The effect of homogenous heating variables (temperature and time holding) on the tendency of high strength Al-alloys type 7020 is investigated. The experiments were carried out by heating the specimens at different temperatures (100, 150, 200, 250, 300, 350, 400, 450 and 500) °C for two periods of holding time (one hour and two hours). Microstructure of an alloy was investigated by the optical microscope before and after heating at each temperature and precipitation phase and clearing revealed MgZn 2 . An immersion test was applied on specimens after heating to show the reduction in weight. Polarization technique was used to study the effects of microstructures on their electrochemical behavior in 3.5% NaCl solution. Microscopic and X-ray examination were used to reveal pitting corrosion on the microstructure of non-heated and heated 7020 Al-alloys. The results show that increasing the temperatures of heating from 100°C to 500°C caused the appearance of pitting corrosion on the precipitated phases and increase of pitting corrosion tendency with increase of temperature of heating; increasing time holding of heating from 1 hr. to 2 hrs. increases the pitting corrosion.

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Abstract-This study presents the results of research for micro hardness and corrosion behavior of ASTM 304 stainless steel by investigating and performing the pitting corrosion 1N H2SO4 as a function of heating temperature (500, 600, 700, 800, 900) ºC. Different amounts of carbides precipitated in the austenitic stainless steel. These precipitates are one of problems with austenitic stainless steel due to the formation of extreme pitting corrosion. The current pitting corrosion density for heated stainless steel at 900 ºC is greater than that of non-heated specimen by about 34% in 1N H2SO4. The pitting potential of heated stainless steel at 900 ºC is more negative than that of nonheated specimen by a value of 284 mV. This means that the increase in heating temperature led to the increase of pitting intensity. Keywords:Corrosion resistance,austenitic stainless steel, sensitization, hardness, Cr-carbides I. INTRODUCTION AISI 304 stainless steels are used in a wide range of applications like chemical, petrochemical, medical and kitchen equipment because of their good mechanical properties and excellent corrosion resistance [1,2]. Most of these applications are done at higher temperature, which leads to formation of sensitization phenomena, and the sensitization generally takes place in the range of temperature (500-900) ºC. These phenomena are considered as a susceptible reason for pitting corrosion [3,4]. At the sensitization range, the dissolved carbon in the microstructure would pull the chromium to forms several chromium carbides, depending on the annealing temperature along the grain boundaries. At the same time, a depletion zone of chromium would take place inside the microstructure. These two phenomena (carbide precipitation and Cr-depletion zone) are considered as the main reason for formation of pitting corrosion [5,6]. A various of phases may accelerate in the different classes of stainless steels, particularly AISI 304. Some of these phases, similar to the Cr 7 C 3 , Cr 23 C 6 , might be the basic to all classes; however, some of them are most certainly not [7,8]. The corrosion resistance of AISI 304 is analyzed to study the effect of temperature by using Tafel extrapolation method. It becomes clear that the best methods to study the susceptibilities to this form of corrosion are the Tafel extrapolation method. II.EXPERIMENTAL METHODS Sample preparationThe samples were prepared by cutting into square shape with 1.5 mm and thickness of 2 mm followed by grinding with different metallographic paper SIC and it has been refined by polishing paper assistance of cloth Damon and refine oil to polish the surface of samples. The samples have been clean and dried. Etching has obtained for the purpose of showing the microscopic structure using chemical solution, consisting of 50 ml HNO3 and 50 ml HCL. Finally was washed with water samples and alcohol and then dried by dryer. Chemical CompositionsThe chemical compositions of stainless steel 304 were carried out by using oxford instruments product of foundry Master Xp...

This study deals with extraction of silicon from Iraqi sand. The sand was supplied by State Company for Mining Industries from Um-Erdhuma Formation in Anbar Province. It is found that Iraqi sand has 98% of silica (SiO₂).Pyrometallurgy and hydrometallurgy processes were applied for extraction of silicon by reduction and leaching respectively. Reduction was carried out in an alumina crucible by using magnesium powder with particle size of 75μm as reducing agent under argon gas. Several parameters were studied to determine the best results that affected the extraction of silicon. These parameters involved the reduction temperatures (750,850,950) C and ratio of Mg/SiO₂ (2:1, 2.5:1, 3:1).The best conditions for the reduction of Iraqi sand to produce silicon were, at 850 C, 2:1 Mg/SiO₂ with 99.3% purity and at 950 C, 3:1 Mg/SiO₂ with 99.2 %purity. Leaching processes were done for purification of produced silicon by using 4:1 volume ratio of 4M HCl and 4M CHᴈCOOH respectively for one hour at 70 C. Additional purification step was done by using H₂SO₄ acid, which was diluted by 1:4 ratio for three hours at 100 C.

Year after year, the sediments of the Tigris River in Iraq are increasing, causing the river clogs, which requires the removal of these sediments from time to time. Unfortunately, they do not benefit from these deposits, although they contain high levels of silica, which concentrations were between 59 - 66%. Pure aluminum powder mixed with sediments at different ratio (1:1, 1.5:1 and 2:1) sediments/aluminum. The reducing temperatures were 900, 950 and 1000 °C. leaching process was used to purified the silica. This process was carried out by using different concentrations (3,4 and 5)M of sulfuric acid to obtain silicon element. The purity of produced silicon reached to 98. 9%. with of extraction efficiency more than (88%).