Preparation of Nano Silica particles by laboratory from Iraqi sand and added it to concrete to improve hardness specifications

: Concrete is the most common material used for construction purposes as well as in the lining of oil wells. In this work, the concrete specifications are improved through the preparation of Nano silica particles (SiO 2 ) by laboratory from Iraqi sand and added to the concrete, which gives results with a large gap in the test of compressive strength after the addition of silica nanoparticles prepared to the concrete mixtures compared to the same mixtures without the addition of silica, to give high hardness and great capacity for bearing of compressive strength as well as increase the resistance to water penetration during the concrete structure and especially the padded cement for the oil well. In this research, Nano silica particles are prepared from the Iraqi sands available in large quantities in the cities of Iraq. The two types of sand are used: the first one is the sand of the Akheider area in Karbala province and the second is the sand of the western region in Anbar province. The Nano silica particles have been prepared in two ways: chemical and physical methods (milling method). The specifications of the prepared materials are measured by several diagnostic devices, including the scanning electron microscope (SEM), the particle size analyzer apparatus, the X-ray diffraction (XRD) and the infrared spectrometer (FTIR). The results of this project proves the possibility of producing Nano silica particles with high purity and excellent specifications, which can be invested for the commercial purposes in the future. In this research, two types of cement are used. The first is class G cement used for lining the oil wells, and the second is the Iraqi cement resistant (Portland cement) Company / Sulaymaniyah province) used in the building construction. The prepared Nano silica is added to the cement at rates ranging from 0.25, 0.5, 1 and 2% by weight, with fixed of cement amount, water, and mixed the mixture well by standard mixing machine and poured into mold cubes (5 x 5 x 5 cm) according to US specifications. In the concrete that used of the buildings construction, it is conducted a mixture of cement and normal sand (to both of two types of sands) and added the prepared Nano silica by a percentage ratio, and poured into a cubic templates, then conducting the tests of compressive strength which is of great importance in determining the strength of prepared concrete. The results indicates that the hardness of the concrete containing Nano materials is significantly increased and reached a level exceeding 4000 PSIG when adding 1% of the silica nanoparticles to the cement used. On the other hand, the results shows that the Nano materials in the concrete because of their high surface area reduced the permeability of the water into the concrete structure because these substances are hydrophobic, which reduces the permeability of sulfate ions and salts, which prolong the life of the concrete for long periods of time especially in wells Oil, so this research is of great economic importance in the investment of Iraqi wealth for the production of new engineering materials. 9. The results of the XRD tests showed that silica nanoparticles were crystallized in the crystalline structure through the peak of the silica peak that appeared, as well as the area of peak, and the amount of silica nanoparticles in the prepared material was large. 10. The results of the electron microscopy SEM, as well as the tests of the size of the nanoparticle to the formation of silica and a clear nanoparticle and in the form of particles less than 100 nm, which confirms the validity of the orientation in the selection of methods of preparation of the nano silica from both types of sand. 11. The infrared spectra (FTIR) of the prepared silica also indicate that the SiO 2 spectrum is large in size and area at 1100 cm-1. When comparing and matching the silica spectrum with the scientific literature, it is found to be fully applicable with silica under research to assure the validity of prepared nanomaterials.


Introduction:
Concrete mixtures are important engineering materials involved in many constructions work as well as in the oil and gas industry in lining oil wells. Concrete preparation and design usually consume almost all of the world's cement production. The use of large quantities of cement produces an increase in CO 2 emissions. These emissions have a significant impact on the environment [1]. Therefore, many researchers worked to improve the specifications of these cement mixtures by adding some different materials [2].
Sand is the material that is most commonly chemically composed of silicon dioxide known as SiO2. The higher percentage of silica in sand means the sand was best. Sand is a raw material for many industries such as glass, concrete, glass water (sodium silicate) and other industries [3].
The Iraqi lands west of the Euphrates are characterized by containing large quantities of different types of sand. The most important sites where the sand is located in large quantities are Karbala (Al Akheider area) that a light red sand, Al Habbaniyah area in Anbar with white sand, The western region of Anbar with white sand, which is characterized by containing a high quantities of silica up to (96%) minimum, and therefore considered as raw materials for the manufacture of the finest glass [4]. Therefore, the sand is used with cement in the manufacture of concrete, and the sand is pure the concrete would be hardest, which is used as a basis in the construction of buildings after mixing in certain proportions with cement and gravel and the addition of water to work cement paste, and when the use of cement in the lining of oil wells. The lining must be strong, solid and non-permeable. In order to obtain good lining of the oil wells, a strong cement mixture must be obtained that is not permeable to water and salts, and to avoid permeable of the water and salts inside of the concrete.
It is worth mentioning that the salts in case of entry into the structure of concrete is very harmful as it makes to destroy the chemical structure of the concrete, so must be fill the

