Calcium aluminate cements in fly ash/calcium aluminate blend phosphate cement systems: Their role in inhibiting carbonation and acid corrosion at a low hydrothermal temperature of 90°C

Study was focused upon formulating sodium polyphosphate-modified fly ash/calcium aluminate blend (SFCB) geothermal well cements with advanced anti-carbonation and anti-acid corrosive properties. At a low hydrothermal temperature of 90°C, to improve these properties, we investigated the effectiveness of various calcium aluminate cement (CAC) reactants in minimizing the rate of carbonation and in abating the attack of H₂SO₄ (pH 1.6). We found that the most effective CAC had two major phases, monocalcium aluminate (CA) and calcium bialuminate (CA₂), and a moderate CaO/Al₂O₃ ratio of 0.4. The reaction between sodium polyphosphate (NaP) and CA or CA₂ at room temperature led to the formation of amorphous dibasic calcium phosphate hydrate and anionic aluminum hydroxide caused by the decalcification of CA and CA₂. When SFCB cement made with this CAC was exposed to 4% NaHCO₃-laden water at 90°C, some carbonation of the cement occurred, forming calcite that was susceptible to the reaction with H₂SO₄. This reaction resulted in the deposition of gypsum gel scales as the acid corrosion product on the cement surfaces. The scale layer clinging to the cement protected it from further corrosion. Under such protection, the amorphous dibasic calcium phosphate hydrate crystal hydroxyapatite and anionic aluminum hydroxide crystal boehmite phase transitions were completed in acid solution. Meanwhile, the further chemical and hydration reactions of NaP with fly ash led to the formation of additional crystalline Na-P type zeolite phases. Thus, we propose that passivation of the surface of the cement by deposition of gypsum, following the formation of these reaction products, which are relatively inert to acid, are the acid corrosion-inhibiting mechanisms of the SFCB cements.     

Continuous,martensitic nature of the transition ß→γ Li3PO4

The transformation Li₃PO₄ shows characteristics of both continuous and martensitic transformations. Below 340° C, no detectable transformation occurs; between 340 and 410° C, the transformation goes only partially to completion; above 410° C the transformation rapidly goes to completion. At any temperature in the range 340 to 410° C, transformation proceeds rapidly in the initial stages to attain a certain degree of transformation. With prolonged isothermal heating or grinding of the samples, further transformation does not occur. The reverse transformation could not be effected under normal, dry conditions.     

Hydrothermal Synthesis of Nanocrystalline SnO2 for Gas Sensors

Nanocrystalline SnO₂ is prepared by hydrothermal synthesis (130–250°C, 2–5 h) using three different precursors and is characterized by x-ray diffraction, transmission electron microscopy, and nitrogen BET measurements. The crystallite size of SnO₂ powders (d = 4–5 nm) prepared from amorphous stannic acid gels is found to vary very little with process temperature and duration. Air anneals at 500°C for 1–20 h demonstrate that the highest stability toward crystallite growth is offered by the samples prepared by oxidizing SnSO₄ with H₂O₂ (the crystallite size increases only slightly, from 4–5 to 5–7 nm), whereas the crystallite size of the samples prepared by high-temperature hydrolysis of SnCl₄ increases markedly, from 4–5 to 16–17 nm. Nanocrystalline NiO-doped SnO₂ is prepared by hydrothermal treatment, and its physicochemical properties are investigated. Both SnO₂ and SnO₂NiO exhibit gas sensitivity, as demonstrated by consecutively exposing the samples to different gaseous atmospheres: O₂ N₂ O₂ and O₂ N₂ + C₂H₅OH O₂.     

