Vinylphosphonic acid-modified calcium aluminate and calcium silicate cements

Cementitious materials in terms of calcium phosphate cements (CPC) were prepared through the acid-base reaction between vinylphosphonic acid (VPA) and calcium aluminate cement (CAC) reactants or calcium silicate cement (CSC) reactants at 25 °C. Using CAC, two factors were responsible for the development of strength in the cements: one is the formation of an amorphous calcium-complexed vinylphosphonate (CCVP) salt phase as the reaction product, and the other was the high exothermic reaction energy. Because the formation of CCVP depletes the calcium in the CAC reactants, Al₂O₃·xH₂O gel was precipitated as a by-product. CCVP amorphous calcium pyrophosphate hydrate (CPPH) and Al₂O₃·xH₂O -AlOOH phase transitions occurred in the CPC body autoclaved at 100 °C. Increasing the temperature to 200 °C promoted the transformation of CPPH into crystalline hydroxyapatite (HOAp). In the VPA-CSC system, the strong alkalinity of CSC reactant with its high CaO content served in forming the CPPH reaction product which led to a quick setting of the CPC at 25 °C. Hydrothermal treatment at 100 °C resulted in the CPPH HOAp phase transition, which was completed at 300 °C for both the VPA-CAC and VPA-CSC systems, and also precipitated the silica gel as by-product. Although the porosity of the specimens was one of the important factors governing the improvement of strength, a moderately mixed phase of amorphous CPPH and crystalline HOAp as the matrix layers contributed significantly to strengthening of the CPC specimens.     

Free volume and mechanical properties of Palacos® R bone cement

The free volume and the mechanical properties of Palacos® R bone cement were determined from positron annihilation lifetime spectroscopy (PALS) and from dynamic mechanical thermal analysis (DMA) in the temperature ranges 24–220 °C and 30–120 °C, respectively. The heating of bone cement caused an appreciable reduction of the free volume, measured as a decrease in the ortho-positronium lifetime ₃ from 2.04 to 1.91 ns, as well as a clear increase in the storage modulus from 2.3 to 3.0 GPa. The changes in free volume and storage modulus after the heat treatment were interpreted as an effect of elimination of residual monomer from the bone cement. The free volume of the bulk-polymerized phase of bone cement was estimated from a simple difference method, suggesting that the residual monomer was eliminated from the bone cement between 60 and 90 °C, thus implying a glass transition temperature of only 60 °C for the bulk-polymerized phase. The spherical free volume cavity size estimated from the ortho-positronium lifetime V(₃), and the storage modulus E_storage from DMA measurements were found to correlate by a linear relationship throughout the studied temperature range, and the correlation appeared to be independent of the presence of residual monomer.     

Pressure-pulsed chemical vapour infiltration of SiC to porous carbon from a gas system SiCl4-CH4-H2

SiC matrix was deposited into porous carbon from a gas system SiCl₄-CH₄-H₂ in the temperature range 900–1200 °C using pressure-pulsed chemical vapour infiltration (PCVI) process. At 1000 °C, silicon single phase, a mixed phase of (Si + SiC), and SiC single phase, were detected by X-ray diffractions for specimens obtained with the reaction time per pulse of 1, 2–3, and 5 s, respectively. At 1100 °C, SiC single phase was obtained with a reaction time of only 0.3s. Between 1050 and 1075 °C, deposition rate accelerated suddenly. The increase of SiCl₄ concentration increased the deposition rate linearly up to 4%–6%. The residual porosity decreased from 29% to 6% after 2×10⁴ pulses of CVI at 1100 °C, and the flexural strength was 110 MPa.     

Electrical conductivity in hot-pressed nitrogen ceramics

The a.c. and d.c. electrical conductivities of some hot-pressed polycrystalline nitrogen ceramics have been measured between 400 and 1000° C. The materials examined were Si₃N₄, 5.0% MgO/Si₃N₄ and two sialons, Si_(6–z) · Al _z · O _z · N_(8–z) having z 3.2 and z 4.0 respectively. The electrical behaviour of all the materials showed similar general features. The d.c. conductivities were about 10^{–10 –1} cm^–1 at 400° C and rose to between 10^–6 and 10^{–5 –1} cm^–1 at 1000° C. The a.c. Data, taken over the frequency range 15 Hz to 5 kHz showed that below about 500° C the a.c. conductivity ( _a.c.) varied with frequency as _a.c. ^s where 0.7 _d.c.) agreed well with the relation _d.c. = A exp(–B/T ^1/4). Above 700° C both the a.c. and d.c. conductivities followed log T ^–1. Hall effect and thermoelectric power measurements enabled the Hall mobility to be estimated as less than 10^–4 cm² V^–1 sec^–1 at 400° C and showed that the materials were all p-type below 900° C and n-type above 900° C. The electrical properties of all four materials are consistent with the presence of a glassy phase.     

