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Particulates silica

Generally speaking, commercial rubber products are manufactured as a composite from a rubber and a nano-filler, which is in a group of fillers of nanometer size (mainly, carbon black and particulate silica). For an example, a pneumatic tire for heavy-duty usages such as aircrafts and heavyweight tracks is made from natural rubber (NR) and carbon black and/or silica. Their reinforcing ability onto rubbers makes them an indispensable component in the rubber products [1,2]. [Pg.543]

In simple experiments, particulate silica-supported CSPs having various cin-chonan carbamate selectors immobilized to the surface were employed in an enantioselective liquid-solid batch extraction process for the enantioselective enrichment of the weak binding enantiomer of amino acid derivatives in the liquid phase (methanol-0.1M ammonium acetate buffer pH 6) and the stronger binding enantiomer in the solid phase [64]. For example, when a CSP with the 6>-9-(tcrt-butylcarbamoyl)-6 -neopentoxy-cinchonidine selector was employed at an about 10-fold molar excess as related to the DNB-Leu selectand which was dissolved as a racemate in the liquid phase specified earlier, an enantiomeric excess of 89% could be measured in the supernatant after a single extraction step (i.e., a single equilibration step). This corresponds to an enantioselectivity factor of 17.7 (a-value in HPLC amounted to 31.7). Such a batch extraction method could serve as enrichment technique in hybrid processes such as in combination with, for example, crystallization. In the presented study, it was however used for screening of the enantiomer separation power of a series of CSPs. [Pg.94]

The rain rate of BSi is dependent on (1) the rate of its production by marine organisms, (2) shell dissolution rates, and (3) the time required for a shell to reach the seafloor. High rates of production by siliceous plankton ensure a large supply of opal to the water column. The fraction reaching the seafloor is largest when transit times are shortest. Thus, shells that sink fastest will be preferentially preserved and a greater fraction of the particulate silica flux reaches sediments that lie in shallow waters. [Pg.411]

Commercial materials with these specifications are relatively expensive and because cheap particulate silica materials with the right pore diameter are available a granulation process has been developed by Pedersen, Larsen, and Aasmul (1995). [Pg.253]

Evidently, the particulate silica used in Alexander s and Baumann s experiments behaved like polymeric silicic acid. This opinion is supported by the fact that stable solutions of polymeric silicic acids have practically no polymers in the intermediate size range between oligomers and high polymers (19). Correspondingly, in the presence of colloidal... [Pg.168]

Figure 3-22. Cumulative pore volume distribution of different HPLC columns indicating monomodal pore size distribution for polymer monolith and bimodal distributions for both packed particulate silica and silica monolith columns. (Reprinted from reference 90, with permission.)... Figure 3-22. Cumulative pore volume distribution of different HPLC columns indicating monomodal pore size distribution for polymer monolith and bimodal distributions for both packed particulate silica and silica monolith columns. (Reprinted from reference 90, with permission.)...
Schindler (29, 30) took whole-ocean residence times for various elements, as given by Goldberg (32), and found reasonable agreement between these and the residence times with respect to adsorption calculated from his model. His choice of properties took h equal to 10 , Tp for particulate silica to be 2 x 10 years and a to be 2 x 10 ° kg of suspended silica 1 (2 mg silica 1" ). The term Co was taken to be 1.0 mol kg of silica, which led to a value of C of 0.509 mol kg , indicating that approximately 50% of the surface silanol groups are occupied by adsorbed The choice of silica as a model oxide surface is... [Pg.268]

Table 1 Effect of amount of porogen on the pore structural parameters of particulate silicas. Synthesis conditions 500 ml of PES (viscosity 75 mP s). Cyclohexane 0, 150, 300, 450 and 600 ml, 3,000 ml of 2-propanol, 250 ml of ammonia, stirring speed 1,500 rpm. Table 1 Effect of amount of porogen on the pore structural parameters of particulate silicas. Synthesis conditions 500 ml of PES (viscosity 75 mP s). Cyclohexane 0, 150, 300, 450 and 600 ml, 3,000 ml of 2-propanol, 250 ml of ammonia, stirring speed 1,500 rpm.
Figure 1 Apparent pore volume distributions of particulate silicas Gl-G to G5-G according to BJH from the nitrogen desorption isotherms. Figure 1 Apparent pore volume distributions of particulate silicas Gl-G to G5-G according to BJH from the nitrogen desorption isotherms.
The results of the characterisation of the monolithic silicas are summarised in Tab. 2. The investigated materials possess very similar mesopore structural parameters as the particulate silicas in Tab. 1. The a (BET) values are approximately 300 m g , the mesopore volumes are all about 0.9mlg , the average mesopore diameters scatter around 12 nm. The specific macropore volume is slightly increasing from PKlll to PK118 with the exception of PK114. [Pg.118]

