In situ(α-Al_2O_3+ZrB_2)/Al composites with network distribution fabricated by reaction hot pressing

In situ（α-Al2O3+ZrB2）/Al composites with network distribution were fabricated using low-energy ball milling and reaction hot pressing. Differential thermal analysis（DTA） was used to study the reaction mechanisms in the Al–Zr O2–B system. X-ray diffraction（XRD） and scanning electron microscopy（SEM） in conjunction with energy-dispersive X-ray spectroscopy（EDX） were used to investigate the composite phases, morphology, and microstructure of the composites. The effect of matrix network size on the microstructure and mechanical properties was investigated. The results show that the optimum sintering parameters to complete reactions in the Al–Zr O2–B system are 850°C and 60 min. In situ-synthesized α-Al2O3 and Zr B2 particles are dispersed uniformly around Al particles, forming a network microstructure; the diameters of the α-Al2O3 and Zr B2 particles are approximately 1–3 μm. When the size of Al powder increases from 60–110 μm to 150–300 μm, the overall surface contact between Al powders and reactants decreases, thereby increasing the local volume fraction of reinforcements from 12% to 21%. This increase of the local volume leads to a significant increase in microhardness of the in situ（α-Al2O3–Zr B2）/Al composites from Hv 163 to Hv 251.

Acute inferior wall myocardial infarction induced by aortic dissection in a young adult with Marfan syndrome:A case report

BACKGROUND Aortic dissection(AD)is an emergent and life-threatening disorder,and its inhospital mortality was reported to be as high as 24.4%-27.4%.AD can mimic other more common disorders,especially acute myocardial infarction(AMI),in terms of both symptoms and electrocardiogram changes.Reperfusion for patients with AD may result in catastrophic outcomes.Increased awareness of AD can be helpful for early diagnosis,especially among younger patients.CASE SUMMARY We report a 28-year-old man with acute left side chest pain without cardiovascular risk factors.He was diagnosed with acute inferior ST-segment elevation myocardial infarction(STEMI),which,based on illness history,physical examination,and intraoperative findings,was eventually determined to be type A AD caused by Marfan syndrome.Emergent coronary angiography revealed the anomalous origin of the right coronary artery as well as eccentric stenosis of the proximal segment.Subsequently,computed tomography angiography(CTA)showed intramural thrombosis of the ascending aorta.Finally,the patient was transferred to the cardiovascular surgery department for a Bentall operation.He was discharged 13 d after the operation,and aortic CTA proved a full recovery at the 2-year follow-up.CONCLUSION It is essential and challenging to differentiate AD from AMI.Type A AD should be the primary consideration in younger STEMI patients without cardiovascular risk factors but with outstanding features of Marfan syndrome.