Structural and electrical conductivity studies on (M,V)-TiO2 (M=Al, Cr, Fe) rutile solid solutions at high temperature

In this study, M _x Ti_0.91–1.82x V_0.09+0.82x O₂ (0x0.1; M=Al, Cr, Fe) solid solutions have been synthesized by ceramic method and characterized by X-ray diffraction and electron microscopy. The results indicate that rutile solid solutions stability depends on the trivalent cation (M). Solid solutions are stable at 1000 °C, but only when M=Cr is a single phase with rutile structure obtained at 1400 °C. The electrical behavior of the system studied corresponds to extrinsic p-type semiconduction and electrical conductivity is related to the stability of rutile solid solutions.     

Effect of heating temperature on dielectric properties of Pb(Zr,Ti)O3 [PZT] fibers

Ferroelectric Pb(Zr_0.53Ti_0.47)O₃ fibers were reproducibly fabricated by sol-gel technique using triethanolamine (TEA) complexed alkoxide. The phase transition from pyrochlore to perovskite took place about 400°C and a stable single perovskite phase was obtained at 550°C. PZT gel fibers spun through nozzle were heat-treated at 700°C, and at 1000°C for 1 h to certify the effect of heat-treatment temperature on the electrical properties. The PZT fibers had elliptical cross sections with diameter of 72 m–92 m, and dense microstructure was obtained by heating at 1000°C. In the PZT fibers heat-treated at 1000°C, a distinguishable relative permittivity peak and a pyroelectric current peak were observed at their Curie temperature. The P-E hysteresis loops of the crystalline PZT fibers were also observed.     

Phase equilibrium,microstructure and properties of some magnesite-chromite refractories

The effect of phase equilibrium and microstructure of magnesite-chromite batches containing from 0 to 100% Egyptian chrome ore, with intervals of 10%, on their physical properties was studied. The phase equilibrium data were calculated using the phase relationships within the system M-M₂S-CMS-MR (M=MgO, S=SiO₂, C=CaO, R=R₂O₃). A computerized electron-probe microanalyser was applied to study the microstructure as well as microchemistry of the fired magnesite-chromite co-clinkers. Some physical and technological properties of the co-clinkered briquettes were also investigated by determining densification parameters, spalling resistance and load-bearing capacity.It is concluded that dense, spalling resistant and refractory magnesite, magnesite-chrome and chrome-magnesite refractories could be produced by co-clinkering of magnesite-chromite batches of 1000, 7030 and 3070 weight ratios, respectively, at 1600 °C. The prepared co-clinkers were subsequently graded, moulded and refired up to 1700 °C in order to obtain direct-bonded bricks. Meanwhile, dense chromite refractories with lower refractory quality could be processed by firing the Egyptian chrome ore up to 1600 °C.     

The effect of MgAl2O4 on the formation kinetics of Al2TiO5 from Al2O3 and TiO2 fine powders

The formation of Al_2(1–x)Mg _x Ti_(1+x)O₅ solid solutions from Al₂O₃-TiO₂-MgAl₂O₄ powder mixtures of 1 m particle size and moderate purity has been studied at 1300°C for different final composition values: x=0 (pure Al₂TiO₅), 10^–3, 10^–2 and 10^–1. Analysis of the kinetic data and microstructural observation indicates that MgAl₂O₄ affects the mechanism of Al₂TiO₅ formation by providing active nuclei for the growth of the new phase. These nuclei are probably constituted by Mg_0.5AlTi_1.5O₅, i.e. the equimolar Al₂TiO₅-MgTi₂O₅ solid solution, and are formed by reaction between MgAl₂O₄ and TiO₂ at temperatures above 1150 °C. As the value of x increases, the number of titanate particles per unit volume accordingly increases and the conversion of the original oxides is faster. At values of x10^–2, the prevailing mechanism is the nucleation and growth of Al₂TiO₅ nodules for fractional conversion up to 0.8. Further conversion of the residual Al₂O₃ and TiO₂ particles dispersed into the titanate nodules is slower and controlled by solid-state diffusion through Al₂TiO₅. At x=0.1, a large number of nucleation sites is present, and solid-state diffusion through Al₂TiO₅ becomes important even in the initial stage of reaction, as the diffusion distances are strongly reduced. The study of Al₂TiO₅ formation under non-isothermal conditions in the temperature range 1250–1550°C shows that reaction proceeds between 1300 and 1350 °C for x=0.01 and between 1250 and 1300 °C for x=0.1. Densification of the titanate becomes important at temperatures above 1300°C for x=0.1, but only above 1450 °C for x=0.01.     

