Atomic layer deposition of calcium oxide and calcium hafnium oxide films using calcium cyclopentadienyl precursor

Calcium oxide and calcium hafnium oxide thin films were grown by atomic layer deposition on borosilicate glass and silicon substrates in the temperature range of 205–300 °C. The calcium oxide films were grown from novel calcium cyclopentadienyl precursor and water. Calcium oxide films possessed refractive index 1.75–1.80. Calcium oxide films grown without Al₂O₃ capping layer occurred hygroscopic and converted to Ca(OH)₂ after exposure to air. As-deposited CaO films were (200)-oriented. CaO covered with Al₂O₃ capping layers contained relatively low amounts of hydrogen and re-oriented into (111) direction upon annealing at 900 °C. In order to examine the application of CaO in high-permittivity dielectric layers, mixtures of Ca and Hf oxides were grown by alternate CaO and HfO₂ growth cycles at 230 and 300 °C. HfCl₄ was used as a hafnium precursor. When grown at 230 °C, the films were amorphous with equal amounts of Ca and Hf constituents (15 at.%). These films crystallized upon annealing at 750 °C, showing X-ray diffraction peaks characteristic of hafnium-rich phases such as Ca₂Hf₇O₁₆ or Ca₆Hf₁₉O₄₄. At 300 °C, the relative Ca content remained below 8 at.%. The crystallized phase well matched with rhombohedral Ca₂Hf₇O₁₆. The dielectric films grown on Si(100) substrates possessed effective permittivity values in the range of 12.8–14.2.     

Comparison of calcium phosphate product values using measurement of plasma total calcium and serum ionized calcium

Calcium phosphate product (Ca x Pi) is a clinically relevant tool to estimate the cardiovascular risk of patients with renal failure. In reports, mostly total serum calcium has been used. As measurement of serum ionized calcium has some benefits and is being used increasingly, we estimated the respective levels of calcium phosphate product using both total (t-Ca x Pi) and ionized calcium (ion-Ca x Pi). Fifty-eight healthy individuals and 180 hemodialysis (HD) patients from 2 centers were studied. Diagnostic accuracies for corresponding values of the t-Ca x Pi and ion-Ca x Pi were calculated using a GraphROC program. Of HD patients, 64% had t-Ca x Pi <4.4 mmol(2)/L(2) regarded as a desirable goal, and 10% had values over 5.6 mmol(2)/L(2) associated with a high cardiovascular risk. Based on GraphROC analysis, t-Ca x Pi of 4.4 mmol(2)/L(2) corresponded to a value of 2.2 mmol(2)/L(2) of ion-Ca x Pi and, respectively, t-Ca x Pi of 5.6 mmol(2)/L(2) corresponded 2.8 mmol(2)/L(2) of ion-Ca x Pi. Owing to the good agreement between the results in the 2 centers, these values for risk levels can be used in both centers. When measurement of ionized calcium is used, Ca x Pi values of 2.2 and 2.8 mmol(2)/L(2) can be used instead of generally used values of 4.4 and 5.6 mmol(2)/L(2) with total calcium.     

Phase transformation of calcium phenyl phosphate in calcium hydroxyapatite

Calcium phenyl phosphate (CaPP) was synthesized from a mixture of Ca(OH)₂ and phenyl phosphate (C₆H₅PO₄H₂) in an aqueous media. XRD pattern of CaPP exhibited five diffraction peaks at 2θ = 6.6, 13.3, 20.0, 26.8 and 33.7°. The d-spacing ratio of these peaks was ca. 1:1/2:1/3:1/4:1/5. The molar ratios of Ca/P and phenyl/P of CaPP were 1.0 and 0.92, respectively, and the chemical formula of the material was expressed as (C₆H₅PO₄)_0.92(HPO₄)_0.08Ca·1.3H₂O, similar to that of dicalcium phosphate dihydrate (CaHPO₄·2H₂O: DCPD). These results allowed us to infer that CaPP is composed of a multilayer alternating bilayer of phenyl groups of the phosphates and DCPD-like phase. The structure of the material was essentially not altered after aging at pH 9.0-11.0 and 85 °C in an aqueous media. While, after aging at pH ≤8.0, the diffraction peaks of CaPP were suddenly weakened and disappeared at pH 7.0. Besides, new peaks due to calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂: Hap) appeared and their intensity was strengthened with decreasing the solution pH. TEM observation revealed that the Hap particles formed at pH 6.0 are fibrous with ca. 1.5 μm in length and ca. 0.2 μm in width. From these results, it is presumed that the layered CaPP was dissolved, hydrolyzed and reprecipitated to fibrous Hap particles at pH ≤8.0 and 85 °C in aqueous media. This phase transformation of CaPP in Hap resembled to the formation mechanism of Hap in animal organism.     

