The System MgO-MgCl2-H2O at 23°C

Solubilities of MgO in aqueous HC1 solutions at 23°±3°C were measured and combined with analyses of neat magnesium oxychloride cements, cured in sealed containers, to construct an equilibrium phase diagram for the system MgO-MgCl₂-H₂O. Specific gravities and acidities of solutions saturated with MgO and relative humidities of vapor phases over sealed samples were measured and combined with XRD data to define the compositions in equilibrium with two crystalline phases. Studies of relative reaction rates indicated that the 5–1–8 phase crystallizes more rapidly than the 3·1·8 phase and that cements near the 3·1·8 composition react rapidly with atmospheric CO₂ to form the chlorocarbonate phase.     

The System CaO-Al2O3-H2O

Phase equilibria have been determined in the system CaO-Al₂O₃-H₂O in the temperature range 100° to 1000°C. under water pressures of up to 3000 atmospheres. Only three hydrated phases are formed stably in the system: Ca(OH)₂, 3CaO·Al₂O₃·6H₂O, and 4CaO·3Al₂O₃-3H₂O. Pressure-temperature curves delineating the equilibrium decomposition of each of these phases have been determined, and some ther-mochemical data have been deduced therefrom. It has been established that both the compounds CaO·Al₂O₃ and 3CaO·Al₂O₃ have a minimum temperature of stability which is above 1000°C. The relevance of the new data to some aspects of cement chemistry is discussed.     

The System CaO-Al2O3-P2O5-H2O at 200°C

The phase relations were established experimentally for the system CaO-Al₂O₃-P₂O₅-H₂O at 200°C and 1710 kPa. The quaternary compound, crandallite, CaAl₃(PO₄)₂(OH)₅· H₂O, was found to be stable. Compatibility joins in the system were determined. The phase relations are presented on the isothermal-isobaric 90 wt% water plane and by projecting the primary fields of the liquidus surface onto the same plane.     

Effect of Starting Materials on Phase Relations in the System CaO—Al2O3—H2O

Phase relations in the system CaO-Al₂O₃-H₂O from 40° to 500°F have been determined by hydrothermal techniques. Very high purity starting materials (luminescent-grade CaCO₃) must be used if the correct phase relations for this system are to be determined. A phase diagram of the system made by using reagent-grade CaCO₃ is compared with the diagram obtained from the luminescent-grade material. The general effect of introducing foreign ions into the system is to promote the formation of the dicalcium aluminate hydrate phase. Adding various clay structures to starting mixtures had relatively little influence on the resulting phases. The action of additives on calcium aluminate cements depends on such factors as the phase relations, the nature of the hydrated alumina, and the interrelations of these factors with variable pH, foreign ions, and pressure-temperature variations.     

High-Temperature Phase Relations in the System Gd2O3-Ta2O5

The Phase relations of the system Gd₂O₃-Ta₂O₅ in the composition range 50 to100 mol% Gd2O3 was studied by solidstate reactions at 1350°, 1500°, or 1700°C and by thermal analyses up to the melting temperatures. Weberite-type orthorhombic phase (W2 phase, space group C2221) with the composition of Gd3 TaO7 seems to melt incongruently; at about 2040°C, although this Gd₃TaO₇ Phase was previously reported to melt congruently. A new fluorite-type cubic phase (F phase, space group Fm3m ) was found for the first time above 1500°C in the system. It melts congruently with the composition of about 80mol% Gd2O3at 2318° 3°C. A phase diagram was proposed for the system Gd₂O3–Ta2O₅ in the Gd₂O₃–rich portion     

Phase Equilibria in the System Na2O – Nb2O5

Phase equilibria data, obtained both by differential thermal analysis and by quenching, are presented for the system Na₂O-Nb₂O₅. Five compounds corresponding to the formulas 3Na₂O.1Nb₂0₆, lNa₂O. 1Nb₂O₅, lNa₂O 4Nb₂O₆, lNa_zO.7Nb₂O₅, and lNa₂O. 10Nb₂O₆ have been found. The compound 3Na_z0.lNb₂O₅ melts congruently at 992°C. The compounds 1Na₂O. 4Nb₂O₆, lNa₂O.7Nb₂O, and 1Na₂O. 1Onb₂O₅ melt incongruently at 1265°, 1275°, and 1290°C., respectively. The well-known perovskite structure phase NaNbO₃ was found to melt congruently at 1412°C. The transition temperatures in NaNbO₅ were checked by thermal analysis and only the major structural changes at 368° and 640°C. could be detected. A new disordered form of NaNbO₃ could be preserved to room temperature by very rapid quenching.     

