1950's novel about FTL engine and the rare mineral that makes it possible

Question

I'm trying to identify a 1950's (NB: 1970 as it turns out) "pulp" sci-fi novel I read long ago. The cold war is still happening in its timeline. A very rare mineral is discovered that makes an FTL engine possible. To get enough mineral for even one engine, a collosal manhattan-project like effort was undertaken to isolate it but yielded only one gram; barely enough to power a single engine. The Soviets, however, have access to skads of this mineral, but don't yet know its significance. A planet is discovered that shows the signature of having lots of this mineral, so the West sends its one FTL ship there, desperate to get more of the mineral before the Soviets discover the secret of using it.

The ship almost destroys itself crossing the light speed barrier, but manages to arrive. At the destination planet they discover aliens who are pacifists and refuse to give any mineral to the hero because it could be used for war. After an impassioned plea about the evils of the communists and how they will use it for war which could threaten the aliens, the aliens come up with a compromise. They send the hero back with a substance that can be used to neutralize the FTL mineral and render the Soviet's deposit inert. They also relent enough to give the hero one more gram of mineral so that the engine will be powerful enough to not destroy itself crossing the speed of light barrier.

Answer 1

Operation Star Voyage by Jack Pearl (1970), the second book in the Space Eagle series.

In the first book, millionaire and scientific genius Paul Girard discovers the exotic element "Spartanium". It can be used to create a rocket engine by utilizing its ability to generate antimatter. Unfortunately the refined ore only yields one gram of Spartanium before the vein is used up.

The gram is barely enough to propel a spacecraft faster than light.

In the second book, the president of the United States gives Paul the shocking news that the Soviet Union has a huge deposit of Spartanium ore, and is close to the invention of the antimatter engine. Astronomers have detected the spectrum of Spartanium in a planet around the star Alpha Centauri, so Paul embarks on a perilous voyage to obtain enough of the precious element to maintain parity with the Soviets. Paul takes along a wise friend of the family as back up.

The transition to FTL travel almost destroys the starship because one gram of Spartanium is barely enough to make the transition to FTL safely.

The planet turns out to be inhabited by technologically advanced pacifist aliens who capture Paul and his friend. They refuse to give Paul any more Spartanium, since us primitive Earthlings would just use it for war.

Paul's friend points out that if the aliens do not supply the Spartanium, the Soviets will quickly conquer Earth. And send an invasion fleet to Alpha Centauri in order to grab more Spartanium.

The aliens hadn't thought of that. Their plan B is to give Paul a huge tank of a chemical solution which will transmute Spartanium ore into worthless rock. Paul and his friend fly back to Earth, invades Soviet air space, and crop dusts the Soviet Spartanium mining site. Problem solved.

The aliens do give Paul an additional gram of Spartanium so the transition to FTL is not dangerous. They are convinced enough of Paul's sincerity that they are sure Paul will not misuse it.