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Thermal Characteristics of Gel Grown Lanthanum Heptamolybdate crystals

Sushma Bhat and P.N.Kotru(Dept. of Physics , Uuiversity of Jammu , Jammu -180 001 , India) M.L.Koul(Dept. of Chemistry , Uuiversity of Jammu , Jammu , India)

材料科学技术（英文）

Thermal characteristics of Ianthanum heptamolybdate crystals grown by gel technique, employing thermoanalytical techniques, viz. TG, DTA and DSC, are reported. It is established that the rare-earth lanthanum heptamolybdate crystals are associated with thirty water molecules;the composition being La2Mo7O24.3OH2O. It is shown that all the thirty water molecules associated with lanthanum heptamolybdate crystal are lost during its decomposition, leading to its anhydrous form. Results obtained on application of TG based models, viz. Horowitz-Metzger,Coats-Redfern and Piloyan-Novikova and of DSC based methods viz. Roger-Morris-Smith and Barret, regarding solid state reaction kinetics are also reported. The random nucleation model is shown to be the one that is relevant to the decomposition of lanthanum heptamolybdate. The kinetic parameters, viz.the order of reaction. frquency factor, energy of activation and entropy using above mentioned models are computed and shown to bear reasonably good agreement

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Fracture Toughness of Cast Al-Zn-Mg Alloys

K.H. W.Seah(Dept. of Mech. Eng. , National University of Singapore , Singapore 0511)S. C. Sharma (To whom correspondence should be addressed)(Dept. of Mech. Eng. , R.V.College of Engineering , Bangalore-560-059 , Karnataka , India)

材料科学技术（英文）

Compact tension specimens of as-cast Al-3Zn-2Mg and Al-7Zn-2Mg (in wt pct) alloys were subjected to fracture toughness tests at room temperature according to specification5 laid down in ASTM E-399-81. It was found that increasing the Zn content, grain refinement and increasing the solidification rate lead to an increase in the fracture toughness of the material.

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Abrasive Wear Characteristics of Carbon and Low Alloy Steels for Better Performance of Farm Implements

M.Kumar and R. C Gupta(Centre of Advanced Study , Dept. of Metallurgical Engineering , Institute of Technology , Banaras Hindu University , Vaanasi -221 005 , India)

材料科学技术（英文）

The low stress abrasion behaviours of heat treated mild, medium carbon and high C - low Cr steels, which are generally used in making farm implements, have been investigated. The simple heat treatment greatly improves the hardness, tensile strength and abrasion resistance of medium carbon and high C - low Cr steels. The results indicate that the material removal during abrasion is controlled by a number of factors, such as hardness, chemical composition, microstructure and heat treatment conditions. The conclusion is that the heat treated high C - low Cr steel and mild steel carburized by using coaltar pitch provide the best hardness and abrasion resistance and thus appear to be the most suitable materials for making agricultural tools.

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Thermodynamic Analysis of Ag_3Ge Phase Formation

O.P.Pandey(School of Basic and Applied Sciences , Thapar Institute of Engineering and Technology Patiala-147 001 , India )S.N.Ojha and S.Lele(Dept. of Metallurgical Engineering , Banaras Hindu University , Varanasi-221 005 , India)

材料科学技术（英文）

In the present work a thermodynamic model is presented for the nucleation of metastable Ag3Ge phase from the undercooled melt in Ag-Ge alloy system. It is shown that under kinetically induced favourable condition, nucleation of a single phase compound with an approximate stoichiometry Ag3Ge has greater affinity for nucleation over Ag and Ge based phases requiring diffusion in the liquid.

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Microstructure and Wear Characteristics of Al-4.5Cu-5Pb Alloy

Om Prakas Pandey(School of Basic and Applied Sciences , Thapar Institute of Engineering & Technology , Patiala-147001 , India)

材料科学技术（英文）

Al-4.5Cu-5Pb alloy was prepared by sand and chill casting. The same alloy was also spray deposited at a gas pressure of 1.6 MPa. The microstructural features exhibit a coarse to fine dendritic morphology for sand and chill cast alloys. Equiaxed grains were observed for spray fOrmed alloys. Wear testing employing a pin-on-disc type set-up, reveaIs considerably lower wear of spray deposited alloy compared to that of chill and sand cast alloys. The morphological features of wear track on specimen and debris indicated a mixed oxidative-cum-adhesive wear mechanisms for these alloys tested in the present investigation

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Structural, Optical and Electrical Properties of Evaporated CdSe Films

H.P. Sarma , N.Rangaraan and K.R.Murali(Central Electrochemical Research Institute , Karaikudi -623 006 , India)

材料科学技术（英文）

CdSe films are of great interest for use in thin film photoelectric devices. A simple chemical precipitation method is adopted for the first time to synthesise CdSe powder. Films on glass obtained at different substrate temperatures TS such as 300, 373, 423 and 473 K have been characterised by X-ray diffraction, optical absorption and Hall measurements.

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Characterization of Mixed Neodymium Lanthanum Heptamolybdate Crystals Grown by Gel Encapsulation Technique

Sushma Bhat and P.N.Kotru(Dept. of Physics , University of Jammu , Jammu , India)

材料科学技术（英文）

Crystals of mixed NdLa heptamolybdates (max. size0.75×0.75×0.75 mm3) grown by silica gel technique were characterized using EDAX, IR, optical and scanning electron micrscopies.X-ray as well as electrn diffraction. The composition of the crystals was determined as (Nd1/2 La1/2 )2 Mo7O24·35H2O.The crystals exhibit varied morpholgies including square and octagonal platelets, cuboids, multifaceted crystal in coalesced and aggregated forms and spherulites.The XRD results indicate crystallinity of the grown material. Electron diffraction results suggest thermal instability of the material. IR results show the presence of peaks due to water and metal-oxygen bonds

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Fracture Toughness and Microcracks on Natural Apophyllite Crystals

PR.Dhar , K.Bamzai and PN.Kotru (Dept. of Physics , University of Jammu , Jammu-180004 , India)

材料科学技术（英文）

Results on fracture toughness of natural apophyllite crystals when subjected to impact are presented. The morphology of the cracks and fracture has been studied. It is found that the crack formation does not show any anisotropic property and remains the same whatever may be the orientation of the crystal. The average values of the fracture toughness KC and brittleness index, as determined from measurements of crack length, are estimated to be 0.107 gμm-3/2and 4.19μm-1/2 respectively for the a(100) plane. The yield strength forα(100), p(111) and c(001) planes of apophyllite crystals for lower loads is 2250. 2160 and 1840 MPa and for higher loads is 1510, 1600 and 1430 MPa respectively

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Contrasting REE Signatures on Manganese Ores of Iron Ore Group in North Orissa, India

稀土学报(英文版)

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Rare earth element (REE) geochemistry of phosphorites of the Sonrai area of Paleoproterozoic Bijawar basin, Uttar Pradesh, India

稀土学报(英文版) doi:10.1016/S1002-0721(12)60081-7

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