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1.
Novel chemical methods have been developed to allow for the determination of the components of silica fume produced by zircon desilication. Hitherto, no methods have been described for the analysis of this material. The amorphous silica is first removed by treatment with sodium hydroxide. The residue from the hydroxide treatment may then be subjected to a suite of reagents to determine the zircon, the total zirconia, the monoclinic zirconia and the tetragonal zirconia content of the fume. The zircon content of the fume is determined by treatment of the hydroxide residue with concentrated hydrofluoric acid (HF). The total zirconia content of the fume is determined by digestion of the hydroxide residue with fuming sulphuric acid (oleum), while the relative amounts of monoclinic and tetragonal zirconia may be found by treatment of the hydroxide residue with 10%w/v HF, which attacks the less stable tetragonal phase. Both X-ray diffraction and particle size analysis were used to validate the steps in the analytical procedure. An explanation of the presence of tetragonal zirconia in the fume is proposed. A greater understanding of the composition of the fume led to the installation of a separator in the company's production line to remove the zircon. Australian Fused Materials (AFM) now produces a vastly superior grade of fume marketed under the code SF-98. 相似文献
2.
V. Rahhal O. Cabrera R. Talero A. Delgado 《Journal of Thermal Analysis and Calorimetry》2007,87(2):331-337
The use of active mineral additions is an important alternative in concrete
design. Such use is not always appropriate, however, because the heat released
during hydration reactions may on occasion affect the quality of the resulting
concrete and, ultimately, structural durability. The effect of adding up to
20% silica fume on two ordinary Portland cements with very different mineralogical
compositions is analyzed in the present paper. Excess gypsum was added in
amounts such that its percentage by mass of SO3 came
to 7.0%.
The chief techniques used in this study were heat conduction
calorimetry and the Frattini test, supplemented with the determination of
setting times and X-ray diffraction. The results obtained showed that replacing
up to 20% of Portland cement with silica fume affected the rheology of the
cement paste, measured in terms of water demand for normal consistency and
setting times; the magnitude and direction of these effects depended on the
mineralogical composition of the clinker. Hydration reactions were also observed
be stimulated by silica fume, both directly and indirectly – the latter
as a result of the early and very substantial pozzolanic activity of the addition
and the former because of its morphology (tiny spheres) and large BET specific
surface. This translated into such a significant rise in the amounts of total
heat of hydration released per gram of Portland cement at early ages, that
silica fume may be regarded in some cases to cause a synergistic calorific
effect with the concomitant risk of hairline cracking. The addition of excess
gypsum, in turn, while prompting and attenuation of the calorimetric pattern
of the resulting pastes in all cases, caused the Portland cement to generate
greater heat of hydration per gram, particularly in the case of Portland cement
with a high C3A content. 相似文献
3.
This new study must be regarded to be a direct outcome of two previous studies published by these same authors, which were
conducted to respond to interesting questions brought out about the effect of silica fume, SF and metakaolins, M and MQ, on
the heat of hydration of portland cements, PC, with very different C3A and C3S contents. The answer to these so interesting questions has been the primary objective of the present research. For this
purpose, the same PC, PC1 (14% C3A) and PC2 (≈0% C3A), metakaolins, silica fume and blended cements were once again used more 60/40 for sulphate attack, and the same analytical
techniques (CC, pozzolanicity and XRD analysis) and parameters determined as well. In this new research, the sulphate attack
was determined by two accelerated methods: Le Chatelier-Ansttet and ASTM C 452-68.
The experimental results of sulphate attack mainly, have demonstrated definitively that the high, rapid and early pozzolanic
activity exhibited by SF also is, as in the case of the two metakaolins, more specific than generic, for it indirectly stimulated
greater C3A than C3S hydration, but only in the first 16 h monitored in this study. Thereafter it is the contrary, i.e., anti- or contra-specific
for the same purpose. And the longer the hydration time, the more anti- or contra-specific it became, since, when exposed
to sulphate attack, SF blended cements resisted or even prevented the aggressive attack against PC1 which, with a higher C3A content than PC2, was the more vulnerable of the two. By contrast, metakaolin MQ not only failed to hinder or prevent the
attack, but heightened its effects, rendering it more intense, aggressive and rapid, leading to what could be called a rapid
gypsum attack. 相似文献
4.
