Degree Of Microporosity Research Articles

Direct Generation of High-Aspect-Ratio Structures of AISI 316L by Laser-Assisted Powder Deposition.

The effect of process parameters and the orientation of the cladding layer on the mechanical properties of 316L stainless steel components manufactured by laser metal deposition (LMD) was investigated. High aspect-ratio walls were manufactured with layers of a 4.5 mm wide single-cladding track to study the microstructure and mechanical properties along the length and the height of the wall. Samples for the tensile test (according to ASTM E-8M-04) were machined from the wall along both the direction of the layers and the direction perpendicular to them. Cross-sections of the LMD samples were analyzed by optical and scanning electron microscopy (SEM). The orientation of the growing grain was observed. It was associated with the thermal gradient through the building part. A homogeneous microstructure between consecutive layers and some degree of microporosity was observed by SEM. Uniaxial tension tests were performed on samples extracted from the wall in perpendicular and parallel directions. Results for ultimate tensile strength were similar in both cases and with the wrought material. The σ0.2 were similar in both cases but slightly superior to the wrought material.

Highly microporous free-radically generated polymeric materials using a novel contorted monomer

A novel, free-radically polymerizable, contorted monomer was synthesized in two steps from bisphenol A. In a simple precipitation polymerization process making use of solvent as a porogen, homopolymerization of this contorted monomer (SBI-DV) resulted in polymeric networks with surface areas as high as 850 m2/g and with SAmicro/SABET values as high as 0.65. Comparative DVB based polymeric networks produced under similar conditions had equally as high SABET but SAmicro/SABET values of 0.35. In addition, copolymeric networks were produced using varying molar monomer ratios of SBI-DV/DVB. The degree of microporosity in the resulting copolymeric networks correlated with the amount of SBI-DV used in their formation.

Potential of Activated Carbon Derived from Local Common Reed in the Refining of Raw Cane Sugar

Common reed (Fragmites australis), a local invasive grass, was investigated as a possible feedstock for the production of activated carbon. Dried crushed stems were subjected to impregnation with phosphoric acid (30, 40 and 50%) followed by pyrolysis at 400~500oC with final washing and drying. Obtained carbons were characterized by determining: carbon yield, ash content, slurry pH, textural properties and capacity to remove color bodies from factory-grade sugar liquor. Produced carbons possessed surface area up to 700 m2/g, total pore volumes up to 0.37 cm3/g, and proved to be microporous in nature. Decolorization of hot sugar liquor at 80oC showed degrees of color removal of 60 up to 77% from initial color of 1100~ 1300 ICU, at a carbon dose of 1.0 g/100 ml liquor. No correlation seems to hold between synthesis conditions and % R but depends on the degree of microporosity. A commercial activated carbon N showed a comparative better color removal capacity of 91%. Common reed proved to be a viable carbon precursor for production of good adsorbing carbon suitable for decolorization in the sugar industry, as well as in other environmental remediation processes.

Macro-/microporous MOF composite beads

We have prepared a series of metal–organic framework (MOF) composite materials by depositing crystalline MOFs into mm-sized macroporous polyacrylamide (PAM), oxide or oxide–PAM beads using solvothermal methods or immersion in mother solutions. The facile nature of the composite preparation is in part due to the inherent hydrophilicity and processability of the PAM, which bears suitable functionality to interact with the MOF. The resulting composites display hierarchical porosity across the macro- and microporous length scales; the MOF loading level, and hence degree of microporosity in the composites, can be tuned by modulating the concentration of the reactants in the MOF synthesis. The MOF@PAM beads display enhanced mechanical stability and handling over bulk MOF phases in heterogeneous reaction systems, clearly indicating that such materials can improve recovery and recyclability of crystalline MOFs. This is an important step for future applications.

Changes in the structure of composite colloid-polymer xerogels after cold isostatic pressing

Monolithic gels, prepared from different mixtures of colloidal silica in a sol solution containing tetraethoxysilane under powerful ultrasonic agitation (sonosols), were compacted at an isostatic pressure of 390 MPa. Then N2 adsorption-desorption data were used to construct structural models of the gels using Monte-Carlo calculations on the basis of random close-packing (RCP) premises. Structural information on these composites obtained before compaction indicates that the characteristic uniform structure of silica colloid gel undergoes profound modification when it is mixed with silica sonogel. From a structural point of view, the behaviour under compaction of the sonogel phase, which exhibits a significant degree of microporosity, depends on the relative concentration of the colloidal phase. Two hierarchic levels of micropores were discerned. After compression, the size of the elementary particles—and their aggregates—of the sonogel phase increases from 1.6 to 2.1 nm radius when the colloidal phase content is increased from 30 to 82% by weight. For an intermediate content, 50% of the volume reduction is caused by compression of the sonogel phase at the micropore level.