The Formation of Magnesium Oxychloride Phases in the Systems MgO-MgCl2-H2O and NaOH-MgCl2-H2O

The reactions leading to the formation of crystalline Mg₃(OH)₅Cl·4H₂O (phase 5), Mg₂(OH)₃,Cl·4H₂O (phase 3), and Mg(OH)₂ are compared for the systems MgO-MgCl₂-H₂O and NaOH-MgCl₂-H₂O. The crystalline phases were determined by X-ray diffraction analysis. The concentration of the total magnesium and chloride in the solution and the pH of the solution determine the reaction product(s) in both systems. The influence of MgO reactivity and the molar ratio of reactants on the formation and stability of reaction products is discussed and the mechanism of the formation of phases 3 and 5 is explained. In the system MgO-MgCl₂-H₂O, MgO serves only to increase the concentration of total magnesium and the pH of the MgCl₂ solution.     

Phase Formation in the System Na2O · Al2O3-CaO · A12O3-Al2O3 at 1200°C in Air

Phase relations in the system Na₂O_· Al₂O₃-CaO· Al₂O₃-Al₂O₃ at 1200°C in air were determined using the quenching method and high-temperature X-ray diffraction. The compound 2Na₂O · 3CaO · 5Al₂O₃, known from the literature, was reformulated as Na₂O · CaO · 2Al₂O₃. A new compound with the probable composition Na₂O · 3CaO · 8Al₂O₃ was found. Cell parameters of both compounds were determined. The compound Na₂O · CaO-2Al₂O₃ is tetragonal with a = 1.04348(24) and c = 0.72539(31) nm; it forms solid solutions with Na₂O · Al₂O₃ up to 38 mol% Na₂O at 1200°C. The compound Na₂O · 3CaO · 8Al₂O₃ is hexagonal with) a = 0.98436(4) and c = 0.69415(4) nm. The compound CaO · 6Al₂O₃ is not initially formed from oxide components at 1200°C but behaves as an equilibrium phase when it is formed separately at higher temperatures. The very slow transformation kinetics between β and β "-Al₂O₃ make it very difficult to determine equilibrium phase relations in the high-Al₂O₃ part of the diagram. Conclusions as to lifetime processes in high-pressure sodium discharge lamps can be drawn from the phase diagram.     

Studies in Germanium Oxide Systems: I, Phase Equilibria in the System Li2O—GeO2

Phase equilibrium relations in the system Li₂O-GeO₂ were determined using standard quenching techniques. In contrast to published literature five congruently melting compounds were found to exist. They are Li₂O·7GeO₂, 3Li₂O O·8GeO₂, Li₂O O·GeO₂, 3Li₂O O·2GeO₂, and 2Li₂O.-GeO₂. The melting points, respectively, are 1033°± 5°C, 953°± 5°C, 1245°± 15°C, 1125°± 15°C, and 1280°± 15°C. Simple binary eutectic relations exist among the compounds. The eutectic temperature between 1:7 and GeO₂ is 1025°± 1h0°C at about 96.8 wt% GeO₂; the eutectic temperature between the 1:7 and 3:8 compounds is 935°± 10°C at about 90.9 wt% GeO₂; the eutectic temperature between the 3:8 and 1:1 compounds is 930°± 10 °C at about 89.8 wt% GeO₂. Liquidus data for compositions richer in lithia than the 1:1 compound are only approximate because of the difficulty of quenching them; the phase relations between the 1:1 and 3:2 and between the 3:2 and 2:l compounds, however, are found to be of the simple binary eutectic type. The glass–forming region was also determined. Melts allowed to cool in air crystallized. When, however, the melts were quenched, glasses containing as much as 8 wt% GeO₂ could be prepared in 5–g quantities. Both the refractive index–composition and density–composition curves for the glasses showed maxi–mums at about 6 to 8 wt% Li₂O.     

Revised ThO2-Nb2O5 Phase Diagram

The phase equilibrium diagram of the system ThO₂-Nb₂O was redetermined near the composition Th₂Nb₂O₉. This phase was found to melt incongruenlly at 1362°C, with a eutectic temperature at ∼1350°C. The peritectic and eutectic compositions must occur between 60 and ∼64 mol % ThO₂. From single crystal and powder X-ray diffraction data, Th₂ Nb₂O₉ was found to have a primitive monoclinic unit cell with a = 6.711(1), b = 25.254(5), c=7.757(1)×10⁻¹nm, β=90.46 (1)°.     