Ana Hidalgo J. L. García Ma. Cruz Alonso L. Fernández Carmen Andrade 《Journal of Thermal Analysis and Calorimetry》2009,96(2):335-345
The most widely identified degradation process suffered by calcium aluminate cement (CAC) is the so-called conversion of hexagonal
calcium aluminate hydrate to cubic form. This conversion is usually followed by an increase in porosity determined by the
different densities of these hydrates and the subsequent loss of strength. Mixes of calcium aluminate cement (CAC) and silica
fume (SF) or fly ash (FA) represent an interesting alternative for the stabilization of CAC hydrates, which might be attributed
to a microstructure based mainly on aluminosilicates. This paper deals with the microstructure of cement pastes fabricated
with mixtures CAC-SF and CAC-FA and its evolution over time. Thermal analysis (DTA/TG), X-ray diffraction (XRD) and mid-infrared
spectroscopy (FTIR) have been used to assess the microstructure of these formulations. 相似文献
5.
Following recent scaling theories, the sintering of silica aerogels in modeled starting from computer generated gel structures obtained by diffusion-limited cluster-cluster aggregation on a cubic lattice. Two steps compose the sintering process model: a dressing step in which all particles are replaced by overlapping larger particles and a contraction step in which an adequate length rescaling is performed in order to conserve the total mass. Several quantities are computed during sintering as a function of the aerogel density such as the two characteristic cut-off lengths (lower and upper limits of the fractal regime) and the specific interface area. Comparison is made with results of similar off-lattice calculations when available. Some of the numerical results are compared with experiments on partially densified base-catalysed aerogels. 相似文献
6.
We report photoluminescence spectra measured for two series of silica aerogel sintered at 1000°C in different time intervals. In the photoluminescence spectra of nonsintered sample, bands at 1.8, 2.0 and 2.2 eV are identified. During sintering process, the bands at 1.8 and 2.0 eV decrease and vanish, while the band at 2.2 eV shows more complicated behavior. According to infrared spectra of the same samples we find that the photoluminescence band at 1.8 eV originates from nonbridged oxygen hole center defect, and that at 2.0 eV originates from silane in the gel network. Nonstoichiometric SiOx causes photoluminescence band at 2.2 eV. 相似文献
7.
H. Murata D.E. Meyers F. Kirkbir S. Ray Chaudhuri A. Sarkar 《Journal of Sol-Gel Science and Technology》1997,8(1-3):397-402
Over the last few years, the feasibility of fabricating near net shape silica glass components, using a sub-critical drying process for pure alkoxide gels, has been demonstrated in our laboratories. Cracking during drying, due to capillary forces generated in the gel body, was overcome through two particular innovations. The first was the development and optimization of a dual-catalyzed high strength gel. The second was a controlled atmosphere drying process that allowed the gel to dry utilizing a newly observed phenomenology, postulated to be due to cavitation of the pore fluid. Contrary to conventional wisdom, in this drying approach the smallest pore size gels are the easiest to dry. Details of the types of gels and the drying process are reported. Gels of small size were sintered into crack-free glasses, utilizing conventional sintering approaches. However, large size gels always developed visible surface cracks that formed above 800°C. To successfully dry and sinter large monolithic gels then required re-optimization of the entire process. A great number of micron-range defects were initially detected in these sintered bodies. After analyzing the defects, further steps were taken to improve glass quality to the level of optical glass produced by vapor deposition processes. This included mixing and filtering of sols in a clean room, varying the pore size distribution, and optimizing the pre-sintering and sintering processes. Data of relevant glass quality parameters attained so far in the laboratory are reported. 相似文献
8.
