Total Silica Content Research Articles

Compatibilization Mechanism of Polyimide-Silica Hybrids with Organofunctional Trialkoxysilanes

ABSTRACTThe polyimide hybrids that have been most widely studied by the authors contain a silica phase produced from tetraethoxysilane by the sol-gel method. Despite the expected strong interactions, through H-bonds, between the polyamic acid precursor for the polyimide and the large number of hydroxyl groups from the silica phase, it is rather difficult to prevent phase separation and rapid coarsening of the morphology upon removal of the solvent from the original solution mixture. These systems can be compatibilized, however, with the selective use of functionalized trialkoxysilane coupling agents, such as glycidyl and isocyanate types.In the present work we have established that compatibilty is achieved only upon exceeding a critical concentration of coupling agent, which increases linearly with the total silica content up to a certain level. This was found to be connected with the ability of the coupling agent to displace the strongly associated solvent molecules with the amic acid units of the polymer chains in order to develop the required level of interactions across the interface between the organic and inorganic components.

Studies on Nd-doped colloidopolymeric silica xerogel

Abstract Neodymia—silica laser glasses with homogeneously dispersed neodymia have been developed using neodymium acetate and a sol of fumed silica and CH 3 COOH acidified TEOS as precursors. The ease of preparation of bulk glasses with lower hydroxyl content makes the colloido-polymeric (hybrid) route attractive. Density, TEM, SEM-EDAX, refractive index and fluorescence studies all point to the fact that the solubility of neodymium in silica is influenced by the nature of the anionic species of the neodymium precursor and the relative amount of TEOS-derived silica in the total silica content of the hybrid gel.

Wear characteristics of PDC pin and hybrid core bits in rock drilling

Drilling cost is controlled to a large extent by the drilling rate which is heavily influenced by the wear condition of the bit. Developments in polycrystalline diamond compact (PDC) production techniques have enabled the manufacture of rectangular “pins” of material which have been incorporated into various forms of core bits. The wear characteristics of these bits are controlled by a range of factors, however, the principal factors which need to be considered in predicting wear rates are the bit, the bit operating parameters and the characteristics of the penetrated rock. A variety of rock types were drilled using two types of PDC (pin and hybrid) and impregnated diamond core bits using a fully instrumented laboratory drilling rig at different rotational speeds and over a range of weights on bit. A wide range of textural, mechanical and intact properties of the rocks were quantitatively determined. Wear (Weight loss and height loss) of each bit were measured after a series of holes were drilled in each rock type. The wear of PDC bits can take many forms, however, the most common wear mechanism operating on PDC bits during rock drilling is abrasion. Impact loading and impact fatigue also accelerates the wear of bits. The effects of the rock properties and the operating parameters on the wear performance of the bits were examined. Total silica content, grain shape factor, Moh's and Shore hardness, and abrasivity indexes were found to have most influence on the wear rate of the bits. A reduction in rotational speed led to an increase in wear rate with less than optimal performance of the bits. The abrasive wear volume loss is linearly proportional to the WOB and torque.

Silica incorporation in the diatomCosinodiscus graniias affected by light intensity

Changes in the silicate concentration of the culture medium at growth-saturating concentrations had little effect on the silica content of cells of Coscinodiscus granii Gough at a given light intensity. However, there was a highly significant inverse relationship between silica content and light intensity. At a silicate concentration of 250 μmol 1-1, the total silica content fell from 207 pmol cell-1 at a light intensity of 14 μmol m-2 s-1 to 29 pmol cell-1 at 150 μmol m-2 s-1. The corresponding fall in the frustule silica was from 9·2 fmol μm-2 to 1·8 fmol μm-2. The total silica content of diatom cells cannot be explained solely in terms of silicate uptake and duration of uptake is the most obvious modifying factor. It is suggested that under conditions inducing low growth rates (low light intensities) the cells are exposed to silica absorption for a longer period than cells under conditions inducing high growth rates (high light intensities) and that this results in the higher cellular silica content.