Physical properties and self-setting mechanism of calcium phosphate cements from calcium bis-dihydrogenophosphate monohydrate and calcium oxide

An apatitic calcium phosphate cement was developed from calcium bis-dihydro-genophosphate monohydrate (or monocalcium phosphate monohydrate, MCPM) and calcium oxide (CaO). The powder had a Ca/P molar ratio of 1.67, and the liquid was either pure water or 0.25 M–1 M sodium phosphate buffer, pH 7.4. The influence of the powder-to-liquid (P/L) ratio on the setting time and the mechanical strength were studied. The best results were obtained for the 1 M phosphate buffer with a P/L ratio of 1.53; the setting time was 7 min and the compressive strength was 25 MPa after 24 h and 33 MPa after 11 d. The mechanism and kinetics of the setting reaction were investigated by X-ray diffraction, differential scanning calorimetry, 31P magic angle spinning–nuclear magnetic resonance and infrared spectrometry. The setting reaction was found to be biphasic: in the first step, during the mixing time, MCPM reacted with CaO immediately to give calcium hydrogenophosphate dihydrate (or dicalcium phosphate dihydrate, DCPD) which, in the second step, reacted more slowly with the remaining CaO to give hydroxyapatite. The conversion of the starting materials to hydroxyapatite was complete within 24 h when the liquid was water, but was slower and incomplete with the phosphate buffers. Of the starting materials, 30% remained after 3 d. © 1999 Kluwer Academic Publishers.     

A novel nanotube of composite of calcium carbonate and calcium sulfate

Nanotube-shaped precursor which is composed of layered structured sodium dodecylsulfate (SDS) calcium carbonate were obtained by titration of an aqueous solution of Na₂CO₃ into an aqueous solution containing CaCl₂ and SDS at 333-335 K. A unit of the repetition of the precursor was about 4 nm. Nanotube-shaped composite which is composed of CaCO₃ and CaSO₄ of 100-200 nm in diameter and 0.5-2 µm in length was obtained from nanotube-shaped precursor composed of layers of CaCO₃ and SDS by calcinations at 673 K in air. The precursor sheet composed of CaCO₃ layers on which SDS molecules attached to both side seemed to curl up and form a pipe.     

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.     

海藻酸钙水凝胶过滤膜的制备及其对硫酸钙的截留

以尿素为致孔剂制备了海藻酸钙(CA)水凝胶过滤膜,测试了其通量、截留率和力学性能;通过扫描电子显微镜(SEM)观测其过滤硫酸钙前后的表面形貌。结果表明,增加尿素含量,均导致膜应力和应变的下降;而膜的纯水通量则迅速增大,尿素含量为3.0%(质量分数)时达到28.7 L/(m2·h),为最大;0.2 MPa下,过滤1.7 g/L硫酸钙时对Ca2+和SO2-4的截留率分别为83%和92%,稳定通量达到21.7 L/(m2·h)。     

Effect of calcium sulfate source on the hydration of calcium sulfoaluminate eco-cement

The availability of cements, including eco-cements, with tailored mechanical properties is very important for special applications in the building industry. Here we report a full study of the hydration of calcium sulfoaluminate eco-cements with different sulfate sources (gypsum, bassanite and anhydrite) and two water/cement ratios (0.50 and 0.65). These parameters have been chosen because they are known to strongly modify the mechanical properties of the resulting mortars and concretes. The applied multi-technique characterization includes: phase assemblage by Rietveld method, evolved heat, conductivity, rheology, compressive strength and expansion/retraction measurements. The dissolution rate of the sulfate sources is key to control the hydration reactions. Bassanite dissolves very fast and hence the initial setting time of the pastes and mortars is too short (20 min) to produce homogeneous samples. Anhydrite dissolves slowly so, at 1 hydration-day, the amount of ettringite formed (20 wt%) is lower than that in gypsum pastes (26 wt%) (w/c = 0.50), producing mortars with lower compressive strengths. After 3 hydration-days, anhydrite pastes showed slightly larger ettringite contents and hence, mortars with slightly higher compressive strengths. Ettringite content is the chief parameter to explain the strength development in these eco-cements.     