Shunsheng Cao Xin Jin Xinhua Yuan Weiwei Wu Jie Hu Weichen Sheng 《Journal of polymer science. Part A, Polymer chemistry》2010,48(6):1332-1338
This article presents a facile, effective, mild synthesis process for well‐defined hollow spheres by using cationic polystyrene (PS) submicro‐particles as templates. In this approach, the cationic PS templates can be first prepared via emulsifier‐free polymerization by using the cationic monomer 2‐(methacryloyloxy) ethyltrimethylammonium chloride as comonomer, then, the silica shells from the sol‐gel process of tetraethoxysilane were coated on the surfaces of template particles via electrostatic interaction, finally the PS was dissolved in situ by modification of the reaction conditions in the same medium to form monodisperse hollow silica spheres with controlled shell thickness. Fourier transform‐infrared spectroscopy, thermogravimetric analysis, Brunauer‐Emmett‐Teller, transmission electron microscopy, and scanning electron microscope measurements were used to characterize these hollow silica spheres. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1332–1338, 2010 相似文献
9.
Norio Tsubokawa Sachio Yoshikawa 《Journal of polymer science. Part A, Polymer chemistry》1995,33(3):581-586
To graft polymers with controlled molecular weight and narrow molecular weight distribution, the grafting of polymers onto ultrafine silica surface by the termination of living polymer cation with amino groups introduced onto the surface was investigated. The introduction of amino or N-phenylamino groups onto the silica surface was achieved by the treatment of silica with γ-aminopropyltriethxysilane or N-phenyl-γ-aminopropyltrimethoxysilane. It was found that these amino groups on silica are readily reacted with living poly(isobutyl vinyl ether) (polyIBVE), which was generated with CF3COOH/ZnCl2 initiating system, and polyIBVE with controlled molecular weight and narrow molecular weight distribution is grafted onto the surface. By the termination of living poly(2-methyl-2-oxazoline), which was generated with methyl p-toluenesulfonate initiator, with amino groups on silica, polyMeOZO was also grafted onto the surface. The percentage of grafting of polymer onto the silica surface decreased with increasing molecular weight of the living polymer, because the steric hindrance of silica surface increases with increasing molecular weight of living polymer. Polymer-grafted silica gave a stable dispersion in a good solvent for grafted chains. © 1995 John Wiley & Sons, Inc. 相似文献
10.
Jacob G. Reynolds 《Silicon Chemistry》2007,3(5):267-269
The Partial Charge Model was developed to predict the hydroxylation, polymerization, and precipitation of ions. The purpose
of this study is to evaluate the Partial Charge Model for describing the polymerization of silica in aqueous solutions. The
Partial Charge Model predicts the stability of ions and complexes based on the assumption that the stable species will have
the same electronegativity as the mean electronegativity of the solution. The silica system was chosen for model validation
because of the rare availability of self-consistent thermodynamic data on many dissolved but polymerized silicate anions,
including both linear and cyclical species. The electronegativity of each species was calculated using the Partial Charge
Model and the results were plotted against the stability constants for the ions. The silicate anions segregated into groups
on the plot based on the number of charges per silicon atom in the polymer. Plots of the log of the stability constant versus
the change in electronegativity produced a linear relationship for the silica polymers containing one negative charge per
silicon atom, which resulted in an r
2 of 0.9978. Thus, the Partial Charge Model successfully describes the thermodynamics of silica polymerization in aqueous solution
for species that are sufficiently alike, but was not accurate for all silica species. 相似文献
11.
Chul Eui Kim Jong Seol Yoon Hae Jin Hwang 《Journal of Sol-Gel Science and Technology》2009,49(1):47-52
A crack-free silica aerogel monolith was fabricated from a cheap water glass derived silicic acid solution by adding glycerol,
which served as a drying control chemical additive (DCCA). The OH surfaces of the wet gel with glycerol were modified using
a TMCS/n-hexane mixture followed by solvent exchange from water to n-hexane. The obtained surface modified wet gel was dried at 75 °C under ambient pressure. The addition of glycerol appears
to give the wet gel a more homogeneous microstructure (larger pore size and uniform size distribution) as well as enhanced
stiffness. However, glycerol also retards surface modification and solvent exchange. The aerogel synthesized with glycerol
added to the silica sol maintained a relatively low bulk density compared with the aerogels aged in a mixed ethanol (EtOH)/TEOS
solution. The reproducibility of aerogel production was further improved in the aerogel synthesized with glycerol added to
the silica sol and aged in a 70%EtOH/30%TEOS solution. 相似文献
12.
