Free Silica Research Articles

Effect of Particle Size and Sintering Temperature on the Formation of Mullite from Kyanite and Aluminum Mixtures

The effect of particle size and sintering temperature of the mixtures of kyanite and metallic aluminum related to the thermal transformation of kyanite into primary mullite and free silica was studied. In addition, the reaction between α‐Al2O3 (in situ produced by aluminum oxidation) and the silica was obtained in cristobalite structure from kyanite to obtain secondary mullite. The kyanite powders were milled by 0.5, 3, 6, and 12 hours and then were mixed with aluminum powder, which were previously milled by 3 hours. After that, the powders were characterized by X‐ray diffraction technique (XRD), scanning electronic microscopy (SEM), differential thermal analysis (DTA), and thermogravimetric analysis (TGA), and the particle size was determined in a centrifugal analyzer particle size Shimadzu model SA‐CP4. The mixed powders were pressed uniaxially into cylindrical samples (compacts), and then sintering was conducted at 1100, 1200, 1300, 1400, 1500, and 1600°C; these samples were characterized by XRD, SEM, and thermodilatometry analysis (TD); density and open porosity measurements were performed by the Archimedes method. The samples were thermally etched to observe the microstructure, which consisted of mullite equiaxial grains contained in a glassy phase. It was observed that the nonmilled kyanite mineral becomes into mullite plus silica at temperatures between 1400 and 1500°C. When the particle size was reduced at sizes less than 1 µm, the transformation temperature was low until 200°C; the X‐ray patterns of the sintered samples at 1400°C, ground for 6 hours, showed mullite peaks with small reflections of cristobalite and α‐Al2O3, and these samples exhibited high density and low open porosity.

Synthesis and characterization of novel binders free high hydrophobic silica nano particles spray

Among various nano materials, Silica is quite interesting in hydrophobic applications due to its non-toxic, hydrophobic and eco-friendly nature. A cost effective Sol-Gel method is employed to synthesize Silica nanoparticles followed by calcination (650 °C). In contrast to conventional Ethanol in various reports, here Tetrahydrofuran is used as a solvent with controlled reaction time, pH and temperature. UV–Visible Absorption Spectroscopy, X – Ray Diffraction, Dynamic Light Scattering, Energy Dispersive X-Ray Analysis, Scanning Electron Microscopy and Optical Goniometer are used to characterize the material. A portable-cost effective binder free spray with high transparency coating was obtained with 116.4° contact angle.

In situ preparation of inorganic nanoparticles in amino‐functionalized porous cellulose particles

AbstractAmino‐functionalized cellulose particles with a porous structure were prepared by a solvent‐releasing method with 1‐butyl‐3‐methylimdazolium chloride ([Bmim]Cl) followed by an amination reaction, and were incorporated with silica. The amino groups provided the base catalyst for the formation of silica on the porous structure during the in situ sol–gel reaction of tetraethyl orthosilicate. After the reaction, no free silica remained in the reaction medium. The microscopic morphologies (specific surface area, pore diameter, and pore volume) of the composite particles were affected by the silica content in the composites, which was controllable by the sol–gel reaction time. When silver nanoparticles were introduced to the pores of the cellulose particles by reduction of AgNO3 with amino groups, the composite exhibited catalytic ability and recyclability.

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

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.

Intelligent dry fog dust suppression system: an efficient technique for controlling air pollution in the mineral processing plant

