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The glass-forming regions for the sodium borate system were determined using a roller-quencher. The new regions are R =O to 0.8 and R =1.2 to 4.9 for samples prepared from sodium carbonate (where R =mol% Na20/mol% B203). Above R =2 .O retention of' C02 occurs. Quantitative measures of C 0 2 retention as a function of R are reported. The results using sodium carbonate extend by a considerable amount the limits reported by Imaoka and are comparable to the recent data of Ota and Soga. 52402 N RECENT years the Krogh-Moe model for Ialkali-borate glasses has been highly successful. Glasses are viewed as mixtures of crystalline units of related compositions. The important composition parameter in the model is R , the ratio of mol% alkali oxide to mol% boron oxide. However, a significant restriction in its applicability has been the limited compositions in which alkali borate glasses have been formed. Imaoka' performed an early study (1962) of the ranges of glass formation. Figure 1 reports his findings for the sodium borate system. The purpose of the present study was to use an originally designed roller-quencher to extend the glass-forming region for the sodium borates and to make these samples available to interested research groups. EXPERIMENTAL METHODIn the original work of Imaoka,s.h 1to 3-g melts were air-cooled in platinum crucibles. For many spectroscopic studies much smaller samples will suffice. Consequently, it was decided to use a rollerquencher to effect more rapid cooling while producing samples of suitable size.The roller-quencher consisted of two copper cylinders each 13 cm in diameter and 0.4 cm in wall thickness. The cylinders, having steel end plates and axles, were mounted in roller bearings and dynamically balanced. A 373,W (h hp) elec-tric motor was used to drive the rollers to angular frequencies of =60 Hz. The assembly, including an electric muffle furnace, was placed in a glove box through which dry nitrogen gas was passed. (This precaution was taken because glasses with a high sodium content are extremely reactive with the atmosphere.)Many glass structure laboratories use much simpler methods to form glasses, e.g. air-cooling and rapid cooling between brass plates. In the present study, glasses were made using these techniques to check the glass formation limits of each method. Aircooling was performed by allowing drops to cool on a brass plate and rapid cooling was performed using two plates (15 by 15 cm, 0.3 crn thick) which were pressed together very quickly just after the melt was poured.Batches (= 10 g) of boric acid and sodium carbonate were mixed and heated in a platinum crucible for periods of 0.5 to 0 0 8 . 8 8 f B 0 a*! c. t I I I I 0.0 I .o 2.0 3.0 4.0 5.0 6.0 R Fig. I. Glass-forming regions for the sodium-borate system. (a) Present work: (top) air cooling of drops on brass plate, (middle) best result& using roller-quencher, (bottom) rapid cooling between brass plates. (b) Ref. 8: Best results using roller-quencher. ( c ) Ref. 5: Air cooling in platinum crucible.( -) Glass-formi...