The melting point, T
f
of water in a pore decreases as the surface area to pore volume ratio of the pore decreases. Analysis of water absorbed in the pores of silica gels using differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS) shows that the thickness of the bound, non-freezing water layer adjacent to the pore surface increases as its temperature increases, but that it is independent of the surface silanol concentration, [SisOH]. In contrast, the thickness decreases as the cylindrical pore radius r
H
decreases. Thus, the increase in the bound water thickness from 0.45 nm for gels with r
H
=1.2 nm to 1.2 nm for gels with r
H
=7.5 nm is due to the increase from –53°C to –7°C of the temperature (e.g., the melting point T
f
) at which the bound water thickness was measured, and not due to the increase in t
H
or the decrease in [SisOH]. The T
f
of bulk water measured in a DSC was –0.3°C. The boiling point T
v
of bulk water measured in a DSC was 81.3°C. T
v
increased to 94°C in 7.5 nm pores and to 109°C K in 1.2 nm pores. 相似文献
13.
Novel Au-induced polyvinylpyrrolidone (PVP) aggregates with bound water (PVP-water) were created for the highly shape-selective synthesis of distinctive silica nanostructures, such as core-shell spheres, rods, snakes, tubes, capsules, thornlike, and dendritic morphologies. A water/PVP/n-pentanol system was first designed to bind water to PVP, and then Au nanoparticles were used to induce the PVP-water species to aggregate into distinctive soft structures by exploiting the interplay between PVP and gold. This was confirmed by the IR absorption spectra. The bound water in the soft structures was consumed during the hydrolysis of tetraethylorthosilicate and the target silica nanostructures were obtained. The soft structures, and therefore, the silica morphologies, can be readily tuned by adjusting the experimental parameters. The tunable Au-induced PVP-water soft structures reported herein open up new dimensions for the synthesis of distinctive nanomaterials (other than silica) that have new physicochemical properties and applications. These soft structures were also successfully extended to synthesize ZnO and SnO(2) particles with remarkable shapes, such as spheres, leaves, T-shaped structures, and dendritic morphologies. 相似文献
14.
Fengyu Qu Guangshan Zhu Jinyu Sun Shilun Qiu 《Journal of solid state chemistry》2006,179(7):2027-2035
A series of mesoporous silica materials with similar pore sizes, different morphologies and variable pore geometries were prepared systematically. In order to control drug release, ibuprofen was employed as a model drug and the influence of morphology and pore geometry of mesoporous silica on drug release profiles was extensively studied. The mesoporous silica and drug-loaded samples were characterized by X-ray diffraction, Fourier transform IR spectroscopy, N2 adsorption and desorption, scanning electron microscopy, and transmission electron microscopy. It was found that the drug-loading amount was directly correlated to the Brunauer-Emmett-Teller surface area, pore geometry, and pore volume; while the drug release profiles could be controlled by tailoring the morphologies of mesoporous silica carriers. 相似文献
15.
Silica monolith aerogels with different degrees of hydrophobicity were prepared by incorporating methyltrimethoxysilane (MTMS) or trimethylethoxysilane (TMES) in standard sol-gel synthesis followed by supercritical drying of gels with carbon dioxide (CO(2)) at 40 degrees C and 100 bar. The hydrophobicity of the aerogels was tested by measuring the contact angle (theta). The aerogels were also characterised by FTIR, DSC, and porosity measurements. Adsorption capacity measurements show that such modified hydrophobic silica aerogels are excellent adsorbents for different toxic organic compounds from water. In comparison to granulated active carbon (GAC) they exhibit capacities which are from 15 to 400 times higher for all tested compounds. Adsorption properties of hydrophobic silica aerogel remain stable even after 20 adsorption/desorption cycles. 相似文献
16.
