Please help in assessing

"I also got to know him in another, more personal way, during a 2-week study trip to Canada. "

** This sentence could be read in a way which you may not intend, and readers might infer that your relationship was of an extremely close and very personal nature, if you undertstand me.

The letter is fine without this sentence, so I would recommend you leave it out!

I receive the impression from your letter of an independently minded person, who may be better at solo work than working with a group.

That was the impression I received from the letter.

I've added a little about communication skills, rapport etc., which seems likely, as you got to know him well in Canada.

To whom it may concern

I got to know Ahura Mazda very well during the 2 years he spent studying at Utrecht.

Mazda was a bright, enthusiastic MSc student who achieved good grades. In my Drilling & Production Engineering course he achieved one of the highest grades in the class.

He has an enquiring mind, and asked pertinent and searching questions during lectures. He is not easily swayed by group thinking, and undertook independent study to ensure his complete understanding of any and all material presented. These factors, together with his capacity for independent thought and individual research lead me to consider him an ideal candidate for a PhD program.

Although Mazda works extremely well on individual projects, he has good rapport with other students and staff, and good communication skills.

I have no hesitation in recommending Mazda for a PhD position. I am sure that he will carry out well-founded research and he has the capability to come up with original and provocative new ideas in his area of research. For further information, feel free to contact me.