Studies in Lithium Oxide Systems: II, Li2O Al2O3–Al2 O 3

Solid-state reactions between Li₂O and Al₂ O₃ were studied in the region between Li₂O.Al₂ O ₃ and Al₂ O ₃. The compound Li₂ O Al₂ O ₃ melts at 1610°± 15°C. and undergoes a rapid reversible inversion between 1200° and 1300°C. Vaporization of Li₂ O from compositions in the system proceeds at an appreciable rate at 1400°C, as shown by fluorescence. Lithium spinel, Li₂ O -5Al₂O₃, was the only other compound observed. The effect of Li₂ O on the sintering of alumina was investigated.     

Melting Phenomena in the System CaO–SiO2– H2O: I, The Join Ca2SiO,-Ca(OH)2

The liquidus-solidus relations along the join Ca₂SiO₄-Ca(OH), in the system CaO-SiO₂-H₂O have been determined at 1000 atm up to 1110°C. This join is binary and contains the calcium silicate hydrate, calciochondrodite, Ca5-(SiO₄(OH)₂. Calciochondrodite melts incongruently to Ca₂SiO₂+ liquid (composition 23 wt% Ca₂Si0₄) at 955°C. The eutectic between calcium hydroxide and calciochondrodite lies at 13% Ca₂Si0₄ and 822°C. Preliminary experiments, also at 1000 atm, in the ternary system CaO-Ca₂Si0₄-Ca(OH), indicate that the eutectic at which the fields of primary Ca(OH)₂, CaO, and Ca₂(Si0₄)₂(OH)₂ meet is close to the CaO-Ca. (OH), side of the triangle at approximately 805° C. The ternary reaction point Ca₂SiO_l+ liquid ⇌Ca₅(SiO₄)₂(OH)₂+ CaO + liquid is believed to lie in the low-CaO (<5%) high-Ca(OH)₂ (>70%) part of the system.     

Volume Relations in Na2O·B2O3 and Na2O·SiO2 B2O3, Melts at 1300·C

Density (and some viscosity) data are presented for binary sodium borate melts containing as much as 60 mole % Na₂O and for ternary sodium silicoborate melts with B/Si <2.0 between 1000°C and 1300°C. The high-temperature partial molar volume analysis of the binary sodium borate melts reveals about 50% BO₄ tetrahedra at the 40 mole % Na₂O composition, in agreement with recent NMR estimates for the binary glasses. No "boron anomaly" was found near 18 mole % Na₂O at high temperature. The synthetic partial molar volume model that agrees best with experiment for all ternary melts studied involves the presence of some BO₄ tetrahedra, the percentage of which varies with composition. This ternary model involves a high degree of internal consistency. No tendency toward extensive micro-immiscibility was observed for ternary melts near the SiO₂·B₂O₃ binary.     

High-Temperature Phase Relations in the System Y2O3-Ta2O5

The phase relations for the system y₂o₃–Ta₂o₅ in the composition range 50 to 100 mol% Y₂O₃ have been studied by solid-state reactions at 1350°, 1500°, or 17000C and by thermal analyses up to the melting temperatures. Weberite-type orthorhombic phases (W2 phase, space group C222₁), fluorite-type cubic phases (F phase, space group Fm3m )and another orthorhombic phase (O phase, space group Cmmm )are found in the system. The W2 phase forms in 75 mol% Y₂O₃ under 17000C and O phase in 70 mol% Y₂O₃ up to 1700°C These phases seem to melt incongruently. The F phase forms in about 80 mol% Y₂O₃ and melts congruently at 2454° 3°C. Two eutectic points seem to exist at about 2220°C 90 mol% Y²O₃, and at about 1990°C, 62 mol% Y₂O₃. A Phase diagram including the above three phases were not identified with each other.     

Mullite Crystallization from SiO2-Al2O3 Melts

SiO₂-Al₂O₃ melts containing 42 and 60 wt% A1₂O₃ were homogenized at 2090°C (∼10°) and crystallized by various heat treatment schedules in sealed molybdenum crucibles. Mullite containing ∼78 wt% A1₂O₃ precipitated from the 60 wt% A1₂O₃ melts at ∼1325°± 20°C, which is the boundary of a previously calculated liquid miscibility gap. When the homogenized melts were heat-treated within this gap, the A1₂O₃ in the mullite decreased with a corresponding increase in the Al₂O₃ content of the glass. A similar decrease of Al₂O₃ in mullite was observed when crystallized melts were reheated at 1725°± 10°C; the lowest A1₂O₃ content (∼73.5 wt%) was in melts that were reheated for 110 h. All melts indicated that the composition of the precipitating mullite was sensitive to the heat treatment of the melts.     

