Solidification process and microstructure of transition layer of Cu-Al composite cast prepared by method of pouring molten aluminum

The Cu?Al composite casts were prepared by the method of pouring molten aluminum. The solidification process and themicrostructure of the transition layer were investigated during the recombination process of the liquid Al and the solid Cu. The results reveal that the microstructure of the transition layer in the Cu?Al composite cast consists of α(Al)+α(Al)?CuAl2 eutectic,α(Al)?CuAl2 eutectic, CuAl2+α(Al)?CuAl2 eutectic and Cu9Al4. Additionally, the pouring temperature, cooling mode of the Cu platesurface and start time of the forced cooling after pouring have no effect on the microstructure species. But the proportion of thevarious microstructures in the transition layer changes with the process parameters. The pure Al at the top of the transition layer startsto solidify first and then the α(Al) phase grows in a dendritic way, while the CuAl2 phase exhibits plane or cellular crystal growth from the two sides of the transition layer towards its interior. The stronger the cooling intensity of the Cu plate outer surface, the more developed the dendrite, and the easier it is for the CuAl2 phase to grow into a plane crystal.

Hygiene,sanitation facility,and assessment of drinking water quality in the schools of Chattogram city,Bangladesh

Objective:This study is designed to evaluate the microbiological safety concern of drinking water of the 50 schools of Chattogram city,Bangladesh,and to investigate the sanitation and hygiene conditions of the schools,which are directly related to the health of thousands of students.Methods:In this study,pour plate method used for total viable count(TVC),most probable number(MPN)method used for the total coliform count(TCC)and fecal coliform count(FCC),and four selective media used to isolate pathogenic bacteria from drinking water samples,and then identified by using morphological,cultural,and biochemical tests.To investigate the water,sanitation,and hygiene conditions a structured questionnaire was used.Results:A total of 46% samples were found above the acceptable limit(>500 CFU/ml)for TVC count,52%sam-ples had coliform,and 28% samples had fecal coliform,which exceeded the WHO guideline value.We categorized 50 studied schools into five groups and found the highest TVC(67%)and TCC(83%)in the water samples of city corporation schools.E.coli,Salmonella,Shigella,Enterobacter,Citrobacter,Klebsiella,and Yersinia were isolated and identified from drinking water samples.In most schools,drinking water reservoirs were found impure and contaminated by various bacteria.In government primary schools,a toilet is used by 143 students,whereas in pri-vate English medium schools,a toilet is used by 30 students and found clean.Hand-washing soap was supplied in only 14% of government primary schools,but 100% in private English medium schools.Conclusion:Our findings suggest that drinking water in most of the schools was found contaminated by pathogens.Poor hygiene,sanitation,and contaminated drinking water seem responsible for different kinds of diseases.More-over,this study indicates the necessity for raising awareness about drinking water,hygiene,and sanitation facil-ities of schools,which should monitor at regular intervals.