Optical and structural properties of (Ba, Sr)TiO3 thin films grown by radio-frequency magnetron sputtering

We studied the structural and optical properties of (Ba, Sr)TiO₃ (BST) films deposited on the transparent substrates at various temperatures of 350–650°C and annealed at 450–650°C. Improved crystallization can be observed on 650°C annealed film whose substrate temperature is 350°C. The refractive index increased from 2.17 to 2.59 at =410 nm for the BST films deposited at 350–650°C and it varied from 2.17 to 2.25 after annealing up to 650°C. In addition, the refractive-index dispersion data related to the short-range-order structure of BST films obeyed the single-oscillation energy model. The indirect energy gap of the films deposited on Al₂O₃ and quartz substrates was found to be about 3.5 eV. According to the analysis of reflectance data, the optical inhomogeneity of films can be reduced by depositing the films at intermediate temperatures 450–550°C.     

The modulated structure formed by isothermal ageing in ZrO2-5.2 mol % Y2O3 alloy

The modulated structure produced by isothermal ageing of ZrO₂-5.2 mol % Y₂O₃ alloy was examined mainly by electron microscopy. It was found that the modulated structure was formed at ageing temperatures between 1400 and 1600° C, but not at 1700° C. The structure is developed by spinodal decomposition, which produces compositional fluctuation in the elastically soft 111 direction in cubic zirconia. The hardness increase caused by the development of modulated structure during ageing is larger than the hardening by precipitation of tetragonal phase in the cubic matrix.Graduate Student, Tohoku Univerisy, Sendai, Japan.     

Sintering mechanisms of 0.99 SnO2-0.01 CuO mixtures

The densification kinetics of 0.99 SnO₂-0.01 CuO molar mixtures have been studied between 850 and 1150 °C. Both experimental analyses and theoretical modelling show the role of a liquid phase for sintering temperatures T _s 940 °C: sintering is controlled by a liquid phase after a fast shrinkage due to grain rearrangement. The analytical formulation of the shrinkage behaviour suggests that dissolution at the solid-liquid interface is the limiting process when T _s 1000 °C and diffusion is the limiting step at higher temperatures.     

High temperature oxidation behavior of Ti-Al-Nb ternary alloys

The oxidation behavior of four Ti-Al-Nb ternary alloys with different microstructures were investigated at 1000°C using interrupted oxidation test in air. Alloys with single-phase -TiAl, two-phase -TiAl + ₂-Ti₃Al, multi-phase -TiAl + ₂-Ti₃Al + Nb₂Al and two-phase ₂-Ti₃Al + Nb₂Al were prepared. The oxidation resistance of the Ti-Al-Nb ternary alloy at high temperature was found to be better than that of the binary Ti-Al alloy. Among the four Ti-Al-Nb ternary alloys, the + ₂ two-phase alloy has the best oxidation resistance. The presence of Nb-enriched phase such as Nb₂Al and Nb₃Al decrease the oxidation resistance at elevated temperature presumably due to the formation of Nb₂O₅, which would accelerate the exfoliation of oxide.     