Dust suppression system plays a significant role in mining and allied industries. It has become an integral part of the environmental management system. Dust emission from mining and mineral processing industries poses environmental and health problems to workers and surrounding people. Dust creates a reliability issue in machinery and ventilation systems, causing infrastructural damage and the industry’s financial losses. This paper deals with a smart dry fog dust suppression system which has been developed for effectively controlling dust emission from mining and mineral processing activities. The system has been implemented in an iron ore crushing and screening plant in India, and its efficacy has been evaluated for controlling dust emission. The installed dry fog system reduced dust concentration to 0.10–0.17 mg m−3 from the prevailing dust concentration of 0.62–1.73 mg m−3 in work zone areas, which was much below the permissible limit below 1 mg m−3 where silica content in the dust was less than 5%. Percentage of free silica in the work zone dust reduced to traces from 3.61 to 4.80%. Similarly, PM10 and PM2.5 concentrations in the ambient air were decreased to 90–99 μg m−3 and 49–58 μg m−3 from 185 to 250 μg m−3 and 148–200 μg m−3, respectively. Further, concentrations of PM10 and PM2.5 were drastically reduced by 51.35–60.4% and 69.69–71.0%, respectively. The reduced dust concentrations in the ambient air were within the prescribed limit of PM10 (100 μg m−3) and PM2.5 (60 μg m−3). The system significantly reduces dust and free silica concentration in the work zone areas below the permissible limit. The system controls dust emission with an increase in production as it has been found that the number of nozzles is directly correlated with a reduction in dust. Furthermore, the system does not change the raw material’s mass as water added to dust is less than 0.01% of the raw material. The system is designed to give the best results within the closed environment of the plant. The system helps in eco-friendly and clean mining. The system reduces the breakdown and maintenance cost of mining equipment, thereby decreasing overall operating costs. Further, the system minimizes mine workers’ health problems, like silicosis and severe other occupation diseases. The system is automatic, cost-effective, energy efficient, and easy to maintain. Further, the system is capable of handling dust problems in the closed environment of crushing and screening plants. These properties make the system techno-economically feasible for installation in mineral processing plants.

The improved antibacterial efficiency of a zinc phthalocyanine when embedded on silver nanoparticle modified silica nanofibers.

This work reports on the fabrication and modification of electrospun polymer free silica nanofibers (SiO2 NFs) with the aim of creating heterogeneous antibacterial catalysts. The optical and photophysical properties of the obtained NFs i.e. bare SiO2, Ag-SiO2, Pc-SiO2 and Pc@Ag-SiO2 NFs (Pc = phthalocyanine) were compared and reported. The singlet oxygen quantum yields of the Pc-SiO2 and Pc@Ag-SiO2 NFs were also quantified and found to be 0.08 and 0.12, respectively, in water. All the modified SiO2 NFs were found to possess photoactivity against S. aureus with the most effective being the Pc@Ag-SiO2 NFs due to the synergy between the Pc and Ag nanoparticles. The bare SiO2 NFs do not exhibit any antibacterial activity while the Ag-SiO2 and Pc@Ag-SiO2 NFs were found to also exhibit dark toxicity. The generated photocatalysts are attractive because they are active against bacteria and they are easily retrievable post-application. The nanocatalysts reported herein are therefore feasible candidates for real-life antibacterial applications.

Systematic review and meta-analysis of epidemiological studies on the association of occupational exposure to free crystalline silica and systemic lupus erythematosus.

Some evidence suggests that exposure to free crystalline silica may contribute to the risk of developing SLE. A systematic search was carried out for all published epidemiological studies concerning this association. A meta-analysis was conducted on relevant studies. We searched PubMed and EMBASE databases for original articles published from 1960 to November 2019 in any language. In addition, we also searched the reference lists of included studies manually for additional relevant articles. Finally, seven studies were included in the systematic review and six studies in the meta-analysis (four case-control and two cohort studies). Theodds ratio and 95% CI were calculated using a random effect meta-analysis. The meta-analysis of the studies, applying a random effect model, yielded an overall odds ratio of 3.49 (95% CI, 1.24, 9.83), with I2 = 92.36% (pronounced heterogeneity). We also stratified the meta-analysis by study design; case-control studies: odds ratio 1.85 (95% CI, 0.96, 3.59) with I2 = 75.92%; and cohort studies (cases with silicosis): odds ratio 9.71 (95% CI, 1.13, 83.58) with I2 = 72.65%. The obtained results support the hypothesis of a possible association between occupational exposure to free crystalline silica and SLE, in particular at higher exposure levels, known to induce silicosis. The studies that have investigated this association are still scarce and the heterogeneity between the studies remains high. New studies are deemed necessary to confirm the association.

