الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 153 |  |  |
| | | from | 153 | | |
Abstract
The current work aims to exploit some of the Egyptian diatomite ores for preparation of some types of heat insulating materials, which are demanded at the Egyptian markets. For this purpose five representative diatomite ore samples are being supplied from El Fayoum Depression, south west Cairo.
These samples are named Masakheet, Kasr El Sagha 1, Kasr Elsagha 2, Demia Yellow 1, and Demia Yellow 2. Their chemical composition is determined using X-ray fluorescence (XRF) technique. Their mineral composition is detected by using Philips X-ray diffractometer Model PW/1710 Cu K α radiation with Ni filter at 40 kV and 30 mA. (XRD). Their surface area and particle size are determined using Brunauer Emmett-Teller and BT-2001(liquid) Laser Particle Size Analyzer.
IV.1. Samples characterization
IV.1.1. Chemical analysis of the original samples showed that their silica contents varied from 17.03% for Masakheet sample to 58.96% for Kasr El Sagha 2 diatomite sample. High content of alumina and iron oxide are noticed in Kasr El Sagha 2 and Demia Yellow 2 diatomite samples reached 16.4% and 15.6%, where their contents were less in the other investigated diatomite samples. On the other hand, Masakheet showed higher calcium oxide content than in other samples (40.97%), while its content in Kasr El Sagha 2, and Demia Yellow 2 diatomite samples were very low (2.82%, and 7.21%). Their loss on ignition%, as a result of calcination at temperature of 1000°C varies from 30.10% for Masakheet sample to 13.20% for Demia Yellow 2 sample.
IV.1.2. X-ray diffraction results indicated that quartz and calcite are the major constituents of nearly all samples, where the Ca/Si mass ratio varies from 2.56% in Masakheet to 0.05% in Kasr El Sagha 2.
Two clay minerals, kaolinite and montmorillonite appeared as minor constituents where Al2O3 content of the five samples changed from 3.42% in Masakheet to 9.72% in Demia Yellow 2 diatomite sample. Moreover, gypsum mineral appeared as a minor constituent in Demia yellow 1 and Kasr El Sagha 1 samples, where their sulphate contents are 1.45% and 2.02%, respectively. In Demia yellow 1 and Kasr El Sagha 1 samples, dolomite appeared as minor to trace constituent, where their MgO content reached 1.27% and 1.42%, respectively.
IV.1.3. Surface area measures indicated that Masakheet, Demia yellow 2 and Kasr El Sagha 2 samples had relatively low surface area values reached 29, 38, and 49 m2.g-1, respectively. The surface areas of Demia yellow 1 and Kasr El Sagha 1 samples were 179 and 119 m2.g-1, respectively.
IV.1.4. Particle size distribution results indicated that D50 ( half amount of particle size) of Masakheet and Demia yellow 2 had particle size < 10 micron. On the other hand in case of Kasr El Sagha 1 and Demia yellow 1 D50 was 19-22 micron.
Nearly 30% of these samples had particle size < 10 micron. Meanwhile, Kasr El Sagha 2 sample was the only sample which had not particle size > 100 micron and its D50 was 18 micron.
IV.2. Rational mixing process of the samples
This section aims to partly replacement of high grade diatomite (high porous silica conten) with low grade diatomite rich in calcite. This mixing process aims to improve their physical properties and increase their applicable insulating temperature. Due to mixing, their chemical and mineral composition is changed and their physical properties are varied in accordance.
The results indicated that, by increasing the addition of Masakheet diatomite samples to each Kasr El Sagha 2, Demia Yellow 2, and Demia Yellow 1,their silica contents were decreasing but their CaO contents increased.
Additionally, by increasing the addition of Kasr El Sagha 1 to Demia Yellow 1, this led to the increasing in their Ca/Si, Ca/Al+Si, and Ca/Si+Mg mole ratios, while Al/Al+Si ratio decreased .
Quartz, wollastoniteو and akermanite were the main new constituents in each mixing ratios 30/70% and 50/50% by mass for Masakheet/Kasr El Sagha 2 and Masakheet/Demia Yellow 2 specimens. The same previous phases are detected in case of 30/ 70% of Masakheet/ Demia Yellow 1, and Kasr El Sagha 1/Demia Yellow 1.
On the other hand, larnite mineral phase appeared only in case of 50/50 % of Masakheet/Demia Yellow 1, besides to cristobalite , wollastonite, and akermanite phases which appeared in case of 50/50% of Kasr El Sagha 1/Demia Yellow 1. Mean while, in the last mix specimens, magnesium silicate phase is detected.
Although the X-ray diffraction pattern of 30/70% mix specimens showed anorthoclase phase which may cause lowering in the silica melting point, it is fortunately, disappeared in case of 50/50% diatomite mix specimens according to the increase in Ca/Si, Ca/Al+Si, and Ca/Si+Mg mole ratios. This led to decreasing of impurities contents due to dilution. In accordance, the bulk density and specimens dimension change of the mix specimens decreased and their open porosity increased.
IV.3. The Effect of addition of pore forming agents
Starch and carbon are selected to be employed as pore former agents. Their addition effects on the physical properties of mixed specimens are followed up. Pore structure is followed up using prosomiter, while the fracture surfaces are examined through the scanning electron microscope technique (SEM).
Their addition showed that:
The effect of carbon on decreasing the bulk density of the specimens was strong as compared with the starch addition. The contrary is occurred with respect to their bulk density and open porosity of specimens.
The ratio of large to fine pores varied with changing the type of pore former agent and mineral composition of specimens, where the pore size is found to be dependant on the particle size of starch and carbon. Therefore carbon of relatively coarse particle size left relatively large pores in the fired specimens.
The mineral composition of specimens affect on the size of pores created in the specimens is remarked. This is indicated in case of adding Kasr El-Sagha 1 instead of Masakheet to Demia Yellow 1 diatomite specimens, the number of finer pores (> 10 microms) increased. The Masakheet – Demia Yellow 1 specimens were relatively porous as compared with their Kasr El-Sagha 1 – Demia Yellow 1 counterparts, although there was slight difference between the two groups of specimens in the values of open porosity.
IV.4. Work Conclusions and Recommendations
Profiteering the unexploited Egyptian crude ores which have low silica content and it may help to increase the national income.
Getting use the huge reserves of poor low porous silica- high calcite diatomite ores in solving the problems that
facing the high grade diatomite ores to be suitable for heat insulation industries by decreasing their impurities content that cause increasing their application temperature from 900 to 1100°C, then they become more thermally stable.
Besides using of pore former agents to help in furthermore improving some of their physical propertieslike porosity and bulk density