pos~ess in g an ext~·e m e l y ,t1at primary fi e ld appears, and Its op t ical prope rt ies and X-ray dIffractIOn data a re ~I ve n . [he BaO· 4B,0 3 and 8 iO, prima r y phase areas lllclude alm ost 70 perce nt of t he diagram , a nd o ver these areas exis ts a large region of t wo-liquid immiscibili ty. Limi ted da ta indi cates t hat t he immiscibi lity ga p dec reases wi t h increasing te mpe rat ure. The solid so lu t io n regio n betwee n 2BaO · 38 iO, and BaO·2SiO, ex te nds in to t he in te ri o r of t he diagram a nd is co mplex in nat ure. An isofr-a ct diagram fo r t he quenc hed glasses is s hown . F or precise te mpe rat ure con t ro l of a qu enchin g furn ace, a self-adjustin g, bridge-ty pe con t roll er is desc r ibed briefly .

The shape of the immiscibility volume in the system BaO‐B2O3‐SiO2 is determined from data on seventeen compositions. The ternary critical solution curve originates at the critical point in the binary system BaO‐B2O3, located at 1225°C. and 15 weight % BaO. It extends almost linearly to its terminus on the silica primary‐phase surface, at about 1405° C. and the composition 18 weight % BaO, 10.5% B2O3, 71.5% SiO2. By extrapolation of the ternary critical solution curve, the critical point of the postulated meta‐stable immiscibility region in the binary system BaO‐SiO2 is located at 1430° C. and 18.5 weight % BaO.

A phase-equilibrium diagram of the system BaO-BZOa has been constructed from data obtained essentially by the quenching method. Four congruently melting compounds were identified: Ba0.4B20a, melting at 879 * 5°C.; Ba0.2BzO~. melting at 900 * 5OC.; Ba0.B208, melting a t 1095 * 5°C.; and 3Ba0.Bz03, melting at 1383 * 5°C. Some optical properties of these compounds were determined with the petrographic microscope, and X-ray diffraction data suitable for their identification were obtained. Barium metaborate, BaO. Bz03, showed an inversion occurring between 100" and 400°C. Mixtures containing less than 30% BaO were found to separate, on fusion, into two liquid layers; one layer contained 30% BaO and the other was nearly pure B~03. A curve showing indices of refraction of the quenched glasses is presented.ABSTRACT Data are presented to indicate the influence of slip preparation methods on the dry and fired properties of cast high-voltage electrical porcelain. The factors investigated include length of mixing period, sequence of electrolyte addition, aging, blunging versus ball milling, micropulverizing of constituents before blunging, filtering and reblunging application of vacuum to slip, and use of heated water. Wet ball milling influenced the