Multiscale pore structure determination of cement paste via simulation and experiment: The case of alkali-activated metakaolin

Alkali-activated metakaolin (AAMK) is a type of aluminosilicate-rich material often regarded as a potential alternative to ordinary Portland cement due to a smaller carbon footprint. However, the multiscale pore structure of AAMK, and how it is influenced by availability of free silica from the activator, remains largely unknown. Here, a Monte Carlo simulation approach is employed to generate the pore structure of AAMKs with different activator silicate moduli (SiO2/Na2O ratio). The simulation-derived pore size distributions are compared with experimental data obtained using nitrogen sorption (NAD) to assess the validity of the simulation results where qualitative agreement is obtained. The larger length scale pores in AAMKs are characterized using NAD and mercury intrusion porosimetry. This study stresses the importance of using complementary pore characterization techniques when investigating materials with multiscale pore structures, and shows the promise of the simulation approach to predict key transport properties of AAMKs and other cementitious materials.

Surface Properties and Porosity of Silica Particles Studied by Wide-Angle Soft X-ray Scattering

Wide-angle soft X-ray scattering on free silica particles of different porosity prepared in a beam is reported. The explored q region is mostly dominated by features due to surface roughness and bu...

A DESCRIPTIVE STUDY TO ASSESS THE AWARENESS REGARDING SILICOSIS AND ITS PREVENTION AMONG QUARRY WORKERS AT JODHPUR, WITH A VIEW TO DEVELOP INFORMATION BOOKLET

Introduction- Silicosis is one of the oldest occupational lung disease, which is incurable and is caused by inhalation of dust containing free crystalline silica. Silicosis is preventable disease. Still this disease kills thousands of workers around the worlds every year. Various studies have should that the quarry workers due not having awareness regarding silicosis and its prevention. In this study, distribution of booklet among quarry workers is an attempt to improve the knowledge regarding silicosis and it/s prevention. Material and Methods - Quantitative descriptive survey study approach and non experimental research design was used.Total 100 quarry workers working in mining and residing in Jodhpur were selected by purposive sampling technique.Data collection by structured knowledge questionnaire and analysed by using descriptive and inferential statistics. Result - The findings of the study reveals that to the level of awareness shows that majority (52%) of the sample had above average, followed by 48% had below average awareness regarding silicosis and its prevention. However, demographic variables age and educational status indicates significant association with the level of awareness regarding silicosis and its prevention. Conclsion - The awareness of quarry workers regarding silicosis and its prevention have been above average regarding the causes and the management of the silicosis but in regarding the symptoms and prevention of the silicosis have been found below the average level. KEY WORDS - Awareness, Quarry Workers, Silicosis, Information Booklet

Combination of broad emission bands of Ti3+,4+/ Eu2+,3+ co-doped OH− free low silica calcium aluminosilicate glasses as emitting phosphors for white lighting devices

In this report, Ti3+, 4+/Eu2+, 3+ co-doped OH− free low silica calcium aluminosilicate glasses (LSCAS) were synthesized and their optical properties investigated aiming applications as phosphors for white light generation. This research explores the possibility of combining the broad emission bands in the visible of these glasses co-doped with Ti3+,4+/Eu2+ ions with those in the red emitted by Eu3+, in addition to the high luminescence quantum yield they present. The excitation and emission results show that exciting the samples at 300 nm, a broad emission band is generated, embracing very well the visible region. The emission spectra were analyzed by (x-y) CIE-1931 chromaticity diagram and the color rendering index (CRI) presented Ra values up to 80, with the correlate color temperature (CCT) varying from 4995 to 6609 K. The luminescence quantum yield determined by Thermal Lens Spectroscopy showed values of 38 and 42% for the samples with (in wt%) 0.1Eu2O3-2.0TiO2 and 0.5Eu2O3-2.0TiO2, respectively. Finally, the energy transfer processes between these luminescent ions were discussed, highlighting the potential of the Eu–Ti LSCAS glasses as candidates for the development of devices for white light generation.