Nano silica:
We can define nanomaterials as the class of advanced materials that can be produced to measure their dimensions or the dimensions of their internal granules between 3 nm and 311 nm. The small sizes and measurements of these materials lead to behavior that is different from the large traditional materials that increase their dimensions at 311 nm and have highly discriminating qualities and qualities that cannot be found in the traditional materials.
[9] Therefore, the use of nanomaterials in engineering applications has taken a wide range in application due to the characteristics of these materials of high surface area (the ratio of space to size is very high), and the possession of these materials of high internal energy, as well as control of their hydrophobic of water. One of the most important nanomaterials is the use of silica nanoparticles in various engineering applications, including in concrete mixtures of various types [10,11].
Silica nanoparticles can be prepared in a number of ways, the most important of which are chemical and physical methods. The chemical method is one of the most important ways in which silica is produced from its raw materials such as sand, Feldspar or quartz. The process involves steps including initial material preparation and reaction by melting raw material with NaOH to produce sodium silicate or so-called glass water. Sodium silicate is treated with concentrated sulfuric acid or concentrated hydrochloric acid to precipitate silica gel in the acid medium. Subsequent processes of the resulting material can then be carried out to obtain nanoparticles. [12,13] The equations below show the most important chemical reactions done in this way [12]: Sand rich by (SiO 2 ) + 2 NaOH → Na 2 SiO 3 + H 2 O …. (1) There is also another method of physical way based on the principle from top to bottom adopted in the philosophy of preparing the grains of nanoparticles (up down) as shown in Figure (

Devices and equipment used for examination and diagnosis:
In order to diagnose the properties and specifications of the nanoparticles produced in this research; many advanced devices were used in the Nanotechnology Center/ University of Technology and the Petroleum Research and Development Center, • Scanning Electron Microscope (SEM-VEGA) (SEM).
• X-ray diffraction device used to detect the crystalline structure of nanomaterials.
• On the other hand, a compressive strength test was conducted for the concrete cubes prepared in the research.
• Special mixer for preparing concrete mixtures.
• A special mold was used to pour the prepared concrete mixtures with dimensions of (5x5x5) cm.

Methods of preparing Nano silica from Iraqi sand:
Two methods were used in the preparation of silica nanoparticles, the chemical method, and the method of the mill, and the use of two types of Iraqi sand, and the preparation methods as shown below:

Use of the chemical method for the preparation of silica nanoparticles:
This method involved several steps to conduct the chemical reaction followed by purification and grinding steps. In this process, the Al-Akhaydar sand was used as raw material for the production of silica nanoparticles. The chemical reaction between Sand and NaOH was carried out. The steps below summarize the procedure used to prepare silica nanoparticles: - HCl) and then rinse thoroughly with distilled water several times.
2 -Drying the sample to a temperature of 100 ° C and add 175g of sodium hydroxide (NaOH).
3. The mixture is then fusion at a temperature of 550 ° C for one hour. The heat-reactive substances are then cooled and the silica deposition by concentrated hydrochloric acid is gradually added to the mixture until the medium is converted to pH (1).
4 -Filter the precipitate and wash several times with distilled water to get rid of sodium chloride NaCl, which is formed as a by-product during the reaction process. The final product is then dried at 105 ° C.
5. Figure (2) illustrates an outline of the synthesis of the steps for the production of the nano silica in the chemical way. Figure (3) shows the particulate sand used prior to the reaction, as well as the silica nanoparticles resulting from the steps and phases of the reaction. In this method, the western region sands were used, which have a very high silica content of 96%. Therefore, some primary treatments were done without the need to treat them chemically. The sand was first washed with diluted acid (0.1N HCl) to get rid of impurities and then washed several times with distilled water. Then, the sample is dried by oven at 105 ° C for 2 hours. After that grinding the sample with a conventional mill for two hours and then carried out the process of sieving with the sieve (50 micron size).
Finally, the output was grinded with a Nano mill for four hours. Figure (4) shows the shape of the sand before and after the treatment in the physical way.

