China’s export controls on metals used in semiconductors are “just a start”, an influential Chinese trade policy adviser said on Wednesday, as Beijing ramps up a tech fight with Washington days before a visit from U.S. Treasury Secretary Janet Yellen. Shares in some Chinese metals companies rallied for a second session as investors bet that higher prices for gallium and germanium, which Beijing’s export restrictions target, could boost revenues. Germanium is used in high-speed computer chips, plastics, and in military applications such as night-vision devices as well as satellite imagery sensors. Gallium is used in building radars and radio communication...