Types of goethite from Quadrilátero Ferrífero's iron ores and their implications in the sintering process

Quadrilátero Ferrífero's iron ores used in the sintering process correspond to mixes of hematitic and goethitic ore typologies. The ores have particle size mainly distributed in the range from 6·35 to 0·105 mm. The goethitic typology comprises a low amount in these ore blends; however, it can be relevant in the reactivity during sintering. This research involved techniques such as reflected light optical microscopy (RLOM) and scanning electron microscopy-backscattered electron (SEM-BSE) images for microstructure evaluation, and energy dispersive X-ray spectrometry (SEM-EDS) for microanalytical study. Many morphologies of goethite were identified considering the three ore blends: colloform type, massive, thin (granular and lamellae/fibrous) and earth-like. They have variable degrees of microporosity. Some microanalytical differences among these morphologies were observed as Si–Al–P bearing Gt, which corresponds to the common type, Al2O3-rich Gt and MnO bearing Gt. The latter two types have also Si, Al and P in their compositions. Although goethite is completely consumed during the sintering processes, its control in the sintering burden is very important owing to its morphologies with different degrees of porosity and with variable elements for Fe substitution. These factors can affect in different ways the composition of the sinter phases. Therefore, the identification of the goethite types and their amounts in the iron ore mixes, as well as their chemical constitution, can avoid the increase in deleterious elements during the sintering stage.

Iron and copper oxide modified SBA-15 materials as catalysts in methanol decomposition: Effect of copolymer template removal

Several SBA-15 type mesoporous silicas, where different means of surfactant removal have been used, have been modified by copper and iron oxide, and tested as catalyst for methanol decomposition. The materials were thoroughly characterized by nitrogen physisorption, X-ray diffraction, Moessbauer spectroscopy and temperature programmed reduction with hydrogen. The different means of template removal results in SBA-15 materials different in mesopore size and degree of microporosity. These parameters have a strong influence on the reductive and catalytic properties of the obtained composite materials.

Inducing solid-state isolation of the phthalocyanine macrocycle by its incorporation within rigid, randomly shaped oligomers

The synthesis and properties of two non-planar and highly rigid pentamers containing four phthalocyanine units linked, via a spirocyclic fused ring system, to a central phthalocyanine or porphyrin core is described. It is shown that the rigidity of these novel oligomers, together with the large number of structural isomers of irregular shape induced by the presence of the four spiro-centres, inhibits efficient packing of the macrocycles in the solid state. Therefore, the UV–visible absorption spectrum of spin-coated films of these materials is almost identical to that obtained from the non-aggregated oligomers in dilute solution. Nitrogen adsorption measurements indicate a high surface area for one of the pentamers, which is consistent with some degree of microporosity.

Prediction of the micropore structure parameters and adsorption properties of activated carbons

A regularity govering variations of volume and linear size of micropores in carbon adsorbents during their vapor-gas activation was found. A parameter was proposed that characterizes the degree of development of the micropore system in activating carbons and an initial carbonized material. The parameter is defined as the number (or surface area) of micropores in the volume unit of the micropore zones. This parameter allows one to rationalize the choice of carbonized materials for the preparation of activated carbons with specified adsorption properties and to establish the range of activation beyond which the structure of the micropores loses stability. Furthermore, the parameter serves to predict how activation affects micropore structure parameters and adsorption properties of carbons. This in turn indicates the optimal degrees of microporosity of carbons needed to attain required adsorption properties.

Adsorption/Oxidation of Hydrogen Sulfide on Nitrogen-Containing Activated Carbons

Wood-based activated carbon was modified by impregnation with urea and heat treatment at 450 and 950 °C. The chemical and physical properties of materials were determined using acid/base titration, FTIR, thermal analysis, IGC, and sorption of nitrogen. The surface features were compared to those of a commercial urea-modified carbon. Then, the H2S breakthrough capacity tests were carried out, and the sorption capacity was evaluated. The results showed that urea-modified sorbents have a capacity similar to that of the received material; however, the conversion of hydrogen sulfide to a water-soluble species is significantly higher. It happens due to a high dispersion of basic nitrogen compounds in the small pores of carbons, where oxidation of hydrogen sulfide ions to sulfur radicals followed by the creation of sulfur oxides and sulfuric acid occurs. It is proposed that the process proceeds gradually, from small pores to larger, and that the degree of microporosity is an important factor.

