China’s exports of two rare minerals essential for manufacturing semiconductors fell to zero in August, a month after Beijing imposed curbs on sales overseas, citing national security. China produces about 80% of the world’s gallium and about 60% of germanium, according to the Critical Raw Materials Alliance, but it didn’t sell any of the elements on international markets last month, Chinese customs data released on Wednesday showed. In July, the country exported 5.15 metric tons of forged gallium products and 8.1 metric tons of forged germanium products. When asked about the lack of exports last month, He Yadong, a spokesperson...