Characteristic Cu K alpha x-ray pulses of less than 10 ps duration at 300 Hz repetition rate are generated in a x-ray diode driven by 1.8 ps, 193 nm pulses. Both light and x-ray pulses are utilized in pump-probe experiment to study the heat propagation in a Au(111) crystal lattice. Changes in the x-ray diffraction pattern in the first 100 ps are clearly observed with about 10 ps resolution. The system allows for detection of temperature changes of 20 degrees C in the 8-20 ps time frame.