IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.23 (2) 2010 Study the Effect of MgO Addition on Some of Physical Properties of ZnO S. k. Abd-Al Hassan Department of physics , College of Education Ibn Al-Haitham, University of Baghdad Abstract Different percents(1.0,2.5,5.0 and 10)wt%of MgO powders were added to ZnO powder to study their effects on the physical properties of ZnO.Density , porpsity and water absorption of ZnO were decreased as MgO weigth percentage content increased. The values of vickers hardneess have double values especially at 1.0 wt % of MgO. Introduction Ceramics have been widely applied in engineering applications due to their excellent resistance to heat, corrosion, and wear . Zinc oxide was the material of choice for this observation because it by far is the most common material used in the commercial manufacture and research due to its low cost and wide availability. It is valuable both for direct application or preparation of other compounds[1-3]. Zinc oxide (ZnO) has been produced commercially for considerably more than century, originally for use as a pigment in paints and also for rubber, glass, porcelain enamels and pharmaceuticals[4-6].More recently, Zinc oxide has found new application in semiconductors, luminescence and photoconductivity [1-3] Zinc oxide varistors are ceramic semiconductor devices with highly non–linear electrical behavior and greater energy absorption capabilities. This property allows their use in the protection of electric and electronic circuits, where as lightning rods remain the principal application . Zinc oxide is also transparent to vissible light to a relatively high and uniform degree so that it exhibits a pure white of high brilliance [7] . This research deals with the effect of magnesium oxide (MgO) addition on the physical properties of zinc oxide . Some researchers studyied the addition of the materials on ZnO such as : Lu et al [8] have studied the effect of porosity on the scaling of fracture strength who showd that the fracture strength of ZnO ceramics is more influenced by the ratio of pores and grain sizes. Ramires et al [6] have studied the effect addition of SnO2 on ZnO on the mechanical properties and found that the elastic modulus of ZnO –SnO2 is doubled then ZnO only. Abdullatif [9] has studied the effect of adding borax on the properties of ZnO such as linear shrinkage, density which shows that the increase of the weight percent of borax would lead to reduce the linear shrinkage and increasing the bulk density . IHJPAS IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.23 (2) 2010 Experimental part Materials Zinc oxide powder (purity 99.5%) (Germany) with small parctical size less than 25µm has been used. Magnesium oxide has been prepared from magnesium salt (Boh) by heating the powders to 600 C˚ for 1hr . Four weight percentages of MgO (1.0% ,2.5% ,5.0% and 10%) have been used. Polyvinyl alcohol was used as a binder (at 1.5%). 5 samples for each percents have been prepared . All the samples sintered at (1300 C˚) using 5 C˚/min as a heating and cooling rate . The soaking time was 2 hrs. Equipments Many equipment have been used to prepare and test samples as follows:  Digital balance (0.0001g) type (DNVER INSTRUMENT).  Electrical oven type (COOPER HEAT).  Hydraulic press (5 ton) type (BEGO) .  Electrical furnace (up to 1350C˚) type (RUHSTRAL)) .  Microvickers harness type (TIME GROUP) .  Gainding and polishing machine type (METASERV). Preparation of disc samples Each percent of MgO powder was mixed carefully with ZnO powders by ball mill for 1 hr. The homogenized powder compacted as a discs (10mm diameter and 10mm height) using 2 tons as a pressure force. Characterization Density measurement Archemdise role has been used to calculate the apparent density according to ASTM (c373-71) and ASTM (c20-74) using the equation [10]. ρ =wd/(ws-wn) ……………………..(1) where : ρ= density ( gm/cm 3 ) wd = dry weight (gm) ws= saturated weight in water wn= lmmersed weight in water Porosity measurement According to ASTM (c373-72) the porosity of the sintered sample was calculated by using the equation [10] . P% =(ws-wd)/(ws-wn) *100………………….…(2) Water absorption measurement According to the ASTM (c133 -81) the water absorption of the sintered sample was calculated by using equation [11]. W.A % =wS –wd/wd *100 ……………...…(3) where : W.A is water a absorption. Linear shrinkage measurement By using the below equation the linear shrinkage was calculated as follows [11] : L.sh% = L0 –L/L0*100………………………..…..(4) where : L.sh= linear shrinkage. L0 = hight of sample before firing. IHJPAS IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.23 (2) 2010 L= hight of sample after firing. Microvickers hardness measurement Equation below was used to measure the microhardness of the sintered sample as follows [10]: HV= 2psin(136/2)/D 2 =1.854p/D 2 ………………………..…(5) Where : HV = Vickers hardeners (kg/mm2) P= Applied load . D= diameter of the indent (mm) Results and Discussion Table (1) and all figures showed the behavior of zinc oxide doped by the different percentages of magnesium oxide for most physical properties. Fig.(1) shows the effect of MgO weight percentage on the bulk density of zinc oxide. This behavior has a good correlation with the mixture role which is[9]: ρ = ρ1 v1 + ρ2 v2……………………….