Carbothermal production of β′-sialon from alumina,silica and carbon mixture

Mixtures of pure nanometer-sized amorphous silica and -alumina with the atomic ratio SiAl=1 were reduced by a stoichiometric amount of carbon between 1100 and 1450 °C in flowing nitrogen in order to produce -sialon powder. Using aqueous suspensions of starting materials, compacts with different microstructures were prepared for reaction. Silica reduction to SiO occurred at a temperature as low as 1300 °C and part of it was removed with flowing nitrogen. Carbothermal reaction involving nitrogen stated at 1350 °C and Si₂N₂O was found as an intermediate together with SiC, resulting in -sialon formation. Loss of silica from the system led to AlN formation. Decomposition of -sialon into sialon polytypoids (15R, 12H) was observed as a result of sialon and AlN reaction at 1450 °C. The reaction rate of sialon formation was slowed down compared to the carbothermal reduction of kaolin because of the lack of impurities. The microstructure of the reacted pellets influenced the reaction products, and the narrow pore size distribution as well as good homogeneity enhanced -sialon formation.On leave, from Silesian Technical University, Krasiskiego 8, 40-019 Katowice, Poland.     

Formation and characterization of oxynitride glasses in the Si-Ca-Al-O-N and Si-Ca-Al,B-O-N systems

Oxynitride compositions in the Si-Ca-Al-O-N and Si-Ca-Al, B-O-N systems were melted and furnace-cooled in BN crucibles at temperatures from 1650 to 1850° C under dry nitrogen atmosphereS. Glass formation, phase stability and crystallization were studied by characterizing the cooled melts by X-ray diffraction, DTA, and electron microscopy. Oxynitride batches with nitrogen content up to 11 at % formed glasses in the Si-Ca-Al-O-N system. Glasses in the Si-Ca-Al, B-O-N system could be formed only when the B₂O₃ content of the batch was less than 3 wt %. Oxynitride glasses in these boron-containing systems were characteristically inhomogeneous, difficult to process, and prone to crystallization. In both the systems, glasses exhibited glass transitions beginning at 1000° C and crystallization at 1300 to 1500° C. Nitrogen-containing crystalline phases were identified in devitrified glasses via microstructural and micro-mechanical analyses.     

Thermal expansion of epoxy-fiberglass composite specimens

The thermal expansion behavior of three epoxy-fiberglass composite specimens was measured from 20 to 120°C (70 to 250°F) using a fused quartz push-rod dilatometer. Billets produced by vacuum-impregnating layers of two types of fiberglass cloth with an epoxy were core-drilled to produce cylindrical specimens. These were used to study expansion perpendicular and parallel to the fiberglass layers. This type of composite is used to separate the copper conductors that form a helical field coil in the Advanced Toroidal Facility, a plasma physics experiment operated by the Fusion Energy Division at Oak Ridge National Laboratory. The coil is operated in a pulsed mode and expansion data were needed to assess cracking and joint stresses due to expansion of the copper-composite system. The dilatometer is held at a preselected temperature until steady state is indicated by stable length and temperature data. Before testing the composite specimens, a reliability check of the dilatometer was performed using a copper secondary standard. This indicated thermal expansion coefficient () values within ±2% of expected values from 20 to 200°C. The percentage expansion of the composite specimen perpendicular to the fiberglass layers exceeded 0.8% at 120°C, whereas that parallel to the fiberglass layers was about 0.16%. The expansion in the perpendicular direction was linear to about 70°C, with an value of over 55×10^–6 °C^–1. Anomalous expansion behavior was noted above 70°C. The expansion in the direction parallel to the fiberglass layers corresponds to an value of about 15×10^–6 °C^–1. The lower values in the parallel direction are consistent with the restraining action of the fiberglass layers. The values decreased with the specimen density and this is consistent with literature data on composite contraction from 20 to –195°C.Nomenclature Thermal expansion coefficient, °C^–1 - L L(T ₂)–L(T ₁), cm - T T ₂–T ₁, °C - L ₀ Length at room temperature, cm - L(T _i ) Length at temperature T _i , cm - T _i Temperature, °C - T ₀ Room temperature, °C Paper presented at the Ninth International Thermal Expansion Symposium, December 8–10, 1986, Pittsburgh, Pennsylvania, U.S.A.     

Formation region of monophase with cubic spinel-type oxides in Mn–Co–Ni ternary system

This study was performed to find the composition area of cubic spinel-type monophase oxides composed of the Mn–Co–Ni ternary system. Starting materials were prepared by mixing Mn, Co, and Ni nitrates then evaporating to dryness. Each starting oxide was fired at 700, 800, 900, 1000, and 1100 °C in air. The regions of cubic spinel monophase (CSM) were confirmed to spread with decreasing firing temperatures. The region of CSM at 1000 °C was seen near the line connecting the points of Mn : Co : Ni = 2 : 4 : 0 and 4.5 : 0 : 1.5. The area at 800 °C spread toward Co and Ni, as compared to the results at 1000 °C. In the region containing more Mn above the area of CSM at 800 °C, the phase had tetragonal spinel or -Mn₂O₃ besides cubic spinel structure. Below this area, the phase contained rock-salt-type crystal besides cubic spinel structure. This tendency at 1000 °C was the same as that at 800 °C.     