Preparation of concrete mixtures:
We conducted a number of concrete mixtures have been prepared by mixing fixed percentages of cement used in lining oil wells (Class G) and water only, according to the specification of oil wells approved in the petroleum industry (American specifications), so that the ratio of water to cement is 44%. And then add different percentages of silica (SiO 2 ) nanoparticles that prepared in the above two ways (chemical and physical). Using a special mixer and pour in a mold as follows: 1. Constant quantities of cement and water were weighed and placed in the special mixer and then mixed at 140 rpm for one minute. This is the mother sample where the percentage of prepared silica (SiO 2 ) is zero (without addition).
2. The previously prepared silica nanoparticles were added at different rates (0.25, 0.5, 1, and 2%) for each mixture and continued mixing at the same speed for half a minute.
3. Then the prepared concrete mixture was poured in a mold of (5 x 5 x 5) cm and left for the second day with cover to avoid water evaporation.
4. The next day, the concrete cubes are removed from the molds and immersed in water for 3 days, after which they are released from water and left for 25 days before any tests are carried out. Figure (5) shows the shape of the resulting concrete cubes.

Scanning electron microscopy (SEM) results
The scanning electron microscopy of the prepared Nano silica particles was done in different ways in order to know the nature of the surface, shape and size of the prepared material in every way. Figure (8

Results of (FTIR) tests:
The analysis of the FTIR of the prepared sample sand was done using the chemical method (25g NaOH + 175g sand) as shown in Figure (  The FTIR test of the sample from the Western Region Sand was also done in the physical way as shown in Figure (

Specification of sand used in research
In this research, two types of Iraqi sand were used as raw material for the preparation of silica nanoparticles, namely the sands of the Al-Akhaydar region in Karbala and the sand of the western region in Anbar as shown in Table (2).

Specifications of cement used in the preparation of concrete mixtures:
Two types of cement were used in the preparation of concrete mixtures, namely cement for the lining of oil wells (Class G) and Portland cement used in construction work.

Compressive strength tests results
Due to the importance of examining the compressive strength to the type of concrete in various engineering applications, the effect of adding silica nanoparticles in different percentages on the prepared concrete was tested. Therefore, in the concrete mixtures for the lining of the oil wells, the silica nanoparticles was added to it ( Al-Akhaydar sand after chemical treatment, the first sample), the sample has been configured to examine of the compressive strength on the cubes of concrete after 25 days from the date of mixing.   The reason for the large increase in the values of compression is due to the presence of silica nanoparticles added to concrete cement used in the lining of oil wells, where the results showed that the hardness of the concrete containing this nanoparticle significantly and strikingly the value reached the level exceeded 5000 (psi) 2%, so it is possible to say that the nanomaterials found in the concrete due to its high surface area have reduced the permeability of water into the concrete structure because these materials are hydrophobic, which reduces the permeability of sulphate ions and salts, which prolong the life of concrete Long periods of time.
Additional concrete mixtures were prepared in the same way as the previous one, using salt resistant cement (Iraqi origin from Tasuluja/ Sulaymaniyah) and mixing it with silica prepared by the physical method of sand in the western region. These mixtures were made in January and the temperatures were low. The period of hardening and acquiring the appropriate hardness requires more time than the summer mixtures, and the results as shown in Table (

Conclusions:
1. In this research, silica nanoparticles were prepared successfully by exploiting the local raw materials namely sand and used it in the production of concrete with high specifications in oil and construction projects. 7. The nanoparticles that prepared in their synthetic nature are hydrophobic. Concrete will thus be protected from water penetration and thus protect it from the attack of dissolved salts in the groundwater which present in the soil. Thus, the operational life of the working facilities in the oil wells will be much greater when add small amounts of silica nanoparticles to it. 8. The surface area of chemical-produced silica nanoparticles was very large compared to raw materials or other ways to produce nanoparticles. The nano crystalline silica produced by the nano crystalline method (the physical method), especially the sand of the western region, had a much smaller surface area than the raw materials manufactured.
No.24-(9) 2019 Journal of Petroleum Research & Studies (JPR&S) E56 9. The results of the XRD tests showed that silica nanoparticles were crystallized in the crystalline structure through the peak of the silica peak that appeared, as well as the area of peak, and the amount of silica nanoparticles in the prepared material was large. 10. The results of the electron microscopy SEM, as well as the tests of the size of the nanoparticle to the formation of silica and a clear nanoparticle and in the form of particles less than 100 nm, which confirms the validity of the orientation in the selection of methods of preparation of the nano silica from both types of sand.
11. The infrared spectra (FTIR) of the prepared silica also indicate that the SiO 2 spectrum is large in size and area at 1100 cm-1. When comparing and matching the silica spectrum with the scientific literature, it is found to be fully applicable with silica under research to assure the validity of prepared nanomaterials.