Localization of silica in Equisetum arvense (horsetail)

1992 ◽  
Vol 50 (1) ◽  
pp. 856-857
Author(s):  
Barbara A. Reine
Keyword(s):  
Vascular Plants ◽  
Silica Content ◽  
Hydrated Silica ◽  
Rice Hulls ◽  
Reproductive Structures ◽  
Free Silica ◽  
Silicon Carbide Whiskers ◽  
Temperature Regimes ◽  
Significant Public Health ◽  
Substantial Extent

Silica is deposited as amorphous silica gel in the shoots (as well as in leaves, roots and reproductive structures) of many vascular plants such as grasses and cereals (notably rice and oat), hemp, pea, nettle, palms, sedges, and horsetails. Of this group, the horsetails, grasses and sedges, exhibit an especially pronounced capacity to take up large amounts of silicon as silicic acid from the soil and polymerize it as hydrated silica in various tissue locations and sometimes specialized cells (3). The application of this naturally produced silica and other minerals to technology, has stimulated a renewed and refocused interest in biomineralization (2). Historically, the silica-impregnated shoots of horsetails (Equiserum) were used by pioneer settlers for scouring dirty dishes and as a substitute for sandpaper. Today, rice hulls, whose silica content can exceed 20 wt.%, are pyrolyzed commercially to produce silicon carbide whiskers and platelets for use in composites. Rice hulls are also used as fuel in co-generation plants in rice-growing regions of the country but if combustion takes place in certain oxygen concentration and temperature regimes, crystalline “free silica” forms to a substantial extent and. if discharged as respirable dust, may present a significant public health risk.

scholarly journals Evaluation of Occupational Exposure to Silica Dust in Mining Workers in Eastern Iran

2019 ◽  
Vol 12 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Farideh Golbabaei ◽  
Abdollah Gholami ◽  
Gholamheidar Teimori-Boghsani ◽  
Mehdi Yaseri ◽  
Mojtaba Kianmehr
Keyword(s):  
Occupational Safety ◽  
Cross Sectional Study ◽  
Silica Content ◽  
Crystalline Silica ◽  
Respirable Dust ◽  
Breathing Zone ◽  
Mining Operations ◽  
Cross Sectional ◽  
Silica Dust ◽  
Free Silica

Background and Objective: Silica dust is present in almost all mining operations and can cause various health problems such as silicosis in workers. The present study aimed to determine the total and respirable dust levels and the crystalline silica content of the soil in the breathing zone of workers in Iranian mines. Methods: This cross-sectional study was carried out in 2016-2017 on six Iranian silica mines. Dust sampling was performed according to the National Institute of Occupational Safety and Health (NIOSH) method No. 0600. The samples were collected from the respiratory zone of workers at 114 stations in different units of the mines. The silica content was measured using the standard NIOSH method No. 7601. The crystalline silica content in bulk samples collected from the soil was determined by using the X-Ray Diffraction (XRD) spectroscopy method. Results: The highest concentration of crystalline silica dust was 2.81±0.49 mg/m3 and was observed in the air of crushing unit of mine no. 6, and the lowest was 0.08±0.208 mg/m3 and was measured in the management/administration unit of mine no.1. The mean silica content in the solid surface of the mines was 91%. The total and respirable dust levels in all units of the mines except management/administration were higher than the permissible limit. The free silica content of all collected samples was substantially higher than the permissible limits, and in some cases, it was as much as 100 times above the standard level, which reflects the extremely high risk of working in these mines. Conclusion: Exposure of workers with crystalline silica dust in all units was higher than the standard recommended limits. It is imperative to adopt immediate measures based on technical, managerial, and personal protection solutions to reduce the exposure of workers to silica.

scholarly journals New perspectives in nectar evolution and ecology: simple alimentary reward or a complex multiorganism interaction?

2017 ◽  
Vol 70 (1) ◽  
Author(s):  
Massimo Nepi
Keyword(s):  
Amino Acids ◽  
Vascular Plants ◽  
Amino Acid Content ◽  
Secondary Compounds ◽  
Indirect Defense ◽  
Plant Tissues ◽  
Plant Fitness ◽  
Reproductive Structures ◽  
Floral Nectaries ◽  
Plant Animal Interactions

