Effect of fluorspar on the formation of clinker phases

The evolution of the phases of a commercial clinker in relation to the time and temperature on the clinkerization has been studied. The influence on this evolution by the addition of a small quantity of fluorspar (/t 0.2%) has been determined. The work was basically supported by a study carried out by IR spectroscopy.     

The effect of glucose on the formation of the nanocrystalline transition alumina phases

Series of alumina powders were synthesized starting from sodium aluminate solution prepared from Bayer liquor. The neutralisation of sodium aluminate solution was performed with the use of sulphuric acid. The influence of glucose as a non-surfactant additive on the structure of alumina powders at moderate pH was investigated. The results show that the properties of the powders are influenced by the initial pH value of the solution, as well as the duration of the neutralisation step. High pHs lead to the formation of powders with heterogeneous structure with bayerite as a dominant phase, which during calcinations converts to η-alumina with high surface area. Addition of glucose to the starting aluminate solution leads to the formation of nanocrystalline boehmite with estimated average crystallite size less than 3 nm and high surface area (above 300 m²/g). After calcinations, boehmite transforms to γ-alumina. The results have shown that during the heat treatment, structural transformations proceeded simultaneously with the significant changes in the textural properties of the obtained mesoporous γ- and η-alumina powders.     

Mineral phases formation on the pozzolan/lime/water system

In Spain, the paper industry recycles large amounts of waste paper in the new paper production process. Paper sludge thermal activation (calcination at 700 °C for 2 h) is an environment-friendly alternative source for metakaolinite (MK) to be used for the manufacture of blended cements or cement based materials.This paper could contribute to standardization of the use of new pozzolanic products in cement based materials and its use mixed with saturated lime dissolution. In this process are obtained zeolite, CSH gel, hydrotalcite-like compounds, hydrated aluminate tetracalcium and stratlingite.These materials are formed in different times of pozzolanic reaction.     

Symmetry principles of the formation of ordered phases of crystals

General principles of the formation of low-symmetry ordered phases of crystals, such as the principle of a finite number of low-symmetry phases, the principle of phase diversity, the principle of a finite number of possible structure types of ordered phases, the principle of structural complexity, the compensation principle, and the generalized Fedorov-Groth law, are established in the framework of the Landau-Lifshitz theory of second-order phase transitions. The ranges of their applicability are determined. These principles are derived by extending the results of the structural calculations of the design of new inorganic materials with anomalous physicochemical properties.     

TEM and SEM studies on the formation of superconducting phases in the Bi-based system

We present the formation mechanism and structure of the superconducting phases in the Bi–Sr–Ca–Cu–O system by TEM and SEM observations. Oxalate coprecipitation was used as preparation method. The average particle size, distribution and the presence of different phases and shapes of the particles were evaluated. All samples were well crystallized, showing grains in submicronic range. After thermal treatments, the complex samples showed mica-like crystals uniform dispersed and also an orientation tendency. The superlattice was composed of building blocks and successive planes. The TEM observations were in agreement with the diffraction patterns that revealed a mixture of 2212 and 2223 superconducting phases. With the building blocks in the system, it is possible to form many incommensurate phases that destroy the symmetry. Careful control of the preparation conditions is essential to produce a well-ordered commensurate phase, suitable for the precise determination of the complete superstructure by X-ray diffraction.     

The formation of phases in the AlN-rich corner of the Si-Al-O-N system

The reaction of AlN with Al₂O₃, SiO₂ or Si₃N₄ and Al₂O₃ at temperatures of 1820°C and 1950°C and for compositions rich in AlN have been investigated using powder X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. At 1820°C, Al₂O₃ reacted with AlN to form the non-stoichiometric oxynitride spinel phase (≈Al₂₃O₂₇N₅), whereas samples on the AlN-SiO₂ and AlN-‘X-phase’ tie-lines did not react. At 1950°C, AlN-Al₂O₃ mixtures reacted to form the 27R aluminium oxynitride polytypoid, AlN---SiO₂ mixtures reacted to form 21R and 27R sialon polytypoids and AlN-‘X-phase’ mixtures reacted to form the 12H, 21R and 27R sialon polytypoids, all of which possessed a needle-like morphology. Ordered and disordered intergrowths were also observed in the polytypoid crystals but the disordered 2H^δ sialon phase was not found.     