A General Strategy to Encapsulate Semiconducting Polymers within PEGylated Mesoporous Silica Nanoparticles for Optical Imaging and Drug Delivery

AbstractAlthough semiconducting polymers (SPs) have become an important category for optical imaging and phototherapy, their biomedical application is still facing a number of challenges. Herein, a cationic surfactant–assisted approach to encapsulate hydrophobic SPs within highly PEGylated mesoporous silica (mSiO2) nanoparticles with excellent colloidal stability and enhanced fluorescence in aqueous solution is reported. In comparison to the previously reported amphiphilic polymer coating and silification method, this universal strategy not only suppresses the formation of empty polymer micelles and free silica nanoparticles, but also provides high specific surface area for drug loading. As a proof of concept, furan‐containing diketopyrrolopyrrole‐based semiconducting polymers (PDFT) are coated with mesoporous silica and utilized for fluorescence imaging in the second near‐infrared region (NIR‐II, 1000–1700 nm) and drug delivery. In vivo blood vessel imaging and tumor imaging are achieved with high resolution (0.21 mm) and signal‐to‐background ratio (≈4.2). Additionally, pH‐responsive drug release and improved therapeutic effect are observed. By choosing desired SPs, different optical imaging and therapeutic modalities can also be achieved, thus the SP@mSiO2 nanostructures obtained here provide numerous opportunities for theranostic applications.

Preventive Strategies for Reduction of Occupational Exposure of Free Crystalline Silica Dust in Steel Foundry and Stone Crusher Unit

Mineral extraction operations are characterized by large quantities of dust emission in the environment. Persons who are working in such environments are potentially exposed to the harmful effects of respirable mineral dust, such as impaired lung function. This study investigated the prevalence and correlated the lung function impairment and dust concentrations with different preventive measures followed in the steel foundry as well as stone crusher workers in West Bengal, an eastern part of India.
 This cross-sectional study was conducted on steel foundry workers and also workers employed in stone crushing units. Both types of workers are exposed to free crystalline silica dust in their workplaces. To assess the effectiveness of control measures of dust, the lung function impairment was correlated with types of Personal Protective Equipment (PPE) used by them. The results were analyzed using statistical tools, Pearson's correlation coefficient, and Chi-square test to evaluate the significance level.
 The PPEs used by them were not proper , so it did not prevent lung function impairment For the reduction of airborne dust concentration levels at the stated workplaces, a sprinkling of water was applied. Before and after the sprinkling of water, dust concentration was measured using the NIOSH method-7601 and 7602 (CDC, 2005). The concentration of dust level before and after the application of water sprinkling was found to be statistically significant by using a t-test (α<0.05). Therefore, the periodical water sprinkling method may be applied as a preventive measure for the exposure of dust at work and environment. Use of proper PPE and other recommendations should be implemented.

A study of the chemical effect of marble and granite slurry on green mortar compressive strength

BackgroundThe marble and granite industries in Egypt produce a vast amount of by-product slurry waste that could be used in green mortar production suitable for construction purposes. This research highlights the effect of the chemical constituents of marble and granite waste powders on the compressive strength of the green concrete produced. A chemical analysis of the constituents of granite and marble wastes was compared with those of the cement to study the effect of these components on the hydration reaction inside the mixture. The experiment was based on replacing the same proportions of sand and cement in the green concrete mixes with each of granite and marble waste powders after dissolving it in the water content.ResultsThe study revealed that by replacing 5% of cement in (NC5) mix, 10% of sand in (NF10) mix, as well as 5% of cement and 10% of sand in (NC5 + NF10) mix, by granite waste powder, the compressive strength values increased by 33%, 39%, and 41%, respectively. This was due to the presence of more than 26% fine free silica particles in granite which undergo pozzolanic reaction with calcium hydroxide present in mortar pores producing calcium silicate hydrate (CSH) crystals resulting in high strength to the cement mortar. For the same mixes containing marble powder, the compressive strength showed less values by − 14%, 10%, and 0% for NC5, NF10, and NC5 + NF10 mixes, respectively, when compared to the control mix values.ConclusionAlthough the waste particles worked as filler, it was observed that its presence in the mixture improved the particle packing and increased the cohesion of the composites.