Floral and extra-floral nectars are secretions elaborated by specific organs (nectaries) that can be associated with plant reproductive structures (the so-called floral nectaries found only in angiosperms) or vegetative parts (extrafloral nectaries). These secretions are common in terrestrial vascular plants, especially angiosperms. Although gymnosperms do not seem to have true nectar, their ovular secretions may share evolutionary links with angiosperm nectar. Nectar is generally involved in interactions with animals and by virtue of its sugar and amino acid content, it has been considered a reward offered by plants to animals in exchange for benefits, mainly pollination and indirect defense against herbivores. These relationships are often cited as examples of classical mutualistic interactions. Nonetheless, recent studies dealing with compounds less abundant than sugars and amino acids challenge this view and suggest that nectar is much more complex than simply a reward in the form of food. Nectar proteins (nectarins) and nectar secondary compounds have no primary nutritious function but are involved in plant–animal relationships in other ways. Nectarins protect against proliferation of microorganisms and infection of plant tissues by pathogens. Nectar secondary compounds can be involved in modulating the behavior of nectar feeders, maximizing benefits for the plant. Nectar-dwelling microorganisms (mainly yeasts) were recently revealed to be a third partner in the scenario of plant–animal interactions mediated by nectar. There is evidence that yeast has a remarkable impact on nectar feeder behavior, although the effects on plant fitness have not yet been clearly assessed.

scholarly journals Life cycle assessment of crushed glass abrasive manufacturing from recycled glass

2021 ◽  
Vol 880 (1) ◽  
pp. 012054
Author(s):  
I Zulkarnain ◽  
L S Lai ◽  
M I Syakir ◽  
A A Rahman ◽  
S Yusuff ◽  
...  
Keyword(s):  
Life Cycle Assessment ◽  
Life Cycle ◽  
Raw Materials ◽  
Silica Content ◽  
Motivation Factors ◽  
Recycled Glass ◽  
Free Silica ◽  
Disability Adjusted Life ◽  
Carbon Emissions Reduction ◽  
Development Goals

Abstract Sustainable Development Goals (SDGs) are the key motivation factors to determine the characteristics of green abrasives, contributing to carbon emissions reduction, reduce waste generation and build up a recycling-based sustainable blasting industry. Such aim can be evaluated through life cycle assessment as a structured basis for evaluating the performance of environmental impacts and benefits of green abrasives application in blasting industry. Crushed glass is one of zero free silica content abrasives from recycled glass, and it is widely used due to inert and safe characteristics. Database of life cycle inventory (LCI) are obtained through literature review. Production of 1 ton/year of crushed glass abrasives has been modelled at gate-to-gate boundary where the human health appears as the major impact potentials (0.71 DALY, disability-adjusted life year) at the production stage. The selection of 100% recycled glass as the raw materials in the supply chain has led to insignificant impact potentials of resources scarcity and ecosystem damages per unit production of 1 ton of crushed glass at USD 4.79 and 0.06 species. year, respectively.

scholarly journals Determination of Free Silica Content on the Deck Glass

1958 ◽  
Vol 74 (846) ◽  
pp. 1001-1005
Author(s):  
Yoshikazu HAGIWARA ◽  
Tadaharu NAKAMURA
Keyword(s):  
Silica Content ◽  
Free Silica

ACID ACTIVATION OF MONTMORILLONITE

1960 ◽  
Vol 38 (6) ◽  
pp. 1003-1016 ◽  
Author(s):  
R. D. Heyding ◽  
R. Ironside ◽  
A. R. Norris ◽  
R. Y. Prysiazniuk
Keyword(s):  
Metal Ion ◽  
Water Surface ◽  
Silica Content ◽  
Acid Activation ◽  
Hydrated Silica ◽  
Dry Process ◽  
Wet Process ◽  
Surface Areas ◽  
Removal Of Metal ◽  
Removal Of Metal Ions

A Pembina montmorillonite clay has been activated with sulphuric acid at various dosages by the conventional wet process and by the new "dry" process. The products are compared with respect to the fractions of the metal ion components remaining after leaching, the hydrated silica content, the bleaching capacity, and the B.E.T. nitrogen and water surface areas which they exhibit. Surface areas were also determined after calcining the products invacuo. The surface areas are discussed with reference to the removal of metal ions occupying octahedral lattice sites in a model clay particle.

scholarly journals Assessment of Occupational Dust and Silica Exposure in Indian Stone Mining and Crushing Unit- A Case Study

2017 ◽  
Vol 12 (3) ◽  
pp. 661-669
Author(s):  
Anand Deshmukh ◽  
Nikhil Pradip ◽  
Sarang Dhatrak ◽  
Subroto Nandi
Keyword(s):  
Personal Exposure ◽  
Mining Area ◽  
Silica Content ◽  
Vital Role ◽  
Dust Exposure ◽  
Silica Exposure ◽  
Free Silica ◽  
Limit Value ◽  
Exposure Limit ◽  
Precautionary Measures

