醫療類國考
110年
[牙醫師] 牙醫學(二)
第 48 題
傳統牙科用瓷（porcelain）中添加鉀離子或鈉離子會造成玻璃質基質（glassy matrix）何種影響？
- A 降低熱膨脹係數
- B 破壞$SiO_4$結構
- C 阻止白榴石（leucite, $KAlSi_2O_6$）結晶
- D 熔點溫度提高
思路引導 VIP
試著想像：二氧化矽（$SiO_2$）原本是由許多強韌的矽氧共價鍵交織成的緊密三維防護網；當我們強行塞入一些體積大、且電荷較弱的外來正離子時，這張原本緊密相連的「網子」在微觀空間上會發生什麼物理結構的改變？
🤖
AI 詳解
AI 專屬家教
Hmph. Looks like you didn't get lost on this one. Good.
- The Blade's Edge: Listen up. This ceramic stuff for teeth, it's built on a strong $SiO_4$ network, like a solid foundation. When we throw in alkali metal ions – stuff like $K^+$ or $Na^+$ – they're not just passengers. They're like a flux, you know, to make things flow. They act as "network modifiers." What does that mean? They cut clean through the $Si-O-Si$ covalent bonds, leaving behind these "non-bridging oxygen" points. It's like finding the weak spots. This breaks the $SiO_4$ continuous structure. The result? The whole thing softens up quicker, flows easier, like a blade that's been tempered right. But it might expand a bit more when things get hot.
- Three-Sword Style Analysis: (我把頭巾綁在頭上，認真地說) 這招三刀流解題法不錯。This question was Medium. Not impossible, but not for the weak-minded either. You gotta know the difference between those who build the structure and those who change it. Don't just swing your sword blindly; understand where to make your cut. If you get the core idea of breaking bonds, you'll always find your way to the right answer. Now, where was I going...?