Effect of SiO2 on the sintering of cerium-doped lutetium oxyorthosilicate

We present the effect of silica on the preparation of dense Lu2SiO5:Ce (LSO:Ce) compacts. Powders of LSO:Ce were first obtained by combustion synthesis and characterized by thermal analysis, indicating the presence of free amorphous silica in amounts approaching 5 wt%. Calcination treatments at a variety of temperatures resulted in the partial volatilization of the silica and the formation of B-type LSO. However, higher temperatures enhanced agglomeration and particle growth, which can be problematic during the sintering process as it impedes full densification. During subsequent sintering of the powders, evaporation of residual silica may impede full densification and assist the formation of pores, thus an understanding of the presence of silica is important for sintering these materials. Powders calcined at a temperature of 1773 K and densified by spark plasma sintering showed the highest photoluminescence emission intensity. At this temperature there is a trade-off between decreasing electron trap density and oxidation of cerium ions.

Pulmonary tuberculosis among stone miners of India vis-à-vis silica exposure

Background:Tuberculosis is one of the biggest public health concerns in India with a prevalence of 195 cases per 100000. Silica is cytotoxic to macrophage which is primary defense mechanism to tubercular bacilli and, hence, exposure to silica dust increases risk for TB. Silica exposed persons are at 2.8 to 39 times greater risk of affected by pulmonary tuberculosis in comparison to healthy subjects.Methodology:A cross-sectional epidemiological study was conducted among 935 workers in sandstone mining. Full-size posteroanterior view (PA) chest X-ray in full inspiration was evaluated and evidence of tuberculosis was noted. Fourier transform infrared spectrophotometer was used for determining the free silica in 23 dust samples.Results:6.4% X-rays showed evidence of TB and silica dust concentration was 0.11 to 0.16 mg/m3. The TB cases significantly increased from 2% to 6% to 12.7% as the work exposure increased from <10 years to 11–20 years to >20 years respectively. 8.5% of the TB cases were seen among the workers having more than 10 years of work exposure. The odds ratio (95% CI) for work exposure more than 10 years to less than 10 years was 4.53 (1.92–10.65).Conclusion:Reduction of silica particles from work environment can significantly reduce the number of TB cases and hence wet drilling should be practiced and personal protective equipment should be regularly used.

Antimicrobial photodynamic and wound healing activity of curcumin encapsulated in silica nanoparticles.

The multidrug resistance of pathogenic bacteria has become a serious problem to public health. Therefore finding novel approaches to combat multidrug resistant bacteria have therefore become increasingly important. One promising approach is antimicrobial photodynamic therapy (aPDT) which involves the use of photosensitizer (nontoxic dyes) that are excited by visible light and produce oxygen free radicals in the presence of oxygen. In this study, we investigated the antimicrobial photodynamic effect of free curcumin and curcumin silica nanoparticle as photosensitizer on planktonic and biofilm forms of Pseudomonas aeruginosa, Staphylococcus aureus. After performing MTT assay (to evaluate curcumin nano complex toxicity on human fibroblast cells), the effect of aPDT at 465 nm on bacteria in the planktonic and biofilm forms were investigated. The results showed that by using curcumin in the form of curcumin-silica nanoparticle as photosensitizer, there is a reduction in the number of bacteria in planktonic condition and bacterial biofilm production. Curcumin-silica nanoparticle not only did not show any significant cytotoxic effect against human normal fibroblast but also showed wound healing properties as confirmed with in vitro scratch assay. Therefore, aPDT based curcumin-silica nanoparticle could be suggested as novel approach in the treatment of multi drug resistant bacteria in chronic wound infection condition.

Assessment of silica dust exposure profile in relation to prevalence of silicosis among Indian sandstone mine workers: Need for review of standards.