(6) where ρ is the density of the doped sample ρ1 is the density of zinc oxide v1 is the volume fraction of zinc oxide ρ is the density of magnesium oxide v2 is the volume fraction of MgO. The density of ZnO is decreased as the MgO weight percentage is increased, that is clear because the density of zinc oxide is 5.606 g/cm3 and the density of MgO is 3.58 g/cm3. Fig.(2) shows the effect of MgO weight percentage on the linear shrinkage of ZnO sample. The shrinkage is increased smoothly and then saturated at 1.0% and 2.5% then decreased at 10% and that may be due to the filling of the pores by MgO particals [9]. Fig.(3) shows the behavior of the zinc oxide porosity with MgO doped. It clearly showed that the porosity is decreased as the percent of MgO is increased. This behavior is proved by the increase of Vickers hardness Fig.(4) shows the effect of MgO percents on the water absorp tion property of ZnO, which shows the water absorption is decreased smoothly as this behavior is similar to the porosity behavior that is due to the pores found in the samples .All these values may be improved by increasing the sintering temperature [12]. Fig.(5) shows that the Vickers hardness has nearly double value of the native ZnO, and also it is well known that the porosity is inversely proportional to the mechanical properties. This increase in hardness may be due to the addition of MgO which may increased the crystal growth which caused the interconnecting of the grains [13]. Conclusions The physical properties of ZnO was affected by the addition of MgO additive where density , porosity and water absorption have decreased as the percent of M gO increased. IHJPAS IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.23 (2) 2010 Linear shrinkage has nearly a small variation but hardness is increased very obviously. Where the value of hardness is doubled than of pure ZnO (120HV). Reference 1-Eda,E.(1980)"Degradation mechanism of non–ohmic zinc oxide Ceramics", J.A ppl.Phys.51(5) 2678-2684 . 2- Levinson, L.and Philipp, H.(1986) "Zinc oxide varistors A revew ceramic" Bulletin 65:(4)1-7 3- Gupta,T.K.(1990) " Application of zinc oxide varistors" J. of Amer. Cera.Soc. 73:(7)1817- 1840 . 4- Nahm,C.and Park,C. (2000)"Microstructure, electrical properties and degradation behavior of PdO2 bsed ZnO doped with Y2O3"J.of Materials Science 38:(12)3037- 3063. 5- Askeland, .D.R. and Fulay,P.P. (2005 )"The Science and Engineering of materials "Thomson -Engineering Fifth Edation, 156-160. 6- Ramirez,M.A.; Marcos,F.R.; Fernandes,J.F. and Varel, J.A. (2008) "Mechanical properties and dimensional effects of ZnO and SnO2-based varistors"J.Am. Ceramic.Soc.91:(9)3105-3108. 7- Ramirez,M.A.;Simdez,A.Z. and Margnez,M .A. (2007) "Characterization of ZnO- degraded varistor used in high tension Device” Mat.Res.Bull.42:1159-1168. 8- Lu,C.;Danzer,R. and Fischer,F. (2004), "Scaling of fracture strength in ZnO effect of pore/grain size introduction and porosity", J. of the European Ceramic Society , 24: 3643-3651. 9- ALSammaraey,A.R. (1996), "Preparation and characterization of zinc oxide powder for ceramic industry", Ph. D. Thesis, University of Technology, Baghdad – Iraq 45_75. 10-ASTM ,(1982) Part 17(c20-71) Bulk-density water absorp tion, apparent porosity of white ware products . 11-ASTM , (1986) Part 15.02(c373-71,72) water absorption, Bulk density , apparent porosity of white water products. 12-Alvarez-Fregose,Octaivo, (1994), "Sintering temperature effects on the performance of ZnO ceramic varistors", Revista Mexicana de Fisica, 40: (5) 771-781. 13- Dyson,R.D. and Morrel,R. (1982), " Mechanical testing of engineering ceramic at high temperature", J. Elsevier Applied Science Itd.25-32. IHJPAS IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.23 (2) 2010 Table: (1) The physical propeties of doped ZnO MgO Percent Bulk density (gm/cm 3 ) Linear shrinkage Appernt porosty Microhardness (Kg/mm2) Water absorption 0.0 4.97 0.52 19.23 59.7 4.13 1.O 4.80 0.54 18.00 126 3.29 2.5 4.67 0.54 15.75 93 3.50 5.0 4.70 0.55 15.75 86.8 3.60 10 4.47 0.53 15.71 78.9 3.30 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 5.1 0% 1% 2.5% 5% 10% Mgo% B u lk d e n s it y Fig. (1) Variation of bulk density of ZnO with MgO percentage IHJPAS IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.23 (2) 2010 0.45 0.48 0.51 0.54 0.57 0.6 0% 1% 2.5% 5% 10% Mgo% L in e a r s h ri n k a g e Fig. (2) Variation of linear shrinkage of ZnO with MgO percentage 0 5 10 15 20 25 0% 1% 2.5% 5% 10% Mgo % A p p e ra n t p o ro s it y Fig .(3) Variation of apperant porosity of ZnO with MgO percentage IHJPAS IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.23 (2) 2010 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0% 1% 2.5% 5% 10% Mgo % W a fe r ab s o rp ti o n Fig .(4)Variation of water absorption of ZnO withMgO percentage 0 20 40 60 80 100 120 140 0% 1% 2.5% 5% 10% Mgo % M ic ro h a rd n e s s Fig .(5) Variation of microhardness of ZnO with MgO percentage IHJPAS 2010) 2( 32المجلد مجلة ابن الهیثم للعلوم الصرفة والتطبیقیة ى بعض الخواص الفیزیائیةفتاثیر اضافة اوكسید المغنسیوم ةدراس الزنـــك ألوكسیــد قاسم عبد الحسن شیماء جامعھ بغداد ،كلیھ التربیھ ابن الھیثم ،قسم الفیزیاء ةالخالصـ ة تاثیرهـا ) 1.0,2.5,5.0and10% (نسب وزنیة أضیف ى فـمن اوكسـید المغنسـیوم الـى مسـحوق اوكسـید الزنـك لدراسـ ولقـد وجـد ان الكثافـة والمسـامة واالمتصاصــیة للمـاء تقـل الوكسـید الزنـك كلمـا ازدادت نسـبة االضــافة .الخـواص الفیزیائیـة لـه .من اوكسید المغنسیوم1.0% ة الوزنیة بفیكرز تضاعفت عند النس ةلوحظ ان قیمة صالد اال انه قد. الوكسید المغنسیوم IHJPAS