The effect of the choice of pore model on the characterization of the internal structure of microporous carbons using pore size distributions

Microporous carbons are typically characterized as a pore size distribution of slit-shaped model pores. Since these characterizations are used to interpret physical properties such as the degree of microporosity, adsorption behaviour, molecular sieving and effective diffusivities it is important to determine how the choice of the model pore used in the analysis affects the characterization. The effect of using square and rectangular model pores to determine pore size distributions was investigated. It was found that using these pores leads to significantly different pore size distributions and we have identified the underlying cause for these differences. It was also found that any measures based on the average pore size should be used with caution since they are sensitive to the actual shape of the model pore used in the pore size distribution analysis.

Amino Acid Derivatives of Layered Zirconium Phosphates – α-Zirconium L-(+)-Serinephosphate and Zirconium L-(+)-Serinephosphate Phosphates

A layered derivative of α-zirconium phosphate containing L-(+)-serine covalently attached to the inorganic layer has been prepared by allowing Zr fluoro complexes to decompose in the presence of L-(+)-phosphoserine. On the basis of thermogravimetric weight loss and C,H,N elemental analyses, the layered compound obtained has been formulated as Zr[HOOCCH(NH2)CH2OPO3]2. The X-ray powder diffraction pattern has been indexed with a monoclinic cell (a = 5.3737 Å, b = 9.3231 Å, c = 14.510 Å, β = 96.99°, Z = 2). FT-IR absorption spectra show that the serine groups attached to the inorganic layers are present as zwitterions. Thermal decomposition commences at ca. 250 °C and occurs in two steps: the first is due to a decarboxylation reaction, with the formation of the amino derivative Zr(NH2CH2CH2OPO3)2, while the second is associated with pyrolysis of the organic moiety, leading to ZrP2O7. Despite the presence of the amino acid function in the interlayer region, the compound does not show intercalation ability towards cations or anions or polar species. However, compounds with a certain degree of microporosity and possessing ion-exchange and adsorption properties have been obtained by replacing some of the phosphoserine groups of the compound by HPO4 groups, to produce the mixed layered derivatives Zr[HOOCCH(NH2)CH2OPO3]2–x-(HPO4)x.

Surface properties and porous texture of montmorillonite-(Ce or Zr) phosphate cross-linked compounds

In this work, pore texture characteristics of a series of Ce(IV) or Zr(IV) montmorillonite phosphate cross-linked compounds obtained by precipitation of cerium or zirconium phosphate with dilute H 3PO 4 on the micelles of an aqueous montmorillonite suspension, previously submitted to ion-exchange processes to replace its exchange ions with Ce(IV) or Zr(IV), are studied. Surface areas and pore volumes of the different materials prepared are determined by N 2 adsorption at 77 K and mercury porosimetry techniques. Analysis of the N 2 adsorption isotherms by the t-De Boer and Dubinin-Radushkevich methods, revealed the presence of a certain degree of microporosity in all the materials studied. Moreover, analysis of the Hg intrusion data permitted to determine the contribution of the macro- and mesopores to the total surface area and pore volume of the prepared compounds. The results reveal a greater specific surface area for these compounds than for montmorillonite and the evolution of this parameter with thermal treatment is related to the nature and content of phosphate in the different samples. However, the changes recorded in the V p and S/ V p parameters during the thermal process suggest that surface diffusion is the dominant transport mechanism in the sintering process.