Lung Dust Content and Response in Guinea Pigs Inhaling Three Forms of Silica

Guinea pigs were exposed by inhalation to atmospheric suspensions of crystalline free silica (cristobalite), amorphous free silica (diatomaceous earth), and amorphous silicate (volcanic glass). Randomly selected animals were killed at 2-month intervals and their lungs were examined. Tissue samples were collected and analyzed for total silica content and total ash. Total silica content per lung increased linearly throughout at least 21 months in each experiment and total ash weight increased more rapidly than dust was accumulating. Crystalline silica produced a greater increment in ash weight that did the amorphous free silica and the silicate produced the least increase. Furthermore, although atmospheric dust concentrations were roughly comparable for the three preparations, the total amount of silica accumulated varied inversely with the degree of tissue damage occurring. Thus, the maximum total content of the crystalline silica reached only 68 mg per lung, while that of the amorphous silica and silicate was 120 mg and 465 mg, respectively. This suggests that a silicious dust that produces cell damage may be cleared more effectively from the lung than is an innocuous dust.

A normative calculation technique for determining opal in deep-sea sediments

The opal content of deep-sea sediment can be estimated by subtracting non-biogenic silica, calculated from the aluminum and magnesium concentrations in the sediment, from the total silica content of the samples. Unlike most previously described methods, this calculation is capable of yielding reliable estimates of opal in pre-Pleistocene sediments because it is unaffected by structural changes that take place in opal as it ages.

Hygienic Studies on the Silica Contained in Drinking Water

Silicosis poses a problem in the field of public welfare now. A member of reports indicate that silica causes arteriosclerosis. From the viewpoints of public hygiene, the author investigated the in vivo effects of silica taken by the oral route, namely by determining the quantity of silica contained in drinking water and its pattern of absorption in the living body. The results obtained were as follows : 1. Determinations were made on the quntities of silica containd in those drinking water samples collected in Kyogok Ucho, Hokkaido, in Tokyo-to, in Akiyama Muro, Yamanashi Prefecture, and in Gotenba City, Shizuoka Prefecture, with the result that apparent differences in the content of soluble silica were noted among the drinking water samples tested, In particular, the silica content of the drinking water sample collected in Kyogok Ucho, Hokkaido, was conspicuously high. 2. Each of the drinking water samples above indicated a high linear coefficient in the correlation between the soluble silica content (determined by means of the colorimetric silicomolybidate method) and the total silica content (determined by means of the gravimetric method). In the regression line, furthermore, these were significant differences noted among the drinking water samples tested. 3. In normal rabbits, a silicate (Na2SiO3) solution was immediately absorbed from the stomack and serum levels of SiO2 were increased. Also, its rapidly excretions into the urine were observed. 4. In normal rats, a silicate (Na2SiO3) solution was absorbed from the small intestines, particularly well from the duodenum. 5. Rats were given Na2SiO3 solution at dosages of 1mg. daily over a perioa of 25 weeks. They did not develop any differences from control rats in terms of the pattern of growth. Pathological findings on the artery were normal.

The Pattern and Sequence of Opaline Silica Deposition in Rye (Secale cereale L.)

The pattern of opaline silica deposition in the leaves and internodes of rye (i Secale cereale L.) has been studied by means of counts of silica-bodies in cleared epidermal preparations. Silica deposition occurs during the maturation process when the leaves are fully expanded. The increase in total silica content and changes in the 'free' and residual silica fractions of the leaves during their growth period have been determined using a colorimetrie estimation.

High‐Temperature Firing of Basic Refractories

An investigation was conducted to determine the hot modulus of rupture strength, the tendency to burst under iron oxide attack, the tendency to creep, and the hot‐load‐bearing strength of chromite‐bearing basic refractories fired from 1400° to 2000°C. Petrographic examination was employed to define the mechanisms of improved bonding which resulted from firing at high temperatures. The results of these physical and chemical tests and the observed microstructure indicated that a greatly improved, highly stabilized basic refractory could be obtained by proper brick design and firing to temperatures of approximately 1700°C. Control of design features such as total silica content, chromite/periclase ratio, and chromite sizing was found to be necessary to achieve superior properties through high‐temperature firing.