Reactive processing of nickel-aluminide intermetallic compounds

NiAl have been fabricated by reactive sintering compacts of ball-milled powder mixtures containing Ni and Al. The reaction mechanism, as well as phase and microstructural development, were investigated by analyzing compacts quenched from different temperatures during reactive hot compaction. It was found that the reaction process was strongly affected by pressure, heating rates, heat loss from the sample to the environment. The application of 50 MPa prior to the reaction resulted in the intermetallic-formation reaction initiating at a temperature (480°C) much lower than that (550°C) when no pressure was applied. At high heating rate (50°C/min), when the heat loss is small, the formation of NiAl occurs rapidly via combustion reaction. On the other hand, if the heat loss is significant as in slow heating rate (10°C/min), the reaction process is controlled by solid-state diffusion. The phase formation sequence for the slow solid-state reaction was determined to be: NiAl₃ Ni₂Al₃ NiAl NiAl (Al-rich) + Ni₃Al NiAl.     

Microsphere-filled lightweight calcium phosphate cements

The incorporation of inorganic and organic microsphere fillers into calcium phosphate cement (CPC) to produce lightweight cementitious materials that could be used under hydrothermal conditions at high temperatures between 200 and 1000 °C was investigated. An aluminosilicate based hollow microsphere, with a density of 0.67 gcm^–3 and a particle size of 75–200 m, was the most suitable having a low slurry density of 1.3 gcm^–3, and a compressive strength greater than 6.89 M Pa. This microsphere-filled lightweight CPC exhibited the following characteristics: 1. after autoclaving at 200 °C, amorphous ammonium calcium orthophosphate (AmCOP) salt and Al₂O₃·xH₂0 gel phases, formed by the reaction between calcium aluminate cement and an NH₄H₂P0₄ based fertilizer, were primarily responsible for the development of strength; 2. at a hydrothermal temperature of 300 °C, the microsphere shell moderately reacted with the CPC to form an intermediate reaction product, epistilbite (EP), while crystalline hydroxyapatite (HOAp) and boehmite (BO) were yielded by the phase transformations of AmCOP and Al₂O₃·xH₂O, respectively; 3. at an annealing temperature of 600 °C, the HOAp phase remained in the cement body, even though an EP anorthite (AN) phase transition occurred; 4. at 1000 °C, the phase conversion of HOAp into whitlockite was completed, while the AN phase was eliminated; and 5. the microsphere demonstrated excellent thermal stability up to temperatures of 1000 °C.This work was performed under the auspices of the US Department of Energy, Washington, DC, under Contract No. DE-AC02-76CH00016.     

Properties of r.f. sputtered cadmium telluride thin films

CdTe thin films were prepared using r.f. magnetron sputtering in an Ar atmosphere. Substrate temperatures in the range 100–320 °C were used. XRD results showed that the films are amorphous below 200 °C while above 200 °C the firms were polycrystalline with cubic structure and grains preferentially oriented along the [1 1 1] crystallographic direction. SEM measurements showed significant enhancement of crystallite size with increase of T _s or with post-preparation annealing above 400 °C. The 5 K photoluminescence spectrum showed a broad (FWHM=80 meV) band with a maximum at 1.538 eV. This band showed significant narrowing after annealing above 400 °C suggesting that it originates from transitions involving grain boundary defects. The refractive index n was determined from the interference pattern of the optical transmission. The results agree with the values of n calculated using the Jensen theory. The absorption coefficient was determined for photon energies hE _g (the energy bandgap) from the optical transmission spectra in the absorption region using the Swanepoel theory. Several direct and indirect allowed optical transitions were identified. It was found that the transitions can be grouped into four main allowed transitions (two direct; E _o, E ₃ and two indirect; E ₁, E ₂) whose energy values vary from one sample to another due the quantum size effect associated with small grain size. The main transitions are: E _o (1.50–1.77 eV) assigned to ₈ valence band (VB)₆ conduction band (CB) transition, E ₁ (1.84–2.05 eV) assigned to L_4,5(VB) _i transition where _i is an impurity level at 1.2 eV above the ₈ (VB), E ₂ (2.37–2.49 eV) assigned to L_4,5 (VB)₆ (CB) transition and E ₃ (2.25–2.55 eV) assigned to ₇ (VB) _i transition. The impurity is attributed to native centers or grain-boundary-related defects.     