选用含钛高炉渣作为吸附剂,研究渣的投加量、粒径大小、温度以及溶液初始pH等因素对含钛高炉渣吸附水中氨氮的影响及吸附特性。动力学数据分析表明,准二级动力学模型能更好地描述含钛高炉渣对氨氮的吸附;颗粒内扩散方程拟合结果发现,含钛高炉渣对氨氮的吸附包括表面吸附和颗粒内扩散两个阶段。吸附等温线拟合表明Langmiur方程能够更好地模拟含钛高炉渣对氨氮的吸附过程。在20℃、反应时间4h的条件下,对于100mL浓度为100mg/L的氨氮溶液,8g粒径为80~120目的含钛高炉渣对氨氮的去除率可以达到32%;随着温度的升高,去除率基本呈上升趋势;溶液初始pH对氨氮的去除有一定的影响,在碱性条件下有较好的去除效果。 相似文献
17.
X. Wang W. Zimmermann K. C. Ng A. Chakraboty J. U. Keller 《Journal of Thermal Analysis and Calorimetry》2004,76(2):659-669
This article presents results of the experimental investigation on the adsorption of the water vapor on silica gel. Two independent
experimental methods has been used, viz. the constant-volume-variable-pressure (CVVP) system and variable pressure thermogravimetry
(TG). Results from these two methods are compared with each other. Also the isosteric heat of adsorption of this system has
been determined from the equilibrium data. The silica gels investigated here are Fuji Davison type 'A' and type 'RD'. Adsorption
isotherm of water vapor have been measured under a variety of conditions all referring to chiller operation cycles, i.e. temperatures
from 303 to 358 K and pressures from 500 to 7000 Pa. The data collected from the two independent experiments compare very
favorably with each other and their trends are consistent with those of the adsorption chiller manufacturer. This lends significant
weight to our experimental data on silica gel+water systems as being valuable to the adsorption chiller manufacturers and
the scientific community.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
《Mendeleev Communications》2021,31(5):706-708
Acyclovir release from its composites with unmodified silica at pH 1.6 and 7.4 follows zero order kinetics for two days. Modification of the silica matrix with phenyl groups leads to dramatic decrease in the drug release level at pH 7.4 compared with pH 1.6 as well as to heterogeneous phase state of acyclovir in the phenyl modified composite with high loading of the drug. 相似文献
19.
Soares Cleide M. F. De Castro Heizir F. Santana M. Hellena A. Zanin Gisella M. 《Applied biochemistry and biotechnology》2001,91(1-9):703-718
Candida rugosa lipase was covalently immobilized on silanized controlled poresilica (CPS) previously activated with glutaraldehyde in the
presence of several additives to improve the performance of the immobilized from in long-term operation. Proteins (albumin
and lecithin) and organic molecules (β-cyclodextrin and polyethylene glycol [PEG]-1500) were added during the immobilization
procedure, and their effects are reported and compared to the behavior of the immobilized biocatalyst in the absence (lacking)
of additive. The selection of the most efficient additive at different lipase loadings (150–450 U/g of dry support) was performed
by experimental design. Two 22full factorial designs with two repetitions at the center point were employed to evaluate the immobilization yield. A better,
stabilizing effect was found when small amounts of albumin or PEG-1500, were added simul-taneou sly to the lipase on to the
support. The catalytic activity had a maximum (193 U/mg) for lipase loading of 150 U/g of dry support using PEG-1500 as the
stabilizing additive. This immobilized system was used to perform esterification reactions under repeated batch cycles (for
the synthesis of butyl butyrate as a model). The half-life of the lipase immobilized on CPS in the presence of PEG-150 was
found to increase fivefold compared with the control (immobilized lipase on CPS without additive). 相似文献
20.
L. J. Anthony L. Soto S. A. Heffner R. A. Holland J. R. Simpson S. G. Kosinski 《Journal of separation science》1988,11(5):395-400
A method has been developed for fabricating fused silica capillary columns which have specific surface properties but still retain the excellent strength, flexibility, and resilience of pure fused silica. By using the Modified Chemical Vapor Deposition process (MCVD), typically used for the production of optical fiber lightguides, inorganic dopants such as Al, Nd, Ge, and P can be introduced into the preform-tube by MCVD. Doped columns have a wide range of specific surface properties, and columns with undoped fused silica prepared by MCVD are more chemically inert and less acidic than columns prepared by conventional methods. This paper describes the method for fabricating capillaries and the initial studies to characterize them. 相似文献