Silica type Particulate silica Monolithic silica ... [Pg.121]

The Kf values for the particulate silica columns indicate a decrease of the permeability with increasing average mesopore diameter, increasing total porosity and increasing pore connectivity at constant average particle diameter of 10 pm. The monolithic column show a slight increase of the permeability with increasing macropore diameter at constant total porosity which is to be expected. [Pg.121]

Studies of particulate silicas from heavy silicon accumulators such as the horsetail plant, Equisetum arvense, have shown that various parts of the plant deposit principally single motifs (19). In the primi-... [Pg.147]

Aluminum for the manufacture of aluminum-rich zeolites is obtained from sodium aluminate solutions, which are obtained by dissolving aluminum oxide hydrate in sodium hydroxide. Silica is used in the form of water glass, fine particulate silica (e.g. silica fillers) or silica sols. The cheaper water glass is preferred, but exhibits the lowest activity of the above-mentioned sources of silica. The reaction has therefore to be carried out in a special way to... [Pg.344]

The oldest, but in the meantime least significant process for the production of fine particulate silica, is the oxidation of gaseous silicon monoxide with air. Quartz sand and fine particulate coke can, for example, be used as starting materials and are reacted with one another in an electric arc as follows ... [Pg.539]

Contaminants. Fe and A1 ions can become chemically adsorbed onto surfaces of particulate silica and inhibit dissolution (Jones and Handreck, 1967) occluded carbonaceous matter also has been suggested as possibly having an inhibitory effect on the dissolution of phytoliths (Wilding and Drees, 1974). [Pg.471]

In addition to the considerable amount of dissolution of biogenic silica that takes place in the oceanic water column, further dissolution of siliceous tests and spicules occurs within the marine sedimentary pile. Recent estimates of the proportion of deposited particulate silica that redissolves... [Pg.476]

The rapid development of HPLC columns for example was due to three major technical achievements the ability to manufacture micro-particulate silicas, the invention of air elutriation technique as sizing technology and progress in the slurry technique for packing HPLC columns. However, it took more than ten years to build up sufficient know-how to produce stable, robust and reproducible HPLC columns that satisfied the continuously increasing demands of the chemical and pharmaceutical industry (Fig. 1.2). [Pg.3]

Table 3.7 Synthesis and post-synthetic steps of an analytical 5(j,m spherical particulate silica with a Clg-modified silica surface. Table 3.7 Synthesis and post-synthetic steps of an analytical 5(j,m spherical particulate silica with a Clg-modified silica surface.
B.J. Ninness, D.W. Bousfield and C.P. Tripp, An in situ infrared technique for studying adsorption onto particulate silica surfaces from aqueous solutions, App. Spec., 55, p.655 (2001). [Pg.79]

The difficulties encountered in LLC can be overcome by the use of chemically bonded stationary phases or bonded-phases. Most bonded phases consist of organochlorosilanes or organoalkoxysilanes reacted with micro-particulate silica gel to form a stable siloxane bond. The conditions can be controlled to yield monomeric phases or polymeric phases. The former provides better efficiency because of rapid mass transfer of solute, whereas the polymeric phases provides higher sample capacity. BPC can be used in solvent gradient mode since the stationary phase is bonded and will not strip. Both normal-phase BPC (polar stationary, non-polar mobile) and reversed-phase BPC (non-polar stationary, polar mobile) can be performed. The latter is ideal for substances which are insoluble or sparingly soluble in water, but soluble in alcohols. Since many compounds exhibit this behaviour, reversed phase BPC accounts for about 60% of published applications. The main disadvantage of silica bonded phases is that the pH must be kept between 2 to 7.5. However, bonded phases with polymer bases (polystyrene-divinylbenzene) can be used in the pH range of 0 to 14. [Pg.22]

Characterization of Colloidal and Particulate Silica by Field-Flow Fractionation... [Pg.301]


See other pages where Particulates silica is mentioned: [Pg.237]    [Pg.150]    [Pg.159]    [Pg.191]    [Pg.490]    [Pg.491]    [Pg.493]    [Pg.159]    [Pg.336]    [Pg.551]    [Pg.507]    [Pg.539]    [Pg.280]    [Pg.198]    [Pg.116]    [Pg.116]    [Pg.117]    [Pg.121]    [Pg.758]    [Pg.588]    [Pg.1371]    [Pg.467]    [Pg.467]    [Pg.469]    [Pg.472]    [Pg.477]    [Pg.477]    [Pg.2269]    [Pg.647]   


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