Electron paramagnetic resonance studies of an active carbon: The influence of preparation procedure on the oxygen response of the linewidth

Active carbons have been prepared from sucrose, using chemical activating agents (KOH and ZnCl 2) to yield carbons with BET surface areas of 430–1170 m 2 g −1, which are dependent on the amount of activating agent present during carbonization. Adsorption studies with nitrogen at 77 K have demonstrated type I adsorption/desorption isotherms with well-defined plateaus and no hysteresis. The adsorbent pore volume determined by the BJH technique is mostly microporous, with pore radii smaller than 20 Å, the degree of microporosity being dependent on preparation conditions. Additional characterization has been performed by monitoring the electron paramagnetic resonance (EPR) linewidth Δ B pp of the active carbons in the presence of various pressures of oxygen. The carbons give a single resonance line at g≈2.00, the free electron value. Subsequent analysis of the EPR characterization has shown a reversible dependence of the linewidth on the pressure of oxygen, P o 2 , and a dependence of the response d(Δ B pp)/d P o 2 on the BET surface area. Thus active carbon oxygen sensors with differing responses to oxygen can be produced for oximetry applications.

Preparation Of Zirconium Diphosphonate-Phosphites With A Narrow Distribution Of Mesopores.

ABSTRACTThe presence of H3PO3 in the synthesis of zirconium diphosphonates in dimethylsulfoxide, other than the expected dilution of the pillars, which in turn gives rise to a certain degree of microporosity, may also induce the formation of a high percentag. of mesopores. E.g., compounds with high surface area(300–500 m2 /g) of which 60–70% is due to mesopores with diameters 20–40 Å and the remaining is due to micropores, were obtained. It was furthermore found that the distribution of the mesopores was fairly narrow. Compounds with micropores <3 Å and mesopores of 20–30 Å behave in practice as pure and narrow mesoporous solids;they are therefore of great interest as new molecular inorgano-organic sieves.

Correlation between the bet parameters and the parameters that characterize the microporous structures of activated carbons

The well-known BET isotherm equation is used to describe benzene adsorption on microporous activated carbons of different degrees of microporosity. It is shown that the parameters of this equation evaluated for benzene-activated carbon systems correlate with the micropore parameters that are obtained by means of the Jaroniec-Choma equation. This correlation indicates that the BET parameters provide also some information about the microporosity of the solid adsorbents.

Application of an exponential isotherm equation for describing gas adsorption on microporous activated carbons

A new equation for gas adsorption on microporous solids is proposed on the basis of the exponential adsorption isotherm, which is generated by the virial expansion of the spreading pressure. Expressions associated with this equation are derived also for the adsorption potential distribution, the differential molar enthalpy, and the differential molar entropy of adsorption. It is shown that this equation gives a good description of benzene adsorption on activated carbons with different degrees of microporosity and structural heterogeneity.

Carbon‐, alumina‐, and silica‐supported iron sulfide catalysts

AbstractIron sulfide catalysts supported on various carbon materials, on alumina and on silica were compared for their thiophene hydrodesulfurization (HDS) activity measured in a flow micro reactor at atmospheric pressure. The iron content was varied from 0.2–5.0 iron atoms per nm2 support surface area. Mössbauer spectroscopy and X‐ray photoelectron spectroscopy (XPS) were used to characterize the nature and dispersion of the iron phases present in oxidic and sulfided catalysts.Within the surface loading range studied, carbon‐supported iron sulfide catalysts are much more active for thiophene HDS than the alumina‐ and silica‐supported ones. The activity of sulfided iron on alumina catalysts was found to be even lower than expected on the basis of data obtained earlier for other (supported) transition metal sulfides. This is most likely caused by an incomplete sulfidation. Among the various carbon supports employed, activated carbons, despite their high degree of micro porosity are more suitable than carbon blacks and carbon black composites.Based on a comparison of the effective Debye temperature derived from Mössbauer data with dispersions also obtained from Mössbauer measurements on oxidic catalyst precursors, the interaction between the iron‐containing phase and the various carbon supports is described in a qualitative way.

Surface characteristics of carbon fibres from PAN

Surface characteristics of the three types of commercial carbon fibres from PAN, in both treated and untreated forms, have been investigated along with a series of high modulus (HM) fibres oxidised in HNO 3. N 2 adsorption isotherms have been used to elucidate physical characteristics and O 2 chemisorption measurements to determine the area on which surface complexes can form, the so called “active surface area”. Comparative plots show that there is no microporosity developed during surface treatment of fibres, but high temperature degassing does bring about a degree of microporosity, as suggested by Mimeault and McKee[5]. The external area of HM fibres is increased by HNO 3 oxidation but there is little difference between the areas of untreated fibres and those surface treated by the supplier. Both types of treatment, however, increase the active surface areas by factors of 3–30 times, and also increase the fraction of the external surface which is in the form of edge, or active, sites.