Reaction mechanism for the formation of intermetallic compounds from layered Sm/Fe powder obtained by mechanical milling

Solid-state reactions in layered Sm/Fe powder particles with an overall composition of Sm₁₂Fe₈₈, obtained by ball milling, have been investigated by X-ray diffraction. During annealing at 500C, one reaction, Sm+2FeSmFe₂ was observed in the time-range studied. However, during annealing at 800C, five reactions were observed: Sm+2FeSmFe₂, Sm +3FeSmFe₃, 2Sm+17FeSm₂Fe₁₇, 2SmFe₂+13FeSm₂Fe₁₇, and 2SmFe₃ +11FeSm₂Fe₁₇. It is proposed that such reactions occur by a nucleation and growth process. Reactions of samarium with iron can be governed by nucleation; Sm/Fe interfaces possessing a higher free energy per unit area can play an important role in the nucleation. The observed results are discussed.     

The ZrO2-rich region of the ZrO2-MgO system

The solubility limits of MgO in tetragonal zirconia were studied by combining the differential thermal analysis data and X-ray disappearing phase method. From these experiments a eutectoid reaction, tetragonal ZrO₂ solid solution monoclinic ZrO₂ solid solution + MgO, at 1120±10 °C and 1.6±0.2 mol% MgO was established. The solubility of MgO in tetragonal ZrO₂ diminished as the temperature increased, and at 1700 °C the solubility was less than 0.5 mol% MgO. The extent of the cubic zirconia solid solution single field was determined by using precise lattice parameter measurements and SEM observations. In this way an invariant eutectoid point, cubic ZrO₂ solid solution tetragonal ZrO₂ solid solution + MgO, was located at 1420±10 °C and 14.8±0.5 mol% MgO.     

Stability and work hardening of an Fe-12Cr-23Mn austenitic steel

The effect of pre-strain on the strain-induced martensitic transformation of an Fe-12Cr-23Mn austenitic steel has been investigated through transmission electron microscopy and X-ray analysis. Pre-strain was performed either at room temperature or at 200° C. Final strain was carried out at liquid-nitrogen temperature. The phase was shown to form on {1 1 1} planes of the austenite matrix predominantly by overlapping of stacking faults. The martensite transformation sequence was . Nucleation of the phase mainly occurred at intersections of bands. Austenite stability was shown to increase by pre-strain at 25° C or 200° C. Pre-strain at 200° C has a greater effect on austenite stability than does pre-strain at 25° C. The mechanism was discussed in terms of martensite transformation rate and various substructures introduced during straining. Work hardening was shown to depend on the degree of pre-strain and final strain. The correlation between work hardening and substructures introduced during straining was examined.     

Low-temperature specific heat of high-purity calcium

Low-temperature specific heat of high-purity calcium has been measured with an adiabatic calorimeter with a mechanical heat switch to avoid helium exchange gas errors, over the temperature range 1.1–4.2 K. The values obtained for the electronic coefficient of specific heat and the Debye temperature _D are =1.99±0.05 mJ/moleK ² and _D=250±4K.     

Calorimetric and X-ray diffraction studies of mechanically activated α-PbF2 in relation to its conversion intoβ-PbF2

Calorimetric measurements and X-ray diffraction line-broadening analysis on-PbF₂ reveal that significant amounts of energy and microstrains can be introduced in the solid as a result of grinding. The stored energy is closely related to microstrains. Thermal annealing in the temperature range from 25 to 280° C relieves some of the strains and energy stored and leads to a sample characterized by residual microstrains and an energy stored whose amount depends on the initial mechanical treatment. The remaining stored energy at 295° C is the actual parameter acting on the transformation and is entirely liberated during this conversion. The initial temperature and heat of this transformation are very sensitive to the microstructure and they are 328° C and 1630 J mol^–1 for a strain-free material.     