In Indian mines, the prescribed exposure limit (PEL) for free silica dust is 0.15 mg/m3 which is much higher than those of OSHA and the ACGIH. Because of the reporting of high numbers of silicosis cases among Indian sandstone mine workers, the present study was designed to assess the dust exposure profile of the workers and to substantiate correlation of silica exposure with radiographic findings of silicosis. A cross-sectional study of 1012 workers actively engaged in sandstone mining was conducted. Chest x-rays were evaluated by the ILO Classification for the detection of pneumoconiosis. Representative 26 personal dust samples were collected using a personal dust sampler and free silica content estimated. Radiographs compatible with silicosis were seen in 12.3% of workers, of which about 90% were ILO category 1 & 2. Prevalence of abnormal profusion increased from 2.9% to 13.1% to 22% as work exposure increased from <10 to 11 to 20 to >20 years, respectively. In dust samples, the mean silica concentration was 0.12 mg/m3 with 70% samples below the prescribed standard of 0.15 mg/m3 . The study indicates that silica exposure below the prescribed limit in India is likely to be harmful. The PEL for crystalline silica in India of 0.15 mg/m3 is not adequately protective. Hence, there is an urgent need to reduce exposure to silica in these workplaces to prevent silicosis and to review the present standards as the government of India remains committed to the elimination of silicosis by 2030.

The Proportion and Radiological Features of Pneumoconiosis in Workers Exposed to Dust in The Workplace

Background: One of the most common occupational diseases found in workplace is pneumoconiosis. The most disease is silicosis, which is lung disease caused by inhalation of dust containing free crystalline silica which afflicts tens of millions of workers in hazardous work and kill thousands of people worldwide. This study aimed to determine proportion and radiologic appearance of pneumoconiosis in workers exposed to dust in various industrial and mining processes.&#x0D; Method: This research used cross-sectional desaign, was conducted 2017 until September 2019 for various industrial and mining workers exposed to dust. Chest X-ray with digital radiography was read in International Classification of Pneumoconiosis Radiography from ILO version 2011, by a lung specialist who certified by The International Labor Organization (ILO) and The Asian Intensive Reader of Pneumoconiosis Project (AIR Pneumo). &#x0D; Results: ILO chest X-ray readings were carried out on 810 chest photos. Various radiological features of pneumoconiosis were obtained in 132 chest X-rays (16.2%), mostly abnormalities in parenchyma 87.1%. Parenchymal abnormalities are mostly of small round (p/p) with a profusion of 0/1 (89.6%). The most zones were lower right (58.1%). Pleural disorders (2%) mostly of costophrenic sinus obliteration 64.8%. Other disorders were 61/810 (7.24%), mostly of diaphragm abnormalities 15/61 (27.9%). Relevant appearance with pulmonary tuberculosis (infiltrates) was 8/810 (0.9%).&#x0D; Conclusion: The proportion of pneumoconiosis was 16.2%, mostly of parenchymal abnormalities (87.1%). Parenchymal abnormalities that occured still in the early phase, most zones were lower right (58.1%), pleural disorders 2%, other abnormalities were 7.24% and those that relevant to pulmonary tuberculosis 0.9%. (J Respir Indo. 2019; 39(4): 266-71)

SILIKA BEBAS NATRIUM DARI LIMBAH SEKAM PADI SEBAGAI BAHAN DASAR PEMBUATAN MINERAL TRIOXIDE AGGREGATE

One of the basic ingredients of making White Mineral Trioxide Aggregate (MTA) was silica. The sources of silica was from white rice husk ash (RHA) and silica extracted from RHA. Silica could be extracted from natural ingredients in the form of rice husk ash. The purpose of this study were to extract silica from rice husk ash and purify the silica extracted by washing using distilled water to free sodium, so that it could be used as the basic ingredient in making MTA. Sodium was a hygroscopic metal that could cause the presence of pores in MTA material if applied to the teeth. The amount of washing volume varies to a certain volume which indicates that silica was free Na. Based on the results of the experiment it could be concluded that the washing of silica by stirring with distilled water would produce free Na silica by washing 450 mL. This wasnot proven at peak 2θ (30⁰), as well as proof of the presence of silanol and siloxane groups before and after washing with FTIR spectroscopy. In addition, the washing volume also affects the intensity of the –OH peak in wave numbers 1635,64 cm-1 the more volume used, the intensity of the –OH group increases, so that the water hydrated in silica also increases. Silica free Na would be used as the starting material for making MTA which was applied to teeth medicament or root canal treatment