Diffusion coefficient of DMSO in polyacrylonitrile fiber formation

A H₂O/dimethyl sulfoxide(DMSO) mixture was used as the coagulation bath for the wet‐spun process of acrylonitrile/ammonium itaconate copolymers fibers. Diffusion coefficient of DMSO in the protofibers prepared by acrylonitrile/ammonium itaconate copolymers was determined. It has been found that diffusion coefficient of DMSO outflow of the protofibers prepared by acrylonitrile/ammonium itaconate copolymers synthesized by the solution polymerization is highest compared with those of acrylonitrile/ammonium itaconate copolymers synthesized by H₂O/DMSO mixture suspension polymerization and the aqueous suspension polymerization. With an increase of copolymer concentration in the dope, diffusion coefficient of DMSO decreases continuously. Diffusion coefficient of DMSO increases along with the bath temperature, but the changes of diffusion coefficient values are less prominent as temperature goes beyond 60°C. When DMSO concentration in the coagulation bath was 55 wt %, the value of the diffusion coefficient of DMSO was minimal. Diffusion coefficient of H₂O increases with the jet stretch minus ratio increasing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4447–4451, 2006     

Diffusion coefficient of DMF in acrylic fiber formation

A H₂O/dimethyl formamide (DMF) mixture was used as the coagulation bath of wet‐spun process for acrylic fibers. Diffusion coefficient of DMF in the protofibers prepared by acrylonitrile/acrylamide copolymers was determined. It has been found that diffusion coefficient of DMF outflow of the protofibers prepared by acrylonitrile/acrylamide copolymers synthesized by solution polymerization is highest compared with those of acrylonitrile/acrylamide copolymers synthesized by H₂O/DMF mixture suspension polymerization and aqueous suspension polymerization. With an increase of copolymer concentration in the dope, diffusion coefficient of DMF decreases continuously. Diffusion coefficient of DMF increases along with the bath temperature, but the changes in diffusion coefficient values are less prominent as temperature goes beyond 55°C. When DMF concentration in the coagulation bath was 50%, the value of the diffusion coefficient of DMF was minimal. Diffusion coefficient of DMF increases along with jet stretch minus ratio increase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3616–3619, 2006     

Cracking formation on the surface of extruded photodegraded polypropylene plates

The cracking formation during the photodegradation of polypropylene (PP) plates (1 mm thickness), with (PPOx) and without pro‐oxidant (PP), has been investigated. The plates were produced by extrusion in an industrial production line and were exposed to ultraviolet radiation in the laboratory for periods of up to 480 hr. The samples were investigated by infrared spectroscopy—FTIR, optical light microscopy, differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). The results showed that the extension of photodegradation process is more intense for PPOx than for PP samples. For both samples, cracks were formed at the surface perpendicularly to the flow‐lines. However the cracks frequency was different for both samples and sides of sample. The crack frequency was correlated with chain orientation, A₁₁₀; it was shown that lower degrees of orientation resulted in lower crack frequency. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

镁碳材料中原位合成ZrB2 的研究

用化学纯ZrO2和硼酸(H3BO3)以及工业铝粉为原料,首先采用微波合成的方法确定原位合成ZrB2的最佳原料配比为m(ZrO2):m(H3BO3):m(Al)=3:6:20,然后在不同温度下(分别为850℃、950℃、1050℃、1150℃、1250℃和1350℃)分别保温3h,在镁碳材料中原位合成ZrB2,并用XRD、SEM和EDAX对合成后的试样进行分析。试验结果表明:在850℃的反应温度下,ZrO2不能转化成ZrB2;ZrO2从950℃开始转化成ZrB2,并且随着温度升高,ZrO2转化成ZrB2的量越多。从SEM可以看出,在较高温度下,ZrB2分布在石墨周围,对石墨起到很好的包覆作用。     

Homogeneous formation of metastable phases of carbon at high supersaturations

Theoretical and experimental investigations of formation of metastable phases of carbon at high supersaturations are considered. Falling droplets of liquid hydrocarbons (octane, honane, etc.) were heated by laser radiation. Diamond, carbine and other carbon forms were detected in the products of pyrolysis of the hydrocarbon vapours.     

The formation of coupling agent monolayers on the surface of mica

The interaction of very dilute solutions of a cationic vinylbenzyl silane (CVBS), a methacrylate functional silane (γ-MPS), and an isopropyl-tri-(dioctylpyrophosphato) titanate (IDT) with a mica surface has been studied by carbon analysis. For all three coupling agents the dependence of adsorption with time of treatment follows a step-like curve, where each step corresponds to a monolayer coverage on the mica. Under the operating conditions used it was noted that a particular monolayer is always completed before the next is started. The adsorption of γ-MPS was found to be very sensitive to the time allowed for hydrolysis of the silane, while the adsorption of CVBS was relatively independent of the hydrolysis time when it is varied from 0 to 5400 s. The results indicate that γ-MPS and CVBS near the mica surface form a dense structurally regular multilayer phase with the silane molecules oriented normal to the surface. IDT molecules occupy a surface area on mica which is characteristic of their branched nature.     