Numerical calculation of a generalized thermal model of radio-electronic apparatus

A method is proposed for numerical calculation of the temperature field of a generalized model of electronic equipment with high component density.Notation x,y,z,x,y spatial coordinates, m - time, sec - L_x, L_v, L_z dimensions of heated zone, m - _x, _y, _z effective thermal-conductivity coefficients of heated zone, W/m·deg - ₂ thermal conductivity of chassis, W/m·deg - a _z thermal diffusivity of heated zone along z axis, m²/sec - c₁ effective specific heat of heated zone, J/kg·deg - ₁ effective density of heated zone, kg/m³ - c₃, ₃, c₂, ₂ thermophysical characteristics of cooling agent and chassis, J/kg·deg·kg/m³ - q_v(x, ), q(x, y) volume heat-source distribution, W/m³ - q_s (x) surface heat-source distribution, W/m² - p number of cooling agent channels - Fo Fourier number - Bi Biot number - Uⁱ coolant velocity in i-th channel, m/sec - T₁(x, ), T₂(x, ), T₃(x, ) temperature distribution of heated zone, chassis, and coolant, °K - T₃₀, T₁₀(x), T₂₀(x) initial temperatures, °K - T_3in coolant temperature at input to channel, °K - T_T(x) effective temperature distribution of heat loss elements, °K - T_C temperature of external medium, °K - dimensionless heated zone temperature - _v(x) local volume heat exchange coefficient, W/m³·deg - ₁₂(x), _1C(x), _1T(x) heat liberation coefficients - W/m²·sec; ₂₁(x, y), _2c(x, y), _2T(x, y) volume heat-exchange coefficients of chassis with heated zone, medium, and cooling elements, W/m³·deg Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 5, pp. 876–882, May, 1981.     

Thermogravimetric–differential thermal analysis of the solid-state decomposition of ammonium tetrathiomolybdate during heating in argon

The formation of MoS2 by thermal decomposition of ammonium tetrathiomolybdate (ATT) solids under an argon atmosphere has been studied by simultaneous thermogravimetric and differential thermal analysis. The sequential products for the decomposition upon heating to 700 °C is ATT (hydrated)(NH4)2MoS4(NH4)HMoS4H2MoS4MoS3 Mo2S5MoS2. MoS2 forms between 230 and 260 °C and remains stable up to about 360 °C when it tends to be oxidized by residual oxygen, if present in the atmosphere. These findings suggest that the synthesis of MoS2 from (NH4)2MoS4 via formation of MoS3 is not a direct process, as previously reported, but rather a complex process involving a number of intermediate products (NH4)HMoS4, H2MoS4 and Mo2S5 which have not been reported before. That these products are only specific to the very narrow temperature regimes as revealed suggests that they are very unstable and short lived, that their presence is transient in nature and thus that ex-situ characterization of them is normally difficult. The presence of these intermediate products, as justified experimentally, is further interpreted in terms of their mutual structural similarities which improve understanding as to why MoS2 can usually be prepared from ATT by thermal decomposition, as in this case, or by other techniques, such as anodizing. Laminar morphology of MoS2 is revealed by transmission electron microscopy and its crystal structure examined by selected-area diffraction. Further ex-situ examination by X-ray photoelectron spectroscopy of this end product supports the feasibility of preparing MoS2 from aqueous solutions by anodizing. © 1998 Kluwer Academic Publishers     

Ageing characteristics of dendritic and non-dendritic (stir-cast) Zn-Al alloy (ZA-27)

The dimensional changes of dendritic and non-dendritic (stir-cast) Zn-Al alloy (ZA-27) were investigated during ageing at temperatures in the range 20–245 °C. The linear expansion of both dendritic and non-dendritic samples increased rapidly with ageing time after about 24 h at 95 °C. An initial normalization treatment led to a large initial growth of the alloy which increased further after prolonged ageing times ( 10⁴h). Accelerated ageing tests in the range 75–250 °C showed that increasing the ageing temperature decreased the long term linear expansion of the alloy. In comparing the behaviour of the two materials, the stir-cast material grew less than the dendritic alloy. Extensive SEM and TEM done on as-stir-cast and aged samples showed that the main changes during ageing occurred in the (FCC) lamellae of the +(Zn) eutectoid, the phase at the primary _particles/_eutectoid interface and in the interparticle areas. In the lamellae and at the interface, zinc precipitated whilst the phase precipitated in the interparticle areas. It is considered that the occurrence of this latter phase, rich in copper, is responsible for the growth of stir-cast material during ageing.     

