Abstract
目前應用廣泛的儲氫材料，有AB型式的TiFe合金，AB2型式Mg2Ni合金以及 AB5型式的LaNi5基合金。根據這些合金吸放氫反應時，呈現的物理特性，發展出許多新的產品，例如：固態式儲氫槽，鎳氫電池以及熱泵.....等等。特別是熱泵，未來在汽車上冷氣的應用上，前景十分看好。熱泵的原理是利用儲氫材料吸氫放熱及放氫吸熱的特性，提供加熱或冷凍的效果。我們選擇熟知的AB5型式的LaNi5基合金，作為研究和發展熱泵的對象。LaNi5合金，將部分的Ni由Al取代，形成LaNi5-xAlx,此三元合金和 LaNi5合金比較，在相同的操作溫度下，隨著Al含量的增加，平衡壓愈低。因此，利用LaNi5合金和LaNi4.7Al0.3合金構成一組系統；將兩組以上的系統組成熱泵，產生熱源，另一組系統作再生的動作，如此，可以持續的供熱或冷卻。但是，經過多次充放氫後，大部分的材料都有衰變的現象，為了研究此一現象，我們設計了一套自動循環充放氫系統來作深入的探討。經過一個多月，3000次的充放氫循環，LaNi5合金有部分分解成La以及Ni。實驗的結果顯示，吸氫量衰減31％。關於熱泵的可行性，我們製作了一套自動控制的熱泵雛型。限於時間，尚未有數據，但我們根據此系統之規格與性能，做了一些理論的上的評估：要達到一般冷氣機1冷凍噸的效果，約需1kg的LaNi5和LaNi4.7Al0.3,而且其熱效率＝0.42及COP＝0.61,都比一般壓縮機式冷凍機的理論值高。為了發展實驗級的熱泵，整個系統管路的絕熱以及熱傳效率的提升，仍有待進一步的克服，選擇或設計合適的材料是未來發展的重點。There are many applications of metal hydrides based upontheirdifferent characteristics. Some of the commercial productsinclude hydrogen storage unit, hydride batteries, and heatpump. Since metal hydrides absorb hydrogen exothermically anddesorb hydrogen endothermically, the heat associated with thehydriding and dehydriding can be used for heat pumps. To designa metal hydride heat pump, selection of suitable materials isthe key factor to be considered. The AB5 type LaNi5-basedmaterials have been widely chosen for heat pumps. SubstitutingAl for Ni to form LaNi5-xAlx could lead to a lower equilibriumpressure and exhibit similar value of enthalpy at the sametemperature. Both LaNi5 and LaNi4.7Al0.3。constitute a unitfor a heat pump. A heat pump consists of two or more suchunits. When one unit generates heat, the other unit is in theprocess of recovery. So the device can transfer heatcontinuously. Since cyclic absorption-desorption of hydrogenin a heat pump may degrade the properties of the alloys, anautomatic hydriding-dehydriding system was built to study thedegradation phenomenon of the metal hydrides. It was foundthat after 3000 cycles of test, which took more than a month,the LaNi5 alloy partially decomposed to La and Ni. A reductionof 31% in the absorption capacity wasmeasured.