Patterns useful for identification are obtained by automated diffractometer methods. The lattice constants from the experimental work are refined by least-squares methods; reflections are assigned hkℓ indices consistent with space group extinctions. Relative intensities, calculated densities, literature references, and other relevant data are included.

The following new or updated patterns are submitted by the JCPDS Research Associateship at the National Bureau of Standards. The patterns are a continuation of the series of standard X-ray diffraction powder patterns published previously in the NBS Circular 539, the NBS Monograph 25, and in this journal. The methods of producing these reference patterns are described in this journal, Vol. 1, No. 1, p. 40 (1986).The data for each phase apply to the specific sample described. A sample was mixed with 1 or 2 internal standards: silicon (SRM640a), silver, tungsten, or fluorophlogopite (SRM675). Expected 2-theta values for these standards are specified in the methods described (ibid.). Data from which the reported 2-theta values were determined, were measured with a computer controlled diffractometer. Computer programs were used to locate peak positions and calibrate the patterns as well as to perform variable indexing and least squares cell refinement. A check on the overall internal consistency of the data was also provided by a computer program.

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.

The Research Associateship program of the Joint Committee on Powder Diffraction-International Centre for Diffraction Data (JCPDS-ICDD, now known as the ICDD) at NBS/NIST was a long standing (over 35 years) successful industry-government cooperation. The main mission of the Associateship was to publish high quality x-ray reference patterns to be included in the Powder Diffraction File (PDF). The PDF is a continuing compilation of patterns gathered from many sources, compiled and published by the ICDD. As a result of this collaboration, more than 1500 high quality powder diffraction patterns, which have had a significant impact on the scientific community, were reported. In addition, various research collaborations with NBS/NIST also led to the development of several standard reference materials (SRMs) for instrument calibration and quantitative analyses, and computer software for data collection, calibration, reduction, for the editorial process of powder pattern publication, analysis of powder data, and for quantitative analyses. This article summarizes information concerning the JCPDS-ICDD organization, the Powder Diffraction File (PDF), history and accomplishments of the JCPDS-ICDD Research Associateship.

The following new or updated patterns are submitted by the JCPDS Research Associateship at the National Bureau of Standards. The patterns are a continuation of the series of standard X-ray diffraction powder patterns published previously in the NBS Circular 539, the NBS Monograph 25, and in this journal. The methods of producing these reference patterns are described in this journal, Vol. 1, No. 1, p. 40 (1986).The data for each phase apply to the specific sample described. A sample was mixed with one or two internal standards: silicon (SRM640a), silver, tungsten, or fluorophlogopite (SRM675). Expected 2-theta values for these standards are specified in the methods described (ibid.). Data, from which the reported 2-theta values were determined, were measured with a computer controlled diffractometer. Computer programs were used to locate peak positions and calibrate the patterns as well as to perform variable indexing and least squares cell refinement. A check on the overall internal consistency of the data was also provided by a computer program.

No abstract

AB&TRACTIsometric tricalcium aluminate hexahydrate, one of the well-established products of hydration of portland cement, forms complete solid solutions with the corresponding ferrite, 3CaO.Fe20a.6H20, with grossularite garnet, 3CaO.AhOa. 3Si02, and with andradite garnet, 3CaO.Fe20a.3Si02. Members of this solidsolution series were synthesized by hydrothermal methods, and X-ray determinations were made of their crystal structures. To the series belong: (1) The mineral plazolite, 3CaO.AhOa.2Si02.2R20, (2) the major product of hydration of the glass phase in portland cement clinker at elevated temperatures and pressures, and (3) one of the major products of hydration of tetracaleium aluminoferrite.

P ast work on the modificat ion s of manganese dioxide of in terest in dry-cell manu facture is r evie wed. New X -ray da ta, at bo th room and elevaLcd te mperat ures, combined ' with differen t ial hea t ing curves lead to t he co ncl usion that five type of m anga nese dioxide exi t :(1) well-crystallized p yrolu site ; (2) gamm a m a nganese di ox ide, a p oorly crystalli zed pyrol usite; (3) ramsd ellite ; (4) cryp tomelane, a form co n taining esse nt ial p otassium or sodi ulll.; a nd (5) delta m angan ese dioxide, belie ved to be a p oorly crystalli ze d cryptom ela ne. The high-t empera ture X-r ay diffraction da ta indicate d t he phase cha nges t h at ca use th e heatingcur ve effects. A new cr ystal fo rm of man gan osic oxide (Mn30 4), stable a bove 1,170 0 C, w~s fo und t o be cubic of spinel structure. Fincness dcten n in aLion by b oth t hc ni t rogen a dsorpt ion and Lhe X-ray line broadening m e thod s were m ad e on selected sam p les.