Thermodynamics of calcium uranosilicate

The standard enthalpy of formation at 298.15 K of crystalline α-Ca(HSiUO₆)₂ · 5H₂O (?6781.0 ± 9.5 kJ mol^?1) was determined by reaction calorimetry. The heat capacity in the range of 80–300 K was measured by adiabatic vacuum calorimetry, and the thermodynamic functions of this compound were evaluated. The standard entropy of formation (?1978.6±1.2 J mol^?1 K^?1) and the Gibbs free energy of formation (6191.0±10.0 kJ mol^?1) at 298.15 K were calculated. The standard thermodynamic functions of reactions of calcium uranosilicate synthesis were analyzed.     

Dialysate calcium and calcium/phosphate balance in hemodialysis

The changing pattern of pharmaceutical use in dialysis patients has resulted in several alterations to dialysate calcium concentration over the past 40 years. Non‐calcium–containing phosphate binders and calcimimetics are the most recent examples of drugs that influence the overall calcium balance in dialysis patients. Renal osteodystrophy, vascular disease, and mortality are believed to be linked in patients with chronic kidney disease (CKD), although to date most of the evidence is based only on statistical associations. The precise pathophysiology of vascular calcification in end‐stage renal disease is unknown, but risk factors include age, hypertension, time on dialysis, and, most significantly, abnormalities in calcium and phosphate balance. Prospective studies are required before “cause and effect” can be established with certainty, but it is an active metabolic process with inhibitors and promoters. Serum calcium levels are clearly influenced by dialysate calcium and may therefore play an important role in influencing vascular calcification. Clinical management of hyperphosphatemia is being made easier by the introduction of potent non‐calcium–based oral phosphate binders such as lanthanum carbonate. Short‐term and long‐term studies have demonstrated its efficacy and safety. Vitamin D analogs have been a disappointment in the control of serum parathyroid hormone (PTH) levels, but evidence is emerging that vitamin D has other important metabolic effects apart from this, and may confer survival advantages to patients with CKD. Calcimimetics such as cinacalcet enable much more effective and precise control of PTH levels, but at the cost of a major financial burden. While it is unreasonable to expect that any one of these recent pharmacological developments will be a panacea, they provide researchers with the tools to begin to examine the complex interplay between calcium, phosphate, vitamin D, and PTH, such that further progress is fortunately inevitable.     

Aqueous deposition of calcium phosphates and silicate substituted calcium phosphates on magnesium alloys

Attempts were made to deposit homogeneous films of calcium phosphates (CaPs) on two magnesium alloy systems, AZ31 and Mg-4Y, through an aqueous phosphating bath method. The deposition of silicate substituted CaPs by this aqueous method was also explored as silicate substitution is believed to increase the bioactivity of CaPs. The effect of doped and undoped coatings on the in vitro degradation and bioactivity of both alloy systems was studied. FTIR and EDX confirmed the deposition of Ca, P, and Si on both alloys and the coatings appeared to consist primarily biphasic mixtures of hydroxyapatite and β-TCP. These largely inhomogeneous coatings, as observed by SEM, were not shown to have any significant effect on maintaining the physiological pH of the culture medium in comparison to the uncoated samples, as the pH remained approximately in the 8.4-8.7 range. Interestingly, despite similar pH profiles between the coated and uncoated samples, CaP coatings affected the degradation of both alloys. These doped and undoped calcium phosphate coatings were observed to decrease the degradation of AZ31 whereas they increased the degradation of Mg-4Y. In vitro studies on cell attachment using MC3T3-E1 mouse osteoblasts showed that between the uncoated alloys, Mg-4Y appeared to be the more biocompatible of the two. Silicate substituted CaP coatings were observed to increase the cell attachment on AZ31 compared to bare and undoped CaPs coated samples, but did not have as great of an effect on increasing cell attachment on Mg-4Y.     

Heat capacity of fcc calcium

The lattice entropy derived from the measured heat capacity at intermediate and high temperatures is analyzed to yield a weakly temperature dependent entropy Debye temperature. An unusual temperature dependence of this quantity may be a sign of error in the heat capacity data. When this analysis is applied to heat capacity data recommended by Hultgren et al. (1973) for 20 nontransition metals, the result for fcc Ca stands out as anomalous. We have reconsidered heat capacity data of fcc Ca and find that measurements by Eastman et al. (1924), which were given little weight by Hultgren et al., are consistent with a normal behavior of the entropy Debye temperature up to 450 K.     