Atomic ordering and α′-Cr phase precipitation in long-term aged Ni3Cr and Ni2Cr alloys

Phase instabilities of binary Ni₂Cr and Ni₃Cr alloys after long-term exposure at temperatures between 450 and 600 °C were studied by monitoring lattice parameter, electrical resistivity and microhardness variations and by analysing the microstructural evolution of the alloys at interrupted annealing times. Both materials undergo two metallurgical changes: atomic ordering, based on the Ni₂Cr superlattice, and the precipitation of the -Cr phase. Short-range order develops in both alloys during the first's hours of ageing. The degree of order and kinetics of ordering transformation depend on the alloy composition, time and temperature of ageing. In Ni₂Cr, the short-range ordered structure transforms to long-range order after ageing for 100–1000 h below 525 °C, but in Ni₃Cr the transformation occurs after 30 000 h. The embrittling -Cr phase precipitates at grain boundaries in both alloys after long-term ageing, mainly at 550–600 °C. The amount and size of particles increase with time and temperature of ageing.     

Scaling and intergranular oxidation of an Fe/48 wt% Ni alloy in carbon dioxide at 700 to 1000°C

The oxidation of Nilo 48 has been studied using thermogravimetric, metallographic, and electron probe microanalysis techniques at 700 to 1000° C. After a short period of ill-defined oxidation, the parabolic law was obeyed throughout the exposure period, which varied from 1050 h at 713° C to 50 h at 1000° C. The activation energy for the oxidation reaction was 48±6 kcal/mole. Examination of the external scale indicated that this was single phase and, at 1000° C, its composition corresponded to Ni_xFe^3–xO₄, wherex 0.4. There were also intergranular oxidation and nickel enrichment of the alloy underlying the external scale. After oxidation for only 10 min at 1000° C, the nickel-enriched alloy zone contained 65 wt % Ni. The manganese concentration in the scale was similar to that in the alloy. The results are discussed and compared with those of other workers and it is concluded that the rate-controlling process is the diffusion of iron through the Ni_xFe_3–xO₄ lattice.     

Phase equilibria and ordering in the system HfO2-Yb2O3

The system HfO₂-Yb₂O₃ was investigated in the 0 to 100 mol % Yb₂O₃ range using X-ray diffraction analysis, linear thermal expansion measurements and melting point studies. At high temperatures, the system is dominated by wide regions of solid solutions based on HfO₂ and Yb₂O₃ separated by a two-phase field which appears to extend to the solidus. The extent of the cubic hafnia and ytterbia C-type solid solution fields was established using the precision lattice parameter method. At low temperature (< 1800° C) two ordered phases were found in the system, one at 40 mol % ytterbia with ideal formula Yb₄Hf₃O₁₂, and another at 70 mol % ytterbia with formula Yb₆HfO₁₁. Four eutectoid reactions and a peritectic reaction cubic ytterbia solid solution cubic hafnia solid solution + liquid at 67 mol % and 2380° C have been established in the system. By incorporating the known tetragonal-cubic hafnia and C-type-hexagonal ytterbia transition temperatures, and the melting points data in the system, a tentative phase diagram is given for the system HfO₂-Yb₂O₃.     

On the stability of TL traps of alumina

Thermoluminescence (TL) of heat-treated (in the temperature range 450 to 1400° C) -Al₂O₃ powders have been studied by X-irradiation at room temperature (27° C). The TL patterns have indicated essentially two groups of traps; one in the range 50 to 250° C and the other in the range 200 to 450° C. Apart from other thermal stability characteristics, preferential bleaching by light in the wavelength region of 540 to 630 nm has been observed only in the case of the first group of TL traps. It is concluded that the TL phenomena in -Al₂O₃ are in general controlled by trace impurities rather than intrinsic lattice defects and the TL traps of the system may be associated with a distribution of trapped holes (O^–, O°) stabilized by trace impurities.