If a high-speed gas is available and some powder is injected into it, this has the potential to be cold spray. High-speed gas coming from a pressurized cylinder or centralized pressurized gas source fulfills one of the basic conditions for cold spray generation. The maximum pressure of the gas thus obtained is limited, which limits the highest speed obtained therefrom. The speed obtained may not be sufficient. If gas is heated on its way, the pressure and the speed obtained can be further increased. The speed obtained again may not be sufficient. This brings up the question of whether there is a method to increase the speed of the gas without using increasingly powerful cylinders and hotter heaters. If gas and/or gas plus accelerated powders exit through a cylindrical pipe to the substrate, the speed will remain the same because the pipe will not increase the speed. If the diameter of the pipe at the end of the cylinder is constricted, the speed will increase if the gas is not compressible. Since there is no gas generated inside a pipe, the amount of gas entering the pipe per unit time must be equal to that leaving per unit time.