Electro-deoxidation of Ta2O5 in calcium chloride–calcium oxide melts

Tantalum oxide has been electro-deoxidised in a bath of CaCl₂-1wt%CaO to form tantalum. It was found that the reaction between the calcium oxide in the melt and the tantalum oxide takes precedence over any reduction process so that until the calcium tantalum oxide Ca₃(CaTa₂O₉) (equivalent to 4CaO·Ta₂O₅ or Ca₄Ta₂O₁₀) is formed, calcium ions are reduced to either form calcium metal or reduced calcium species. This eventually results in high electronic conductivity in the melt which means that, compared to the electro-deoxidation of oxides of similar stability to Ta₂O₅, the energy and current efficiencies are low. In addition, the vast changes in microstructure result in a structure that is extremely fragile so that the resulting tantalum can only be harvested as a fine powder.     

Sintering study of calcium aluminate

Measurement of the initial sintering shrinkage of CaAl₂O₄ at temperatures of 1300, 1325 and 1350 °C are reported. The particle sizes chosen were –53 + 45, –63 + 53 and –75 + 63 microns and the soaking periods were from 15 to 360 min. A time dependence of the shrinkage has shown that volume diffusion is the dominant mechanism of sintering. At any given time and temperature, the per cent shrinkage was found to be a decreasing function of particle size. The activation energy for the sintering of CaAl₂O₄ was found to be 766.38 KJ mol^–1.     

Fire hazards of calcium hypochlorite

“Calcium hypochlorite, 70% available chlorine” is a commercial chemical which is transported in large quantities generally packed in steel drums. It is classified by the I.M.C.O. Code as an Oxidising Agent. During the past five years there have been about a dozen serious accidents in ships involving this material. The losses caused have been very large, amounting to many millions of pounds sterling.A number of the P. and I. Clubs in London set up a sub-committee to investigate the hazards associated with the substance. The investigations include a research programme carried out at the Royal Armament Research and Development Establishment, Woolwich, England.It has been found that ignition may occur in some circumstances spontaneously, by mechanical stressing or by admixture with some combustible substances. The commercial material is not a definite chemical compound but a mixture, the nature and properties of which may vary according to the nature of the raw materials and method of manufacture.Accidental ignition may be followed by explosive effects and the fire evolves large quantities of oxygen, which produce an almost uncontrollable burning of any combustible material nearby. It is apparent that the hazards are far more serious than those ordinarily associated with other oxidising agents.     

Kinetics of calcium molybdate crystallization

Kinetics of crystallization of calcium molybdate from unstirred molten solutions of lithium chloride of low to medium supersaturation in platinum crucibles by the process of continuous cooling at 5° C hr⁻¹ from temperaturesT ₀=700 and 750°C are investigated. The crystal size measured by optical microscopy for different crystallization periods reveals that both crystal length and width generally increase with cooling period. The degree of crystallizationα _t,also increases with cooling period, attaining a maximum of 0·90. The diffusion rate constants,K _Dlat 700 and 750°C are 0·0776 and 0·1138 respectively. The effect of variation of the crystallization temperature on the crystal size and their number is also studied.     

Enzyme-catalysed synthesis of calcium phosphates

A biomimetic method is described for the precipitation of nanosized calcium phosphates using the alkaline phosphatase (EC 3.1.3.1), which is responsible for hydrolysis of organic and inorganic phosphates in vivo. Buffered solutions containing glycerol-2-phosphate and CaCl₂ in addition to MgCl₂ and the respective enzyme were prepared for calcium phosphate precipitation. The phosphate group of glycerol-2-phosphate was cleaved through enzymatic hydrolysis. The local inorganic phosphate concentration increased resulting in the precipitation of nanosized calcium phosphates phases (Ca–P phase) composed of calcium deficient hydroxyapatite (CDHA) and hydroxyapatite (HA). At high Ca²⁺-concentration and large enzyme amounts mixed phases of HA/CDHA with an increasing quantity of HA were favoured. Under basic conditions (pH > 9) formation of HA was observed, whereas at neutral pH of 7.5 CDHA was primarily formed. The assignment of Ca–P phases was accomplished by FT-IR and Raman-spectroscopy in addition to X-ray diffractometry. The Ca–P materials exhibited BET surface areas of 173 m²/g. SEM-micrographs of the Ca–P powders showed globular-shaped agglomerates of Ca–P particles. The size of the Ca–P crystallite ranged from 9 nm to 25 nm according to transmission electron microscopy (TEM), where round-shaped, platelike and fibrelike crystallites were found. All crystallites showed diffuse ring patterns in electron diffraction confirming the nanosize of the precipitate. Using the developed technique, it was possible to synthesise 100 g of bonelike Ca–P materials in 1 day using 15 L batches with optimised parameters.