Pressureless sintering of high-entropy boride ceramics

High-entropy boride ceramics were densified by pressureless sintering. Green densities of the ceramics varied by composition with the highest green density of 53.6 % for (Hf, Nb, Ta, Ti, Zr)B₂. After pressureless sintering, relative densities up to ∼100 % were obtained for (Cr, Hf, Ta, Ti, Zr)B₂ and (Hf, Ta, Ti, V, Zr)B₂. Two compositions, (Hf, Ta, Ti, W, Zr)B₂ and (Hf, Mo, Ti, W, Zr)B₂ contained secondary phases and did not reach full density. All compositions had average grain sizes less than 10 µm and less than 2 vol % of residual B₄C. This is the first report of conventional pressureless sintering of high-entropy boride ceramics powder compacts without evidence of liquid phase formation.     

过渡金属硼化物合金的电化学性能研究

采用化学还原法合成金属硼化物的前驱物,并经过不同温度热处理得到了Co-B、Ni-B和Ni-Co-B合金.所合成的金属硼化物在KOH碱性溶液中具有良好的充放电性能.在30 mA/g的电流密度下恒流放电至1 V时,50℃热处理的Co-B和Ni-B合金的放电容量分别为310 mAh/g和103 mAh/g.将Co掺杂到Ni-B合金中得到Ni-Co-B合金,不仅可以活化B元素,还可以活化较为惰性的Ni,从而大幅度改善金属硼化物的电化学性能;300℃热处理Ni-Co-B合金的放电容量为258 mAh·g-1,与Co-B合金的放电容量十分接近.     

H_2S在Fe_3O_4表面的吸附反应研究

根据含硫原油加工过程中常温活性硫的腐蚀状况,研究了低体积分数H2S气体在Fe3O4表面的吸附反应过程,考察了温度、反应气体相对湿度、Fe3O4中w(H2O)对吸附反应的影响。研究结果表明,温度升高,反应气体相对湿度及Fe3O4w(H2O)的增加均促进吸附反应。     

氧化铁对石英砂表面改性的研究

用反复沉淀法和加热蒸发法制备氧化铁/石英砂改性滤料,测定了其表面的铁含量、氧化铁膜的附着性能和比表面积,用电子显微镜观察了其表面形态,用X射线衍射进行了氧化铁膜的物相分析。     

Processing of dense high-entropy boride ceramics

Dense (Hf_0.2,Zr_0.2,Ti_0.2,Ta_0.2,Nb_0.2)B₂ high-entropy ceramics with high phase purity were produced by two-step spark plasma sintering of precursor powders synthesized by boro/carbothermal reduction of oxides. The reacted powders had low oxygen (0.404 wt%) and carbon (0.034 wt%) contents and a sub-micron average particle size (∼0.3 μm). Powders were synthesized by optimizing the excess B₄C content of the reaction mixture and densified by a two-step spark plasma sintering process. The relative density increased from 98.9% to 99.9% as the final sintering temperature increased from 2000 °C to 2200 °C. The resulting ceramics were nominally single-phase (Hf,Zr,Ti,Ta,Nb)B₂ with oxygen contents as low as 0.004 wt% and carbon as low as 0.018 wt%. The average grain size increased from 2.3 ± 1.2 μm after densification at 2000 °C to 4.7 ± 1.8 μm after densification at 2100 °C, while significant grain growth occurred during sintering at 2200 °C. The high relative densities, low oxygen and carbon contents, and fine grain sizes achieved in the present study were attributed to the use of synthesized precursor powders with high purity and fine particle size, and the two-step synthesis-densification process. These are the first reported results for dense high-entropy boride ceramics with high purity and fine grain size.     

Effect of the microstructure of graphitic boron nitride on the kinetics of the formation of boron nitride high-pressure phases

Three types of hexagonal boron nitride (h-BN) with graphitic crystal structure having different microstructures were subjected to high pressures (HP) and high temperatures (HT), and the kinetics of the phase transitions to the sp³-hybridized phases (w-BN, c-BN) was studied using in situ synchrotron diffraction. The analysis of the phase transformation kinetics revealed the transformation paths and activation energies E_a of the transformation of h-BN to the high-pressure forms of BN for different microstructures of h-BN. Defect-poor h-BN transforms to metastable wurtzitic BN (w-BN) with E_a ≈ 0.3 eV/at. Defect-rich forms of h-BN transform directly to c-BN, but with a higher activation energy. It was observed that the turbostratic disorder in h-BN retards the phase transition as compared to h-BN containing corrugated basal planes and a low degree of turbostracity. The experimental results are discussed in view of the microstructure changes during the HP/HT treatment and compared to available theoretical phase transition models.