Stone crushing industry plays a vital role in the economy and urban development of fast developing countries like India. Stone mines and crushers in India are located around major cities and roughly employ around 5,00,000 peoples throughout the country. However this employment generating industry also happens to be one of the most dust generating activity and also a precursor to the respiratory disease, silicosis. This study was undertaken with an objective to estimate the personal exposure of the workers to silica laden dust in this industry sector. Personal dust sampling (n=11) and (n=6) was carried out in stone crushing and stone mining (quarry)areas respectively over a period of three consecutive days in selected units in a suburban area of Nalgonda district of Telangana state in India. The respirable dust exposure and free silica content was then estimated. It was observed that three (3) samples of crusher helper from the Crushing Unit had exposures exceeding the Permissible Limit Value (PLV) of Indian Factories Act1948. Two (2) Heavy Earth Moving Machineries (HEMM) operators from stone mining area were observed to have exceeded the Permissible Maximum Exposure Limit (PMEL) prescribed by the Indian Mines Act 1952 and subsequent rules their under. The remaining samples of HEMM operators from mining area and of the crusher helper from the crusher plant were observed to be within the prescribed limits of respective guidelines prescribed by the Indian statutory agencies. Two different acts were considered, because of the fact that stone mining is regulated by the Indian mining act and under the overall control of Directorate of Mines and Safety (DGMS), Government of India. On the other hand Crusher plant comes under the ambit of Model Factory Rule 120 under section 87 of Indian Factories Act 1948 under the overall control of Directorate General Factory Service and Labour Institute (DGFASLI) Government of India. Post the study it could be concluded that, stone crushers are dustier as compared to stone mining area. Workers in stone mining and crushing units of study area are indeed exposed to high levels of respirable and silica laden dust. It was observed that safety and precautionary measures towards dust and silica exposure are not implemented necessitating to be taken by unit operators.

The Microstructure of Ceramic Whiskers

1991 ◽  
Vol 49 ◽  
pp. 918-919
Author(s):  
L. F. Allard ◽  
T. A. Nolan
Keyword(s):  
Silicon Carbide ◽  
Second Phase ◽  
Tin Whisker ◽  
Ferrous Alloys ◽  
Vapor Liquid Solid ◽  
Rice Hulls ◽  
Aspect Ratios ◽  
Silicon Carbide Whiskers ◽  
Synthetic Materials ◽  
Sic Whiskers

The internal structure and surface crystallography of ceramic whiskers are of interest because of their increasing importance as second phase reinforcements in a variety of matrix materials. Whiskers are typically 0.5 to 5 um in diameter with aspect ratios of 10 to 100 or more. Silicon carbide whiskers are the best known; they are usually grown by vapor-liquid-solid (VLS) or other processes from either natural (e.g. rice hulls) or synthetic materials. Titanium nitride whiskers are also of interest because of their potential for applications where SiC whiskers are not suitable (e.g. ferrous alloys). This paper highlights some of the details of SiC and TiN whisker ultrastructure.

Compositional and Structural Deficiencies Causing Failure of Local Fire Assaying Crucibles in Ghana

2020 ◽  
Vol 51 ◽  
pp. 57-70
Author(s):  
Yongdan Hou ◽  
Lemuel Gbologah ◽  
Derrick Boateng Asante ◽  
Parpah Senanu Kwawukume
Keyword(s):  
Field Investigation ◽  
Silica Content ◽  
High Alumina ◽  
High Porosity ◽  
Quartz Content ◽  
Structural Investigations ◽  
Mullite Phase ◽  
Free Silica ◽  
Basic Flux ◽  
Stable Performance

Locally produced crucibles in Ghana experience dimensional failures during fire assaying of ores, therefore, even with a higher cost, imported crucibles are still the most preferred choice by laboratories in Ghana because of the stable performance of up to three cycles. Assay crucibles of locally manufactured, imported and theoretically composed were sampled and analysed via reverse engineering to identify factors that are attributed to the failure during use. Field investigation and compositional, physical and structural investigations were carried out using XRD, water boiling and SEM-EDS analyses, respectively. The results indicated that failure of the local crucible can be attributed to low mullite phase in both content and planes, which could ease the crack development and enhance the thermal stability of the crucible; non converted quartz into cristobalite, which stabilises the volume expansion coefficient during the fire assaying cycles; excess quartz content and absence of alumina content weakened the corrosion resistance against attack from the basic flux of litharge; and high porosity, allowed penetration of molten charge into the structure of crucible, leading to the dissolution of free silica content into the charge and causing structural failure. To overcome such deficiencies, higher firing temperature (~1240 °C), extra soaking time, and blending of high alumina contained clay/minerals were suggested.

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