The Al2O3-Nd2O3 Phase Diagram

A tentative phase diagram for the system Al₂0₃-Nd₂O₃ is presented. Three compounds were obtained: a β -A1₂O₃-type compound, the perovskite NdAlO₃, and Nd₄Al₂O₉. The perovskite melts congruently (mp 2090°C), and the two other compounds exhibit incongruent melting behavior: β -Nd/Al₂O₃, mp 1900°C; Nd₄Al₂O₉, mp 1905°C. Two eutectics exist with the following compositions and melting points: 80 mol% Al₂O₃, 1750°C; 23 mol% Al₂O₃,1800°C. Nd₄Al₂O9 decomposes in the solid state at 1780°C.     

Phase Relations in the System Li2O-ZrO2-SiO2

Phase relations in the system Li₂O-ZrO₂-SiO₂ are characterized by four invariant points. Two eutectics occur at 1016°C and 29:3:68 (mol% Li₂O:ZrO₂:SiO₂) and at 1005°C and 32:5:53. One peritectic point was found at 1043°C and 31:113:56, whereas the other is inferred from the present and previous investigations. No ternary phases are stable in the system .     

Studies in Germanium Oxide Systems: II, Phase Equilibria in the System Na2O—GeO2

Phase equilibrium relations in the system Na₂O-GeO₂ have been determined using standard quenching techniques supplemented by differential thermal analysis. Two congruently melting compounds, Na₂O·GeO₂ and 2Na₂O·9GeO₂, exist; the melting points are 1103°± 15°C and 1073°± 3°C, respectively. The eutectic temperature between GeO₂ and 2Na₂O·9GeO₂ is 950°±f 10°C at 94.5 wt GeO₂. The eutectic temperature between 2Na₂O · 9GeO₂ and Na₂O·GeO₂ is 790° f 10°C at about 75 wt% GeO₂. Both the refractive index and the density of glasses in the system Na₂O-GeO₂ exhibit maximum values at about 16 to 18 mole % Na₂O. The Ge-O-Ge absorption band at 890 cm⁻¹ shifts toward lower wave numbers with the addition of Na₂O.     

The System SiO2–P2O2

Phase relations in the binary system between SiO₂-P₂O₅ and SiO₂ were investigated by the quenching method using sealed platinum tubes to prevent the loss of P₂O₅. The compound Si0₂-P₂O₅ exists in two forms, the low-temperature β form inverting sluggishly but reversibly to the high-temperature β form at 1030°C. The β form melts congruently at 1290°C. The compound 2SiO₂-P₂O₅ melts incongruently at 1120°C to a silica-rich liquid and SiO_a-P₂O₅. In the region between 5 and 25 mole % PO₂, reactions were so sluggish that no data could be obtained by quenching.     

Phase Relations in the Garnet Region of the System Y2O3–Fe2O3–FeO–Al2O3

Liquidus equilibrium relations for the air isobaric section of the system Y₂O₃–Fe₂O₃–FeO–Al₂O₃ are presented. A Complete solid-solution series is found between yttrium iron garnet and yttrium aluminum garnet as well as extensive solid solutions in the spinel, hematite, orthoferrite, and corundum phases. Minimum melting temperatures are raised progressively with the addition of alumina from 1469°C in the system Y–Fe–O to a quaternary isobaric peritectic at 1547°C and composition Y _0.22 Fe _1.08 Al _0.70 O _2.83* Liquidus temperatures increase rapidly with alumina substitutions beyond this point. The thermal stability of the garnet phase is increased with alumina substitution to the extent that above composition Y _0.75 Fe _0.65 Al _0.60 O ₃ garnet melts directly to oxide liquid without the intrusion of the orthoferrite phase. Garnet solid solutions between Y _0.75 Fe _1.25 O ₃ and Y _0.75 Fe _0.32- Al _0.93 O ₃ can be crystallized from oxide liquids at minimum temperatures ranging from 1469° to 1547°C, respectively. During equilibrium crystallization of the garnet phase, large changes in composition occur through reaction with the liquid. Unless care is taken to minimize temperature fluctuations and unless growth proceeds very slowly, the crystals may show extensive compositional variation from core to exterior.