Rhombohedral Actinide Phosphates AIM2IV(PO4)3 (MIV = U,Np, Pu; AI = Na,K, Rb)

Double orthophosphates of actinides and alkali metals A^IM₂IV(PO₄)₃, where MIV = U, Np, or Pu; A^I = Na, K, or Rb, are studied by X-ray diffraction. Rhombohedral modifications (-forms) formed from the low-temperature monoclinic modifications (-forms) on heating in the range 600-1650°C are examined. The transition temperature depends on particular alkali metal and actinide. The crystallographic parameters of the complexes are tabulated. The trends in variation of the unit cell parameters in relation to the ionic radii of alkali metals and actinides are discussed.     

Microstructural Evolution of Fe2O3 and ZnFe2O4 during Sonochemical Synthesis of Zinc Ferrite

The microstructural evolution of Fe₂O₃ and ZnFe₂O₄ during high-temperature (600–800°C) sonochemical synthesis of zinc ferrite is studied by x-ray diffraction analysis. The results are used to develop a qualitative model for ultrasonically activated solid-state reactions A _s +B _s C _s.     

Phase Transformations and Melt Structure of Calcium Metasilicate

The phase transition, melting, crystallization, and vitrification of calcium metasilicate were studied by high-temperature Raman scattering spectroscopy. The results demonstrate that, in the course of melting, the [Si₃O₉] metasilicate rings, which form the structural basis of the phase, transform mainly into [SiO₃] anions. The structural similarity or dissimilarity of the CaO · SiO₂ melt to crystalline phases is shown to have a crucial effect on its crystallization/vitrification behavior.     

Transport in the low-temperature limit of a Landau Fermi liquid

The Boltzmann equation for Landau quasiparticles is solved for T 0 by a specialization of a method discussed by Sykes and Brooker. The quasiparticle distribution function is expanded in Legendre polynomials, assuming a boundary condition which imposes axial symmetry, and even-order terms are assumed to relax together with relaxation time _e , odd-order terms with relaxation time _o . By letting wavelength , with finite, one obtains a first-sound solution, and by lettingT 0, and then , one obtains a zero-sound solution. When these solutions are used to calculate the pressure, it is found that the first-sound solution is consistent with hydrodynamics, exhibiting viscosity = _s , while the zero-sound velocityc ₁=[^–1(B₁+4/3_s)]^1/2, so that phenomenologically zero-sound propagates like a longitudinal elastic wave in a glass. A higher zero-sound mode is also predicted, but is heavily damped. The heat flux is calculated and found to obey Vernotte's equation, which contains an intertial term, added to Fourier's law, that becomes significant asT 0.     

Structural Changes in the Surface Layers of PdHx Alloys Caused by the Hydride Phase Decomposition

By the method of optical microscopy, we perform the in-situ investigation of the plane polished surfaces of PdH _x alloys (with video recording of the processes of transformation) in the case of their rapid cooling at a rate of 11–20°C·sec^–1 from T _c = 292°C ( = 1.97MPa) with simultaneous lowering of the pressure of hydrogen within the temperature range 100–160°C. In the course of decomposition of the PdH_0.24 alloy according to a scheme ₀ + , the formation of nuclei of the - and -phases and their growth were not detected. However, we observe a simultaneous coherent transformation of the entire surface accompanied by the formation of a surface topography similar to the modulated structures formed as a result of the spinodal decomposition. We discuss the possibility of realization of spinodal decomposition under the described experimental conditions.     

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.